Micro-lavorazioni meccaniche e micro

Transcription

POLITECNICO DI BARI
DOTTORATO DI RICERCA IN IGNEGNERIA
MECCANICA E GESTIONALE XXVIII CICLO
DIPARTIMENTO DI INGEGNERIA MECCANICA MATEMATICA E MANAGEMENT
Micro-lavorazioni meccaniche
e micro-misure per componenti
meccatronici
Coordinatore: Prof. Ing. G. PASCAZIO
Tutor: Prof. Ing. Luigi M. GALANTUCCI
PhD Student: Marta PESCE
ANNO ACCADEMICO 2012-2013
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Introduzione
Il micromachining può essere definito in diversi modi: a seconda della dimensione o della funzione del
componente o in base al settore o area di interesse. Il processo in genere comporta la definizione di processi di
rimozione di materiale, come il taglio, la lucidatura, incisione, sputtering, processi di rimozione termici e altri.
Molti di questi processi sono utilizzati nel settore dei semiconduttori e Micro Electro-Mechanical Systems
(MEMS) e tendono ad essere indicati come micro o nano lavorazioni. Per questo studio, il micromachining è
strettamente definito come le caratteristiche meccaniche di taglio per ottenere in forma con l'uso di strumenti
di dimensioni inferiori a 1 mm con taglienti geometricamente definiti.
Tra tutti i processi di microlavorazione, la microfresatura e la microforatura dei metalli sono molto importanti,
per applicazioni in diversi settori quali il biomedicale (fresatura di stent coronarici), la fotonica ed ovviamente,
la meccatronica (ugelli e iniettori dei motori diesel o altri MEMS ad alto contenuto tecnologico). La lavorazione
di geometrie complesse con elevata precisione dimensionale in alcuni materiali, diventa estremamente difficile
con i metodi convenzionali di lavorazione ed in particolare quando si parla di componenti miniaturizzati. La
produzione di parti in miniatura richiede quindi, l'applicazione di tecniche di micromachining avanzate.
Ci sono diversi processi di microlavorazione che possono essere utilizzati per la lavorazione dei metalli.
Tuttavia, ulteriori progressi sia per quanto concerne l'efficienza di rimozione, che per quanto concerne la
qualità del componente lavorato, sono limitati dalla comprensione incompleta della meccanica di base del
processo[1], [2]. Si consideri, ad esempio, la criticità del processo di microforatura degli iniettori dei motori
diesel che attualmente vengono realizzati con EDM o la difficoltà di realizzare un micro stampo di forma
complessa, per processi di micro-stampaggio ad iniezione. Il micromachining non è semplicemente il
ridimensionato delle tecniche di lavorazione convenzionali, ma ha le proprie caratteristiche come l’effetto di
scala, il dimensionamento del raggio della punta del tagliente, lo spessore minimo del truciolo, produzione di
oggetti con superficie di scarsa qualità, formazione di bave ed usura precoce ed improvvisa rottura dell'utensile
[3], [4], [5], [6]. Di conseguenza, molti fattori che sono spesso ignorati nei processi di lavorazione tradizionali,
diventato significativi per le microlavorazioni e quindi, ottenere le prestazione desiderate in micro-scala, risulta
più complicato [7], [8]. La difficoltà diventa ancora più pronunciata quando il pezzo è di un materiale di difficile
lavorazione, come ad esempio una particolare lega di titanio molto utilizzata in applicazioni aerospaziali e
mediche per il suo alto rapporto durezza/peso e per le caratteristiche di resistenza alla corrosione e
biocompatibilità [9]. Lo studio e la comprensione dei fenomeni che regolano il processo di taglio a livello micro,
sono dunque la base per migliorare la produzione di componenti meccatronici sia a livello qualitativo che
quantitativo.
L’obiettivo ultimo del presente lavoro di ricerca è quello di realizzare parti con geometria complessa, con
caratteristiche di lavorazione aventi dimensioni comprese tra 10-9–10-3 m, ottenute per asportazione di truciolo
con un utensile di diametro inferiore ad 1mm e con taglienti geometricamente definiti.
Con lo scopo di perseguire l’obiettivo prefissato, si è deciso di focalizzare lo studio di questo primo anno di
ricerca, sul processo di micro-foratura meccanica e sul tema delle misure di alcuni componenti micro-lavorati,
attraverso l’utilizzo di macchine di misura commerciali ed home-made.
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Stato dell’arte
Per le applicazioni nel campo della meccatronica, EDM (Electro Dischange Machining) e laser drilling sono le
tecnologie attualmente più utilizzate per la produzione di micro-fori, malgrado presentino problemi relativi a
zone termicamente alterate, che facilitano la formazione di bave all’ingresso e all’uscita degli orifizi. In
particolare, l’EDM è ampiamente utilizzato per applicazioni nell'industria aerospaziale per la produzione di fori
di raffreddamento sulle palette delle turbine. Questa tecnologia, tuttavia, presenta alcuni problemi legati alla
rifusione del materiale nelle zone colpite dal calore e gli alti costi degli utensili. Inoltre, la velocità di
perforazione dell’EDM è molto bassa (0,0125 mm/s) se confrontata con la foratura meccanica (>0,25mm/s) ed
il laser drilling (>1000mm/s). KUPPAN et al. [10] hanno sperimentato un aumento del tasso di asportazione
(MRR) quando, durante l’operazione di foratura, l’elettrodo è messo in rotazione: all’aumentare della velocità
di rotazione dell’elettrodo il MRR aumenta, mentre la finitura superficiale raggiunge un punto di ottimo, e poi
peggiora. Ottimizzando i parametri di processo, per la realizzazione di micro-fori (diametro medio 130μm) su
Inconel 718, il massimo MRR è stato ottenuto con una rugosità superficiale di circa 3-3,5 μm (Fig. 1). Pertanto il
tempo di micro-foratura con EDM può essere ridotto, ma a scapito della finitura superficiale.
Fig. 1. Immagini SEM dell’entrata di micro-fori ottenuti con EDM, per differenti velocità di rotazione dell’elettrodo.
L’applicazione della tecnologia laser per la lavorazione di micro-fori, invece, presenta problemi di scarsa qualità
superficiale, causata dalla presenza di uno strato di materiale rifuso ed una zona termicamente alterata (Fig. 2).
Il processo di micro-foratura laser diventa ancora più compresso se la parte in lavorazione è cava e si rischia,
dunque, il danneggiamento della parete posteriore [11].
Fig. 2. Micro-fori realizzati su Inconel 718 con laser pulsato Nd:YAG (lunghezza d’onda 1064 nm), durata della pulsazione 0.3 ms,
assistito con gas alla pressione di 5 bar.
Evoluzioni della micro-foratura laser in continuo verso tecniche ad impulso a percussione o trapanazione,
hanno permesso di migliorare la qualità superficiale dei componenti lavorati [12]. Tuttavia, pur operando con
durate dell’impulso dell’ordine del nanosecondo, non è possibile trascurare i fenomeni di alterazioni termiche.
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È stato dimostrato che nella foratura di materiali metallici, la profondità di penetrazione dipende dalla
diffusività termica e dalla durata dell'impulso e quindi, che è possibile migliorare la finitura superficiale,
riducendo la durata dell'impulso, fino ad arrivare ad impulsi ultra-corti [13, 14]. Infatti, come è possibile notare
in Fig. 3, i fori realizzati con tecnologia di micro-foratura laser ad impulsi dell’ordine del nanosecondo,
presentano una maggiore quantità di materiale rifuso rispetto a quelli prodotti con tecnologia di micro-foratura
laser ad impulsi dell’ordine del femtosecondo.
Fig. 3. Altezza delle bave di lavorazione per processi di micro-foratura laser ad impulsi su acciaio [13]
Per la lavorazione di micro-fori con aspect ratio maggiore di 10, la tecnologia ad asportazione di truciolo
risulterebbe essere più adatta rispetto alle tecnologie EDM e laser drilling, poiché permetterebbe di ottenere
una migliore qualità della superficie lavorata e maggiori precisioni dimensionali.
Tuttavia anche la tecnologia di micro-foratura meccanica non è esente da problemi: l’oscillazione dell’utensile
o le vibrazioni di lavorazione, potrebbero causare un diverso punto di contatto tra l’utensile ed il pezzo
(rispetto a quello programmato). In una tale situazione, forze di taglio non previste durante la progettazione
del processo, potrebbero dare come risultato una superficie di scarsa qualità e/o la rottura prematura
dell’utensile.
Vi sono, infine, soluzioni ibride al problema della micro-foratura, che combinano le tecnologie appena
descritte. In [17] gli autori propongono un processo ibrido per la realizzazione di micro-fori, combinando la
tecnologia di laser drilling con la tecnologia ad asportazione di truciolo, eseguendole in modo sequenziale. Il
risultato è un foro esente dai tipici difetti di alterazione termica associati al processo di foratura laser, e con
bave di altezza minore rispetto a quelle ottenibili con un processo di micro-foratura, che utilizza
esclusivamente la tecnologia ad asportazione di truciolo. La vita dell’utensile aumenta, ma aumentano anche i
tempi di lavorazione. Un’ulteriore soluzione ibrida, che combina le tecnologie laser ed EDM, è stata proposta
da Li et al. [18]. Per la realizzazione di fori di diametro inferiore a 140 μm, gli autori hanno riscontrato una
riduzione del 70% nel tempo di foratura ed un aumento, quindi, della capacità di produzione del 90%, rispetto
ad un processo di micro-foratura che utilizza esclusivamente la tecnologia EDM. Principale problema che
accomuna le soluzioni ibride sono gli elevati costi.
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Il processo di micro-foratura meccanica
Capire e controllare un processo di micro-foratura meccanica è molto complesso poiché esistono una
moltitudine di fattori che influenzano il risultato. Il primo problema da affrontare nello studio di un processo di
micro-foratura meccanica, riguarda la complessità dell’interazione utensile/pezzo, nel momento in cui questi
vengono a contatto. Quando si opera su scala microscopica, il problema è più critico che in un tradizionale
processo ad asportazione di truciolo a livello macroscopico. Esistono, infatti, problemi legati alla prematura
rottura della punta ed al movimento oscillatorio della stessa, causati dalla geometria (utensile snello) ed alle
elevatissime velocità di rotazione del mandrino (min 20.000 giri/min) [15]. Il problema della rottura prematura
dell’utensile è ancora più accentuato per operazioni di micro-foratura su superfici non planari, poiché in queste
condizioni, l’utensile è sottoposto a una forza con una elevata componente nella direzione ortogonale al suo
asse, applicata nel punto di contatto con la superficie. Questa forza tende a far slittare la punta dell’utensile
che si troverà, quindi, in una posizione diversa da quella programmata e che causerà una sua inflessione,
nonché una sua probabile rottura[16].
Tra i parametri che influenzano l’interazione utensile/pezzo, e quindi la qualità della lavorazione, l’angolo di
inclinazione tra l’asse dell’utensile e la superficie da lavorare, risulta di particolare importanza. In [19] Weinert
and Surmann hanno proposto un algoritmo di simulazione basato su analisi geometriche delle varie condizioni
di interazioni del tagliente con la superficie, per ottimizzare tale parametro.
Fig. 4. Confronto tra i risultati ottenuti con un centro di lavoro CNC a 3 assi comandati ed un centro di lavoro CNC a 5 assi comandati
Gli autori hanno riscontrato che al variare dell’angolo di inclinazione dell’utensile, si riscontra una variazione
dello spessore del truciolo. Viene quindi generata una variazione del gradiente delle forze di taglio ed una
variazione del profilo delle velocità di taglio. Biermann et al. [20] hanno verificato l’algoritmo di ottimizzazione
di fresatura meccanica in un processo di foratura, su barre a sezione circolare (Ø34.1 mm) in NiTi. Gli
esperimenti sono stati condotti su un centro di lavoro CNC a 5 assi comandati, utilizzando utensili sferici Ø1.0
mm in carburo cementato, rivestiti di TiAlN. La strategia tipica di un programma a controllo numerico per una
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fresatura a 3 assi produce una bassa finitura superficiale (profilo con elevata rugosità e zone di incollaggio tra
utensile e pezzo), dovute ad un crescente angolo di inclinazione tra l’utensile e la superficie da lavorare. La
strategia a 5 assi produce un foro con una qualità superficiale decisamente migliore (Fig. 4) e questo è la prova
dell’ influenza dell’angolo di inclinazione utensile/pezzo e della validità dell’algoritmo di ottimizzazione
presentato in [19] per controllare la qualità della superficie controllando l’inclinazione dell’utensile durante la
lavorazione.
La qualità del componente lavorato e l'affidabilità del processo di microlavorazione sono fortemente
dipendenti dal dispositivo che si utilizza. Utensili di taglio di precisione e macchine utensili sono fondamentali
nei processi di microlavorazione meccanica, poiché piccole vibrazioni e forze eccessive, influenzano fortemente
la qualità della superficie lavorata. La maggior parte dei centri di lavoro per microlavorazioni meccaniche sono
simili alle macchine per lavorazioni meccaniche convenzionali ultra-precise ad alta rigidità, ed operano in
ambiente controllato [21].
Fig. 5. Centro di lavoro ultra preciso KERN Evo a 5 assi controllati
I centri di lavoro per microlavorazioni meccaniche disponibili attualmente sul mercato, hanno un controllo
multi-asse, con vari gradi di libertà, che consentono di produrre piccole parti con texture e geometrie
complesse, nonché modelli di superfici in micro scala come stampi e matrici.
Le lavorazioni per condurre la sperimentazione, saranno realizzate utilizzando un centro di lavoro CNC ultra
preciso Kern Evo a 5 assi controllati (Fig. 5) che sarà disponibile presso il laboratorio Microtronic del DMMM del
Politecnico di Bari. Questo centro di lavoro può sviluppare una potenza di 6,4kW, sufficiente per lavorare
acciaio temprato e altri materiali caratterizzati da elevata durezza. Le elevate accelerazioni (8m/s2) e velocità di
avanzamento (fino a 16.000 mm/min) consentite dalla Kern Evo consentono di lavorare con ridotti tempi di
processo. Il centro di lavoro consente di lavorare oggetti aventi dimensioni massime di 300 X 280 X 250 mm, ed
è corredato da un sistema per il caricamento automatico del materiale, con una precisione di posizionamento
di ± 0,5µm. Infine la qualità superficiale certificata da Kern per questo centro di lavoro è inferiore a 0,1 µm.
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Fig. 6. Pattern di micro-fori
Nell’attesa che il centro di lavoro sia disponibile presso il dipartimento, si è pensato di sfruttare il mandrino a
25.000 giri montato su una tradizionale fresatrice a tre assi controllati, per realizzare delle operazioni semplici
di micro-foratura su alluminio anodizzato. Le lavorazioni che si intendono realizzare consistono in due pattern
di fori: uno con fori aventi diametro Ø0.60mm ed un altro con fori aventi diametro Ø0.30mm, come quello
presentato in Fig. 6. La profondità di penetrazione è pari allo strato di ossido deposto sulle piastre (~20µm).
A tale scopo sono state scelte delle frese cilindriche con codolo rinforzato in metallo duro, rivestite con TiALN,
con le seguenti specifiche: D1 rispettivamente di 0.60mm e 0.30mm, D = 3.00mm, L = 38mm, Z = 2 (Fig. 7).
Queste punte sono in grado di lavorare una moltitudine di materiali tra cui acciai legati ed inox austenitici,
ghise, titanio e sue leghe, alluminio e sue leghe, plastica, leghe di rame difficili da lavorare e metalli nobili.
Fig. 7. Utensile per la realizzazione del pattern di micro-fori
Per ogni materiale esiste un valore di velocita di taglio Vc espressa in m/min, dalla quale dipende la velocità di
rotazione del mandrino. Supponendo una durezza dello strato di ossido da asportare > 250HB, la velocità di
taglio Vt suggerita dal fornitore per questo utensile è 70 m/min - 90m/min. Tuttavia questo, risulta un valore
esageratamente elevato, considerata la piccola quantità di materiale che verrà asportata. Si è deciso pertanto,
di scegliere una velocità di taglio <40m/min. La velocità di rotazione del mandrino la si può calcolare come:
n = vt x 1000 / d x π [giri/min]
Indicando con Fz l’avanzamento al dente e con Z il numero di taglienti dell’utensile, la velocità di avanzamento
al giro Vn è il prodotto tra la velocità al dente per il numero di denti. La velocità di avanzamento Vf la si ottiene
moltiplicando la velocità di avanzamento al giro per il numero di giri, o equivalentemente come:
Vf = Fz X Z X n
Infine, il tempo di taglio per un foro, può essere calcolato come:
Tc = Im / Vf [min]
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avendo indicato con Im la profondità di penetrazione del foro.
In Tab. 1 sono indicati i parametri di taglio scelti per realizzare le due lavorazioni.
Parametri di taglio
Velocità di taglio
Rotazione del mandrino
Avanzamento al dente
Numero di denti
Avanzamento al giro
Velocità di taglio
Tempo di taglio
Vc
n
fz
Z
Vn
Vf
Vc
Fori Ø0.60mm
40 m/min
21.231 giri/min
0,0060 mm
2
0,0120 mm/giro
255 mm/min
0,005 s
Fori Ø0.30mm
20 m/min
21.231 giri/min
0,0030 mm
2
0,0060 mm/giro
127 mm/min
0,009 s
Tab. 1. Parametri di taglio per la realizzazione dei micro-fori
Le operazioni di micro-foratura che si intendono realizzare per asportazione di truciolo, sono già state
realizzate con tecnologia laser. L’intento è quello di confrontare il risultato di una micro-foratura meccanica
con quello di una micro-foratura laser, e verificare quindi quanto studiato in bibliografia circa la qualità delle
due tecnologie di lavorazione.
Realizzazione di un componente con caratteristiche microscopiche
Principale obiettivo della scuola estiva frequentata a Copenaghen presso la DTU, è stato quello di progettare e
realizzare un micro-dispenser che funga da cartuccia per una stampante 3D a polimero fotosensibile. Le
specifiche del dispositivo da realizzare sono riportate di seguito:
• Viscosità del polimero 0.001-0.005 Pa∙s.
• Deposizione di gocce con volume massimo di 0.1mm3.
• Frequenza di dosaggio minima 1 Hz.
• Ingombro Massimo del dispositivo 17 mm x 17 mm
• Temperatura del polimero all’ingresso 20-30°C e temperatura ambiente 25°C
• La tecnologia di fabbricazione deve risultare economicamente conveniente per produzione su larga scala
Fig. 8. Modello CAD del prototipo di cartuccia per stampante 3D a polimero fotosensibile.
In Fig. 8 è riportato il progetto del prototipo: si tratta di un dispositivo in policarbonato con tre diversi circuiti di
pompaggio, realizzabile tramite tecnologia di micro stampaggio ad iniezione. I circuiti contengono ognuno tre
camere di pompaggio, profonde 200 μm e con diametro Ø 3mm. L’ultima camera è passante, ed ha una
rastremazione conica che termina in un piccolo foro che funge da ugello. I tre circuiti sono caratterizzati da
ugelli con diverse dimensioni (Ø 120 μm, Ø 220 μm, e Ø 320 μm), poiché questo consente di utilizzare lo stesso
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dispositivo per diverse viscosità di fluido, in accordo alle specifiche richieste. Il foro più piccolo, cieco, ha una
geometria a scalino, che funge da camera di raccolta del fotopolimero in ingresso.
Il progetto prevede l’incollaggio di una sottile e flessibile membrana plastica (spessore 200 µm) sulla superficie
superiore del dispositivo, e l’inserimento di una cannula Ø 1.2mm attraverso la membrana, al fine di realizzare
un collegamento meccanicamente stabile e privo di perdite, per far fluire il polimero dal serbatoio al
dispositivo.
Fig. 9. Stampo ottenuto con tecnologia di micro-lavorazione meccanica.
Lo stampo utilizzato per il processo di micro stampaggio ad iniezione (Fig. 9), è stato realizzato con tecnologia
di micro-lavorazione meccanica ad asportazione di truciolo, utilizzando la Mikron UCP 600. Come materiale si è
scelto un acciaio indurito (32-36 HRC) per le sue buone proprietà termiche e di resistenza all’usura. Il grezzo di
partenza aveva dimensioni 19X19X6mm.
Il ciclo di lavorazione prevedeva dunque una operazione di sgrossatura per la rimozione del sovrametallo, una
fase di fresatura della superficie progettata, foratura e alesatura dei due fori centrali, barenatura per ottenere
la rastremazione conica ed infine una operazione di finitura. In Tab. 2 sono riportate le specifiche degli utensili
e dei parametri di taglio utilizzati.
Operazione
Sgrossatura
Fresatura
Finitura
Foratura
Alesatura
Barenatura
Utensile
Fresa end mill Ø1 mm
Fresa end mill Ø0.8 mm
Fresa sferica Ø0.8 mm
Punta a forare
Alesatore Ø2 mm
NC Boring
Spindle Speed [rpm]
18000
18000
15000
1675
1114
1000
Avanzamento [µm]
900
720
600
80
115
50
Tab. 2. Utensili e principali parametri di taglio utilizzati per la lavorazione dello stampo.
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Il prototipo realizzato, completo di membrana elastica e cannule, è riportato in Fig. 10: il polimero viene fatto
confluire nella camera di raccolta attraverso una cannula, e viene condotto all’ugello tramite un sistema di
pompaggio a micro-attuatori piezoelettrici. Regolando la frequenza di oscillazione dei micro-attuatori, è
possibile regolare il flusso di polimero.
In appendice è riportato il report completo della progettazione e realizzazione del prototipo.
Fig. 10. Prototipo completo di cartuccia per stampante 3D a polimero fotosensibile
Misure di micro-componenti
Le operazioni di misurazione dei componenti che saranno lavorati con il centro di lavoro ultra preciso,
dovranno essere realizzate con attrezzature che rispondono a specifici requisito. Pertanto, è stato effettuato
uno studio per la definizione delle procedure e dei metodi per la misura, il rilievo superficiale ed il controllo
delle superfici micro lavorate, al fine di individuare le necessità di misura dei componenti micro-lavorati.
Quando si opera su scala microscopica, le necessità metrologiche possono essere suddivise principalmente in
tre gruppi: Strutture 2D (aspect ratio < 1), strutture 2½D (aspect ratio >= 1), e strutture tridimensionali 3D
(aspect ratio >> 1).
Fig. 11. Strumenti per la misura di parti micro-lavorate
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Fra tutte le tecnologie disponibili per la misurazione di parti micro-lavorate (Fig. 11), coerentemente con le
necessità degli oggetti che verranno misurati, si è scelto ti utilizzare strumenti che fossero in grado di realizzare
misure verticali ed orizzontali comprese nel range di 10-2 - 10-9 m e aspect ratio da 1:1 a 1000:1. Pertanto, per la
misurazione delle parti micro lavorate, è stata utilizzata la tecnologia della micro topografia a scansione laser
confocale.
(a)
(b)
Fig. 12. Provini utilizzati per le operazioni di misurazione
Misurazioni con tecnologia micro-topografica
In Fig. 12 sono riportati i provini scelti per le operazioni di misura. La Fig. 12 (a) riporta un provino realizzato
mediante tecnologia Fused Deposition Modeling con la FDM 3000. Il file Stl utilizzato per la fabbricazione del
provino è stato ottenuto attraverso un’operazione di reverse engineering di un benchmark, tramite sistema di
scansione a testa laser e braccio articolato. In Fig. 12 (b) invece, è riportato un prototipo di cartuccia per
stampante 3D a polimero fotosensibile, realizzato mediante tecnologia di micro injection molding, durante la
scuola estiva frequentata a Copenaghen. I provini risultano particolarmente interessanti e coerenti con il tema
della presente ricerca, in quanto presentano caratteristiche di dimensione microscopica, nonché superfici
tridimensionali complesse (free-form).
Fig 13. Ricostruzioni 3D dei provini ottenuti con scansione micro-topografica
Le misurazioni con tecnologia micro-topografica sono state realizzate con uno scanner Optimet, allo scopo di
caratterizzare forma e dimensione dei provini. Questo strumento utilizza la scansione ottica con microscopia
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confocale e fornisce informazioni di tipo quantitativo sulle altezze, rispetto alla posizione della dimensione
misurata. La microscopia laser a scansione confocale è una tecnica ottica basata sul principio di rilevazione
mediante messa a fuoco, grazie al quale ogni singolo elemento della superficie è soggetto a rilevazione. In
questo modo è possibile misurare fino a 500 punti al secondo in modo dinamico. È uno strumento adatto per
realizzare misure con elevata precisione, accuratezza e ripetibilità, senza contatto, su superfici tridimensionali
in metallo, plastica, e gomma. Cambiando la lente sulla sonda, si possono misurare con esattezza, lunghezze
che vanno da 1µm ai 200mm. In Fig. 13 sono riportate le ricostruzioni tridimensionali dei provini mostrati in
Fig. 12.
Provino (a)
La scansione del provino (a) è stata realizzata con il sensore ConoProbe Mark 3.0, utilizzando una lente da
50mm che consente di ottenere punti con una precisione di 6µm ed un discreto working range (8mm).
Allineando il modello tridimensionale al piano XY del Sistema di Coordinate, e sezionandolo con un piano
parallelo al piano XZ, si è ottenuta la “Sezione 1”. Il provino è stato così caratterizzato per forma e dimensione:
l’altezza misurata per i gradini è di circa 250 µm, mentre l’altezza complessiva è di 2mm nella parte più bassa, e
di 4.3 mm nella parte più alta.
Fig. 14. Sezione 1 del modello del provino (a) ottenuto con tecnologia micro-topografica
13
Sezione 1
Nome
H2
H3
H4
H5
H6
Altezza [µm]
250
244
254
266
245
Nome
H7
H8
H9
H10
Altezza [µm]
267
265
268
261
Tabella 3 Misura delle altezze dei gradini del provino (a) per la Sezione 1.
Sezionando il modello con un piano parallelo al piano YZ, si è ottenuta invece, la “Sezione 2”. Anche per questa
sezione, l’altezza de i gradini è di circa 250 µm. L’altezza complessiva è di 2mm nella parte più bassa, e di 4.3
mm nella parte più alta.
Fig. 15. Sezione 2 del modello del provino (a) ottenuto con tecnologia micro-topografica
Sezione 2
Nome
H13
H14
H15
H16
H17
Altezza [µm]
248
244
245
249
243
Nome
H18
H19
H20
H21
Altezza [µm]
253
253
266
248
Tabella 4. Misura delle altezze dei gradini del provino (a) per la Sezione 2.
Provino (b)
La scansione del provino in Fig 12(b) è stata realizzata utilizzando il sensore NanoCono Probe, adatto per
l’acquisizione di oggetti con superfici riflettenti. In questo caso è stata scelta una lente 25 mm che consente di
14
rilevare i punti con una precisione di 0.5µm e risoluzione di 0.1µm, a scapito di un ridotto working range
(1mm). Di seguito sono riportate le misure di alcune caratteristiche micrometriche del provino.
Allineando il modello tridimensionale al piano XY del Sistema di Coordinate, e sezionandolo con un piano
parallelo al piano XZ, si è ottenuta la “Sezione 1”. Il provino è stato così caratterizzato per forma e dimensione:
l’altezza misurata per gli alloggiamenti dei micro attuatori piezoelettrici è di circa 200 µm (Tab. 5).
Fig. 16. Sezione 1 del modello del provino (b) ottenuto con tecnologia micro-topografica
Sezione 1
Nome
H1
H2
H3
Altezza [µm]
201
198
187
Nome
H4
H5
H6
Altezza [µm]
200
190
202
Tabella 5. Misura della profondità degli alloggiamenti per i micro attuatori del provino (b) per la Sezione 1.
15
Sezionando il modello con un piano parallelo al piano YZ, si è ottenuta invece, la “Sezione 2”. Anche per questa
sezione, l’altezza degli alloggiamenti dei micro attuatori piezoelettrici risulta di circa 200 µm (Tab. 6). Inoltre,
nell’analisi di entrambe le sezioni, la misura dei diametri degli alloggiamenti dei micro attuatori piezoelettrici
risulta di 3mm coerentemente con le specifiche di progetto.
Fig. 17. Sezione 2 del modello del provino (b) ottenuto con tecnologia micro-topografica
Sezione 2
Nome
H7
H8
H9
Altezza [µm]
200
199
193
Nome
H10
H11
H12
Altezza [µm]
203
192
211
16
Misurazioni con tecnologia Micro-fotogrammetrica
Dai risultati ottenuti, è evidente che la tecnologia micro-topografica incontra in modo soddisfacente, le
necessità di misura dello studio condotto nel presente lavoro di ricerca, ma ad un costo relativamente alto
(Optimet Miniconoscan 3000, con un costo di 30.000€, risulta essere tra gli strumenti di misura più
convenienti). A tal proposito si è pensato di realizzare un sistema di misura 3D, basato su una tecnologia
capace di dare buoni risultati in termini di precisione, bassi costi, con discrete capacità dimensionali di
scansione, e buone profondità di campo.
Sfruttando le competenze nel campo fotogrammetrico, acquisite grazie a lavori in campo meccanico e
biomedicale, si è pensato di sfruttare tale principio per costruire un microscanner composto da:
Il sistema realizzato si compone dei seguenti principali elementi:
 Tavola rotante motorizzata tramite un motore elettrico a corrente continua, e controllata attraverso un
controllo numerico e retroazione ad encoder ottico;
 Fotocamera Canon EOS 40D, con obiettivo macro 56mm;
 Un computer per controllare sia la fotocamera che il movimento della tavola;
 Un flash anulare ed una struttura a 16 led, montati a sbalzo sulla tavola rotante e solidale ad essa, che
forniscono una adeguata ed uniforme illuminazione dell’oggetto da scansionare.
Fig. 18. Modelli 3D dei provini, realizzati con scansione micro-fotogrammetrica, senza texture (in blu) e con texture.
17
Si posiziona l’oggetto da scansionare sulla tavola, e si avvia la rotazione mediante il controllo numerico. Il
sistema di acquisizione cattura i fotogrammi mentre l’oggetto è in rotazione. I led, solidali alla tavola rotante,
assicurano una illuminazione uniforme dell’oggetto in tutte le immagini, mentre il flash anulare, offre una
perfetta esposizione durante lo scatto. Tramite un programma in codice G ed un software di gestione della
fotocamera, è stato possibile rendere il processo di acquisizione completamente automatico: programmando
una sosta per ogni rotazione pari a 10° della tavola rotante, è quindi possibile realizzare un’acquisizione
tridimensionale dell’oggetto a 360°.
Provino (a)
La scansione del provino in Fig 12(a) è stata realizzata con obiettivo macro 65mm. Le immagini sono state
scattate con un tempo di esposizione pari a 1/100 ed una sensibilità ISO 200. La risoluzione delle immagini è di
3888X2592 pixels. Analogamente a quanto fatto in precedenza, anche in questo caso le ricostruzioni
tridimensionali sono state sezionate e caratterizzati per forma e dimensioni.
Fig. 19. Sezione 1 del modello del provino (a) ottenuto con scanner micro-fotogrammetrico
18
Sezione 1
Nome
H2
H3
H4
H5
H6
Altezza [µm]
223
259
255
259
255
Nome
H7
H8
H9
H10
Altezza [µm]
267
250
259
251
Fig. 20 Sezione 2 del modello del provino (a) ottenuto con scanner micro-fotogrammetrico
Sezione 2
Nome
H13
H14
H15
H16
H17
Altezza [µm]
262
268
241
276
209
Nome
H18
H19
H20
H21
Altezza [µm]
239
241
234
257
Provino (b)
La scansione del provino in Fig 12(b) è stata realizzata con obiettivo macro 65mm. Le immagini sono state
scattate con un tempo di esposizione pari a 1/100 ed una sensibilità ISO 400. La risoluzione delle immagini è di
3888X2592 pixels. Di seguito si riportano le misure delle altezze degli alloggi per i micro-attuatori piezoelettrici,
così come è stato fatto anche precedentemente sul modello ottenuto con scansione micro-topografica. Da
specifiche di progetto la profondità di tali alloggi è di 200 µm, mentre il diametro è di 3mm.
19
Fig. 21. Sezione 1 del modello del provino (b) ottenuto con scanner micro-fotogrammetrico
Sezione 1
Nome
H1
H2
H3
Altezza [µm]
197
187
158
Nome
H4
H5
H6
Altezza [µm]
207
155
233
20
Fig. 25. Sezione 2 del modello del provino (b) ottenuto con scanner micro-fotogrammetrico
Sezione 2
Nome
H7
H8
H9
Altezza [µm]
191
202
197
Nome
H10
H11
H12
Altezza [µm]
197
163
225
21
Analisi dei dati
Per testare l’accuratezza dello Scanner Micro-Fotogrammetrico realizzato, sono stati condotti confronti
bidimensionali e tridimensionali, delle ricostruzioni ottenute con i due sistemi di scansione.

Analisi bidimensionale
È stata condotta quindi, un’analisi della deviazione delle misure, realizzate sulla ricostruzione tridimensionale
dei provini, ottenuti con i due sistemi di scansione. Come è possibile notare, le misure presentano una
deviazione media di circa 10 µm - 20 µm su entrambi i modelli, con deviazione massima di 35 µm. Il risultato è
alquanto soddisfacente se si considera che, in questo primo stadio di ricerca, l’ottica è stata utilizzata senza
calibrazione. Le distorsioni sono state compensate tramite un algoritmo di compensazione utilizzato dal
software di elaborazione delle immagini, impiegato per la costruzione dei modelli tridimensionali.
Fig. 26. Scostamenti dei valori misurati sui modelli 3D del provino (a) nella Sezione 1 e nella Sezione 2.
Fig. 27. Scostamenti dei valori misurati sui modelli 3D del provino (b) nella Sezione 1 e nella Sezione 2.
22

Analisi tridimensionale
Una ulteriore analisi per testare l’accuratezza dello Scanner Micro-Fotogrammetrico realizzato, è il confronto
3D dei modelli ottenuti con i due sistemi di scansione. Come si può vedere in Fig. 28, lo scostamento medio
misurato complessivamente sul modello tridimensionale del provino (a) è di 120µm. Essendo questo un valore
medio, è fortemente influenzato dai valori minimo e massimo misurati. In particolare, si vuol far notare che le
zone in blu scuro ed in rosso scuro, indicano rispettivamente, gli scostamenti massimi negativo e positivo del
modello ottenuto con il Micro-Scanner Fotogrammetrico, rispetto al modello ottenuto con l’Optimet (100µm).
Queste zone sono maggiormente concentrate nella periferia del modello. Infatti, per il basso overlap tra i
fotogrammi (Fig. 29), la ricostruzione è meno precisa in questi punti. Inoltre, è possibile notare che l’errore
maggiore viene commesso sugli spigoli dei gradini, indice di un’operazione di smoothing nella fase di
costruzione del modello, con acquisizione micro-fotogrammetrica. Ad ogni modo, ignorando le zone periferiche
del modello, l’errore commesso nella ricostruzione del modello, è inferiore a 40 µm.
Fig. 28. Mappa di colore del provino (a) effettuata con Optimet 3000 e con lo Scanner Micro-Fotogrammetrico
Fig. 29. Schema delle posizioni assunte dalla fotocamera e di overlap delle immagini
23
Lo scostamento medio misurato complessivamente sul modello tridimensionale del provino (b) invece, risulta
leggermente superiore (200µm). La zona in verde, che indica uno scostamento <10 µm è piuttosto estesa.
Tuttavia la ricostruzione ottenuta con lo scanner micro-fotogrammetrico risulta imbarcata lungo una diagonale.
Infatti nella parte centrale del modello è evidente una zona in azzurro chiaro (circa -25 µm) con picchi di 100
µm in alcuni punti, mentre due dei quattro spigoli sono in giallo (25 µm) e arancione (40 µm). inoltre, anche
per questa ricostruzione, come nel caso del provino (a), i bordi risultano leggermente arrotondati.
Fig. 30. Mappa di colore del provino (b) effettuata con Optimet 4000 e con lo Scanner Micro-Fotogrammetrico
24
Bibliografia
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micro cutter edge radius and minimum chip thickness, International Journal of Machine Tools &
Manufacture 48 (2008) 1–14.
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Technology Volume 213, Issue 4, April 2013, Pages 532–542.
[3] M.C. Shaw, Precision finishing, CIRP Annals 44 (1) (1995) 343–348.
[4] C.-J. Kim, J. Rhett Mayor, J. Ni, A static model of chip formation in micro scale milling, ASME
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[5] X. Liu, M.P. Vogler, S.G. Kapoor, R.E. DeVor, K.F. Ehmann, R. Mayor, C.-J. Kim, J. Ni, Microendmilling With meso-machine-tool system, NSF Design, Service and Manufacturing Grantees and
Research Conference Proc., Dallas, TX 1 (2004) 1–9.M.P.
[6] Vogler, R.E. Devor, S.G. Kapoor, Microstructure-level force prediction model for micro-milling of
multi- phase materials, ASME Journal of Manufacturing Science and Engineering 125 (2004) 202–209.
[7] A. Dhanorker, T. Özel, Meso/micro scale milling for micro-manufacturing, International Journal of
Mechatronics and Manufacturing Systems (2008) 23–43
[8] C.D. Torres, P.J. Heaney, A.V. Sumant, M.A. Hamilton, R.W. Carpick, F.E. Pfefferkorn, Analyzing the
performance of diamond-coated micro end mills International Journal of Machine Tools and
Manufacture (2009) 599–612.
[9] S.I. Jaffery, P.T. Mativenga, Assessment of the machinability of Ti-6Al-4V alloy using the wear map
approach, International Journal of Advance Manufacturing Technology (2009) 687–696.
[10] Kuppan P, Rajadurai A, Narayanan S (2008) Influence of EDM Process Parameters in Deep Hole
Drilling of Inconel 718. International Journal of advanced Manufacturing Technology 38(1-2):74–84.
[11] Li L, Low DKY, Ghoreshi M, Crookall JR (2002) Hole Taper Characterisation and Control in Laser
Percussion Drilling. CIRP Annals Manufacturing Technology 51(1):153–156.
[12] C. Fornaroli, J. Holtkamp, A. Gillner (2013) Laser-beam helical drilling of high quality micro holes.
Lasers in Manufacturing Conference 4: 654 – 662.
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[13] Friedrich Dausinger , Helmut Hügel , Vitali Konov ( ) Micro-machining with ultrashort laser pulses:
From basic understanding to technical applications a Stuttgart University, Institut für Strahlwerkzeuge
(IFSW), Pfaffenwaldring 43, D-70569 Stuttgart, Germany1 b General Physics Institute, Moscow,
119991,Vavilova str., 38, Russia
[14] Pal Molian, Ben Pecholt, Saurabh Gupta (2009) Picosecond pulsed laser ablation and
micromachining of 4H-SiC wafers. Applied Surface Science 255: 4515–4520
[15] Man Sheel C, Dong-Woo C, Ehmann KF (1999) Identification and Control for Micro-Drilling
Productivity Enhancement. International Journal of MachineTools & Manufacture 39(10):1539–1561
[16] Chae J, Park SS, Freiheit T (2006) Investigation of Micro-Cutting Operations. International Journal
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[17] M.M. Okasha, P.T. Mativenga, N. Driver, L. Li (2010) Sequential laser and mechanical microdrilling of Ni superalloy for aerospace application. CIRP Annals - Manufacturing Technology 59 (2010)
199–202
[18] Li L, Diver C, Atkinson J, Giedl-Wagner R, Helml HJ (2006) Sequential Laser and EDM Micro-Drilling
for Next Generation Fuel Injection Nozzle Manufacture. CIRP Annals Manufacturing Technology
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[19] K. Weinert and T. Surmann, Geometric (2003) Simulation of the Milling Process for Free Formed
Surfaces. Simulation Aided Offline Process Design and Optimization in Manufacturing Sculptured
Surfaces, K. Weinert, Ed., p 21-30
[20] D. Biermann, F. Kahleyss, E. Krebs, and T. Upmeier (2010) A Study on Micro-Machining
Technology for the Machining of NiTi: Five-Axis Micro-Milling and Micro Deep-Hole Drilling. Journal of
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[21] Y.B. Bang, K. Lee, S. Oh (2004) 5-Axis micro milling machine for machining micro parts. Advanced
Manufacturing Technology
26
Appendice
Design and production of a microfluidic
dispenser for additive manufacturing
using photopolymers
41790 Micro mechanical system design and production
(PhD summer school)
28-06-13
27
1
Introduction.................................................................................................................................................. 30
2
Project management .................................................................................................................................... 30
3
Design process .............................................................................................................................................. 31
3.1
Concept development .......................................................................................................................... 32
3.1.1
Functional requirements .............................................................................................................. 32
3.1.2
Constrains ..................................................................................................................................... 32
3.1.3
Selection criteria ........................................................................................................................... 33
3.2 System-Level Design ................................................................................................................................... 33
3.2.1 Design solutions................................................................................................................................... 33
3.3
Concept screening ................................................................................................................................ 34
3.3.1
First iteration ................................................................................................................................ 34
3.3.2
Second iteration ........................................................................................................................... 35
3.3.3
Third iteration ............................................................................................................................... 35
3.3.4
Fourth iteration ............................................................................................................................ 36
Fig.3.5
Fourth iteration device design .............................................................................................................. 36
3.4
Design considerations........................................................................................................................... 37
3.4.1
Calculations .................................................................................................................................. 37
3.4.2
Critical features and requirements ............................................................................................... 39
3.4.3
Dimensions and tolerances ........................................................................................................... 40
3.5
4
References ............................................................................................................................................ 41
Tooling.......................................................................................................................................................... 42
4.1 Design of the Tool....................................................................................................................................... 42
4.2
Process Chain........................................................................................................................................ 43
4.2.1
Direct tooling vs. indirect tooling .................................................................................................. 43
4.2.2 Selection of Tool Material.................................................................................................................... 44
4.2.3 Selection of Manufacturing Method.................................................................................................... 45
4.3 CAM & Production ...................................................................................................................................... 45
4.4
5
References ............................................................................................................................................ 46
Polymer ........................................................................................................................................................ 47
5.1
Introduction .......................................................................................................................................... 47
28
5.2
Polymer selection ................................................................................................................................. 47
5.3
Requirements to the polymer .............................................................................................................. 47
5.4
Theoretical aspects of PC ...................................................................................................................... 48
5.4.1
Shrinkage of molded PC ................................................................................................................ 48
5.4.2
Demolding Force ........................................................................................................................... 49
5.5
Injection molding of the part ................................................................................................................ 51
5.1.1
5.6
6
References ............................................................................................................................................ 54
Additive manufacturing ................................................................................................................................ 54
6.1
Introduction .......................................................................................................................................... 54
6.2
3D Printing for actuators ...................................................................................................................... 55
6.3
Actuator 1: camshaft ............................................................................................................................ 56
6.3.1
7
8
Parameter optimization ................................................................................................................ 51
Design and construction of the 3D printed actuator .................................................................... 56
6.4
Actuator 2: push/pull solenoid with piston .......................................................................................... 57
6.5
Introduction to linear variable differential transformer ....................................................................... 58
6.6
Piston displacement measurements with LVDT ................................................................................... 59
6.7
Functional tests on the device .............................................................................................................. 60
6.8
References ............................................................................................................................................ 61
Joining Techniques and LISA ......................................................................................................................... 62
7.1
Methods ............................................................................................................................................... 62
7.2
Selection of method ............................................................................................................................. 63
7.3
Experimental setup ............................................................................................................................... 63
7.4
Results from the experiments on the final structures .......................................................................... 68
7.5
Comments from the actuation results .................................................................................................. 69
7.6
Conclusion ............................................................................................................................................ 70
7.7
References ............................................................................................................................................ 70
Metrology ..................................................................................................................................................... 71
8.1
Introduction .......................................................................................................................................... 71
8.2
Critical features and metrological equipment ...................................................................................... 71
8.3
Conforming the measurements tools to the standards ........................................................................ 73
29
8.5
Statistical Process Control and monitoring ........................................................................................... 74
8.6
Measurements ..................................................................................................................................... 76
8.6.1
Part measurements ...................................................................................................................... 76
8.6.2
The mold ....................................................................................................................................... 78
8.7
Discussion of the results ....................................................................................................................... 78
8.8
References ............................................................................................................................................ 78
9 Conclusion and outlook ..................................................................................................................................... 79
9.1 Conclusion .................................................................................................................................................. 79
9.2
Outlook: ................................................................................................................................................ 79
Appendix 1 ........................................................................................................................................................... 80
Appendix Metrology ............................................................................................................................................. 81
Calculation of the uncertainty budget .............................................................................................................. 81
Measurements results ...................................................................................................................................... 81
Appendix 2 ........................................................................................................................................................... 84
30
1
Introduction
This report was made for course 41790 Micro mechanical system design and production. The main objectives
of the project work were the design, manufacturing and test of a micro fluidic dispenser for application as a
cartridge in 3D photopolymer printer. The initial demands to the device were:
•
•
•
•
•
•
•
2
Should dispense fluid with a viscosity in the range of 0.001-0.005 Pa s.
Allow fluid supply in finite volumes of maximum drop volume 0.1mm 3.
Minimum dosage frequency of 1 Hz.
Should consist of passive/active elements
Produced by means of low cost replication technologies (polymer injection molding)
Maximum area of the device is 17 mm x 17 mm
Temperature of fluid at inlet of 20-30°C and ambient temperature of 25°C
Project management
The preliminary work on the design was performed by varying between work in random groups (diverging) and
work in plenum (converging). After deciding on an overall design concept the class was divided into 6 groups,
each with their area of responsibility:
1. Design coordination, modeling and project management
a. Design optimization and incorporation of input from other groups (after the initial
determination of overall design performed in plenum)
b. Determination of critical features and tolerances
c. Coordination of project
2. Tooling
a. Evaluation on possibilities for fabrication of injection molding insert
b. Define tooling process chain
c. Select process parameters and machining strategy
3. Polymer
a. Selection of suitable polymer for device fabrication
b. Determine optimal injection molding parameters
c. Determine shrinkage and impact of this on the tool design
d. Ensure de-molding by estimating the de-molding force and changing tool design accordingly
e. Mold devices
4. Additive Manufacturing
a. Set up test solution for prototypes and the final device
b. Fabrication and test of prototype for validation of device functionality
c. Validate functionality actuation system
d. Design and fabricate new mechanical actuation system using additive manufacturing if primary
actuation system fail
31
5. Joining and LISA
a. Evaluate different solutions for joining the various parts of the device
b. Select the best suited joining solutions
c. Optimize and validate the selected solutions
d. Join the devices
e. Verify the use of LISA for sensor and/or actuators integration
6. Metrology
a. Identify features’ characteristics critical for the functionality/performance
b. Selection of suitable metrological equipment for characterization of critical features
c. Define a suitable measuring strategy for the quality control of parts and insert
d. Conduct performance measurements for qualification of insert and parts
The groups worked individually on their tasks every afternoon from 13.00 to 16.30. In this timespan
communication between the groups were conducted directly for optimal work efficiency. In order to
summarize and inform on the work progress of all the groups a common meeting was held at 16.30 every day.
At the meeting the latest changes to the device design was furthermore presented, evaluated and updated to
fulfill the demands set forward by all the groups.
In order to facilitate knowledge sharing the internal network at DTU (CampusNet) was used for data exchange.
Furthermore the blackboard in the class room was converted to an “information board” were the current
status and work tasks of the groups were updated regularly. This made it possible for everybody to be updated,
even if working most of the time at a different location.
3
Design process
During the course of this project a photopolymer dispenser has been designed and produced in accordance
with the design process illustrated in Figure 3.1.
Figure 3.1:
Design process [3.1].
The planning was mainly done by the course responsible before the beginning of the course and thus the work
presented in this report starts with the concept development. During this phase the functional requirements
along with constrains and selection criteria were considered and reviewed continuously in order to obtain a
general design concept. Afterwards, the system-Level Design was done by performing a concept screening, see
section 1.4. The concept screening resulted in a single product design that was utilized for the initial
considerations in the work groups. Following the initial group work, it was adjusted continuously until a final
design was made (design phase) Friday evening and sent for production (initial build phase) Monday morning.
The building phase stretched from Monday to Wednesday when the devices were assembled. The tests were
32
initiated as the first devices were finished and continued Thursday. As the course is only two weeks there was
no room for iterations and thus no production ramp-up.
3.1
Concept development
In the following a short description of the functional requirements, constraints and selection criteria are
presented. These were used for developing a general concept before moving on to the design phase.
3.1.1 Functional requirements
The functional requirements are a set of requirements that describes the input, behavior and output of a
system. In the case of the microfluidic dispenser considered in this project the primary functional requirement
is that the cartridge should be able to facilitate a flow of photopolymer and in the end divide the flow into
individual droplets of a finite size and at a constant frequency.




Open system
o Flow in
o Flow out
Droplet formation/flow control
o Actuation
 Local pressure increase
 Non-capacitive device polymer
o Leek prove channel
o No backflow
 Valve
Droplet control
o Frequency
o Volume
Block UV-light
3.1.2 Constrains
After having determined the initial functional requirements of the microfluidic dispenser, the constrains were
considered. Most of these were set beforehand and were mainly used to revisit the functional requirements
and add the feature of not allowing UV light to enter the device.







Polymer device
Handle photopolymer
Viscosity: 0.001- 0.2 Pa s
Max. drop volume: 0.1 mm³
Minimum dosage frequency: 1 Hz
Maximum area: 17x17 mm
Temperature of fluid at inlet: 20-30°C
33
 Ambient temperature: 25°C
3.1.3 Selection criteria
After having determined both the functional requirements and the constrictions of the dispenser an initial
design proposal could be proposed. However, some selection criteria had been found during the previous
work. These are listed below and mainly affect the material choice and method.






Cheap large scale fabrication method (e.g. polymer injection molding or hot embossing)
Cheap polymers
Availability of tools
Ease of manufacture
Time taken to manufacture
Robustness of the device
3.2 System-Level Design
After having determined the functional requirements, constraints and selection criteria for the device a design
had to be found. Initially different solutions were found to support the demands to the device, see
section 3.2.1. Next a concept screening was performed by, in turn, brainstorming in groups (diverging) and
discussing in plenum (converging).
3.2.1 Design solutions
In order to fulfill the functional requirements several solutions were proposed for each individual requirement.
These were the basis for the following concept screening.
Table 3.1 Morphological table for different functional requirements
Functional Requirement
Flow in
Flow out (design of outlet)
Flow out (placement of
outlet)
Actuators
Leakage proof
Droplet frequency control
Droplet volume control
Means to achieve the functional requirement
Leur connector
Needles
Conical
Constriction of walls
Side
Bottom
Blockage of UV light
Right device material
Piezoelectric
Peristaltic pump
Actuators
Deflection of thin film
Mechanical deflection
External pump
External pump
Hydraulic resistance based
on channel dimensions
Packaging
Cylindrical
Rectangular
Electrostatic
Electro magnetic
Pressure in the
channel
Painting
External pump
Protective layer
Based on the functional requirements, a morphological table (Table 3.1.) was made where different methods
to accomplish each requirement were discussed. Then based on the selection criteria, one or a combination of
methods was selected (green in Table 3.1.). Keeping this in consideration, the final design was made. For
example, in order to pump the liquid inside the device, two methods were proposed: peristaltic pump (left) and
external pump (right) as shown in Fig. 3.1. Considering the ease of manufacture and robustness of the device,
the peristaltic pump design was chosen.
34
Fig. 3.1. Two different pump designs.
3.3
Concept screening
During concept screening, various rounds of designing the device were conducted. During the fourth and final
iteration of the designing and screening process, final device design was chosen. After the screening, the device
was further tuned to get the exact design that fulfills the functional requirements along with critical features,
their dimensions and tolerances. Here is the concept screening process:
3.3.1 First iteration
During the first iteration, brainstorming of the main functional requirements estimate of the design was
performed and an initial estimate of the device design was made. Some of the designs that came out of this
iteration are illustrated in Fig. 3.2.
Fig. 3.2. Initial device designs.
35
3.3.2 Second iteration
Fig. 3.3. Second iteration of device designs.
The second iteration was done after defining the functional requirements in detail and brainstorming on the
various selection criteria and device constraints. This time the class was divided in the group of four to come up
with five various designs, which are shown in Fig. 3.3 After each design was presented, the most complicated
design (Fig. 3.3 (bottom)) was discarded as it did not meet the selection criteria of ease and time of
manufacturing. Then the other four designs were basically group into two basic designs of 1) use of pump and
no thin film membrane (Fig. 3.3 (top))and 2) use of no external pump to control droplet volume and flow but
use of actuators to do so with a thin film membrane (Fig. 3.3 (center))
3.3.3 Third iteration
After the five designs made in the second iteration, one was rejected and rest four were divided in two groups.
The class was divided into two groups working on each concept: 1. External pump group and 2. Actuator and
thin film group. Three designs came out from this iteration (Fig.1.4.3). One (Fig.1.4.3 (bottom left)) was
rejected based on the complexity of the design failing the ease and time of manufacturing criteria. The rest two
designs were discussed in detail and finally the “actuator and thin film” design was chosen.
36
Fig. 3.4 Third iteration of device designs
3.3.4 Fourth iteration
The fourth iteration gave us a benchmark for final design (Fig.1.4.4.1). The design consisted of an inlet
through-hole with a channel designed to align three actuators. The channel is supposed to be sealed by a thin
film membrane and actuation needs to be done on this membrane to control the volume, flow and leakage of
the photopolymer fluid.
Fig.3.5
Fourth iteration device design
The fourth iteration design went through many rounds of re-designing. It was refined further and various
features and parameters of the design were explored and discussed. Finally, Fig.1.4.4.2 was fixed as the final
design. The final device consists of one molded plastic part with actually three different pumping circuits. A
200 µm thick thin film membrane is supposed to be used to seal the channels of 200 µm depth and 400 µm
height between the pumping sites. The inlet is realized by 1.2 mm thick cannulas which will be punched
through the polymer thin film and glued to the device for leakage-free and mechanically stable connection. For
connecting the cannulas the device is equipped with matching cavities. Each cavity contains a stop, so that a
fluidic connection between the cannula and the first pumping chamber is ensured. The cannulas can be
equipped with flexible plastic hoses for connecting the reservoir. Peristaltic pumping was considered to control
the flow of the fluid in the channel. Therefore, the circuits contain three pumping chambers of 3 mm diameter
37
each. The pumping chambers are 200 µm deep. The last pumping chamber is conically tapered through the
entire device ending in a tiny through hole which functions as the actual nozzle. The nozzle diameters are
chosen as 120 µm, 220 µm, and 320 µm. This enables to try the behavior of three different sizes on the same
chip. Since the nozzle is by far the narrowest fluidic structure, it determines mainly the fluidic resistance of the
device and the necessary pressure to shot out the drops. Having three different nozzles provides flexibility in
the hydraulic resistance of the nozzle, so that the nozzle can be changed according to the viscosity of the
handled fluid. The mold insert can be derived as the negative of the part structure and will be discussed in
more detail in the tooling chapter (chapter 2). The drawings of the insert for production can be found in the
appendix (Appendix A).
Fig. 3.6 Final device design after fine tuning of fourth iteration device design
3.4
Design considerations
To realize the functionality of the device it is necessary to avoid the leakage but also realize the volume flow by
using the activators. For the first the burst pressure of micro valve has to be greater than hydrostatic pressure.
For the second the pressure realized through the activators has to be over the burst pressure.
3.4.1 Calculations
3.4.1.1 Micro capillary burst valve
Two pressures act on the liquid/air interface at the ejection nozzle. On the one hand there is the pressure of
liquid column that presses on the liquid surface and on the other hand the pressure of air due to surface
curvature, resulting out of surface tension and contact angle. Assumptions for calculating the hydrostatic
pressure that presses onto the liquid surface at the ejection nozzle.
Assumptions:
-
Volume flow is vertical (Z-direction -> worst case)
Nozzle is fixed in height
Outlet of the monomer tank is on the same height as the device inlet)
Reservoir filling level hf = 30 mm
Channel height hc = 3 mm
Density of water  = 1200 kg/m3
38
- Gravity g = 9.81 m/s2
- Contact angle β = 90 ° (output of the nozzle)
- Diameter of the nozzles: d1 = 120 µm, d2 = 220 µm, d3 = 320 µm
- Thermal expansion  = 70*10-6 1/K
Measured values:
- Surface tension  = 73 mN/m (typical value for water to PC in literature 31.0 mN/m [xy])
- Contact angle  = 72 ° (typical value for water on PC in literature 87.2° [xy])
Results:
Hydrostatic pressure can be calculated to be phyd = 390 Pa. The calculated burst pressure for assumed nozzle
diameters is between approx.. 870 to 2300 Pa. So the compliance is ensured. For further optimization a
diagram of burst pressure to channel diameter is shown in Appendix 1.
3.4.1.2 Test of the surface tension effect of fluid in micro channel
As the surface tension affects the fluid flow greatly in micro size, surface tension effect is tested. The
experimental setup is shown in Fig. 3.7.
Bottom
Plate
Flow inlet
Gravity
direction
Covering
tape
Channel
Fig. 3.7 Experimental setup for test
Since the fabrication of the channels with the same dimensions as the final target is not accessible, the
test was done with the available PC fluidic channel chips. Tape was used to cover the channels. The
channel width of 0.8mm with channel height of 0.3mm is tested. A syringe is used to insert the liquid
into the channel through the inlet. The result shows that the liquid coming through the channel will not
fall down under gravity force due to the surface tension. However, if pressure is applied in the inlet,
there will be flow to the outlet. Therefore, we can reach to the conclusion that as long as there is no
actuation, no liquid will leak out through the channel with a channel width of 0.8mm. Furthermore,
channel width smaller than 0.8mm will also hold the liquid [3.3].
3.4.1.3 Deflection of membrane
The peristaltic pump system is based on three different chambers with flexible membranes realized as polymer
thin film. The membranes are deflected by applying an external force which is provided by an actuator. Due to
the requirements for the amount of pumped fluid, the necessary membrane deflection can be estimated.
Assumptions:
39
- The deflected membrane has the shape of a spherical cap.
- The whole displaced fluid will be pumped in forward direction.
Results:
The necessary deflection for displacing the maximum target volume of 0.1 mm³ can be calculated as
w = 30 µm. Since not all displaced volume is pumped in forward direction, the respective deflection must be
higher to meet the requirements. For a deflection of 100 µm, the displaced volume is about V = 0.35 mm³.
Nonetheless, the given target volume is an upper limit. As a result, smaller displacements are acceptable, too.
Moreover, the actually displaced volume might be smaller, because the membrane does not describe a perfect
spherical cap.
3.4.2 Critical features and requirements
There are multiple critical features of the nozzle device which are either crucial for the functionality of the
system or the success of the process chain. The following features must be particularly considered for the
design of the part and mold insert:
 Ejection nozzle (diameter, shape)
 Channels (depth, width, shape of cross-section, roughness)
 Pumping chamber (diameter, depth, spacing)
 Edges perpendicular to flow direction
 Ejector holes (diameter, roughness)
 Elevated plateau (dimensions)
The ejection nozzle is the core element of the device. The diameter is very important as it decides about the
burst pressure of the capillary micro valve. Moreover, the shape of the nozzle influences the release and
shaping of the droplet.
The pumping chambers of the peristaltic pump must be large enough to allow the membrane to deflect
without breaking and to provide enough space to couple the actuators. The deflection is again linked to the
volume that must be pumped. The spacing between the chambers should be short to prevent from high
hydraulic resistance of the channels in between.
Any edges being perpendicular to the flow direction must be rounded. Sharp edges are favorable locations for
the formation or pinning of bubbles inside the channel which might block or tremendously hinder the flow.
The mold insert is fixed in the mold by a frame with an open window for the plastic of 17 x 17 mm². The
protruded plateau of the mold insert must meet this size very precisely. If the gap due to alignment between
the frame and the insert is too big, polymer will be able to flow inside. This results in flash which might affect or
hinder the bonding. The upper tolerance is chosen as 0 µm. If the plateau is larger, the frame cannot be
mounted on the insert. The lower tolerance is chosen as -40 µm. This will ensure on the one hand the
mounting and on the other hand a very tight fitting.
The ejector holes are not a functional part of the nozzle device, but they contribute to the robustness of the
system. They must meet requirements regarding their diameter, because they have to fit very precisely to the
40
ejector pins. If the gap is too large, polymer could flow into the gap during injection. This results in flash which
can negatively influence or completely prevent from bonding. The roughness of the ejector holes must not be
too large. Otherwise, the friction between holes and pins will increase significantly. A larger ejection force will
be thus necessary, so that a higher risk of damaging or deforming the part arises.
3.4.3 Dimensions and tolerances
Tolerances state in general the range of a property of an object in which changes caused by a disturbing
influence does not affect the functionality of the object. Some of the aforementioned critical features must
therefore be equipped and manufactured with tolerances in order to keep correct functionality and meet the
actual design. Uncritical features do not need any tolerances, as the machining precision can be assumed as
being sufficient. Introducing too tight tolerances will be very costly and time-consuming.
The diameter of the ejector nozzle will become larger due to the shrinkage of the plastic. Here, very tight
tolerances are necessary to stay within the calculated specifications. To counteract the shrinkage the upper
and lower tolerances of the nozzles are chosen as +0 µm and -10 µm. This will result in high demands on the
machining precision. Nonetheless, the time consumption is little as the structures cover only a small part of the
whole machining. The roughness should be Rz=1 µm to prevent from big changes in contact angle and thus in
the valve capillary pressure.
The depth and width of the channels are not as crucial as the size of the nozzle. It can be assumed that the
machining precision is sufficient for providing a tolerance that still enables the capillary filling of the channels.
The viscosity is given in a range of 0.001 Pa*s (water like) to 0.2 Pa*s (maple syrup like). The higher viscosity is
more critical with regards to the hydraulic resistance. However, it can be assumed that the actuators provide
enough pressure to drive the flow even with a higher hydraulic resistance of the channels. Furthermore two
The usually achievable tolerances of few micrometers are small compared to the size of the channels. The
roughness is however very important and hence chosen as Rz=2 µm. The risk of large changes in contact angle
and thus in capillary pressure increases with increasing roughness.
The diameter of the pumping chambers was chosen to be 3 mm. This size is necessary for sufficient deflection
of the membrane. Moreover, it provides enough space to avoid the necessity of a very precise and elaborate
alignment of the actuators. The safety margin is large enough, so that the usual achievable machining tolerance
is sufficient. It will be negligible compared to the large size of the chamber. The spacing is chosen as 4 mm to
allow the rounding of the channel edges between the chambers. On the other hand, the channel length and
hydraulic resistance is minimized. The narrowing between the chambers is favored over one broad channel
with three different actuation sites to guide the flow.
The diameter of suitable standard ejector pins is given as 2 mm g6 [3.2]. Due to the possible flash issues, the
diameter of matching ejector holes was chosen as 2 mm G6. Roughness requirements to the ejector holes were
not stated in particular, as it can be assumed that the machining process will yield a roughness that will not
tremendously increase the friction.
41
The radius of the fillet of the edges is chosen as 0.5 mm. This allows using only one tool diameter for the fine
machining and it will not be necessary to change tool and realign. The tool diameter of 1 mm is still large
enough to provide sufficient mechanical stability to prevent from bending of the tool leading to a loss of
machining precision.
3.5
References
[3.1] Ulrich, K. T. and Eppinger, S.D. Product Design and Development. McGraw-Hill, 2008
[3.2] www.hasco.de, accessed 24-06-2013.
[3.3] [Ref] D.S. Kim, “Micro-channel filling flow considering surface tension effect”, J. Micromech. Microeng,
vol. 12, pp. 236–246 (2002)
42
4
Tooling
Tooling is an important part of many manufacturing processes. While producing micro-components using
micro-injection moulding, the designing and production of an appropriate tool insert is essential for ensuring
accurate feature generation on the moulded part. However, unlike traditional macro-scale manufacturing,
tooling for micro-components have a tighter tolerance and require better surface quality. In this section we
discuss the strategies adopted for creating the tool for micro-injection moulding a micro-fluidic droplet
dispenser for an additive manufacturing device.
4.1 Design of the Tool
The tool for micro-injection moulding was designed using the CAD model of the desired product. The microinjection moulding setup allowed a maximum tool size of 19mm X 19mm X 6mm. However, the clamping
mechanism for the tool reduced the available area to 17mm X 17mm only. Appropriate tolerances and
roughness values were prescribed after identifying the critical functional features of the final component. The
critical features and the associated tolerance and/or roughness values were:

Roughness value of bottom wall of micro-channel: The micro-channel bottom surface needed to have a
good surface roughness to allow the product to function as designed. Thus, a maximum roughness (Rz)
of 2 microns was planned.
 Tolerance of output nozzle: The output nozzles were designed to allow outflow of the fluid under
certain pressure. As the micro-channel device would undergo shrinkage when cooling after moulding,
the nozzle is expected to increase in diameter. However, the amount of tolerance to accommodate
this phenomenon is small and thus considerations were made based on the manufacturability and the
time required for achieving the tolerance. Thus only a negative tolerance of 10 microns was allowed on
the tool, which would correspond to a negative tolerance of the nozzle diameter.
 Roughness of nozzle wall: The output nozzle as mentioned earlier is a critical functional feature. Thus, a
maximum roughness (Rz) of 1 micron was prescribed for the region of tool corresponding to the inner
walls of the nozzle.
The micro-injection moulding setup makes use of two different sets of ejector pins for removing the product
after moulding. However, based on preliminary simulations of demoulding process (Section), the inner ejector
pins were chosen to be used. This implied a need for having two through holes of 2mm diameter near the
middle region of the tool insert. As flashing of polymer is an undesired phenomenon, tight tolerances were
given for the ejector pin holes. The 3D CAD drawing of the tool is shown in Fig 4.1 and the corresponding
engineering drawing with dimensions and tolerances is shown in Appendix 2.
43
Figure 4.1
4.2
3D CAD drawing of the tool.
Process Chain
After the tool design was made, the manufacturing process chain for achieving it had to be planned. The key
steps involved in producing the tool were the selection of tool material, selection of tool manufacturing
method and the planning of the production steps.
4.2.1 Direct tooling vs. indirect tooling
While producing a tool for micro-injection moulding, an important decision is whether to use direct tooling or
indirect tooling. Direct tooling is when the tool is manufactured directly from a CAD drawing [Fig 4.3] and has a
negative geometry with respect to the original part to be manufactured. This sort of tooling can be achieved
either with an additive process or subtractive process. The additive manufacturing processes, such as Direct
Metal Laser Sintering or Fused Deposition Modeling, add material in a layer by layer manner to build the tool.
The subtractive processes, such as milling and Electro-Discharge Machining, involve removing material from a
block of bulk material.
Indirect tooling is where a tool is made by an in-between step. First a positive master is produced. From this
master, a negative mold is formed, which is then used as a tool for the polymer replication process, see Fig 4.2.
The advantage of using direct tooling is the lower manufacturing time. Direct tools are thus preferred when the
structures on the tool are easy to manufacture using standard techniques such as micro-milling, micro-forming
or micro-EDM The disadvantage is the limited robustness of the tool; direct processes gives tools that can be
used approx. 5,000 times [4.1]. A second disadvantage is the limitation on the materials that can be used for
direct tooling, which might be unsuitable for injection moulding certain polymers.
The primary advantage of using indirect tooling is that the tools are stronger and more robust. Therefore,
typically a significantly larger volume of injection-moulded units can be produced with each tool. The most
44
apparent disadvantage is that it involves extra manufacturing step. This increases the cost of production for the
parts and is thus only suitable when the number of parts is high or when the tool cannot be manufactured
using direct tooling. Since the requirement for the current micro-fluidic device is only 100 pieces, direct tooling
is sufficient for this project.
Figure 4.2: Direct tooling and indirect tooling.
4.2.2 Selection of Tool Material
The material for the tool should have the following characteristics:
1. Good heat conductivity: The tool would need to transport heat away from the process so the polymer
repetition process is not influenced by heat.
2. Thermal stability: The tool should not undergo any phase transitions during the polymer repetition
process.
3. High wear resistance and surface hardness: The tool should be able to withstand high and repeated
loadings. For polymer device replication the hardness of the tool needs to be between approx. 80 and
550 HV.
The material for the tool was chosen to be hardened steel (Impax supreme, Uddeholm) [4.2]. This kind of steel
has a high degree of homogeneity and isotropic hardness. The hardness is listed in Table 4.1 and shows a
sufficient hardness for injection molding.
Furthermore, the density is only changing from 7,800 kg/m3 to 7,750 kg/m3 when the temperature changes
from 20 oC to 200 oC, and similarly the elastic modulus is only changing from 205.000 N/mm 2 to 200.000
N/mm2 over the same temperature range. This indicates high thermal stability.
The heat conductivity of the steel is 28 W/m·K ± 15%, which is intermediate, but possible high enough to
transfer heat in the injection molding process away from the polymer.
Table 4.1: Hardness of the tooling material hardened steel (Impax supreme) from Uddeholm.
Hardness
Impax supreme
Brinell HB
290-330
Vickers HV
~289-335
Rockwell HRC
~32-36
Rockwell HRB
~106-109
45
4.2.3 Selection of Manufacturing Method
The choices for primary manufacturing method involved micro-milling and micro-EDM. The considerations for
choosing between the methods are provided below.
1. High geometrical freedom: When the tool can be made can be in 3 dimensions, the need for multiple
tools are less likely.
2. High accuracy: The tolerance of the tool is partly defining the tolerance of the injection molded device.
3. High surface quality: The surface quality requirements are dependent on the component, the
repetition process and the joining method.
4. High surface integrity: The integrity means the amount of micro cracks, tensile stresses and heataffected zones. These effects should be in a low amount as possible.
5. Capability to machine hard materials: Since the tool material should be of a highly hard material, the
tooling process should be able to work with these kinds of materials.
The not so important considerations of the tooling methods include productivity and cost. This is because the
tool is only made once and is used over and over again. This is in contrast to the polymer replication process
which needs to be highly productive and cheap, since the polymer device needs to be made in a high number.
The tooling method chosen is micromilling. This is a subtractive method, where a rotating screw is removing
one layer at a time and thereby revealing a structure. This structure will be the tool for the injection molding.
Micromilling is chosen because the structures that we want are in the hundreds of micrometer to millimeter,
and the tolerances are not too strict. Also since there are structures that go all the way through the polymer, a
lot of material needs to be removed to form the tool. For this, the micromilling method is optimal.
4.3 CAM & Production
Upon selection of micro-milling as the manufacturing method, the appropriate machining tools and the
processing sequence had to be chosen. The CAD model for the tool was sent to the micro-machining workshop
for development of process plan and production. The CAD geometry was used to create a processing sequence
involving 6 different tools. Based on the tools used, appropriate processing parameters were chosen using a
database which provided the operating ranges. This information was used to create a final processing plan
which was simulated and validated using a CAM software. The six different tools and their operating
parameters are listed in Table 4.2.
Table 4.2 Tools used during micro-milling of insert.
Tool Type
NC Boring
Drilling
Reaming Φ2H7
End Mill Φ1
Tool Speed (rpm)
1000
1675
1114
18000
Tool Feed (μm)
50
80
115
900
46
End Mill Φ0.8
Ball Mill Φ0.8
18000
15000
720
600
The 1 mm diameter end mill is used for arbitrary stock roughing operation where a 19 mm X 19 mm X 6 mm
block of Impax is machined to remove a large portion of material. The roughing tool path is generated with a
roughing offset of 1 mm. Subsequently, the 0.8mm diameter end mill is used for contour milling of the
designed structures and for finishing operations. The 0.8 mm ball mill is used for z-level finishing operation. The
holes for the ejector pins are created with the drilling tool with peck drillling and then produced to accurate
size with a 2mm diameter reaming tool. The boring tool is used to create a tapered hole for the nozzle.
The tool insert was finally created on a Mikron UCP 600 milling machine. The manufactured tool is shown in
figure 4.4.
Figure 4.4: Manufactured tool insert for the micro-injection moulding process
4.4
References
[4.1] Patrick Grant and Stephen Duncan. Spray-on-steel. Ingenia, 2005, Issue 25, pp. 30-32.
[4.2] Data sheet from Uddeholm - Impax supreme.
47
5
Polymer
5.1
Introduction
Injection molding is one of the most widely used processes for large scale plastic manufacturing. The master
can be repeatedly used with faithful replication. Injection molding utilizes a ram or a screw-type plunger to
force molten polymer into a cavity. This molten polymer will conform to the contour of the mold.
Parts that are to be injection molded have to be carefully designed to facilitate the process. The material used
for the part, the desired shape and features of the part, the material of the mold, and the properties of the
molding machine must all be taken into account. Often, thermoplastics polymers are used in this process. The
process itself is a combination of time, temperature and pressure variables with a multitude of manufacturing
defects that can happen without the correct processing parameters and design components [1].
In this section, the details of the polymer replication of the designed component using injection molding will be
covered. Both the requirements to the polymer and the processing parameters are covered using analytical,
numerical and empirical tools.
5.2
Polymer selection
The microdevice will be molded by injection molding on a suitable thermoplastic polymer. The following
polymers are of interest to us, due to their impermeability to visible (and thereby probably also UV) light and
their suitability in micro injection molding:
(i) Acrylonitrile butadiene styrene (ABS)
(ii) Polycarbonate (PC)
(iii) Polypropylene (PP)
(iv) COC (TOPAS)
Other polymers could possibly also be used, but only the four listed candidates are considered.
5.3
Requirements to the polymer
The four candidates must be analysed based on the requirements for the final device. Table 5.1 shows the list
of main requirements that the polymer is required to have. The requirements have been ranked according to
the importance to the final device functionality, 5 being an essential requirement and 1 being less important. A
few of the requirements should be elaborated on: The heat deflection temperature is meant as a lower limit,
ensuring that the device will not deform during normal operation. The requirement on electrical conductivity is
stated in order to facilitate integration with an electrical actuation mechanism. Finally, amorphous polymers
are preferred over semi-crystalline polymers due to their lower shrinkage during cooling. Based on the results
obtained, PC (black colour) is the most preferred material for the bulk of the device. The molded structures on
the PC will then be bonded to a thin foil, which does not necessarily need to be of the same material. The
material of choice will be investigated in the bonding section of the report.
48
Table 5.1 Tabulation of the necessary requirements for the four different kinds of polymers often used in injection molding.
5.4
Theoretical aspects of PC
In injection molding processes, software packages are often used to predict the process [2]. Often, the molded
parts are at the risk of being subjected to defects at the ejection stage. Numerous authors have investigated
the parameters that influence the ejection forces. Shen et. al. have reported that increasing diameter and
thickness of the part will result in higher demolding forces. Packing pressure [4], demolding temperature [4, 5],
cooling time and roughness [6] are all interlinked. These parameters not only contribute to the ejection forces,
they also influence them. Charmeau et. al. had also reported on investigating the application of different mold
surface coatings at the ejection process.
In this section, we will also be discussing the demolding force based on mathematical calculations and
simulations of the deformation of the molded PC part. The software, Comsol Multiphysics (ver 4.3), was used
to perform the simulations. First, the expected contraction of the polymer was estimated to evaluate the
potential impact on the design of the mold tool. Then, approximate analytical estimates and detailed
simulations of the actual tool and polymer part were performed to investigate the impact on the demolding on
contraction. The former is used to supply order-of-magnitude estimates of the demolding force, while the
latter is used to evaluate the optimal ejector pin positioning and potential weak points of the tool.
5.4.1 Shrinkage of molded PC
In order to evaluate the requirements of the mold, the expected shrinkage of the polymer needs to be taken
into account. According to the polymer specifications, the shrinkage should be in the order of 0.7 % at
maximum. Thus, at a distance, , from the center of contraction, the shrinkage will be
The relative change in channel dimensions will therefore be a function of the channel location with respect to
the center of contraction. Assuming that the center of contraction coincides with the geometrical center of the
49
part, the channel will experience the largest distortion if it is placed near the edge. For a channel of width 400
µm, the relative geometrical distortion for a 17 mm wide part will thus at the most be
Assuming the channel is placed in the center of the mold, the estimated relative geometrical distortion will be:
For the worst case scenario of 14 %, the channel distortion is 56 µm. However, as the channel functionality is
not critically impaired by such a change, it is decided not to compensate for the shrinkage in the tool
manufacturing. This would also require very accurate simulations of the molding process.
5.4.2 Demolding Force
The shrinkage can also be used to evaluate the demolding forces. According to the polymer specifications, the
stress at 85 C (the molding temperature) and a strain of 0.7 % (the maximum expected strain) is in the order of
10 MPa.
The corresponding normal force on a channel of height h and length L is thus
Note that this is independent of the channel position, , relative to the center of contraction. Note also that
the force is calculated only on one channel wall. Only walls with surface normals pointing away from the center
of contraction will be affected. Assuming a static friction coefficient of 0.3, the force on the channel walls
during demolding will therefore be
The order of magnitude for the demolding force as a function of channel height and length is sketched in
Fig. 5.1. To estimate the optimal position of the ejector pins, a simulation of the final designed part was set up
in Comsol, see figure 5.2. It was found that when the ejector pins are closer to the center of the part, the
simulated maximum stress on the part is much lesser than when they are located at the ejector parts. Comsol
was also used to simulate the same stresses acting on the tool insert. It was observed that the stress was no
higher than 34 MPa, i.e. lower than the typical yield strength of steel. Thus, it was estimated that even when
relatively fragile pins were to be made for the through-hole connections, the tool insert would be able to
withstand the demolding forces. Figure 5.3 shows the simulation of the eventual part.
No investigations on the effect of clamping force on the pins were made, as it was assumed that the tool is
made is such a way that it will not collide with the mold.
50
Fig. 5.1 Estimation of the required demolding forces as a function of channel height displayed for three different channel lengths.
Note that the simulations are approximate as they use a rough estimate of the friction forces. In order to
achieve more accurate results, the actual stresses in the molded part should be evaluated using numerical
software such as MoldFlow. However, in order to model micro injection molded parts, precise knowledge and
modeling of the entire mold and injection nozzle is a requirement to get usable results. Therefore, this has not
been done.
Fig 2.2 Simulation of the demolding forces for two different positions of the ejector pins. The left figure shows
the ejector pins located at the ejector parts, and the right figure shows the situation with the ejector pins
located at the center of the part.
51
Fig 5.3
Simulation of the demolding forces on the mold tool.
5.5
Injection molding of the part
5.1.1 Parameter optimization
As mentioned earlier, the injected molded part is dependent on several parameters during injection molding.
Therefore, it is necessary to optimize the following parameters: the injection volume, packing time, packing
pressure and molding temperature. Below is the flow of the optimization process, we will be following when
molding the desired part.
Optimisation and flow process of injection molding:
1. No packing. Increase the injected volume until 98 % filling. This defines the final injection volume.
3. Set the packing pressure to 40 % or 80 %.
4. Increase packing time until the weight of the piece becomes constant.
5. Check the surface/channel quality.
6. If channels are not replicated well, increase the mold temperature and repeat the process.
The ENGEL machine was used in the injection molding process.Initially, an injection temperature of 75°C was
experimented and the surface quality of the part was poor. However, once the mold temperature was
increased to 85°C, the surface quality improved hugely. This was therefore used for molding the parts. The next
parameter that we had to optimize was the injection volume by adjusting the stroke length.
Effects of injection stroke length on the injected molded part
The injection molding machine was operated at a cooling time of 15 s and an injection speed of 50 mm/s. To
investigate the effect of the injection stroke length, packing pressure was not applied. The injected molded
pieces from different injection stroke lengths were collected and compared visually.
52
Figure 5.1
(c)
(b)
(a)
Effects of injection stroke length on the eventual part. (a) Stroke length = 10mm; (b) Stroke length = 10.5mm; (c)
Stroke length = 11mm
As seen from figure 3.1, the volume and shape of the injected molded part is highly dependent on the injection
stroke length. With increasing injection stroke length, the part will be filled to a higher degree. The optimal
stoke length fills roughly 98 % of the part, leaving a small portion for the subsequent packing. Our
investigations had showed that the optimized injection stroke length is 11 mm as seen in Fig. 3.1 c.
Effects of packing time on the injected molded part
Having optimized the injection stroke length, the next step was to optimize the packing time. Keeping the
cooling time at 15 s, injection speed at 50 mm/s, we added a 40 % of packing pressure which corresponded to
44 bars. The percentage is taken with respect to the maximum injection pressure, being 110 bars.
3.2 Injection molded device
(a)
(b)
Figure 3.2 Effects of packing time on the surface finish of the injected molded part. (a) Packing time = 0.5 s; (b) Packing time = 2 s
The packing time was increased gradually and the molded parts were weighed. Once the weight of the molded
parts stagnated, the time that the part first reached the plateau weight was chosen. As can be seen from figure
3.3, this corresponds to a packing time of 2 seconds. The packing time also affected the finished surface of the
injected molded part. As seen from figure 3.2, with a shorter packing time, the surface of the part showed
shrinkage voids, thereby affecting the flatness of the surface. This shrinkage, even in non-visible amounts, is
easily verified by using the before mentioned weighing procedure.
53
The last parameter we optimized was the packing pressure. The packing pressure was increased to 80 % which
corresponds to 88 bars. We also varied the packing time for this pressure to obtain the optimum packing time.
Figure 5.3 Effect of packing time with respect to the measured weight.
As seen from Fig 5.3, for both packing pressure, the optimum packing time was at 2 s. Fig 5.3 also showed that
with increasing packing pressure, the weight of the part also increased. With an optimum packing time of 2 s,
at 80 % packing pressure, the weight of the part was 0.715 g whilst at 40 % packing pressure, the weight was
0.705 g. The 80 % packing pressure was chosen, as the injected molded part showed a better and smoother
surface finish and better filling as evidenced by the higher weight. Table 5.1 shows the tabulated optimized
injection molding parameters that were used to produce the parts.
Table 3.1 Optimised parameters for the injection molding process.
54
5.6
References
1. Pantani, R. and Titomanlio, G., ‘‘The Simulation of Post-Filling Steps in Injection Molding,’’ in Injection
Molding—Fundamentals and Applications, M.R. Kamal, A.I. Isayev and S.-J. Liu, Eds., Carl Hanser
Publisher, Cincinnati, OH (2009).
2. Vietri, U., Sorrentino, A., Speranza, V., Pantani, R., ’Improving the Predictions of Injection Molding
Simulation Software’, Polymer engineering and science, 2009, 51, 12, 2542-2551
3. Shen, K., Chen, L-M., Jiang, L., ʻCalculation of ejection force of hollow, thin walled, and injection molded
cones’, Plastics, rubber and composites, 1999, 28, 7, pp. 341-345(5)
4. Pontes, A. J. and Pouzada, A. S., ʻEjection Force in Tubular Injection Moldings. Part I: Effect of Processing
Conditions’, Polymer engineering and science, 2004, 44, 5, pp. 891-897
5. Pontes, A. J., Brito, A. M., Pouzada, A. S., ʻAssessment of the ejection force in tubular injection moldings’,
Journal of injection molding technology, 2002, 6, 4, 343-352
6. Sasaki, T., Koga, N., Shirai, K., Kobayashi, Y., Toyoshima, A., ʻAn experimental study on ejection forces of
injection molding’, Journal of precesion engineering, 2000, 24, 3, 270-273.
7. Charmeau, J.-Y. , Chailly, M., Gilbert, V., Béreaux, Y., ʻInfluence of mold surface coatings in injection
molding application to the ejection stage’, International Journal Material Form, 2008, 1, 1, 699-702
6
Additive manufacturing
6.1
Introduction
The first form of creating layer by layer a three-dimensional object using computer-aided design (CAD) was
rapid prototyping, developed in the 1980’s for creating models and prototype parts. Rapid prototyping is one
of the earlier additive manufacturing (AM) processes and it allows for the creation of printed parts, not just
models [6.1]. It is also known as 3D printing or digital fabrication and its primary distinguishing feature is to
create parts by the controlled addition (rather than subtraction) of material [6.2].
Fig. 6.1 MakerBot Thing-O-Matic
55
Among the major advances that this process presented to product development are the time and cost
reduction, human interaction, and consequently the product development cycle, also the possibility to create
almost any shape that could be very difficult to machine.
AM processes take the information from a computer-aided design (CAD) file that is later converted to a
stereolithography (STL) file. In this process, the drawing made in the CAD software is approximated by triangles
and sliced containing the information of each layer that is going to be printed.
Recently, AM technologies have been standardized and classified by the American Society for Testing and
Materials (ASTM) International Committee F42 on Additive Manufacturing Technologies. The committee has
classified AM processes and their variants into seven main categories including: photopolymer vat, material
extrusion, powder bed fusion, directed energy deposition, sheet lamination, material jetting, and binder jetting
[6.1, 6.3]. They differ in the way layers are deposited to create parts and in the materials that can be used.
Some methods melt or soften material to produce the layers, e.g. selective laser melting (SLM) or direct metal
laser sintering (DMLS), selective laser sintering (SLS), fused deposition modeling (FDM), while others cure liquid
materials using different sophisticated technologies, e.g. stereolithography (SLA). With laminated object
manufacturing (LOM), thin layers are cut to shape and joined together (e.g. paper, polymer, metal, …). Each
method has its own advantages and drawbacks, and the costumer should find the best solution to be applied in
each specific case.
6.2
3D Printing for actuators
An actuator is a device that takes energy in some form and converts it to perform some type of mechanical
work, which is typically motion (i.e. blocking, clamping or ejecting). It also can be used to apply a force.
One of the most challenging and exciting frontiers in self-replicating machine research is the development of
printable actuators: actuators that can be built using the constrained set of materials and processes available
to a 3D printer.
Smart materials exhibit changes in their physical properties, such as size or shape, in response to external
stimuli (e.g. temperature, or electric current). Smart materials can function as actuators i.e. devices that
provide movement or changes in shape, for robotics and related applications. Some examples are:
 piezoelectrics, that produce a voltage when stress is applied;
 “shape memory” materials, in which large deformation can be induced and recovered through
temperature changes, stress changes (shape-memory alloys and polymers) or a significant variation in
the magnetic field (magnetic shape-memory alloys);
 temperature-responsive polymers, which undergo changes upon temperature;
 photomechanical materials, changing shape under exposure to light;
 …
Complete actuators including active membranes and support structures can be 3D printed in one go, resulting
in a great improvement in fabrication speed and increases in accuracy and consistency
A major advantage related to the employment of this technology is that more complex 3D structures can be
constructed if more flexibility in layer deposition is possible, for example by enabling the forming of variable
thickness layers and the deposition of actuator layers at different angles [6.4].
In 2011 Walters et al. [6.5] presented a 3D-printed bio-actuator comprising a pressure inlet, a diaphragm
fabricated from soft silicone elastomer, a magnetic switch, a “smart” control valve incorporating a NiTi fibre
actuator, and an outlet. The 3D printing process employed in the fabrication was photopolymer jetting in which
56
a liquid photopolymer resin was deposited by inkjet printing and immediately cured by ultraviolet light. This
biologically-driven actuator will serve as a proof-or-concept “artificial heartbeat” for future use within biorobotic art and design.
Fig 6.2
6.3
Bio-actuator 3D printed working prototype.
Actuator 1: camshaft
6.3.1 Design and construction of the 3D printed actuator
For the actuation of the nozzle- device a camshaft-device was designed and 3D-printed. The single cams are
actuating with a 60 degree phase-shift to each other to follow the actuation principle suggested by Tan, et al.
[6]. The actuation principle is shown in Figure 6.3.
Fig. 6.4 Actuation principle of camshaft actuator. Grey: Cam 1, Purple: Cam 2, Blue Cam 3.
In Figure 6.3 each line symbolizes the movement of a certain point on one of the cams. If the value is higher
than zero the cam is pushing on the membrane and pumping the chamber underneath. For values lower than
zero there is no contact between the membrane and the actuator.
To enable the actuation of all three channels of the nozzle-device a x-y-stage was implemented in the design.
This stage enables the positioning of the nozzle-device underneath the cams using M2-screws. This leads to a
57
position accuracy of 400 µm per 360 degree revolution of the screw. The position in z-direction can be defined
by four M2- screws in the corners of the device (Figure 6.4).
Fig. 6.5 Left: Camshaft-device after 3D-printing and rinsing of the support material, right side: Assembled system.
The camshaft can be connected to a “Como Drills 951D10216V” DC-Motor for the necessary actuation speed of
the nozzle device.
For first prototypes of the camshaft-device 3D-prints with different tolerances (50 µm, 100 µm, 150 µm, 200
µm, 250 µm) for the axle clearance bearing were printed on a “Objet 30” 3D-printer. The tolerance range was
choosen because it was not possible to predict the minimum clearance that could be used. Even if the
resolution of the printer is higher than the chosen tolerances, the limiting factor for the clearance was the
removal of the support material which is necessary to produce a rotating axis in a 3D-printed device. This was
possible for all the clearances without the 50 µm tolerance. The material used by this printer is an acrylate like
photopolymer with the Tradename “VeroWhitePlus RGD835”.
6.4
Actuator 2: push/pull solenoid with piston
The actuator consists of a push/pull solenoid which displaces a piston located through it. It is an on/off type
actuator and develops force in one direction when energized with electric current. The return force is provided
externally by a return spring.
Piston
Spring
Figure 6.5
Actuator (RS code: 347652).
In order to determine how much current should be applied the get the right piston displacement for actuating
the fabricated device, a linear variable differential transformer (LVDT) transducer was used as sensitive
electromechanical detector of linear movement with appropriate electronics.
58
Figure 6.6
6.5
LVDT measurement setup for piston actuator.
Introduction to linear variable differential transformer
The basic LVDT design consists of a cylindrical array with a primary winding centered between two identically
wound secondary windings. The coils are wound on a hollow glass-reinforced polymer (GRP) former, which is
surrounded by a high-permeability magnetic shield. This assembly is then secured into a stainless steel tube
that is sealed at both ends. This tubular element is the static part of the LVDT construction. [6.6]
Figure 6.7
LVDT
LVDT produces a linear electrical output that is directly proportional to the position of a movable ferromagnetic
core of nickel-iron alloy. Typically, the LVDT body is fixed in place and the core is attached to the object whose
position is to be measured, slides along the axis of the tube.
Inside the LVDT are three windings: one primary and two secondary coils that are 180° out of phase.
A sinusoidal RMS voltage between 2.5 and 10 kHz excites the primary winding. The two secondary coils share
the magnetic field generated by the primary coil, inducing a voltage in the secondary windings similar to a
transformer. However, the position of the ferromagnetic core determines how much magnetic flux each
winding senses and thus the resulting output voltage. At an end-of-travel position, one secondary senses
almost all of the magnetic flux while the other winding senses almost none. The two secondaries flip division of
the magnetic field when the core moves to the opposite extreme. When the core is in the center (null
position), both secondaries receive equal amounts of the primary magnetic field, producing output voltages
that are identical, though 180° out of phase [6.7, 6.8]. That signal is easily collected by any data acquisition
device.
In machining centers LDVTs are used for positional feedback on the tool and tool holder since they can make
measurements directly inside the machine during the machining process.
59
a.
b.
Fig. 6.8
a. Cutaway view of an LVDT. Current is driven through the primary coil at A, causing an induction current to be generated
through the secondary coils at B. ~ b. LVDT schematic.
6.6
Piston displacement measurements with LVDT
LVDT sensor was used for displacement measurement to assess how much the piston moves when applying a
force. To do that the piston was used to place the sensor in the null position. This is crucial for measuring
through the most linear portion of the transducer range.
Fig. 6.9 Illustration of measuring principle for LVDT sensor.
Null position could be found by varying the applied force on the actuator; however this was not achieved due
to spring softening and collapsing. This resulted in lack of repeatability for each measurement and could be
explained taking into account different phenomena:
1. change of magnetic properties of the piston due to the presence of different magnetic fields in the
measurement setup ;
2. heating of actuator and piston;
3. variability in aligning the piston on LVDT sensor.
To contrast the first problem, the piston was removed from the magnetizing actuator and heated in order to
demagnetize it. Nevertheless the approach had only a small effect and was not sufficient to overcome the
problem.
In order to overcome the overheating, nitrogen gas was applied on the actuator to cool it down. Since it
showed only a little effect, another approach was tried by lowering the current flow through the actuator: this
allowed measurements on the system. This suggests that overheating was a more influencing problem if
compared to magnetization.
60
For that concern variability in aligning the piston on LVDT sensor, the issue could not be solved because of the
huge space of movement of the piston inside the actuator. Even though the problems stated above were
minimized as much as possible, the null position for the sensor was not established. Therefore displacement
measurements were done somewhere within the LVDT linear range, with a differential approach.
Measurements were done 5 times for each of the three pistons to check system reproducibility and data are
reported in the Table 6.1.
Piston #2 was not able to get stable positions and therefore measurements were not taken for it. Pistons #1
and #3 showed an acceptable reproducibility but they did not allow the displacement of maximum 100 µm
needed for the device actuation.
Table 6.1 LVDT measurements for minimum displacement.
# Piston
1
2
3
Upper value [µm]
-360
-420
-490
-420
-410
-340
-340
-400
-410
-390
-370
Lower value [µm]
-216
-300
-307
-260
-280
-150
-240
-330
-280
-270
-240
Δ Displacement [µm]
140
120
180
160
130
190
100
70
130
120
130
However since the force applied to displace the piston inside the actuator was also used to put the LVDT within
its measuring linear range, this force cannot be directly translated to the force needed for displacing the
membrane of the fabricated device. Therefore the measurements here reported do not coincide with the real
piston displacement provoked by the actuator, thus functional tests were done directly on the device.
6.7
Functional tests on the device
Figure 3 shows the testing setup exploited to assess the functionality of the device. The device with thin film
bonded to the injection molded component was tested as first and it turned out that the maximum
displacement force which could be produced by the actuator was not high enough to move the membrane.
Therefore testing experiments were done with the backup solution consisting of a tape sealed chamber. A
syringe was used to put water through cannels until a droplet was seen at the nozzle output to verify that the
device was completely filled. Then, the needle was disconnected from tubing leaving it filled with water to
create an open reservoir. To control the actuator, provided software and code were exploited and modified so
that the three actuators were moving in the right sequence, with a frequency of 1 Hz. Liquid moved through
the tubing. After approximately 20 seconds the tape was punctured and leakage at the inlet was observed,
therefore it was not possible to determine if the system was pumping in an effective way the liquid through.
61
Actuator #3
Actuator #1
Actuator #2
A.
B.
Fig. 6.10 a. Test setup for the fabricated device. ~ b. Zoom in showing actuator pushing chambers.
6.8
References
1. “A Review of Additive Manufacturing” KV Wang et al. ISRN Mechanical Engineering 2012
2. “Three-DimensionaI Printing: The Physics and ImpIications of Additive Manufacturing” E Sachs et al.
CIRP Annals - Manufacturing Technology 1993
3. “Multiple material additive manufacturing - Part 1: a review” Vaezi et al. Virtual and Physical
Prototyping 2013
4. “Printing 3D dielectric elastomer actuators for soft robotics” J Rossiter et al. EAPAD 2009
5. “Digital fabrication of a novel bio-actuator for bio-robotic art and design” P Walters et al. IS&T Digital
Fabrication 2011
6. “Technical article: Applied Measurements discusses the LVDT operating principle” Applied
measurements 2013
7. “New Uses for Linear Variable Differential Transformers (LVDTs)” R Rapas Machine Design 2010
8. “The LVDT: construction and principles of operation” Technical Paper by Measurement Specialties Inc.
62
7
Joining Techniques and LISA
When a microfluidic part has been designed and fabricated, a major concern is often how to seal the channels
on the chip. Several processes have been developed for joining of two polymer devices without collapsing the
small channels. These include laser welding, thermal bonding, tape and glue. Each of these methods will be
presented below and a preferred procedure for the fabricated device will be chosen. Also the method of LaserInduced Selective Activation (LISA) is introduced.
7.1
Methods
Laser welding
Welding is extensively used in the metal industry for its ability to locally heat the substrate above the melding
temperature, and thereby creating a joined point of two parts when cooled. It is however not possible to
directly transfer the method into polymer fabrication. Since many polymers are transparent to the wavelength
of the laser, only a small portion of the energy will be converted into heat in the polymer. Therefore this
method has a set of requirements for it to work:
1. One of the materials to be joined must have a higher absorption of the laser energy compared to the
other.
2. The other material should be transparent to the laser.
3. The two materials should be compatible for each laser welding to each other [1].
The first requirement is set since the laser energy has to be absorbed at the interface between the two
materials in order to create a strong bond. This also means that the top material should be transparent (hence
the second requirement). Thirdly a list of compatible materials for laser welding has been made by [1], which
shows how well a joint can be made between two materials. This method is very fast as it only relies on
positioning of a laser beam.
Thermal bonding
Bonding of two polymers by applying heat and pressure has been a much used method for sealing microfluidic
channels [2,3]. By heating the polymer to around the glass transition temperature it is possible to form an
invisible, seamless seal. However the process is slow as often many minutes (or even hours) have to be used in
the bonding press. By keeping the temperature at the glass transition it is possible to join the polymers without
destroying the structure of the channels. Y. Wang et al. reported thermal bonding of two PC parts by treating
the chip with air plasma for 5 minutes, followed by a 5 minute bonding procedure.
Taping of channels
An easy solution for sealing a surface is to use tape. The tape will then act as the last part of the channel, and if
the seal is strong enough to withstand the pressure of the fluid inside the channel, this can be a suitable
solution for many devices. However one side of the channel will be covered in the glue from the tape, which
63
can be a severe contamination of the fluid sample. Also the tape has to be compatible with the use of the
device.
Gluing of parts
Another solution is to use glue (e.g. epoxy) between the materials. This however has to be implemented in the
design of the device, as grooves have to be made where the glue should be placed. The glue also suffers from
some of the same drawbacks as taping when it comes to compatibility and contamination of the fluid sample.
7.2
Selection of method
Laser welding was quickly tested for joining of the black PC template chip and a transparent PC thin film, since
this method should be the fastest to conduct of the presented methods. Unfortunately the test showed that
the amount of heat created at surface of the black structure, was too high and basically just cut straight
through the thin film. Another problem was also that the laser left a track of burned polymer around the laser
path. Therefore this method was disregarded.
Through further discussions within the group it was decided to use thermal bonding of the parts, as this
method should provide the strongest seal of the channel. Even though a plasma oven was not available the
method was still chosen. Taping and gluing was disregarded due to the contamination issues. Taping was
however kept as a backup plan, if there would be troubles with the thermal bonding.
LISA
Laser-Induced Selective Activation (LISA) is a method that can incorporate small electric circuits on polymer
films. This is done through metallization of specific parts of the polymer. By scanning the surface of the
polymer in the desired pattern, it is possible make the surface porous, which enables autocatalytic electroless
plating of copper [4]. Metal lines on the order of 80 µm [5] can be produced by this method, which makes it
useful for implementation in micro devices. The fabricated circuits can serve as e.g. sensors or heating devices,
which increases the functionalities of the final device without decreasing the portability.
In this project we have chosen not to implement LISA elements, as temperature control was considered not to
be a “need to have” feature. Future version of the design could possibly benefit from the inclusion of LISA
elements, if e.g. temperature control proves to be an important factor.
7.3
Experimental setup
For the experimental part we used a thermal bonding press. As can be seen in Figure X.1, it is mainly composed
by a hydraulic unit (max 12 ton), polished pressing plates, dial face thermometers, and pressure gauge. By
placing the two polymer parts in the press, the force exceeded by the plates can be manually adjusted and the
parts bonded. An external temperature control was implemented in order to ensure that the desired
temperature was reached and maintained throughout the bonding process.
64
Fig. 7.1. Experimental setup with thermal bonding press, which includes two parallel plates for bonding, hydraulic unit for
controlling the pressure and a temperature control. An external temperature control (green wire) was used to monitor the
actual temperature.
The internal temperature control (right next to the press), was first set to 128 °C on both the upper and lower
plate, see Figure 7.2. This is close to the glass transition temperature (138 °C) of the PC used in this device (see
Table 7.1). A closer margin could be used, but the temperature was only guaranteed to be within ±5 °C.
Unfortunately the external control showed very varying temperature (up to 150 °C), which made the first set of
experiments unpredictable, but nevertheless bonding was attempted.
65
Fig. 7.2. The Internal temperature control was set to 128 °C, which is just below the glass transition temperature of the PC
used in the device.
Table 7.1. Thermal properties of the polycarbonate used for bonding.
PC Sabic Lexan 141R
Glass Temperature, Tg
Melt Temerature, Tm
138 °C
320 °C
For testing the strength of the bond achieved in the bonding press a mass was applied in one end of the
bonded thin film. By increasing the total mass it was possible to determine a force required to break the
bonding. A custom made cup holder (Figure 7.3a)) was made which could contain smaller weights (Figure
7.3b)).
a)
Fig. 7.3
b)
a) Picture of the cup holder, which should be attached to an extruding part of the bonded thin film, and serve as a holder
for smaller weights (b)).
The cup holder was attached to a small extruding part of the thin film through the use of a paper clip, see
Figure 7.4. It was then examined how much weight it would take to make the film start delaminating from the
bulk surface.
66
Fig. 7.4 The cup holder was free hanging only in a small extruding part of the thin film. This was achieved by using a paper clip.
Materials
Two sets of experiments were performed on the bonding press; one using the template structure and one
using the real device. The first was done, since the real device was not yet available for testing. A small piece of
the template structure was cut in order to mimic the size and shape of the final device, see Figure 7.5. The
dimensions are roughly 25 mm x 28 mm compared to the final 17 mm x 17 mm (Figure 7.6).
Fig. 7.5. The test pieces for the first set of experiments were cut from the template structure provided. The dimensions are
roughly 25 mm x 28 mm.
Fig. 7.6. Picture of the final device and thin film to be bonded. The dimensions are 17 mm x 17 mm.
Preliminary results (first set of experiments)
A DOE analysis was conducted to determine the influence of bonding time and pressure on the bonding
process between thin film and substrate. For this preliminary analysis a microfluidic component in PC Sabic
Lexan 141R 25 x 27 mm was used. The thin film was Makrofol® DE 1-1 000000. The temperature of the plates
was kept constant at 128 ±5 ° C for both plates.
67
A factorial plane 22 was generated and for each set of values 3 replications of the experiments have been
performed. The values are summarized in Table 7.2 and Figure 7.7 and 7.8.
Table 7.2 Experimental results gathered for the first set of experiments with the template structure.
n°
Time
Pressure
1
2
3
4
5
6
7
8
9
10
11
12
13
[min]
4
8
4
8
4
8
4
8
4
8
4
8
6
[Mpa]
7,0 (0.5 ton)
7,0 (1 ton)
14,0
14,0
7,0
7,0
14,0
14,0
7,0
7,0
14,0
14,0
10,5
Main Effects Plot (data means) for Breaking force
Time
0,54
Interaction Plot (data means) for Breaking force
0,65
Force
Time
4
8
0,60
0,52
0,50
0,55
Mean
Mean of Breaking force
Breaking
force
[N]
0,3
0,6
0,4
0,8
0,7
0,4
0,7
0,7
0,3
0,3
0,2
0,3
0,7
0,48
0,50
0,46
0,45
0,44
0,40
0,42
0,5
4
8
0,5
1,0
Figure 7.7. Main Effects Plot and Interaction Plot
1,0
Force
68
Contour Plot of Breaking force vs Force; Time
1,0
Surface Plot of Breaking force vs Force; Time
Breaking
force
< 0,45
0,45 - 0,50
0,50 - 0,55
0,55 - 0,60
> 0,60
0,9
0,8
Force
0,60
Breaking force
0,7
0,55
0,50
0,45
1,00
0,6
0,75
4
Time
0,5
4
5
6
Time
7
6
8
Force
0,50
8
Figure 7.8. Contour Plot and Surface Plot
It should be noticed that breaking force increases a lot for both higher pressure and longer bonding time. This
was expected as both parameters ensure a tighter bond between the thin film and the chip. However manual
inspection of the chip was needed, in order to verify that the channel and other structures have been properly
sealed and not collapsed. The parameters tested in this experiment did not show any sign of collapsing
channels, but a full seal between the channels was not always achieved. This can be attributed to the very
varying temperature, which was hard to keep steady. Some experiments resulted in almost melted chips, which
have not been included in the data shown.
7.4
Results from the experiments on the final structures
For the actual bonding experiments of the final device, a series of optimized parameters was chosen according
to the previous test. As is mentioned above, it is preferable to choose a larger pressure and longer bonding
time to obtain a tighter seal. Since we did not observe any collapse of the channels, it was decided to increase
the parameters a slight bit. In this experiment, we used 1.5 tons, 8 minutes and 128°C. As is shown above in
Figure 7.6, the PC thin film now has the same area as the PC plate.
The first experiments on the final device showed, that after thermal bonding, some regions of the joined part
were not united. This meant that the channels where not fully separated and sealed. This was attributed to the
fact that the pressure distribution of the bonding press was not very uniform. To fix this, two silicon wafers
where tried to serve as pressure distributors on both of the bonding plates. These however shattered
immediately due to the high pressure and large amount of dirt in the bonding press. Consequently, an assisting
sheet was added around the chip (see Figure 7.9). This piece of metal had roughly the height of the chip, but a
small metal piece had to support the chip to align it fully.
69
Fig. 7.9. A metal sheet was placed between the bonding plates in order to even the pressure load on the final device. A
smaller metal piece have been inserted under the chip in order to align the two structures.
After this adjustment a nice seal was obtained, except for some small bubbles between the channels. These
were vented by making two holes in the thin film between the channels. This resulted in a bonding as shown in
Figure 7.10. As can be seen, the middle channel has a lesser tight seal than the two edge channels; however a
sealing is still obtained. This proves that thermal bonding of the device is possible, but it requires a lot of
optimization before a satisfying result can be obtained.
Fig. 7.10. The final bonded device. It can be seen, that a tighter seal is achieved for the two outer channels compared to
the middle one. This can be further optimized in future devices.
7.5
Comments from the actuation results
When the bonding was completed, the final device was handed on to the testing facilities. It however quickly
became evident that the 200 µm thick PC thin film was too stiff for the actuation to work. Therefore the backup
solution of using tape for sealing was initiated. In order to provide the best device for testing, two different
tapes were used, see Figure 7.11. Also three inlet tubing were glued (Locktite super glue power easy gel) onto
the device for easy handling.
70
Fig. 7.11. The two different taped chips with three inlet tubing glued on.
7.6
Conclusion
This part presents the influence of bonding time and pressure on the breaking force. Test results show that a
larger pressure and a longer bonding time lead to a higher breaking force. By adjusting the pressure
distribution across the bonding plates is was possible to achieve a satisfying bonding. Further optimization
would however be needed in future devices.
7.7
References
[1] S. E. Nielsen, J. K. Kristensen, M. Strange, Laser welding of plastics – weld compatibility investigations,
online at http://www.forcetechnology.com.
[2] C.-W. Tsao, D. L. DeVoe, Bonding of thermoplastic polymer microfluidics, Microfluid Nanofluid, 6 2009,
p. 1-16.
[3] Y. Wang, H. Chen, Q. He, S. Soper, A high-performance polycarbonate electrophoresis microchip with
integrated three-electrode system for end-channel amperometric detection, Electrophoresis, 29, 2008,
p. 1881-1888.
[4] Y. Zhang, H. N. Hansen, P. T. Tang, J. S. Nielsen, Verification of a characterization method of the laserinduced selective activation based on industrial lasers, Int J Adv Manuf Technol, 2013.
[5] IPU homepage regarding the LISA process, http://www.ipu.dk/indhold/mikroteknologi/lisaprocessen.aspx
71
8
Metrology
8.1
Introduction
In this section the topics related to the measurement process with the aim to control and improve the
manufacturing process quality are discussed.
In the first section, the critical features for the functionality of the part are identified and described, as well as
the most suitable measurement systems. In the second chapter the issue related to the uncertainty of
measurements is handled presenting also the strategy used for obtaining precise measurements on the parts,
to make sure that those are not influenced by external factors. A statistical process method to keep the
manufacturing process under control is introduced on a theoretical way in the third chapter. Finally, in the
fourth and in the fifth chapter, the measurements performed and the discussion about the results are
presented.
8.2
Critical features and metrological equipment
After a careful study of the design of the part and of the mold, and considering all the functional
characteristics, the main critical features are detected and reported in Table 8. The ID Numbers are shown also
in Fig. 8.1.
ID NUMBER
1
CRITICAL FEATURES
OVERALL
DIMENSION OF
THE PART
2
CHANNELS
3
RESRVOIRS
5
NOZZLE
Height
Width
Diameter
Depth
Roughness < 2 microns
Profile shape
Diameter
Depth
Diameter of the tip
Outlet hole Roundness
Roughness < 1 microns
MEASUREMENT
MACHINE
A
A
A
B
B
B
(B)
A
A
A
B
Table 8.1 Critical features of the part a the related more suitable measurement systems (A = DeMeet Optical System, B = Alicona
InfiniteFocus).
72
Fig. 8.2 Technical drawing with the identification of the critical features.
Considering the critical features identified, two measuring instruments are chosen: DeMeet Optical System
and Alicona InfiniteFocus (Fig. 8.2).
Fig. 8.3 DeMeet optical system on the left of the picture and Alicona Infinite Focus on the right of the picture
DeMeet 220 is a micro optical system of 3D coordinates (CMM) used for 2D measurements. Data are collected
one point at a time with each point having a discrete X, Y, Z location.
The measuring area (image view) is defined by the magnification of the applied lens (from 40X to 400X). For the
measurements of the part it was used a 5x magnification.
73
A Sony CCD color camera is integrated for a clear image with an excellent contrast and a high resolution.
Telecentric optics are supplied as a standard to avoid perspective image distorsion.
As illumination is essential for accurate measurements, this machine is equipped with LED based illumination
(backlight, coaxial light and segmented ringlight). The ringlight can be set in intensity and angle to achieve the
best contrast with clearly defined edges. The LED based backlight and coaxial light can be adjusted in intensity.
The coaxial light can be used for illumination inside deep located structures. For the measurements of the part
he lights have been adjusted according to the characteristic to be measured.
Alicona infinite focus, instead, is a 3D non-contact optical metrology useful for analyzing surfaces with complex
geometries and for the measurement of the roughness of flat surfaces. In Table 8 are given the specifications.
8.3
Conforming the measurements tools to the standards
The term Quality Assurance (QA) is used to indicate the “total effort made by the manufacturer to ensure that
its products conform to a detailed set of specifications and standards” (Kalpakjian, 2010). Therefore to ensure
that the measurements taken on the produced parts fulfill the set requirements and that these are conformed
to the standard it is necessary to calculate an uncertainty budget. All the measurements results can’t be
compared between themselves or with any reference values if not provided with estimation on the uncertainty
factors. The final measured valued has to take into consideration this estimation and it is explained by the
equation (DeChiffre, 2010):
Fig. 8.4 Explanatory diagram of the uncertainty of measurements.
Also shown in Fig. 8.5 where is possible to see, within the lower and upper tolerance limit (SLS and USL), the
conformance zone, which is the value of the tolerance that takes into consideration the calculation of the
uncertainty. Hence, the calculated uncertainty has to be subtracted from the value of the tolerance after the
measurement is taken.
74
With Uncertainty is defined the qualification of the doubt of the measurement result (DeChiffre, 2010). When
performing a measurement there are several factors that can affect the quality of the operation and they are
associated with typical uncertainty, such as the calibration of the instrument, the quality of the surrounding
environment, i.e. temperature, and the fabrication of the workpiece itself. Each of this category is then
considered as contribute for the evaluation of the Uncertainty of the measured value and it is calculated with
the following equation (DeChiffre, 2011):
√
Where |b| represents the systematic difference between the value measured on the calibrated ring and the
value stated in the certificate, while k is the coverage factor,
is the uncertainty of the calibrated value and it
is taken from the certificate,
is the uncertainty obtained from the standard deviation. For the calculation of
the specimen shown in Figis scanned three times. The same specimen is used both for the Alicona and the
DeMeet calibration. In the red circles are the two patterns used for the calibration of the measuring machine.
Fig. 8.5 Specimen used for the calculation of the uncertainty budget and to verify the repeatability of the measuring process.
For each scan the measurements are performed three times. Therefore there will be 9 measurements that are
used for calculating the standard deviation. Notice that whilst the U factor is calculated only once before the
process, its value is then applied to each measurement taken and the |b| factor is used only for the DeMeet
measurements. Procedure and results are shown in the measurements chapter.
8.5
Statistical Process Control and monitoring
Another aspect that has to be considered when approaching a serial production is a Statistical Process Control
and monitoring of the production. In first instance the reason for doing that is to ensure that the machinery
that is intended to use is capable to perform the production at all. Subsequently it is necessary to estimate the
75
stability of the process along a planned period. This procedure is very common in the industry and it is of a
crucial importance to ensure a high quality of the produced parts. a standard procedure for doing this follows
several steps and it is intended to be made on a production over the 100 parts:
1. stability check of the machine
2. full day study
3. statistical process control
The stability check of the machine consists in the production of 50 parts and the measurements of them in
session. As mentioned before, this operation is made to ensure that the machine can perform the production
at all. Subsequently a full day study is made, meaning that the machine is run for 24 hours continuously. During
these 24 hours a minimum of 125 random parts are taken and measured in chronological order in order to see
how the machine reacts to the different environment conditions. For example, during the night the
temperature might drop significantly resulting in a different behavior and therefore in a difference among the
parts produced. Gaining knowledge over these factors would help to reduce the errors in the production and
avoid failure and to maximize the level of reproducibility of the parts. The number of 125 parts is taken in order
to have a reasonable statistical amount of data which in this case correspond to the minimum of 20%. The
parts are measured and then plot in a x-bar and R chart that will show an eventual instability of the process
and/or if the machine used is in trouble. where the red horizontal lines represent the UCL (upper control limit)
and LCL (Low control limit); the black dots are the measured samples that are within the control limits and the
red spot are the measured parts suggesting that the process is in trouble, since they are clearly outside the
control limits. Usually the control charts are of two kind, one representing the sample average (Fig5 top figure,
each spot is the average of the measurement of 5 parts in the same sample) and the range from 5
measurements (Fig5 low figure, where every spot is the average of five measurements on the same piece).
Due to the lack of time for this project, this procedure will not be followed entirely. It is assumed that the
process is stable and a full day study has been made. Therefore few specimens will be taken from the
production namely the first two and one every twenty pieces for a total of 7 specimens. Subsequently they will
be measured according to what has been said in the previous chapters (critical features, etc) and compared.
The results and procedure is explained in the following chapter.
76
Fig. 8.6 Example of X-bar and R Chanrt of a process under control.
8.6
Measurements
For measuring the parts few samples from the production were taken. As said, over a production of 100 parts,
the first two pieces and one every 20 pieces, for a total of 7 parts are taken. Measurements are taken
according to the Table 8.1.
8.6.1 Part measurements
In the following table are reported the measurements of the roughness and depth of the channels taken with
the Alicona. Results are for injection moulded parts with 40% of Pressure Where Rz is the average of the five
higher peaks and the five lower points and Ra is an arithmetic mean of the value.
Table 8.1 Roughness and channel height of 40% parts
sample
roughness roughness
(Rz)
(Ra)
sample
2
20
40
60
80
100
0,8243
1,0484
1,0495
1,0611
1,2006
1,5642
2
20
40
60
80
100
0,1511
0,1891
0,1757
0,1551
0,1657
0,2441
chennel
height (um)
1st
measurement
210
200
200
205
206
200
chennel
height (um)
2nd
measurement
220
210
77
As it is possible to notice, both the roughness and the depth channels are in tolerance (below 2µm) already
with 40% of presure on the mould, therefore due to the lack of time to perform additional measurements, it
will be assumed that also for the second production with 80% they will respect the tolerances.
Regarding the measurements of the parts with the optical system instead, the roundness of the diameters and
width of the channels are measured. After the measurements the uncertainty is subtracted from the value to
obtain a result that is conform to the standards. In the end the upper and lower limits are identified using a six
sigma method to verify the process stability, see and example in figure 8.7. An example of the measurements
taken are shown in Table 8.3. The rest of the results can be seen in the final appendix. Note that the
uncertainty factor is applied only to the parts molded with the 80% pressure.
Diameter
Diameter
Diameter
Distance
Distance
Distance
1st
77,60
177,60
260,40
516,55
505,15
508,75
2nd
71,80
175,00
267,40
505,65
503,95
511,35
20th
71,30
173,20
265,30
507,35
504,45
512,85
40th
75,20
172,30
266,70
506,85
504,25
512,55
60th
76,20
173,60
269,00
500,95
501,65
512,15
80th
82,00
181,60
278,70
514,15
513,85
504,35
100th
71,60
175,20
265,00
505,65
504,15
516,15
Fig. 8.7 Measurements on the molded parts with 80%. Measurements take in consideration the uncertainty factor of the
measurement and the systematical error of the machine.
Diameter [um]
Nozzle 1
90,00
80,00
Diameter
70,00
Average value
60,00
UCL
1
2
3
4
5
6
7
LCL
# Sample
Fig. 8.8 Example of the plot of the process. The remaining graphs are in the final appendix.
Notice that not all the measurements could be taken. the roughness inside of the nozzle, and the profile shape
of the channels and the height of the nozzle Due to the fact that the Alicona has some difficulties in detecting
the verticals walls. Therefore these measurements were not carried out. However by taking a replica of the
nozzle by using a silicon material, it would be possible at least to measure the height of the nozzle but due to
the lack of time, since for every piece the silicon has to stabilize before it is possible to measure it, this
alternative method was not pursued. Additionally, during the replication process, some of the tolerances might
be lost due to the very small size of the device.
78
As far as the planar measurements with the DeMeet are concerned, the diameter of the reservoirs could not
be measured as well. Indeed their size is too big to be captured with the magnification of the machine.
8.6.2 The mold
The mold was measured with the Alicona Infinte focus. In particular the height of the nozzles, the diameter of
the nozzles’ tip and the roughness of the nozzles were measured. In Table 8.2 it is possible to see the results of
the measurements. Notice that the mold has been measured after the injection molding process.
Table 8.2 Measured results of the mold
Channel
Height
(um)
200
200
210
8.7
Nozzle
width(um) height
(mm)
510
450
501
1.99
2.051
1.89
Nozzle
tip
Roughness Roughness
diameter (Rz)
(Ra)
(um)
98
198
298
1.891 0.2704
1.863 0.278
1.789 0.269
Discussion of the results
The tasks accomplished in this project are the following: identification of the critical features on the designed
part, the choice of the measurements tools, the definition of a measuring strategy and the measurements of
the parts and the mold. As it is possible to see from the above section the results can be considered
satisfactory. The only features not meeting the tolerances are the diameters of the nozzles on the parts which
measure an average of 30 µm less in respect of the nominal value. However this value is compared with the
tolerances assigned to the mold and not specifically to the part. Therefore if the deformation during the
injection molding process and the contraction of the material after cooling are considered the difference in the
value could be considered acceptable. Also, if the mold is considered, the measurements on the same feature
meet the tolerances on the drawings. Finally the measurements taken are implied in the Statistical Process
Control of the process(see graphs in the appendix). From the analysis of the data obtained from this process
SPC the process results under control.
8.8 References
DeChiffre, L., 2010. Geometrical Metrology and Machine Testing (compendium course 41731). s.l.:DTU
Mekanik.
DeChiffre, L., 2011. Geometrical Metrology and Machine testing. s.l.:DTU Mekanik.
Kalpakjian, S., 2010. Manufacturing Engineering and technology. sixth ed. s.l.:s.n.
79
9 Conclusion and outlook
9.1 Conclusion
During the summer school, the assigned device was designed, manufactured, characterized and tested to fulfill
the objectives of the project. The device was a prototype micro fluidic dispenser for application as a cartridge
in 3D printing of photopolymers. Here are few concluding remarks about the work:


Polycarbonate (PC) polymer was chosen as the primary material for the device.
Final design with an inlet reservoir, a channel, three actuators for peristaltic pumping and an outlet
nozzle was chosen. Three different nozzle diameters were made for the design.
 Tool was successfully fabricated using micro-milling. The diameters of the nozzles (one of the most
critical feature of the design) for the three designs was measured to be around 98 µm, 198 µm and 291
µm when the actual dimensions were 120 µm, 220 µm and 320 µm, respectively with -10 µm
tolerance. So it was found that the tooling was not accurate enough.
 Applying the tool, 200 parts were fabricated using injection molding. Here again, the diameters of the
nozzles were measured to be around 82 µm, 181 µm and 278 µm, which is way lower than the
designed diameters aforementioned.
 Thermal bonding of a thin PC film was discarded as it was too thick to be deflected enough for the
requirements. Finally, a transparent tape was used to seal the channels.
 Two designs for actuators were made: 1) push-pull-solenoid-with-piston and 2) camshaft. The pushpull-solenoid-with-piston was borrowed from the DTU mechanic and the camshaft was made by the
class using 3D printing. Camshaft worked better than push-pull-solenoid-with-piston in controlling the
flow of the liquid in the device.
The prototype dispenser fulfilled the functional requirements partially. Fluid could be sent to chip and the
channel, a certain volume of the fluid comes out of the nozzles. The actuators controlled the flow of the fluid
partially. The system needs further improvements.
9.2
Outlook:
Based on the results, the device could have been optimized and tuned to fulfill all the functional requirements
around specifications and limitations. Material for the thin film for sealing the channel could be explored
further. The fact that the diameters of the nozzles cannot be replicated exactly as the design should be taken in
the future design. The process of manufacturing the tool and the molded parts could be tuned in a better way
for the replication of accurate parameters. Actuator design could be made more precise and robust. Finally,
more experiments could be performed for the validations of the design so that the tolerances can be made
smaller and the process can be improved.
80
Appendix 1
Fig 1. Calculated channel diameter to burst pressure for the assumed values (Chapter 2)
81
Appendix Metrology
Calculation of the uncertainty budget
uc
up
b
Standard uncertainty of the calibrated workpiece
Standard uncertainty due to the measurement process
Systematic error
k
confidence 95%
U
EXPANDED MEASURING UNCERTAINTY
x
0,48
0,35
1,05
y
0,48
0,22
-1,30
2
2
[um]
1,19
1,06
Range
2,38
2,12
[um]
[um]
[um]
Measurements results
Parts
40%
Diameter
Diameter
Diameter
Distance
Distance
Distance
1st
0,0614
0,1699
0,2613
0,4887
0,5008
0,5027
2nd
0,0827
0,1922
0,2909
0,3970
0,4976
0,5066
20th
0,0742
0,1854
0,2839
0,4733
0,4987
0,5015
40th
0,0685
0,1811
0,2762
0,4783
0,4955
0,5059
60th
0,0756
0,1767
0,2867
0,4429
0,5012
0,5062
80th
0,0652
0,1853
0,2786
0,3986
0,5006
0,5035
100th
0,0733
0,1887
0,2633
0,4271
0,4997
0,5022
Average
0,0716
0,1828
0,2773
0,4437
0,4992
0,5041
Std.Dev.
0,0071
0,0076
0,0113
0,0378
0,0021
0,0021
80%
1st
2nd
20th
40th
60th
80th
100th
std.dev
Average
[um]
75,10
Diameter
77,60
71,80
71,30
75,20
76,20
82,00
71,60
3,93
Diameter
177,60
175,00
173,20
172,30
173,60
181,60
175,20
3,19
175,50
267,50
Diameter
260,40
267,40
265,30
266,70
269,00
278,70
265,00
5,62
Distance
516,55
505,65
507,35
506,85
500,95
514,15
505,65
5,37
507,11
504,30
Distance
505,15
503,95
504,45
504,25
501,65
513,85
504,15
3,90
Distance
508,75
511,35
512,85
512,55
512,15
504,35
516,15
3,72
84,64
182,82
84,64
182,82
UCL
84,64
182,82
84,64
182,82
84,64
182,82
510,11
UCL and LCL
84,64
182,82
84,64
182,82
82
282,12
520,98
513,76
519,01
282,12
520,98
513,76
519,01
282,12
520,98
513,76
519,01
282,12
520,98
513,76
519,01
282,12
520,98
513,76
519,01
282,12
520,98
513,76
519,01
282,12
520,98
513,76
519,01
65,56
168,18
252,88
493,24
494,84
501,21
65,56
168,18
252,88
493,24
494,84
501,21
65,56
168,18
252,88
493,24
494,84
501,21
LCL
65,56
168,18
252,88
493,24
494,84
501,21
65,56
168,18
252,88
493,24
494,84
501,21
65,56
168,18
252,88
493,24
494,84
501,21
65,56
168,18
252,88
493,24
494,84
501,21
Graphs
Diameter [um]
Nozzle 1
90,00
80,00
Diameter
70,00
Average value
60,00
UCL
1
2
3
4
5
6
7
LCL
# Sample
Diameter [um]
Nozzle 2
185,00
180,00
175,00
170,00
165,00
160,00
Diameter
Average
UCL
1
2
3
4
# Sample
5
6
7
LCL
83
Diameter [um]
Nozzle 3
290,00
280,00
270,00
260,00
250,00
240,00
Diameter
Average
UCL
1
2
3
4
5
6
7
LCL
# Sample
Distance [um]
Channel 1
530,00
520,00
510,00
500,00
490,00
480,00
Distance
Average
UCL
1
2
3
4
5
6
7
LCL
# Sample
Distance [um]
Channel 2
520,00
515,00
510,00
505,00
500,00
495,00
490,00
Distance
Average
UCL
1
2
3
4
5
6
7
LCL
# Sample
Distance [um]
Channel 3
525,00
520,00
515,00
510,00
505,00
500,00
495,00
490,00
Distance
Average
UCL
1
2
3
4
# Sample
5
6
7
LCL
84
Appendix 2
85
86

Micro-lavorazioni meccaniche e micro

Transcription

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