Cutting Costs And Time With DFMA

Cutting costs and
time with DFMA
Applying Design For Manufac turing and Assem bly
methodologies in early stages of produ ct design can redu ce th e
nu mber of par ts in a produ ct and thus redu ce cos ts.
By Steven Ashley, Associate Editor
I \ I R \ I yL\R v .'\( ;U .
S
D o u ul.r-,
Co u u ucrcia l Ai rcr.i f Co. ill
Lon g Bc.u-h. Calif". LUI ' 0 111(.'
vimul .u io n -, of th eir tit-si gn .m d
m.umt.u-nmng opera tions [0 determ ine wh .i t lin n 's t ill' costs o f ;I i l"li nn co nstru cti o n . T hL' CUlll p ,llly
di ' l()\,l'n ,d th.ir the costs o f .rsscmbl v. f.tbric.uiou. qua lirv ;\ " SU L llI Cl' ,
and 1'\"l.' 11 ovcrhc.rd-e-invc nto rv k,'1;' ]..;. tr.ukin g. and purch.i-iug-e-al l
dep end 011 the p .Ub co un t.
ROll Suit er. gl.' lI L'r;l 1 1ll.1I1.lg l'r to r
aircr.ui 'y,rL' 1I1' .utd in tcrior dt', ign
.it I )Oll gl.l "', .urd <cvcra l col leaguewere g in:1l the tack of findin g o u t
wh.u cou ld b e d one to cn r r h c
p.ur - co unt of ' 0 1111;' of th e com p.tny', pmducrv. Thev lined up ca ndid .uc, fo r prod u ct rvdcvicn .ui d
av-cm blcd m n ltid ic-ipl iu .rrv d e ,i~1l
tl..' ,I111 \ th .it in clud ed dcvign l' 1l ~ i­
n vvrv . m.uiufacr urin g l' llg illl' l·r,.
-ho p Ilo o r mech anics. and <nppli - The integr ati on of Boothr oyd Dewhurst's DFA software with Parametri c Technology's Pro/EN GINEER enables
cr n -p rc-cur.ui vcs. ;h \\'l·11 .1' <pv- a user to build a conceptual design as a three -dimensional solid model while simultaneously creati ng a DFA
structure chart complete with part names and dimensions.
ciali src ill prod u ct io n ' lIp po n,
wav," Su it er c.ud. " A n,llyz ing eve r-y p.nt .m d o peration ill
m.unr.riu.rbilirv, and n -lt.ihi lu v,
;1 b,l,i c ,l,,",l..'lllh ly IIl.1h·, th e rc.un ri goroll\l y confront th e
Te.u n mc m lu-rv were t.rug hr I k \i gn f o r I\ LlIluflCtli r i ll g
co mplexi ty o f ,I d l'\i gn .m d w o rk to ,i lll p l i t~ · it."
.urd A" l' l11bl y (I )F.\ lA) tt' l"i lll iq Ul'\-,lIl ex act ing d c-i gu T Ilt' rc-uh - of th e D Ollgl.l, I )r~ lA proj ect were imp rcvrev ie w me tho d t h.u id en tifi c-, th e o p tima l p ut d t'\i glL
m .ncri .il- choice..m d .I"l· mhly an d tab r ic.m o n opcr.uionsivc. Sui ter <ud . O ne ' lI CCI..'''"' ' to ry \ \ ',1\ th e rcd evign of the
D ill ,IiI' d o o r ,I\\l'mhly 011 th e ~ II )- 11. th e t"l Hllp,lIly" ,\{ II 1to p rodt u -c .m e tfi ci vn t .1I1 d rovr -c tfc crive produ c t.
vc.tt .urlinc r. Th e origi nal r.un .rir doo r ,1'\l'l1lh ly. ,1 p ,l "",,l g l'
" \\';ll king th ro ugh th e cx ivtinu lk'ig n in .1 n' ry \ pl..·citlc
th ro ugh w h ich outsid e- ,IiI' cuter- the c lhin ', .ur co nd itio nproced ure pro mpted throu gh out hy rhe I) F.\I A m ethod o lngy. l'\T ry bo dy star te d loo king .u th e dl..', igm ill ,I 111..' \\
ing -vsrctu. \\"" .t lon g-sen'illg d l'\igll bor rowed trot u the
D ouglas DC- IO airli ner. With 2 172 part s. the co m p lex
do o r unit was co nsidered difficult to install and ad just.
Simpl ifyi ng th e ram air door asse mbly des ign u sing
D H"l A techniqu es took abo u t two week s. T he effort led
to a 36 pe rc e nt re du c tio n in th e n um ber of p;uts (to
13H3), a 34 perce nt decrea se in the numbe r of assembly
o peratio ns (fro m 40 3H to 2()49 ). and th e elim inatio n of
107 po unds, a significant mass red uctio n in an air plane.
M or eove r, th e new ly reco nstituted door un it design w as
signific antly more reliable and easier to ma int ain . " T here
are fewer parrs to wear our," Suiter said. " Eve n th e uni t's
fu ncti on has improved ."
TYP I CAL RESULTS
The suc cess o f Do uglas Com m ercial Aircraft in applying
DFM A practices to its designs is not unusual . Accordi ng
to a su rve y of D FM A users co n d uc ted by Bo o t h ro yd
D ew h u rst Inc. (BDI) in Wa kefiel d, R .I. , the fo re mo st
developer of D FMA strategies and software, typi cal results
arc a 51 perce nt reductio n in part s co u nt , a 37 percent
decrease in parts cost, SO percen t faster tim e-to-market , a
()H perce nt imp ro vem en t in qu alit y and rel iabi lity, a (12
percent drop in assembly tim e, and a 57 perce n t red uctio n ill n u uu fact ur ing cycle tim e.
O ther u se rs have achieved sim ila r result s. " In mo st
cases, we end up with from 30 to HO pe rcellt fewer parrs
an d fro m th ree to five m ore funct ions than pr ev io u sly.
depending on th e product ," said Sandy M un ro, principal
in M u n ro & Asso c. ln c., a prod u ct -desig n consu lting
fi r m in Troy, M ich ., an d anot her lead er ill im plem enti ng
I) F!'vlA techniqu es.
I)FMA, said Peter D ew hurst. dir ector of g radua te studie s in manufact uring e nginee r ing at th e U n iversit y o f
R h od e l sla n d in K i n g st on a n d a p rin ci p al in BD !.
"makes o ne lo o k cr itically at the structu re of producr sthe relatio nsh ip betwee n parts, th e nu mber of par ts. th e
sec uring m ethods- and try to design the assem bly co ntent out of it w hile the de sign is still fl exible."
Th ough the division is so mewh at arb itrary, DFMA is
generally split int o D esign Fo r Assembly (DFA) and D esign For M anufa ct uring (D FM). In DFA. the key to 100\'er
cost and im proving reliability is to prod uc e designs with
fe wer parr s. T he DFA approa ch also sugges ts w hen it is
appropriate to design ori enting and insert ion fe atures into
th e part. In gelle ral, DFA focu ses OIl parrs co nsolidatio n,
to p-dow n (gravity-ass iste d) assem bly, and co nce pt-s tage
design review th ro ugh team co nsensus. DFM , 011 the ot her hand , co m pares the lise of selec te d mater -ials and m anufactu ri ng pro cesses fo r th e parts of an asse m bly, determ in es th e cos t im pact of those mat eri als and processes,
and fi nds the most efficie nt use of th e com po nen t design.
DI~ A and DFM evaluate a design by ro ug hly estim ating
th e re so urce s and e ffor t ne ed ed to b uild th e prod uct
based o n ind ustr y average estim ates . Ikwh ur st said . T his
kind of "sc o rekcc ping" allows di rect com pariso n among
designs. Fo r ex am ple, red ucing the number of parts may
sim plif)' the entire assembly, but co m bining several fuu crio ns ill on e co m po ne n t co u ld result in a co m plicate d
part th at is pro hibitively expe nsive to manufa ctu re. M o re
typi cally, howe ver, the cost o f prod ucing extra feat ures o n
o ne part is m uc h less th an th at o f p ut ting th ose featu res
o n separate parrs. T hus, DI:MA allow s for diffe rent design
scenarios. By see ing the result s up from , D ewh u rst said,
o ne can ge t th e m ost out of each m ater ial and pro cess.
T he m ethodology, said D avid M eeker. pr in cip al eng ineer at the Systems Business Technology unit o f D igital
Eq u ipment Corp. in M ayna rd . M ass.. m akes the team
physically and syste m atically walk throu gh th e d esign
and talk about its adv an tages and sho rt co m in gs, w hi ch
co m pe ls clear decisio ns o n rradc- otl s. " It also f()f(..' es yo u
to keep go od design reco rds, w hich are useful dow n th e
line." M eeker adde d. By th e en d o f a D FMA pro cess. a
step- by-s te p descriptio n o f th e ag ree d- upo n m auu fa ctu ring and assem bly process has been wr itt en dow n .
BEYOND KEEPING IT SIMPLE
Wh en co m pute r- aide d design (CAl )) technology was devclopcd . D ew hurst said . design enginee rs acq uired powertul q uantitative an alyti ca l to ols that provid ed the basis
for making a j udgem ent of a design 's perfo r mance. " Un til
I)FMA came aro und, manufact urin g engin eers did n't have
sim ilar q uantitative tools. The qu alitative evaluat io ns the
ma nufa cn ui ng engine ers had to o ff er ill ;lllY discu ssio ns
di dn 't carry mu ch w ei ght wh en th e d esign ers had rea l
numbers fro m CAD upon whi ch to base th eir decision s."
" M anu fac tu r in g te c h n ol o g y h as impro ved over t h e
years, but no t necessar ily in th e mi nd of the de sign eng ineer, wh o is typi cally used to ap plyin g th e ' Kee p It Sim ple. Stupid' ap proa ch ," said Mel H unter. corporate m anager of co st improvem en t at Em erson Electr ic C o. in St.
Louis, Mo. " H oweve r, more co m plica te d pa rt s capa ble
of fulfil ling several functions usually m ean using a d ifferent ma nu factur ing pro ccss. Df MA allows o ne to estimate
th e cost ramifi cat ions of that cho ice ."
DFMA is a way to get away fro m tradition al pro d uct design pr actic es, in which deep- seated habit s 0 11 th e part of
rh e design engine ers lead to seq ue nt ial eng inee ring . creat io n of single- fuuc n o n parts with ma llY fasreu ers. and
th e iteratio n of multiple pro d uctio n models. It also helps
avo id the in teror g.uu zation al and int erdi scipl inar y pro blem s that ofi eu plag ue new prod uct tea ms.
T he techn iq ue has gained popula rity as a benchmarking
tool becau se it helps define the design and nunufa crurm g
cap .rbilirics of compcri rors and their cost- to - nu rkct -e nn-v
tar get s, as we ll as pro vidin g com pa r-iso ns to co m pe titors '
pro d uct s, M eek er said. But D FM A call go eve n b eyo nd
those tasks, D ew hurst said. " We realized it was a co uuu unicnti on tool tor te.uu work iug. Ha ving arisen at the same
time as th e movem ent toward co nc u rre nt e ng inee ring.
DFMA provi des a focu , for th e d iff ere nt organi zat io nal
cultu res repr esented by the team members."
Thou g h th ere a re seve ra l d iffer in g va ri e ri e s of th e
DFMA m cr hodologv, th e ge ne ral co ncep t be hind all o f
th em o riginated in Britain in th e late 1970s, wh en manu fac t u r in g re sear c h ers w ere in vest iga ting \vays to rcdesign produ cts so th ey co uld be easily assem bled by ;1tI rotuat ed eq u ipme nt . Soon it was realized that this work
was lead ing to 'a set o f guidelines that wo u ld point prod:>.HT llAN IC A I I'. N C I :-.JU ' R I N C
",I AR C II 1' )'1 .:; 7 5
u c t design e rs tow ard d esign s tha t wo uld b e easier to
build ill ge neral. But w he n Br-i tish industry failed to support th e new research , th e co nce pt ende d up bein g appli ed initially in th e U nite d Sta te s. UDI introduced its
first Il FA so ftware in l Y81 in respons e to requests from
earlv practitioners, incl uding electrical co nnecto r- ma ker
AJ\l P Iuc.. Di gital Equipment C orp.. G en eral Electric
Co rp.. We\ ting ho use Electric C o .. and X erox Corp.
In the B1 )1 approa ch (w hich is repr esen tative of others),
several qu estions arc asked about each part in a product
design : D o cs t he pa rt m ove w it h respec t to t he ot her
parts already asse m blc d? M ust th e part b e m ade from a
d ifferent mat er ial o r isolated from all th e other parts already a.. sembled? M ust th e part be separate from all ot he r
parts because assembl y or disassem bly wo uld ot he rw ise be
imp ossible? These qu estio ns lead th e reviewe rs to n -cvaluate each part and process th at has been specified.
" T he idea is to ge t away from piece-functional design
and move to ward syste m - func tio nal design . w h ich im pro vcs system efficien cy' Sandy M UIln> said . H is com pany 's I>FMA ap proach pro m o tes a ser-i es of "good design
pr incip les" related to DFMA: I . USt' team wo rk. 2 . M inimi ze th e number of part s. 3. Design so the assem bly can
proceed in a layered fa.. hion from above . -l. D esign mating
parts that are t'asy to insert and align . 5. Avoid expe nsive
fasteni ng operations. 6. 1k sign out hand ling problems-
After Dougla s Aircraft enginee rs redesigned the ex isting waste pipe and
wire harn ess bra cket on the MD·9Q airliner (left) using DFMA procedures.
the unit's part count droppe d from 15 to 3, assembly operations were cut
from 210 to 8, assembly time decreased from 46 min. to 3 min., weight
was reduced from 2.1 oz. to 0 .8 oz.• and tota l product cost was lowered
from $64 .01 to $4.74 (rightl.
7h
M AR Cil l'l'l~ M F.C H . .,NI CA L EN(;INF.F.RINC
go for bulk sto rage. 7. Design for " Po ke Yoke" o r erro rproof assembly H. Design th e p:uts to affix th em selves one
t o ano the r. <J . Sim p lify se rvici n g an d pack agin g . 10 .
Eliminate adjustm ents and ph ysical reorientation s.
GETT ING MANAGEME NT ON BOARD
IJcspite th e relative success of I)FMA it rem ains a woefitllv
uud cru sed tool. said consultant Rob C arr inge r. senior vice
president of the Georg e Group Inc. in Dallas. " By the time
th e lit-sign is in m an u factu ri ng, abo ut SO perc ent o f the
cost is locked in , but it's hard to tackle the root causes."
Althoug h everyo ne in product t' ngin eering is aware of
the ben efits o f DFMA, Bill Sprague . BDI's vice president
of implementati on services, said th at few h ave bo ug ht
int o th e full-fledged process changes it dem ands or lived
th rou gh it so th at th ey tr uly under stand its pot ential.
Em er son 's Iv1e1 H unr cr said th at unl ess m an agem ent is
educ ated about th e DFMA approa ch , and co m m itted to
the proj ect , it will fail. "They have to put th eir bacon on
th e line to ensure there is no co nfli ct between part s of
th e organiz at ion . Man ag e m c ur also h as to se t aside
eno ug h tim e for th is fu ndam e nt al cha nge to take place.
It do esn 't happ en instantly,"
Assembling and manag ing the int erdi sciplin ary produ ct
dcsign team is also no sm all o rde r. ""A lot of co m pan ies
just throw a bu nch a peo ple toge ther," M eek er said . " O f..
ten th ey don 't pull together and wo rk for th e co m m on
goa l, becau se man agem ent do esn't g ive th em eno ugh auth ority or co ntro l over w hat th cv are doi ng." H e adde d
tha t m anagem ent m ust also reward th e team as a w hole.
T hen the re are the pe rsonal dynam ics involved . All of
the team m em bers. M unro said, " have to adm it to th emselves that th ey cau'r do it all by th em selves. for team work
is the key to success. Using DFMA in a vacuum w ill yield
lim ited results because no one knows everything .'
Early o n , it is useful to give the team structured tasks to
spark crearivirv and to ge t m embers used to working to get he r. " J)FMA pro vid es a nonthreat ening wa y to ge t
peopl e talkin g abo ut a design w itho ut feeling like others
arc e ncroachi ng o n the ir territor y," said J im 'Ib ut , dire ctor o f d esign e ug iuec ring at roy tu aker H ashr o Inc. in
Pawtu cket , R .I. , w hich has succe ssfu lly app lied J>FMA to
several products.
It is also esse nt ial to ge t hand s- on kn owl ed ge from
th ose o n th e sho p floor and fr o m inst allers [0 tr uly un dervtan d th e p robl em.. wi th th e exi sting design . M arry
design engineers say they had no idea ho w mu ch wo rk
p e opl e go throu gh t o put t h ci r produ ct s to geth er.
"When peopl e really und er stand th e other team m em ber s' requirem en ts. it removes most of rhe subj ectivity or
rivalry from the decisio n-making pro cess," Sprague said .
C on vinc in g reams to rely on the cost and cycle tim e esrimat cs for eac h design choice is also a problem . " N o bod y trust s what yo u say on face value : ' Munro said.
" T hey wan t to sec w he re th ose cost and tim e estim ates
co me from. The estimates have to have eno ug h credibility fo r peop le to buy into th e program . In fact. the ent ire
issue o f choosing m etr ics is important because di ff erent
kinds of scorekeeping lead to diflerenr result"."
Following a DFMA design review by Hasbro engineers, the ladder assembly
on the Tonka Talk n' Play Firetruck was redesigned in plastic, the number
of components was reduced fr om 33 to 5 , and assembly ti me dropped
from 198 to 22 sec.
T h ere is also so me di sp ut e ab o ut wh eth er everyt h ing
sho uld be boiled down co cycle tim es and mon ey. "I think
it's a big m istake to calibrate every thing in terms of do llars,"
said Mel H unt er, " beca use it allo ws peo ple to twe ak th e
figures to push the analysis in on e directio n o r ano ther."
Spr ague said that th ere is a need to calibrate the analysis
m et ho ds to th e spec ific activities of th e part icular o rganization and the ind ustry to mak e su re tha t th e ter m s me an
so me th ing to th em . Fo r ex am ple, in mo st D FJ\l A system s, th e ma nufactu r-ing eng ineer e m set up preferen ces
to fit th e o rgani zatio n 's syste m o r e nviro u m en t-c-t' th e
typc of tool s yOll use, th e d istan ce s yOli m o ve. and so
forth ," Spra gue said . In gene ral. th e er ro r associated with
th e cost and tim e estima tes is in the range of S to 10 perce nt, " Ifth ere is a discrep an cy, it's usually because ce rtain
aspect s o f th e process are being ignored." he said.
DESI GNIN G FOR CU STOMERS ' OPERATION S
T he next frontier for DFMA lllay be de signin g prod uct s
for effic ient use in the custo mer's manufactu ring op eration s, ac co rd ing to Pet er M ark s, ma n agin g d irect or o f
D esign Insight in Los Cntos, C alif. As pan of a survc y o f
th e best desig n an d m anu facturi ng pract ices, he fou nd
th at co m pa n ies like AM P were designing th eir connectors no t j ust for m an ufact ura bilirv in th eir own pla nts but
fo r co m patibility w ith th e custo m er's operations. Sim ilar
effo r ts, M arks said , we re taking place at Ko dak (fast photo labs, digital im agin g), G e neral Electr ic Aircraft Engin es (easie r integr atio n wi th airfram e d esigns), H arr is
(faste r p rint job ch an ge overs ). and Ke nn c m eral (o pt im ized tool select io n and mana gem ent ).
1\;10st cut -re nt DF M A pro grams are followed using so fiwa re devel o ped fo r the pro cess. "Software is cr uc ial to
en fo rcin g str uc tu re an d add ing rigo r to th e pr oj e ct ,"
Spragu e said , " T he re are to o man y var iables to keep in
yo ur head , and th e so ftware collec ts all th e data,"
n r:MA software is provided by UD!. Lucas Engin eering &Syst em s Ltd . in Sol ih ul l. U. K. (d istr ib u te d in N o rt h
Am eri ca by Mu nro }, and Sapphire I)esih:rtl System s Inc. in
Palo Alto, C alif. " Each syste m has the same mi ssion ," said
M eeker. " they j ust do it differently or to different degrees."
O ne no table recent develo pm ent Ius been th e int egra tion of UUI's D FA package in to Pro / EN(; IN EER from
Param e tr ic Techn o logy Corp, ill Walt ha m , Ma ss. Th e
integrnte d syste m allo ws feature d im e nsio ns and parts
lists bui lt into the solid model to be auto ma tically dow nloaded into DFA files. An enginee r can build a co nce ptual design as a th ree-d im ensio nal mo del and automa tically
creat e a Dr:A str ucture ch art , co m ple te with part s nam es
and dim en sions . ready fo r sim ultane o us design revi ew.
BI) I also o ffers DFM co st-esti m ating mod ules for several
manuf acturi ng processes, including ma chining. shee rme tal
wo rk ing. inject ion molding, powd er m et al fo rm ing. and
die casting, f o r exam ple. BDI recently released M achi nin g
for Windows. versio n 2, wh ich derives m ach ini ng tim es
and costs to r co nc ept-stage design s. Based o n eco no mic
mo dels of the pro cesses, these DFM tool s permit eng inee rs
to calcul ate the cost savings resultin g from easier assembly
versus the adde d co st o f more co m plicate d to oling an d
ot her process factor s for a mo re co mplex part.
A success fu l e xam p le of th ese DFM capabi liti es to o k
place ;1£ H asbro. T he largest toy co m pany in th e world is
using D[= J\.l A to identify design aud cos t imp ro vem ents at
th e w ry earli est co ncl'pt stages of design .
Toy ret ailers do no r wa nt to car ry inven tori es. said Ji m
To ur. " Be ca use tim ing is so critica l, till' em phasis is on
gett ing pro du cts shippe d o n sche d ule, DFMA is a big part
of th is move ment because it helps eliminate pro blem s ill
the de -bu g prod ucti o n sta rt - u p p ro ce ss by an alyzin g
part s co unts, asseil lbly tim es. and m ater ial cos ts before a
d esig n c o nce p t is lo cked in an d cha nges be com e too
tim e-consum ing to imple ment ,"
Co st wa s t h e c h all e nge for t h e Ton k a Tal k n ' Pla y
Pircn-uck , one of H ashro 's suc cesses o f the I<J<J3 Christm as seas o n , A fte r DFMA ana lysis. it be came clea r that
co sts co uld be red uced if th e traditio nally m et al firerruck
we re red esigned in plastic.
T he red esign invol ved m oving the ligh ts fro m th e front
cab to th e rear assembly, changing aesth etics, co m bining
so me part s, an d el im in atin g m any fast e ners. T h e bi g
ch ange, howe ver, was to th e ladder assem bly, explaine d
Ha sbro proj ect enginee r Pat Egan . The o r iginal ladd er
was co m posed. of a tota l of 33 parts and assemblies, w ith
an assembly tim e of 19R seco nds. T he redesigned ladd er
brought th e num ber of part s down to its th eore tical min innuu of o nly five. all pla stic. w ith all assembly tim e of
just 22 sec o nds, " It looks as n ice as th e m et al asse mble.
and it performs the sam e fu nction s," Ega» said . " Plu s. it 's
more reliable wh en subjecte d to abuse-testin g." In additio n , th e toy tru ck met its cost targets.
DH\;lA co nsul tan ts are typ ically brought in as a last reso rt , Sp ragu e said, wh en a co m p any w ants to up g rad e
prod u ct-devel op m en t capabilities to tig ht it s co m petition , o r wh en it has specific cos t obj ectives for a product
co nside red to be cr itical to the co m pany an d n r:M A is
th e onl y way to do it. T he "lu xury of ad versi ty," however, sho uld not be the pri m e reason to ad o pt n r:MA prac tices, Einstein on ce said th at " the best de sign is the simplest o ne th at wo rks." DFMA provid es the ch eapest way
to reach tha t go al. •