Modelling of cutting force in dry hard turning of X38CrMoV5

CNMI-2014
CNMI, UMAB, 09-10 Décembre, 2014

Modelling of cutting force in dry hard turning of
X38CrMoV5-1 machined by multilayer coated
carbide GC3015 using Taguchi technique
S. Benlahmidi1, H. Aouci1,2, M. Elbah2 and M.A. Yallese2
, ENST-ex CT siège DG. SNVI, Route Nationale N°5 Z.I. 16012, Rouiba Algérie fax: 021815674
2
Laboratoire mécaniques et structures (LMS), Université 08 Mai 1945, BP 401, Guelma 24000, Algérie
1
Abstract — In the present work, the performance of
multilayer coated carbide tool was investigated
considering the effect of cutting parameters during
turning of hardened X38CrMoV5-1 high alloy steel.
Nine experimental runs based on an orthogonal array
(L9) of the Taguchi method were performed to derive
objective functions to be optimized within the
experimental domain. The objective functions were
selected in relation to the parameters of the cutting
process: cutting forces. The correlations between the
cutting parameters and performance measures like
cutting forces, were established by multiple linear
regression models. The correlation coefficients found
higher than 0.84, showed that the developed models
are reliable and could be used effectively for
predicting the responses within the domain of the
cutting parameters. Highly significant parameters
were determined by performing an Analysis of
variance (ANOVA). Experimental results show that
the radial force is the highest. Cutting force
components get affected mostly by depth of cut. Its
contributions on axial force Fa, radial force Fr and
tangential force Ft are (91.72 ; 79.43 and 77.03)%,
respectively.
Keywords — Taguchi technique; X38CrMoV5-1;
coated carbide tool; cutting force; ANOVA; RSM.
ap
NOMENCLATURE
Depth of cut, mm
f
Feed rate, mm/rev
Fa
Axial (Feed) force, N
Fr
Radial (Thrust) force, N
Ft
Tangential cutting force, N
HRC
Rockwell hardness
R²
Coefficient of determination
rε
Tool nose radius, mm
Vc
Cutting speed, m/min

Relief angle, degree

Rake angle, degree
λ
Inclination angle, degree
χ
Major cutting edge angle, degree
I. INTRODUCTION
T
HE machining of hardened steels using
polycrystalline cubic boron nitride (PCBN) and ceramic
tools is widely accepted as a best replacement to costly
grinding operations. However, development in the
cemented carbide grades, coating materials and coating
deposition technologies have attracted many researchers
in the field of hardened steel machining using coated
carbide tools (Chinchanikar & Choudhury 2012).
In dry hard turning of AISI H11 steel treated at 50
HRC machined by the following cutting materials: the
carbides (H13A and GC3015), the reinforced ceramic
CC670 and the cermets (CT5015 and GC1525) and for
this cutting regime: Vc = 120 m/min, ap = 0.15 mm and f
= 0.08 mm/rev, the tool life of the uncoated cermets
CT5015 and the coated cermets GC1525 are less than 2
minutes. The tool life of the uncoated carbide H13A is 4.5
minutes. The tool life of the reinforced ceramic CC670 is
only 8 minutes. However the tool life of the coated carbide
GC3015 is 16 minutes. This experimental study confirms
that in dry hard turning of this steel and for the cutting
regime tested, the coated carbide GC3015 is the most
powerful tool in terms of wear resistance and lifespan
(Fnides et al 2013).
The productivity in terms of volume chip carved of
five cutting tools at two different cutting conditions in
straight hard turning of X38CrMoV5-1 (50 HRC) was
investigated. For the first cutting regime (Vc = 120
m/min, ap = 0.15 mm et f = 0.08 mm/rev), the
productivity of the coated cermets GC1525, the uncoated
cermets CT5015, the uncoated carbide H13A, the
reinforced ceramic CC670 and the coated carbide
GC3015 are (1440; 2160; 6480; 11520 and 23040) mm3,
respectively. The productivity of these two selected tools,
i.e. reinforced ceramic CC670 and coated carbide
GC3015 for the second cutting regime (Vc = 90 m/min, ap
= 0.15 mm and f = 0.08 mm/rev) are (12960 and 30780)
mm3, respectively. These results prove that the coated
carbide GC3015 is more efficient than other tools used in
terms of productivity (Fnides et al 2013).
Taguchi’s orthogonal arrays are highly fractional
designs, used to estimate main effects using very few
experimental runs. These designs are not only applicable
for two level factorial experiments, but also can
investigate main effects when factors have more than two
levels. Designs are also available to investigate main
effects for some mixed level experiments where the
factors included do not have the same number of levels.
For example, a four-level full factorial design with five
factors requires 1024 runs while the Taguchi orthogonal
array reduces the required number of runs to 16 only
(Sharma & Bhambri 2012).
In dry hard turning of X38CrMoV5-1 steel treated at
50 HRC machined by whisker ceramic tool (Al 2O3+SiC),
the results of ANOVA show that the depth of cut affects
Fa in a considerable way. Its contribution is 85.84%. The
second factor influencing Fa is feed rate. Its contribution
is 8.42%. As for cutting speed, its effect is less important
and its contribution is 1.56%. The interaction f×ap is
significant. Its contribution is 3.08%. The depth of cut is
the most important factor affecting radial force Fr. Its
contribution is 63.23%. The second factor influencing Fr
is feed rate. Its contribution is 29.90%. As for the cutting
speed, its contribution is 3.42%. The depth of cut is the
dominant factor affecting tangential cutting force Ft. Its
contribution is 72.46%. The second factor influencing Ft
is feed rate. Its contribution is 22.62%. As for cutting
speed, its effect is less significant because its contribution
is 0.73%. The interaction f×ap is significant. Its
contribution is 3.70%. For this cutting regime (0.12 ≤ f ≤
0.16 mm/rev and ap = 0.45 mm), the authors confirm that
the tangential cutting force becomes the major force
(Fnides et al 2012).
In turning hardened AISI H11 hot work tool steel, the
workpiece was machined by a mixed ceramic tool (insert
CC650 of chemical composition 70%Al2O3+30%TiC)
under dry conditions. Based on 33 full factorial design, a
total of 27 tests were carried out. The range of each
parameter is set at three different levels, namely low,
medium and high. Mathematical models were deduced by
software Minitab (multiple linear regression and response
surface methodology) in order to express the influence
degree of the main cutting variables such as cutting speed,
feed rate and depth of cut on cutting force components.
The results indicate that the depth of cut affects Fa in a
considerable way. Its contribution is 94.22%. The second
factor influencing Fa is cutting speed. Its contribution is
2.23%. As for feed rate, its effect is less important and its
contribution is 1.72%. The interaction Vc×ap is
significant. Its contribution is 1.02%. The depth of cut is
also the most important factor affecting radial force Fr. Its
contribution is 81.14%. The second factor influencing Fr
is feed rate. Its contribution is 10.69%. As for the cutting
speed, its contribution is 6.39%. The interaction Vc×ap is
significant. Its contribution is 0.85%. The depth of cut is
the dominant factor affecting tangential cutting force Ft.
Its contribution is 77.84%. The second factor influencing
Ft is feed rate. Its contribution is 16.15%. As for cutting
speed, its effect is less significant because its contribution
is 3.06%. The interaction f×ap is significant. Its
contribution is 2.06% (Fnides et al 2011).
The aim of the present work is, thus, to model cutting
force in hard turning of X38CrMoV5-1. Nine machining
tests were carried out under dry conditions with the
multilayer coated carbide GC3015 inserts using Taguchi
technique.
The model predicting equations for cutting force were
developed. To calculate constants and coefficients of these
models, the software’s Minitab 15 and Design-Expert 8
characterized by analysis of variance (ANOVA), multiple
linear regression and response surface methodology
(RSM) were exploited.
In order to achieve this: statistical analysis of the
experimental, the analysis of variance (ANOVA) was
applied. This latter is a computational technique that
enables the estimation of the relative contributions of each
of the control factors to the overall measured response. In
this work, the parameters were used to develop
mathematical model using multiple linear regression and
response surface methodology (RSM). RSM is a collection
of mathematical and statistical techniques that are useful
for the modelling and analysis of problems in which
response of interest is influenced by several variables and
the objective is to optimize the response (Uvaraja &
Natarajan 2012, Fnides et al 2009).
II. EXPERIMENTAL PROCEDURE
Experiments were performed using commercially
available coated tungsten based cemented carbide inserts.
The grade of the inserts is GC3015 (CVD coating layer
sequence TiCN/Al2O3/TiN) with three main layers and
several more sub-layers of coating with a total thickness
of 14 µm (figure 1). The main coating layers include:
medium temperature titanium carbonitride (TiCN),
finegrain alpha structure aluminum oxide (Al 2O3), and a
thin layer of titanium carbonitride (TiCN) and titanium
nitride (TiN). The insets have identical geometry
designated by ISO as SNMA 120408-KR (with 0.8 mm
nose radius) (SANDVIK 2009).
piezoelectric dynamometer consists of stacks of
piezoelectric crystals, produces an electric charge which
varies in direct proportion with the load acting on the
sensor. The dynamometer consists of three-component
force sensors; sensitive to pressure in the Fr direction and
the other two responding to shear in the Ft and Fa
directions, respectively. The generated charge is then
converted to a voltage by a charge amplifier.
Fig.1. Multilayer coated carbide GC3015 insert.
A right hand style tool holder designated by ISO as
PSBNR 2525M12, has a geometry of the active part
characterized by the following angles: χ = 75°; α = 6°; γ =
-6°; λ = -6°, was used for mounting the inserts.
The work piece used for experiments was of 300 mm
length and 75 mm in diameter, hardened to 50 HRC. Its
grade is X38CrMoV5-1, hot work steel which is popularly
used in hot form forging. It is employed for the
manufacture of the module matrices of door for car and
helicopter rotor blades. Its chemical composition is given
in Table 1.
TABLE 1: CHEMICAL COMPOSITION OF X38CrMoV5-1.
Composition
C
Cr
Mo
V
Si
Mn
S
P
Fe
Other components
Wt(%)
0.35
5.26
1.19
0.5
1.01
0.32
0.002
0.016
90.31
1.042
The lathe used for machining operations was from
TOS TRENCIN Company; model SN40C, spindle power
6.6 KW.
Average values of the cutting force components (Fa,
Fr and Ft) (Fig. 2) were measured by using a three
component piezo-electric dynamometer (KISTLER Type
9257 B) mounted on the cross slide of the lathe. A
Fig.2. Illustration for cutting forces components.
III. EXPERIMENTAL RESULTS AND DISCUSSION
Experimental matrix and results of cutting force
components (Fa, Fr and Ft) when turning a work material
hardened to 50 HRC with multilayer coated carbide
GC3015 insert using an orthogonal array (L9 = 9) of the
Taguchi method; are shown in Table 2. The
investigations prove that the radial force is the highest.
The enlightenment is that the chip formation mainly
occurs on the tool radius in hard turning and the
machining is done with negative rake angle. It is different
from the force relation which is valid in the traditional
cutting where the main cutting (tangential) force is the
highest. The same observations were reported by
Bagawade et al (2012).
TABLE 2: ORTHOGONAL ARRAY L0 OF CUTTING FORCE
EXPERIMENTAL RESULTS
A. ANOVA for cutting force components
Tables 3, 4 and 5 show the ANOVA for axial force Fa,
radial force Fr and tangential force Ft, respectively. It can
be seen that the depth of cut is the most major cutting
parameters for affecting cutting force components. Its
contributions on Fa, Fr and Ft are (91.72; 79.43 and
77.03) %. This is due to the fact that, increase in depth of
cut results in increased tool work contact length.
Subsequently, chip thickness becomes significant causing
the growth in the volume of deformed metal that requires
greater cutting forces to cut the chip. The feed rate impact
on Fa is 2.24%, on Fr is 11.08% and on Ft is 15.38%. As
for the cutting speed, its effect on Fa is 3.55%, on Fr is
4.52% and on Ft is 4.73%.
C. Main effects plot for cutting force components
Figures 3, 4 and 5 show the main effects plot for Fa, Fr
and Ft. It can be seen that the depth of cut is the most
important parameter affecting cutting force components
followed by feed rate and cutting speed.
TABLE 3: ANOVA for Fa
Fig.3. Main effect plot for Fa.
TABLE 4: ANOVA for Fr
TABLE 5: ANOVA for Ft
Fig.4. Main effect plot for Fr.
B. Cutting force models
Regression equations for axial force (Fa), radial force (Fr)
and tangential force (Ft) were developed based on
experimental data. The values of the coefficients involved
in the equations were calculated by regression method
using the software’s Minitab 15 and Design-Expert 8.
Equations (1), (2) and (3) developed for three components
of cutting force (Fa, Fr and Ft) are given below:
Fa = –18.236 – 0.552Vc + 258.833f + 489.556ap
(1)
Fr = 30.307 – 0.754Vc + 826.354f + 578.872ap
(2)
Ft = –38.066 – 0.757Vc + 867.187f + 520.117ap
(3)
The coefficients of correlation R2 are (94.9; 84.8 and
94.6) %, respectively.
Fig.5. Main effect plot for Ft
D. 3D Surface plots of cutting force components
Figures 6 (a, b, c, d, e and f) present 3D surface plots of
cutting force components Fa, Fr and Ft. These figures
were drawn using response surface methodology (RSM)
according to experimental results.
(a)
(b)
(f)
(e)
Fig.6. 3D Surface plots of cutting force components
E. Contour plots of cutting force component
Contour graphs of cutting force components Fa, Fr and
Ft are ploted in figures 7 (a, b, c, d, e and f). These
figures were drawn using response surface methodology
(RSM) according to experimental results.
(c)
(a)
(b)
(d)
(c)
components. Its contributions on Fa, Fr and Ft
are (91.72 ; 79.43 and 77.03)%, respectively.
2- The feed rate impact on Fa is 2.24%, on Fr is
11.08% and on Ft is 15.38%.
3- As for the cutting speed, its effect on Fa is 3.55%,
on Fr is 4.52% and on Ft is 4.73%.
4- The correlation coefficients found higher than
0.84, showed that the developed models are
reliable and could be used effectively for
predicting the responses within the domain of the
cutting parameters.
(d)
REFERENCES
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(e)
(f)
Fig.7. Contour plots of Fa, Fr and Ft
IV. CONCLUSION
Based on the experimental results of the present work
that was done in dry hard turning of X38CrMoV5-1 high
alloy steel treated at 50 HRC machined by multilayer
coated carbide GC3015 tool using Taguchi technique, the
subsequent conclusions can be derived:
1- The depth of cut is the most major cutting
parameters
for
affecting
cutting
force
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