Now days optimal machining parameters are of great concern in manufacturing environments, where economy of machining operations plays a key role in competitiveness in the market. This paper aims at developing a statistical model to optimize the surface parameters such as material removal rate (MRR) and surface roughness (SR).Response Surface Methodology (RSM) experimental design was used for conducting experiment. The experimental study was carried out in a CNC vertical machining center. The work piece material was EN45 (steel alloy).EN45 is widely used in the motor vehicle industry for leaf springs, truncated conical springs, helical springs and many general applications.
2. Parameter Optimization In Vertical Machining Center CNC For En45 (Steel Alloy) Using
Response Surface Methodology
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Cite this Article Ajay Kumar, Simranjeet Singh, Sahil Barry, Shivam
Bhardwaj, Er. Ajay Sharma and Er. Harpreet Singh. Parameter Optimization
In Vertical Machining Center CNC For En45 (Steel Alloy) Using Response
Surface Methodology. International Journal of Mechanical Engineering and
Technology, 7(2), 2016, pp. 288–299.
http://www.iaeme.com/currentissue.asp?JType=IJMET&VType=7&IType=2
1. INTRODUCTION
With the increase in the precise demand of the modern engineering products, the
surface texture has more importantly to be controlled. It is revealed from the study
that surface texture greatly influences the functioning of the machined parts.
Whatever may be the manufacturing process used, it is not possible to produce
smooth surface. In this work, the machining parameters such as depth of cut (dc),
spindle speed (N) and feed rate (f) that affect the surface roughness and the MRR in
the milling operation was studied. EN45 is a manganese spring steel with high carbon
content. EN45 is used widely in the motor vehicle industry for leaf springs, truncated
conical springs, helical springs and spring plates and many general engineering
applications. EN45 springs steel is used for manufacturing the main components of
cultivator. EN 45 spring steel material is used in the manufacturing of reversible
shovel. Response surface methodology is used to plan the experiments and for the
process of optimization. The confirmation test was conducted using optimum
combination of cutting parameters. From the literature survey, it was under stood that
no research work has been reported in VMC of EN45 material to find out the MRR
and Surface Roughness. So, in this study, Response Surface Methodology (RSM) is
used for the development of optimization of MRR and surface roughness with three
different parameters feed rate, spindle speed and depth of cut.EN45 steel finds its
typical applications in the manufacturing of automobile and machine tool parts.
Because of its wide application EN45 steel has been selected as the work material in
this work.
Chemical composition of EN45 ALLOY:
C
%
Mn
%
P
%
S
%
Si
%
Al
%
Ni
%
Cr
%
V
%
Mo
%
0.4863 0.7292 0.03974 0.02180 1.838 0.0050 0.0730 0.0459 0.2624 0.1056
2. RESPONSE SURFACE METHODOLOGY
Response surface methodology (RSM) is a collection of mathematical and statistical
techniques for empirical model building. By careful design of experiments, the
objective is to optimize a response (output variable) which is influenced by several
independent variables (input variables). An experiment is a series of tests, called runs,
in which changes are made in the input variables in order to identify the reasons for
changes in the output response. The application of RSM to design optimization is
aimed at reducing the cost of expensive analysis methods (e.g. finite element method
or CFD analysis) and their associated numerical noise. Response surface method is
the most effective method to study the result obtained from factorial experiments. It is
an effective tool for modeling and studying the manufacturing problems. It delivers
more information with fewer numbers of investigations. It is an investigation strategy
for exploring the limits of the input parameters and emerging experiential statistical
model for the measured response, by approximating the relationship existing between
3. Ajay Kumar, Simranjeet Singh, Sahil Barry, Shivam Bhardwaj, Er. Ajay Sharma and
Er. Harpreet Singh
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the response and input process parameters. The limit of the process parameters has to
be defined in response surface method and the first experimentation was done to
recognize the machining parameters that affect the MRR and Surface roughness and
to discover the range of the selected cutting parameters.
3. METHOD OF EXPERIMENT
Work piece material
The work piece material used for this experiment is EN45 steel alloy. The work piece
is shape of rectangular slabs with dimensions of (51mm×48mm×14mm). Composition
of material was obtained using spectro analysis and is given above. Due to its long life
as compared to the mild steel and the wide applications of the EN45 in automobile
industry and its surface finish application, this material is selected for the research
work.
Experimental Setup
The experiment was conducted at Ambala College of Engineering, Ambala with the
following experimental setup, the equipment used was Vertical Machining Center
CNC of Siemens series named as VMC 8410.the tool used was a solid carbide tool of
the diameter ɸ10mm.The work piece material used was EN45 steel alloy. The
operation performed was face milling operation. Parameters used for the experiment
were Feed rate, Spindle speed and Depth of cut. The responses considered in this
study are surface roughness and material removal rate (MRR).the surface roughness
was measured with the help of SRT-8210 surface roughness tester. Material removal
rate is used to evaluate machining performance.MRR is expressed as the amount of
material removed under a period of machining time. The process parameters are
shown in the table 3.1 below.
TABLE 3.1 Process parameters with their values at three levels
Parameter Level 1 Level 2 Level 3 Output parameter
Feed Rate (mm/min) 50 275 500
MRR and Surface
Roughness
Spindle Speed (rpm) 700 1350 2000
Depth of Cut (mm) 0.1 0.3 0.5
Response Surface Methodology was used for the design of the experimental array
with the three different values at different levels. Table 3.2 shows the DOE with
actual values.
TABLE 3.2 Actual values of process parameters
Std. Run Block
Factor 1 Factor 2 Factor 3
Feed Rate Spindle Speed Depth of cut
3. 1. Block 1 50 700 0.30
1. 2. Block 1 275 700 0.10
12. 3. Block 1 275 2000 0.50
8. 4. Block 1 500 2000 0.30
13. 5. Block 1 275 1350 0.30
2. 6. Block 1 50 1350 0.10
4. 7. Block 1 500 1350 0.10
7. 8. Block 1 50 2000 0.30
6. 9. Block 1 275 2000 0.10
4. Parameter Optimization In Vertical Machining Center CNC For En45 (Steel Alloy) Using
Response Surface Methodology
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Std. Run Block
Factor 1 Factor 2 Factor 3
Feed Rate Spindle Speed Depth of cut
9. 10. Block 1 275 700 0.50
5. 11. Block 1 500 700 0.30
10. 12. Block 1 50 1350 0.50
11. 13. Block 1 500 1350 0.50
4. RESULT AND DISCUSSIONS
Response surface methodology indicates the area in the design region where the
process is likely to give desirable result simultaneous consideration of multiple
responses involves first building an appropriate response surface model for each
response and trying to find operating conditions that in some sense of optimizes all
response or at least keeps them in the desired range. The milling parameters such as
the cutting speed, the depth of cut and the feed rate etc. are the investigated parameter
that affects the surface quality and the material removal rate of the milled parts. Table
4.1 represents the experimental results with actual process parameters.MRR is
calculated by the equation (1)
MRR= (Wb-Wa)/tm (g/min) (1)
Where, Wb= weight of the work piece before machining (g).
Wa= weight of the work piece after machining (g).
tm= time consumed in machining (min.).
TABLE 4.1 Experimental results with actual values of process parameters.
Std. Run Block
Factor 1 Factor 2 Factor 3
Response
1
Response
2
Feed
rate
Spindle
speed
Depth of
cut
MRR
S.R(Ra)
3. 1. Block 1 50 700 0.30 0.807 0.278
1. 2. Block 1 275 700 0.10 1.466 1.335
12. 3. Block 1 275 2000 0.50 7.8 0.618
8. 4. Block 1 500 2000 0.30 5.95 1.283
13. 5. Block 1 275 1350 0.30 3.056 1.008
2. 6. Block 1 50 1350 0.10 0.212 0.384
4. 7. Block 1 500 1350 0.10 1.833 0.873
7. 8. Block 1 50 2000 0.30 0.801 0.756
6. 9. Block 1 275 2000 0.10 1.366 0.827
9. 10. Block 1 275 700 0.50 6.366 1.316
5. 11. Block 1 500 700 0.30 6.166 1.342
10. 12. Block 1 50 1350 0.50 1.460 1.218
11. 13. Block 1 500 1350 0.50 9.3 1.303
(a) Effect of the process parameters on the Material Removal rate (MRR)
Deign expert 6.0 has been used for the calculation as shown in the above table
4.1.Based on the ANOVA the table4.2 depicts the effects of the process variables and
the interactions based on the 2FI model for MRR. This model was developed for the
95% confidence level. The model F value 27.45 implies that the model is significant.
There is only 0.04% chance that a model “F value” this large could occur due to
noise. Values of “Prob>F”less than 0.0005 indicate model terms are significant. By
checking the values of F values, it is seen that the factor A, C and AC are the most
5. Ajay Kumar, Simranjeet Singh, Sahil Barry, Shivam Bhardwaj, Er. Ajay Sharma and
Er. Harpreet Singh
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significant effect on the MRR. Values greater than 0.1000 indicates the model terms
are not significant.
TABLE 4.2 ANOVA for Response Surface 2FI Model for MRR
Source Sum of Squares DF Mean Square F value Prob>F
Model 110.51 6 18.42 27.45 0.0004 Significant
A 49.85 1 49.85 74.28 0.0001 Significant
B 0.15 1 0.15 0.23 0.6483 Not significant
C 50.25 1 50.25 74.87 0.0001 Significant
AB 0.011 1 0.011 0.016 0.9022 Not significant
AC 9.67 1 9.67 14.41 0.0090 significant
BC 0.59 1 0.59 0.88 0.3853 Not significant
Residual 4.03 6 0.67
Cor Total 114.54 12
Std.Dev. 0.82 R-squared 0.9648
Mean 3.58 Adj.R-squared 0.9297
CV 22.86 Pred. R-squared 0.8143
PRESS 21.27 Adeq. Precision 16.643
The “Pred. R-squared” of 0.8143 is in reasonable agreement with the “Adj. R-
squared” of 0.9297.
"Adeq Precision" measures the signal to noise ratio. A ratio greater than 4 is
desirable.
The ratio of 16.643 indicates an adequate signal. This model can be used to
navigate the design space. Final equation (2) in terms of actual factors:
MRR = ( 3.58+2.50×Feed rate + 0.14 × Spindle speed + 2.15 × Depth of cut -
0.052 × Feed rate × Spindle speed + 1.55 × Feed rate × Depth of cut + 0.38 ×
Spindle speed × Depth of cut). (2)
Figure1 (a) Main factor plots on MRR with varied feed rate.
50.00 162.50 275.00 387.50 500.00
0.21
2.48
4.76
7.03
9.30
A: FEED RATE
M.R.R.
One Factor Plot
Warning! Factor involved in an interaction.
6. Parameter Optimization In Vertical Machining Center CNC For En45 (Steel Alloy) Using
Response Surface Methodology
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The main factor plot on MRR with varied feed rate from 50-500mm/min. at
spindle speed =1350rpm and Depth of cut =0.30mm as shown in figure1 (a).
Figure 1(b) Main factor plot on MRR with varied Spindle Speed.
The main factor plot on MRR with varied spindle speed from 700-2000 rpm at
feed rate=275mm/min. and Depth of cut=0.30mm as shown in figure 1(b).
Figure 1(c) Main factor plot on MRR with varied Depth of Cut.
The main factor plot on MRR with Varied Depth of cut from 0.10-0.50mm at feed
rate= 275mm/min. and Spindle speed= 1350 rpm as shown in fig.1(c).Figure 2 (a) and
(b) shows the three dimensional interaction response surface and contour plot for the
response MRR in terms of feed rate and depth of cut at spindle speed =1350 rpm. A
contour plot plays a very important role in the study of response surface. From the
700.00 1025.00 1350.00 1675.00 2000.00
0.21
2.48
4.76
7.03
9.30
B: SPINDLE SPEED
M.R.R.
One Factor Plot
Warning! Factor involved in an interaction.
0.10 0.20 0.30 0.40 0.50
0.21
2.48
4.76
7.03
9.30
C: DEPTH OF CUT
M.R.R.
One Factor Plot
Warning! Factor involved in an interaction.
7. Ajay Kumar, Simranjeet Singh, Sahil Barry, Shivam Bhardwaj, Er. Ajay Sharma and
Er. Harpreet Singh
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examination of the contour plot and response surface, it is observed that MRR
increases from 1.76g/min. to 5.27g/min. with depth of cut from 0.10-0.50mm with
feed rate from 50mm/min. to 500mm/min.
2(a) 2(b)
Figure 2(a) and (b) contour plot for MRR and response surface for MRR.
The figure 3(a) and 3(b) below shows the interaction plots with feed rate and
depth of cut with a spindle speed =1350 rpm and normal probability distribution plot
residuals respectively. Figure 3(c), 3(d) below shows the residual Vs predicted values,
residuals Vs run respectively. It is clear from the figure that all the data points are
following the straight line. Thus, the data is normally distributed. It can be seen from
figure (c),(d) of figure 3 that all the actual values are following the predicted value
and thus declaring model assumptions are correct and within the limits.
3(a) 3(b)
M.R.R.
A: FEED RATE
C:DEPTHOFCUT
50.00 162.50 275.00 387.50 500.00
0.10
0.20
0.30
0.40
0.50
1.76
2.64
3.52
4.39
5.27
0.21
2.48
4.76
7.03
9.30
M.R.R.
50.00
162.50
275.00
387.50
500.00
0.10
0.20
0.30
0.40
0.50
A: FEED RATE
C: DEPTH OF CUT
C: DEPTH OF CUT
Interaction Graph
A: FEED RATE
M.R.R.
50.00 162.50 275.00 387.50 500.00
0.12
2.62
5.12
7.62
10.13
C-
C+
Studentized Residuals
Normal%Probability
Normal Plot of Residuals
-1.51 -0.58 0.34 1.27 2.19
1
5
10
20
30
50
70
80
90
95
99
8. Parameter Optimization In Vertical Machining Center CNC For En45 (Steel Alloy) Using
Response Surface Methodology
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3(c) 3(d)
Figure 3 (a) Interaction plot, (b) Normal plot of residuals, (c) Residuals Vs predicted plots,
(d) Residual Vs run plots.
(b)Effect of the process parameters on surface roughness (Ra)
The model F value of 10.72 implies that the model is significant. There is only a
chance of 0.25% that “model F -value” this large could occur due to noise. By
checking F values P values, it is clear that values of “prob.>F” less than 0.0500
indicates model terms are significant. In this model the term A, (feed rate) has the
most significant effect on Surface Roughness. Values greater than 0.1000 indicate that
the model terms are not significant.
TABLE 4.3 ANOVA for Response Surface Linear model for Surface Roughness.
Source
Sum of
Squares
DF
Mean
Square
F value Prob>F
Model 1.96 3 0.65 10.72 0.0025 Significant
A 1.84 1 1.84 30.08 0.0004 Significant
B 0.077 1 0.077 1.27 0.2894 Non-
significant
C 0.050 1 0.050 0.82 0.3888 Non-
significant
Residual 0.55 9 0.061
Cor Total 2.51 12
Std.Dev. 0.25 R-squared 0.7814
Mean 0.93 Adj.R-squared 0.7085
CV 26.58 Pred. R-squared 0.5199
PRESS 1.21 Adeq. Precision 8.427
The “Pred. R-squared” of 0.5199 is in reasonable agreement with the “Adj. R-
squared” of 0.7085. “Adj. R-squared” measures the signal to noise ratio. A ratio
greater than 4 is desirable. The ratio 7.982 indicates an adequate signal. This model
can be used to navigate the design space. The final equation (3) in terms of actual
factors:
Predicted
StudentizedResiduals
Residuals vs. Predicted
-3.00
-1.50
0.00
1.50
3.00
0.12 2.62 5.12 7.62 10.13
Run Number
StudentizedResiduals
Residuals vs. Run
-3.00
-1.50
0.00
1.50
3.00
1 3 5 7 9 11 13
10. Parameter Optimization In Vertical Machining Center CNC For En45 (Steel Alloy) Using
Response Surface Methodology
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4(e)
Figure 4: Main plots on Surface roughness (a) with varied feed rate (b) with varied spindle
speed (c) with varied Depth of cut (d) Contour plot for surface roughness (e) Response
surface plot for surface roughness.
The main plots on surface roughness with varied feed rate from 50-500mm/min. at
spindle speed =1350rpm and Depth of cut =0.30mm is shown in fig.4 (a) and with
varied spindle speed from 700-2000 rpm at feed rate=275mm/min. and depth of
cut=0.30mm is shown in fig.4 (b) and with varied Depth of cut from 0.10-0.50mm at
feed rate=275mm/min and spindle speed=1350 rpm is shown in fig.4(c).The three
dimensional interaction response and contour plots as shown in the fig. 4(d) and 4(e)
for the response Ra in terms of feed rate and depth of cut. By generating response
surface analysis it is easy to characterize the shape of the surface and locate the
optimum with reasonable precision from the examination of the contour plots and
response surface, it is observed that Ra increases from 0.572µm to 1.317µm.with feed
rate from 50-500mm/min and depth of cut from 0.10-0.50mm.
5(a) 5(b)
0.38624
0.665428
0.944615
1.2238
1.50299
SURFACEROUGHNESS
0.10
0.20
0.30
0.40
0.50
50.00
162.50
275.00
387.50
500.00
C: DEPTH OF CUT
A: FEED RATE
A: FEED RATE
Interaction Graph
C: DEPTH OF CUT
SURFACEROUGHNESS
0.10 0.20 0.30 0.40 0.50
0.158
0.494
0.830
1.167
1.503
A-
A+
Studentized Residuals
Normal%Probability
Normal Plot of Residuals
-1.33 -0.55 0.24 1.03 1.82
1
5
10
20
30
50
70
80
90
95
99
11. Ajay Kumar, Simranjeet Singh, Sahil Barry, Shivam Bhardwaj, Er. Ajay Sharma and
Er. Harpreet Singh
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5(c) 5(d)
Figure 5 (a) Interaction plots, (b) Normal plots of residuals, (c) Residuals Vs Predicted, (d)
Residuals Vs Run.
The figure 5(a) and 5(b) above shows the interaction plots with feed rate and
depth of cut with a spindle speed=1350rpm and normal probability distribution plot
residuals respectively. Figure 5(c), 5(d) below shows the residual Vs predicted values,
residuals Vs run plot respectively. It is clear from the figure that all the data points are
following the straight line. Thus, the data is normally distributed. It can be seen from
figure (c),(d) of figure 5 that all the actual values are following the predicted value
and thus declaring model assumptions are correct and within the limits.
CONCLUSION
The observed MRR and surface roughness of the experimental result are 2.866g/min
and 1.198 µm respectively. Table 5.1 shows the error percentage for experimental
validation of the developed models for responses with optimal parameter setting
during the milling of the EN45 on vertical machining center VMC. From the analysis
from the table 5.2, it can be observed that the calculated error is small. The error
between experimental and predicted values for MRR and Surface roughness lies
within the 14% and 6% respectively. Obviously, the above experimental result
confirms excellent reproducibility of the experiment conclusions.
TABLE 5.1 Multi-optimal parameter settings for MRR and Surface Roughness.
Parameters Units Optimal parameter
FEED RATE mm/min 275
SPINDLE SPEED R.P.M 1350
DEPTH OF CUT Mm 0.30
TABLE 5.2 Experimental validations of the developed models with optimal parameters.
Responses
Predicted
Value
Experimental
Value
Error Desirability
MRR(g/min) 3.57 3.06 14% 0.61
Surface
roughness(µm)
0.945 1.008 6% 0.59
Predicted
StudentizedResiduals
Residuals vs. Predicted
-3.00
-1.50
0.00
1.50
3.00
0.37 0.66 0.94 1.23 1.52
Run Number
StudentizedResiduals
Residuals vs. Run
-3.00
-1.50
0.00
1.50
3.00
1 3 5 7 9 11 13
12. Parameter Optimization In Vertical Machining Center CNC For En45 (Steel Alloy) Using
Response Surface Methodology
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In this study, the MRR and Surface roughness in parameter optimization in vertical machining center
(VMC) for EN45 (steel alloy) was modeled and analyzed through Response surface methodology
(RSM).Feed rate, spindle speed and depth of cut have been employed to carry out the experimental
study. Summarizing the main features, the following conclusions could be drawn:
The predicted values lies very close to the experimental values reasonably close, with
R5 of 3.06(g/min) for MRR and 0.945(µm) of surface roughness.
The error between the experimental values and predicted values at the optimal
combination of parameters for MRR and Surface roughness lies within 14% and 6%
respectively.
From multi- response optimization, the optimal combination of parameters setting are
feed rate =275mm/min. and spindle speed = 1350 rpm and depth of cut =0.30mm for
achieving the required maximum Material removal rate (MRR) and minimum Surface
roughness.
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