90
V. Sisodia et al.
Table 4 Confirmation test results for geometric error
Conf. test
no.
Dummy
sheet
thickness
Step size Wall angle Feed rate Predicted
RMSE
Measured
RMSE
% error
1
0.51
0.4
45
2500
1.2
1.389
14.72
2
0.71
0.45
50
3000
1.44
1.698
15.01
3
0.91
0.7
55
3600
1.54
1.706
9.543
4
0.51
0.8
60
4000
1.04
1.22
14.75
Table 5 Criteria for optimization
S. No. Process parameter and
responses
Goal
Lower limit Upper limit Optimized value
1
Dummy sheet thickness In range
0.51
0.91
0.5162
2
Step size
In range
0.35
0.95
0.936
3
Wall angle
In range
40
65
41.537
4
Feed rate
In range
2200
4400
2225.41
5
Geometric error
(RMSE)
Minimize 0.783
1.854
0.718
5 Optimization of Geometric Error (RMSE)
The optimized set of process parameters is selected to reduce the geometric error
(RMSE). The optimized values of process parameters are listed in Table 5. The
obtained vale for desirability is “1” and hence can be accepted.
6 Conclusion
In the present work, influence of process parameters on geometric error (in terms
of RMSE) of formed part in SPIF process with dummy sheet has been studied.
Following are the conclusions drawn from the present experimental study:
1. Step size, dummy sheet thickness, and wall angle are significant process
parameters influencing RMSE. No significant influence of feed rate is observed.
2. Geometric error increases with increase in dummy sheet thickness and wall angle,
while it decreases with the increase in step size.
3. As feed rate increases, there is nominal decrease in geometric error which is
desirable. So high feed rate is recommended to reduce forming time.
Based on analysis of results, a mathematical model for RMSE has been proposed.
Adequacy and accuracy of developed mathematical model for RMSE have been validated by performing confirmation experiments. The obtained experimental results