A full factorial design technique is used to investigate the effect of machining parameters, namely, spindle speed
Increasing product quality, delivery time, and productivity of the machined parts are the main challenges of metal-based industry. There has been increased interest in optimizing machining conditions to satisfy manufacturing requirements including the most prominent one, which is surface finish. Surface quality is considered as one of the most important criteria in manufacturing engineering. The performance and quality of a product are directly associated with surface integrity achieved by final machining, which is reflected in having small tolerance and minimum surface roughness,
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The current work focuses on providing a comprehensive study on the effect of machining process parameters, namely, feed fate, cutting speed, and depth of cut, on the surface roughness, through a DOE full factorial design for face milling of high strength steel using carbide tools. Four levels for each process parameter are investigated. Analysis of variance (ANOVA) will be used to determine the effects of the machining parameters on surface roughness and to develop a mathematical model through regression analysis that best describes the variation within the experimental data.
This research study aims to investigate the effect of main factors on the surface roughness of high strength steel in face milling process using CNC milling machine and carbide inserts. Emco Mill Concept 45 CNC vertical milling machine equipped with Sinumeric 840-D with technical specifications including a speed range of 50–10,000 rpm and feed rate 0–10 m/min was used. Workpiece samples are high strength steel with the chemical composition shown in Table
Chemical composition for high strength steel material.
C | Si | Mn | Ni | Cr | Mo | V | S | Cu | P | Al | Fe |
---|---|---|---|---|---|---|---|---|---|---|---|
0.356 | 0.221 | 0.728 | 2.697 | 1.030 | 0.617 | 0.103 | 0.005 | 0.176 | 0.010 | 0.006 | Balance |
Test rig for machining the workpieces.
Test rig measuring the surface roughness.
The test plan was carried out through 64 test specimens, group (A), and repeated for producing replicates in group (B). Each group was divided into 16 groups. Every four groups are subjected to one common machining spindle speed. Groups 1–4, 5–8, 9–12, and 13–16 were processed using spindle speed machining of 500 rpm, 750 rpm, 1000 rpm, and 1250 rpm, respectively. Each group has been machined using four levels of cutting depth (0.25, 0.50, 0.75, and 1.0 mm) and each depth was processed using four levels of table feed rates (50, 75, 100, and 125 mm/min). To apply the above conditions, CNC milling machine equipped with Sinumeric 840-D was used. The surface roughness tester TESA was used to measure the surface roughness parameters,
Full factorial design is a comprehensive technique that requires a large number of experiments and yields a detailed description of all system relations and interactions. In this research, full factorial design was used to build the experiment with three independent variables (factors) and four levels for each. Table
The cutting parameters and their levels used in the factorial design experiment.
Designation | Process parameter | Level 1 | Level 2 | Level 3 | Level 4 |
---|---|---|---|---|---|
|
Spindle speed (rpm) | 500 | 750 | 1000 | 1250 |
|
Depth of cut (mm) | 0.25 | 0.50 | 0.75 | 1.00 |
|
Feed rate (mm/min) | 50 | 75 | 100 | 125 |
Figures
The effect of table feed rate on
Effect of table feed rate on
Using Minitab 17 multiple regression option, the data were fit into a cubic model. However, the results showed a high level of multicollinearity between the cubic terms (third-order terms) and linear terms, even with coded data. To avoid this problem, the cubic terms were removed from the model. The adequacy of the model fit, measured by the coefficient of determination (adjusted
ANOVA results of the model are presented in Table
ANOVA for
Source | DF | Adj. SS | Adj. MS |
|
|
---|---|---|---|---|---|
Regression | 10 | 0.476642 | 0.047664 | 47.92 | 0 |
|
1 | 0.005935 | 0.005935 | 5.97 | 0.016 |
|
1 | 0.102187 | 0.102187 | 102.74 | 0 |
|
1 | 0.317063 | 0.317063 | 318.79 | 0 |
|
1 | 0.01274 | 0.01274 | 12.81 | 0.001 |
|
1 | 0.017414 | 0.017414 | 17.51 | 0 |
|
1 | 0.011724 | 0.011724 | 11.79 | 0.001 |
|
1 | 0 | 0 | 0 | 0.999 |
|
1 | 0.002544 | 0.002544 | 2.56 | 0.112 |
|
1 | 0.00683 | 0.00683 | 6.87 | 0.01 |
|
1 | 0.000205 | 0.000205 | 0.21 | 0.65 |
Error | 117 | 0.116365 | 0.000995 | ||
Lack-of-fit | 53 | 0.116245 | 0.002193 | 1174.66 | 0 |
Pure error | 64 | 0.000119 | 0.000002 | ||
Total | 127 | 0.593006 |
ANOVA for
Source | DF | Adj. SS | Adj. MS |
|
|
% contribution |
---|---|---|---|---|---|---|
Regression | 7 | 0.473893 | 0.067699 | 68.2 | 0 | |
|
1 | 0.005935 | 0.005935 | 5.98 | 0.016 | 10.0 |
|
1 | 0.102187 | 0.102187 | 102.95 | 0 | 17.2 |
|
1 | 0.317063 | 0.317063 | 319.42 | 0 | 53.5 |
|
1 | 0.01274 | 0.01274 | 12.83 | 0 | 2.1 |
|
1 | 0.017414 | 0.017414 | 17.54 | 0 | 2.9 |
|
1 | 0.011724 | 0.011724 | 11.81 | 0.001 | 2.0 |
|
1 | 0.00683 | 0.00683 | 6.88 | 0.01 | 1.2 |
Error | 120 | 0.119114 | 0.000993 | |||
Lack-of-fit | 56 | 0.118994 | 0.002125 | 1138.02 | 0 | |
Pure error | 64 | 0.000119 | 0.000002 | |||
Total | 127 | 0.593006 | ||||
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The results show that spindle speed, depth of cut, and table feed rate have a significant effect on the surface roughness (
Figure
Residual plots for the response
Anderson-Darling normality test results for
Model adequacy measures, reflected in the values of the coefficients of determination (
Equation (
Optimization plot for
Surface plots for
Surface plots for
Surface plots for
Running the analysis as described in Section
ANOVA for
Source | DF | Adj. SS | Adj. MS |
|
|
% contribution |
---|---|---|---|---|---|---|
Regression | 10 | 23.6589 | 2.3659 | 56.45 | 0 | |
|
1 | 0.0003 | 0.0003 | 0.01 | 0.928 | 0.0 |
|
1 | 4.7025 | 4.7025 | 112.21 | 0 | 16.5 |
|
1 | 14.9689 | 14.9689 | 357.19 | 0 | 52.4 |
|
1 | 0.9405 | 0.9405 | 22.44 | 0 | 3.3 |
|
1 | 0.8653 | 0.8653 | 20.65 | 0 | 3.0 |
|
1 | 1.0068 | 1.0068 | 24.02 | 0 | 3.5 |
|
1 | 0.0193 | 0.0193 | 0.46 | 0.499 | 0.1 |
|
1 | 0.1679 | 0.1679 | 4.01 | 0.048 | 0.6 |
|
1 | 0.2752 | 0.2752 | 6.57 | 0.012 | 1.0 |
|
1 | 0.7122 | 0.7122 | 16.99 | 0 | |
Error | 117 | 4.9032 | 0.0419 | |||
Lack-of-fit | 53 | 4.9031 | 0.0925 | 37711.35 | 0 | |
Pure error | 64 | 0.0002 | 0 | |||
Total | 127 | 28.5622 | ||||
|
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|
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|
Figure
Residual plots for the response
Anderson-Darling normality test results for
The coefficients of determination values are comparable to that of
Though reducing the feed rate and depth of cut improves the surface roughness, it also reduces the metal removal rate
A target was set to minimize
Multiobjective optimization plot for
High strength steel has relatively high hardness that correlates well with good surface quality. This is due to the harder material possessing low plastic flow capability which results in better surface finish. This is attributed to the brittle nature of the interaction between the cutting tool and the workpiece surface, for the hard materials, that leads to material separation rather than plastic flow that would result in surface irregularities. Surface roughness was found to increase with increasing feed rate and depth of cut which both result in bigger cut areas that are consequently associated with higher cutting forces and higher friction which lead to poor surface finish. It was noticed from the surface roughness profile that high feed rates were associated with larger roughness markings horizontal spacing. Also, with higher depth of cuts, the vertical spacing between peaks and troughs of the surface irregularities was larger. Thus, higher feed rates and depth of cuts led to higher surface roughness.
Figure
Optical microscopy of the machined surface under spindle speed = 1250 rpm, depth of cut = 0.5 mm, and table feed rate = 50 mm/min.
Optical microscopy of the machined surface under spindle speed = 1250 rpm, depth of cut = 0.5 mm, and table feed rate = 125 mm/min.
ANOVA and regression analysis, through a DOE full factorial design (43), were conducted to relate the surface roughness of face milled high strength steel to the most common machining parameters, namely, table feed rate, depth of cut, and spindle speed. Two surface roughness indicators, namely,
See Tables
Cutting conditions for group A.
Test | Group | Spindle speed | Depth of cut | Table feed | Surface finish ( | |
---|---|---|---|---|---|---|
number | # | (rpm) | (mm) | (mm/min) |
|
|
A1 | A1 | 500 | 0.25 | 50 | 0.042 | 0.295 |
A2 | 75 | 0.120 | 1.039 | |||
A3 | 100 | 0.151 | 1.198 | |||
A4 | 125 | 0.202 | 1.419 | |||
A5 | A2 | 500 | 0.5 | 50 | 0.055 | 0.336 |
A6 | 75 | 0.129 | 0.945 | |||
A7 | 100 | 0.171 | 1.256 | |||
A8 | 125 | 0.210 | 1.366 | |||
A9 | A3 | 500 | 0.75 | 50 | 0.073 | 0.855 |
A10 | 75 | 0.165 | 1.132 | |||
A11 | 100 | 0.194 | 1.369 | |||
A12 | 125 | 0.233 | 1.426 | |||
A13 | A4 | 500 | 1.00 | 50 | 0.087 | 0.928 |
A14 | 75 | 0.206 | 1.216 | |||
A15 | 100 | 0.241 | 1.400 | |||
A16 | 125 | 0.253 | 1.596 | |||
A17 | A5 | 750 | 0.25 | 50 | 0.083 | 0.607 |
A18 | 75 | 0.184 | 1.220 | |||
A19 | 100 | 0.208 | 1.736 | |||
A20 | 125 | 0.239 | 1.478 | |||
A21 | A6 | 750 | 0.5 | 50 | 0.085 | 0.871 |
A22 | 75 | 0.104 | 1.069 | |||
A23 | 100 | 0.115 | 1.149 | |||
A24 | 125 | 0.143 | 1.177 | |||
A25 | A7 | 750 | 0.75 | 50 | 0.094 | 0.901 |
A26 | 75 | 0.118 | 1.103 | |||
A27 | 100 | 0.136 | 1.316 | |||
A28 | 125 | 0.167 | 1.547 | |||
A29 | A8 | 750 | 1.00 | 50 | 0.109 | 1.002 |
A30 | 75 | 0.201 | 1.991 | |||
A31 | 100 | 0.294 | 2.140 | |||
A32 | 125 | 0.354 | 2.263 | |||
A33 | A9 | 1000 | 0.25 | 50 | 0.046 | 0.334 |
A34 | 75 | 0.104 | 0.899 | |||
A35 | 100 | 0.120 | 1.005 | |||
A36 | 125 | 0.140 | 1.174 | |||
A37 | A10 | 1000 | 0.5 | 50 | 0.094 | 0.601 |
A38 | 75 | 0.116 | 0.950 | |||
A39 | 100 | 0.134 | 1.109 | |||
A40 | 125 | 0.236 | 1.719 | |||
A41 | A11 | 1000 | 0.75 | 50 | 0.109 | 0.743 |
A42 | 75 | 0.220 | 1.364 | |||
A43 | 100 | 0.239 | 1.675 | |||
A44 | 125 | 0.259 | 1.855 | |||
A45 | A12 | 1000 | 1.00 | 50 | 0.115 | 0.853 |
A46 | 75 | 0.243 | 1.598 | |||
A47 | 100 | 0.265 | 1.914 | |||
A48 | 125 | 0.278 | 2.140 | |||
A49 | A13 | 1250 | 0.25 | 50 | 0.060 | 0.859 |
A50 | 75 | 0.110 | 1.082 | |||
A51 | 100 | 0.144 | 1.112 | |||
A52 | 125 | 0.165 | 1.435 | |||
A53 | A14 | 1250 | 0.5 | 50 | 0.064 | 0.404 |
A54 | 75 | 0.121 | 0.896 | |||
A55 | 100 | 0.137 | 0.907 | |||
A56 | 125 | 0.165 | 0.996 | |||
A57 | A15 | 1250 | 0.75 | 50 | 0.068 | 0.321 |
A58 | 75 | 0.128 | 1.233 | |||
A59 | 100 | 0.174 | 1.348 | |||
A60 | 125 | 0.203 | 2.186 | |||
A61 | A16 | 1250 | 1.00 | 50 | 0.072 | 0.409 |
A62 | 75 | 0.163 | 1.514 | |||
A63 | 100 | 0.190 | 1.713 | |||
A64 | 125 | 0.223 | 1.820 |
Cutting conditions for group B.
Test | Group | Spindle speed | Depth of cut | Table feed | Surface finish ( | |
---|---|---|---|---|---|---|
number | # | (rpm) | (mm) | (mm/min) |
|
|
B1 | B1 | 500 | 0.25 | 50 | 0.044 | 0.298 |
B2 | 75 | 0.122 | 1.042 | |||
B3 | 100 | 0.153 | 1.200 | |||
B4 | 125 | 0.204 | 1.417 | |||
B5 | B2 | 500 | 0.5 | 50 | 0.056 | 0.338 |
B6 | 75 | 0.130 | 0.948 | |||
B7 | 100 | 0.173 | 1.257 | |||
B8 | 125 | 0.211 | 1.368 | |||
B9 | B3 | 500 | 0.75 | 50 | 0.075 | 0.854 |
B10 | 75 | 0.166 | 1.133 | |||
B11 | 100 | 0.196 | 1.371 | |||
B12 | 125 | 0.235 | 1.428 | |||
B13 | B4 | 500 | 1.00 | 50 | 0.087 | 0.928 |
B14 | 75 | 0.208 | 1.216 | |||
B15 | 100 | 0.242 | 1.401 | |||
B16 | 125 | 0.256 | 1.598 | |||
B17 | B5 | 750 | 0.25 | 50 | 0.085 | 0.605 |
B18 | 75 | 0.186 | 1.223 | |||
B19 | 100 | 0.209 | 1.738 | |||
B20 | 125 | 0.240 | 1.479 | |||
B21 | B6 | 750 | 0.5 | 50 | 0.088 | 0.872 |
B22 | 75 | 0.106 | 1.067 | |||
B23 | 100 | 0.117 | 1.150 | |||
B24 | 125 | 0.146 | 1.179 | |||
B25 | B7 | 750 | 0.75 | 50 | 0.098 | 0.900 |
B26 | 75 | 0.121 | 1.102 | |||
B27 | 100 | 0.138 | 1.318 | |||
B28 | 125 | 0.169 | 1.549 | |||
B29 | B8 | 750 | 1.00 | 50 | 0.110 | 1.002 |
B30 | 75 | 0.200 | 1.990 | |||
B31 | 100 | 0.296 | 2.143 | |||
B32 | 125 | 0.356 | 2.261 | |||
B33 | B9 | 1000 | 0.25 | 50 | 0.049 | 0.338 |
B34 | 75 | 0.100 | 0.896 | |||
B35 | 100 | 0.120 | 1.007 | |||
B36 | 125 | 0.140 | 1.176 | |||
B37 | B10 | 1000 | 0.5 | 50 | 0.096 | 0.605 |
B38 | 75 | 0.118 | 0.952 | |||
B39 | 100 | 0.136 | 1.112 | |||
B40 | 125 | 0.239 | 1.722 | |||
B41 | B11 | 1000 | 0.75 | 50 | 0.110 | 0.746 |
B42 | 75 | 0.221 | 1.362 | |||
B43 | 100 | 0.240 | 1.677 | |||
B44 | 125 | 0.262 | 1.857 | |||
B45 | B12 | 1000 | 1.00 | 50 | 0.118 | 0.856 |
B46 | 75 | 0.242 | 1.600 | |||
B47 | 100 | 0.268 | 1.917 | |||
B48 | 125 | 0.279 | 2.142 | |||
B49 | B13 | 1250 | 0.25 | 50 | 0.060 | 0.861 |
B50 | 75 | 0.110 | 1.084 | |||
B51 | 100 | 0.145 | 1.113 | |||
B52 | 125 | 0.165 | 1.437 | |||
B53 | B14 | 1250 | 0.5 | 50 | 0.065 | 0.406 |
B54 | 75 | 0.122 | 0.899 | |||
B55 | 100 | 0.138 | 0.908 | |||
B56 | 125 | 0.166 | 1.000 | |||
B57 | B15 | 1250 | 0.75 | 50 | 0.068 | 0.323 |
B58 | 75 | 0.129 | 1.235 | |||
B59 | 100 | 0.175 | 1.346 | |||
B60 | 125 | 0.201 | 2.189 | |||
B61 | B16 | 1250 | 1.00 | 50 | 0.075 | 0.412 |
B62 | 75 | 0.165 | 1.516 | |||
B63 | 100 | 0.192 | 1.715 | |||
B64 | 125 | 0.225 | 1.822 |
Depth of cut, mm
Working engagement, mm
Spindle speed, rpm
Cutting speed, m/min
Table feed rate, mm/min
Total number of teeth in cutter
Metal removal rate, mm3/min.
The authors declare that they have no competing interests.
This project was supported by King Saud University, Deanship of Scientific Research, College of Engineering Research Center.