Analysis of surface roughness sound level vibration and current when machining AISI 1040 steel

2.1. Workpiece Material

The turning tests were carried out on hot rolled AISI 1040 steel cylindrical workpiece. Table 1 gives the chemical composition AISI 1040 steel. The workpiece part was 50 mm in dimension and 100 mm in length. Table 1. Chemical composition of AISI 1040 steel (wt. %) Fe 98.6-99

2.2. Test Procedure, Test Parameters and Tooling

The machining tests were performed dry by single point continuous turning on a TAKSAN TTC 630 turning centre, with a variable spindle speed of up to 4000 rpm and power rating of 37 kW. The cutting tools used were commercial grade TiCN-Al2O3-TiN coated carbide with the geometry of WNMG 080408 MT and manufactured by TaequTec. These cutting tools had TT5100 TaeguTec designation conforming to ISO P20-35. A MWLNR 2525 M08 tool holder was used to rigidly mount the cutting tools. The workpiece parts were clamped using a three-jaw precison chuck. The length of the workpiece parts overhanging from the chuck was 70 mm. As 424

the length of the workpiece was quite short, the tailstock was not used to support the workpiece. In order to avoid excessive vibration, the overhang of the tool holder was held as short as possible. The test parameters and their levels are given in Table 2 and they were selected based on the cutting tool manufacturer’s recommendation, previous studies and industrial practice. Table 2. Test parameters and their levels Factor

The vibration measurements were performed using a Pro Vibro PVM 303 unit. This unit was mounted behind the chuck. The measurements were obtained in mm/s during the machining operations. In order to measure the sound level, a Lutron SL-401 (The measurement was taken when the device is in position A weighting Character and function of SL) model sound level meter was used. This device was located to a position 1 m away from the chuck and was set to slow mode for eliminating the possible momentary fluctuations in the sound level. The current measurements were conducted using a UNI-T UT201 digital clamp multimeter. The current value passing through a phase was measured and multiplied by three to find the total current value. The pictures of the used devices are given in Figure 1. Output parameters of the vibration, sound level and motor current values were indicated during the machining tests as shown in Figure 1. These indicated values were recorded using a video camera throughout the machining tests. Their average values were calculated.

Figure 1. The used devices for measurement of a) vibration, b) sound and c) motor current On the turned surfaces, surface roughness (Ra) measurements were performed using a Mitutoyo SJ 201 with a cut-off length of 0.8 and sampling length of 5 mm. Three measurements were made on each turned surface. The whole test setup is given schematically in Figure 2. For the statistical analysis, Minitab 16 version was used.

3.1. Surface Roughness

Main effect plots are given in Fig. 3 for the surface roughness values. As can be seen from Fig. 3, the most effective cutting parameter on surface roughness is the feed rate. With increasing the feed rate, the surface roughness increases. That is because; increasing feed rate leaves larger feed marks on the turned workpiece when turning with a cutting tool having a defined nose 427

radius. Similar findings were also reported in the published studies [13,17,29]. Contrary to Plot the for Ra (µm) Main Effects Data Means feed rate, increasing the cutting speed decreases the surface roughness. However, this decrease is (mm) V (m/dak) quite low. In machining operations, increasing cutting speed usually results ain decreases in 4 surface roughness. This is obviously seen when machining workpieces of high ductility. This 3 decrease I surface roughness can be attributed to the decreased built-up edge (BUE) tendency. With increasing depth of cut, the surface roughness values increases until a maximum value is 2 reached beyond which Main they decreased. Effects PlotPlot for for Ra Ra (µm) Main Effects (µm) 1 DataData Means Means

3.2. Vibration

As shown in Fig. 5, the increase in the depth of cut and feed rate increase the vibration values. The increasing the depth of cut and feed rate increases the load acting on the cutting tool holder. This increase in the load is likely to result in more vibration. Unlike the depth of cut and feed rate, the cutting speed does not have a substantial influence on the vibration. Increasing the cutting speed decreases the vibration to some extent. Although the vibration in the machine tool spindle is expected to increase slightly due to the increase in the cutting speed, the increasing cutting speed decreases built-up edge (BUE) formation and this, in turn, helps decrease the vibration. Low engine power causes the machine tool to be forced more and results in increased vibration value. The increase in vibration value results in an increase in tool wear and surface roughness values. Therefore, low feed and depth of cut should be preferred when machining materials. This reduces the amount of vibration. Reduction in the amount of vibration results in increased tool life, reduced surface roughness and increased rigidity.

Main Effects Plot for for AT AT (mm/s) Main Effects Plot (mm/s)

3.3. Sound Level

Figure 7 shows that the sound level varies depending on the cutting parameters employed. The most influential cutting parameter on the sound level is seen to be the feed rate. This is followed by the cutting speed and depth of cut. Increasing the feed rate and Main cutting speed Effects Plot for SS (dB) Data Means increases the sound level. However, with the increasing depth of cut, the sound level increases a (mm) V (m/dak) until a maximum value is reached beyond which they decreased. Increasing depth of cut was 78 expected to increase the sound level similar to the influence of increasing feed rate. However, this 77 did not happen. During the turning operation, the chip morphology76 was seen to change with the depth of cut. At the lower depth of cuts, continouous chips were formed while at the higher depth 75 74 of cuts short chips wereMain formed. This was in the sound level. Main Effects for SS (dB) to result in the irregularities Effects PlotPlot for SSthought (dB) 1,0

Figure 78 78 7. The effect of cutting parameters on means response characteristics for sound level. 77 77 76 76 75 75 74 74 0,1 0,1

The ANOVA results are given in Table 7. It is seen from Table 7 that the sources f and v have significant influences on the sound level. The percentage contributions of f and v on the sound level are seen to be 56.92 and 13.61, respectively. Fig. 8 shows the influences of cutting parameters on the sound level. Table 7. ANOVA for sound level Sound level Source D a 1 v 1 f 1 a2 1 V2 1 f2 1 axV 1 aXf 1 Vxf 1 Error 70 Total 79

Seq SS 17.490 65.206 272.745 19.153 10.153 5.778 8.757 2.322 35.725 41.816 479.145

Adj SS 17.490 65.206 272.745 19.153 10.153 5.778 8.757 2.322 35.725 41.816

Adj MS 17.490 65.206 272.745 19.153 10.153 5.778 8.757 2.322 35.725 0.597

P Value 0.000 0.000 0.000 0.000 0.000 0.003 0.000 0.053 0.000

Contr.(%) 3.65 13.61 56.92 4.00 2.12 1.21 1.83 0.48 7.46 8.73 100.00

c) Figure 8. Sound level versus a) feed rate and depth of cut, b) feed rate and cutting speed and c) depth of cut and cutting speed.

3.4. Motor Current

Determination of the cutting forces in a machining operation is important. That is because, the cutting forces have a direct influence on the generation of heat, and thus on tool wear, quality of machined surface and accuracy of workpiece. They are also used in the design of machine tools, cutting tools and fixtures [30]. The cutting forces are generally measured using dynamometers which are expensive devices and not easy to use. There are some indirect methods to determine the cutting forces. These methods are generally practical and inexpensive. Motor current is suchPlot a for TA (A) Main Effects Data Means way to determine the cutting forces. V (m/dak) Motor current values obtained in this study are given in Figure 9. As the feeda (mm) rate, the depth 18 of cut and the cutting speed increase, the motor current value generally increases. These increases in the motor current are the expected results as the increasing depth16of cut, cutting speed and feed 14 rate increases the power consumption. Fig. 10 shows the influences of cutting parameters on the 12 motor current. Main Effects Plot forfor TA TA (A)(A) Main Effects Plot 10

Figure 9. The effect of cutting parameters on means response characteristics for motor current. 18 18 16 16

The ANOVA results are given in Table 8. It is seen from Table 8 that the sources f, v and a 14 14 have significant influences on the motor current. The percentage contributions of f, v and a on the 12 12 sound 10level are seen to be 59.96, 24.322 and 6.506, respectively. Fig. 10 shows the influences of 10 0,3 0,4 0,1 0,1 0,2 0,4 cutting parameters on0,2the0,3sound level. Table 8. ANOVA for motor current Current Source a v f a2 V2 f2 axV aXf Vxf Error Total

Seq SS 94.10 351.77 867.21 26.43 5.48 2.04 0.13 0.03 52.95 46.17 1446.31

Adj SS 94.10 351.77 867.21 26.43 5.48 2.04 0.13 0.03 52.95 46.17

Adj MS 94.096 351.769 867.214 26.428 5.476 2.038 0.128 0.033 52.952 0.660

P Value 0.000 0.000 0.000 0.000 0.005 0.083 0.662 0.825 0.000

Contr.(%) 6.506 24.322 59.960 1.827 0.379 0.141 0.009 0.002 101.827 3.192 100.000

c) Figure 10. Motor current versus a) feed rate and depth of cut, b) feed rate and cutting speed and c) depth of cut and cutting speed.

3.5. Optimum Values of Cutting Parameters

In particular, it is difficult to determine the optimum cutting parameters in a machining operation as there are a lot of input factors. Table 9 shows the effects of optimum levels of the input factors on the output factors. The lowest values of the output factors were defined as the optimum levels and these are shown in boldface type. Table 9. Optimum values of cutting parameters for surface roughness, vibration, sound level and motor current Ra (µm)

3.6. Regression Equations

Regression equations were obtained for surface roughness, vibration, sound level and motor current using Minitab 16 software. These equations are given below. Regression equation for surface roughness: 𝑆𝑆𝑟𝑒𝑠𝑖𝑑𝑢𝑎𝑙 𝑅2 = 1 − 𝑆𝑆𝑚𝑜𝑑𝑒𝑙 + 𝑆𝑆𝑟𝑒𝑠𝑖𝑑𝑢𝑎𝑙 𝑆𝑆𝑟𝑒𝑠𝑖𝑑𝑢𝑎𝑙 = 3.517 𝑆𝑆𝑚𝑜𝑑𝑒𝑙 = 135.776 (Tablo3 den) 3.517 𝑅2 = 1 − = 0.974751 = 97.47% 135.776 + 3.517 𝑅𝑎 = −1,88578 + 1,77020 ∗ 𝑎 + 0.0108943 ∗ 𝑣 + 4,40365 ∗ 𝑓 − 0.2741107 ∗ 𝑎2 − 0.0000134 ∗ 𝑣 2 + 13,0875 ∗ 𝑓 2 − 0.00575267 ∗ 𝑎 ∗ 𝑣 − 0.0741667 ∗ 𝑎 ∗ 𝑓 + 0.00573067 ∗ 𝑣∗𝑓 R2=97.47 % R2(adj)=97.08% Regression equation for vibration: 𝑉𝑖𝑏 = 0.30025 + 0.39875 ∗ 𝑎 − 0.00706 ∗ 𝑣 − 3,203 ∗ 𝑓 − 0.087 ∗ 𝑎 2 + 0.000052 ∗ 𝑣 2 + 5,25 ∗ 𝑓 2 − 0.0021 ∗ 𝑎 ∗ 𝑣 + 1,255 ∗ 𝑎 ∗ 𝑓 + 0.00832 ∗ 𝑣 ∗ 𝑓 R2=94.88% . R2(adj)=94.22% Regression equation for sound level: 𝑆𝐿 = 71.7433 + 6.02082 ∗ 𝑎 − 0.08743 ∗ 𝑣 − 11.3235 ∗ 𝑓 − 1.16964 ∗ 𝑎2 + 0.00057 ∗ 𝑣 2 + 26.875 ∗ 𝑓 2 − 0.01674 ∗ 𝑎 ∗ 𝑣 − 2.155 ∗ 𝑎 ∗ 𝑓 + 0.21384 ∗ 𝑣 ∗ 𝑓 R2(adj)=91.27%. R2(adj)=90.15% Regression equation for motor current: 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 = 5.9091 − 4.07496 ∗ 𝑎 + 0.079151 ∗ 𝑣 − 0.80285 ∗ 𝑓 + 1.37393 ∗ 𝑎2 − 0.0004186 ∗ 𝑣 2 + 15.9625 ∗ 𝑓 2 + 0.00202 ∗ 𝑎 ∗ 𝑣 − 0.255 ∗ 𝑎 ∗ 𝑓 ∗ +0.260344 ∗ 𝑣 ∗ 𝑓 R2=96.81%. R2(adj)=96.40%