3.2 Analysis Of Chip Chips: Analysis Of Chip Formation

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3.2 Analysis of chip formation

Fig. 7 shows the chip forms obtained during milling of the Al7075 (a) and MMCs (b) using the uncoated carbide inserts at a feed rate of 0.1 mm/tooth, machining speed of 290 m/min and axial depth of cut of 1.3 mm. The Al7075 chips formed during milling exhibited a smooth and shiny surface, and were in a semicircular and parabolic trapezoidal wave with a small radius and a saw-tooth-form, as shown in Fig. 7 (a). Fig. 7 (b) shows the chip shapes formed during the milling of the MMCs. The composite chips had large radii, and were semi-circular helical type and saw-toothed. The SiC foam reinforcement in the Al matrix diminished the ductility and converted the workpiece material for generating saw-toothed and segmented-type
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The Taguchi method uses a loss function to determine the deviation between the directly measured test values and the optimal machining values. Additionally, these functions are transferred into the signal to noise (S/N) ratio as the quality features [22]. There are three signal-to-noise ratios in the analysis of the S/N ratio: the-smaller-the-better, the-larger-the-better and the-nominal-the-best. For each level of the cutting variables, the S/N ratio is calculated on the basis of the S/N analysis. The-smaller-the-better characteristic (in dB) has been considered to calculate the S/N ratio in this study to achieve minimum response within the optimal cutting parameters. The effect of each machining parameter on surface roughness was evaluated with an S/N response table, and the optimal machining parameters were obtained on the basis of the higher S/N ratio in the levels of the control factor. The S/N ratio for surface roughness has been determined considering the-lower-the-better characteristic (LB; in dB) according to Eq. (1), where Ri is the obtained value of the surface roughness for the ith test in the experiment and n is the number of trials in the experimental work. Higher values of S/N ratios are always preferred to minimize the …show more content…
8 and Fig. 9. From the main effect plots, response table for the S/N ratios in Table 5 and response table for the mean in Table 6, the optimal milling parametric constitutions for surface roughness for both workpiece types are observed to be a machining speed of 170 m/min, a feed per tooth of 0.08 mm/tooth and a axial depth of cut of 0.8 mm.

Table 4 Experimental results and S/N ratio values
Cutting parameters Al7075 SiC foam reinforced Al7075 composite
Exp. No Vc fz ap, Ra µm) Ra (dB) Ra (µm) Ra (dB)
1 170 0.08 0.8 0.243 12.3058 1.544 −3.7729
2 170 0.08 1.0 0.247 12.1637 1.706 −4.6396
3 170 0.08 1.3 0.262 11.6423 1.954 −5.8163
4 170 0.10 0.8 0.286 10.8727 2.039 −6.1862
5 170 0.10 1.0 0.287 10.8575 2.177 −6.7572
6 170 0.10 1.3 0.302 10.4143 2.548 −8.1223
7 170 0.13 0.8 0.344 9.2751 2.591 −8.2685
8 170 0.13 1.0 0.356 8.9771 2.798 −8.9362
9 170 0.13 1.3 0.361 8.8619 3.030 −9.6274
10 220 0.08 0.8 0.242 12.3147 1.717

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