OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 Comparison of surface roughness of SS 316, EN 8, SAE 8620 and Al 380 To obtain a complete understanding of the infl uence of input parameters on surface roughness, threedimensional (3D) surface diagrams were constructed for all cutting materials by varying process parameters. These visual representations use empirically derived equations to ensure accuracy. Figure 2 shows threedimensional surface diagrams illustrating the surface roughness changes during turning of SS 316, EN 8, SAE 8620 and Al 380 with PVD-coated (TiAlN) tools generated using Eqs. (I)–(IV). From fi gure 2 it becomes clear that the surface roughness is primarily aff ected by the feed. However, this eff ect can be considered to be more signifi cant for Al 380 and SS 316. During the processing of aluminum alloys, built-up edges are formed due to the adhesion of chips to the cutting tool, which leads to an increase in surface roughness. In the case of SS 316, there is a tendency for the formation of drain chips that spin around the work material, damaging the new surface, and this may be the cause of poor surface fi nish. EN 8 and SAE 8620 materials seem well suited for machining, mainly due to their low hot hardness and easy machinability. Therefore, the roughness of these materials is higher compared to others. It was also observed that as cutting speed increases, there is a tendency for surface roughness to improve for all materials. The literature reports that at high cutting speeds, the tool-chip contact length is reduced, thereby minimizing cutting tool vibration and improving surface roughness. In addition, at higher speeds, the cutting temperature increases; this contributes to the softening of the material. This in turn helps reduce cutting forces, thereby minimizing vibration and improving surface fi nish. Figure 3, a shows the eff ect of f on Ra at Vc = 140 m/min and doc = 0.6 mm for both regression and semiempirical values. Aluminum material has poor surface fi nish because aluminum produces more continuous chips than other materials. In addition, this continuous chip damages the fi nished parts [23]. Figure 3, b shows the eff ect of f on Ra at Vc = 190 m/min and doc = 0.7 mm. As f increases, Ra increases compared to other materials, the thermal conductivity of SS 316 is lower, due to the increase in temperature, a b c d Fig. 2. Surface roughness 3D-plots for SS 316 (a), EN 8 (b), SAE 8620 (c) and Al 380 (d)
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