Surface Roughness and Profile Error in Precision Diamond Turning of C18000

Abstract

Nickel–silicon–chromium–copper (C18000) alloy is widely used for many precision applications due to its high thermal conductivity, hardness, and moderate strength in fabrication of parts of molds. This study was carried out on this material for achieving mirror finish and minimizing profile error. Four machine and tool parameters were varied at different levels in a single point diamond turning operation to create a spherical profile on the workpiece. The surface roughness and profile accuracy were significantly affected by tool nose radius, feed rate, and spindle speed and depth of cut had insignificant effect. The process was optimized separately for both surface roughness and profile accuracy. Increased tool nose radius caused a ripple like effect on the machined surface as compared to a digging effect with low or no tool nose radius and thus showed a better surface finish. The profile error, however, increased with tool nose radius. Subsequently, both surface roughness and profile accuracy were optimized together using grey relational grade to obtain a globally optimized solution. The final parameter setting in an optimal solution identified feed rate as the most significant parameter followed by nose radius and spindle speed. A surface roughness and profile error of 15 nm and 0.464 µm, respectively, was attained during the confirmation experiments.

Keywords:

• Diamond tool
• Profile error
• Surface roughness
• Ultra-precision machining

Notes

Note: SS = sum of squares, PC = percentage contribution.

Percentage of improvement of the grey relational grade = 39.31%.

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