Experimental investigations on slow tool servo process parameters for freeform optics machining

Freeform surfaces are gaining popularity in vast engineering applications including optical engineering, aerospace, automotive, and biomedical. Success of freeform surfaces lies with its complex design and fabrication methods. Ultraprecision machining is the most suitable process to develop the complex shapes with nanometric surface finish. Slow tool servo (STS) arrangement of ultraprecision machining is controlled by interrelated motion of three axes (CXZ). The quality of freeform surface generation by STS process has direct association with selection of its input process parameters, i.e. X-axis motion increment, C-axis angular increment, depth of cut, tool nose radius, and spindle speed. In this paper, the optimization techniques are adopted to understand the weightage of individual machining parameters and the optimum range of these input parameters are found to achieve the desired surface finish. Further, detailed experimental investigations are carried out for in-depth understanding of the effects of these individual parameters in relation to fabrication of freeform profile. By utilizing the optimized process, the profile accuracy of 0.82 µm, three-dimensional surface finish (S a ) of 26 nm, and two-dimensional surface finish (R a ) of 11.6 nm are achieved in very first cut. The investigation helps to understand the relationship between the STS machining parameters and the achieved surface finish and profile accuracy of freeform optics.