A Study of Optimized Tool Path for Uniform Scallop-height in Ultra-precision Grinding of Freeform Surfaces

Freeform surfaces have been widely used in complex optical devices to improve the functional performance of imaging and illumination quality and reduce sizes. Ultra-precision grinding is a kind of ultra-precision machining technology for fabricating freeform surfaces with high form accuracy and good surface finish. However, the complexity and variation of curvature of the freeform surface impose a lot of challenges to make the process to be more predictable. Tool path as a critical factor directly determines the form error and surface quality in ultra-precision grinding of freeform surfaces. To study the influence of wheel path and path parameters on the surface generation in ultra-precision grinding of freeform surfaces, a freeform mold is designed and two kinds of tool planning strategies are used to fabricate the freeform surfaces in this paper. They include constant angle and constant arc-length methods and the form errors and surface scallop-height are analyzed. Moreover, a theoretical surface generation model is developed to study the influence of grinding parameters and the radius of curvature of the freeform surface profile on the ground surface. An iterative closest point (ICP) matching method is adopted to determine the surface error between the measured surface and the designed surface. Hence, an optimized tool path generator is built to realize both the uniform scallop-height and good surface finish on the freeform surfaces.