An investigation of the surface waviness features of ground surface in parallel grinding process

The high precision tungsten carbide (WC) and silicon carbide (SiC) optical mold inserts used in glass molding are usually machined by ultra-precision grinding, but the residual surface waviness error is difficult to be eliminated. This paper mainly focused on the surface waviness features related to the grinding wheel run-out error and the non-integer rotation-speed-ratio (RSR) in parallel grinding process. After the integrate consideration of grinding kinematics and microscopic material removal, the generation mechanism and distribution trend of surface waviness features were revealed. In order to simulate the surface waviness topography of parallel ground components, a mathematical model was developed and experimentally proved, which was appropriate for both integer and non-integer RSR. Besides, the mechanism of surface waviness reduction was explained when RSR was non-integer, which was due to the material removal again by the secondary grinding zone of grinding wheels. Then prediction models for the surface-waviness-period-feature (SWPF) and surface-waviness-amplitude-feature (SWAF) was built and experimentally verified, which was based on the waviness profiles overlapping effect. It found that the wave-shift resulted from the non-integer RSR had significant influence upon the surface waviness features. In the end, a convenient method was proposed to reduce the surface waviness error of parallel ground components through proper adjustment of grinding wheel rotation speed to achieve proper non-integer RSR and wave-shift, which was proved practically feasible and effective for both plane components and Fresnel components.