Surface generation in high-speed grinding of brittle and tough ceramics

Grinding induced sub-surface defects substantially impair the functionality of ceramic components. Effective control of such defects is possible through identification and understanding the governing factors. The present work investigates the interaction of abrasive grits over the ground surface to identify the governing factors for effective control of such defects during high-speed grinding of a brittle (alumina) and a tough (yttria-stabilized zirconia (YSZ)) ceramic. High-speed grinding was carried out using single-layer electroplated diamond grinding wheels in the speed range of 40-200 m/s. The important grinding characteristics, such as material removal mode, residual stress, surface roughness, etc., were correlated with the maximum uncut chip thickness (h(m)) and the scallop height (S-g). The h(m) represents the interaction of active grits at the exit of the grinding zone, whereas the interaction of active grits while entering the grinding zone (at ground surface) leads to the formation of scallops. Instead of hm, material removal mode and other related grinding characteristics are found to be governed by the S-g. An efficient reduction of approximately 90 % in S-g is realized by increasing the grinding speed from 40 m/s to 200 m/s. For a brittle ceramic like alumina, such a drastic reduction in S-g reduced grinding induced defects by more than 75 %. For a tougher ceramic like YSZ, a reduction of more than 30 % in the magnitude of compressive residual stress is observed with a reduction in S-g at a higher grinding speed of 200 m/s. This study manifests S-g as a predominant factor in governing the ground surface characteristics during ceramic grinding, which can be effectively utilized to control grinding induced defects in ground ceramic parts.