Study on geometrical patterns of textured fixed-abrasive pads in sapphire lapping based on trajectory analysis

Abstract

Geometrical patterns of textured fixed-abrasive pads (T-FAPs) play a key role during the lapping or polishing process, which not only affect the fluid liquidity but also affect the global distribution of fixed abrasives located at the pad surface. However, the T-FAP performance caused by the changed abrasive distribution was seldom revealed and evaluated. As the trajectory distribution on the workpiece surface is mainly determined by the abrasive distribution and machining parameters, the present work intended to evaluate trajectories induced by the different geometrical patterns of T-FAPs and their influences on the lapping process. For this purpose, a test method consisting of T-FAP digital modelling and kinematic analysis was demonstrated. A digital modelling method of T-FAPs was proposed to build T-FAPs containing information of testing abrasives distributed on the pad geometrical surface, and the kinematic analysis was used to obtain trajectories on the workpiece surface. Based on the method, the trajectory profiles and their non-uniformity induced by the specific T-FAP and the non-textured fixed-abrasive pad (NT-TAP) were studied. Validation experiments were carried out in lapping of sapphire slices, using 90 min of lapping time and the distilled water as lubricant. The surface profile, total thickness variation, surface roughness and material removal due to the lapping were measured. The results show that better lapping performance can be reflected by the lower non-uniformity of trajectory (NUT) induced by the geometrical patterns of T-FAPs. The values of NUT influenced by the different T-FAPs were found to be either minimized or maximized according to the specific geometrical patterns on the T-FAP surface, and the maximum value could be up to 0.3 while the minimum value is less than 0.1.