Machining Stability Research of Soft-Brittle Crystals Lapping by Fixed-Abrasive Pad

Abstract

Fixed-abrasive (FA) lapping and polishing process is the main approach to realize the residual-free and low damage processing of soft-brittle crystals. The hardness of matrix and the abrasive micro-fragmentation are the key parameters impacting the stability of the continuous batch machining. The FA pads were prepared with hard and soft matrix, respectively, and the single diamond (SD) and the aggregated diamond (AD) were mixed in the FA pads, respectively. The FA lapping tests were carried out with LN wafers under the applied load of 10.5 kPa. The continuous batch machining stability of four pads tests were evaluated by the evaluation indexes of the material removal rate (MRR), surface roughness Ra and the material removal rate variation (MRRV). The workpiece surface morphology and abrasive wear pattern were analyzed. The results indicate that: hard matrix is not conducive to the shedding and replacement of abrasive grains because of the high holding force, causing a MRRV of 50%. The MRR of the hard matrix pad tests signally decrease from 3.71 μm/min to 1.9 μm/min. By contrast, the low hardness matrix pad can be applied to improve the machining efficiency owing to its MRRV only about 30%. The MRR of the AD pad is over 600 nm/min, which is far more than that of the SD pad, and the MRRV of the AD pad is just about 20%. While MRRV of the SD pad is as high as 75% with the remarkably decline of MRR. At the view of Ra values, the SD pad and the AD pad both attain nanoscale. The Ra values of the SD pad tests are smaller and the workpiece are superior in surface quality. In the rough lapping and fine lapping stage, the SD can be used to prepare FA pad to improve lapping stability.