Why Parallelism of Workpieces Becomes Convergent During Double-Sided Lapping?

Abstract

Double-sided lapping (DSL) is always employed as a precision process for machining flat workpieces, such as optical windows, wafers, and brake pads taking advantage of its high efficiency and parallelism. However, the mechanism of parallelism error reduced by the DSL process was rarely investigated. Furthermore, the relationship between parallelism and flatness was not clearly illustrated. To explain why the parallelism of workpieces becomes convergent by the DSL, a theoretical model has been developed in this paper by calculating the parallelism evolution with the consideration of various contact situations between workpieces and lapping plates for the first time. Moreover, five workpieces, including a slanted and four parallel ones, are applied to develop the parallelism evolution guaranteeing the model close to the actual process, and the mechanism of the parallelism error reduced by the DSL process is elucidated. The calculation result revealed that the parallelism was improved from 100.0 µm to 25.6 µm according to the proposed model. The experimental results showed that the parallelism error reduced from 108.6 µm to 28.2 µm, which was consistent with the calculation results.