What Is Lapping?
Lapping is a precision polishing method often employed for workpieces requiring high accuracy. This process involves rubbing abrasive grains (lapping agent) between a flat base (lap) and the workpiece. This action eliminates surface irregularities through abrasion, achieving a highly smooth finish.
While less efficient than grinding, lapping excels in delivering extremely smooth surfaces with high dimensional accuracy, making it ideal for the final finishing of workpieces.
Typically performed with specialized lapping machines, lapping can also be done by hand for intricate adjustments of shapes and dimensions not easily achieved with machines. Hand lapping, however, demands significant skill.
Uses of Lapping
Lapping is crucial in the finishing stages of products and parts where precise machining accuracy is paramount.
Effective in achieving high dimensional precision and mirror-smooth finishes, lapping reduces frictional resistance, enhancing the performance of mating and sliding parts. Consequently, it finds extensive use in precision components such as optical parts, gauges, and bearings. It is also integral in manufacturing semiconductor wafers, where smooth, parallel surfaces are essential.
Principles of Lapping
In hand lapping, for instance, a workpiece is pressed against a moving flat base (lap) with abrasive grains (lapping agent) in between. This movement causes the abrasive grains to grind away the workpiece surface gradually, resulting in a uniformly smooth and undistorted surface.
Machine lapping varies in its configuration, with changes in the shape and number of laps, driving methods, and types of lapping agents, depending on the workpiece’s material, shape, and processing requirements.
Lapping is categorized into wet and dry processes, based on the lapping agent used. Wet lapping employs a slurry of abrasive grains in a fluid, leading to a large-scale, non-directional finish. Dry lapping, in contrast, semi-fixes the abrasive grains on the lap, creating a sliding, scratching action that produces a more mirror-like finish with less work involved.