Observations in the flat lapping of stainless steel and bronze

Lapping is a finishing process, in which material removal takes place due to relative motion between the workpiece, loose abrasive grains, and the lapping plate. This process is used in achieving finer surfaces and closer fits, correction of minor imperfections, and maintaining close tolerances. Although a significant underlying science-base exists with regards to the physics, mechanics, dynamics, and thermal effects, lapping has been considered an art, rather than a science. Exploring lapping at a fundamental level will help improve its application. This study discusses the effects of using various abrasive materials on surface topography via flat lapping. Stainless steel and bronze specimens were lapped using a set of different abrasives. Topography of the surfaces generated by lapping is investigated using a scanning electron microscope. The surface generated as a result of abrasive particles has been characterized based on concepts in tribology. The goal of this research was to quantify the influence of abrasives material properties in flat lapping with an application in reconditioning valve seats. The lapping process using different abrasives as applied in this study showed no significant material removal rates. However, the surface roughness and the surface topography are seen to be readily affected by the use of different abrasives. The results on MRR obtained by lapping stainless steel and bronze with garnet, alundum, and crystolon indicate that, even though crystolon is harder than alundum, alundum abrasive was more efficient in removing material than crystolon. In general, the surface finish and flatness was observed to improve with the hardness of the abrasive grit.