Surface finish of precision machined advanced materials

This paper studies the surface finish and integrity of glass, silicon, some advanced ceramics and aluminum-based metal matrix composites (MMCs) reinforced with ceramic particles, precision machined by various machining processes. The studies revealed that grinding/lapping operations using inexpensive machine tools can produce ductile streaks on glass and silicon surfaces under good grinding/lapping conditions. This resulted in significantly shortened polishing time to secure an acceptable surface finish. If there are several processes to manufacture a lens, each preceding process is very important for the successive processes. In order to reduce the total manufacturing time, it is preferable to obtain better ground/lapped surfaces with as many ductile streaks as possible in order to reduce the polishing time. Toroidal SiC surfaces ground with flat-face cup wheels indicated 100% ductile machining, and did not require polishing. Ground ZrO2 showed a numerous ductile streaks. Plastic deformation was the major mechanism of material removal at high wheel speeds. Grinding of aluminum-based MMCs reinforced with Al2O3 or SiC particles using a 3000 grit diamond wheel at depths of grinding of 1 and 0.5 mm produced many ductile streaks on the Al2O3 and SiC particles, respectively. There was almost no sub-surface damage. The machines used for the experiments reported in this paper are not expensive ultra-precision machines. # 2002 Elsevier Science B.V. All rights reserved.