Lapping is a mainly room-bound process with geometrically undefined cutting edges. It is defined as a cutting process with loose grits distributed in a fluid or paste, so called lapping slurry, guided by a counterpart, which is usually shape-transferring (also called lapping tool). The cutting paths of the individual grits are ideally undirected [KLOC09, p. 338]. Effective mechanisms are complex and assumed to be a superposition of chip formation, micro-grooving, and brittle machining by micro-cracks and particle break-out [KLOC05a, p. 384 f.].
Known process variants are planar lapping with fixed or freely moving workpieces, external or internal cylindrical lapping, profile lapping and ultrasonic lapping amongst others. Karpuschewski [KARP01, p. 173 ff.] summarizes sensors for lapping operations.
Common abrasives for lapping processes include silicon carbide, corundum, boron carbide (B4C), and diamond [KLOC05a, p. 394, STAD62, p. 24]. Boron nitride (B4N) is used for lapping of carbides [MARI04, p. 394]. Regular grit dimensions are as follows [MARI04, p. 442]:
• Silicon carbide and corundum: 5-1 ^
• Boron carbide: 60-5 цm
• Diamond: 5-0.5 ^
• Chromium oxide: 2-1 ^
Diamond slurrys are designed so that even coarse grits remain homogeneously dispersed in the fluid. The abrasives will not settle out, even if the slurry binder has a low viscosity [KLOC05a, p. 393]. Conventional abrasives are continually fed onto the lapping plate to restore broken down particles. Recharge of diamond grits occurs less frequently [DAVI74].