Some abrasive processes use abrasive material applied to the workpiece at low surface speeds. One type uses free abrasive grains flowing in a slurry on a hardened steel plate (Figure L-30) to generate a flat surface on the workpiece. This type is capable of comparatively large amounts of stock removal, but not highly refined finishes, because the abrasive grain tumbles along the hardened steel plate as it cuts the workpiece material.
Figure L-30 Free abrasive grinding machine has a hard, water-cooled plate on which the abrasive is fed in a slurry. The abrasive grains do not become embedded, as they do in lapping.
Hence, the grains always roll around under the workpieces.Figure L-31 Single-sided lapping machine. The pressure plates on top hold down parts to be lapped by abrasive embedded in the lapping plate beneath (Courtesy of Peter Wolters of America, Inc.).
A similar machine that works on a different principle is the lapping machine (Figure L-31). Here abrasive grains are embedded into a relatively soft lapping plate. Because there is only a single layer of abrasive, small amounts of material are removed in lapping, but extremely flat and highly finished surfaces can be produce by this method.
The measuring surface of a gage block is an example of a finely lapped surface.
Parts such as engine cylinders may be finish machined by the honing process. The honing machine can be used for both internal and external parts.
Superfinishing is another slow-speed abrasive process.
Abrasive carried on a continuous film is held against the workpiece (Figure L-32) and reciprocated a small amount while the workpiece is turning. The result is a highly finished accurate surface. Superfinishing typically removes less than .0005 in. from the surface, usually sufficient to remove residual metallurgical disturbance that can result from grinding.
Sharp edges left from almost all machining processes can be removed by vibratory deburring (Figure L-33). The abrasive materials are in pellet form. Differing sizes and shapes of deburring media are used to match part configurations.
Parts, fluid, and abrasive media are vibrated together to remove burrs. This process can also be used to remove internal burrs that would be difficult or impossible to reach from the outside.