superfinishing

Superfinishing, also known as microfinishing and short-stroke honing, is a metalworking process that improves surface finish and workpiece geometry. This is achieved by removing just the thin amorphous surface layer of fragmented or smeared metal left by the last process with an abrasive stone or tape; this layer is usually about 1 μm in magnitude.

==Process== After a metal piece is ground to an initial finish, it is superfinished with a finer-grit abrasive stone. The stone is oscillated or rotated while the workpiece is moved in such a way that each bonded grain of abrasive follows an effectively random path with variations in speed, direction, and pressure. This multi-motion is a key feature of superfinishing because it prevents the sort of smeared finish that results from a built-up edge. In this way, superfinishing is similar to lapping, but with a bonded-abrasive stone rather than loose or embedded abrasive. The geometry of the abrasive depends on the geometry of the workpiece surface; a stone (rectangular shape) is for cylindrical surfaces, and cups and wheels are used for flat and spherical surfaces. A lubricant is used to minimize heat production, which can alter the metallurgical properties, and to carry away the swarf; kerosene is a common lubricant.