Contact Mechanics of Superfinishing

Abstract

Superfinishing is an abrasive finishing process in which a smooth work surface is produced by simultaneously loading a bonded abrasive stone against a rotating workpiece surface and oscillating (reciprocating) the stone. The surface topography of a 600 grit aluminum oxide stone used for superfinishing is quantitatively described using scanning phase-shift interferometry. A bounded three-parameter lognormal distribution is found to provide a more accurate representation of cutting edge height distribution than a bounded normal distribution, especially in fitting the upper tail end of data. Moreover, the stone surface characteristics are nearly constant throughout stone life suggesting that superfinishing is a self-dressing process. This stone surface geometry is used to develop a contact mechanics model of the superfinishing process. The model estimates the number of cutting edges involved in material removal, the load distribution on these edges, and the resulting surface roughness of the superfinished surface. The effect of contact pressure on these estimated values has been studied. Only a very small percentage (less than 0.16 percent) of the cutting edges, which are comprised of the large cutting edges occurring in the tail end of distribution, are actively engaged in material removal. Further, the arithmetic average surface roughness, Ra, is found to be related to the average depth of penetration while the peak-to-valley surface roughness, Rt or Rtm, is related to the maximum depth of penetration. The prediction of surface roughness made with this model is found to agree reasonbly well with experimental results for superfinishing of hardened steel surfaces. [S0742-4787(00)00302-7]