Influence of Surface Roughness on Press Fits

Abstract

A press fit, also known as interference fit or friction fit, is a form of fastening between two tight fitting mating parts (usually two bodies with cylinder or conical surfaces) that produces a joint which is held together by friction after the parts are pushed together. I discuss the influence of surface roughness on the design of press fits. This topic has been addressed in the engineering community but only on an empirical level without a scientific backup. Here, I will apply the Persson contact mechanics theory to show how to include the surface roughness in the design criteria. I argue that one should use what I denote as the cylinder “stylus width” rather than the “caliper width” when determining the influence of the surface roughness of the compression (also denoted as the interference). In the classical approach using the caliper width, the compression is assumed to be independent of the elastic properties of the solids, but in the more accurate approach presented here using the stylus width the compression depends on the elastic properties and on the surface roughness power spectra of the involved solids. A detailed discussion of the relation between the root-mean-square roughness amplitude h_{mathrm{rms}} and the maximum asperity height h_{mathrm{max}}, of interest in its own right, is also presented as it is needed for determining the relation between the stylus and caliper derived compression’s.Graphical