Combined effect of cylindricity, roundness and roughness on axial load-carrying ability of interference fits

Abstract

Interference fits are commonly used in engineering for various applications. While the effect of many factors on the load-carrying ability of interference fits has been studied extensively, the combined effect of cylindricity, roundness and roughness does not appear to have been considered to that extent, and this paper is an attempt to remedy the situation. As a first step, finite element method was used to verify that there will be a reduction in the load-carrying ability due to the introduction of perfect geometrical deviations on the shaft. Thereafter, a detailed experimental investigation was carried out to study the effect of cylindricity and their joint effect with various other factors on the axial load-carrying ability of shaft–bearing interference fitted assemblies. A number of shafts of C40 steel of nominal diameter 20 mm were manufactured with varying cylindricity values and selectively assembled with standard deep grove ball bearings, thereby achieving interference fits with a grade of H7/u6 between them. The assembled specimens were tested on a Universal Testing Machine with a specially made fixture and the maximum extraction load determined. The effect of the various factors on the extraction load was examined using statistical methods. It was found that shaft cylindricity error did reduce the load-carrying ability of interference fits. The combination of interference, cylindricity and surface roughness was found to give the best prediction for extraction load. Certain other parameters were also examined, but they were not found significant.