The properties of a repeatedly ballised hole surface

Abstract

Ballising is a hole sizing and finishing method by cold-working. The process, normally carried out once or twice to improve surface finish, roundness and dimensional tolerance, involves forcing a precision-ground tungsten-carbide ball through a slightly undersized premachined hole. In the present study, the properties of repeatedly ballised holes are investigated. The surface finish of the ballised holes was found to have improved by as much as 97% after three passes of the ballising process. An average roughness value of 0.04 to 0.05 μm Ra was achievable after six passes. As almost all the improvement is accomplished during the first pass, properties such as the diametric change, the surface hardness, the roundness and the fatigue performance of the hole remain approximately constant after the first pass. © 1993.