Stress analysis of a ballised hole

Ballising is a micro-finishing process where an oversized ball is forced through an undersized hole resulting in superior roundness, refined surface quality and increased dimensional precision of the hole. In addition, the internal pressure exerted on the wall of the hole, due to the interference between the diameter of the hole and that of the ball, renders a plastically deformed region from the bore to a radius that forms the elastic-plastic boundary. Beyond the elastic-plastic boundary, only elastic deformation occurs as the material recovers upon the exit of the ball. Stress analysis using the theory of plasticity and von Mises yield criterion predicts a resultant compressive stress state surrounding a ballised hole. The resultant stress state is a function of the radius of the elastic-plastic boundary which in turn is a function of the interference. Experimental investigation with varying interferences into the resultant stress state of a ballised hole in a medium carbon steel concurs with the theoretical predictions.