The Control of Buildup and Diametral Growth in Shear Forming

Abstract

The two major problems in shear forming cylindrical blanks are buildup of metal ahead of the tool ring and diametral growth of the part. The process variables (feed per revolution, reduction, tool ring contour) beneficial to diametral fit unfortunately enhance buildup and vice versa; the introduction of a fourth variable, roll tilt, has been found to reduce the severity of both problems, as well as frictional drag and residual stress in the part wall. The mechanisms of axial and circumferential growth are proposed, being mainly an analogy with wedge indentation. The elastic-plastic boundary about the point of contact is calculated, as is the instantaneous velocity of extrusion. The variation of buildup with feed and reduction is shown for annealed 1100 and 7075 aluminum blanks. The effect of tool ring contour on the growth of AMS 6323 and B120 VCA parts was investigated. It was found that a sharp tool ring could cause a significant reduction of diameter and that the deep feed lines could be safely eliminated by a gradual relief at the back side of the tool ring.