Residual Stresses in Cold-Formed Workpieces

Abstract

Every workpiece contains residual stresses which can affect its performance in service. Especially metal-forming processes leave high residual stresses in the workpiece because of the inherent nonuniform plastic deformation pattern. The knowledge of the magnitudes of these stresses in such workpieces is of prime importance for the industry in order to evaluate their influences and particularly to optimize the manufacturing process with regard to a convenient residual stress state. For this purpose, in this study several cold metal-forming processes have been analysed regarding the residual stresses left in the products, such as rod extrusion, containerless extrusion, tube extrusion and upsetting. The trend to evaluate convenient process parameters for a manufacturing process optimization amounts to numerical process simulations, because they become more and more economic compared to protracted experimental methods. Hence, this analysis has been basically conducted with the Finite-Element-Method. For the rod extrusion case also an experimental study has been performed in order to compare measurements with computations. The agreement is satisfactorily. As a result of the analysis, two ways of manipulating the residual stresses in extrusion-processes turn out to be as: Varying the cone-angle and/or varying the die-stiffness.