Optimal preform design for the free forging of 3D shapes by the sensitivity method

The sensitivity method, which is successfully applied to optimal blank design for sheet metal stampings, has been applied to find optimal preform shape that gives a desired shape after free forging. Starting from a predetermined target shape, the corresponding preform shape which transforms into the desired shape after free forging has been found. With the aid of a well-known forging analysis code Deform-3D(R), deformation sensitivity has been obtained numerically from a pair of deformation process analyses with an original workpiece and an offset workpiece. In order to verify this method, preforms which do not show barreling at the free surface have been found for circular cylinder, elliptic cylinder, clover shaped cylinder, rectangular right prism and stepped rectangular prism. For every case, the optimal preform shapes have been obtained after only a few modifications without any predetermined deformation path and excellent agreements are obtained between final shape from the predicted preform and the desired shape. Through this investigation, the sensitivity method is found to be an excellent method to find optimal perform shape for the free forgings of arbitrary 3D shapes. (C) 2002 Elsevier Science B.V. All rights reserved.