Strain Path Analysis of an Axisymmetric Part Within a Controlled Forming Process

Abstract

Many researchers have attempted to design a controlled sheet metal forming process to achieve a desired product shape without defects. An optimal blank holder force (BHF) profile is an efficient way to control the material flow during the forming process. The study in this paper tried to find an optimal BHF profile for an axisymmetric part using the finite element method. Up to now, the two main methods used vary the BHF as a function of time or space. Thus, time-variant and space-variant BHF profiles, which are imposed on the integrated and the divided blank holder respectively, were studied and compared in this paper. Two time-variant BHF patterns, such as linearly shaped and stepped ones, and various trends, such as ascending and descending, are discussed. The paper also examines six space-variant BHF patterns. Based on the numerical simulation results, the strain path in different areas under the various BHF schemes was analysed and compared. The results revealed that the ascending BHF type is the optimal pattern used to prevent wrinkling and optimize the strain distribution during the forming process as compared to the descending BHF type. In terms of energy opinion, it is found that the ascending BHF is the most effective way to prevent wrinkling and achieve a desired product shape. Taking another aspect, the preferable space-variant BHF pattern is the type where less force is imposed on the corner area than on the straight flange area. This is confirmed by a the comparison of strain paths under six space-variant BHF patterns.