Application of a rigid—plastic finite-element method to some metalforming operations

Abstract

In massive metalforming processes, a billet of a simple cross-sectional geometry—such as round or round-cornered square—is formed usually in several operations to produce a part with more complex geometry than that of the initial billet. In today's practice, the design and optimization of each forming operation is accomplished using empirical knowledge and extensive experience. Thus, considerable amounts of trial and error are necessary to set up a reliable and reproducible forming process. It is therefore one of the major goals of metalforming research and development to reduce this necessary trial and error procedure by mathematical analysis and simulating of metalforming operations. Among various methods available for analyzing practical plastic flow problems, the rigid—plastic finite-element method appears to be the most promising technique. Recently, a user-oriented computer program called ALPID (Analysis of Large Plastic Incremental Deformation) has been developed for analyzing and simulating axisymmetric metalforming operations. ALPID is based on a general method of analysis which uses high-order elements and combines the features of the upper-bound and the conventional finite-element methods. This analysis is valid for both rigid—plastic and rigid—viscoplastic materials and can handle both constant-friction shear stress or Coulomb-type friction at the tool—material interface. At this time, ALPID is being further developed for application to forming operations with complex die shapes and metal flow conditions. The present capabilities of ALPID have been evaluated by predicting metal flow, stresses and forming load in three basic deformation processes: cylinder upsetting, ring compression and spike forging. In cylinder upsetting, the present method with one quadratic element predicted the metal flow as well as it could be predicted with the conventional FEM using 88 linear elements. Metal flow predictions in ring compression and spike forging also showed good agreements with preliminary experimental results.