Modeling Techniques in Forming Processes

THE OBJECTIVE OF MANUFACTURING is the production of a consistent quality product at a minimal cost. Generally effective goals include shortening the lead time in the design cycle, reducing tooling cost and machine downtime at the production stage, and developing a stable process with a minimal reject rate. The ability to predict the performance of a particular manufacturing process and to compare it with alternative manufacturing processes at an early stage in the process design cycle furthers these goals by reducing costly trial-and-error design iterations using production equipment. Numerous analytical techniques have been developed to improve the process designer’s ability to evaluate a process and to predict various aspects of the metal forming process. Early methods relied on simple analytical techniques, such as the slab method, the slip-line method, the upper bound method, and heuristics to predict forming load, critical ratios, workability limits, and die design features. Complex analytical equations were converted to charts, which could be applied by the designer. As computer technology became prevalent in the engineering and manufacturing industry, analytical techniques, such as the upper bound method, were used to develop specialized computer programs, which could be used to analyze a particular process, such as tube sinking, strip rolling, or extrusion. The finite element method (FEM) for metal forming applications was first introduced in early 1970 (Ref 1). The continuous improvements in computer technology and FEM finally made an important impact in the metal forming industry in the mid-1980s. Due to its unique capability in describing complex shapes, boundary conditions, and realistic material thermomechanical response, the development of a general-purpose metal forming analysis software has been realized. The method has been used as an essential tool for product and process design engineers to reduce development time and cost. Due to the demand from the industry to produce more accurate simulation models, the FEM has continuously evolved from two-dimensional analysis into the true three-dimensional models since the late 1980s and early 1990s (Ref 2–4). This chapter reviews the overall development of modeling techniques for forming processes, including: