Preform Design for Flash-Less Die Forging

The use of accurate preform dies and billets in forging can improve quality, conserve material, reduce manufacturing costs, and eliminate rehabilitative processes. This paper presents a Finite Element (FE) simulation-based preform die design method that might require a few iterations to find an optimal preform shape. The preforms are iteratively searched by backward tracing of material points in the FE models. The proposed scheme for establishing preform geometries for flash-less forging exploits the ability of FE software packages to track material points at any given process time and location. In this methodology, “flash” is considered a defect—one that can easily be induced by using a slightly larger volume of a preform shape than the exact volume that results is flash-less forging. Since the materials under plastic deformation seek the path of least resistance, other defects are bound to occur. Several case studies on preform designs of 3D forgings are presented. The viability of the methodology is assessed based on strain distribution patterns and forging loads. The methodology was also used on a few example parts which are currently forged with flash. The preform designs with this methodology resulted in a substantial reduction in the flash. Besides aiding in the development of new progression sequences for flash-less die forging, the method could be used to modify preforms in a production line to minimize material waste due to flash. The method can also be used to probe preform shapes that occasionally result in defects caused by variability emanating from interface friction, die temperature fluctuation or other factors.