Papers by Author: H.J. Choi

Abstract: This paper is concerned with the analysis of the forming load characteristics of a forward-backward can extrusion in both combined and sequence operation. A commercially available finite element program, which is coded in the rigid-plastic finite element method, has been employed to investigate the forming load characteristics. AA 2024 aluminum alloy is selected as a model material. The analysis in the present study is extended to the selection of press frame capacity for producing efficiently final product at low cost. The possible extrusion processes to shape a forward-backward can component with different outer diameters are categorized to estimate quantitatively the force requirement for forming forward-backward can part, forming energy, and maximum pressure exerted on the die-material interfaces, respectively. The categorized processes are composed of combined and/or some basic extrusion processes such as sequence operation. Based on the simulation results about forming load characteristics, the frame capacity of a mechanical press of crank-drive type suitable for a selected process could be determined along with securing the load capacity and with considering productivity. In addition, it is suggested that different load capacities be selected for different dimensions of a part such as wall thickness in forward direction and etc. It is concluded quantitatively from the simulation results that the combined operation is superior to sequence operation in terms of relatively low forming load and thus it leads to low cost for forming equipments. However, it is also known from the simulation results that the precise control of dimensional accuracy is not so easy in combined operation. The results in this paper could be a good reference for analysis of forming process for complex parts and selection of proper frame capacity of a mechanical press to achieve low production cost and thus high productivity.

Abstract: In this paper, the forming process of a central hub by radial-forward extrusion has been analyzed by the rigid-plastic finite element method. In this process, the material flows in radial direction and then deflects 90 degrees into the same direction as that of punch movement. Radial extrusion is used to produce parts that generally feature a central hub with radial protrusions. Design factors such as mandrel diameter, punch nose radius, deflection corner radius, gap width in annular direction, and frictional conditions are applied to the present study by simulation. AA 6063 aluminum alloy is selected as a model material for analysis in the present study. The influence of these design factors on the force requirement during the forming operation and the pressure exerted on the tooling such as the punch and mandrel is investigated and the simulation results are quantitatively summarized in terms of pressure distribution, force-stroke relationships, and maximum force requirement, respectively. The main goal of this study is to investigate the effect of those process parameters on the deformation pattern in radial-forward extrusion process, especially the effect of deflection corner radius. It has been concluded from the simulation results that a) the frictional condition between workpiece and tool does not affect the punch load very much, but the load supported by mandrel is more or less significantly influenced by the frictional condition compared to that of punch, b) the deflection corner radius turns out to be a major process parameter in terms of maximum force requirement, and c) a similar trend is found in the punch and mandrel forces during the radial extrusion process.