Due to its lightweight and good performance in EMI resistance, magnesium alloy has been widely used in the electronics industry, mainly for thin-walled structural components, such as cell phone and notebook cases. Although the principal manufacturing process has been die casting, the stamping of magnesium alloy sheets has considerable potential because of its competitive productivity and performance. In addition to die design, the major difficulty in stamping a magnesium alloy sheet is its poor formability at room temperature due to inherent hexagonal closed-packed (HCP) crystal structure, in which only the basal planes can move [1]. In the present study, the stamping process for manufacturing cell phone cases with magnesium alloy AZ31 sheets was studied using both the experimental approach and the finite element analysis. In order to determine the proper forming temperature and set up a fracture criterion, tensile tests and forming limit tests were first conducted to obtain the mechanical behaviors of AZ31 sheets at various elevated temperatures. The mechanical properties of Z31 sheets obtained form the experiments were then adopted in the finite element analysis to investigate the effects of the process parameters on the formability of the stamping process of cell phone cases [2]. An initial die design and selected preliminary process parameters were used in the finite element analysis as a pilot run. In the finite element analysis, both wrinkle and fracture were appeared in the products manufactured with the initial die design at an elevated forming temperature. The fracture defect was easily removed by increasing the forming temperature and the punch corner radius. However, the wrinkle defect was difficult to cope with. The effect of blank-holder force on the elimination of wrinkle was first investigated, followed by an intention of determination of an optimum blank shape. The finite element simulation results revealed that the wrinkle defect could not be eliminated completely by the above methods. A drawbead design was then performed using the finite element simulations to determine the size and the location of drawbead required to suppress the wrinkle defect. An optimum stamping process, including die geometry, forming temperature, and friction condition, was then determined for manufacturing cell phone cases.In order to validate the finite element simulation results, an actual stamping process for producing cell phone cases was performed. Two sets of tooling, made of SKD11 steel, were machined to the profiles according to the finite element simulation results. The AZ31 sheets were then stamped into the shapes of cell phone cases with the process parameters determined above. The sound products validated the finite element analysis of the stamping process design for magnesium alloy AZ31 sheets.
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