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【正文】 uch process successfully avoided the difficulty of forming two geometric features simultaneously, but increased the material flow of the blank sheet. The next step was to trim the blank outside the sidewalls, and to calibrate the corner radius of 4 mm to the desired value of mm. The hinge was thus formed, as shown in Fig. 5(b). The third step was to fold the open side, so that the sidewall could be pleted around its periphery, as shown in Fig. 5(c). The effect of trimming the extra sheet outside the sidewalls in the second step on the third step was studied. 12 When the extra sheet was not trimmed, the thickness at the corner was mm, as shown in Fig. 5(d). The thickness of the corner increased to mm, as shown in Fig. 5(e), if the trimming was implemented in the second step. The excessive material produced by the folding process in the third step was then trimmed off according to the parts design. The last step was the striking process that is applied to calibrate all the corner radii to the designed values. The minimum thickness at the corner of the final product was mm, and all the strains were above the forming limit diagram. It is to be noted that Fig. 5(a–c) only shows the formation of one hinge. The same design concept was then extended to the stamping process of the plete top cover case. Fig. 5. Fouroperation stamping process. (a) First operation, (b) second operation, (c) third operation, (d) without trimming and (e) with trimming. View thumbnail images 5. Experimental validation In order to validate the finite element analysis, an actual fouroperation stamping process was conducted with the use of mm thick LZ91 sheet as the blank. The blank dimension and the tooling geometries were designed according to the finite element simulation results. A sound product without fracture and wrinkle was then manufactured, as shown in Fig. 6(a). To further validate the finite element analysis quantitatively, the thickness at the corners around the hinge of the sound product, as shown in Fig. 6(b), were measured and pared with those obtained from the finite element simulations, as listed in Table 1. It is seen in Table 1 that the experimental data and the finite element results were consistent. The fouroperation process design based on the finite element analysis was then confirmed by the experimental data. 13 Fig. 6. The sound product. (a) Without fracture and wrinkle and (b) locations of thickness measured. View thumbnail images Table 1. Comparison of thickness measured A B C D Experiment mm mm mm mm Simulation mm mm mm mm Error % % % % 6. Concluding remarks The press forming of magnesium alloy sheets was studied in the present study using the experimental approach and the finite element analysis. The formability of both AZ31 and LZ sheets was examined first. The research results indicated that the LZ91 sheet has favorable formability at room temperature, which is similar to that of AZ31 sheet at the forming temperature of 200 176。C are close to each other. LZ101 sheet at room temperature exhibits even better ductility than LZ91 and AZ31 do at 200 176。 ? Formability 1. Introduction Due to its lightweight and good performance in EMI resistance, magnesium alloy has been widely used for structural ponents in the electronics industry, such as cellular phones and notebook cases. Although the prevailing manufacturing process of magnesium alloy products has been die casting, the stamping of magnesium alloy sheet has drawn interests from industry because of its petitive productivity and performance in the effective production of thinwalled structural ponents. As for stamping process, AZ31 magnesium alloy (aluminum 3%, zinc 1%) sheet has been monly used for the forming process at the present time, even though it needs to be formed at elevated temperature due to its hexagonal closedpacked (HCP) crystal structu
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