【正文】 t simulations were performed to study the parameters that affect the occurrence of fracture. Several approaches were proposed to avoid the fracture as well. 4. Multioperation stamping process design In order to avoid the occurrence of fracture, a multioperation stamping process is required. In the current industrial practice, it usually takes at least ten operational procedures to form the top cover case using the magnesium alloy sheet. In the present study, attempts were made to reduce the number of operational procedures. Several approaches were proposed to avoid the fracture, and the fouroperation stamping process had demonstrated itself as a feasible solution to the fracture problem. To limit the length of this paper, only the twooperation and the fouroperation stamping processes were depicted in the following. . Twooperation stamping process The first operation in the twooperation stamping process was sidewall forming as shown in Fig. 4(a), and the second one was the forming of flange of hinge presented in Fig. 4(b), the height of the flange of hinge being 5 mm. Fig. 4(c) shows the thickness distribution obtained from the finite element simulation. The minimum thickness of the deformed sheet was mm and the strains were all above the forming limit diagram. It means the fracture defect could be avoided. In addition, the height of the flange conformed to the target goal to be achieved. However, this process produced a critical defect of 11 wrinkling, as shown in Fig. 4(d), on the flange of hinge, which induces a problem in the subsequent trimming operation. Hence, even though the twooperation stamping process solved the fracture problem at the corner of the bottom and the flange of hinge, a better forming process is still expected to solve the wrinkling of flange of hinge. Fig. 4. Twooperation stamping process. (a) Formation of sidewalls, (b) formation of hinges, (c) thickness distribution and (d) wrinkle. View thumbnail images . Fouroperation stamping process The fouroperation forming process proposed in the present study starts with the forming of three sidewalls and the flange of the hinge with a generous corner radius, as shown in Fig. 5(a). Since the sidewall close to the flange was open and the corner radius was larger than the desired ones, the flange was successfully formed without fracture. Such 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 validat