فهرست مطالب s.j. hosseinipour

In this paper, to fabricate a pin-shaped bipolar plate for a proton exchange membrane fuel cell, the deformation behavior of a thin 8111 aluminum alloy sheet by the hot metal gas forming (HMGF) process was investigated. The effect of gas pressure, forming time, pin diameter, pin height, and die fillet radius on the specimen profiles, as well as the thickness distribution were analyzed by finite element method using ABAQUS 6.10 software. In addition, experimental tests were performed to validate numerical outputs. The results indicated that the sheet thinning rate grew sharply by the gas pressure exceeding 4 MPa. The specimens were cracked following decreasing the die fillet radius to 0.1 mm. Furthermore, the die filling rate was high at the beginning of forming time and then diminished gradually after 1000 sec. Moreover, the thickness reduced sharply by augmenting the ratio of pin height to diameter to over 0.4. Finally, perfect specimens were produced in experiments, which verified the feasibility of fabricating a pin-shaped bipolar plate out of a thin AA8111 sheet by the HMGF process.

The production of fine-grained materials by Severe Plastic Deformation (SPD) methods has made these methods more attractive. The basic condition for producing specimens with better mechanical properties and more homogeneous structure is the application of high and uniform plastic strain. Many researchers have tried to modify the existing SPDs or introduce new techniques to achieve these goals. In this research, in order to improve the mechanical properties of the specimens, a new method is introduced, which is the combination of the two processes of torsional extrusion and ECAP. Then, by performing the design of experiments, the optimal die geometric parameters, including the internal angle of the ECAP channel α, the outer angle of the ECAP channel , the length of the torsional region L, the ratio of large diameter to small diameter of the ellipse, m, and the torsional angle of the elliptical section, θ, were obtained 90.5◦, 39◦, 34mm, 1.65 and 120◦, respectively.

In this paper, the loading path was optimized in hot metal gas forming (HMGF) process for making AA6063 cylindrical stepped tubes. For this purpose, the response surface method (RSM) and finite element method (FEM) were applied using Design-Expert and ABAQUS softwares, respectively. The parameters of internal pressure, pressure rate, axial feeding, and punch speed were examined based on the central-composite design in the three levels. The maximum die filling and the minimum tube thinning percentages were selected as the objective functions. The analysis of variance showed that the axial feeding, internal pressure, and their interaction were the most significant parameter in the die filling and tube thinning. The optimum loading path at the temperature of 550 oC was obtained at pressure of about 7 bars, pressure rate of 0.01 bar/s, axial feeding of 7 mm from each side and punch speed of 0.02 mm/s. Experimental tests were performed for the specified process parameters. The numerical results were validated by experimental testing.