Development of Mushy-state Forging Method Using Resistance Heating

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With an aim of developing a method for mushy-state forging using resistance heating, experiments and finite element simulations were carried out to clarify the resistance heating characteristics of A357 aluminum alloy billet and find out measures for stable and homogeneous billet heating. In the method, insertion of heat resistant, low thermal conductive austenitic stainless steel SUS304 discs between the copper electrodes and billet as thermal insulators was devised to improve the efficiency of the billet heating. In the original plan, using SUS304 stainless steel clad electrodes was planned, but the research was carried out in the mode of inserting the thermal insulators for easy operation of the experiments. In the resistance heating, it is necessary to apply a contact pressure between the electrodes and billet for ensuring their electric contacts. In the meanwhile, it is strongly desired to suppress the deformation of the billet as much as possible in the heating. It is possible to … More reduce the deformation by decreasing the applied contact pressure, but the excessive decrease causes sparking between the billet and thermal insulators and stops the forging operation. Then, first of all, the condition of the contact pressure on the spark occurrence was investigated in relation to the current density and it was made clear. And then, the thickness of the thermal insulators required for homogeneous billet heating was investigated in relations to both the current density and the contact pressure. Based on the findings through the investigations, experimental mushy-state forging of the aluminum alloy into a gear was made to investigate the influence on the forging condition of the operational conditions of the input electric energy and forging pressure. The results indicated that the mushy-state forging method is highly feasible but the metallurgical structure is strongly influenced by the thickness of the thermal insulators used. Therefore, proper adjustment of the thermal insulator thickness corresponding to each individual case is essential in the practical application. The findings obtained through this study were publicized as listed in the REFERENCES below. Less