The wall thickness around an inner corner of 3-stage-formed cups with a flange was increased using conical punches in the 1st and 2nd stages. Since the strength of the formed cups is greatly improved by increasing the wall thickness, the weight of the formed products is reduced by an optimum distribution of the wall thickness resulting from the increase in wall thickness. The increase in thickness around the inner corner was achieved by compressing the side wall and the conical bottom of the cup using an outer punch in the 3rd stage. The amount of compression in the 3rd stage was expressed in terms of the drawn volume after the 2nd stage, and the drawn volume was optimized. Although the maximum increase in wall thickness around the inner corner for the conical punches of 25o was about 9% that with the flat punches, the maximum forming load with the conical punches decreased by about 30%.
A large quantity of lubricant waste has become a very serious environmental issue. For the zero emission of lubricants, dry deep drawing is efficient; however, it is generally very difficult to apply it to metal sheets. As one of the most promising methods, the use of ceramic tools is proposed because of their high tribological properties. However, the workability of the ceramic tools is poor. Therefore, the forming of a complex shape is difficult and even the forming of a simple shape is expensive. Thus, the use of electroconductive ceramic tools in this research is proposed. The electroconductive ceramic tools can be formed by electrical discharge machining methods (e.g., wire and die milling electric discharge machining methods). Therefore, the shape of a metal mold can easily be molded. Using an electroconductive ceramic as a plastic forming tool, a high drawability was confirmed and dry deep drawing of 10,000 times was achieved. The surface roughness of a dry deep drawing cup was as large as that of a non-dry (oil) deep drawing cup.
The frictional behaviour of aluminium alloy is evaluated by a tapered plug penetration test under semidry conditions. Cemented tungsten carbide (WC) plugs at room temperature are penetrated into the cylindrical hollow workpieces of aluminium alloy. A small quantity of lubricant (2.0-3.0 g · m-2) on the plug surface is effective in preventing the seizure of the workpieces. It is found that the seizure of the workpieces occurs when the inclination of the applied load exceeds a critical value, approximately 0.5 kN · mm-1. To examine the deformation behaviour of the workpieces during plug penetration, finite element simulation is carried out. From the obtained simulation and experimental results, the critical coefficient of shear friction between aluminium and WC is estimated to be about 0.3 when the seizure occurs.