Effects of forming conditions on limit of drawing ratio during cold drawing and ironing process of Ti-6Al-4V alloy sheets

The low ductility of Ti–6Al–4V alloy at forming temperatures below 780°C is still a problem. Ti–6Al–4V is usually hot press formed at 780 to 900°C. A hot press formed Ti–6Al–4V alloy has been utilized in various devices such as medical and aerospace equipment. However, hot press forming increases cost, especially because it uses a furnace. To reduce cost, hot stamping by electric heating has been applied to titanium sheets or continuous resistance heating has been applied to the bar forming of Ti–6Al–4V alloy. Both electric heating and continuous resistance heating reduce the heating time in the forming temperature range from 780 to 900°C. Hence, it is necessary to develop a new press forming for Ti–6Al–4V alloy sheets at forming temperatures below 780°C to improve productivity. We have developed a method to achieve of cold press forming of Ti–6Al–4V alloy sheets by combining press motion control and clearance between a die and a blank. In this study, we tried to form various forming conditions for developed press forming method. In this method, the following two processes were separated: punch motion process without BHF and BHF motion process without punch motion. These two processes were carried out alternately during deep drawing or drawing and ironing. Three forming parameters, namely, the punch speed Spi, punch stroke Psi, and blank holding force BHFi, were controlled separately and the effect of forming conditions on deformation behavior was investigated by using experiment and finite element analysis(FEA). As a result, the effects of forming conditions on limit of drawing ratio of Ti–6Al–4V alloy sheets were investigated.