Superplastic forming of bellows expansion joints made of titanium alloys

A new forming technology was developed for bellows expansion joints. This technology uses superplastic forming (SPF) method of applying gas pressure and compressive axial load. It is developed and can be used to manufacture large diameter “U” type bellows expansion joints made of titanium alloys. The forming technology for bellows expansion joints made of titanium alloys is presented to make a two-convolution bellows expansion joint of Ti–6Al–4V alloy as an example. Welded pipe bent by a hot bending method with a set of specific dies and welded by plasma arc welding was used as a tubular blank in the SPF. During the SPF process the tubular blank is restrained in a multi-layer die block assembly which determines the final shape of convolution. The forming load route is divided into three steps in order to obtain optimum thickness distribution. This technology can also be used to fabricate stainless steel bellows expansion joints.