Pressure-time loading profile for tube superplastic free bulging

An analytical model to determine the pressure-time loading profile for tube superplastic free bulging was presented in this work. The analytically determined loading profile was in good accordance with that determined by FEM codes, which proved the analytical model effective and correct. The pressure-time loading curve starts at a peak pressure, and then declines with time. Initial tube radius r 0 and strain rate significantly affect the loading curves. Peak pressure at 880 °C is from 7.7 MPa for r 0 = 5 mm to 2.2 MPa for r 0 = 25 mm and from 5.8 MPa to 1.6 MPa at 920 °C. The tube bulging experiment showed that tube superplastic forming under the optimized pressure-time loading profile got more uniform thickness distribution than that under the constant pressure loading curve, and thinning was improved from 77 to 64.7% at 920 °C.