Effects of flow stress behaviour, pressure loading path and temperature variation on high-pressure pneumatic forming of Ti-3Al-2.5V tubes

摘要

High-pressure pneumatic forming (HPPF) is an internal high-pressure forming process at elevated temperatures, which is based on quick plastic forming (QPF), hot metal gas forming (HMGF) and hydroforming. In this study, the HPPF experiments were performed on Ti-3Al-2.5V tubes using a square cross-sectional die at higher pressure levels and lower temperatures. The uniaxial tensile tests were carried out at various temperatures and strain rates before the HPPF experiments. The flow stress of Ti-3Al-2.5V tubes is evidently affected by both temperature and strain rate. Because of this, the corner radii all change linearly over time at the pressurization stage but exponentially over time at the constant pressure stage. The cooling effect of the inflow process on the tubes results in temperature differences between the centre of the straight wall areas and the corner areas of the tubes during the inflow process. Adopting the lower pressurization rate and filling regenerative materials into the tube are effective methods for decreasing or eliminating the temperature difference.