Deformation analysis of double-sided tube hydroforming in square-section die

- Experiment of double-sided tube hydroforming in square-section die was achieved.
- Theoretical analysis and numerical simulation of effect of external pressure were conducted.
- Higher external pressure increases thickness thinning ratio and effective strain.
- Effect of external pressure on microstructure and hardness was studied.
- Formability of transition zone can be improved by increasing external pressure.