Material characteristics evaluation for DC04-welded tube hydroforming

Tube hydroforming (THF) technology is widely applied especially in the automotive and aircraft industries. Material characteristics of tubular workpieces should be evaluated in terms of bending and THF processes. A mathematical model, which combines the assumption of the elliptical contour of a bulged wall and the prediction equation of wall thickness, was designed to analyze the THF process and to obtain the strain–stress relationship of tubes. Material characteristics of a DC04-welded tube were obtained by using a self-designed THF test machine. Considering the effects of pre-work hardening, the material strain–stress relationships of the tube and original sheet blank were discussed. An approximate determination method was proposed to obtain the stress–strain curve of the tube by using the curve of the original sheet blank and the hardness of the tube and sheet blank. A suitable constitutive equation with pre-work hardening was applied to the DC04-welded tubes through simulation and experimental methods.