Study On The Deformation Behaviors Of Tailor-Welded Tube In Hydroforming

Tailor-welded tubes (TWTs) are more and more used in tube hydroforming due to its low cost, high productivity, high quality and varieties in products. The research of tailor-welded tubes in hydroforming becomes highlight in the field of plastic forming. Material properties, finite element (FE) simulation and deformation behaviors of a STKM11A tailor-welded tube in hydroforming are investigated in this paper.The constitutive relationships of HAZs of the TWT are built based on the tensile properties for the base and the weld materials as well as the Vikers Hardness (HV) distribution in circumferential direction.The FE model including the weld and the HAZs of TWT is constructed based on the characteristics of tube hydroforming by slicing the tube according to material properties of the base, weld as well as HAZs. The results of FE simulation are compared with those of common models and experiment results for verifying the present model.The deformation behaviors of TWT in hydroforming are investigated by the FE simulation and experiment. The emphasis are laid on the deformed profile, wall thickness distribution , the limited forming pressure and the maximum bulge height of the tube under different forming conditions such as different tube length, loading path and the weld position in the die.The mechanics characteristics are studied by combining the plasticity theories with simulation results, and the formability of TWT in hydroforming is analyzed.The following conclusions can be drawn from the present research work.The method for determining the constitutive relationships of HAZs of a STKM11A TWT based on the Vikers Hardness distribution is reasonable to some extent. The TWT can not maintain symmetrical profile in free hydraulic bulges (FHB), a nonuniform thickness distribution is observed in the FHB. The minimum thickness is located at the HAZ close to the base. The minimum wall thickness, limited forming pressure and the maximum bulge height of the TWT with the weld expanded are less than those with the base expanded in T-shape hydroforming. The mechanics characteristics are bi-axial tensile and monaxial compressive stresses in the weld and HAZs of the STKM11A TWT, respectively. The closer to the base in the FHB the greater the tensile stress in circumferential direction. The bi-axial tensile stresses appear at the weld and HAZs of the STKM11A TWT in T-shape hydroforming and the closer to the base, the smaller the effective stress is.The present FE model including the weld and the HAZs is accurate for prediction of the limited forming pressures, wall thickness distribution and potential bursting locations of TWTs in hydroforming.Some new progress is made in this paper: a simple function is used to describe the Vikers Hardness distribution in circumferential direction of a STKM11A TWT; the constitutive relationships of HAZs at different circumferential locations are constructed based on the hardness distribution, and the FE model including the weld and the HAZs of TWT in hydroforming is constructed by the slicing approach.The results achieved by the present research work are useful for deeper research and wide application of TWT in hydroforming.