Theoretical and experimental study on the hydroforming of bifurcation tube

Hydroforming is one kind of plasticity working, which can be used to increase the diameter, to change the geometry, or to expand the outer walls of cylindrical shells or tubes. The forming principle of hydroforming is by using a die to constrain the outer geometry of a tube and then pumping high pressure oil into the inner tube, so as to force part of the tube to flow into the die cavity. In order to prevent local thinning and to improve material flow capability, an axial force may be imposed on the both sides of the tube. If the axial force is not imposed correctly, a buckling defect will occur. The forming theory and plasticity of the hydrostatic bulging process are studied. The parameter effects on the hydrostatic bulging process will be analyzed by using a DEFORM-3D finite element analysis package. A new approach to measure 3D deformations and plastic strains in forming parts is also presented. A strain analysis module is also built based on the geometry of deformed grids and initial grids. The principal stretch ratios and angle changes of grid patterns are calculated, and the logarithmic strains are also computed.