Analysis of the wall thickness distortion in tube hydro-forging

The tensile deformation is the most common forming principle in the sheet forming process, but there is a new tube forming process - tube hydro-forging has been developed based on the principle of compression deformation. In addition to the instabilities problem, a new surface defect - thickness distortion was found in the compression deformation. In this paper, the wall thickness distortion is analyzed from the point of view of mechanics and deformation. It is revealed that in the Low Pressure Tube Hydroforming process, a bending moment is exist and leads to some small wrinkles in the straight wall. In the Tube Hydro-forging, the small wrinkles would develop to the thickness distortion with the increase of compressive deformation. The wall thickness and compressive strain are two major effect factors. It is verified by experiments and simulation. This study helps to recognize the new surface phenomenon in compressive deformation.