Research on Multi-Steps Tube-Compression of Thin-Wall Parts with Variable Diameter by Viscous Pressure Forming

Tube-compression is one of the usual forming methods for variable diameter parts. Due to the influence of compression instability, buckling and wrinkling are prone to occur in tube-compression process, especially for the thin-wall parts, which restricts the diameter reduction ratio limit. In this paper, the viscous pressure forming (VPF) method is proposed for the problems in tube-compression. Utilizing the mechanical property and easily achieved loading mode of viscous medium, the buckling in the tube-compression process can be delayed and wrinkles caused by buckling can be eliminated, so as to increase the diameter reduction ratio limit. The multi-steps forming can divide the large total deformation into much small deformation, thus the small deformation can be controlled in the range of buckling and wrinkling. The process has the more ability to improve material’s forming capability than one-step forming. The deformation of the multi-steps tube-compression process by VPF is analyzed by finite element method (FEM). The variation of length-to-diameter and wall thickness after each step forming has influence on the next step compression. This forming method can also be used in tube-compression of high strength materials and can realize precise plastic forming of parts with high strength, thin-wall and large diameter variation ratio.