Investigation of thickness variation in axial hydro-forging sequence for variable-diameter tubes

Abstract

Abstract Axial hydro-forging sequence is an emerging process to form the variable-diameter tubular components. In axial hydro-forging sequence, the excessive thickness thinning of the tube can be reduced and even eliminated by axial compression deformation. In this case, a new type defect is discovered, where the thinning of the transition zone is not decreased and a barrelling defect occurs at the end of the maximum diameter zone. To reveal the reason of the defect and provide a clue to avoid it, the stress distribution, the deformation sequence as well as the thickness distribution are investigated by mechanical analysis, finite element simulation and experiments. Two key process parameters considered in this study include the corner radius and the friction coefficient. The results show that the marked drop of the effective stress in the corner segment of the transition zone caused by the normal concentrated force is the determining factor of the defect in hydro-forging stage. It is shown that the defect can be decreased by increasing the corner radius, but only barrelling defect is decreased by improving friction coefficient. Based on the results, a new improvement approach was proposed in this paper and verified that it can effectively reduce the defect.