Dieless incremental hole-flanging of thin-walled tube for producing branched tubing

Extending incremental forming technology into the production of tubular parts has promising prospects; however, fundamental rules of the approach have not yet been fully revealed and knowledge on the technology is lacking. This paper is focused on the dieless incremental hole-flanging of thin-walled tube for producing branched tubing. 316L stainless steel tubes with an outer diameter of 38 mm and thickness of 0.5 mm were used for the experiment and numerical simulations. Considering the uncertainty of initial curl direction of the tube wall at the extrados, where buckling is also prone to occur due to the excessive axial pressure during the forming course, an improved bar tool with a conical surface was proposed. Estimation of the precut hole size and processing route planning were discussed based on the designed branching. Force and deformation behavior along with the defects in the process, which are quite different from those in conventional incremental sheet forming, were summarized. The results prove that it is feasible to produce specific tubular parts by means of incremental forming with obvious flexibility, agility, and expandability.