Investigation of new tool design for incremental profile forming

Abstract

Abstract Incremental Profile Forming (IPF) is a highly flexible and versatile process for the manufacture of tubular parts with variable cross-section design along the centre-line of the tube. Within an incremental approach multiple forming tools with arbitrary geometries indent into the tube and move along predefined tool paths to deform the desired tubular shape. Since rigid forming tools are used, a sliding friction contact between tool and workpiece exists leading to several process limits. On the one hand tearing occurs in the forming zone due to high tensile stresses near the contact area between tool and workpiece. On the other hand the workpiece properties in terms of surface quality decrease due to wear. Unlike incremental sheet forming processes, where the workpiece surface area is under contact load twice (assuming a 50 % side overlap between subsequent tool paths), the deformed surface areas in IPF experience several repetitive contact loads leading to comparatively higher occurrence of wear. In order to improve surface qualities as well as to lower the loads in near contact regions by the reduction of friction, novel tool designs for IPF are introduced which allow a smoother transition of the material flow into the forming region. Besides a rigid tool, a roller-based tool is designed for substituting the conventional sliding friction by a rolling friction mode. Within experimental studies the influence of the tool shape as well as the rolling friction condition was examined. Comparative analyses show that the process forces are decreased by the use of the new tool designs leading to higher formability in IPF since a higher radial tool infeed is achievable. For the analysis of the component loads e.g. contact stresses and corresponding distributions in the contact region between workpiece and forming tool a numerical model is developed. A significant reduction of process limiting tensile stresses in contact near regions could be proven. Beside the reduction of process forces an improvement of the surface quality as well as a more accurate geometry of the workpiece were achieved by the use of the new tool designs.