Explanation of the mushroom effect in the rotary forging of a cylinder

Rotary forging is an incremental forging process and is available to form various axisymmetrical parts from cylindrical billets. However, under certain conditions, a cylindrical billet is liable to be formed into a mushroom-shape after rotary forging, but not a drum shape in upsetting. A 3D rigid–plastic finite element method is used to simulate the rotary forging process to reveal the deformation mechanism of the mushroom shape workpiece. The stress, strain rate and strain distributions at different positions of the workpiece and at different times during the process are presented, and then the deformation zones are presented in detail for analyzing the deforming patterns. The reasons why the part with H0/D=0.5–1.0 (ratio of initial height to diameter) is formed into a mushroom shape are analyzed and it is concluded that these are non-uniform deformation under the effect of the eccentric loading and the different deforming degrees along the tangential direction at various heights of the workpiece. However, this kind of effect can be used to manufacture a part with a flange from a cylinder, instead of being regarded as a defect.