Investigation of the 'surface dimple' defect occurring during the production of an electric upsetting process by viscoplastic finite element modeling

摘要

Electric upsetting process is used to prepare a preform before proceeding to a hot forging process of a long aspect ratio part (L/D 40), such as an axial shaft and engine valve. Many researchers have been studied and investigated the effect of process parameters on the forming defects by experiments and simulations. The examples of the defects are surface burnt and buckling at the surface due to high electrical current and high compressive load, respectively. The "surface dimple" contacted at the anvil surface is another defect which is normally occurred during the production and has not been investigated a possible cause. This defect is a major cause of the underfilled for later the hot forging process. The objective of this paper is to investigate the cause of this defect by viscoplastic finite element modeling. It is found that the shifting of the high-temperature location comes from the chamfer. The non-chamfered workpiece will have the high temperature occurring around the middle of the anvil and the gripper which makes the high amount of the material rollover to the anvil caused of the high degree of the dimple when comparing to its with the chamfered workpiece.