Healing Conditions of Large Forgings

Internal Voids Defect

REN Yunlai  NIE Shaomin  NIU Longjiang  ZHU Lei

(College of Mechanical Engineering, Yanshan University, Qinhuangdao 066004)

Abstract: Theoretic studies on the healing conditions of internal voids defect in large forgings and the application in workshop production are introduced. As far as nonlinear viscous materials are concerned a function, which is expressed with the velocity field, far-field stress and strain around voids, is presented. During the forging process of a infinite body with voids inside and made of incompressible material, the function with the condition of the actual velocity field always gets the minimum. According to this principle, the relationship between the boundary velocity field and far-field stress and strain of a void is provided, thus, the void’s shape after forging is predicted. Superimposed velocity field is employed to get the designed velocity field better represent the deforming characteristics and maximize the rate of convergence in which the function gets the minimum. By ways mentioned above, the healing of spherical internal voids inside the forging stock during upsetting is investigated. The results show that it is very difficult to heal voids only by increasing the far-filed stress because far-field stress and strain increase with the dwindling of the volume of the void. Therefore, it is reasonable that technical requirements for large forgings allow a certain amount of voids in large forgings. Based on the theoretic analysis, experiment is conducted and experimental results agree well with analytic calculations.

Key words: Large forgings  Forge  Healing conditions

CLC No: TG316

Received 20070326, received in revised form 20071012