Residual Stress State in Tools Used for Thermo-mechanical Metal Forming Processes

Abstract

In thermo-mechanically coupled forming processes for industrial mass production residual stresses are an unavoidable consequence of the alternating inhomogeneous fields of temperature and mechanical stress developing in tools and components dependent on the process parameters applied. Hence, a considerable interest exists to get reliable information about origin and distribution of the relevant residual stress fields and to understand the basic principles of their formation. By way of example a metal forming process based on a predefined locally and temporally differential temperature profile is described, which leads to a characteristic materials property profile and geometrical shape. The development of residual stress in tools (steel AISI H11) used for the thermo-mechanical forming operation of cylindrical flange shafts (steel SAE 6150) is outlined. To this end residual stress analyses by X-ray as well as by neutron diffraction were carried out. The loading situation of the tool was simulated by isothermal, thermal and contact fatigue tests, providing information about cyclic stress and plastic deformation during the manufacturing process.