On thermal-mechanical analysis of metal casting process using micro-macroscopic model with finite element method

A stress modeling methodology has been developed for analyzing cast iron defects such as shrinkage, distortion, and metal penetration in which the major contributing factors, either alone or in combination, are mold deformation and volume expansion associated with graphite precipitation during eutectic solidification. A fully-coupled micro-macroscopic method incorporating mathematical models for temperature, microstructure evolution, and stress has been formulated and implemented into MARC, a commercial finite element program. Key features of the methodology include (i) determination of transformation strain on the basis of micromodeling results and specific volume models which account for both temperature and fraction and composition of phases present, and (ii) a thermo-mechanical coupling procedure to determine the interfacial heat transfer coefficient on the basis of the casting-mold contact condition. During the course of a simulation, a coupled, iterative procedure is used to determine the size of the gap or the magnitude of the contact pressure at the interface. Depending on the state of the interface, appropriate relationships are used to obtain the interfacial heat transfer coefficient. Simulation results for several cases indicated that solidification of the last region of molten metal in a casting may result in shrinkage or metal penetration, depending on casting geometry, alloy composition, mold stability, and other factors.