A study of interfacial heat transfer in the permanent die low pressure and counter pressure casting processes

Counter pressure casting (CPC) process is a relatively new, emerging technology developed for producing load-bearing parts. It is believed that CPC produces parts with superior quality compared to those produced by the conventional low pressure die casting (LPDC) process since the die cavity is placed within a pressurized chamber (2-3 bar) in CPC. This feature is claimed to benefit the process with respect to both filling and solidification. However, few studies are available in the literature providing data to support this claim. Therefore, this research program is aimed to improve the fundamental understanding of the transport phenomena occurring in the CPC process with a focus on the heat transfer through the die/casting interface, using a combination of experimental and modelling techniques. A series of experiments were conducted on a commercial CPC machine to produce a custom-designed “H-shaped” aluminum casting. Three process conditions, where the chamber pressure was varied, were tested. Results showed that in-die temperatures at various locations, and the secondary dendrite arm space (SDAS) were not significantly affected by the chamber pressure in the range tested (1200-3000 mbar). However, die filling was delayed at a higher counter pressure, possibly due to the increased viscosity and density of the air in the die cavity. A thermal model and a coupled thermal-stress model of the CPC process have been implemented within the commercial finite element (FE) package ABAQUS™ to simulate the process conditions in the experiments. The coupled thermal-stress model was developed using a novel modelling methodology established in the research. The model is able to utilize the deformed state of the hot die and update the casting geometry based on the hot die geometry at the beginning of a casting cycle. Thus, the stress-strain evolution of the die and the casting, the die/casting interface behaviour, and the associated heat transfer can be fundamentally described. A thermal-only model was also formulated and utilized to develop a second interfacial heat transfer coefficient that is a function of interface temperature. The results of the comparison indicated a slight improvement in accuracy obtained with the thermal-stress model in areas prone to gap formation.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat