Interface heat transfer in investment casting of aluminum alloys

Via design of experiments and using a newly developed inverse method, the heat-transfer boundary conditions in the investment casting process have been studied. It has been shown in the past that these conditions, expressed as interface heat transfer coefficients (HTCs), vary during alloy solidification and cooling. In this work, the authors have studied the additional effects of alloy solidification range, metallostatic head, investment shell thickness, preheat, and interface geometry. This provides an improved set of relationships from which to build realistic boundary conditions into computer simulations of shape casting. Using axisymmetric solidification experiments and numerical inverse analysis, it is shown that the effect of metallostatic head is only significant for long freezing-range alloys. Increasing shell mold thickness and preheat also have effects that are alloy-dependent, and significant differences in thermal behavior are reported between the alloy/mold interface and the alloy/core interface. The four alloys used in the experiments are aluminum-based and vary from short freezingrange commercially pure to an alloy with a freezing range of 120 °C.