Interface heat transfer in investment casting of aluminum alloys

Abstract

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 ЊC.

An Investigation into the Effective Heat Transfer Coefficient in the Casting of Aluminum in a Green-Sand Mold

“…(2) Most studies presented in the literature assume the presence of quasi-steady state conditions at the interface, 8,11) i.e. the heat flux flowing out of the metal is equal to that which flows into the mold.…”

“…Hwang et al 10) conducted a similar investigation using an A356 aluminum alloy casting in a sand mold. Utilizing an inverse technique, Browne and O'Mahoney 11) showed that the interfacial thermal resistance in an investment casting process was related to the solidification range of the alloy, the hydrostatic pressure of the liquid metal, the thickness of the investment shell, the pre-heat conditions, and the interface geometry. Chiesa 12) measured the temperature of the molten metal during the filling of a flat plate mold, and concluded that the difference between the measured temperature value and the numerically-derived temperature value implied the presence of a thermal resistance at the mold/ metal interface even though the metal was in a molten state.…”

Simulation of the aluminum alloy A356 solidification cast in cylindrical permanent molds

“…As the cooling of the ingot progresses, an unusual experimental behavior is noticed. This could be interpreted in terms of the variation of the heat transfer coefficient between the metal and the mold, just as it has been suggested by authors such as GRIFITH [3], BROWNE and O'MAHONEY [4], and TAHA et al [5]. Figure 6 represents the experimental and theoretical cooling curves for the case in which the alloy was cast in a mold at 300°C.…”

Experimental determination of heat transfer coefficients during squeeze casting of aluminium

“…Controlling both stages is of major importance for obtaining sound casts with the required geometry and mechanical properties as observed by (Kobryn and Semiatin, (2000), Browne and O'Mahoney, (2001) and Martorano and Capocchi, (2000). When molten metal is poured into the mould cavity, it is initially in the liquid state with a high fluidity.…”