Experimental Study and Numerical Verification of Heat Transfer in Squeeze Casting of Aluminum Alloy A443

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ANY researchers investigated the interfacial heattransfer coefficient (IHTC) between a solidifying aluminum casting and metal mold during die casting.[1–19] The heat flow across the casting–mold interface can be characterized by a macroscopic average metal–mold IHTC based on Eq. [1]. q ½1 h¼ AðTcs  Tds Þ where h is IHTC; q is average heat flux at the metal–die interface; A is section area; and Tcs and Tds are the casting surface temperature and die surface temperature, respectively. The heat-transfer coefficient shows a high value in the initial stage of solidification. As solidification progresses, the mold expands due to the absorption of heat, and the solid metal shrinks during cooling. As a result, a gap develops because pressure becomes insufficient to maintain a conforming contact at the interface. Once the air gaps forms, the heat transfer across the interface decreases rapidly, and a relatively constant value of h is attained.

ZHIZHONG SUN, Senior Engineer, is with Caterpillar, Inc., P.O. Box 1875, Peoria, IL 61656-1875. Contact e-mail: zhizhongsun@ yahoo.com HENRY HU, Professor, is with the Department of Mechanical, Automotive & Materials Engineering, University of Windsor, Windsor, ON N9B 3P4, Canada. XIAOPING NIU, Specialist, is with the Promatek Research Centre, Cosma International, Brampton, ON L6T 5R3, Canada. Manuscript submitted November 6, 2011. Article published online October 2, 2012. 1676—VOLUME 43B, DECEMBER 2012

A lot of techniques have been attempted to determine IHTCs in metal mold and obtained widely divergent values. The IHTC various values, from 85,000 W/m2K to 2000 W/m2K, have been reported for solidifying aluminum alloys in steel or cast iron molds. The IHTCs with different casting alloys, die materials, processes, and geometry shapes have been listed in Table I. The accuracy of a solidification simulation depends on the accuracy of the heat-transfer modeling. Modeling of the heat transfer at the metal/mold interface of a casting is very challenging due to a number of factors. One of the greatest modeling challenging is the handling air gap formation. Besides the different casting techniques, casting process parameters, and casting geometry shapes, some additional influencing factors need to be also considered in order to determine IHTC accurately. These factors include the pressure at the interface, alloy characteristics, mold processing conditions, die surface roughness, and coating. Since so many factors play a role in the heat transfer between the surface of the solidifying casting and the mold, determining accurate IHTCs is very specific to a given casting shape and process. For metal castings, the inverse method of heat conduction is useful in the determination of heat flux or heattransfer coefficient at the metal/mold interface. However, the inverse heat-conduction analysis is an ill-posed problem, and the output of an inverse solution to a heat conduction problem is very sensitive to measurement errors.[21] Actually, in the die casting practice, the different thicknesses at different locations o

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