This paper presents a design for a robust sensor suitable for determining heat flow and heat transfer coefficient in high pressure die casting. A design methodology for the sensor is presented, together with the conclusions of this analysis. A sensor has been manufactured to these principles and some typical results from its operation are introduced.

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In permanent mold casting or gravity die casting (GDC) of aluminum alloys, die coating at the casting-mold interface is the most important single factor controlling heat transfer and, hence, it has the greatest influence on the solidification rate and development of microstructure. This investigation studies the influence of coating thickness, coating composition, and alloy composition on the heat transfer at the casting-mold interface. Both graphite and TiO 2 -based coatings have been investigated. Two aluminum alloys have been investigated: Al-7Si-0.3Mg and Al-9Si-3Cu. Thermal histories throughout the die wall have been recorded by fine type-K thermocouples. From these measurements, die surface temperatures and heat flux density have been evaluated using an inverse method. Casting surface temperature was measured by infrared pyrometry, and the interfacial heat-transfer coefficient (HTC) has been determined using these combined pieces of information. While the alloy is liquid, the coating material has only a weak influence over heat flow and the thermal contact resistance seems to be governed more by coating porosity and thickness. The HTC decreases as the coating thickness increases. However, as solidification takes place and the HTC decreases, the HTC of graphite coating remains higher than that of ceramic coatings of similar thickness. After the formation of an air gap at the interface, the effect of coating material vanishes. The peak values of HTC and the heat flux density are larger for Al-7Si-0.3Mg than for Al-9Si-3Cu. Consequently, the apparent solidification time of Al-9Si-3Cu is larger than that of Al-7Si-0.3Mg and it increases with coating thickness.

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The present article deals with the application of a new measurement method to determine the heat-transfer coefficient (HTC) and the heat flux density at the casting-die interface during highpressure die casting (HPDC) and solidification of the magnesium AZ91D alloy. The main measurements during the trial included velocity and the position of the piston that delivers the metal into the die, the pressure in the die cavity and at the tip of the piston, the alloy surface temperature, and the die temperature at different depths from the surface of the die. The temperature data were analyzed using an inverse method to determine the HTC at the castingdie interface during solidification. This article examines in detail the influence of the piston velocity and in-cavity pressure on heat transfer at the casting-die interface during casting and solidification of the magnesium AZ91D alloy.