Determination of Heat Transfer Coefficients for Different Initial Tool Temperatures and Closed Loop Controlled Constant Contact Pressures

Abstract

The boron steel quenching requirement on hot forming manufacturing processes allows the industry to create tailored parts to improve their mechanical functionality. During the cooling, the microstructure of the material changes depending on the imposed cooling rate. However, an accurate prediction of the cooling ratios is needed in order to correctly design the process. In this work the interfacial heat transfer coefficient (HTC) has been determined at different contact conditions, varying the initial die temperature. Experimental tests have been realized in a SCHMIDT micro servo-press, which is able to compensate the thermal contraction of the blank and tools to precisely keep constant the contact pressure. Temperature evolution of the tools and the blank has been monitored with nine thermocouples. For the determination of the heat transfer coefficient (HTC) an analytical-numerical method has been used leading to a fast and reliable calculation method able to determine the HTC value for each process time. This methodology allows relating the HTC to the blank temperature, difference on temperature on the interface to improve the tailor tempering of boron alloys simulation.