Effect of the heat-transfer coefficient in ring-compression tests

Abstract

This work was a part of a project where eleven Nordic companies and five Nordic research institutes cooperated in order to simulate massive-forming processes. Heat-transfer conditions play a critical role in many forming and subsequent operations. In a hot metal-forming process both the friction coefficient and the heat-transfer coefficient act on the surface and affect the material flow. Better understanding of their role is therefore needed in order to obtain accurate results in numerical simulations. In this paper the effect of the heat-transfer coefficient in ring-compression tests has been evaluated using the finite-element method. Calculations with different-sized rings made of Al 5083 and with different heat-transfer coefficients have been carried out, from which calculations the following could be concluded. The heat-transfer coefficient has an effect in ring-compression tests. However, the effect can be considered small compared with the inaccuracies involved with the calibration curves. According to the calculations, smaller rings give better results than bigger rings in ring-compression tests, because the contact time between the die and ring is shorter for a smaller ring when the rings are subjected to the same amount of reduction. In the ring test the heat-transfer coefficient has a different effect on the flow pattern than that of the friction coefficient.