Potentials of induction heating for hot metal forming of car body parts

Due to growing challenges regarding crash-performance, CO2 emission as well as increasing demand for lightweight construction, hot forming of car body parts has risen to one of the most important technologies for saving weight of a car body. During hot forming shaped blanks of steel, mostly made of 22MnB5, are heated and austenitized at around 950°C and subsequently quenched for martensitic formation. Currently the heating is realized in roller hearth furnaces which allow only a slow heating and, therefore, limited the production. Additionally, due to the indirect heating principle of such furnaces the energy efficiency is low. Induction heating of the blanks offers a big potential to increase the production rate dramatically and also to improve the energy efficiency. Only due to the fact, that the heated parts typically are already pre-shaped and mostly have already holes and cut-outs induction heating becomes a very complex task. Beside, induction heating always accompanied by driven forces can lead to problems if the blanks are coated by a low melting coating alloy like AlSi. In the first part the paper compares different possible induction heating methods (longitudinal heating, transverse flux heating, single stage induction heating, hybrid heating by induction and conventional heating) and describes the potentials and limitations of induction heating in dependence of the production conditions. In the second part numerical and experimental results of an investigation in the frame of a research project and the final design of a single stage induction heating for hot forming of pre-shaped blanks are presented.