Effect of workpiece deformation on Joule heat losses in electromagnetic forming coils

Coils in electromagnetic forming operations are exposed to mechanical as well as thermal loads. Especially in case of high volume production the thermal loading due to Joule heating needs to be considered in the coil and process design to prevent thermal overstressing. An analytical approach for the calculation of Joule heat losses in electromagnetic forming coils considering the changing gap width between coil and workpiece is presented. An electromagnetic sheet metal forming application using a straight one-turn coil is used as reference case to prove the accuracy of the model. A comparison of the analytical calculation and the numerical results based on a simulation with a coupling of structural, thermal, and electromagnetic effects is provided. It is proved that the coil heating in case of a deforming workpiece ranges between the heating without workpiece and the heating with rigid workpiece. It is shown that with increasing workpiece velocities the heat losses in the coil tend more and more towards the lower bound represented by a coil without workpiece.