Measurement and modeling of thermal evolution during induction heating and thixoforming of low carbon steel

A comparative study of thixoforming and forging of double-cup parts in low carbon steel was performed using a combination of process in-situ experimental analysis and modeling. First, the thermal profile resulting from induction heating of the slug prior thixoforming was experimentally determined using thermocouples and compared to the results of 3D numerical simulation of induction heating. The thermal profile was found to be heterogeneous with temperature ranging from 1150 degrees C to 1425 degrees C. Numerical modeling of the thermocoupled slug demonstrated that the geometry alteration induced by thermocouples disturbs the magnetic field and thermal diffusion during induction heating resulting in a significant modification of the temperature distribution within the slug. Thermal evolution during transfer from the heating cell to the press was also monitored and the data were used to determine the heat transfer coefficient which was found to be approximately 150 W.m(-2).K-1 on a temperature range of 1300 degrees C-1400 degrees C. Numerical simulation of thixoforming and forging processes was performed using a micro-macro model and the calculated forming load evolution was compared with the in-situ experimental data collected in-situ using a force sensor located on the upper punch. The comparative study demonstrates the essential influence of the input thermal profile to carry out reliable numerical simulation. The load applied to thixoform the double-cup part was found to be 40 % lower than in forging condition whereas the extruded length resulting from thixofming is approximately 12 % higher than for the forged specimen. Post-process analysis shows that thixofomring does not affect the microstructure and tnsile propeties of the specimen in comparison with forging, except for a sligh grain coarsening of the non-extruded part of the specimen.