Research on the effect of boundary pressure on the boundary heat transfer coefficients between hot stamping die and boron steel

Boundary heat transfer coefficient (BHTC) between the hot stamping die and boron steel is one of the most important thermal physical parameters in the hot stamping. A software of inverse heat conduction problem (IHTP) was developed based on the optimization method and finite element method. NiCr-NiSi thermocouples were used to measure the temperature of sample, and the high speed data collection device was used to acquisite the electrical signal from the thermocouples. The BHTC between hot stamping die and boron steel was calculated by the IHTP software according to the temperature curve. Main factors affecting the evaluation accuracy of BHTC were discussed, such as surface temperature of test device, surface temperature of sample, height to diameter ratio (H/D) of sample, boundary pressure between the test device and sample. The research results show that, the surface temperatures of test device and sample have little effect on the BHTC. The heat conduction of sample with thermal insulation material can be simplified into one-dimensional process if H/D is not more than 0.6. The boundary pressure has a significant effect on the BHTC. The relationship between the BHTC and boundary pressure is approximately linear.