Heat transfer in hot stamping of high-strength steel sheets

Abstract

This paper focuses on the determination of the heat transfer coefficient (HTC) between blanks and dies in the hot stamping of high-strength steel sheets. Experiments to record the temperature evolution inside the dies were carried out on custom-built test equip- ment, where process conditions typical of hot stamping could be reproduced, but avoiding any deformation of the metal sheet. The HTC was determined by using an inverse analysis procedure, based on the comparison between temperature measured inside the dies and temperatures calculated by means of a numerical model of the test. HTCs between the steel blank and dies made of different materials were identified, showing that the use of ceramic inserts can modify the cooling rate inside the blank in order to avoid a complete martensitic transformation. Moreover, the influence of the contact pressure was investigated, proving that HTC dependence on this factor is not negligible

Sensitivity of the final properties of tailored hot stamping components to the process and material parameters

“…Significant variations have been observed in available data particularly in the conductivity for this tool material, and also noting that HTC is also sensitive to contact pressure which is difficult to measure experimentally. The Böhler-Edelstahl (2014) data sheet has reported the conductivity values of 26-29.2 W/m K in the temperature range of 100-700 • C, while Tondini et al (2011) have reported the value of 42.2 W/m K.…”

Numerical Model to Quantify the Influence of the Cellulosic Substrate on the Ignition Propensity Tests

“…Although the internal heat transfer mechanism of organic fibrous materials is complex at the microscopic scale, where radiation and convection mechanisms among fibres take place, it can be adequately described at the observation scale by means of effective heat conduction coefficients (27). Also the thin air film in-between the substrate can be modelled at the macroscopic scale assuming a thin thermally resistive layer which insulates the heat conduction through the different layers (28). According to KASHIWAGI and NAMBU (29), cellulosic substrate shows three different reactions during thermal oxidative degradation.…”

Investigation of formability and surface micro-crack in hot deep drawing by using laser-welded blank of Al–Si and Zn-coated boron steel

“…Active research aimed at solving such problems is currently focused on the hot stamping process. [1][2][3][4][5] Research on martensite formation according to temperature, 6 effects of the forming parameters in a hot process 7 and effects of spring back and residuals on the product 8 have been reported. Although hot stamped products have high stiffness, they are used restrictively in components requiring collision absorption because of their low elongation.…”