Investigations on parameters influencing thermal and frictional properties within hot stamping

Abstract

In the automotive industry hot stamping of boron manganese steels represents one of the major technologies to manufacture crash relevant structures within body in white considering aspects of light weight construction. Hot stamping can be described as a non-isothermal hot sheet metal forming process. Temperature control in the forming process plays an important role. The process is quite complex as temperature dependent material and process properties such as flow curves, heat transfer and friction coefficients have to be considered. To improve the knowledge about the process the influence of different process parameters and tool coatings on the heat transfer between tool and specimen is investigated. Additionally, the impact of monolayer, multilayer and superlattice coatings on the wear behavior and on friction is characterized. Furthermore, the effect of different austenitization parameter settings is analyzed with regard to the tribological conditions and resulting adhesive wear.

Investigation of the influence of process parameters on adhesive wear under hot stamping conditions

“…They explained the observed behavior with the diffusion phenomena of Fe and Al which are strongly influenced by the temperature. Several investigations like [15] and [16] measured increased adhesive wear due to increased contact pressure, which would contradict to the results of the current study. However, it has to be pointed out that the referenced studies observed the increased adhesive wear at the die radius.…”

Characterisation of Tool Coatings for Press Hardening

“…Due to the many process control variables that influence the result of forming as well as the mechanical properties of the component, the process layout tends to be portrayed as very complex, especially as the component geometry also plays an important role in it. In forming, the tribology for itself is determined to any substantial extent by a number of factors including austenitisation temperature [4] and duration [5], blank temperature during forming [5], workpiece coating [6], die surface (topology and material) [7], [8], die temperature [9] forming velocity [5], [10] and contact pressure [4], [6]. For the design of the dies, therefore, it is reverted to a thermo-mechanical Finite Elemente (FE) Simulation, with which it is possible, by means, for example, of sensitivity analyses, to quantify a number of parameter influences.…”

Tribological interactions and modelling of friction in hot stamping

“…On the other hand, Ademaj et al (Ademaj, Weidig and Steinhoff 2013) observed a decreasing COF for increasing furnace time up to 360 seconds for all furnace temperatures (880-950 °C). Merklein et al (Merklein, Stoehr, et al 2011) observed a decrease in COF for longer furnace times (5 to 20 minutes 950 °C). They assume that the surface exhibits fragments of the oxide layer and they might change the friction mechanism from sliding to rolling.…”

“…Three tool steels resulted in approximately the same COF and only HTCS 150 resulted in a higher COF. Merklein et al (Merklein, Stoehr, et al 2011) observed equal friction values if the standard deviation is taken into account for DIN 1.2367 and cast steel GP4M. Schwingenschlögl et al (Schwingenschlögl, Niederhofer and Merklein 2019) compared two hot work tool steels (DIN 1.2367 and DIN 1.2383) and measured similar friction coefficients.…”

“…(Schwingenschlögl, Niederhofer and Merklein 2019). The cast steel material GP4M is also used in investigations and in the hot stamping industry (Merklein, Stoehr, et al 2011).…”