Tribological Behavior of Different Tool Steels and Surface Properties under Hot Stamping Conditions

Abstract

Hot stamping is a well-established technology for producing safety relevant components. The use of hot stamped components in modern car bodies offers the possibility of improving the crash performance while reducing the fuel consumption by using thinner sheet thicknesses. Hot stamped components are mainly produced out of the boron-manganese-steel 22MnB5. To avoid oxide scale formation during the heat treatment and the subsequent forming process AlSi coatings are applied on the workpiece surface. Due to the high forming temperatures, the use of lubricants is not suitable for the hot stamping process. Consequently, high friction and severe wear occur during the forming process and affect the resulting quality of hot stamped parts as well as the tool wear. In order to improve the part quality and increase the efficiency of industrial hot stamping applications, measures for reducing the tribological load during the forming have to be found. Within this study, the tool-sided impact on the tribological conditions is analyzed. Three different hot working tool steels were characterized based on strip drawing experiments under hot stamping conditions. Based on these investigations the tool steel characteristics hardness, thermal conductivity as well as chemical composition have been identified as possible influencing factors on the tribological conditions. Furthermore, the influence of the surface finish on the tribological performance was investigated by analyzing tool surfaces with three different roughness values and two PVD coatings. The experiments indicate a significant reduction of friction and wear due to application of PVD coatings while the tool roughness did not affect the tribological behavior under hot stamping conditions.

A Comparative Study in the Tribological Behavior of DLC Coatings Deposited by HiPIMS Technology with Positive Pulses

“…The molds involved in the operation are two steel stamps or dies, one of which slides through a guide while the other is fixed. In the case of standard parts, there are various partial solutions in terms of materials, and additional treatments in order to improve their properties and durability, which offer a highly contrasted stable behavior [14]. The importance of the continuous development of solutions to improve the performance of this type of tool is a key and essential factor for increasing the productivity of manufacturing processes [15].…”

Properties of Tool Steels for Application in Hot Stamping

“…Normal and drawing forces were applied by means of hydraulic cylinders, whereas the contact pressure was applied by a friction jaw which simulated the tool. More details of the test setup can be found in the study by Schwingenschlögl et al As workpiece material, sheets of 22MnB5 (1.5 mm in thickness) featuring an AlSi‐coating were used. The latter was applied with 150 g m − 2 , thus resulting in an average thickness of 25 μm.…”

Novel tool steel for application in hot stamping

“…The novel tool steel mentioned in section 1.3 is named Thermodur HSP Superclean. Further information on the development of the alloy is given in [14]. An overview of all steel grades used in this study and their chemical composition is given in table 1.…”

“…A specifically designed test rig was used for this testing method which is able to simulate tribological processes occurring in hot stamping closer to reality than standardized wear resistance tests could do. Analysis of cause-effect relations between the parameters tool and workpiece temperature, contact pressure and drawing velocity for different workpiece and tool materials can be concluded [14]. Counter body material in all strip drawing tests were steel sheets of AlSi-coated 22MnB5.…”