Weight reduction is an ongoing trend in multiple industries. Especially in the mobility sectors, hot forming of sheet metal parts has become an alternative production process for high strength components. New material concepts, e.g., boron-manganese steels, enable the design of lighter parts at equivalent or even higher strength. During the preliminary process development phase detailed knowledge of the thermo-mechanical material properties of these sheet metals is required at elevated temperatures and high strain rates. Since hot tensile tests can only be evaluated up to comparably low strains, new test designs are needed to supply material parameters at elevated temperatures and higher strain rates. Therefore, the hot gas bulge test has been developed, that allows for such test conditions. In this paper, first the concept of the hot gas bulge test and the developed test bench are described. Opposed to standardized bulge tests, which use hydraulic oil as forming medium, the newly designed test uses gas as medium to account for the hot stamping conditions, i.e., temperatures of up to 950°C. As the forming speed has an increasing influence on the material behaviour at increasing temperatures, a closed loop control of the forming speed was developed. Since there are no proportional pneumatic valves available for the required pressure range, a parallel valve concept was chosen. By combining different valves, the characteristics of a larger proportional valve are imitated. A control algorithm was developed, that maps the required valves conductance into a valve combination to control the mass flow into the pressure chamber. The developed control system is presented and experimental results from the material test procedure are shown. These results reveal that the developed system is capable to track the required mass flow rate for low as well as high forming speeds up to a certain deformation when the deformation of the sheet becomes uncontrollable.
- Fluid Power Systems and Technology Division
Pressure Control for a Hot Gas Bulge Test Using Parallel On-Off Valves
Matthiesen, G, Murrenhoff, H, Storz, J, & Braun, A. "Pressure Control for a Hot Gas Bulge Test Using Parallel On-Off Valves." Proceedings of the ASME/BATH 2017 Symposium on Fluid Power and Motion Control. ASME/BATH 2017 Symposium on Fluid Power and Motion Control. Sarasota, Forida, USA. October 16–19, 2017. V001T01A019. ASME. https://doi.org/10.1115/FPMC2017-4239
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