Determination of the Active Medium Temperature in Media Based Press Hardening Processes

Abstract

Safety, lightweight design, and reduction of emissions are terms which are key issues in modern vehicle construction. These challenges can be met by new lightweight design strategies, e.g., by using lightweight materials and high-strength steels as well as innovative forming technologies such as media based press hardening (MBPH). MBPH as a sub-production technique of hydroforming is a tempered internal high-pressure forming process of closed profiles, which this article is about, or sheet metals by gaseous media. Due to the high process requirements (internal pressure up to 70 MPa and temperatures up to 1000 °C), it has not been possible to measure the temperature curve of the active medium in a reliable way until now. The aim of the research project described in this article was to develop an innovative measuring instrument to determine the gas temperature curve with a measuring frequency of at least 1 Hz. Analytical and numerical calculations have indicated that the active medium has a significant influence on the thermodynamic of the forming process. The finite element analysis (FEA) of the heat flow during the forming process has indicated that the influence of the gas on the cooling process of the work piece is about 15% of the total influence of the tool. Consequently, the active medium in media based press hardening processes is an important thermal influencing factor. Experiments have confirmed that it is possible to determine the calculated curve of the gas temperature and maximum temperatures of the active media up to 500 °C. The findings of these studies make a significant contribution to identifying and analyzing the complete temperature balance in tempered active media based forming processes.

Effect of feeding length on deforming behavior of Ti-3Al-2.5 V tubular components prepared by tube gas forming at elevated temperature

“…3b. Welf-Guntram Drosse [27] designed an innovative measuring instrument to determine the gas temperature curve, and the result shows that the cold gas will cool the heated tube. In this paper, some steel filler was put inside the tube, which used to reduce the volume of the tube cavity and preheat the argon gas.…”

Effects of flow stress behaviour, pressure loading path and temperature variation on high-pressure pneumatic forming of Ti-3Al-2.5V tubes

“…This should not be neglected during the HPPF process in spite of gas' low thermal conductivity [14]. In our previous work about the HPPF process of Ti-3Al-2.5V alloy parts with square cross-sections [15], there was a preforming process during the closing of the die because of the mere 10 % circumferential expansion ratio.…”

“…Elsenheimer et al set up hot tube bulge test equipment with the maximum pressure of 35 MPa to obtain stress-strain curves at elevated temperatures [13]. Drossel developed a measuring instrument to determine the gas temperature curve during pneumatic forming processes and to analyse the influence of gaseous medium with high pressure on the cooling process of work pieces [14]. Liu et al presented a HPPF process based on QPF, HMGF and hydroforming [15].…”

“…The effects of pressure loading path and temperature on corner-filling behaviour were investigated further, and the corner-filling curves were fitted more accurately. The influence of the inflow process of gaseous media with high pressure on tube temperature was studied, which was inspired by the work of Drossel et al [14]. The corner-filling time and thickness profiles of the fully formed tubular components under different forming conditions were also discussed.…”

Enhanced granular medium-based tube and hollow profile press hardening

“…The critical cooling rate for martensitic transformation is achieved by applying compressed air. One disadvantage of using gaseous medium is that it only contributes to the cooling process by 15 % compared to the total tooling, [8]. The final hardness of tubes formed by gas differs locally and depends mainly on the pressure rate, the maximum pressure value, and the tool temperature, [9].…”