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Temperature-time courses of a) furnace heating with 220 s heating time and b) resistance heating with 4.3 s heating time
Source publication
Hot stamping is a well-established and frequently used manufacturing process in automotive body construction. The number of components manufactured in this way is continuously increasing. Hot stamping is used to produce components with a completely martensitic structure, resulting in high strength and hardness. These components are mainly used in s...
Contexts in source publication
Context 1
... heating, reference tests were carried out using an industrial furnace from Nabertherm with an output of 60 kW. The furnace was preheated to 950 °C. The material was heated to a temperature of 930 °C within 220 s. The sheet temperature during heating in the furnace was observed and measured by means of a temperature sensor positioned in the sheet (Fig. 4a). The energy measurement of the furnace is carried out with an energy measuring belt above the primary power supply. Comparison experiments using resistance heating were carried out with three different heating rates from ambient temperature to 930 °C within 4.3 s, 13 s and 44 s. In order to ensure the uniformity of heating by means of ...
Context 2
... to hardness tests. The measurement of the hardness was carried out using the hardness tester Qness. The specimens are 10 × 15 mm in size and were embedded and polished for the hardness measurement. The hardness was measured at three different points, each exactly in the middle of the sheet thickness over the entire length (15 mm) of the specimen. Fig. 4a shows an example of the heating process for a sheet heated in a furnace. It is noticeable that the heating time (220 s) is the longest step in the process chain. Rapid heating by means of electrical current offers great potential for shortening the process cycle time. Fig. 4b shows an example of the heating curve for resistance heating ...
Context 3
... of the sheet thickness over the entire length (15 mm) of the specimen. Fig. 4a shows an example of the heating process for a sheet heated in a furnace. It is noticeable that the heating time (220 s) is the longest step in the process chain. Rapid heating by means of electrical current offers great potential for shortening the process cycle time. Fig. 4b shows an example of the heating curve for resistance heating of the same sheet blank. The target temperature of 930 °C was reached in 4.3 s. This means a reduction in heating time by more than 90 %. The transfer and hot-stamping durations are identical in both processes. Hot stamping takes place at a temperature above 720 °C, which ...
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Citations
... Direct resistance heating involves passing an electrical current through the material to be formed, heating it through joule effect. In most cases, copper or aluminum electrodes linked to a generator are placed against the sheet to allow current flow [3,4]. This process is already promising, with studies showing it allows heating steel sheets over 800 • C in about 2 s with good temperature uniformity [5]. ...
... It is a crucial point in this process to allow uniform ductility over the entire sheet. Along the width, it mainly depends on the current density uniformity, which changes with the contact uniformity of the electrodes 2 of 7 and sheet [4]. Furthermore, the process demonstrates an efficiency between 75% and 95% when it is used to heat a steel sheet in a hot stamping process [6]. ...
... Eng. Proc. 2023, 43, x FOR PEER REVIEW 2 of density uniformity, which changes with the contact uniformity of the electrodes and shee [4]. Furthermore, the process demonstrates an efficiency between 75% and 95% when it i used to heat a steel sheet in a hot stamping process [6]. ...
... Principle of resistance heating of a rectangular sheet metal[26] ...
The manganese-boron alloy 22MnB5 is particularly used for structural and safety-relevant parts in the automotive industry. Parts made from this alloy are usually produced using the hot forming process. Here, the sheet is heated to over 950 °C using an industrial roller hearth furnace. The heated sheet is then simultaneously formed and quenched in a cooled tool with a temperature gradient of more than 27 K/s. This leads to the formation of a martensitic microstructure with a hardness value of over 450 HV10 and an elongation at break of less than 6%. The small strain potential of such components makes them difficult to form after hot-stamping. Due to the high temperature gradients of resistance heating, a sheet can be heat-treated locally without a large temperature transition zone. This can be used to locally soften already hot-stamped components for subsequent operations such as bending. Within the scope of this paper, resistance heating is used to soften a hot-stamped 22MnB5+AlSi sheet stripe of 3 mm width. The sheet could consequently be bent over an angle of 90° without cracking the substrate.
