Numerical and experimental analysis of heat transfer in resistance spot welding process of aluminum alloy AA5182
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ORIGINAL ARTICLE
Numerical and experimental analysis of heat transfer in resistance spot welding process of aluminum alloy AA5182 Michael Piott1 · Alexandra Werber1 · Leander Schleuss2 · Nikolay Doynov3 · Ralf Ossenbrink3 · Vesselin G. Michailov3 Received: 3 March 2020 / Accepted: 29 September 2020 / Published online: 15 October 2020 © Springer-Verlag London Ltd., part of Springer Nature 2020
Abstract In this work, a numerical model and experiments are used to investigate heat transfer processes during resistance spot welding process of aluminum. For this purpose, calibrated heat transfer conditions and thermal contact conductance are transferred from a previous work to a coupled thermal-electrical-mechanical finite element model. First, all domains of the numerical model are validated by an experimental study. The experimental setup includes the measurement of current, voltage drops, electrode force, electrode displacement, and temperatures while two sheets of aluminum alloy AA5182 are joined. Computational results show that most of the generated Joule heat (78%) is stored in the electrodes or transferred to cooling water until the end of weld time. Heat transfer by natural convection and thermal radiation is very small and can in general be neglected for complete process. Afterwards, the influence of electrode water-cooling on welding process is investigated numerically. The results indicate that the generation of Joule heat and thermal energy of the sheets during weld time is only slightly affected by electrode water-cooling. As a consequence, water-cooling conditions do not affect nugget formation. In contrast, electrode water-cooling highly influences cooling conditions during hold time. Keywords Aluminum resistance spot welding · Heat transfer · FE-simulation · Electrode water-cooling · Instrumented experiments
1 Introduction Presently, resistance spot welding (RSW) process is the dominating joining process in the automotive body in white shop. The process can be structured into four process steps [1]. First, electrodes press two or more sheets together. Afterwards, an electric current causes heat generation by Joule heating, which depends on the current magnitude and the characteristic distribution of contact and bulk resistances. The Joule heat leads to a temperature increase of materials, the sheet material softens, and a characteristic Michael Piott
[email protected] 1
Daimler AG, Sindelfingen, Germany
2
Institute of Low-Carbon Industrial Processes, German Aerospace Center (DLR), Cottbus, Germany
3
Department of Joining and Welding Technology, Brandenburg University of Technology (BTU) Cottbus-Senftenberg, Cottbus, Germany
nugget forms when melting temperature of material at faying surface is exceeded. Subsequently, the current is switched off and the nugget solidifies under electrode pressure during hold time. Finally, the electrodes are removed. With the increasing use of aluminum alloys in car bodies, the joining of aluminum alloys by RSW becomes more important. Besides lower density,
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