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Development of low stress No Distortion Welding for Industrial Applications

Final Activity Report Summary - LSND-WELD (development of low stress no distortion welding for industrial applications)

A stress and distortion mitigation technique for Tungsten Inert Gas (TIG) arc welding thin sheet is presented. The proposed welding technique incorporates a trailing heat sink (an intense cooling source) with respect to the welding torch, and it is also named Low Stress No Distortion (LSND) welding. The development of this mitigation technique is based on both detailed welding process simulation using advanced finite element method and systematic laboratory trials. For understanding well LSND welding, finite element method is used to investigate the mechanism of the technique.

With detailed simulation, it is found that by the introduction of a heat sink at some distance behind the welding arc, a saddle shape temperature field is formed due to the cooling effects of the heat sink; there exists the lowest temperature in the zone where the heat sink is applied. High tensile action on surrounding zone is generated by abrupt cooling and contraction of the metals beneath the heat sink, which decreases the compressive plastic strains developed in heating process, and therefore mitigates the residual stresses and plastic strains within and near the weld.

For developing LSND technique, a production level system has been made for LSND welding. In the unit of LSND welding, the heat sink is made to provide a localised intensive cooling action at the weld that just solidified and still at high temperature, and is achieved by an impinging cooling jet from a nozzle to the top surface of the weld. The cooling intensity can be adjusted through controlling the coolant amount and the distance between welding arc and heat sink. Test welds have been successfully welded using LSND welding prototype. With LSND technology, buckling distortion-free thin-walled welded structures have been achieved with low welding residual stress. The LSND technique is an economical and efficient technology, the research also proved that no harmful influence on the microstructure and mechanical property of the weld has been found.

With more and more weight saving designs being done, LSND will be a popular welding technology within sheet metal fabrication in the aerospace, automotive and ship building industries. The coolant doesn't make any extra-noise during the welding process and is not harmful to people and environment.