Active In-Process Control and Fabricating Precision Improvement of Weld Distortion by Using Temperature Distribution Control

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It is well known that evaluating welding distortion and residual stress is important in order to assure material weldability, structural fabricability, and structural integrity. Prediction of welding distortion and its reduction are essential in order to control dimensions and reduce the fabrication cost of welded structures. Therefore, from the viewpoint of manufacturing efficiency, in-process control of welding distortion is more desirable than post-welding rectification or other methods. There are many methods for predicting welding distortion and residual stress, and they are useful for developing an in-process method for controlling weld distortion and residual stress. Welding distortion and residual stress can be calculated under various welding conditions and for various configurations of welded structures by the thermal elastic-plastic analysis. Methods using mechanical prestraining, cooling, optimizing the welding sequence, or using vibration have been developed for residual s … More tress control in welding. Conventional in-process control of weld distortion is performed by using restraint, elastic prestraining, preheating, preheating or/and stretching, or heat control by cooling. These methods have been applied to actual welded structures, but the reduction mechanism-of welding distortion has not been completely studied because most of these techniques were only experientially established for specific conditions. The easiest way to reduce welding distortion is in-process heat control, when both the equipments needed to prevent distortion and the applicability to general purpose are considered. Therefore, in-process control of welding distortion by using a heating or cooling source in addition to the welding torch is considered to be very practical for actual use. The effectiveness of the in-process controlling method is verified by experiment and by three-dimensional thermal elastic-plastic finite element analysis in a welded joint. The appropriate conditions are determined through studying the mechanism by which welding distortion is reduced, and the effectiveness of the in-process method during welding is finally validated. Less