Shoji Imanaga

Development of torch position control and welding condition control technology for all‐position, multi‐layer GTA welding. Development of fully automatic GTA welding system for pipes (2nd Report)

Various welding operations involved in the construction of power generation plants, chemical plants, etc. requiring high standards of weld quality have routinely been performed by trained welders. Various occupational factors, such as what is known in Japan as 3K (kiken, kitsui, kitanai = dangerous, arduous, dirty) working as well as the shortage and advancing age of trained welders, have led to a growing demand for full automation of welding. To enable welding operations to be performed without the physical attendance or technical skills of human operatives, the authors have been previously engaged in the development of an all-position fully automatic GTA welding system providing advanced sensing functions and appropriate welding control functions of a nature and scope able to replace trained welders. Focused on stainless steel pipes, the proposed system offers a range of fully automatic welding and quality assurance functions from initial layer back welding, including tack welding, to final pass welding and appearance inspection of each welding pass. The first report describes the development of a wire height position control technology able to prevent electrode damage and poor weld bead quality due to wire deposition and wire contact. This report initially outlines the functions of the proposed fully automatic GTA welding system, then describes the laser slit sensor, the technology for measurement of the dimensions of the groove fitted with blocks (joint assembly attachments), the torch position tracking control technology in each welding pass and the technology for adaptive control of welding conditions. The results achieved by the system in multi-layer welding of pipes are finally evaluated.