Systemization with CAD/CAM welding robots for bridge fabrication

Innovations for the sub-assembly process have been implemented with CAD/CAM multirobot welding system. There are 26 sets of arc welding robot have been under operation for steel bridge panel fabrication in NKK´s Tsu Works. The first step was taken in 1992. The box girder panel sub-assembly lines with 14 welding robots were developed. The second step, the plate girder panel sub-assembly line with 10 welding robots was developed in 1994. During the same period, the T-shaped transverse rib sub-assembly line with 2 welding robots was developed. The key technologies of welding systemization are classified into 4 groups, such as welding process, sensor, robot and computer system. Doubled welding efficiency has been attained with high-speed rotating arc welding process. Furthermore, this process is more effective to reduce panel deformation because of the lower welding heat input. The welding is stabilized with precise accuracy by multifunction arc sensor based on the high-speed rotating arc i.e. joint end detecting, bead end detecting and seam tracking arc sensor. The welding tasks of the panel are distributed into multiple robots and executed coordinately as if autonomous distributed robot system. All the welding robots are controlled by the teaching-less CAD/CAM system. This system is especially effective for these kinds of works where almost all the panels are different shapes. The line management system is installed to assure more effective production. The Ethernet LAN is used to communicate between the lines and office