In welding of small diameter pipe, delicate control of heat input is required because of counter heat flow against the welding direction. In the process without control, the heat flow causes too much heating and over penetration at the last quarter, and wide weld bead or melt down often occurs. These defects decrease the strength of the joint. In order to avoid these problems and to obtain the uniform weld bead over the entire circumference of the pipe, a new system was developed for automatic Tungsten Inert Gas (TIG) welding of fixed pipe. In order to estimate validity of the system, aluminum alloy pipe of 38mm in diameter was used. In the welding control system, visual sensing, speed control and fuzzy logic such as human skilled welder is doing in the welding process were adopted. The visual sensing device consists of a CCD-camera and a hyperboloidal mirror which are set in the pipe and capture inner image of the molten pool. The image was processed to find the edge of the molten pool. Then, the optimum welding speed was calculated by detected width of molten pool. As a result, the effectiveness of the system was confirmed.
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