Automatic Real-Time Bead Height Control with Arc Sensor (Report 2) : Development of Multi-Pass MAG Arc Welding System

The automatic seam tracking system by arc sensor method developed by NKK has an original feature, that a weaving arc in a groove performs groove surface tracking under constant arc length control (AVC or ACC) and the turning point of weaving is controlled by the condition when torch height reaches to constant preset level. In this system, weaving width well corresponds to groove width independently to variation of deposited amount of metal. Namely, variation value of weaving width is same as that of groove width. Based on this relationship, welding speed control system has been developed. Where, only the variation value of weaving width is used as detected parameter, and optimum value of welding speed to keep bead height constant is calculated and output at every cycle of weaving. The pulsed MAG arc welding system for multi-pass welding of V shaped butt joint has been developed. Main function of this system is adaptive microcomputer control with above mentioned arc sensor method, such as seam tracking, weaving width control and bead height control for every pass of welding.In addition, following functions are also composed: built-up sequence control where number of passes is automatically decided from weaving width, simplified operating system by man-machine dialogic style with liquid crystal display and a key board, and use of a couple of optical fiber cable for transmission of multiple control signals. This system has been already applied to the fabrication of steel box columns.