2005 Volume 23 Issue 2 Pages 252-258
Arc sensors have been widely used for real-time weld-seam tracking in various applications of MAG (Metal Active Gas) welding. Among the applications, the high-speed oscillating MAG process has an advantage over conventional MAG process in the accuracy and fast response of seam-tracking control due to its high sensitivity. For a relatively low current MAG welding in which short-circuiting transfers occur, however, fluctuations in the sensing signals caused by the electrical short-circuiting reduce the sensitivity.
The present paper describes the characteristics of the arc sensor focusing on the sensitivity to the torch oscillating frequency f in the low-current and high-speed oscillating MAG process. First, a mathematical model of the short-circuiting droplet transfer phenomena is established based on a conventional mathematical model of the spray transfer phenomena in MAG welding. Then, the relationship between f and the number of short-circuiting Ns is discussed using the model. Numerical calculation results reveal that, when f equals to around half Ns0, which is the value of Ns during welding without torch oscillation, short-circuiting transfers regularly occur at both the oscillating edges and the findings agree with the experimental results. Finally, numerical analyses in the frequency-domain show that the arc sensor indicates the maximum of sensitivity in a specified frequency range that short-circuiting transfers are synchronized with the torch oscillating motion. As a result, when f is set at around half Ns0, the sensitivity is maximized and an accurate control can be achieved in the high-speed oscillating MAG process even at low current levels.