(A) study on the analysis of weld pool convection and seam tracking by considering the arc length characteristics in GMA welding

Abstract

Fusion welding is a joining method chosen mainly for assembling large metal structrues such as spips, bridges, piplines, heavy construction machinery, rolling stocks, and cars. Among the variety of fusion welding processess available, gas metal arc weldign(GMAW) is one of the most frequently used methods, primarily because it is highly suited to a wide range of applications, and also to automation. GMAW is an electric arc welding process which produces coalescence of metals by heating them with an arc established between the continuous filler metal electrode and workpiece. A number of the problems related to automating arc welding processes include modeling, sensing and control of the process. Among the problems, the modeling of the process is very useful not only for the control but also for the analysis of the process and determination of appropriate process parameters because the tip-to-workpiece distance can affect the weld pool form,ation and bead geometry. In this sutdy, the modeling of relationship between the tip-to-workpiece distance and welding parameters was proposed and the effect of tip-to-workpiece distance on the weld shape was investigated through the analysis of flow and heat transfer in the GMA weld pool. And finally, some weld seam tracking systems for butt joints were developed by using the realtionship between the welding current and tip-to-workpiece distance. CMAW systems are often used in the self-regulating mode where the power source has a flat or constant voltage characteristic, thereby producing the current change in response to the variation of tip-to-workpiece distance. This paper dealt firstly with one aspect of weld process modeling by mathematical analysis, representing the relationship between welding current and tip-to-workpiece distance. An experimental model was also proposed to predict the welding current variation. The linearized model which is able to determine the relationship of welding current to tip-to-workpiece distan...