2 - PROBLEMS ASSOCIATED WITH CONTINUOUS DC WELDING

Abstract

This chapter discusses the problems that are associated with continuous Direct Current (DC) welding. For all arc welding that starts at ambient workshop temperature, there is a rise in workpiece temperature as welding progresses. If welding continues for sufficiently long, a steady state is reached when heat input from the arc equals the heat lost from the workpiece by convection, conduction, and radiation. The steady state temperature might easily be a few hundred degrees Celsius, resulting in considerably greater depth of penetration and bead width at the end of a weld than at the start, even at constant welding current and arc energy. On a linear joint between the components with a high specific heat capacity, the rise in temperature is not normally large and poses no serious problems. For circumferential joints, particularly in thin walled tubular sections and in the materials with low specific heat capacity, weld bead geometry would almost certainly be adversely affected by undue rise in temperature caused by build-up of heat and over penetration or burnthrough might eventually occur. The chapter focuses on Tungsten Inert Gas (TIG) welding to participate in the development of the process to a sufficiently reliable state for precision work to be carried out with confidence.