Fusion characteristics in P-GMAW of mild steel

The influence of process parameters on deposition and fusion characteristics of mild steel with Pulsed Gas Metal Arc Welding has been investigated using a transistorized power supply. A simple model of melting behaviour has been developed which allows the prediction of dilution behaviour and explains the interplay between mass and heat in P-GMAW. In order to predict heat affected zone area, a model driven from the former one has also been developed. Deposition characteristics were studied taking the care of studying the influence of each welding parameter at each time, whenever it was possible. Emphasis was given to shielding gas mixture which was found to significantly influence metal transfer mode and arc stability. A systematic approach to choose process parameters in Pulsed Gas Metal Arc Welding with a constant current power supply is proposed. It was found that mean current and welding speed play the most important role in determining fusion characteristics, thus, based on a simple model, methods of controlling these aspects are suggested. Emphasis was placed on understanding dilution behaviour. It was found possibility to develop.procedures allowing the independent choice of deposition rate and dilution behaviour and to give an account of many observations with simple models of melting phenomena. The developed model is combined with calorimetric heat transfer measurements to investigate the result that only a small fraction of the total process power is required to melt the observed fusion areas. A "dual Heat" source fusion model is suggested where plate melting is largely in response to direct arc heating, providing means of optimising plate dilution and thereby reducing the risk of fusion defects. A generalized representation of fusion characteristics is given which allows independent selection of required fusion characteristics to be assessed.