EXPERIMENTAL AND ANALYTICAL STUDY OF HEAT TRANSFER IN WELDING

Welding processes are used extensively as a means of joining metals together. The heat transfer that occurs during welding is important because of its influence on the mechanical properties of the base material. An experimental apparatus was constructed and experimental measurements were obtained for various welding speeds, shielding gas flowrates, and electrical power inputs. Temperature measurements were obtained employing sensors embedded in the base material, and the rate of heat transfer to the water coolant was also determined experimentally. The length and width of the weld bead was obtained by direct measurements and the depth of the weld bead was obtained by sectioning the weld specimen and doing a macro-etch procedure. The size of the arc was determined photographically. Numerical and analytical heat transfer models were developed to relate the temperature distribution in the base material to the heat input from the arc and its heat flux distribution. These heat transfer models were also used to determine the importance of the heat conduction in the direction of motion. The significance of this phenomenon was shown to depend on a dimensionless velocity. The importance of this effect was also studied with numerical heat transfer models. It was found that when the heat conduction in the direction of motion is not accounted for, the models predict a lower heat input and also underestimate the extent of the melt region. The most accurate heat transfer model was used to determine the heat input and the radius of the heat source by comparing calculated results with experimental measurements The values of the heat source radius obtained from the model were shown to compare favorably with experimental observations. The effective thermal conductivity of the melt was found to have a strong influence on the predicted weld pool dimensions and the rate of heat transfer to the base material