Thermal Characteristics of Narrow Gap GMA Welding at Vertical Position with Arc Swinging and Shifting

Research on thermal characteristics is the base for deeply understanding the process of narrow gap–fine wire–gas protection–one pass one layer–arc swinging and shifting–vertical welding. The plane analytic geometry method is adapted to solve the arc speed and welding line energy by analyzing the arc movement path. Based on classic heat source model of double ellipsoid, update of arc center position and orientation is achieved by coordinate transformation. The dynamic evolution of the weld pool under certain conditions is simulated, and thermal cycle curves of single layer and multilayer are extracted. The results show that the line energy of the process is pulsed and alternately assigned to both sides of the side wall, which lead to a narrow coarse-grained heat-affected zone (CGHAZ). The thermal cycle curve of CGHAZ presents the double characteristic of multi-peak, dwell time at high temperature is short, and cooling rate at low temperature is low. In addition, the weakest CGHAZ in the joint transforms into several micro-zones along the thickness of the weld, and the area ratio of reheated CGHAZ by normalizing, incomplete normalizing, and tempering is 3:2:5. If the thickness of the welding layer is properly controlled, the original CGHAZ of base metal are subjected to the grain refinement under the different layer welding thermal cycles conditions.