Study On Mechanical Behavior Of Weld Formation During CO₂ Gas Shielded Arc Welding Weaving Process

During all-position weaving welding process, the forces of the weldpool liquid metal which have different effects on the weld formation will change their effects constantly when the welding torch at different positions and even have seriously effects on the shape and quality of the weld. Now, the researches of domestic and foreign scholars about weldpool focus on unweaving process, and there are few theoretical researches on the common used CO₂ gas shielded arc weaving welding in welding production. On this ground, based on the Gauss distribution, the model of strip heat source simulating the electric arc weaving was derived. And based on this heat source model, the dynamic development process of weldpool's three-dimensional shape from part penetration to full penetration during weaving welding was simulated. The Mechanical behavior of the weldpool at downhand weaving welding position, vertical weaving welding position, horizontal weaving welding position and overhead weaving welding position were analyzed and the weldpool liquid metal's flowing action under different forces was researched. The influences of weaving way on weld formation at different positions were analyzed. The theoretical mode of weldpool mechanical behavior and weldpool deformation were established, and the flow field and velocity field of weldpool were simulated. The results show that during downhand weaving welding process, the width and length of the weldpool increase quickly at the beginning, then slower, and when the weldpool doesn't change anymore, the width and length of the weldpool also don't change. The maximum depth of the weldpool increases gradually along with the time before the weldpool being full penetration. The temperature of the nodes near the welding seam can exceed 1100℃while the heat source is close to these nodes, and the temperature of these nodes will be less than 130℃while the heat source is away from them. If the temperature of the node near the welding seam is less than 200℃, the node's temperature-rising speed is smaller, and if the temperature exceeds 200℃, the node's temperature-rising speed is greater. The maximum flow velocity of the liquid metal during downhand welding appears at the position which is under the weldpool center. As for vertical weaving welding, the gravity has bad effect on the weld formation. During vertical-up welding process, the liquid metal of the lower weldpool will run down under gravity and the weld reinforcement is a little big. During vertical-down welding process, the liquid metal of the lower weldpool will run down under gravity and arc push force, and the welding seam in good shape is get by the welding torch weaving. The maximum flow velocity of the liquid metal appears at the weldpool center during vertical welding. During horizontal weaving welding process, when the oblique weaving angle of the horizontal welding is 45 degrees, the size of the gravity's component force causing the weldpool liquid metal running down reduces by 30%, and the bigger the angle, the less the gravity's component force causing the weldpool liquid metal running down. The maximum flow velocity of the liquid metal during horizontal welding appears at underside bevel. As for overhead weaving welding process, the weldpool which is at the state of falling head isn't supported by the solid metal, and the effect of the arc pressure on the weldpool must be controlled to reduce the effect of the gravity on the weld formation. The maximum flow velocity of the liquid metal doesn't appear at the position which is above the weldpool center, but below the weldpool center slightly during overhead welding. For whichever weld position, there are circulation phenomena at the weldpool center especially according the weldpool edges where the fluid flows.