14. Welding Parameters

Weld quality and weld metal deposition are both influenced by the various welding parameters. These parameters are, welding current, arc voltage, welding speed, electrode feed speed, electrode extension, electrode diameter, electrode orientation, electrode polarity, shielding gas composition. Each of these parameters has influence to a varying degree on the deposition rate, weld bead shape, depth of penetration, cooling rate and weld induced distortion. To achieve a sound welded joint proper selection of welding parameters is needed. Hence a proper understanding of the effects of these parameters or process variables is required. Weld penetration in a welding process is driven by electromagnetic force, surface tension gradient, buoyancy force and impinging force of arc plasma. High temperature gradients within the molten weld pool results in variation of the surface tension over the weld pool surface. This surface tension gradient changes the convection mode of the molten metal in the weld pool. This is known as Marangoni convection. The cooling rate of the weld zone determines the metallurgical structure of the weld metal and the HAZ. As adverse microstructural transformations may take place in the HAZ, it is preferable to choose such welding parameters which also keep the HAZ to a minimum.