Short-circuiting

Short-circuiting
Further developments in welding steel with GMAW led to a variation known as short-circuiting or short-arc GMAW, in which carbon dioxide shields the weld, the electrode wire is smaller, and the current is lower than for the globular method. As a result of the lower current, the heat input for the short-arc variation is reduced, making it possible to weld thinner materials while decreasing the amount of distortion and residual stress in the weld area. As in globular welding, molten droplets form on the tip of the electrode, but instead of dropping to the weld pool, they bridge the gap between the electrode and the weld pool as a result of the greater wire feed rate. This causes a short circuit and extinguishes the arc, but it is quickly reignited after the surface tension of the weld pool pulls the molten metal bead off the electrode tip. This process is repeated about 100 times per second, making the arc appear constant to the human eye. This type of metal transfer provides better weld quality and less spatter than the globular variation, and it allows for welding in all positions, but generally the process is much slower than globular GMAW. Another difficulty is maintaining a stable arc, because it depends on achieving a consistent and high short-circuiting frequency, which can only be accomplished with a good power source, suitable welding conditions, and significant welder skill. Like the globular variation, it can only be used on ferrous metals.