MIG welding fuses metal by adding a continuous feed of filler metal which joins the two surfaces being welded by and electrod arc. Metal is only deposited where the electrode comes in contact with the metal. Shielding is provided by inert gases to control arc and heat of weld. Typically MIG welding is used on thicker materials where a heavy seam is desired and allowable. If used on thin materials, the risk of burning through the layers is higher than with TIG welds.