 These processes use a welding power supply to create and maintain an electric arc between an electrode and the base material to melt metals at the welding point . They can use either direct ( DC ) or alternating ( AC ) current , and consumable or non @-@ consumable electrodes . The welding region is sometimes protected by some type of inert or semi @-@ inert gas , known as a shielding gas , and filler material is sometimes used as well . 
