Electric discharges can convey substantial energy to the electrodes at the ends of the discharge. A spark gap is used in internal combustion engines to ignite the fuel/air mixture on every power stroke. Spark gaps are also used to switch heavy currents in a Marx generator and to protect electrical apparatus. In electric discharge machining, multiple tiny electric arcs erode a conductive workpiece to a finished shape. Arc welding is used to assemble heavy steel structures, where the base metal is heated to melting by the arc's heat. An electric arc furnace sustains arc currents of tens of thousands of amperes and is used for steelmaking and the production of alloys and other products.