Production of airplanes may be speeded up by a new ultrafast machine for welding aluminum sheets. Tests on duralumin strips like those used in airplane fuselages produced a spot weld of double the strength required by the government for rivets, taking just 1/300 second for the weld. The manufacturers assert the machine could replace with welds virtually all the 450,000 rivets that go into a four-engined “flying fortress” and that the time for building one of these big bombers might be cut in half. The weld is accomplished by a “pulsating” direct current of 25,000 amperes, at seven volts.