Stud welding  Stud welding is a technique similar to flash welding where a fastener or specially formed nut is welded onto another metal part, typically a base metal or substrate. The fastener can take different forms, but typically fall under threaded, unthreaded, or tapped. The bolts may be automatically fed into the stud welder. Weld nuts generally have a flange with small nubs that melt to form the weld. "Weld studs" are used in stud welding systems. Manufacturers create weld studs for the two main forms of stud welding: capacitor discharge stud welding and drawn arc stud welding  Drawn arc stud welding process joins a stud and another piece of metal together by heating both parts with an arc. The stud is usually joined to a flat plate by using the stud as one of the electrodes. The polarity used in stud welding depends on the type of metal being used. Welding aluminium, for example, would usually require direct-current electrode positive (DCEP). Welding steel would require direct-current electrode negative (DCEN). Stud welding uses a flux tip to aid in welding and a ferrule, a ceramic ring which concentrates the heat generated, prevents oxidation and retains the molten metal in the weld zone. The ferrule is broken off of the fastener after the weld is completed. This lack of marring on the side opposite the fastener is what differentiates stud welding from other fastening processes. Drawn arc studs range from a #8 to 1" diameter. The lengths are variable from 3/8" to 60" (for deformed bars). Arc studs are typically loaded with an aluminium flux ball on the weld end which aids in the welding process. Drawn arc weld studs are commonly made from mild steel and stainless steel. Short cycle stud welding is a faster form of drawn arc stud welding which can use capacitor discharge weld studs instead of drawn arc studs. This method can tolerate welding studs to thinner sheet metals than the drawn arc process, though it doesn't achieve welds that are as strong or penetrative. It also doesn't require the use of ceramic ferrules. Sometimes operators using this process use shrouding gas to reduce spatter. A type of stud welding called capacitor discharge stud welding differs from drawn arc stud welding in that capacitor discharge welding does not require flux. The weld time is shorter, enabling the weld to bond with little oxidation and no need for heat concentration. It also allows for small-diameter studs to be welded to thin, lightweight materials.