Arc-Welded Studs

In stud welding, the heat of an electric arc drawn between the fastener and the work melts a quantity of metal, after which the two heated parts are brought together under pressure. Welded fasteners must be made of a weldable material, and one end of the fastener must be designed for welding. Stud welding makes leakproof, pressure-tight connections and is adaptable to either automatic or semiautomatic operation. Automatic welds can be made at rates of up to 60/min. Electric arc and capacitor discharge are the two main stud-welding processes. In this semiautomatic electric-arc process, the heat for end welding the studs is from motor-generator or transformer-rectifier supplied dc current passing through an arc from the stud (electrode) to the plate (work). Weld cycle depends on stud diameter and may vary from 0.1 to 1 sec. A high-strength bond is obtained because the full cross-sectional area of the fastener or stud is fused to the base metal. Electric-arc stud welding is best used when the base plate is heavy enough to support the full strength of the welded fastener. However, lighter-gauge materials are often arc welded. To avoid burn-through, the plate thickness should be at least one-fifteenth the weld-base diameter. To develop full fastener strength, basic plate thickness should be a minimum of one-third the weld-base diameter. The second basic stud-welding process derives heat from an arc produced by a rapid discharge of capacitor-stored electrical energy, with pressure applied to the stud during or immediately following the electrical discharge. Like arc-stud welding, the heat for end welding of studs is developed by passage of current through an arc from the stud (electrode) to the plate (work). A prime advantage of the capacitor-discharge system is its ability to weld studs to thin materials without great distortion, burn-through, or discoloration. Also, weld penetration is