Stud welding is a type of spot welding in which a bolt or specially formed nut is welded onto another metal part. The bolts may be fed automatically into the spot welder.

Weld nuts typically have a flange with small nubs that are melted in the welding process to form the weld. Studs have a necked down, unthreaded area for the same purpose.

Stud welding uses a type of flux called a ferrule, a ceramic ring that concentrates the heat generated, prevents oxidation and retains the molten metal in the weld zone.

A key factor that differentiates stud welding from other fastening processes is that the fastener is attached to the workpiece without marring the other side of the workpiece.

This provides highly reliable fastening for a wide variety of applications, and allows almost any size or configuration of a metal stud to be welded quickly to a workpiece, while providing maximum weld penetration and reliability, according to Image Industries Inc.. Image Industires Inc. (www.imageindustries.com) designs and manufactures stud welding equipment.

Capacitor Discharge (CD) stud welding uses very short weld times to permits the welding of small-diameter studs to thin, lightweight materials, Blake Hobson, president of Image Industries, said.

The weld cycle can be completed in 0.01 sec. on material as thin as 0.020 in. (0.5mm).

Such fast weld times minimize heat buildup, and result in welds that have very little distortion, discoloration or burning. Therefore, this process often is used when product appearance is a critical product feature, Hobson said.

Capacitor discharge stud welders use a capacitor storage system to produce a rapid electrical discharge, stud welding weld tools, and fasteners. Capacitor discharge stud welding does not use flux or ferrules.

“Because of the short weld times, you get a minimal amount of heat so it works nicely in cosmetic applications for kitchenware, appliances, and elevator control panel buttons, as well as the panels for ATMs,” Hobson said.

There are two types of capacitor discharge stud welding.

Contact capacitor discharge stud welding is a process in which the stud is loaded into the weld tool and positioned in contact with the workpiece. Energy then is instantaneously discharged from capacitors through the stud projection. Because the size of the ignition tip cannot handle the current density of the capacitor stored energy, it vaporizes, creating a gap that allows an arc to be formed. As the arc begins to melt the stud and workpiece, the two pieces are forced together.

The weld is produced as the metal cools.

Gap capacitor discharge stud welding offers shorter weld times with higher current densities compared with contact capacitor discharge stud welding. With such quick welding capability, this technique is particularly well-suited to cosmetic applications, since it produces very minimal marking on the back side of the material.

Image Industries recently introduced a CD66 Capacitor Discharge stud welder that is designed for the convenience and comfort of the operator.

It has a stud capacity to ¼ in. for steel and stainless steel, and is targeted at light industrial applications. Because it is a small unit with a weight of 10.5 lbs., it provides portability on the job. Its portability is enhanced by an its adjustable shoulder strap. The CD66 permits auto-selection of welding on the spot, by supporting both gap and contact welding, which gives it dual capability to perform the work of two tools in one. It comes in an engineering thermoplastic case that is designed to be rugged. It has been drop tested from 15 ft. It delivers 24 continuous welds per minute.