Typical Welding Torch

Typical Welding set up

Capacitor Discharge Stud Welding

Capacitor Discharge (CD) stud welding is generally used to weld smaller diameter fasteners to thin base metals. Since the entire weld cycle is completed in milliseconds, welds can be made without pronounced distortion, burn-through or reverse side discoloration. As long as one end of the fastener is designed for CD welding, CD studs can be manufactured in almost any shape.

The fastener is placed against the work piece. Most CD studs have a special tip which provides precise weld-time control, for consistent, automatic welds.

The weld gun is activated and stored energy is discharged through the fastener melting the full diameter of its base and a portion of the parent material.

Spring-loading forces the fastener into the molten metal.

The fastener is held in place as the molten metal solidifies and instantly creates a high quality fusion weld.

Arc Stud Welding

Arc stud welding is generally used to weld large diameter fasteners to rougher and thicker base metals. Arc studs may be almost any shape and there are literally hundreds, however, they must have one end of the fastener designed for Arc welding. Mild steel, stainless steel, and aluminum are applicable materials for Arc welding.

A fastener and ceramic ferrule are firmly placed against the work surface under spring tension.

Upon triggering, the weld gun automatically lifts the fastener from the base metal and initiates a controlled electric arc which melts the end of the fastener and a portion of the base metal.

A ceramic arc shield concentrates the heat and retains the molten material in the weld area for maximum weld strength and reliability.

At the precise moment the fastener and the parent metal become molten, the fastener is automatically plunged into the work surface. The metal solidifies and a high quality fusion weld is completed.

For any production work on site a Welding Procedure Specification (WPS) will be required and shall be tested and formally approved following the requirements of a harmonised European Standard.

Prior to application of the process during production Pre-Production Samples (PPS’s) shall be carried to prove the equipment, set up and techniques are satisfactory. It is important these samples are welded under representative conditions to the production environment. Depending on the level of quality and importance of the production stud welds being made a PPS regime will determine the frequency of testing. As a minimum 6 samples would be performed at the start of any shift and be subject to visual examination and bend testing. This regime could increase to start and end of a shift or even, in the event of many studs to be welded, after a given number have been performed. For example every 100 stud welds are made, 6 samples are welded and tested.

The sketch above shows a typical scenario for inspection. The ‘hammer test’ should never be used for formal PPS qualification purposes.

The only inspection, in addition to the PPS regime, to be applied is a visual examination. This is really limited to ensuring consistent fusion around the base of the stud and most importantly the perpendicularity of the completed welded stud.