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Capacitor Discharge / Tip Ignition Stud Welding(CD)

The welding of fasteners to light-gauge sheet metals demands a system which minimises the depth-of-penetration of the weld. The capacitor discharge range of studs, which has been specially developed for this purpose has found increasing application in almost every field of light engineering - in many cases providing a spectacular saving in cost over other production processes.

Employing a weld time cycle of a few milliseconds, so that only the outer skin of the component and the end of the stud are melted, results in a shallow but strong weld. Consistent results are obtained in a wide range of materials, even on very light gauge sheet -- low carbon and stainless steels down to 0.5 mm. In most cases the reverse face can be pre-finished by painting, plastic coating, plating or anodising, before welding without fear of heat damage or distortion. Aluminium sheets are also suitable for stud welding with specially developed aluminium alloy studs (AlMg3).

Applications for Sheet Metal Fabrication :

Some of the fields using capacitor discharge stud welding are automobile body under frames, cookware & kitchen appliances, metal furniture, stainless steel equipment, insulation work (such as in air-conditioned rail coaches) and control panel fabrication. They are used, wherever appropriate, as fasteners or anchors.

Process:

In capacitor discharge stud welding, the welding energy is obtained from banks of capacitors which have previously been charged to the voltage selected for the particular application. This energy is discharged through the stud projection / tip, giving a high density current which disintegrates the small projection / tip on the base of the stud. This leaves an ionised gap between stud and work piece across which the welding current continues to flow in the form of an arc. Pressure from the return spring in the welding tool forces the stud onto the work piece, completing the weld in a split-second.

The capacitor discharge stud welding system operates on a single-phase 50Hz A.C. Mains supply at 220/240 volts.

Arc Stud Welding (SW)

The heat necessary for welding of studs is developed from a DC power source between the stud (electrode) [+] and the work piece [-] to which the stud is to be welded. Welding time and the plunging of the stud into the molten weld pool to complete the weld are controlled automatically through the power source.

The current range employed varies from 150 to 3000 amps. Because stud arc welding time cycles are very short, heat input to the base metal is very small compared to conventional arc welding. Consequently, the weld metal and heat-affected zones are very narrow. Distortion of the base metal at stud locations is minimal.

The most common stud materials welded with the arc stud weld process are low carbon mild steel, stainless steel (304, 310, 316) and aluminium studs for cookware, with argon gas shield. Other materials such as alloy steel are used on a special application basis.

Applications :

Arc stud welding is used extensively in the following fields : automotive, boiler and building construction; farm, industrial and domestic equipment manufacture; shipbuilding; etc. Some typical applications are attaching boiler tube studding; fastening linings or insulation in furnaces (such as refractory anchors); securing inspection covers; and welding of shear connectors and concrete anchors to structures such as steel decks on bridges.

Process :

[To view a detailed illustration of the Drawn Arc process please click here.]

The stud is loaded into a stud welding gun, the ferrule / arc shield is placed in position over the end of the stud, and the gun is properly positioned over the work piece. The trigger is then depressed, starting the automatic welding cycle. A solenoid coil within the body of the gun is energized. This lifts the stud off the work piece and, at the same time, creates an arc. The end of the stud and the work piece are melted by the arc. When the preset arc period is completed, the welding current is automatically shut off and the solenoid de-energized by the control unit. The mainspring of the gun plunges into the molten pool on the work to complete the weld. The gun is then lifted from the stud and the ferrule is broken off.

The arc stud welding system operates on a 3-phase 50Hz A.C. Mains supply at 440 volts using a DC power source with high open circuit voltage.

To learn more about the processes in EN ISO 14555, please click here

To see the many advantages of the stud welding process, please click here.

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