Stud Arc Welding Process
Stud welding is a type of arc welding process, wherein the welding is done through an electric arc drawn between the metal studs, bolt rivet or a similar part, and the base metal.
The stud arc may be categorized into two methods, the Nonconductor ferrule method and the Semi-conductor cartridge method.
Nonconductor ferrule method
Nonconductor ferrule is made up of porcelain or ceramic, surrounds the studs. It Is a non-conductor of heat and electricity that is not melted during the process. In this method, Arc is ignited by touching the stud with the workpiece and moving it a certain distance.
Semi-conductor cartridge method
The semi-conductor cartridge method is a ferrule, non-conductor cartridge placed between the stud and the base metal, conducts current through it, and helps to initiate the arc. The cartridge melts partially during the welding operation. The cartridge is made up of a composition similar to the covering or coating of metallic stick electrodes.
Nonconductor ferrule method
STUD to be welded is held in the collet chuck of the welding gun and non-conductor porcelain or ceramic ferrule is placed around the welding end of the stud. Current and timing controls are set in the controller unit. The welding gun is positioned on the base metal surface where a stud is to be welded. Trigger pressed and the stud is lifted about 1.5mm, thus drawing an electric arc between the stud and the base metal. The arc melts the end of the stud, base metal, and the flux. The flux produces a protecting atmosphere that remains almost confined within the ferrule boundary. After the preset time is gets extinguished and the solenoid coil de-energized. This releases spring pressure and the stud is plunged into the molten metal pool in the base metal. The end of the stud and the base metal are fused together and solidify inside the ferrule. Once the welded joint has cooled, the ferrule may be removed by breaking the same. A new ferrule will be required for the next stud welding operation. Studs from 3mm to 30 mm may be welded. Usually, the arc current (up to 400 Amps.)and arc time(0.08 to 1 second)will depend upon the diameter of the stud and the type of base metal. The end of the stud and the base metal are fused together and solidify inside the ferrule. Once the welded joint has cooled, the ferrule may be removed by breaking the same. A new ferrule will be required for the next stud welding operation. Studs from 3mm to 30 mm may be welded. Usually the arc current (up to 400 Amps.)and arc time(0.08 to 1 second)will depend upon the diameter of the stud and the type of base metal.
On one end stud is held in the collet and on the other it is resting on a cartridge made up of compositions similar to metallic arc stick electrode coatings. This coating partially melts, forms a slag, and protects the molten metal from contamination during the stud welding operation. Stud and cartridge are resting against the base metal under spring load or air pressure. The arc between the stud and the base metal is started through the cartridge and the arcing time depends upon the cartridge size. Under the arc action, the shaded portion of the cartridge meets away and the stud plunges into the molten pool in the base metal, thus completing the weld. Both DC and AC power supply can be used for welding purposes. Stud of any material, for which cartridge of suitable composition is available, can be welded.
Equipment used in stud arc welding
Welding gun located the stud on the place where it is to be weld. On the welding end of the stud, there is a cavity filled with the flux and scaled. The flux contains constituents which stabilize the arc, de-oxidize, and protect the molten metal from contamination, A porcelain or ceramic ferrule is placed around the stud before welding .This ferrule performs the following functions:
It minimizes the metal losses when welding in the vertical and overhead positions. Gives a suitable profile to the welded joint. Keeps the arc heat concentrated in the weld zone, lower cooling.
AC/DC Power source supplies the current(up to 400 Amps.)for arcing action.
Control unit energies the solenoid coil which acts against the action of the spring and the stud gets retracted by a predetermined distance.
Stud welded metals
Stainless steel, Carbon steel, Low alloy steel, Heat treated structural steel, etc.
stud welding is a simple, efficient, economical and speedy process of welding pins, bolts, studs, rivets, rods, etc. But it has some limitations also such as:
Stud shape and size are limited because the stud design must permit chucking of the stud for welding.