Stud Welding : The Drawn Arc Stud Welding Process
Probably no other technique has been more important to the development of humankind than welding. Welding is a technology that provides the fastest, strongest, and most economical method of joining metals together. The welding can be done with many processes such as arc, resistance, friction, and percussion. Stud welding is the common name applied to several different methods of securing bolts, studs, etc. to a workpiece. Compared with processes such as drilling and tapping, it is faster and easier.
Stud Welding Process
The Drawn Arc Stud Welding process utilises the heat generated by an electric arc to melt a very small area and applies pressure to make the joint. The stud welding operation consumes a very short time (portions of seconds) to generate the weld. This short duration can significantly lower the heat input, minimize the risk of distortion and produce a limited fusion zone (FZ) and heat-affected zone (HAZ).
The process can quickly weld steel bolts or studs up to about 25 mm diameter or configuration of a metal stud to a workpiece, with maximum weld penetration and reliability. The process may also be used for stainless steel, copper, and brass items. Aluminum can be welded using the capacitor discharge method.
On depressing the gun trigger, the stud is automatically lifted off from the base material and then a pilot arc is established, melting the end of the stud and the local plate surface. When the arcing period is complete, the current is automatically shut off and the stud is driven into a molten pool of weld metal, attaching the stud to the plate.
Apart from the stud welding gun, the equipment includes a control unit for timing the period of the current flow. Solid flux is contained within the end and centre of each stud to create a protective atmosphere during arcing. The ceramic ferrule that surrounds the weld area not only restricts the access of air to the weld zone but also concentrates the heat of the arc and confines the molten metal to the weld area.
To be Continued….
A proper stud welding process requires a suitable power unit and control equipment for plunging the arc and controlling the various operations. The power unit can be of a conventional type or may consist of a group of capacitors that, after charging, provide a very fast discharge.
Capacitor-Discharge (CD) stud welding welds studs with a small tip on the base, which burns away and ignites the arc. Arc duration is only a few milliseconds. This method is very suitable for welding on to thin metal, as there is little dispersal of heat to the surrounding metal, which means that the surface finish or treatment on the reverse side is not destroyed. The welding time is 2–5 ms, and studs of up to 8 mm diameter can be welded.
A variant of the arc method is the Short-Cycle (SC) method. Short-Cycle welding is a special drawn-arc stud-welding process with a very short weld time, generally, less than 0.1 seconds and the method can be used both with and without a ceramic ferrule and/or shielding gas. The benefit of ‘ferruleless’ welding is that the base material to be welded to can be thinner in proportion to the diameter of the stud (down to 1:8), and the welding process requires minimal surface preparation.
Stud Welding Advantages
Stud welding, instead of using rivets or drilling holes, has advantages such as high efficiency, good welding quality, reliability, and repeatability. Drawn Arc stud welding with ceramic ferrule shielding and Capacitor Discharge stud welding is the most common type of stud welding.
The Drawn Arc stud welding allows a type of shear connector or headed stud connector, to be rapidly fastened to the top flange of the steel beams. Due to its advantages over other forms of shear connection such as rapid installation and the fact that they were equally strong and stiff in shear in all directions normal to the axis of the stud, the stud connector became one of the most popular types of connector used in composite construction.
Nowadays, stud welding shear stud/connectors to structural steel are essential to most major construction projects because labor costs are dramatically reduced with arc stud welding. This is because through-hole preparation is eliminated and the process can be completed by a single worker.
MASON Shear Connectors are widely adopted and commonly used in Singapore and other South East Asia countries, for example, Malaysia, Indonesia, and Thailand.