Spot welding is one form of resistance welding, which is a method of welding two or more metal sheets together without utilizing any filler material by applying pressure and heat to the area to be welded. The process is utilized for joining sheet materials and uses shaped copper alloy electrodes to apply pressure and convey the electrical current through the work-pieces. In all forms of resistance welding, the components are locally heated. The material between the electrodes yields and is constricted together. It then melts, ravaging the interface between the components. The current is switched off and the “nugget” of molten materials solidifies composing the joint.

Resistance welding is one of the oldest of the electric welding processes in use by industry today. The weld is made by a combination of heat, pressure, and time. As the name resistance welding implies, it is the resistance of the material to be welded to current flow that causes a localized heating in the part. The pressure exerted by the tongs and electrode tips, through which the current flows, holds the parts to be welded in intimate contact before, during, and after the welding current time cycle. The required amount of time current flows in the joint is determined by material thickness and type, the amount of current flowing, and the cross-sectional area of the welding tip contact surfaces.

Advantages : ​a) Spot welding is quick & easy b) extra filler / flux not required c) speedy process d)Automation can be done e) can be weld similar or dissimilar metals f) thin sheet to multiple sheets can be welded g) easy available spares & consumables h) unskilled workmen can use machine giving small bit knowledge of welding.

Spot welding gun works on same spot welding principle as discussed above and are portable type. Most of the time, weld work piece are bigger that cannot be moved at welding machines to weld, hence these portable welding guns are used to weld components or word piece.These spot welding guns requires major spares & consumables like electrodes , tips, adapters, gun arms, shanks, holders, brackets, transformer, switch handle, gyro, busbar, flexible shunts, kickless cables, jumper cables, water cooling pipes tubes, hanger etc.

There are two types of spot welding gun – a) C- type b) X-type. Both are portable version

• Heat generation –H = I2R, where I is welding current and R is resistance.
• Time factor –H = I2RTK, where T is time & K is heat loss.

• Spot welding parameters are – Force, electrode face dia, squeeze time, heat or weld time, hold time & weld current.

• Usually Spot welding electrodes are main part & consumable of spot welding gun and welding machines, so selection of correct material for electrode is important.Common spot welding electrodes are made of Copper Chromium Zirconium comes under RWMA class-2 cover by IS-5182.
  ​For welding Steel, electrode material should be Beryllium copper – RWMA- Class-3 & for other electrical conductive material welding, you must use refractory metal like tungsten, tungsten copper, and molybdenum

• Spot welding electrodes – Cap tip, button tip, offset tip, straight, bend – single , double bend, elkonite faced, flat, centre, offset, angle offset, cranked, spade, jobbing, Threaded electrodes, composite electrodes, Male electrodes, swivel head electrodes etc.