The resistance spot welding process use two copper alloy electrode to concentrate weld current and forced between work to be welded. Produce coalescence in one spot for heat generated from resistance to the electrical current through work piece held together under pressure by electrode. It process usually the thickness range of sheet metal is 0.5 to 3.0 mm. the small spot is quickly heated until melting point, in this reason a nugget of welded metal after power supply removed. When the current is applied too long, which result in molten metal become expelled as welded splash (or) can be made a have right through the material become welded. In this spot welding used for welding steel sheet metal.
Resistance spot welding step by step Procedure:
- The weld sheet metal is cleaned together and that are free from dirt, oxide, grease and oxides.
- The electrode tip will be cleaned it should be conduct current; otherwise the electric resistance is generated between work piece and electrode.
- Both side of plate, the electrode are stick. When the pressures is created to the electrodes and maintain a particular time period is known as sequence of time for before starting of weld.
- Now, the current is passed through electrode. The weld time is, time of application of time taken. At the weld time during the process pressure to be maintained and weld current range of 3000 A to 100000 A, it passed to electrode at time of 0.1 to 0.5 sec. The step down transformer controls the magnitude of high current possible.
- The current is passed one electrode to another electrode through the work piece, a small area contact between the work pieces. This spot is known as resistance spot. The spot generate the temperature and increase above 900⁰
- After weld time completed, the current is shout down and pressure will be maintain a particular brief of time is called as hold time. So the heat metal solidified and form of weld hugest.
- After brief time the pressure released, then work piece is removed.
- Now water is supplied to the electrode because of avoid overheating of electrode. In this welding process, set proper welding current and time before welding.
The size and shape of weld gradually limited by size and contour of electrode. It welding configuration can be relatively simple and inexpensive.
Foot operated spot welding machine consist of as shown in figure. That should be having two jaws. One jaw is stationary (it consist of lower) and another jaw is movable (upper jaw). In between the two jaws, the sheet metals are placed and force is applied to per jaw through foot pedal and livers. The motion and pressure are provided from hydraulic or pneumatic operation.
Application of resistance spot welding:
- It mostly used in automobile industry and to weld sheet metal for mostly.
- In orthodontist`s clinic, small spot weld equipment used to resizing the metal “molar bands”.
- The different metal and alloys alloy steel, medium carbon and high carbon steels, low carbon steel can be welded.