Spot
welding is the most widely used form of resistance welding.
It is characterized by low cost, speed and dependability
making it a common electrical welding process.
Spot welding is done at certain points on metallic sheets.
The pieces to be welded are held between the two
electrodes. the spot welding process. When current passes through the electrodes, a
spot weld is produced between thesheets.
this type of welding the workpieces to be welded are pressed
together by mechanical pressure exerted through electrodes.
Electrodes are made up of pure copper er alloy of copper
The mechanical pressure may be developed by pneumatic
pressure or by hydraulic pressure.
The pressure remains applied till the weld cools and have
sufficient strength
Current required is above 4500 A and the voltage between the
electrodes is usually less than 2 volts. The open circuit voltage is less than
12 volts.
The time period of current is about 1/50 seconds for each 0,25 mm of total thickness of the
two shorts to be joined
To word the heating of junction faces between electrode and
work, the electrodes are made up of material having high electrical as well as
thermal conductivity.
Water-cooled electrodes are used to avoid the electrode
sticking.
Efficient spot welds
are possible only by a correct combination of current, pressure, voltage and
welding time
