An electric arc is the flow of electric current through gases.
An electric arc is struck by short circuiting two electrodes and then with drawing them apart by small distance.
The current continue to flow across the small gap and give intense heat.
The heat developed by the arc is also used for cutting of metal.
The electrode is made of carbon or graphite and is to be kept negative with respect of work. The work piece is connected to positive wir. Flux and filler are also used.
Filler is made up of similar metal as that of metal to be welded.
If the electrode is made positive then the carbon contents may flow into the weld and cause brittleness.
The heat from the arc forms a molten pool and the extra metal required to make the weld is supplied by the filler rod.
This type of welding is used for welding copper and its alloy.
In metal arc welding a metal rod of same material as being welded is used as an electrode.
The electrode also serves the purpose of filler. For metal arc welding A.C or D.C can be used.
Electric supply is connected between electrode and work piece.
The work piece is then suddenly touched by the electrode and then separated from it a little. This results in an arc between the job and the electrode.
A little portion of the work and the tip of the electrode melts due to the heat generated by the arc.
When the electrode is removed the metal cools and solidifies giving a strong welded joint.