In the case of arc welding, high current but low voltage is used. This is for two reasons.
The heating action of the arc on a piece of metal is largely dependent on "current density" at the end of the electrode, not the voltage. That is, the amount of current divided by the surface area of the electrode tip.
Note that resistance heating in the arc itself accounts for a small fraction of the heat production. This is due to the "negative resistance" characteristics of electric arcs. as current rises, resistance in the arc tends to drop rapidly.
Most of the heating action in arc welding is produced by free electrons in the arc impinging on the metal surface. Hence current density becomes an important factor.
High voltage would be very dangerous to the operator. Typical arc welding voltages are 20-40 volts. typical current is 80-300 amps.
Here remember the Ohms Law :
Current = Voltage / Resistance
High Current = Voltage / Less Resistance
High current is needed to heat and melt the material
http://www.esabna.com/EUWeb/AWTC/Lesson1... : -
1.8.2.2 The theory of electrical resistance is of great importance in the arc welding process for it is this resistance in the air space between the electrode and the base metal that contributes to the transfer of electrical energy to heat energy. As voltage forces the electrons to move faster, the energy they generate is partially used to overcome the resistance created by the arc gap. This energy becomes evident as heat. In the welding process, the temperature increases to the point where it brings metals to a molten state.
There must be a high voltage gradient in between those two electrodes , and with this, the medium in between them goes through an insulation breakdown and that leads to arc formation. The arc is nothing but a thin link of current flow.
Welders use very high current but realtively small voltages.
explain about arc welding
