Arc welding is a fusion welding technique that uses an electric arc to weld two or more workpieces. It is one of the most commonly used welding methods today. It may be done manually, automatically or semi-automatically.
The electrode used in arc welding may be consumable or non-consumable.
Metal Inert gas welding is an arc welding method that uses a consumable electrode.
Tungsten Inert Gas Welding is an arc welding technique that makes use of a non-consumable tungsten electrode.
Simple Diagram of Arc Welding:
An electrode is connected to one terminal of a power supply. Workpiece is connected to another terminal of the power supply.
The electrode is brought near the workpiece with a small air gap (say 3mm).
Electrons from the negatively charged cathode discharge into the positively charged anode at high velocity. This produces tremendous amount of heat in the anode. Meanwhile, positive ions from the anode discharge into cathode. This produces some heat in the cathode. Heat produced in the anode is always greater than the heat produced in the cathode.
Hence, in consumable electrode processes, to produce deep weld, electrode is made anode and workpiece is made cathode. In non-consumable electrode processes, the exact opposite is done. To produce deep weld, electrode is made cathode and workpiece is made anode.
The overall heat produced in the welding process is used to melt metal and fill the gap in the workpiece. A flux covering may be provided around the electrode to protect the arc and weld. If a consumable electrode is used, the electrode itself melts and fills the gap in the workpiece.
In many arc welding techniques, a filler metal (in the form of rod or wire) with low melting point is used. The usage of filler metal depends on the arc welding method, type of electrode and material of workpiece to be welded.
Advantages of Arc Welding:
- Arc welding equipment is simple and easy to construct.
- A wide range of metals can be welded.
- High quality welds can be produced with little effort.
- Arc welding can be easily automated.
Disadvantages of Arc Welding:
- Arc welding exposes the welder to harmful radiations.
- Protective equipments should be used.
- Manual arc welding requires dexterity.
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