The process by which two metal or non-metal pieces are joined by heating them to the melting point is known as Welding. Electric welding is a process in which two metal pieces are joined together by the heat produced due to the flow of electric current. Due to the reliability of welded joints in comparison to riveted or bolted joints and other welding techniques (such as gas welding), electric welding has been adopted in many fields.
Types of Electric Welding :
There are two methods by which electric welding can be carried out. They are,- Resistance Welding.
- Arc Welding.
Resistance Welding :
In electric resistance welding, two metal pieces are joined by the passage of a heavy current while they are pressed together. The two metal pieces are connected to a suitable electric current by means of electrodes for sufficient time while the surfaces of the metal pieces to be joined are in contact with one another.
The conduction of electric current through metal pieces heats up the surfaces to be joined due to the resistance offered to the flow of current. Once the temperature reaches welding temperature the metal surfaces to be joined will melt and change to a plastic state. Then by applying strong mechanical pressure from both sides with the help of electrodes, two metal pieces are fused together thus completing the weld.
In resistance welding, a heavy current (above 100A) at a low voltage (4-12V) is used for joining metals. Since it is easy to obtain a low voltage high current power supply through a transformer, ac supply is found to be more suitable for resistance welding. Some of the applications of resistance welding are welding rods, tubes, wires, pipes, tanks, refrigerators grills, various containers, sheet metal structures, etc.
The following are the various types of electric resistance welding methods,- Spot Welding.
- Projection Welding.
- Seam Welding.
- Butt Welding.
Arc Welding :
Electric arc welding is the process in which the metal pieces to be welded are brought to the proper welding temperature at the point of contact by the heat liberated at the arc terminals and in the arc stream. So that metals are completely fused into each other, forming a single solid homogenous mass after it solidifies.
In electric arc welding, the electrode and metal piece are connected to the suitable source of electric current, they are brought into contact for a very short time and then separated by a small gap which results in an arc being initiated due to the ionization of the air medium between them. The initiated arc will generate intense heat due to which the metal and filler metal will melt and thus form a joint as shown below.
So, an arc-welded joint is a union of metal parts made by localized heating without any pressure. Hence this type of welding is also known as non-pressure welding. The arc length required for welding depends upon the following factors,
- The type of electrodes used and surface coating.
- The position of welding.
- The amount of current used.
For arc welding process, the temperature of the arc should be 3500°C. Both ac and dc power supplies can be used for the arc welding process. Generally, for ac supply, a voltage in the range of 70 to 100V, and for dc supply, a voltage in the range of 50 to 60V is used to initiate the arc. But once the arc is initiated, 20-30V is sufficient to maintain it.
The arc welding method is used in various fields such as repairing broken parts of machines, shipbuilding, joining of pipes and penstock, construction of buildings and bridges, automotive industry, aircraft industry, manufacturing of vehicles, implementation of railroads, welding of ferrous, non-ferrous and thin metals, etc.