- slide 1 of 4
Why is Welding so Important
Welding is a material joining process performed by application of heat with or without pressure and addition of filler material. The applications of welding are so varied and extensive that it would be no exaggeration to say that there is no metal industry and no branch of engineering science that does not make use of welding in one form or another. Varying from small scale industry to large scale industry and from small machines to large machineries, welding is applied everywhere. Construction of large ships, bridges, huge buildings, railways, roadways, automotive and aircraft construction, pipe lines, tanks and vessels, machinery parts depend a lot on welding technology.
- slide 2 of 4
The Classification of Welding Processes
Modern methods of welding can be classified, depending on the state of the material during welding (plastic or molten state), as follows:
- Plastic welding or pressure welding (explained below)
- Fusion welding or nonpressure welding (explained below)
They can also be classified, depending on the source of heat, as follows:
1. Gas welding
- Oxy acetylene or hydrogen welding (explained below)
- Air acetylene welding
2. Arc welding (explained below)
- Carbon arc welding
- Metal arc welding
- Gas metal arc welding (MIG)
- Plasma arc welding
- Electro slag welding (explained below)
- Submerged arc welding
- Flux cored arc welding
- Gas tungsten arc welding (TIG)
- Atomic hydrogen arc welding
3. Resistance welding (explained below)
- Butt welding
- Resistance butt welding
- Spot welding
- Seam welding
- Projection welding
- Percussion welding
4. Thermit welding (explained below)
5. Solid state welding
- Friction welding (explained below)
- Ultrasonic welding (explained below)
- Diffusion welding (explained below)
- Explosive welding (explained below)
- Cold welding (explained below)
- Forge welding
6. New welding processes
- Electron beam welding (explained below)
- Laser beam welding (explained below)
- Arc weld
- Hard pressing weld
- Oxy acetylene cutting
- slide 3 of 4
Some of the most important welding processes are explained below:
- Plastic welding or pressure welding:
In this process, the piece of metal to be joined is heated to a plastic state and then forced together by external pressure.
- Fusion welding or nonpressure welding:
In this type of welding method, the material at the joint is heated to a molten state and allowed to solidify. This include gas weld, arc weld etc.
- Oxy fuel gas welding:
In this type of welding, the heat is produced by a gas flame which is used for melting the base and the filler metal. This results in the formation of a weld between the two metals. The fuel gas may be acetylene or hydrogen and this is mixed with proper proportion of oxygen.
- Arc welding:
Arc welding is the most extensively used welding method. Here the source of heat is an electric arc which is produced by the electrode connected to the power supply. It is a fusion welding process.
This is a group of welding processes in which the coalescence of metals is the result of the heat obtained from resistance offered by the work piece to the flow of electrical current.
- Cold welding:
Cold welding is a solid welding process in which pressure at room temperature, produces coalescence of metals with substantial deformation at the weld.
- Diffusion welding:
Diffusion welding occurs in the solid state when properly prepared surfaces are kept in contact under predetermined conditions of time, pressure and elevated temperature.
- Friction welding:
Friction welding is the solid state welding process which produces coalescence of material by the heat obtained from a mechanically induced sliding motion between the rubbing surfaces of two cylindrical work pieces under pressure.
- Thermite welding:
Thermite is used in this process to melt the metal. After the metal is in a liquid state, it is poured between the two workpieces to form the joint.
- Electron beam welding:
Electron beam is a welding process which produces coalescence of metals with the heat obtained from a concentrated beam composed primarily of high velocity electrons impinging upon the surface to be joined.
In this laser beam welding method, metals are joined by impinging a concentrated coherent light beam upon the surface to be joined.
- Explosive welding:
Explosive welding is the solid state welding process in which the coalescence is obtained by a high velocity movement of the parts to be joined, produced by a controlled detonation.
- Ultrasonic welding:
Ultrasonic welding is a solid state welding process in which the coalescence is obtained by the application of high frequency vibratory energy as the work parts are held together under pressure.
A welding process producing coalescence of metals with the help of molten slag which melts the filler metal and the surface of the work piece to be welded is called electro slag welding. The weld will be shielded by this slag which moves along the full cross section of the joint as welding process.