There are many definitions of a welding process. But the most comprehensive definition is Welding is a fabrication process to make high strength joint between two or more parts by heating to their melting temperature, with or without the application of pressure and with or without the use of filler metal. The filler metal has a melting point approximately same as the base metal.
The welding process is used to metallurgically join together two metal pieces, to produce essentially
a single piece of metal. The process results a ‘Permanent joint’. A good welded joint is as strong as the parent metal. The product is known as ‘Weldment’.
Classification of welding processes:
Welding process may be classified according to the source of energy used for heating the metals and the state of metal at the place being welded. Depending upon these factors welding processes are classified as
- Chemical welding (Oxygen+combustible fuel)
- chemico-mechanical(pressure gas welding)
- Electro- chemical (Atomic hydrogen welding)
- Electro – Mechanical (Electric resistance welding)
- Electric – Arc welding.
Again the above classified are divided into two groups as follows:
Pressure Process:
Forge welding:
It is a solid state welding process. In this process the two metal surfaces to be joined are bought in contact and then metals are joined by heating them to a high temperature and hammering them together.
Thermit Pressure welding:
Pressure thermit welding is a process in which the heat produced by the thermit reaction is utilized only for heating the ends of the pieces to be joined, while the actual joint formation occurs by solid pressure welding.
Pressure Gas welding:
It does not require filler material. Pressure Gas welding is used for joining pipes, rods, railroad rails.
In this process a weld is made simultaneously over the entire area of a butting surfaces with gas flames obtained from the combustion of a fuel gas with oxygen and the application of pressure. Pressure gas welding has limited uses because of its low flame temperature,but is extensively used for welding lead.
Electric Resistance welding:
In this process two metals are joined by passing a low voltage and very high current through the joints which melts the joint due to their contact resistance. External pressure is used to complete the weld. No fillers are used in Electric Resistance welding.
Fusion Process:
In this process, the material at the joint is heated to the molten state and allowed to solidify to make the joint, without the application of pressure. Here, some joints may be made without the addition of a filler metal, but a filler metal must be added to the weld to fill the space between the parts being welded.The filler metal deposited should ordinarily be the same composition as the base metal.
Gas welding:
It is a fusion welding process where two metals are joined by burning a combustible gas with air or oxygen in a concentrated flame of high temperature. Filler rod may be used to fill up the cavity during welding process.
Electric Arc welding:
Arc welding process in which two metals are joined by heating with an electric arc to the melting temperature and then allowed to solidify. Depending upon the thickness of the base plate, Filler metals may be used.
Radiant Energy welding
It this type of welding a beam of electron strikes the surfaces to be joined and produces heat which causes the metal to melt and fuse.
