Welding

Welding is a process for joining two similar or dissimilar metals by fusion. It joins different metals/alloys, with or without the application of pressure and with or without the use of filler metal. The fusion of metal takes place by means of heat. The heat may be generated either from the combustion of gases, electric arc, electric resistance or by chemical reaction. 

During some type of welding processes, pressure may also be employed, but this is not an essential requirement for all welding processes. Welding provides a permanent joint but it normally
affects the metallurgy of the components. It is therefore usually accompanied by post weld heat treatment for most of the critical components. 

The welding is widely used as a fabrication and repairing process in industries. Some of the typical applications of welding include the
fabrication of ships, pressure vessels, automobile bodies, off-shore platform, bridges, welded pipes, sealing of nuclear fuel and explosives, etc.

Most of the metals and alloys can be welded by one type of welding process or the other. However, some are easier to weld than others. To compare this ease in welding term ‘weldability’ is often used. 

The weldability may be defined as a property of a metal which indicates the ease with which it can be welded with other similar or dissimilar metals.

Weldability of a material depends upon various factors like the metallurgical changes that occur due to welding, changes in hardness in and around the weld, gas evolution and absorption,
extent of oxidation, and the effect on cracking tendency of the joint. 

Plain low carbon steel (C-0.12%) has the best weldability amongst metals. Generally, it is seen that the materials with high castability usually have low weldability.

Classification of Welding:

Advantages & Disadvantages of Welding:

Advantages:

1. Welding is more economical and is much faster process as compared to other processes (riveting, bolting, casting etc.)
2. Welding, if properly controlled results permanent joints having strength equal or sometimes more than base metal.
3. A large number of metals and alloys both similar and dissimilar can be joined by welding.
4. General welding equipment is not very costly.
5. Portable welding equipments can be easily made available.
6. Welding permits considerable freedom in design.
7. Welding can join welding jobs through spots, as continuous pressure tight seams, end-to-end and in a number of other configurations.
8. Welding can also be mechanized.

Disadvantages:

1. It results in residual stresses and distortion of the workpieces.
2. Welded joint needs stress relieving and heat treatment.
3. Welding gives out harmful radiations (light), fumes and spatter.
4. Jigs and fixtures may also be needed to hold and position the parts to be welded
5. Edges preparation of the welding jobs are required before welding
6. A skilled welder is required for the production of good welding
7. Heat during welding produces metallurgical changes as the structure of the welded joint is not the same as that of the parent metal.