Welding can be defined as one of the manufacturing processes by which two or more similar or dissimilar materials can be joined permanently by coalescence formation with or without the applications of external pressure, heat or filler material. Fusion of faying surfaces of parent materials is not necessary for weld bead formation. On the basis of base material fuses or not, welding processes can be broadly classified into two groups—solid state welding and fusion welding. If faying surfaces of parent materials along with filler material melt down to form weld bead, it is termed as fusion welding. On the other hand, if no melting takes place during welding, then it is termed as solid state welding. However, in solid state welding, parent parts may be heated to an elevated temperature (but below its melting point).
What is fusion welding?
Fusion welding processes are all those welding processes where faying surfaces of parent part as well as filler material melt down during welding for weld bead formation. So heat is always associated with these processes. External application of pressure is not required for these processes, except for resistance welding group where substantial contact pressure needs to be maintained during welding for sound joining. Filler material may or may not be applied.
Examples of fusion welding processes
There exist a large number of fusion welding processes and the same can be further grouped on the basis of source of heat. Such processes where heat is applied by means of electric arc are termed as arc welding process. Similarly, all gas welding processes, resistant welding processes, and intense energy welding processes are basically examples of fusion welding. A list of such processes is provided below.
- Arc welding processes
- Shielded Metal Arc Welding (SMAW)
- Gas Metal Arc Welding (GMAW)
- Tungsten Inert Gas (TIG) welding
- Submerged Arc Welding (SAW)
- Flux Cored Arc Welding (FCAW)
- Electro-Slag Welding (ESW)
- Electro-Gas Welding (EGW)
- Arc Stud Welding (SW)
- Carbon Arc Welding (CAW)
- Atomic Hydrogen Welding (AHW)
- Gas welding processes
- Air-Acetylene Welding (AAW)
- Oxy-Acetylene Welding (OAW)
- Oxy-Hydrogen Welding (OHW)
- Pressure Gas Welding (PGW)
- Resistance welding processes (many consider this as solid-state welding)
- Resistance Spot Welding (RSW)
- Resistance Seam Welding (RSEW)
- Projection Welding (PW)
- Percussion Welding (PEW)
- Flash Welding (FW)
- Upset Welding (UW)
- Intense energy welding processes
- Plasma Arc Welding (PAW)
- Electron Beam Welding (EBW)
- Laser Beam Welding (LBW)
Advantages of fusion welding processes
- Filler material can be applied easily. So a large lacuna can be filled.
- No need to apply external pressure, so primary shape of the components does not matter (a suitable shape is required to uniformly apply pressure).
- Joint design and edge preparation are not crucial as these parameters affect only achievable penetration.
- More than two components can easily be welded at a step.
Disadvantages of fusion welding processes
- The process is associated with distortion and residual stress generation as it involves melting and solidification.
- Palpable heat affected zone (HAZ) exists in the welded components. HAZ is always considered as the weak portion in welded assembly.
- Mechanical properties of parent materials are also severely affected by intense heating.
- Joining dissimilar metals by fusion welding is challenging task, especially if the metals have substantially different melting point and coefficient of thermal expansion.