Fusion Welding – Steps Involved, Types, Advantages, and Disadvantages

Fusion welding is the welding process in which two or more materials of similar composition or melting points are joined or fused with each other by melting the materials.
In many of the fusion welding processes, the filler material is added to the molten pool of metal required but some fusion welding can be carried out without using the filler material.
The filler material is added to increase the strength of the weld joint. The welds made without filler materials are called autogenous welds.
If the filler material used and the parent material are the same, then the weld produced in this type of welding is called homogeneous weld.
If the filler material used and the parent material are different, then it is called a heterogeneous weld.

The welding processes are basically divided into two categories:
1) Fusion Welding
2) Solid State Welding or Pressure Welding

In this article, we will discuss the first type that is fusion welding.
Opposite to fusion welding, no melting of material is done in solid-state welding and cold welding.

Unlike pressure or solid-state welding, no external pressure is required in the fusion welding process.

Welding Types
Welding Types

Steps involved in Fusion Welding:

1) At first, the parts to be welded are held in position and the molten metal is supplied to the joint.
2) The molten metal used to weld the two parts may come from the parent metals or a filler metal which may or may not have the composition of parent metal.
3) The joint surface becomes molten because of the heat from the molten filler or other source based on the type of fusion welding used.
4) After that, when the molten metal solidifies or fuses, the joint is formed and the fusion welding process is completed.

Types Of Fusion Welding:

1) ARC Welding 150 x5 with images of each
2) Oxy-Fuel Welding ( OFW )
5) Thermit welding
6) Solid Reactant Welding
7) Induction Welding

1) Arc Welding:
Arc welding refers to the group of welding processes in which the metals are heated to melting points by an electrical arc.
In some arc welding processes pressure is also applied to the workpiece for better weld strength and quality.
Most of the arc welding process makes use of filler material.

Arc Welding is further classified into the following types:
i) Shielded Metal Arc Welding (SMAW)
ii) Gas Metal Arc Welding (GMAW)
iii) Gas Tungsten Arc Welding (GTAW)
iv) Submerged Arc Welding (SAW)
v) Flux Cored Arc Welding (FCAW)
vi) Plasma Arc Welding (PAW)
vii) Carbon Arc Welding.

2) Gas Welding:
Gas welding is a welding process in which a strong high-temperature flame is used to weld two metal parts. The high-temperature flame is generated with help of flammable gases.
The flame is used to generate heat and raise the temperature of the metal piece at the place where the joint is to be made.
Due to the heat from the gas flame, the metal at the joints starts to melt. The molten metal is joined to another metal workpiece.
A filler material is also added to the molten metal to act as a binder. The molten joint is allowed to cool and solidify.
Many different combinations of gases are used to obtain a heating flame. The most common is oxygen-acetylene flame.

3) Thermite welding:
The third type of welding is thermite welding. In this type of welding process, a thermite compound is used to weld two metals together.
Thermite is a type of chemical composition of a metal powder.

3) Thermite Welding:
Thermite welding is a welding process in which a thermite compound is used to weld two metals together. Thermite is a type of chemical composition of a metal powder. Powder normally consists of a metal and a metal oxide. When this powder is ignited, it undergoes an extremely exothermic redox reaction. Here oxide from one metal transfers to the other metal. In this welding process, a huge amount of heat is generated for a brief period. The most common use of thermite welding is to join rail tracks in railways.
This process does not require any heavy machinery and is very fast.
This process is also used to repair rail tracks as the molten metal from
the reaction can be used to repair the tracks.

4) Oxy-Fuel Welding:
It is the type of welding process in which oxygen is used as fuel to produce a flame that heats and joins two metal surfaces. This process is also known as oxy-acetylene welding.
This welding process uses a combination of oxygen and a flammable gas mostly acetylene to create a hot flame to join objects. Oxygen and fuel are mixed in the right proportion within a handheld torch or blowpipe to produce a hot flame with a temperature of about 3200 degrees Celcius.
As steel melts at 1500 degree Celcius, this is the only welding process which can produce such high temperature by combining oxygen and acetylene to melt steel. So steel can be welded using this welding process only. While other non-ferrous metals with low melting points can be welded by using a mixture of oxygen and gases like hydrogen, propane, or coal gas in the oxyfuel welding process.

5) Induction Welding:
In this type of welding process, electromagnetic induction is used to heat the metal surfaces which are to be joined. An induction coil is present in the welding apparatus which is energized with a radio-frequency electric current. This welding process is mainly used to weld materials that are either electrically conductive or are ferromagnetic materials.
Electrical insulators and non-magnetic materials can also be welded using this process by implanting them with ferromagnetic or metallic compounds called susceptors.

6) Laser Beam Welding:

Laser Beam Welding is a fusion welding process in which two metal pieces are joined using a laser.
Laser Beam Welding is done by focusing the laser beam to the cavity between the two metal parts. The laser beam strikes the metal parts and produces heat which melts the material of the two metals or the filler material.
After cooling of the molten metal, a weld is formed which is very strong.

Fusion VS Pressure Welding 200 words

Advantages Of Fusion Welding:

1) Fusion Welding can be used to join dissimilar materials easily.
2) External filler material can be added easily.
3) No external pressure is needed.
4) Using this process, more than two components can be welded at a step.

Disadvantages Of Fusion Welding:

1) Due to intense heating and subsequent melting, many mechanical and metallurgical properties are affected.
2) Because of excessive heat input, high distortion takes place.
3) Noticeable heat affected zone exists around the weld bead due to excessive heat.
4) Welding two dissimilar metals is difficult specially if the metals have different melting points and coefficient of thermal expansion.

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