Welding is a fabrication process which involves the use of high temperature to melt and fuse two metals together. Sometimes, pressure also plays a significant part in the fusion of the two materials. Unlike other joining processes like soldering and brazing which do not require the melting of the base material, welding ensures that the base material melts and interacts microscopically with the filler material, if any.
Most times a consumable metal also called filler metal is melted to form a weld pool which ensures that complete fusion occurs. Various precautions are applied during welding to prevent oxidation of the weld pool. Filler metals are mostly coated with a flux which melts during the welding operation to produce inert gases and slag that cover the surface of the weld pool and prevent oxidation from taking place. Other times, the welding machine supplies the gases during the welding process.
Welding process can be powered by various means ranging from oxy acetylene gas, electricity, ultrasound, electron beam, laser, and friction. There are also welding procedures that can be used underwater, on land or in a pressurised environment.
List of Common Welding Techniques
There are different types of welding techniques, and depending on the nature and geometry of the base metal a particular welding technique may be more suited for the welding operation than the other.
The common welding processes are given below:
MIG welding technique – Gas Metal Arc Welding (GMAW)
TIG welding technique – Gas Tungsten Arc Welding (GTAW)
Stick welding technique – Shielded Metal Arc Welding (SMAW)
The metal inert gas (MIG) welding technique is a form of gas metal arc welding which involves welding metals through the use of steady electric current. This welding technique entails feeding a consumable electrode into a welding gun where it is melted and injected into the base metal, forming a weld pool and consequently fusing together. Concurrently, inert gas is pushed into the welding gun to shield the weld pool from external oxidants and contaminants.
To carry out MIG welding, base metals are first properly cleaned to remove rusts and contaminants. Similar to other types of welding, the welding professional is expected to wear their safety gears and ensure other safety protocols are followed while conducting the welding exercise.
MIG welding uses steady voltage power supply to form the electric arc which joins the workpiece together as the consumable wire is constantly fed through the welding gun. As this is happening, shielding gas is also introduced to the surface of the weld pool to protect it from impurities.
In MIG welding, the metal can be delivered through short-circuit welding, globular welding, spray welding or pulsed mode. The electrode can also be a normal hard wire or a flux core wire. Flux core wires do not require shielding gas because the flux forms slag which covers the surface the weld surface, protecting it from oxidation and impurities.
TIG Welding Technique
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The Tungsten Inert Gas (TIG) welding, also called Gas Tungsten Arc Welding (GTAW) is a welding technique makes use of non-consumable tungsten electrode to weld base metals together. TIG welding may or may not require a filler metal to form a weld pool. Inert gases like argon or helium are supplied to the weld pool to protect it from impurities.
Just like MIG welding, TIG welding also requires a constant supply of current to produce an arc between the tungsten electrode and the parent metal. But unlike MIG welding, the tungsten electrode is non-consumable.
TIG or Gas Tungsten Arc Welding (GTAW) is mostly used in the welding of slim parts of copper alloys, aluminium, magnesium, and stainless steel. However, it can be used to weld other types of metals. This form of welding requires a lot of technical wherewithal to successfully perform it, therefore constant practice and hard work is required to become good at it.
To perform TIG welding, an arc is formed between the tungsten electrode and the two metals to be joined. The arc produces enough heat which melts the metals and fuses them together as shielding gases are supplied to the weld surface to ensure there is no contamination.
The major components needed to perform TIG welding are:
Non-consumable tungsten electrode.
Inert gas supply (helium or argon).
Steady-current power supply.
Shielded Metal Arc Welding (SMAW)
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When performing a welding operation using Shielded Metal Arc Welding, a shielded electrode is used to form an arc with the workpiece. This results in the continuous melting of the electrode to form a weld pool. The electrode is shielded with flux which forms gases that protect the weld pool. With SMAW, the application of pressure is not necessary and this form of welding can be carried out in an open field.
SMAW is one of the oldest forms of welding and it is known for its ease of application. The suitable electrodes for every welding operation are carefully chosen to ensure uniform chemistry between the electrode and the parent material.
The fundamental process of SMAW involves the usage of shielded consumable electrode. The filler material is also called an electrode because it completes the circuit, giving rise to an arc which melts the electrode and parent metal, forming a weld pool.
To achieve the desired weld quality, an electrode must possess the following qualities:
It must be able to maintain a welding arc.
It must continuously melt to add to the weld pool.
It must be able to produce shielding gases which protects the arc and weld.
Flux-Cored Arc Welding (FCAW) Technique
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Flux-Cored Arc Welding (FCAW), just as the name suggests, involves the use of a consistently fed hollow electrode with its core filled with flux. FCAW makes use of the heat produced by the arc formed from the contact of the electrode and workpiece, to melt them and give rise to a weld pool which allows the fusion of the materials upon solidification. The flux in the core of the electrode also melts to produce gases which shield the weld from atmospheric contaminants.
An interesting feature of the FCAW technique is the ease of melting of the flux-core. This makes welding easy and it can be conveniently applied outdoors. Although there can be supply of inert gas from the welding machine through the nozzle to further protect the weld, but this is optional as the flux produces enough gases and slag to protect the weld. Upon solidification, the welded surface can be properly finished to get rid of the slag and reveal the finer weld texture.
Equipment required in performing Flux-Cored Arc Welding
Shielding gas equipment.
Welding is a very vital aspect of fabrication and metallurgy in general. It is a joining technique applied in almost every facet of engineering, therefore it is important to know what it entails and the various methods it can be carried out.
The four welding techniques discussed in this article are not the only known welding techniques. There are others, like Electron Beam Welding (EBW), Laser Beam Welding (LBW), and Atomic Hydrogen Welding (AHW). However, these other welding techniques are not as commonly used in practise as the ones discussed.