Understanding Welding: Essential Techniques and Applications

In welding, two materials are joined together by being melted and then fused together at the melting point. This is the fundamental process that welding relies on.

In most welding methods, a filler material is also added at the joining point to cover the bond and provide additional strength.

Welding differs from similar processes, like soldering and braising. In these processes, the base materials are not melted. Instead, a filler material is just used to create a join.  

Welding is not always done with heat

The welding processes most people know of use heat to melt the materials being joined. Electricity and gas powered, heat-based methods are something most people are familiar with. Alternative welding methods that don’t use heat to melt the base materials are solvent welding, pressure welding and diffusion bonding.

What materials can be welded?

Welding is most used for metal, and most people mainly associate welding with metal. 

While this is the case, welding can be used to join other materials, including glass, thermoplastics and even wood.

There are many different welding methods that have evolved throughout history. The different methods offer a choice of:

• Quality levels

• Simplicity

• Working speeds

• Working environments

• Material welding possibilities

• Costs

The choice of method depends on several factors.

Arc welding methods

MIG, TIG and stick welding are all types of arc welding. They’re also methods that are all in common use.  

In arc welding, an electric current is formed between the base material being welded and an electrode rod. This is used to create a high temperature electric arc that melts the base material and filler material, creating a weld. Flux or shielding gases are also simultaneously used to protect the weld area from oxidation and contamination during the welding process. Oxidation and contamination will weaken the bond if it is allowed to happen.

To set up an arc welder, the metal workpiece is attached to the welder with a ground clamp. With the welder switched on and the electrode in contact with the workpiece, a strong electric current is created. The electrode is then pulled slightly off the surface, creating a high temperature electrical arc.

Different arc welders use different electrodes. They can also use different shielding gases, or they can use flux instead of shielding gases. We’ll explain how MIG, TIG and arc welding work next.

What is MIG welding and how does it work?

Metal inert gas (MIG) welding is also known as gas metal arc welding.

In MIG welding, an automatically fed wire is used as the electrode. It is fed through a welding gun at a continuous speed as the welder performs the weld. As it’s fed, it melts and creates the filler material used to cover the weld. An inert gas, normally argon, is also fed through the welding gun, creating a layer of shielding gas around the weld. Helium and carbon dioxide are also used as shielding gases.

Another type of MIG welding is flux core MIG welding, where flux is used instead of shielding gas.

The main benefits of MIG welding are:

• Faster than other types of welding

• Good for beginners

The main drawbacks of MIG welding are:

• High set up and maintenance costs

• During extended periods of use, you need to stop and let the welder cool down 

MIG welding is a versatile welding method that is used in lots of industries and in lots of applications.

What is TIG welding and how does it work?

Tungsten inert gas (TIG) welding is also known as gas tungsten arc welding.

TIG welding is similar to MIG welding at first glance, but the process is actually quite different. TIG welding is used to create high-quality welds, and it requires a great deal of skill on the part of the welder.

With TIG welding, a welding gun is fitted with a non-consumable tungsten electrode. This is used to create the arc and the heat for the welding process. Shielding gases are also fed through the gun during the welding process. The operator then simultaneously introduces a separate filler material with their other hand as they are performing the weld.

The main benefits of TIG welding are:

• The welder has greater control and can create high-quality welds

• Very useful for thin materials

The main drawbacks of TIG welding are:

• Slow speed

• Need for a highly skilled welder

Some applications where high-quality TIG welds are used are bicycles, aeroplanes and maritime applications.

What is stick welding and how does it work?

Stick welding is often referred to as simply ‘arc welding’, which can create some confusion.

Stick welding does not use a welding gun, like with MIG and TIG welding.

With stick welding, a consumable electrode rod is used as the electrode. Normally, this is made from steel. This electrode rod simultaneously creates the electric arc and heat for the weld while melting to provide the filler material. The rod is also coated in a flux that produces carbon dioxide as the weld is created, protecting it from oxidisation and contamination.

The main benefits of stick welding are:

• Simplicity and low cost

• Skills can be acquired relatively quickly

• Because stick welding can be done outdoors, it makes welding viable in all locations 

The main drawbacks of stick welding are:

• Slower than other welding methods

• Generally limited to ferrous metals

Arc welding is often used for things like structural repairs, construction or shipbuilding.

There are lots of other welding methods besides arc welding methods.

Gas welding, also known as oxyacetylene welding, is less popular than it used to be. It is, however, a well known, simple and cheap welding process. Nowadays, it’s generally used for repair work, or oxyacetylene is used for cutting metal rather than welding.  

Two interesting modern, alternative methods are electron beam welding and laser welding.  

Electron beam welding

In electron beam welding, a beam of high velocity electrons is fired from an electron gun, through a focusing lens and at two materials that will be welded together. This beam generates a high amount of heat on impact. The heat melts the materials, enabling a weld to be formed. The process is handled in a vacuum to prevent oxidisation and to make it more efficient. Filler material isn’t normally needed.

Electron beam welding creates deep penetrating, narrow width and high-quality welds. It is, however, a high-cost process that requires specialist equipment.

Laser welding

Laser welding is like electron beam welding in terms of both the process and the output.

Lasers are used to direct a high energy beam of light onto two materials that will be welded together. This beam heats the materials, allowing a weld to be formed. Laser welding is not performed in a vacuum and is performed either under atmospheric conditions or in a shielding gas. Filler material is not normally required.

Laser welding also produces accurate, high-quality, deep penetrating welds. Welding speed is also fast (as it is with electron beam welding). Laser welding is, however, more expensive than other types of welding.

Argon is a non-reactive and non-combustible gas that’s used as a shielding gas during welding. Other shielding gases, such as helium and carbon dioxide are also used. Shielding gases create a temporary atmosphere around the welding point while welding takes place.  

Why is welding done in an atmosphere of argon?

Having an atmosphere of argon (or of another shielding gas) around a welding point prevents the material that is being welded from reacting with oxygen, water or other elements in the normal atmosphere. Argon is non-reactive, and the welded material does not react with it when it is in a molten state.

If the welded material is left to react with normal atmospheric elements, this can lead to oxidisation or contamination of the weld. If this is allowed to happen, the weld point will be very weak. It will also contain pinpoint holes, an effect known as porosity.

Using argon creates stronger, longer lasting welds.