An In-depth guide to MIG and TIG Welding: Everything you need to know

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An In-depth Guide to MIG and TIG Welding: Everything you need to know

Welding is a big subject. Essentially, it’s about fusing pieces of metal by melting them. And there are many ways of achieving that fusion – laser, electric arc, or flame being the usual three found today. 

The History of Welding

There’s evidence that the Egyptians used a basic form of welding by heating and hammering metal pieces together. A practice that evolved into “forge welding” and was the only method of welding that existed until the end of the 19th century. Sir Humphry Davy discovered the short-pulse electrical arc in 1800, and, entirely independently, the Russian scientist Vasily Petrov created the continuous electric arc in 1802. 

However, it wasn’t until 1881 when other Russian and Polish scientists used this idea to create the first electric arc welding process with carbon electrodes. This is the basis of the arc welding processes we use today.

The late 1800s was also the time when other processes like resistance welding and oxy-acetylene welding were created.

The aftermath of WW1 saw some significant advances in welding technology with the innovation of stud welding and an automatic wire feed which was the birth of MIG welding (more on that later). Shipbuilding changed to a heavily welded construction, and welding was used more in aeroplane manufacture. 

What are the common welding methods today?

 At the last count, there are approximately 90 different types of welding using various methods and materials.

The two main processes we use at Pegasus Precision are MIG and TIG, so this will be our focus in this article. 

Both types of welding use an electric arc to create a small, molten metal pool between the two pieces being joined. A filler material is added into that molten pool to avoid shrinkage and stress on the joint. Both processes use a shielding gas to protect the weld while it is being created. This shielding gas prevents the weld pool from being exposed to oxygen, hydrogen, and nitrogen in the air, making structural problems in the weld. Different shielding gases can help increase weld penetration and stabilise the arc. 

What is MIG welding?

The formal name is Gas Metal Arc Welding (GMAW) and divides into two sub-types MIG welding and MAG welding. Although very similar, there are subtle differences between MIG and MAG welding.

 

What is the difference between MIG and MAG welding?

MIG stands for Metal Inert Gas. MAG stands for Metal Active Gas. So the main difference is the type of shielding gas used in the process.

MIG is generally used when welding non-ferrous materials like aluminium, copper or exotic alloys. MAG is used for ferrous materials.

The two leading inert gases used for MIG welding are the noble gases argon and helium.

When MAG welding, you can use four types of shielding gas – Carbon Dioxide (CO2), Argon, Oxygen, and Helium. 

CO2 is classed as a semi-inert gas and is the most common type as it is relatively inexpensive and is the only one that can be used in its purest form. It provides deep penetration, making it ideal for welding thicker materials. However, it creates significant amounts of spatter, producing a less visually appearing weld and requires a post-welding clean-up operation.

If appearance is vital in the finished part, mixing a high percentage of argon with a low percentage of CO2 will create less spatter and provide a neat weld.

Although oxygen is a reactive gas, it’s useful to introduce a small percentage of it into the shielding gas to increase the fluidity of the weld pool. It does, however, create some oxidisation, so it is only used in mild carbon and low-alloy stainless steel welding. Not with aluminium or other non-ferrous, exotic metals.

Mixing helium into the shield gas creates a hotter weld and increases the molten pool bead speed, so it’s helpful when you need to improve productivity and speed up the welding process. As it’s a costly gas, it’s usually mixed with both argon and CO2. 

What is the MIG/MAG welding process?

Both MIG and MAG use the same equipment. Firstly, the welder attaches an earthing clamp to the workpiece. The filler material is stored on a reel and fed through the torch when the welder presses the trigger. When the filler material touches the workpiece, it completes the electrical circuit and creates an electric arc. This arc melts the materials and creates a small pool of molten metal. The filler wire is continuously fed into the pool, which the welder moves along with the torch.

When the welder presses the trigger, as well as feeding the filler wire through, it also activates the shielding gas to shroud the weld.  

What is TIG welding?

TIG means Tungsten Inert Gas, and it’s officially called GTAW (Gas Tungsten Arc Welding). It has some similarities with MIG/MAG welding in that it uses an electrical arc to create a molten weld pool which then has a filler material introduced.

It also uses a shielding gas, which is always inert, and usually argon. Helium can sometimes be mixed with argon if the workpiece has high thermal conductivity, like aluminium, as it creates a hotter arc. But, generally, argon is the shielding gas of choice for TIG welding. 

What is the TIG welding process?

Like MIG/MAG welding, the welder will connect an earthing clamp to the workpiece. However, unlike MIG/MAG welding, which uses an automatically fed filler material, the filler is manually added to the weld pool in TIG welding.

The welding torch uses a fixed tungsten rod, sharpened to a point, to create the arc. The welder uses their judgement on how far to position the tungsten from the workpiece then presses the trigger to start the current. If the tungsten is placed correctly, it will create an electrical arc to the workpiece, which melts the materials and forms a molten weld pool. The welder then feeds a sacrificial filler rod into the weld pool and moves the weld along the workpiece.

What are the pros and cons of MIG and TIG welding?

MIG/MAG welding is generally more suited to higher volume production runs. It’s a fast and versatile process, particularly with thicker gauge materials. As such, it’s a lower-cost process and relatively easy to teach.

However, it isn’t as precise as TIG welding, and the welds aren’t as clean, which may require a subsequent finishing process.

TIG welding is suited to low volume, high-precision welding. It is a slower process than MIG/MAG, so it has a higher cost and higher training content. The finished weld is neat and aesthetically pleasing, so it has particular use in stainless steel fabrication.

 

At Pegasus Precision, our welders are skilled in both MIG/MAG and TIG welding so that they can provide the highest quality, precision fabrications for any application. 

Contact us on 01233 801649 or email sales@pegasusprecision.co.uk to discuss your specific requirements.