MIG welding is the most widely used form of gas metal arc welding (GMAW) in metal fabrication, but there are times when TIG is the better choice. Here we’ll explain the similarities and differences, then delve into why we’d use one rather than the other.

GMAW Overview

Welding is the process of fusing separate pieces of metal into a single unit. It uses heat to create a small pool of molten metal, which is moved along the joint region to weld the pieces together. Many heating methods are used, but metal fabricators rely primarily on the electric arc.

Arc welding entails creating an electrical circuit between the electrode in a welding torch and the workpiece. Pulling the electrode away from the surface of the workpiece creates an arc across the gap, the temperature of which can reach over 6,000⁰F.

Forming a weld pool requires the addition of more metal, which is the purpose of the filler that’s fed into the arc. Inert gas is pumped through the welding torch to form a shield around the arc. Creating a stable region where oxygen is excluded keeps the arc stable and helps ensure a defect-free weld.

MIG Welding Basics

Metal inert gas welding, which is what MIG stands for, is a method where the electrode is consumed as the filler metal. It’s fed through the torch and into the weld pool automatically by the welding equipment, which means the welder needs only use one hand to hold the torch. The shielding gas is usually 75% argon and 25% CO2 and it flows at 35-50 cubic feet/hour.

About TIG Welding

In tungsten inert gas welding, TIG for short, the electrode and filler metal are separate. The welder holds the torch in one hand and feeds the filler in with the other. The electrode, which is not consumed, is made from tungsten.

Like MIG welding, TIG requires a shielding gas around the arc. This is usually 100% argon, flowing at 15-25 cf/hr. The reason for excluding CO2 from the mix is that this can react with tungsten to erode the electrode. It can also form tungsten oxides which would contaminate the weld.

TIG welding equipment comes with control, usually a foot pedal, for adjusting amperage “on the fly”. This gives the welder a high level of control over the arc.

The Arc Shape Difference

The arc shape is what results in the two welding methods being used in different scenarios.

The tungsten electrode and pure argon shield gas together create a narrow, focused arc. Conversely, the arc created by a MIG welder is larger and less stable. As a result, the TIG arc puts more energy into a smaller area to provide better metal penetration, and it can be positioned to a high level of accuracy. In contrast, MIG welding forms a larger melt pool but without the precision of TIG welding.

Welding Process Selection

The difference in arc shape determines what kind of fabrication task the two welding processes are best suited to.

The strengths of MIG welding are:
  • Welds can be made faster than with TIG
  • Works well with thicker materials
  • Well-suited to aluminum, mild steel, and stainless steel
  • Can be done in almost any orientation
  • More suited to automation
  • Doesn’t demand as high a level of joint preparation as TIG
  • Torches don’t overheat the way TIG welding torches can
The advantages of TIG welding over MIG are:
  • More precise process
  • Produces cleaner, more attractive welds
  • Welds are stronger, due to better penetration and accuracy
  • Less clean-up of spatter needed after welding
  • Good for thinner materials
  • Works with aluminum, copper, steel, and even titanium

Of relevance to anyone considering a career in gas metal arc welding, MIG welding is easier to learn because it doesn’t need the dexterity or amperage control of TIG.

The bottom line is that MIG welding is good enough for most fabrication tasks. However, if the weld will be on show, if the materials are thin, or if strength is critical, we will likely recommend TIG welding. TIG is more expensive, owing to it being slower and having some fit-up constraints, so if we propose TIG, it’s for the reasons listed above.

GMAW Services at Wiley

We carry out both MIG and TIG welding, but our MIG welders outnumber the TIGs six to one. This shows that the bulk of fabrication needs a robust weld that doesn’t have to look perfect. (Perhaps it will be painted or coated before going into service.)

If you need to get quality welding work done as part of a fabrication project or to meet a short-term need, we can help. Contact us and let’s talk about whether your job needs MIG, TIG, or another type of welding process.