When you have two metals which need to be joined securely, you need a weld - but how do you decide between MIG vs TIG welding? Metal inert gas (MIG) and tungsten inert gas (TIG) welding each have their pros and cons, but the question of MIG vs TIG isn’t as easy as picking the “best” - but, rather, carefully choosing based on requirements for speed, strength, aesthetics, and even metrics as fundamental as the thickness of the materials to be joined.

While there are innumerable welding methods available - from simple torch welding to laser- and electron-beam welding - here we concentrate on the differences between, and specific advantages of, MIG vs TIG welding.

The MIG Process Explained

MIG welding, also known as gas metal arc welding (GMAW), is the process of melting and joining metal pieces together using an arc of electricity protected by an inert or semi-inert shielding gas. A consumable electrode rod is fed through a welding gun, melting as it arcs to the metal work piece - adding its material to the mix as a filler. As the gun passes across the join, the weld pool hardens to fix the two metals together.

MIG welding is relatively easy to pick up: The welding rod electrode is fed through the welding gun automatically, allowing the operator to concentrate on running the gun across the joint to be welded. It’s operable, in fact, with a single hand - and is occasionally compared by experienced welders to the use of a simple hot-glue gun.

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The TIG Process Explained

The TIG welding, or gas tungsten arc welding (GTAW), process is, on the surface, extremely similar to the MIG welding process. Both are driven by an electric current creating an arc which melts a weld pool protected by a shield of inert gas, but where MIG requires the continuous feeding of a consumable welding wire - hence its earlier name of “wire-feed welding” - TIG creates the arc between the work piece and a permanent tungsten electrode.

The use of a non-consumable electrode means that TIG welding can be carried out on metal parts alone, directly welding them together without having to introduce additional material - one of the key secrets behind the attractive welds it can offer in the hands of a skilled operator. For parts which don’t fit together smoothly, however, a consumable filler rod - which is manually fed into the welding pool - can be used to bridge any gaps.

Operating a TIG welder is a far more complex process than operating a MIG welder: Where a MIG welder is operable with a single hand, a TIG welder sees the operator juggling the welding gun in one hand, a filler rod in the other, and a foot pedal to control the flow of current - making it a trickier job to learn and more difficult still to master.

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MIG vs TIG - The Weld Differences

While MIG and TIG welding are similar in theory, the results can be very different - a result of the finer details between the two. Where MIG offers fast results and compatibility with thick materials, TIG provides a cleaner finish and stronger welds.

Power Source

Both MIG welding and TIG welding rely on electric current, rather than the flammable gas of traditional torch welding, to heat the metals and weld them together. In MIG welding, only direct current (DC) power is used in order to create a stable arc and provide its characteristic high penetration; in TIG welding, either DC or alternating current (AC) can be used.

It’s the latter which drives TIG’s popularity for aluminum welding: Before the aluminum material can be welded its surface must be cleaned of aluminum oxide - a material with a melting point over three times higher than base aluminum, and which forms quickly on contact with air. By using an AC rather than DC power source with a TIG welder, the shielding gas is ionized - cleaning the oxide layer through ionic bombardment.

Exactly how the power source is configured in terms of voltage and current will depend on the job at hand: Higher currents and voltages can provide stronger welds, but can also damage thinner metals or cause issues with overheating in certain materials. In MIG welding, by contrast, lower voltages with a high wire feed rate can produce the best tensile strength.

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Weld Strength

Handled properly, both MIG welding and TIG welding can deliver strong welds in a variety of materials. Speaking from a purely technical perspective, TIG welding has been proven to provide stronger and more durable welds than MIG welding - but with one major caveat: Its learning curve is considerably steeper than MIG welding, requiring longer training periods and additional experience for a new welder to deliver a quality weld.

In a 2017 analysis by Fauzi et al, TIG welded joints were shown to deliver a 25 per cent higher tensile strength than MIG welded equivalents while the MIG welds showed low Vickers micro-hardness measurements. This, the researchers proposed, was the result of the higher heat input per unit length in the MIG joints than the TIG joints - shown in the extent of the heat-affected zone (HAZ). In other words: TIG is the choice for strength, providing the material isn’t too thick.

That’s not to say MIG joints can’t be strong, however. A 2021 study by Nurdin et al analyzed the tensile strength of MIG joints in low-carbon steel plate and found the joints were stronger than the parent metal - offering a tensile strength of 507.4N/mm². For thicker materials where TIG can’t penetrate, MIG is the obvious choice despite its technically “weaker” welds.

Weld Speed

TIG welding may have the edge in strength, given an experienced welder, but MIG welding has one major advantage: It’s considerably quicker, and as it’s easier and requires less concentration from the operator can be carried out for a longer period without exhaustion.

The speed and relative simplicity of MIG welding is the reason for its popularity, particularly in high-throughput industrial applications - and also makes it easier to automate, further boosting production rates.

There has been a narrowing of the gap, however. A 2007 study by Wilson in Industrial Robot investigated TIP TIG, a TIG welding variant developed by Siegfried Plasch in 1999 which uses the agitation of a filler rod to improve the fluidity of the weld pool - resulting in what Wilson found to be a weld offering the strength and quality of a TIG weld yet carried out far closer to the speed of a MIG weld.

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Welding Gas

Both MIG and TIG welding require the use of shielding gases, which are blown over the arc in order to protect the weld from the effects of oxygen and water vapor. Initially, and as the name implies, MIG welding required truly inert gases - pure argon or helium, typically - making it an expensive alternative to torch welding. The discovery that a mixture of inert noble gases with semi-inert gases like carbon dioxide or nitrogen would also work drove the cost down considerably, and help move MIG welding from non-ferrous to ferrous metals.

The precise gas mix required for MIG welding depends heavily on the materials: Carbon steel is welded with argon and carbon dioxide; stainless steel with an argon, helium, carbon dioxide tri-mix; nickel alloys with an argon-helium mix; and aluminum, where TIG welding isn’t available due to material thickness or lack of trained operator, using either argon or helium to improve heat penetration in thicker materials.

TIG welding, by contrast, is usually still carried out using either pure argon, pure helium, or an argon-helium mix, bumping up the cost compared to cheaper semi-inert MIG gas mixtures. For materials where an extremely high-temperature weld is required, hydrogen is often used - though, speaking technically, you’re no longer performing “tungsten inert gas” welding when you’ve introduced an active gas like hydrogen.

Weld Aesthetics

The mechanical properties of a weld are of vital importance, but they’re not the whole story: For exterior welds, aesthetics are highly valued - particularly on high-end consumer products like luxury vehicles, where ugly welds won’t be tolerated.

The speed and simplicity of MIG welding comes at a cost, here, with the welds typically showing a less even finish, heavy discoloration, and frequent spatter - though all can be improved in the hands of an experienced welder. TIG welding, by contrast, offers minimum spatter and a “stacked coin” appearance to the weld which, when traced smoothly by the operator, needs only a minimum of post-weld finishing.

For internal welds, or welds which are to be covered by paint or another finish, there’s less of an issue with MIG welding’s relatively uglier welds - and the cost and speed benefits of MIG welding can easily override concerns about aesthetics.

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Weldable Metals

When it comes to choosing a process in MIG vs TIG welding, the easiest way to choose the best approach is to look at the materials to be welded. While it’s true that both MIG and TIG welding are suited to a range of metals and alloys, they definitely have their particular suitability.

MIG is best suited to thicker materials, owing to its higher penetration depth. While originally developed for non-ferrous metals, MIG welding is the number one welding method for ferrous metals to date - and is used on everything from high-carbon or stainless steel to copper and nickel alloys, aided by its flexibility in the choice of gas mix and consumable electrode material.

TIG welding offers far lower penetration than MIG welding, making it better suited for thinner materials - as does the higher level of control offered during the welding process. This is particularly true for aluminum, with MIG welding only suited to 14 gauge and heavier and without the ability to use a cheaper carbon-dioxide gas mix - while being able to run an alternating current TIG setup and use ionic bombardment to remove the oxide layer during the weld process is a major advantage in favor of TIG for aluminum welding. Aluminum welds can be further improved using pulsed-current TIG, compared with the traditional continuous current approach.

Welding Process Comparison: TIG vs MIG

The key difference in TIG vs MIG welding is in their relative complexity. MIG welding is easy to pick up, allowing a novice welder to begin producing functional - if not aesthetically pleasing - welds after a very short training period. The use of a continuous-feed gun also reduces fatigue, allowing the operator to perform for longer.

The complexity of TIG welding, whether a filler rod is used or not, makes for a longer training period before an operator can be expected to produce quality welds. The process itself takes longer, too, but given a trained operator and enough time the results - in both functionality and aesthetics - can deliver a great return on investment.

In both cases, though, the process has one key weakness: The shielding gas must be kept in place to protect the weld from contamination. Outdoors, or even indoors given strong ventilation for other manufacturing processes, the gas can be swept away too quickly - meaning alternative methods, like shielded metal arc welding (SMAW) or “stick” welding, need to be used instead.

MIG Welding Applications

The high speed, low cost, and relative simplicity of MIG welding have helped push it to the top of the pile when it comes to metal-joining processes. It’s used everywhere, from component repairs and automotive manufacturing to pipe-welding and ship building.

For thicker metals and larger parts, MIG welding is the only choice: TIG welding can’t penetrate deep enough to heat the material for a good weld. MIG welding is also found where a low defect rate is important: As a simpler welding process which operates continuously, without the foot-operated stop-and-start approach of TIG welding, severe defects become less likely.

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TIG Welding Applications

The complexity of TIG welding means it’s relatively expensive, a problem exacerbated by its slow weld rate and the need for an experienced operator. It’s not a process you’d typically use for something as simple as welding together lengths of pipe, but it certainly has its applications.

The aesthetics of TIG welds, particularly when carried out on well-fitting parts with no filler rod, make it ideal for user-facing projects and luxury goods - but the technology isn’t all about looks. TIG welds are found on sheet metal parts in the aerospace and automotive industries where their smooth finish improves efficiency, while their higher weld strength compared to MIG welds make them ideal for high-risk environments - which is why nuclear waste storage containers are manufactured and sealed using TIG, rather than MIG, welding.

Key Takeaways

The choice of MIG vs TIG welding may well be made for you by your project requirements. Thinner materials, particularly aluminum, will have no choice but to use the TIG process; cost- or time-sensitive projects will benefit from MIG, while projects using thicker materials will require MIG welding. TIG, meanwhile, is the method of choice if you care about the aesthetics of the weld or achieving maximum tensile strength.

Many of the benefits of TIG welding are only present in the hands of a trained operator, however. For work carried out by relatively inexperienced operators learning on-the-job, a MIG weld will likely prove stronger and more aesthetically pleasing than a TIG weld - the latter only surpassing the former as the operator gains the necessary experience.

As technology progresses, some of the biggest disadvantages of TIG welding may be addressed: The TIP TIG process has already proven its value in improving the speed of TIG welding, and activated TIG (ATIG) can do the same for thicker materials - pushing TIG’s penetration depth from mere millimeters to 12cm, according to a recent review of the technology by Fande et al.

References

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A. C. Davies: The Science and Practice of Welding, Cambridge University Press. ISBN 0-521-43404-1.

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