Sheet Metal Welding: Types, Tips & FAQ

Introduction to sheet metal welding

Metal fabrication is a rather complicated process that has several extremely important parts. One such part is metal cutting – turning a basic metal piece into a specific shape with the help of various cutting methods. There are also other processes that may be involved in the metal fabrication process, such as bending, welding, and more.

Welding of sheet metal is going to be the main focus of this article. Welding is a process that is often used in metal structures, it is all about joining several sheet metal pieces together using either high heat to melt the parts together to cause a fusion process once the parts have cooled down, or by using a filler material that gets to incredibly high temperatures, melts and creates a molten substance which is used to join the metal parts together.

Sheet metal welding methods

There are several different methods and approaches to sheet metal welding, and each method has its own uses in different circumstances. Our first goal is to provide information about different welding methods in the list below.

Metal Inert Gas welding (MIG welding)

A well-known welding type, MIG welding (can also be called Gas Metal Arc welding) uses a solid wire electrode in a welding tool to create a pool of melted wire which then becomes the filler material that connects the metal pieces. The MIG welding tool also uses a layer of shielding gas to prevent the molten puddle from being contaminated by the surrounding atmosphere in some way.

MIG welding is used on a regular basis in a number of large industries, such as home improvement or automotive. The main reason for that is the combination of efficiency and price – MIG welding works for the majority of popular sheet metal types (from aluminum to stainless steel and more), creates high-quality welds, is relatively cheap and does not have sophisticated machinery of sorts to be involved in the process.

Another one of the reasons why MIG welding remains one of the more popular welding methods is its newer variation – pulsed MIG welding. As the name suggests, it is a process similar to how MIG welding works, with the main difference being that the current that is used to melt the metal is pulsed and not constant.

The usage of dedicated machinery allows for a lot of variation when it comes to pulsed MIG welding – with different waveforms, pulse amplitudes and pulse durations. This allows for smoother welding with little to no splatter at relatively low currents, higher deposition rates, and many other advantages.

Tungsten Inert Gas welding (TIG welding)

TIG welding is another familiar name on the market – a variation of arc welding that performs the welding process by passing current through a non-consumable electrode made from tungsten. Following a similar logic to MIG welding, TIG method also uses some sort of inert shielding gas to prevent both atmospheric contamination of the weld and oxidation of the electrode – with the most popular variations of shielding gas being helium and argon.

TIG welding is at its most productive when working with various non-ferrous metals – nickel, titanium, chromium, magnesium, aluminum, and so on. It is one of the most common techniques for frame fabrication in doors, feeders and motorcycles. At the same time, the ability to work with non-ferrous metals makes TIG a prime choice for flight-related industries, such as aerospace and aviation.

While it is true that TIG welding provides a strong weld and offers more control over the process compared with other methods, it is also more demanding to the skill of the welder and may sometimes be more time-consuming than other methods.

Pulsed TIG welding also exists, following the same logic as with pulsed MIG welding. It is a regular TIG welding process but the current is distributed in pulses, which offers a number of advantages – better joint quality, smoother welds, better heat control, more versatility in terms of thin or thick metal, and so on. However, it is only logical to see how pulsed TIG welding is harder to master than the classic TIG welding, and it is a common advice to get used to regular TIG welding before trying pulsed TIG welding at all.

Laser welding/Electron Beam welding

Both electron beam welding and laser welding might be the most expensive methods on the list with a very narrow set of use cases. First of all, they use either a laser or an electron beam to produce the heat for the welding operation (which is where their names come from). However, the biggest difference here is that both require specific complicated machinery to perform in the first place.

These techniques are highly accurate (especially when it comes to laser welding), making them a perfect choice for metal parts with high level of detail required. They can also work with tougher metal variants, such as carbon steel, stainless steel or titanium – while keeping the aesthetic visuals of the weld as a whole. Surprisingly enough, both lasers and electron beams can also be used for more common materials such as aluminum or even thermoplastics – even though it might not be the most cost-effective option.

Stick welding

Going for a direct alternative of the aforementioned highly accurate but expensive sheet metal welding method, we move over to stick welding – a method of welding in which the electrode is just a stick covered in flux. As with some of the former examples, the electrode is used to form an electric arc between metal parts, creating the aforementioned weld.

The big difference here is that stick welding does not use any shielding gas in the process. However, that does not mean that there is no alternative way to protect the results of the weld from atmospheric contamination – this is where the flux comes in that the electrode stick is covered with. This flux can react to the heat that is generated by the welding process, disintegrating itself to form a layer of slag over weld that protects it from unwanted disruptions.

As we have mentioned before, this method is pretty much a direct alternative to laser welding – it is not as accurate and does not create that nice of a weld as a result, but it is also extremely convenient and relatively cheap. Its portability also makes it a great option for industries such as shipbuilding, construction and general steel fabrication.

Gas welding

Another relatively simple technique for welding of sheet metal is with the help of burning some form of gas – oxygen, fuel or oxyacetylene – to melt parts of sheet metal and join them together while they are melted. This is a fairly common process in the industry, and also one of the older ones on the list.

Despite its age and simplicity, it is still one of the most popular techniques in the metal industry due to its versatility and effectiveness – it can work for air conditioning systems, pipes, tubes, ventilation shafts, and so on. Gas welding works for both non-ferrous and ferrous metals, does not require electricity to work in the first place, is relatively economical, portable and has a low skill level requirement to operate.

Plasma Arc welding

Plasma Arc welding can be considered somewhat similar to the previously mentioned TIG welding, since it also uses a tungsten electrode in the welding tool. The similarities mostly end here, since plasma arc welding uses a smaller arc and also allows the electrode to touch the body of the welding tool. A plasma is generated from pressurized gas, melting different metal parts together.

Plasma arc welding has no requirement for filler materials and offers welds of high quality, with little to no need for the cleanup afterwards. It is also a relatively fast technique that does not have a lot of power and has an impressive accuracy level – which is why it is common for marine or aviation industries.

Sheet metal welding tips

Of course, there are other variations when it comes to welding of sheet metal that can be somewhat less known and suitable for specific use cases. This list went over the majority of popular sheet metal welding methods – but choosing the proper welding method is only a part of the process. This is why we are also going to present a number of tips for welding of sheet metal as a whole.

• Skip welding is a technique that can be used to combat warping and metal distortion caused by the heat from welding being distributed unevenly. The technique itself involves using a number of so-called stitch welds – welding specific critical spots between two metals instead of going for a single line. Using skip welding allows for the material to cool better and offers more leeway in terms of heat distribution during the actual welding process – but being too slow with welding is still not recommended for similar reasons.
• Smaller wire diameter is far more suitable for most welding cases with the MIG welding method, for several reasons. A smaller wire produces fewer deposits and gives the welder more control over the welding of sheet metal process. At the same time, smaller wire would require less heat for it to melt, which in turn generates less potential issues with excessive heat. However, it is a technique that’s mostly suitable for light gauge sheet metal, and thicker materials such as 18 gauge or higher would require thicker wire diameter to be able to weld it correctly.
• A backing bar can act as another way to improve the cooling speed – it is a relatively simple metal bar that can be used to draw heat off the welded piece, reducing the chances of warping or other heat-related issues. The best material for a backing bar is aluminum, copper or some other material that has high heat conductivity.
• Choosing a correct filler metal for the job is also an important part of the process – the filler metal should always be thinner than the metal you are welding. It is important to remember that a thinner wire would always be easier to melt, offering less heat distribution and less chances of metal damage. However, choosing a filler metal that is too thin is also a risk because it might not be able to keep the welded parts together in the first place. Finding a fitting filler metal for the job also reduces the possibility of all kinds of defects during the process – cracking, rusting, etc.
• That tip about the smaller wire diameter also works for the electrode size – a small electrode would contribute to our combined effort to generate less heat by operating at lower heat values and with lower currents. This kind of approach also reduces the chances of another common issue appearing – burn-through, which is a massive problem for thinner sheet metal pieces.

Additionally, there are several nuances that we have to go over when it comes to the surface of the welded material – there are at least four possible options, and each option has its own preferred welding method and a number of intricacies.

A flat surface is the first option, and possibly the easiest one to work with – the process itself would be called flat welding in this situation. It implies the welder approaching the welding surface from its upper side, so that gravity can help with the flow of molten metal.

If the preferred degree of one welded surface to another is 90 degrees or close, then the ideal welding position would be to place the tip of the welding tool at forty-five degrees to the surface of the metal, pointing towards the metal joint. This approach heavily favors TIG and MIG welding methods for the overall effectiveness of the welding process in this situation.

A horizontal surface, on the other hand, has two different variations to it – even though both of those include the metal sheets being placed horizontally in relation to the welder. As such, it can be either a fillet weld or a groove weld. A filled weld exists strictly for L-shaped welds where the horizontal metal piece and the vertical metal piece are perpendicular to each other. A groove weld is when both pieces of metal are within the same welding plane and the welding surface itself is vertical. For both of these cases the best welding option would be the stick welding due to the difficulty of both TIG and MIG welding with horizontal welds as a whole.

A vertical surface is a surface that faces the welder in its upright position – with the unfortunate consequence of the molten metal flowing downwards and piling up during the welding process. The welder is pointing the welding tool at a forty-five degree angle to the welding location while holding the electrode between the welding pool and the flame. Stick welding is also the best option for this surface type due to the inconvenience of it all, or the welder might just adjust the welding surface axis to make it flat or horizontal for an easier welding process.

An overhead surface is the most inconvenient welding surface on this list – welding a metal piece above your head is complicated and creates a number of difficulties, one of which is the molten metal dropoff during the welding but before it completely cools down. General recommendation here is to use the stick welding method and to use more filler material to ensure that both surfaces are properly connected to one another.

It is worth noting that overhead surface welding is extremely uncommon in the modern day for both safety and convenience reasons.

Frequently asked questions about sheet metal welding

What is the idea behind a “1 for 1” thin metal welding rule?

The “1 for 1” rule describes the calculation of amp needed for specific metal thickness – 1 amp per 0.001 inch of carbon steel. However, this formula varies a lot depending on the material type – stainless steel requires less amps (about 30% less), while aluminum requires more (⅓ more).

Is there a limit on how thin the soon-to-be welded metal can be?

26 gauge mild steel is supposed to be the thinnest the metal can be for you to be able to weld it with no distortions. It is possible to go even thinner, but the distortion and burning would be unavoidable in these scenarios.

Is there an upper limit on how thick the metal can be before it stops being connected with skip welding?

One and a quarter inches is the absolute thickest the metal can be before it becomes unusable in terms of skip welding, for a number of reasons.

Is there a definitive best welding method for most cases?

This particular question is problematic because there are several characteristics that can define the “best” welding method. For example, MIG welding is the #1 when it comes to welding speed first and foremost. TIG welding would be the best on the list of methods with the smallest zone affected by heat (and thus vulnerable to warping and other issues) – but it is also one of the most complicated ones. As such, the answer to this question depends on the specific trait of the welding method.

Conclusion

Sheet metal welding is a useful process for the steel fabrication industry as a whole, and it is also widely used in many other similar industries, from automotive to aerospace. At the same time, it is not an easy topic to get into, with so many different welding methods and nuances being important for the overall process. In this article we have attempted to present both welding methods and welding tips for different situations, explained with as much detail as possible.