When welding thin-gauge metal, inexperienced welders often encounter something called “burn-through”. This is when the metal gets too hot and simply melts away. The result varies from small holes in the sheet to something that looks like lace. It might be pretty, but it’s far from being a good weld.

As experienced metal fabricators, we know something about working with and welding thinner gauge metal. The purpose of this blog is to share our wisdom. That way, if you’re welding thin material, hopefully, you’ll have more success, and if you’re looking for a fabrication shop capable of the quality welding work you need, you’ll know you can trust us.

Defining “Thin”

American Welding Society (AWS) guidance is that “thin” refers to a material with a thickness less than or equal to 3/16”. In gauge terms, that means 6Ga mild steel is not thin, while 7Ga is.

The issue with thin material is that there’s less of it to absorb and conduct heat. With less mass per unit area, a thinner sheet heats up faster during arc welding, which is why it can reach its melting point surprisingly quickly.

Welding Process Selection

There are three options for welding thin gauge metal: MIG, (the default choice for most industrial welding), TIG, and resistance welding. Here’s a look at each one, concluding with the process we prefer for the best results overall.

Resistance welding

In this process, a pair of electrodes clamp two pieces of metal together. Current flows through this “sandwich” with the interface between the two pieces growing hot enough to melt a small nugget of metal. Larger sheets are joined by forming a series of “spot” welds along the overlapping region.

Resistance welding is quick but doesn’t achieve the strength and stiffness of a contiguous weld. The other big limitation is the need for access to both sides of the region being joined. In addition, the “throat” depth of the electrode pair limits the maximum sheet size.

Gas Metal Arc Welding

MIG and TIG (metal inert gas, and tungsten inert gas respectively, to give them their full names), are both forms of arc welding. This is where an electrical arc between a welding torch and the workpiece creates enough heat to melt the parent metals and an additional filler metal. The arc is shielded by an inert gas that prevents oxidation of the weld pool, as this could cause defects.

In MIG welding the electrode is the filler wire. It’s fed into the weld pool at a controlled rate where it melts and contributes to the weld. In TIG the electrode is non-consumable and filler is added separately. The actual arc is more focused, so it puts heat into a smaller area and provides better penetration.

MIG is faster than TIG but lacks the precise control the TIG welding process provides. For this reason, TIG is preferred for quality results in thin gauge metal, and especially for welding aluminum sheets.

Set Welding Parameters

With a thin sheet, it’s vital to avoid putting too much heat into the weld. This means minimizing both amps and volts used. However, turn them down too far and weld appearance and strength will both suffer. For consistently high-quality results it’s best to develop a Weld Procedure Specification (WPS) that defines exactly how to make the weld. Important elements of this for TIG-welding thin gauge material are:

  • Use the smallest possible diameter of electrode and welding wire, as this reduces the amount of heat they need
  • Start by expecting to need 1 Amp per 0.001” of metal, although this ratio falls off at thicknesses greater than ¼”
  • Increase travel speed to reduce the heat going into the sheet
  • Tack weld, then go back and fill in the gaps

Aluminum sheet poses some particular challenges, due to its high thermal conductivity and low melting point. For successful welds in thin gauge aluminum:

  • Use AC rather than DC power
  • Start with the balance at 75% electrode negative, but reduce this if more electrode positive time is needed to get rid of oxidation
  • Use a higher frequency as this increases arc stability, allowing lower amperage or a higher travel speed

Filler Selection

Match the filler to the base metals and check it’s compatible with the specific alloys. This creates the strongest joint and ensures everything melts together, rather than needing to add more heat to melt the filler and risking burning through.

Heat Management Techniques

In addition to turning down the amperage and using the smallest possible diameter electrode and filler, modern arc welding equipment provides another tool for managing heat input: the pulse function.

Pulse cycles the arc current through a series of high and low amperages. The high or peak current provides the energy needed for melting, while the low current just maintains the arc. On most equipment, it’s possible to set both pulse frequency and duty cycle (the proportion of the total cycle for which high current is applied).

Practice, Practice, Practice

Making consistently high-quality welds is difficult with every process, especially when TIG welding. The challenge here is that, in addition to maintaining consistent torch angle, stand-off, and travel speed, both hands are needed to feed in filler wire and hold the torch. And complicating matters further, some TIG welding sets have a foot pedal for current control.

The only way to get good at TIG welding is by practicing. In particular, it’s prudent to practice with some test welds in the same thin gauge alloy before starting on the actual fabrication job.

Partner With Experts in Metal Fabrication

Welding plays an important role in metal fabrication, and it’s not an easy process to get right. Thin gauge metal poses some particular challenges for even the most experienced welders, but the advice given here should help.

If you have a fabrication job or project that involves welding thin sheet, we’d like to offer a helping hand. We’ve been in the metal fabrication business a long time and our welders are both certified and highly experienced. They’ve tackled aluminum welding, thin gauge welding, and many other challenges. Contact us to talk about what else we could do for you.