Beginners’ Guide: How to weld aluminium - Part Two (TIG)
Need to weld aluminium but not sure where to start? You’re not the first. That’s why we’ve put together a 2-part blog series to help you get started.
In part 1, we focused on how to weld aluminium using the MIG welding process. Here, we tackle how to weld aluminium using TIG welding and reveal all those little secrets only the most pro welders know.
TIG welding (tungsten inert gas) is known across the industry for producing the most beautiful welds. It is an extremely accurate process, capable of welding extremely thin metals together as well as very thick metals. How? Because TIG welding doesn’t heat up a large area of the work piece.
TIG welding works by using a torch with a solid tungsten electrode, Argon shielding gas, and a filler rod dipped into the weld puddle. A foot pedal controls the heat of the torch. Unlike many welding processes, TIG lets you weld steel, stainless steel, titanium, magnesium, cobalt alloys, copper alloys, and of course aluminum – the metal most often associated with TIG welding.
As with MIG welding, there are certain things to remember when TIG welding aluminium:
1. You need TIG with AC/DC capability
TIG welder capable of welding in AC (alternating Current) as well as DC (Dirtect Current) cost more than machine that only provide DC welding. Our AC/DC range starts at $995, extrmely cheap compared to our competitors, but still more than DC TIG welders which start at $289.
However, if you’re planning to weld aluminium and you want to save yourself money by buying a DC TIG welder, forget it.
Why? Aluminium forms an oxide layer when exposed to air and this layer has a far higher melting temperature than the base metal itself - 1982C, compared to 648C.
If not removed properly, this oxide layer will inhibit proper weld fusion and affect its quality.
A TIG welder with an AC basically erases this oxide layer from the surface, so that the integrity of the weld is not compromised when the base metal melts.
2. Filler Rod
To weld aluminium, you will need an aluminium filler rod. This will bond the two pieces of metal. Be sure not to use dirty or rusty filler rods that will result in weaker welds.
3. Argon Gas
For TIG welding, you’ll need Argon gas for shielding. The most cost-effective solution is pure Argon, though 3% helium can be added to increase the stability of the arc. Some will even say that 50/50 argon/helium is worthwhile.
4. Clean, clean clean!
The thing about aluminium is that it forms a thin aluminium oxide coating on its exterior, kind of like a skin. The problem is this melts at a far higher temperature than aluminium. So before you can even begin welding, you have to clean off the aluminium oxide – even if it’s a brand new piece of aluminium. One way to do this is to use acetone on the joints, rinse the piece in water and let it dry fully. Then scrub the metal with a stiff brush. You also need to clean the filler rod, as a dirty filler rod can contaminate the weld. As previously mentioned, a welder with alternating current (AC) can also performcleaning of the oxide layer on aluminium.
5. Preheat is your friend
You’ll find that aluminium is easier to weld if the work is already much hotter than room temperature. If you weld thick pieces without preheating, you’ll get a weak and shallow bond. Heating the aluminium is as simple as putting it in the oven, or using a gas torch to the heat sink with the work clamped on – aim for about 176°C.
6. Practice run
Before you start welding have a few practice runs. There’s no need to light the torch for this if you’re trying to save on metal.
- Hold the torch similar to how you would hold a pencil and tilt it back very slightly at about 10-15 degree angle.
- Hold the tip of the tungsten about 6mm from the metal. If you hold it much further than this the arc will spread too wide and the weld will become too difficult to control.
- Practice running the torch along where you plan to weld trying to keep that 6mm gap between the tungsten and the metal. Make sure to practice with your gloves on so you get a feel for how it be once your arc is lit
The filler rod
- Make sure to hold the filler rod at about 90 degrees to the torch tip. You will lead the the weld with the filler rod but you don’t want it to come into contact with the the torch tip because this will contaminate the weld
7. A few final bits of preparation!
Fit your aluminium sheets together as tightly as possible
TIG welders don’t like it when the metals are not fitted together nice and tightly prior to welding. It can result in a weak weld. Fill your sheets before you clamp them to avoid this.
Set your welder to the appropriate settings
- Aim to set your amperage to about 1amp per 25mm in thickness of your aluminium. This may seem low but that is the nature of aluminium welding.
- You can set the amperage slightly higher than your estimated need and then ease it back once under way.
8. Lets weld!
- Use the diametre of your nozzle to gauge the distance between the nozzle and your tungsten electrode. If you’re using a 6mm nozzle, your tungsten should extend no further than 6mm from your nozzle.
- Tap the electrode tip against the aluminium sheet and then pull it away about 3mm. At this point you can strike your arc.
- Melt the work piece until you have a nice sized puddle, the size of this puddle needs to be consistent as you move along your weld.
- As you move along the weld add just enough filler rod to fill the joint and create the the fusion. Continue this along the length of the weld.
- Remember, the heat will increase as you weld so gradually lower the amperage.
- Very slowly push the puddle created by the torch into the joint, adding filler as you go.
If you remember these factors when you TIG weld aluminium, you’ll get a much cleaner and better looking weld. Did you miss our blog on MIG welding aluminium? Check it out here.