TIP #1 The single biggest tip for Tig welding aluminum castings is to use a helium/argon mix instead of straight argon. That’s a pretty strong statement, but I stand behind it 100 percent.
A 50/50 argon/helium mix works great and so do mixes that contain up to 80 percent helium. Helium adds more energy to the arc and makes more difference on heavy aluminum than any other welding technique you can think of.
Did you know that a tig welding arc carries more voltage with helium gas without even adding more current? It’s a fact aluminum die casting china.
Have you ever lit up on a heavy aluminum casting using straight argon gas and had to wait a really long time to even get a puddle? Not so when you add helium. You get a puddle immediately and it’s even a cleaner puddle… an added bonus.
Welding textbooks recommend straight argon for anything less than ¼ inch thick aluminum. But I am telling you that once you use an argon helium mix, I will wager you won’t want to use straight argon again except for really thin aluminum sheet.
TIP #2 The second tip is to preheat the aluminum casting. A 200 degree preheat will work wonders and if you are using a small tig inverter like a Miller Dynasty 200dx or a Lincoln Invertec v205t, you only have about 200 amps to play with and you will need every bit of it. A preheat will get you over the hump.
It doesn’t really matter how you get the part hot…A propane torch or old gas grill both work great.
TIP #3 The third tip is to be careful not to use too much torch gas. Just to be clear, that’s the gas coming out of the tig cup.
Enough is enough and more is worse , not better. Use just enough flow to shield the puddle and not much more. If the noise from the arc is rattling your brains out, you probably have too much gas flow. Think about it, why would you want to blow cool gas on something you are trying to heat?
When you use too much torch gas flow, It is working against the arc, not with it.
Turn the torch gas down to 13-15 cfh and you can actually hear the difference. But remember that not all flowmeters are calibrated the same so if you get a fuzzy puddle, you may need to adjust the torch gas upward…but only enough to clean up the puddle.