Thread: TIG Anguish :( Can't Fillet or Lap weld Aluminium

All the tigging Ive done has been stainless so no clue really. Could it be creating an air gap between the overlap so your top plate is getting to temp but the lower plate is way to cold. Why do you need to overlap, can you engineer to do fillets as like you say your flat plate welds look ok
cheers
blaze

Well - my test welds are with the two flat sides of the chequer plate together, so not much of an air gap (at least not as much as there would be if the plates were around the other way....). However, they are just sitting on top of each other with gravity - do you think clamping them tightly together might help?

The torch is 80% focused on the base sheet so that's where most of the heat'd be going I reckon. Torch angle would be 10 degrees off verticle (looking from the front - pointing in the direction of the weld) and 20 degrees angled back "into" the join.

It has been 25 yrs since my tig time but the edge of the overlap top plate does not have the heat dissipation that the base plate will have and as it is relatively thin at 3mm and presumably with air gap checker plate minimal contact with the base plate, so I would have started with a bead on the base plate and then run the bead up to the top plate edge with the arc flame largely on the bead.

That is basically how I am doing it. I can get a nice shiny puddle on the base sheet, but I can't get the top sheet to "wick" together into the bottom sheet puddle.

It's like dealing with "reverse mercury". The two pools of molten ali do not want to join up and become one

As said it has been a long time but we did have a white paste that was a flux for aluminium. Only remember using it for a couple of small jobs I did with an acetylene torch but cant think why it would not work with TIG. You are trying to do a challenging weld. The difference in heat sink with the 2 plate and a low tolerance between just right and a puddle not easy.

I've got no idea with the Kemppi as ours is an ESAB, also I'm not much into TIG work.

We turn the AC balance of the phases right down to the lowest base level and don't play with it - this stuffs the welds and burns the tungsten if you run too much heat into the tip.

We don't run DC at all with Aluminium - it doesn't allow the TIG to penetrate the Al oxide layer. Run DC when you are TIGing steel.

The high frequency is to start the arc without striking the tip and contaminating it, and so with AC current used for Al it needs to stay on all of the time as the current cycles.

You also need to sharpen to a tip with the grind pattern running down to the tip (ie not around) to prevent the gas from swirling on the tip.

Without being there, I would have also thought that you'd be running somewhere around 40amp to start at least - it just sounds hot, and you may also try to get more filler into it.

As I said, I'm not into TIG so others may have better info.

Originally Posted by Slunnie

We don't run DC at all with Aluminium - it doesn't allow the TIG to penetrate the Al oxide layer. Run DC when you are TIGing steel.

Thanks Slunnie - The DC thing when welding Al is called "Mix" mode. It mostly runs AC, but for a short period (maybe 20%) it goes to DC to get more penetration, then flicks straight back to AC mode. It happens so fast you can't see it, you just hear a slightly difference tone when welding.

Originally Posted by spudboy

Thanks Slunnie - The DC thing when welding Al is called "Mix" mode. It mostly runs AC, but for a short period (maybe 20%) it goes to DC to get more penetration, then flicks straight back to AC mode. It happens so fast you can't see it, you just hear a slightly difference tone when welding.

Ah thanks for this. Our machine doesn't have that. This is more than just altering the time balance between the AC phases by the sounds of it.