Tig Amp Chart, Aluminium ?

[agniusm]

Thanks hotrodder. Today i went and did few attempts so see, maybe there would be further advice. i am using Alutig Mg 5 2.4mm electrodes. I dont have a foot pedal yet. I had set frequency to 200hz. Ally (new) is cleaned with SS wire brush and then acetone. Here is what turned out:
Simple pass on a sheet:

Two sheets joined:

Unlucky open corner joint:

Second go:

Nothing even remotely close to this:

I don't know why i get it contaminated, ally is cleaned and prepared, tungsten sharpened, perhaps i got it wrong? Her it is:

Here are the setting i am using:

I will try to get some video on welding corner, perhaps i am doing something wrong.
I hope i am not hijacking someones thread, just thought no reason to start another with the same situation.
Regards, AG

 

[jordan1]

Noooooo, i wouldn't pay much attention to anyone that recommends purposely contaminating the tungsten. The 'balled' tungsten thing is a result of the tip melting, in the old days (pre squarewave & fixed AC balance, especially with pure tungsten) the tip melts more than it does with modern kit and it wasn't uncommon for people to purposely ball the end by striking an arc on a piece of scrap with the machine set to DCEP. It's the EP (electrode +ve) phase of AC that melts the tungsten as around 2/3 of the total heat occurs at the +ve electrode. Bit more on the subject including AC frequency here... http://www.mig-welding.co.uk/forum/threads/waveshapes.37420/#post-412262

The Miller calculator is occasionally somewhere near the mark but is often miles out. The amperage guide in the tutorial is much closer, granted nothing on ally but as Chevy said the best guestimate for a starting point on ally is the 1 amp per thou (or 40A/mm) rule of thumb. As Paul the thermal conductivity of aluminium is kinda a curve ball... it's why ally typically needs more amps than steel despite it's lower melting temp but small pieces quickly become heatsoaked requiring large changes to amperage or travel speed. Larger offcuts for practice make life a lot easier in that regard, to avoid wasting loads of material can cut a bunch of strips and then tack them all together to make a larger piece with lots of joints. Make two of 'em and you can switch between 'em as a means of controlling how hot they get. To practice fillets/ouside corners just tack 'em up in a \/\/\/\/\/\/ pattern

A couple of threads about weld penetration with ally which have links to other stuff on the subject too... http://www.mig-welding.co.uk/forum/threads/alu-tig-questions.22605/#post-250838 & http://www.mig-welding.co.uk/forum/threads/weld-penetration.36529/#post-402400
Rough and ready butt weld being bashed about here ... http://www.mig-welding.co.uk/forum/useralbums/ally-weld-abuse.743/view

While you can't get things too clean for welding, especially TIG and/or aluminium it's all overdone a lot of the time IMO. When working with new sheet ally i rarely if ever use a stainless brush or sctochbrite etc and if i do never on the frontside- it's the cut edges and backside where the 'cathodic cleaning' from the arc can't reach that need attention. If it's something important or is covered in residue from sticky tape/cutting lubricants etc i might give it a solvent wipe for hydrogen porosity reasons but a lot of the time welding prep consists of peeling off the plastic protection and maybe given the cut edges a scrape with deburring tool if i haven't just cut them
Obviously old/manky ally that's covered in gunk/isn't shiney anymore due to oxidation needs cleaning properly and being a soft metal it's easy to embed crud into it hence a stainless brush that's at least clean and ideally not used for anything else to avoid cross contamination with rust etc

It came from a tuition by a so called pro on UTube.

 

[Wyn F]

agniusm, you seem to be getting much better results then me
When ever I tried to join two pieces together I just ended up curling/melting the edges away on both parts way before I saw any sort of puddle

 

[hotrodder]

Some larger offcuts prepared as described before will make life easier as will tweaking the AC balance to get a bit more 'cathodic cleaning'... there's next to no etched zone on those, the white bands next to the weld which result from the EP phase of the arc breaking up the oxides.
Don't worry about the tungsten too much*, as long as it's clean and any grinding marks run axially it'll be fine whether it's sharpish with a flat tip, a crayon like tip, properly 'balled' or anywhere inbetween
Personally i'd also suggest turning the AC frequency down a chunk too. It's not a right or wrong thing but the arc will be softer below 100Hz and slow things down a little

* it's really not as important as some people think and much of it is personal preferance anyway... http://weldingweb.com/showthread.php?23445-Given-the-current-obsession-with-tungsten-prep

It came from a tuition by a so called pro on UTube.

Some random self proclaimed 'pro' or one of the usual suspects? A contaminated tungsten can make it easier to tack ally in that the contamination tends to totally screw up the arcs focus so instead of initally dancing between each piece it 'gets' both edges as it fans outs lots. Be surprised to see anyone that knows what they're talking about actually recommending it though!

Wyn, are you sneaking up on the amperage slowly with a foot pedal? With ally the edges often tend to pull back as it melts instead of attracting each other like they do with steel. Sneaking up on things tends to make it worse as the backside gets hot and oxidises more. The way forward for tacking ally is hot and quick...

 

[Wyn F]

Personally i'd also suggest turning the AC frequency down a chunk too. It's not a right or wrong thing but the arc will be softer below 100Hz and slow things down a little
Wyn, are you sneaking up on the amperage slowly with a foot pedal? With ally the edges often tend to pull back as it melts instead of attracting each other like they do with steel. Sneaking up on things tends to make it worse as the backside gets hot and oxidises more. The way forward for tacking ally is hot and quick...

That's something else I need to bring into play as I've always gone full pedal straight away on all practise work
Backing off with ally as it travels along, but even then getting it right doesn't always go to plan.
The plate I tried with above is approx 2mm, so used 1.5 tungsten (white & grey) and 1.5 filler rod @ about 70a + or - as I practised
From memory the machine is factory default set at 36 ac balance at 70a. (Lorch T220)
From what I saw it got worse when I altered it either way

As for the tungsten it hardly ever formed a ball on the end ?

 

[agniusm]

I bet you would get similar results wyn F if you went with new sheet of aluminium. One thing I have noticed that welding edges brings up black contaminants even if the pieces are prepared properly when doing same on flat sheet brings up none.
I still have one tuition left on my kemppi account, thats good
Perhaps I shoud try tweaking arc setting for the initiation of the arc and up the amps like hotrodder said cause thats whats happening, my pieces are pulling back and the I cant get them both hot enough for a puddle.

 

[hotrodder]

FWIW i'm usually running around 90A for butt welds on 2mm ally. Obviously arc length, travel speed and even the size of the part all play a role once welding but not so much for tacking. In fact i often turn the juice up a chunk for tacking, upto 150% of the amps i'd weld at sometimes
The edges thing could be argon coverage, when the geometry of the part 'diverts' the gas it can draw air in. A case when less is almost always more i.e. higher flow rates exaggerate things and 5 - 7 litre/min is usually more than enough for most TIG work unless using a giant ceramic with loads of tungsten stick out

 

[agniusm]

Thanks hotrodder. Your tips helped. I have reduced my frequency to 90Hz, upped arc initiation current to 120A for .4S and welding at 65A. it gives a lot better results and tacking is easy now.