help with tungstens please

[scrimshady]

I have just purchased a tig and am totally new to it I have have mig welded everything for years now. I would like to weld ali and after reading on here know it takes alot of practice with dc tig. But i need to buy tungstens and want to know what to buy for a novice tig welder but is good for mild steel and ali.. any help would be brilliant

 

[Paul.]

To weld aluminium successfully you are going to need an AC set, although there are DC methods they are used on heavy sections usually with helium rather than argon, require special cleaning methods to remove the residual oxide, and are often automated and probably obsolete nowadays, I haven't heard of anyone doing it for many years.
For DC on stainless and mild steel you will want some thoriated or ceriated electrodes, size will depend on what you are planning to do, a 1.6 will be ok up to around 130 - 150 amps, and above that use a 2.4, no hard and fast rules here though and I regularly use both sizes outside the recommended range, keep a selection of electrodes collets and collet bodies, and different size ceramics available, have a read through the tutorial, loads of info to get you started there.

 

[Country Joe]

Hi there,
You're going to need a tig with ac capability to weld aluminium - no amount of practice will make it possible with a dc only set.**
As far as tungstens are concerned, ceriated (with a grey tip) are ok to use on ac or dc.
The ones I use are the Huntingdon Fusion "multi-strike" (with a blue tip) tungstens, which are also good for either ac or dc.
All the Best,
CJ

EDIT - TIG Paul types faster than me, and is more well versed at this, too!
**Until I read the above, I truly believed it to be impossible!

 

[scrimshady]

thanks for your replays.. I will get on the shop today.. is it not even worth trying to weld ali with dc tig. If it can then can I do it with the same ceriated tungstens or will I need some different ones

 

[FranV8]

Realistically, no, you'll need an AC machine. The DC techniques with helium sound like they have been left in the past, probably for good reason.

I guess you might end up wincing at helium gas prices too.

Although this might be interesting:

http://www.mig-welding.co.uk/forum/showthread.php?t=659

 

[Shox Dr]

DC Ali welding requires +300amps AFAIK

 

[hotrodder]

.. is it not even worth trying to weld ali with dc tig.

No.

If it can then can I do it with the same ceriated tungstens or will I need some different ones

Material being welded doesn't really come in to it. Traditionally the different tungsten flavours were mainly about welding with DC versus welding with AC. Pure and zirconiated tungsten are/were used for AC welding with thoriated used for DC. Over time other flavours appeared that work with both DC and AC

FWIW there are two different techniques that can be used for welding ally with DC. Neither are even close to practical for most people and jobs 99.9% of the time hence everyone saying don't bother trying
Aluminium starts to grow an oxide layer pretty much immediately it's exposed to the oxygen in air. This oxide layer has a melting point around 3 times higher than aluminium which means it can behave like a choc-ice... in this analogy the chocolate would be the oxide layer which remains solid while the ally (ice cream) has melted.

This oxide layer can be 'cleaned' electrically but the problem is that the polarity required for cathodic cleaning (this is what the white bands are next to an ally weld) is backwards to the usual DCEN (direct current electrode negative) used for TIG. Approx 2/3 of the arcs heat occurs at the positive electrode which melts the tungsten if DCEP is used. The solution is AC which provides both EN (for welding) and EP (for 'cleaning'). Not enough time is spent in EP to completely wreck the tungsten but there's enough to move the oxides.

With DC only if you use DCEN then you get zero cathodic cleaning. As said one way round that is PROPERLY ocd levels of pre weld cleaning together with the use of helium which results in hotter arc. Outside of automated welds it's only really practical on very thick ally, it's not easy and welding grade helium is 'kin expensive
DCEP is the other way. It's restricted to the thinnest of super thin ally as 1) a HUGE tungsten is needed to withstand the heat and 2)the heat is concentrated on the tungsten effectively leaving less for welding. A 3.2mm tungsten (which is typically the biggest that can be fitted into many torches) is good for only about 40A DCEP versus 250 odd AC and a lot more than that DCEN. You need around 65-80A AC for welding 1.5mm thick ally

Again, you need an AC/DC machine if you want to weld both ally and steel, stainless etc with TIG

 

[Shox Dr]

How do you get a 3.2mm to hold an arc, @40amps let alone get it to start?

 

[hotrodder]

Good point, i forgot to mention that arc stability can be a problem with oversize tungstens. Also forgot to say that not all TIGs can even be set up for DCEP, mine for example thinks you're being a numpty and won't work in TIG mode unless the torch is negative.

It wouldn't be the same as trying to use a 3.2 with 40A DCEN. Once the arc is estabilished the tungsten will be running a LOT hotter with DCEP. For some reason it's easier to start a tungsten with EP too... electron flows/tungsten heating/witchcraft Doubt it'd be fun, certainly not practical

 

[Shox Dr]

mine for example thinks you're being a numpty and won't work in TIG mode unless the torch is negative.

Mine does that too, you have to tell it

 

[hotrodder]

Mines more like the missus- it's convinced it's right and telling it otherwise doesn't help

 

[Seano]

Mines more like the missus- it's convinced it's right and telling it otherwise doesn't help

Man, you better not let your lass see that comment, you know whats gonna happen if she does.... LoL