Aluminum GTAW

By Weldmedic (*)

Date 05-07-2001 19:36

Pure Tungsten is typically the choice for AC -HF Gtaw of Aluminum...

By Ti double-G er (*)

Date 05-08-2001 02:57

TimGary
Thoriated electrodes are usually reserved for welding steel or SS. These electrodes are extremely hard and ideally suited for grinding to a sharp point which will aid in maintaining a stable arc in DC welding applications. The problem with using thoriated electrodes with aluminium welding is that they are so hard that they will not "ball" on the end during welding. This smooth ball on the end of the electrode is essential for electron transfer between the work and the electrode. When you use a thoriated electrode it will form multiple transfer areas and the surface of the electrode will be jagged and bumpy. These are areas where the thoria and tungsten have separated sufficiently to form a tiny transfer ball.
Pure tungsten is a good choice but most production aluminium shops use zirconiated tungsten because it is significantly harder than pure tungsten and therefore will carry higher amperages for a given size yet it will form a good current transfer ball. Typically when I am welding unless I contaminate the end of the tungsten with aluminium I can weld for several days without regrinding a tungsten.
This is the rule of thumb for grinding a zirconiated tungsten (Zirtung)
D= Diameter of tungsten
End of tungsten ground to 3/4D
Grind taper back 2xD
Current capabilities of Zirtung and pure tungsten
1/8" Zirtung 160-250A
1/8"pure tungsten 100-180A
Good Luck
tigger

By TimGary (****)

Date 05-08-2001 11:26

Thanks alot for the useful information guys!
Hope I can return the favor some day...
Tim

By awill4x4 (**)

Date 05-10-2001 13:24

Tim, you can also give "ceriated" electrodes a try. They will hold a point much better than zirconiated and when fillet welding on Aluminium they get into the root better than zirconiated which tend to flutter from plate to plate. They also a dual purpose electrode and can be used for both AC/DC welding.
Regards Andrew.

By Lawrence (*****)

Date 05-10-2001 21:15

The latest and greatest minds publishing today, (including AWS and Miller) have begun to lean toward cerium (orange) as the alloying element of choice when welding AC aluminum. Ceriated electrodes have the highest current carrying capacity of all AC contenders, thereby reducing the risk of the electrode *spitting* into the work causing brittleness and making for embarrassing X-rays.

The next best choice would be Zirconium (brown) alloyed electrodes, Zirconiated electrodes have been the top AC electrode for the last 15 years or so, having a higher current capacity and more favorable emitting <arc transfer> qualities than the old standard pure <green> tungsten electrodes.

As we saw in a special article in one of last years "welding journals" AC welding of aluminum has taken several steps forward in the last few years, most notably with the introduction of Asymmetric power sources like Millers *Aerowave* which provide independent current control and adjustable frequency. These advances have made for an excellent proving ground for tungsten alloying, tip prep <many folks are also shying away from the *balled* tip> and manufacturing... we found out quickly that not all brands perform the same. This is a great topic and one I would love to talk to others about in greater detail. I'm very willing to share experiences from our trials.

But to make a long story short, your prolly looking for a tungsten that you can trust to make clean welds without running into bad X-rays and doesn't cost all that much. Zirconiated electrodes have been the standard for years and in my opinion are still perfectly adequate for general shop use.

AWS does provide text in the many times published and updated
"AWS/ANSI A5.12 Specification for Tungsten Arc Welding Electrodes."

Sylvania also has published text, which a layman can understand.

But the best advice of all may be to use a water cooled torch if possible and the longest electrode you can manage regardless of alloy. Cutoff tungstens and button caps on tig torches are great for areas of limited accessability but one looses the heat sink provided by a full length electrode. Believe it or not I have observed some of the Biggest Aerospace manufactures out there still employing thoriated electrodes in AC aluminum hand welding operations with excellent results, they are ever so careful NOT to overheat the electrodes.

Hoped that helped

God Bless

Lawrence Bower
United Airlines
Education Development

By awill4x4 (**)

Date 05-12-2001 13:22

Lawrence, I would be pleased to hear of your experiences with "asymmetric" Tig power sources. I have had on order for some time a similar machine to Miller's Aerowave except made by OTC from Japan.
It has similar features to the aerowave in that it employs Hertz compression up to 500Hz. It just has a lower amperage of 300 amps vs the aerowave's 375. It also employs something called hybrid waveform where it periodically combines ACtig with DCtig to enable good cleaning with deep penetration. This is going to be a steep learning curve I guess, as I have only used non pulse square wave machines like the synchrowave 250.
The machine is finally here in the country, (Australia) and is being demonstrated at an engineering exhibition at the end of May. The reason I chose OTC over Miller, is that I have previously used an OTC Accutig and just loved how it welded and the fact that with our dollar taking a dive recently vs the $US it made the aerowave just too expensive.
I would be very pleased to hear of your experiences with these machines and your electrode trials.
Regards Andrew.

By Lawrence (*****)

Date 05-14-2001 20:31

Andrew

In responce to your query of Asymmetric power sources I can talk about both of Millers Contenders, the Aerowave and the Dynasty.

I'll make a few quick points with as brief a background as possible just to get something out there and we will see where it takes us.

First the Aerowave, We have had several over the last 5 years and employed them on quite a large variety of jobs, all in the hand TIG welding arena. Aluminum Sheet and Castings using AC, Magnesium castings both AC and DC reverse. And DC straight with over 50 flavors of stainless and titanium for dessert.

With hand welding operations of AC Aluminum and Mag. we have discovered no benefit of frequencies above 220 Htz.

Most operators prefer Zirconium electrodes and make the observation that even though the melting point of cerium is a couple hundred degrees higher, Zirtung tends to keep the arc at the tip of the electrode in AC mode at high frequency and low amperage. All other electrodes have been observed to *climb* up the electrode even when in pristine condition working at low amperage (10-40 amps) as a ballpark figure.

At low amperage we find DC arc starting problematic. The mini-pulse of DC reverse which accompanies the HF has been known to "shine" the tips of tungstens during the frequent chattering arc starts. One simply cannot sneak up on thin material using the Aerowave, allowances must be made to come down on the foot pedal with authority or the arc just won't start with consistancy. The inverter used on the Dynasty is way better. When asked specifically about DC straight TIG hand welding our staff to a man prefers the performance of the Synchrowave 250.

The independent current control (amplitude on each side of the half cycle) provides further opportunity to keep to a smaller electrode dia. by way of limiting reverse polarity amps to just enough to get sufficient etch. This is where the Aerowave excells! The exaggerated balance control is also a wonder, providing all kinds of flexability in shaping parameters. But to get the most out of these fancy dials and settings the tungsten prep must be CONSISTANT AND CLEAN, any contamination at all pretty much renders these advanced functions useless.

Another interesting byproduct of the advanced circutry of the Aerowave is its uncanny ability to turn off auto darkening welding lenses (both battery and solar) while in mid weld. A phenomina one doesn't want to experience a second time.

Miller has improved the circuit boards over the last few years and were quickly responcive when our machines have given us trouble. Its been at least two years since an Aerowave has gone down.

However we do still experience disturbing effects such as change of polarity in mid weld on rare occation. Believe it or not one can be welding DC straight for instance, a piece of 321 stainless from 15 to 50 amps and the machine will just on its own switch polarity-the tungsten balls up the operator stops work and as proof we have a little etched circle at the end of the weld. I have experienced this several times as have other operators on several of our machines.

We keep plenty of scrap handy, being in the repair field its difficult to remove all variables and set out exact detailed parameters for our welders. The scrap provides us with material to *tune up* our machines, getting the most out of them without taking them too far.

I wish I had more encouraging things to add. I do still feel that the Aerowave is an excellent special needs machine which provides flexability never dreamed of by most AC welders. Surely the folks who employ automation in welding can also greatly benefit from what it offers.

I hope this helps, if I missed the boat completely please ask as specific a question as you like. There are so many details in every aspect of these machines which can be addressed, we could go on and on if we cared to.

Lawrence

"The Bible is the Rock on which this Republic rests."
President Andrew Jackson

By airweld (**)

Date 05-15-2001 01:42

I just received a new (to me) tungsten today from "Arc-Zone". It is a proprietary non-radioactive formula called "Arc-Time" and is claimed to be excellent for AC or DC. I was curious if you have had the opportunity to try them? Also, I have had problems with auto-hoods and inverters. I had to switch to a chin-operated hood because I could no longer trust the high-tech model. The frequency of the arc must not trigger the sensor as it should. Have you experienced any problems with the Dynasty DX? Especially in AC? I really enjoy this forum. Thanks everyone! Scott.

By awill4x4 (**)

Date 05-15-2001 12:56

Lawrence, thank you for your detailed info on "asymmetric" machines.
I find it curious that you get no obvious benefit of hertz compression above 220 hz. Does this then mean that Millers Dynasty is potentially the better machine with its compression of 250 hz? I'll be very interested when my new machine comes to see if I have similar problems with my Esab auto helmet, I sure hope not.
Do you use hz compression on thin Al sheet, or is it best used on thicker sections?
Is it true that hz compression welding on Al is more like welding DC electrode negative?
Will zirconiated electrodes form a point with hz compression or is grinding still required?
Have you had any experience with Lanthanated electrodes as replacements for thoriated electrodes? If so. What are your thoughts on them and are they suitable for a dual purpose electrode?
Are these machines difficult to "tune up" with so many variables?
I'll be very interested to test back to back with our syncrowave 250 to find out what works and what doesn't.
Thank you for you information. Regards Andrew.

By Lawrence (*****)

Date 05-15-2001 19:33

Hi Andrew,

That's a lot of questions, let's go in order. Keep in mind these responses are gleaned by *Subjective* observation.

The statement I made about the benefits of increased frequency in Hz applies to thin aluminum at low amperage only, For example, to get maximum accessibility to fillets ( Lets say 0.063 to 0.032 in 6061 T6) we have moved away from balled electrode tip prep. With a water-cooled torch and a full length Zirtung you can select a 1/16in or .0.063 diameter electrode with something like 75 degree included angle and an ever so slightly blunted tip. The effect we find most appealing is the (Conical arc), the arc appears to constrict and become much more directional as the frequency in Hz increases up to the afore mentioned 220 or so. The Extreme adjustments in balance control (up to 90% dwell time) the aerowave affords along with the independent power on each side of the AC half cycle (NOT available on the Dynasty) can really extend the capabilities of an electrode.
On heavy aluminum operations Miller suggests lower frequency in Hz. I agree, but my practical experience here is a bit more limited. The Dynasty goes as low as 20 Hz compared to the Aerowaves 40 Hz. This is great on heavy castings where it may be impossible to achieve the purity to weld DC straight on the heavy stuff. A puff of Helium can also extend performance when you're taking things to the limit. The Dynasty also has a more limited duty cycle, but the only time we have made the thing reset was during a training session in an attempt to find the limits of the machine. I'm gonna wait another year to further evaluate durability before a strong recommendation of the Dynasty but for now I will say that Its amazing to have a 250 Amp AC/DC Tig machine with all the options that I can pick up myself and put on the work bench.

On a more theoretical note. We have begun to experiment on scrap stuff, welding AC on Steels with Aerowave settings toward the maximum on penetration and straight polarity such as 80 amps Straight 20 amps Reverse balance to 90% penetration, AC frequency adjusted to between 300 and 400 Hz. When these parameters are applied to alloys such as Inco 718 or Hastelloy X, alloys in which operators usually observe what is called a *muddy pool*, this phenomina is seemingly etched away by that slight puff of Reverse polarity. You can actually see the oxide being etched from the filler wire as you dip it in, and yes we use clean wire in the first place :). Post weld visual examination will reveal a lovely wetting at the toe of the weld, which cannot be gotten by DC straight. The drawback of course is more heat input as a result of the Reverse polarity. The welder can bring the bead profile back to size with a quicker pace. What may or may not be going on at the micro level I'm going to keep propriatary because we have just not taken enough time with it to come to a conclusion that has any authority behind it.

Will you find parameters difficult? That depends on what you do. We are in the repair business so we see a great diversity of projects and very few production jobs that we can come down with exact, repeatable settings for such a machine. The Aerowave set on the normal settings that any other TIG machine might provide still excels them, switching so cleanly between + and - that High Frequency is not even employed. If you have a crack staff they will rise to the challenge and enjoy what your new machine has to offer… However we do have other folks who dislike the complicated nature, and rightly argue that most jobs do not require a Star Wars welding machine and are quite happy to stick with the ever trustworthy synchrowave 250

Lanthanum as a replacement for Thorium is fine, We have found Lanthanum to outperform all comers in the automated TIG arena for hand welding they are adequate but its not a real noticeable difference from Thorium. Try several brands before you settle on a vendor, some will bend rather than break or fracture lengthwise. I have been told that different vendors use different powder metallurgy methods making the things. So performance may vary greatly. I would NOT recommend Lanthanum as an acceptable AC electrode, low amperage arc stability being the chief problem.

I've tried before to get this topic going in the forum, Lets hope others will break open the treasure chests and share some of their wealth. I would sure like to know what other folks have experienced with this technology.

Enjoy

Lawrence

"Human law must rest its authority ultimately upon the authority of that law which is divine....Far from being rivals or enemies, religion and law are twin sisters, friends, and mutual assistants. Indeed, these two sciences run into each other.
"James Wilson, a signer of the Constitution and an original Justice on the U.S. Supreme Court

By awill4x4 (**)

Date 05-16-2001 14:16

Lawrence, again thank you for your detailed information.
As an aside. Is the "aerowave" still at the cutting edge of technology?
I have been hearing reports of something called "chopper technology" and have been told that inverter machines are now old hat and will probably be replaced with this new buzzword.
Unfortunately, I have been unable to find any information with regards to this new technology.
Kind Regards Andrew.

By Lawrence (*****)

Date 05-16-2001 15:54

Andrew,

The only experience I have with choppers has come via time spent with a few gents on my wifes side of the family :)

Here are some links that might help

http://www.lincolnelectric.com/products/tech/chopper.asp

http://www.csorbitale.com/ing/tecno/chopper.htm

http://www.esseti.com/uk/plasweld.htm