Help with tricky Aluminum joint

Date 03-28-2008 21:04

What problems are you experiencing? Guessing you are having difficulty with fillet welds; getting into the corner. Does your machine have squarewave ac with balance control? Set it for maximum penetration and point the ceriated or lanthanated tungsten. Do not ball the tungsten!! If the tungsten balls for the set amperage; increase the diameter of the tungsten by one size.

By 803056

Date 03-28-2008 21:32

Wow!

I've never seen a tungsten that didn't want to ball up when using AC anywheres near the amperage range needed to weld aluminum. The exception was when we welded aluminum using DC with thoriated tungsten. In that case, helium, DC straight polarity, a sharpened EWTh-2 electrode, with clean joints, and you were ready to go!

I'll have to give that a try.

Best regards - Al

By 522029

Date 03-29-2008 12:48

Lanthanated (my preference) and ceriated tungstens will form only a very small ball even when used at the top of their amperage range on AC. This makes it much easier to focus the arc where you need it.

Griff

By rlitman (***)

Date 03-29-2008 13:41

I've used Lanthanated and Zirconated tungstens with no issues. You just need to use a size or two larger than you would with DC.
Basically, you can grind like for DC, with say a 60 degree angle, and knock the point off. Then, under A/C, only the very tip will melt, leaving most of the original grind angle, with just a rounded off tip.

Back to the original question:
If you're having trouble keeping the arc focused, does your machine have a frequency control? This is something only available in inverter machines, but a higher frequency can really tighten the cone of the arc. Much more than you would get than from just controlling the tungsten tip size.

If you're using an air cooled torch (although that's kind of hard to imagine for aluminum production work), a water cooled torch will fit into tighter places.

By Glen Gardner Date 03-29-2008 18:16

Thanks folks,
I'm using a shiny new Lincoln275 square wave TIG machine(not an inverter type). To all you Miller Synchro fiends, I'll tell you, this Lincoln really is a sweet unit! It has the smoothest DC start I have ever seen. Back to my problem. It is a thick/thin section nightmare for me. The Lincoln has an "automatic" option on the square wave control and I have been using this. This feature can be overriden but I have not tried a "full penetration" setting because I am afraid of blowing through the tubing wall, (only .065"). I'm using pointed 1/8" Zirc. electrodes at 180-200 amps (within specs.). Remember, these 1/2"od tubes are set into blind holes in a 1"x3"x3" manifold block and are spaced under 1/2" apart. I get a nice bright, gas tight weld on the first tube BUT when the fillet comes to the tight spot it almost always has a micro leak. Most times I must clean out the area with a burr and try again and again and............... I have tried a wire screen type gas lens but They NEVER seem to work as advertised, 3/4"-1" overhang! Yeah right! I have convinced the designer to add more space between the tubes but i still have several of the old style to get through. Maybe I just have to bite the bullet and consider that the guy on the end of the cable just(me) needs more adjusting. Thanks for your input

GG

By Lawrence (*****)

Date 03-29-2008 21:11 Edited 03-29-2008 21:20

I quit rounding the tips of my tungstens 15 years ago... Never looked back

I will put a blunted point on an electrode with a radical included angle (as opposed to a long slim taper)

With Cerium or Zirconium the tip will slowly round off as time passes. Cerium will take a good 30% higher amperage than Zirconium and 50% more than pure. I use this tip prep regardless if the power supply is a transformer or an inverter.

The only time I would consider a rounded (balled) tungsten would be for a build up on plate or a casting lug, where I had a specific intention to produce a wide puddle with shallow penetration. (never for a fillet) The technique of balling the tungsten was devised to stop pure tungsten electrodes from degrading and spitting into the work... Now-a-days the alloyed tungstens (Ceria, Lanthana, Zirconium) have increased the current carrying capacity to a great extent compared to pure tungstens, so much so that a pointed tip prep can be normative.

With a water cooled torch and a 3/32 or 1/8 cerium electrode prepped as mentioned you should be able to get good arc control with your Lincoln when you over-ride the automatic balance (a stupid function to my mind) and set your balence control to about 8 of 10. (this assumes your surface prep is top notch)

I see little benefit to gas lenses used on aluminum.... The screen gets chattered up too easily if there is any rectification for any reason. I would think more along the lines of a long thin custom cup if nothing regular will get you close enough.

A 50/50 Argon/Helium mix might put just a little more pop into your weld also.

Burn thru on a thick/thin job like you describe will always be controlled by good electrode angle and cooling the puddle with your filler.. Balence control will have a negligable effect on a fillet like you describe if your torch angle is correct.

A removable copper chill ring inside the tubes would be a benefit if there is a way to get them in and take them out.
The job you describe is one of the few out there that would really get a benefit using an inverter with AC frequency control set to about 220 Hz. (This is no knock on your Lincoln) The increased frequency added to a pointed electrode will make a very conical arc plasma and concentrate your heat on the thick member of a thin/thick fillet in a way that transformer machines just can't do.

By Glen Gardner Date 03-31-2008 23:09

Thanks Lawrence,
I will mess around with the balance control. I did try 50/50 but not enough difference to warrant the xtra $$$. I suppose I could try some smaller cups. I'll keep downsizing them until "the smoke comes out". Maybe I should set up a purge line to add a little more cover? Actually burn through of the tubes has not been much of a problem. I know the main problem is getting a good angle on that last 1/4" of weld.
Most of the work I have done in the past was on my sculpture and architectural details. Pressure tested welds were not really an issue, more a matter of pride. A bad fire in the building where I had my workspace left me looking for a job in the "real world" until I can re-locate my studio. So now I am welding aluminum fuel tanks, oil filters, and heat exchangers for a small company that retro fits diesel engine vehicles so they can run on waste vegetable oil, or WVO as it is refered to. This is NOT biodiesel. Because of the viscosity of WVO it needs to be warmed before it can flow to the engine. I'm building the stuff that allows the system to work. And it works beautifully! With only 1-2% difference in engine performance and 75% lower emissions. And, the exhaust smells like french fries, seriously! Anyway, the work is challenging the pay is decent and I'm getting my "Greenie" merit badges to boot.
Thanks for your help. I'll report back after the next few exchangers are finished.

Glen G. in Pgh.

By ssbn727 (*****)

Date 04-01-2008 06:35

Hi Glen!

Where in the "burgh" are you located?

Small world!!! I live in Robinson Township, near the Pitt International... Have you gone to any of the local AWS section meetings yet?

Anywho, I saw that show on the science channel called "Invention Nation" and, the Ford Econoline bus they use to travel around the country operates on the same type of system you're talking about!!! ;) Very interesting "Green" technology being already use or in development that looks real promising to say the least!!! One of these days, I'd like to see one of those systems designed for gasoline engines!!! Send me a PM (Private or Personal Message) so I can send you some pics of some of my sculptures.

Keep up the good work! ;)

Respectfully,
Henry

By 522029

Date 03-29-2008 22:57

A size or two larger.??? Why?

Frequency control "only available in inverter machines" ?????

Griff

By Lawrence (*****)

Date 03-30-2008 03:02

Griff

Can you name a Transformer Rectifier CC power supply that can change the AC frequency to anything other than the 60 Hz that comes from the power company?

Do tell us more.

By DaveBoyer (*****)

Date 03-30-2008 04:54

Griff: Transformer machines are locked to the input frequency, 60Hz in the US and 50 HZ in some other countries. An inverter uses a different type of coil, an inductor operating at high frequency to charge banks of capacitors [You have DC at this point]that are then inverted to AC by transisters. This type of circut can provide an output frequency over a wide range, unlike a transformer.

By 522029

Date 03-30-2008 13:07 Edited 03-30-2008 13:10

You guys are right. I was thinking about the balance control. My bad.

Griff