Blown 6g AL test

Date 08-11-2007 06:16

Have a fellow that was at one time a welder for the company I work for....he has been rehired as a bench sheet metal guy but has been given a little xtra pay on the premise of qualifying as a welder as well for backup when needed. Well it took quite a bit of metal and time for him to feel comfortable and ready to submit coupons for the first alloy group 6061. His 6g failed for porosity (everyone visually approved this one except me), all his others passed. I had him switch over from a synchrowave 250 to my aircrafter 330st tonite just to see if it was settings or technique.

The test is a .032 x 1/2 6061 tube. Running a trickle of backup gas on a fixture I made ...he likes to run it with a slight gap and 45 bevel. I run one at about 45 amps (mid range on 20%) anywhere from 2/3 to full pedal, 1/16 tungsten fairly sharp slight round, #4 cup, 100% argon at 20cfm. Result nice shiny bead, bout 1/4 wide, good laps, just a hair of pen. He runs three or four and all the beads are inconsistent in height, are 3/8 or more wide and all have telltale signs of porosity just under the tops of the weld...(looks like sand trapped in the weld). I correct him on his torch angle and stress keeping his cup pointed almost neutral and closer to the work...he has a habit of pushing the arc around the tube at a severe angle. I am kinda at a loss for suggestions to help this fellow ...he has to submit two of these now that pass or he will have to do the entire test over from scratch. So by doing this on the same machine / settings it has made it obvious to me its a technique thing...he wanted to turn it down some so we did results no different. The only thing I know to tell him is to practice some larger tubing and get that looking perfect then work his way down to the 1/2" I know they are not going to give him forever to "practice" this either. If anyone would like to chip in some advice I can pass on to this fellow it would be welcome.

By yorkiepap (***)

Date 08-11-2007 11:56

Hey Tommy,
It sounds like you're doing your part to help this fellow improve his technique & get the certs he needs for the position. Has he watched you weld & your technique closely so he can see the proper method to get optimum results? I'd really stress the importance of adjusting his technique and make him practice till he gets it...or not. If he can't pass the test, he is not going to be of much value in that area. Simply ask him..."How bad do you want this position & pay?" Hopefully, he'll get the message....Denny

By Lawrence (*****)

Date 08-11-2007 13:02 Edited 08-11-2007 13:10

Tommy,

Your friend is getting good advice from you.

That "trapped sand" phenomena he is observing exactly what you think, very fine porosity. The tiney bubbles are from Hydrogen. When Aluminum is molten it is very souluable to Hy. The longer an aluminum puddle stays hot the more Hy it absorbs. When the puddle cools the Hy is forced back out, unless there is so much Hy that it freezes into the puddle before it can escape. So in simple terms, the puddle/weld has been overheated. This "trapped sand" apperence can be seen even in perfectly prepped material.

Here are a few things your friend can do to reduce the Hy in his aluminum welds.

1. Perfect surface prep and clean wire. I'm sure you have all the particulars here Tommy.

2. Loose the root opening and bevel. (this may well be his cardnal sin) 0.032 aluminum should a tight butt joint and a square groove weld.
The gap and bevel only cause more heat and filler to be required.

3, Perfect torch angle. A torch angle as close to perpendicular will give the deepest pen and the most narrow bead profile. When that angle starts to go to a steep push (as is common on small dia pipe) the puddle becomes oblong and about 50% heat and time are taken to make the weld, as well as increasing the risk of poor gas coverage (in comes Hy)

4, Travel speed. Aluminum likes to be welded hot and fast.. (I know you know this) But folks who Tig on steel and stainless sometimes don't make this connection right away. It takes practice, but the faster you go the more consistant the overall weld will be.

5, With practice some welders can actually cool the weld puddle by adding a bit larger diameter filler. When you see that nice shiney top to your weld and still have the good etching on the toes you know you have cooled your puddle. (This shiney top might signify a cold weld on thick material, but with your 0.032 you will see your backside fusion right away to check)

6, Balence control... The synchrowave has balence control, If he has it set to Max clean there will be more heat on the work than is necessary. A balence control setting (on synchrowave) of about 7-8 is a good place for him to be. Now the Aircrafter (What a missnamed piece of equipment) runs strictly on an AC sine wave so no balence control is available.... With this one you must just concentrate on 1-5 above.

7. Lastly, Does his torch hand have some insulation from the pipe? Lots of new aluminum welders don't take that high rate of thermal conductivity into account and when that hand starts to heat up technique gets a bit sloppy in the distress of pain. (boy do I ever know about this one from *repeated* experience)

By makeithot (***)

Date 08-12-2007 23:03

Well written Lawrence. You have answered alot of question that I have had without haveing to ask them. At what thickness do you consider it benificial to bevel your material ? How is the Hy effected in muti-pass procedures? Can you work it out or will it be trapped in the next pass?

By Lawrence (*****)

Date 08-13-2007 04:16

Richard,

Those are really good questions.

I think the first question about beveling (and root openings) might be addressed in D1.2, but I don't have it handy. Kind of depends on whether we are talking about plate or pipe, whether backing is used, distortion control measures, restraning fixturing etc... Basically an engineering decision beyond my paygrade :) Just by personal experience, 0.090 to 0.125 can be butt welded with a tight square groove. This is made easier with a hybred asymmetric GTAW power supply. Maybe others can speak to thicker stuff.

Multi-pass effects on entrapped Hy? Again above my paygrade. But if you had access to RT equipment it would be interesting to run some trials. Usually multi-pass welds indicative of thicker sections where heat buildup is less of a consern. (although thick sections can be overheated by a slow GTAW operator, especially at weld terminations)

By Kix

Date 08-13-2007 12:59

I would never use a gap on aluminum. I'd go straight butt all the way up to 1/8'' and then start beveling after that still with no gap and as you get up into 5/16'' and thicker start useing a j-bevel with no gap. Your getting porosity from that root opening i'll bet cha. Try what Lawrence suggested and run it with no gap with the same purge. This will be a more consistent technique with better results for your specific application.

By makeithot (***)

Date 08-17-2007 03:37

Thanks lawrence and Kix, I was asking in regards to plate welding 5086 to be exact. I have used no root opening but have beveled one side and back gauged and welded the other in most cases it has worked well on 1/4"-5/16" material. but the odd time there tends to be some porosity. Have also done alot of muti pass work on 3/8' (root and cap ) over head and it has run in well. I was just curious as to how much hy is being trapped if any, using that proceedure. The individual that this work was completed for had no interest in testing or proofing these procedures so I am just trying to satisfy my own interest.

By Sourdough (****)

Date 08-13-2007 17:37

Tommy, how many times have you busted someones visual for arc blow to the side of the cap? Failed my first 30" visual for one spot of arc blow where my hand slipped. It was so minute, you had to really look close to see it.

I know arc blow can really weaken carbon, but how critical is it really?.............

By aevald

Date 08-13-2007 19:10

Hey Sourdough, did you mean to say "arc strike", just curious? There are a couple of threads that have gone to fairly great lengths to discuss the pros and cons or possible damages that can result from arc strikes. Just wondering. Regards, aevald

By Tommyjoking (****)

Date 08-14-2007 06:15

LOL THX for the props SD but I am just a welder I am no inspector....I have no authority to bust anyone. I am just trying to help a guy pass his test which is very rigourous.

I have passed on your advice Lawerence which is really confirmation of what I thought about it all. The spec is D17.1 so gap,bevel, metal prep, machine settings etc. are all up to the individual taking the test. I Have warned him about a gap before and I think now I have him convinced to butt it up and just run it. We will see how it goes I rekon. I purchased him an inspection light so he can check the pens on his practice pieces.....damm hard to get a good look in a 1/2 pipe LOL. It all worries me a bit for him because he has 12 more coupons to do if he passes this one (total 17). Two of them being long fillets on .032 ss and 4130 with minimal distortion, throat pen and absolutly no burn thru (suckback) allowed. Those kinda suck if your 54 and your hands are starting to shake a bit. If he can just get these two 6g's done at least he will be in the door as a welder albeit limited.

THX for the help all

Tommy

By stormey warren Date 06-27-2008 15:06

hey hows it going? i had some questions about the aluminum 6g weld test i just dont know how to get started really? if you have any info please let me know.

By Tommyjoking (****)

Date 06-28-2008 13:48

sTORMY If its the standard 1/2"x.035 6061 6g for aircraft work.....My best advice is 1. practice 2. practice 3. practice.....4. Use about 25% more heat on your fine knob then you think you need. 5. Make sure you use at least a #6 cup with gas at about 20 cfm or a #6 lens with gas at 30 cfm with a 1/16 tungsten. 5. You need to move QUICK....practice rolling your torch around the joint in your fingers on each side before you start (make sure grip and hand position is good) If you have to reposition mid-weld, keep your rod under the gas, back off enough to let it solidify, step back in it hard and move on. 6. Keeping your cup pointed neutral all the way round is very important.

For larger AL tube and pipe.....prepare yourself a heatsink pad out of an old glove or what have you...either attach it with tape or zip ties to your torch hand pinky finger or the pipe....so either way you can rest your torch hand as you work around the joint. If its real heavy stuff you will have a groove to walk your cup in. Other than that there has been enough said in this post to get you going on it. Good luck man.

Tommy

By Sourdough (****)

Date 08-14-2007 21:48

yEP ARC STRIKE, sorry for the mixup.........margaritas.

By mechan

Date 06-29-2008 02:01

1/16th tungsten is pretty over used by air craft guys and has a tendancy to blow apart. 3/32 is alot more versitile and eliminates the issue of failing the cert because of tungsten showing up in the weld when x-rayed.