Al welding problems - pulling out hair -help

[welder-guy]

Hope someone can offer some advice. I have had the same Miller 330 TIG machine (built in the 60s) for about 12 years. It still works great when welding ferrous metals. It has recently had very unpredictable performance on aluminum. I don't think I am the problem as I was able to get good results in past years. Sometimes I get a beautiful, shiny bead and a sound weld. Most of the time I can't even fuse the two pieces together??? When things go bad on aluminum, I get a lot of black appearing on the aluminum surface and cannot reach the puddle with the filler wire without it melting back into a ball. When things go well, I get no black and can easily reach the puddle without the filler wire melting back. It seams that somehow I am getting an oxide layer to form which then prevents a nice puddle from forming, arc heat must not be adsorbed by the metal and instead raises the temp in the surrounding area to the point where I can't get the filler wire in without the balling back effect.

1. Has my welder developed some problem? (adjust the point gaps inside?)
2. Am I doing something wrong - overheating/bad technique?

I have tried various surface prep methods, but primarily use a stainless wire brush dedicated for aluminum. I have ruled out bad shielding gas and bad tungstens. I have repeated my problems on a bunch of different Al alloysHelp - this is driving me nuts.

[HAWK]

welder-guy,

One thing you mentioned in your post really stands out to me: "cannot reach the puddle with the filler wire without it melting back into a ball". I have seen this before. It sounds a lot like torch angle.

If the torch is pointing forward it will direct the heat to the end of the filler rod causing it to blob up before you can get it to the puddle. It does not take a real pronounced torch tilt to cause the problem. Try running some beads on flat plate with the torch on a 90 degree from the work piece. If things clear up, try a fillet. Keep the arc focused in the joint rather than pushing it forward.

You may have other problems, but this is a good starting place. Let me know what happens.

[dyn88]

I think it mat be a combination of torch angle and dirty points, Its much easier for the arc to jump backwards, does the tungsten ball up more than usual. pull the points out put them in a drill and run it on some 800 grit or so emery cloth. replace set gap and try, if this cures your problem then order a new set of points and you are off.

[Luna]

What polarity, filler, material and what gas? Sounds like you are running DC or you are not getting good gas coverage (due to torch angle maybe???)

[Pile Buck]

Hi welder-guy, I agree with everything that has been said here already, but just to add I have a 1980’s 330 amps Miller Gold Star. I was noticing some problems with my machine on Aluminum a few months ago. Nowhere near the problems you’re having. About 3-years ago I had to have the transformer replaced for the High freak, so I was somewhat puzzled why problems now. Come to find out the capacitors were leaking. Replaced both of them, now it works great. Not near as well as an inverter tho

[ATCOEnt]

Welder-Guy,

"...black appearing on the aluminum surface and cannot reach the puddle with the filler wire without it melting back into a ball."

I agree with everyone that the "black" is from contamination caused by lack of shielding gas. I also agree with Hawk that the filler balling "may" be due to torch position but since you have gotten good results in the past, I suspect something else. The fact that these symptoms are happening at the same time leads me to think it is, as Pile Buck suggests, the capacitors.

My theory: If the capacitors "miss fire”, sending more current to the torch. The additional heat would (1) ball any filler material passed under it and (2) very likely increase the size of the weld puddle, maybe to a size where the shielding gas can effectively cover it any more.

I do not know if the capacitors can miss fire as I described but from what Pile Buck says it sounds like the best place to start looking. As an experiment, you might try flooding the weld area with argon to see if that solves your contamination problem.

[welder-guy]

What a great forum. Thanks for all the advice. I'll start troubleshooting by playing around with torch tilt to see if I can get things to improve, without getting into the welder hardware.

It is very interesting that there were suggestions concerning both points and capacitors. About 2 years ago, the fancy ceramic base that holds the points cracked and I had to cobble it back together. Perhaps the alignment is not quite right and something has gone wrong - I'll check it out and try the resurfacing suggestion. Also, there are a couple of large, rectangular capacitors that had leaked some oil a while ago. I had pulled them out, cleaned them up (thought they might have PCBs?) and tested their capacitance (no specs on what they should be - normal caps have this info listed on their case). The Fluke meter indicated about 31 uF each with no current leakage. The oil leaking has stopped, but based on the comments for you folks, I'll try to see if service parts are available. Thanks again and I'll report back with results as I go.

[Pile Buck]

Also, there are a couple of large, rectangular capacitors that had leaked some oil a while ago. I had pulled them out, cleaned them up (thought they might have PCBs?) and tested their capacitance (no specs on what they should be - normal caps have this info listed on their case). The Fluke meter indicated about 31 uF each with no current leakage. The oil leaking has stopped, but based on the comments for you folks, I'll try to see if service parts are available.

Bingo! I’ll bet that’s your problem. Look at this picture; the red arrows show the fluid leaking out of the capacitors, the blue arrows show the capacitors. I was told you can buy after market capacitors for like $20.00. I bought mine from Miller about $90.00 each.

[ATCOEnt]

I believe the "points" are only used for the high frequency. I doubt they are part of your "current" problem (pun intended). If your luck is like mine, your cobbled together points will fail immediately after you fix your capacitor problem.

[Zapit]

ATCOent---we must be using out of the same "luck" pool. That's the way it always works for me too!!!!