Troubke with plug welding (spot welding) with TIG

Date 04-07-2007 13:54

If you can get a preheat on the thicker member it should be no problem to plug weld. Another thing to try in conjunction with this is to put a big washer around the hole to act as a heat sink for the thinner member. The basic problem is to establish an even thermal gradient in the two members. As you discovered, the thinner member melts before the thicker one. So you need to get the heat on the thicker one first, and keep the excess off of the thinner one. As a last resort, and this may not work given joint access, but weld a little dab of filler on the thicker part first. Then center the plug weld hole over this bump and strike your arc on the bump and you should be able to establish a puddle on the thicker member. The instant it flows into the thin stuff, back off the heat and hope for the best.

By medicinehawk (**)

Date 04-07-2007 17:52

If you have a rheostat, point the tungsten directly perpendicular to the thicker base metal....come up on the heat and as the thicker metal starts to melt............ply in your filler wire. You should be using no more than 1/16" filler rod and better yet, use .035 diameter rod which will cut back on the heat required to join the two varied thickness materials.
At one place I worked we had to weld the exact same type thing and they use an on/off type rheostat where we set the amps around 100 (DCSP) and basically slammed the rod in as soon as you light-up the work. Took a couple of tries to get used to it, once you did.......it was alright.
It is really important to keep the tungsten on the thicker metal as you already know what happens to the thinner material IF you don't.
Good luck with that.
Hawk

By berntd Date 04-07-2007 22:37

Hi, thanks for the tips.

I did notice that the arc likes to go to the sides of the drilled hole rather than its bottom (ie the thicker material underneath). Even if I put the tungsten into the hole, the sides still melt first. Perhaps I need a different size hole?
Should I try and use MIG wire as filler rod perhaps?

I can't preheat the material underneath as it is not accessible and part of a larger structural part.

Kind Regards
Bernt

By billvanderhoof (****)

Date 04-08-2007 02:47

Make sure that the bottom piece is grounded.
Bill

By medicinehawk (**)

Date 04-08-2007 18:20

Bernt
Try using a longer stick-out. Instead of 1/4" of the tungsten from the face of the cup, try 1/2" stick-out. Use a really sharp tungsten too. You really should be able to heat the thicker base material first unless the hole you are plug welding is really small. The hole should be at least 3/16" in diameter otherwise you may get the problem you are experiencing.
If you have some mig wire (.035 or .045) and it is all you have......i guess it will have to do. It should work fine. The only reason I suggest using thinner rod is so you'll need less heat to melt the rod to add into your plug weld. Are you using an amp control (rheostat) ??? That'll really help too.
Be well.
Hawk

By berntd Date 04-08-2007 22:18

Hello

I don't have a reostat with foot control but I can use one hand on the front panel of the machine to control the current while welding with the other hand. I will try the longer stickout and sharper tungsten although my tunsten seems to melt rather quickly into a ball after only a very short time of usage.

Thanks for the suggestions!

Kind regards
Bernt

By Lawrence (*****)

Date 04-08-2007 22:33 Edited 04-09-2007 13:40

This is one of the few jobs (if you are producing a bunch of this type of weld) that a good diamond wheel tungsten grinder is a plus.

Hawk said it right when he said make that tungsten extra shap... But there is a little more to it.

When you prep tungstens for very thin work there are two ways you can go, each way provides a distinct difference in arc performance.

Long slim needle type taper
This will produce a bell shaped arc that is wide at the bottom and provides less penetration. This tip prep is excellent for very thin material (<0.040) and makes for the easiest arc starts. (good for groove welds)

radical taper
The more radical taper will will produce a more conical arc that will have a better directional control. This arc will penetrate slightly deeper and is a good choice for fillets. This type of tip prep can make HF arc starting a little more inconsistant in large diameter tungstens but I don't think it would be noticable at all in 0.062 or 0.040 diameter electrodes. No blunt on the end of this tip prep so the end is still sharp. For applications over 100 amps a slight blunt on the tip will give even greater depth in the penetration profile.

For most manual GTA welds this kind of stuff is not all that critical. In your case when you are looking for consistancy on thin/thick stuff you might find a slightly more radical taper is a good way to get the arc to go right where you want and keep the heat focused on the bottom member of that spot/lap. I would also suggest trying a 0.040 tungsten electrode.

Lots of folks think an extra sharp (like a needle) tungsten will give greater penetration... The opposit is true. But extra clean is a must..... any contamination on the electrode negates everything

Try the radical angles... try increasing incrementally and see when you notice a performance difference.

If your tungsten is melting in a ball that is a pretty big problem too. DC electrode negative. DCEN is what you must use for this operation. A water cooled torch is always best when you can manage. If you are using pure tungsten (green) loose it and go with Thorium, cerium or lanthanum

By Lawrence (*****)

Date 04-09-2007 13:42

This is what I'm talking about.

Pro Fusion has a great website with lots of good information.
http://www.pro-fusiononline.com/welding/applications/orbital.htm

By yorkiepap (***)

Date 04-09-2007 17:08

Hey berntd,
I am wondering why your use of TIG seems to be the priority factor to obtain thick/thin fillet welds. I do agree with the other guys on their suggestions with TIG, but the entire process you are trying to accomplish can be so much more effectively done with MIG, especially when you have many holes to do. When I weld the classic car floorpans(.020-.025) to the frame metal(.187-.230), I use .030 ER70S-6 @ 175A and when the puddle forms on the frame and fills the hole(.125dia.), there is a sweet button of weld that completely seals the pan metal and frame together without any elongation of the pan hole. It is fast, hot, and works so well. Just curious....Denny

By berntd Date 04-15-2007 23:38

Hi,

you are right BUT I don't own a MIG at this stage.

I have also been advised that MIG welding produces welds that are too hard to finish with a body file. I can't say if this is the case though.

The MIG is on my list of things to get in the future but then again, I could buy a proper spot welder instead...

So many wishes and soo little money :-(

Kind regards
Bernt