[grega09]

I'm designing a welded tubing structure and I will have to weld it soon. I did some test run welds shown in the photo.
I'm TIG welding carbon steel tubes of outer diameter 12 mm and thickness of 0,75 mm (sorry for metric units) in tubing structure.

I will write the settings I used to make the weld on the photo:
- I use 4T setting on my machine and I don't have a foot pedal,
- I use wp26 size torch and now I'm looking to get tg9 size, so this will make things a little bit easier,
- 1,6 mm electrode,
- cup size: 4, 5 or 6, depends how much room I have,
- argon setting: 7 L/min,
- preflow: 1 s,
- start current: 25 A,
- up slope: 3 s,
- pulse peak amps: 50 - 60 A,
- base amps: 20 A,
- pulse frequency: 33 Hz,
- peak time on: 33 %,
- down slope: 2 s,
- end current: 5 A,
- post flow: 4 s.

I'm not happy with the welds yet. Maybe someone will notice a strange setting or has better experiences with some other settings. Please check and let me know what can I correct.

It is also hard to weld when tubes come together under sharp angle. Sometimes also a strange thing happens, like the puddle "explodes" and jumps on my electrode. I think that happens because of poor shielding, but I'm not sure. I don't use back side argon shielding.

Basically, I'm looking for some pointers for that kind of tubing welding - small and thin. Every advice will come in handy. Thanks.

[Coldman]

Explosion is contamination from the prep or lack of shielding. You may have to flush the inside of the tubes and I would increase the argon flow a little and also double post glow. A gas lense may work better for these joints and you can increase stick out to get to the tight spots no probs


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[grega09]

You may have to flush the inside of the tubes and I would increase the argon flow a little and also double post glow.

What should I flush the tubes with? And sorry, I don't understand that about double post glow. Can you explain a little bit more, please?

[Coldman]

By flushing I didn't mean argon flush I meant get any oil residue or crud out from inside with acetone or similar in case that's what's causing the contamination explosions. Internal rust will do it too. Clean to shiny if possible.

[zank]

Are you venting the tubes? If not, that is likely the cause of the puddle exploding out. Drill a small 3 mm hole into the tube where it gets covered up by the coped tube. It will give the hot expanding gasses a place to go.

[grega09]

Ok, I understand. Outside I clean the tubes with acetone, but inside I cleaned them only with compressed air. I will try and clean them with acetone on each side inside also.
I will do some test welds first without the venting holes, just cleaning and then add the holes if there will still be the same problem.

[grega09]

I forgot to mention one thing.
Usually these "explosions" happen when welding carbon steel with proper carbon steel filler material. I also get porositiy with that filler a lot. It is really strange when I'm looking at the puddle it looks like new small holes are constantly appearing in the puddle as if it was boiling in some way. I tried once with stainless filler and in 95% I got rid of that problem. But sometimes I don't want to weld with stainless filler because the weld I'm making should be structural strong and I want to use proper filler. That's when I'm angry when these problems appear.

[Coldman]

What filler are you using?


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[zank]

You need the vent holes.

[Poland308]

Vent holes are critical. Even on something like a big tank with a jacket once you get close to being totally sealed it will blow out. On a large pipe or a large vessel I can let things cool and close the last hole real quick without it expanding enough to cause issues. But on small stuff you need the hole!

[grega09]

What filler are you using?

For this project I'm using VAC 60 (ER 70 S-6) filler for carbon steel tubes. I have also some carbon steel to stainless 316 welds. There I use 18/8/6 Si (ER 307) filler.

When I got problems with boiling and corosion with less critical welding I used 316LSi filler. Regular filler 1.5125 (ZE SG 2) usually causes me problems.

I will try the venting holes. Didn't know they were so important.

[Coldman]

ER70S-6 should be ideal for this work.


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[grega09]

Here is another image of one of the welds.

When welding I have a feeling that it is going too slow and I heat the area around the weld too much. But for faster welding I have to increase the amperage and then I make a hole quickly. Can I change any setting in pulsing so that will be easier?

[Otto Nobedder]

That is way more weld than the material requires. For 0,75mm, you only need 0,75mm of weld. For confidence, 1,5mm of weld does no harm. Those welds look a good 4-5mm, and undercut from the excessive heat.

Focus your arc closer and make smaller welds, and 90% of your trouble will go away. You can even skip the vent holes, if you pause before closing, let the tube cool a bit, and close in a short burst.

Steve S

[grega09]

Thanks, I will try these things. What is the recomended size of tungsten and filler material for that kind of tube joint dimensions?

[noddybrian]

Tungsten size if kept sharp is fine with the 1/16" / 1.6mm your using in my experience - but at those amps you could drop down if want though I doubt this will help much - the torch size will make a huge difference & I would try to get a regular style tube handle basic torch in #9 series - not that great clumsy euro style thing in the comparison picture - ( personal thing but I hate them ) how well the project goes is going to depend a bit on your experience as until you have enough hours practice welding around small diameter tube joints is very hard to do well - the rapid change of angles required tends to give an erratic travel or you spend too long & overheat everything around the joint - unless you have a good number of hours & can do neat welds in the flat position I might try using the machine with a little up slope / down slope & pulse manually with a torch switch - only do short runs while using filler & stop every time the torch gets to a bad angle or you can't see adequately ( bit like Wyatt ! ) try laying the filler in the joint first & light up on that to prevent blow through - then use lay wire style in short bursts - although slow don't worry how many stops / starts you have & once there is enough filler around the joint you can let it cool & do a " wash " pass to smooth it out ( not ideal but will work till you master a better way ) - if you are trying for a fairly wide weld due to say vibration cracking if this is a part for say a motorcycle then brazing / silicon bronze maybe a better way & was widely used for this application ( many still use it ) as the lower heat input & easier flow characteristics suits thin tube joints - best of luck with it & if you don't mind sharing what this frame will be used for someone may come up with a better way.

[zank]

What diameter wire are you using? 0.9mm would be the max size I would want to use.

[grega09]

I was using 1,6 mm tungsten and 1,2 mm filler with this one.

This is a prototype of an archery sport requisite I'm working on for some time now. Will see how it will work. First impresions were very good. It is subjected to quite some loads, fatigue also. And low weight is also important.

[electrode]

Are you venting the tubes? If not, that is likely the cause of the puddle exploding out. Drill a small 3 mm hole into the tube where it gets covered up by the coped tube. It will give the hot expanding gasses a place to go.

+1 Been there, figured it out, drilled vent holes on the underside of the tubing. You can plug the vents later if you are quick. Or as I learned shortly after that, I drilled my holes under the coped up part where it fit ti the next pipe. Like Zank said.