Welding thin wall tube flush

[bulrich]

In our shop, we have a part where a very thin wall Inconel tube needs to be TIG welded flush into a hole in the side of a much larger, thicker tube. (The small tube is about 0.015" wall thickness and 0.070" OD, while the large tube is about 1.5" OD with a 0.090" wall thickness.) The hole for the small tube is about 1.5" down the length of the larger tube, so it's pretty fiddly to access.

We currently stick the tube in just barely flush, weld it in place, and then spend some very tedious time EDMing the hole back open, which frequently fails and requires us to rework the part again.

Any ideas of how we can keep the end of the tube from closing up during welding? We were going to try sticking a ceramic rod (https://www.mcmaster.com/87065K41/) through the hole, but we tried it under the TIG torch and it just explodes.

[tapwelder]

Can you use a different process for connection? Silver solder would probably provide more strength with flush fit, maintain tube dimensions, and require minimum finish on interior. Dremel work.

If welding is required a Sacrificial brass bar could be inserted then ground away from inside the tube.

[chewinggum]

In our shop, we have a part where a very thin wall Inconel tube needs to be TIG welded flush into a hole in the side of a much larger, thicker tube. (The small tube is about 0.015" wall thickness and 0.070" OD, while the large tube is about 1.5" OD with a 0.090" wall thickness.) The hole for the small tube is about 1.5" down the length of the larger tube, so it's pretty fiddly to access.

We were going to try sticking a ceramic rod (https://www.mcmaster.com/87065K41/) through the hole, but we tried it under the TIG torch and it just explodes.

Maybe try a tungsten rod through the hole?
CG

[smithdoor]

I have been told to gas (CO2 or Argon) in tube as you weld or solder. This would keep the tubing open.

Never had job to try this one.

Dave

In our shop, we have a part where a very thin wall Inconel tube needs to be TIG welded flush into a hole in the side of a much larger, thicker tube. (The small tube is about 0.015" wall thickness and 0.070" OD, while the large tube is about 1.5" OD with a 0.090" wall thickness.) The hole for the small tube is about 1.5" down the length of the larger tube, so it's pretty fiddly to access.

We currently stick the tube in just barely flush, weld it in place, and then spend some very tedious time EDMing the hole back open, which frequently fails and requires us to rework the part again.

Any ideas of how we can keep the end of the tube from closing up during welding? We were going to try sticking a ceramic rod (https://www.mcmaster.com/87065K41/) through the hole, but we tried it under the TIG torch and it just explodes.

[albrightree]

When I do stainless sanitary tubing I use aluminum backer tubes, or rounds that are a few thousanths smaller than the stainless tube ID. You could also use copper, or graphite welding blocks, or rods. Aluminum is cheaper, and easy to machine. Maybe you could use some of the EDM carbons ?

[tapwelder]

I think they are welding small tube from inside the 1.5 inch tube?

[shovelon]

Any ideas of how we can keep the end of the tube from closing up during welding? We were going to try sticking a ceramic rod (https://www.mcmaster.com/87065K41/) through the hole, but we tried it under the TIG torch and it just explodes.

I have used graphite inserts to weld against in the mold repair industry. If used on inconel the residual graphite is removed via passivate.

[bulrich]

I think they are welding small tube from inside the 1.5 inch tube?

Yup -- we don't have access to the outer surface of the large tube, we're slipping the small tube through the assembly that holds the large one.

Otherwise, I would really like albrightree's idea.

[bulrich]

I have been told to gas (CO2 or Argon) in tube as you weld or solder. This would keep the tubing open.

Never had job to try this one.

Dave

Interesting -- as in using the gas pressure to keep the weld metal out of the tube end? I'd have to see what our welders think -- seems like it might blow molten filler all over inside?

[bulrich]

Maybe try a tungsten rod through the hole?
CG

We debated this, but it would be hard to avoid contaminating the weld...

[bulrich]

I have used graphite inserts to weld against in the mold repair industry. If used on inconel the residual graphite is removed via passivate.

This seems like an interesting option. You mention residual graphite -- is this just on the surface of the weld (not mixed in the weld itself)? This is an aerospace application, so I'm going to get a lot of questions in engineering review.

[bulrich]

Can you use a different process for connection? Silver solder would probably provide more strength with flush fit, maintain tube dimensions, and require minimum finish on interior. Dremel work.

If welding is required a Sacrificial brass bar could be inserted then ground away from inside the tube.

Silver solder was the first suggestion both the welder and I had, but it was rejected for some reason. I'll have to push this one again, because it seems like the obvious solution. (I wasn't around when it was rejected, so I'll have to ask more to understand why.)

[smithdoor]

I have use silver solder the down side is cost for high strength solder.

It works great on steel and stainless.
I use on bandsaw blades too.
Silver solder is great for lap joints.

Dave

Silver solder was the first suggestion both the welder and I had, but it was rejected for some reason. I'll have to push this one again, because it seems like the obvious solution. (I wasn't around when it was rejected, so I'll have to ask more to understand why.)

[bulrich]

I have use silver solder the down side is cost for high strength solder.

It works great on steel and stainless.
I use on bandsaw blades too.
Silver solder is great for lap joints.

Dave

Yup, we use a lot of silver solder here. Still trying to find out what the hang up was -- perhaps required heating the part too much? There is a lot of thin sheet metal nearby. Cost is definitely not an issue for these parts. Hopefully I can get a more definitive answer on that soon.

If I'm not allowed to use silver solder, I think I'll look into using graphite to keep the hole open, if we can avoid impurities on that route.

[BillE.Dee]

would ultra sonic vibrations help?

[bulrich]

would ultra sonic vibrations help?

Could you be more specific? What do you mean?

[SweetMK]

I have no idea how big the entire WIDGET is,, or what it is, for that matter,,
but,,
we had a shop of 20+ welders that made similar assemblies, every day, some that size, some a little larger, Inconel 718 was a typical metal for us.
The product that this shop built was thermocouples for gas turbine engines,, we even made the replacements for the original engines on the B52 bomber,,

We TIG welded some, torch brazed some, electron beam welded some, laser welded some, and vacuum furnace brazed a LOT of them,,

To assemble the parts, put a little paste on the joint that looked like toothpaste, and run it through a furnace, and have it come out perfect was just amazing.

So, to give you an answer that will solve the problem with TIG welding,, Hmmmmm,, that might not be the best answer,,

[bulrich]

I have no idea how big the entire WIDGET is,, or what it is, for that matter,,
but,,
we had a shop of 20+ welders that made similar assemblies, every day, some that size, some a little larger, Inconel 718 was a typical metal for us.
The product that this shop built was thermocouples for gas turbine engines,, we even made the replacements for the original engines on the B52 bomber,,

We TIG welded some, torch brazed some, electron beam welded some, laser welded some, and vacuum furnace brazed a LOT of them,,

To assemble the parts, put a little paste on the joint that looked like toothpaste, and run it through a furnace, and have it come out perfect was just amazing.

So, to give you an answer that will solve the problem with TIG welding,, Hmmmmm,, that might not be the best answer,,

We run all of those process in our shop as well (although it's been a while since we've EBW'd anything). Furnace brazing is out due to the construction of the part, and EBW and laser welding don't gain us much over TIG in this case. I'm certainly not set on the idea of TIG welding (silver solder seems nice), but I definitely want to learn more about how we could handle this with TIG. I have heard 3 possible ways:
- Using graphite to stopper up the hole (may need to be passivated to clean up afterwards)
- Using some sacrificial brass to stopper up the hole, which leaves us with something easier to machine out (compared to inconel filler wire)
- Use compressed argon in the tube to keep the end blown clear (which comes with some unknowns in terms of possibly blowing the filler around during the weld, etc)

I'd be happy to hear any other suggestions on how we might do this with TIG (or laser) welding. (I won't turn down suggestions for other processes, but I'm well aware of other options -- just wanting to explore and learn more on the TIG welding option, since I spent so much time scratching my head on that one.)

[tapwelder]

Are you looking for a perfect seal. I would be interested to know how you weld inside a 1.5" inch tube? Seems like it would be difficult to see?

[LtBadd]

The hole for the small tube is about 1.5" down the length of the larger tube, so it's pretty fiddly to access.

So you're welding the .070" tube to the OD of the 1.5" tube? Why is that "fiddly" to access?

The ID of both tubes has to be purged with argon then it shouldn't close up unless excessive heat is used,
then I would expect you'd blow a hole in the thin tube anyway.

Can you post a photo of your setup?

[smithdoor]

What ever welding you do has heat.

Dave

Yup, we use a lot of silver solder here. Still trying to find out what the hang up was -- perhaps required heating the part too much? There is a lot of thin sheet metal nearby. Cost is definitely not an issue for these parts. Hopefully I can get a more definitive answer on that soon.

If I'm not allowed to use silver solder, I think I'll look into using graphite to keep the hole open, if we can avoid impurities on that route.

[danielplace]

Yup, we use a lot of silver solder here. Still trying to find out what the hang up was -- perhaps required heating the part too much? There is a lot of thin sheet metal nearby. Cost is definitely not an issue for these parts. Hopefully I can get a more definitive answer on that soon.

If I'm not allowed to use silver solder, I think I'll look into using graphite to keep the hole open, if we can avoid impurities on that route.

Reading suggests brazing would have to be done in a vacuum.

https://www.industrialheating.com/bl...3-filler-metal

[albrightree]

[tapwelder]

Thanks

[G-ManBart]

Furnace brazing is out due to the construction of the part, and EBW and laser welding don't gain us much over TIG in this case. I'm certainly not set on the idea of TIG welding (silver solder seems nice), but I definitely want to learn more about how we could handle this with TIG. I have heard 3 possible ways:
- Using graphite to stopper up the hole (may need to be passivated to clean up afterwards)
- Using some sacrificial brass to stopper up the hole, which leaves us with something easier to machine out (compared to inconel filler wire)
- Use compressed argon in the tube to keep the end blown clear (which comes with some unknowns in terms of possibly blowing the filler around during the weld, etc)

I'd be happy to hear any other suggestions on how we might do this with TIG (or laser) welding. (I won't turn down suggestions for other processes, but I'm well aware of other options -- just wanting to explore and learn more on the TIG welding option, since I spent so much time scratching my head on that one.)

What about TIG brazing?