Thread: Joining Aluminum Tubing

Hey all, I'm working on a school project and I was wondering what wall thickness I should get for the aluminum we're making the frame out of. The outer diameter is 1". We plan to braze or MIG weld the joints. That brings me to my second question, would brazing work? I've attached some working drawings. Thanks in advance

frame final 2.pngframe final.png

Edit: We are using 6061 Aluminum

G'day aagui and welcome to the forum.
In part process choice relates to the thickness of the tube but I've welded 25mm tube with 1mm wall (1", 0.040" wt) in a mitre configuration, so you can get pretty thin if you want to. The wt is dictated as much by the strength you need. If you are new to Al welding I would suggest thicker material (maybe 80 thou or thicker) as it gives a little more margin for error
My weapon of choice for that joint was TIG. For that thickness MIG might be a bit too vigourous and a brazing process may have problems getting a decent joint given the small surface area on the ends of the tubes.

Michael

Originally Posted by Michael G

G'day aagui and welcome to the forum.
In part process choice relates to the thickness of the tube but I've welded 25mm tube with 1mm wall (1", 0.040" wt) in a mitre configuration, so you can get pretty thin if you want to. The wt is dictated as much by the strength you need. If you are new to Al welding I would suggest thicker material (maybe 80 thou or thicker) as it gives a little more margin for error
My weapon of choice for that joint was TIG. For that thickness MIG might be a bit too vigourous and a brazing process may have problems getting a decent joint given the small surface area on the ends of the tubes.

Michael

Thanks so much Michael! That actually helps a lot, and I'll keep it in mind. As far as the WT, how would I find the thickness I need for my desired strength? Any way better than trial and error?

≈Agui

At the woodwork show I've seen people selling some sort of metal rod and the promotional video shows people joining soft drink tins together.

Is this brazing ?

Google finds this video - joining two soft drink tins.

https://www.youtube.com/watch?v=AXYZ948Smbg

Bill

Yep! That's brazing, most people use that when working with aluminum because welding aluminum tends to be expensive and requires specific materials.

I don't know how expert Steamingbill's operator was but check out the TIG weld produced in this vid.

aagui can you use those plastic joiners instead? Someone on here will know what they're called.

Originally Posted by Legion

aagui can you use those plastic joiners instead? Someone on here will know what they're called.

Cube lock connectors/joiners.
https://www.bunnings.com.au/connect-...oiner_p1138513

Originally Posted by aagui

As far as the WT, how would I find the thickness I need for my desired strength? Any way better than trial and error?

That's something that you spend several years at engineer's school learning. What is the crate for?
You may be better off finding an engineer locally and going to talk to them as there are several different failure modes that you might wish to avoid (for example deflection, yield of the tube, ultimate failure, buckling)

Michael

Originally Posted by Legion

aagui can you use those plastic joiners instead? Someone on here will know what they're called.

Unfortunately Legion, I cannot. That would be helpful though, thanks for the recommendation.

≈Agui

Originally Posted by Michael G

That's something that you spend several years at engineer's school learning. What is the crate for?
You may be better off finding an engineer locally and going to talk to them as there are several different failure modes that you might wish to avoid (for example deflection, yield of the tube, ultimate failure, buckling)

Michael

I figured as much, just figured I'd take a chance that someone here has such experience. I've actually spent some time researching, and I'm starting to find some equations that are helpful. We're making a fully functional serch and rescue backpack that can be turned into a stretcher, I'll keep you guys updated!

≈Agui

Originally Posted by aagui

Unfortunately Legion, I cannot. That would be helpful though, thanks for the recommendation.

≈Agui



I figured as much, just figured I'd take a chance that someone here has such experience. I've actually spent some time researching, and I'm starting to find some equations that are helpful. We're making a fully functional serch and rescue backpack that can be turned into a stretcher, I'll keep you guys updated!

It looks like you are trying to do it with hinges?
This will require short range strengthening which is tricky.
I'd be looking at telescopic extensions - round section has a lot of strength for its weight and telescoping tubing takes up very little space.

Brazing aluminium used to be the only way to do it - using oxy. There's a flux core rod you use, but not many left who can do it now without ending up with a puddle...old school body builders and aviation welders might be the last hold-outs! That other method, without looking at the vid, I assume is the stirring/wire brush thing, is more akin to soldering.

Assuming the tube is in a T6 state, welding it will make it T3 in the vicinity - hardening to T4 over several weeks. More than likely, there's some sort of 90 ° tube insert extrusion out there.

Originally Posted by BobL

I don't know how expert Steamingbill's operator was but check out the TIG weld produced in this vid.

What a cheater, using pulse!

Doing it without pulse, and with a heavy 300A air cooled torch, now that's an exercise in frustration... I had to drink a LOT of cans of soft drink before I got two stuck together decently

To answer your original questions - I would pick 3mm wall thickness if you are attempting to MIG weld this - make sure you do some test welds first to get your settings and technique well sorted. I'm assuming the frame doesn't really need heaps of strength?
As mentioned above, this is an ideal job for TIG, where you could get your wall thickness down to 1.6mm if weight/cost was an issue.
I think welding would be much better than brazing those joints.
Cheers
- Mick

Gidday

Id also be using TIG for a primer check out how Jody from Welding tips and Tips goes about it here:

Tig Welding Aluminum Tube

Regards Lou