Resistance Welding a small 304 S/S tubing assembly

LowEnergyParticle · Jan 1, 2023

I would like to ask for help on using resistance welding to weld together 4 small 304 S/S tubes. I need to fabricate a jig to hold the tubes together as shown in the drawing and then weld them. We don't own any resistance welding or spot welding equipment, so I'd be starting off from scratch.
We've built similar assemblies in the past by oven brazing them. This worked pretty well, but our setup was pretty primitive and so it took a long time and used a lot more energy than a tightly controlled resistance welder.

I was thinking of a single return electrode going in the central 1/2" ID tube, and then a single hot electrode that wrapped around the the outsides of the 3 smaller tubes and pressed the whole mess against a non-conductive surface. But I don't know much about it. So, would someone please set me on the right path here?

Thanks very much, and a Happy New Year to all!
Dave

Scruffy887 · Jan 2, 2023

LowEnergyParticle said:
I would like to ask for help on using resistance welding to weld together 4 small 304 S/S tubes. I need to fabricate a jig to hold the tubes together as shown in the drawing and then weld them. We don't own any resistance welding or spot welding equipment, so I'd be starting off from scratch.
We've built similar assemblies in the past by oven brazing them. This worked pretty well, but our setup was pretty primitive and so it took a long time and used a lot more energy than a tightly controlled resistance welder.

I was thinking of a single return electrode going in the central 1/2" ID tube, and then a single hot electrode that wrapped around the the outsides of the 3 smaller tubes and pressed the whole mess against a non-conductive surface. But I don't know much about it. So, would someone please set me on the right path here?

Thanks very much, and a Happy New Year to all!
Dave

View attachment 382972

This part could be a big problem. 3 nuggets at one shot? And current going through the whole set of tubes? For sure with enough amps something will weld, may not look like what you want. The perimeter tubes will collapse from the heat if you are looking at welding temps.

LowEnergyParticle · Jan 2, 2023

Scruffy887 said:
This part could be a big problem. 3 nuggets at one shot? And current going through the whole set of tubes? For sure with enough amps something will weld, may not look like what you want. The perimeter tubes will collapse from the heat if you are looking at welding temps.

OK, thank you! You just saved me goodness knows how much money and a week of time trying to make it work! I very much appreciate it.

So, how about if I keep the single return electrode going in the central 1/2" ID tube, but have three hot electrodes individually contacting the outside surfaces of the 3 perimeter tubes and the three hots turn on sequentially, 20 or 30 seconds apart? That would keep it down to 1 setup, when the parts are all cold.

Milland · Jan 2, 2023

You might be better off looking at ceramic fixturing with inductive heating elements and braze preforms with flux. If you're making so many of those that you need the speed of resistance welding, sequential copper "pinch" electrodes is what I'd investigate.

newtonsapple · Jan 2, 2023

Laser welding and small stainless tubing are like bread and butter.

How many of these do you need made?

If it dozens or less, a mold repair shop with manual lasers can knock this out quick and reasonably priced. Make a fixture to align everything.

If it is a lot, there are shops that can bang this out on cnc lasers with right fixturing. The y axis lathe equivalent of a laser is pretty common, so designing a fixture that holds everything to access from that approach would be pretty straight forward.

I work with a vendor doing medical work that also has a VERY high volume job doing faucet ball stem weldment assemblies. So the right high volume jobs are often very suitable to for lasers.

DDoug · Jan 3, 2023

Spot welder power supply, carbon electrodes with much lower pressure, to heat the tube assembly for hand brazing.

LowEnergyParticle · Jan 4, 2023

Thank you all! I had not considered braze preforms, and I didn't consider laser welding since I (mistakenly) associated that with high dollar and huge quantity. Also, using a spot welder power supply with low pressure electrodes as a heat source for hand brazing is an new idea to me; seems like it would keep the stainless tubing very clean unlike a flame torch.

I've got quite a bit of research to do at this point. I will update later, if that's OK, with interim results and more questions.

Thank you all again for the great ideas!
Dave

Milland · Jan 4, 2023

Updates are always welcomed - more info is more better...

EmanuelGoldstein · Jan 4, 2023

LowEnergyParticle said:
Also, using a spot welder power supply with low pressure electrodes as a heat source for hand brazing is an new idea to me; seems like it would keep the stainless tubing very clean unlike a flame torch.

I've seen a small induction heater thingy at shows brazing tubes into sockets, it was very fast and clean. Didn't look super expensive.

Little ring of braze preplaced around the joint, induction coils moved into place, everything heated up red and the braze melted into the joint, seemed like maybe fifteen seconds total ? Didn't look like it took a lot of skill, either.

Clive603 · Jan 4, 2023

With multiple parts heat gradients may be an issue with that style of heater.

Braze tends to run towards the heat so its important that the centre part gets hot enough so the braze doesn't run away from it. As I understand it such heaters work from outside in so the small parts could be overheated before the centre is properly warm.
Made that error when silver soldering a similar sort of sticking small bits to a big bit job where I didn't point the torch right so the centre wasn't up to temperature.

Clive

EmanuelGoldstein · Jan 4, 2023

Clive603 said:
With multiple parts heat gradients may be an issue with that style of heater.

Braze tends to run towards the heat so its important that the centre part gets hot enough so the braze doesn't run away from it. As I understand it such heaters work from outside in so the small parts could be overheated before the centre is properly warm.

Sorry, I shoulda used this picture instead, see how the coils are formed in a way that puts the inductive activity, aka heat, where you want it ?

I'm kind of infatuated with this induction heat idea right now, sorry

BT Fabrication · Jan 4, 2023

I wonder if these would work impromptu for brazing?

Mini-Ductor Induction Heater Models | Induction Innovations

View all Mini-Ductor induction heater tool models used to release stuck lug nuts, bolts, and other fasteners in vehicle and equipment repair

www.theinductor.com

use them all the time to heat bolts on a car, a bit spendy but they work.

Clive603 · Jan 4, 2023

EmanuelGoldstein said:
Sorry, I shoulda used this picture instead, see how the coils are formed in a way that puts the inductive activity, aka heat, where you want it ?

I'm kind of infatuated with this induction heat idea right now, sorry

Lovely picture of just how good induction heaters are at getting the heat where you need it when you have the right shape coil.

Been meaning to investigate them but I do brazing jobs about once or twice a year and generalised get it really hot stuff five or six so hardly worth it as I have torch hearth and gas already.

Clive

EmanuelGoldstein · Jan 4, 2023

BT Fabrication said:
I wonder if these would work impromptu for brazing?

Kinda funny, that was the one that got me interested in small stuff

We had sold some systems for doing teeth on large gears but that was totally unreasonable for a small shop. Kinda like this

[video]

This mini one tho, first off when I looked it was about $4,000 ? Yikes. Also, it uses plain copper wire for the coils. These other small ones I've seen use tubing with water running through it for cooling. If you are just doing a few of something it doesn't matter but if you want to do production, the tubing is gonna kick ass over plain wire.

So, all in all, I'd say there are better setups for industrial use.

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Resistance Welding a small 304 S/S tubing assembly

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