resistance welding?

Have some half spheres, hollow 1mm wall, that need to be welded into spheres. 410 & 430 stainless. If it were just a few I'd tig them.. but 100 plus. Don't want to spend days on a tig welder. I was thinking I'd take an old chicago electric welder that is just collecting dust, attach some copper pipe to the leads and use it as a "spot" welder to weld the seams.

Copper pipe would be slightly smaller than the sphere, flare the end a bit.. should provide enough continuity that the two halves of the sphere have the most resistance and viola a resistance weld along the seam. If the cheap chicago electric can't do it then I could use a 200+ amp arc welder.

Anyone see any issues with this setup? Or have any input? Thanks, Bob.

er.. well, yes as a matter of fact, there are a few issues with your plan(ing).


where should I start, perhaps with "old Chicago electric welder". that is a model boat anchor (if you don't mind killing whatever is living in the pond), at best.

one (of many) things you need to know, welding power sources are NOT interchangeable, they are designed very specifically for the type of welding they are intended for.

doesn't sound like you are well informed or otherwise ready to take on anything like this job. I respectfully recommend that for your safety you avoid such projects, at least until getting some basic education in electrical engineering.

My itty bitty resistance welder that I use to weld to 27 gauge wire to 1/16" leads is running at 800 amps. It goes to 2500 amps, and that's a specialty unit on the small side in resistance weld land. Without knowing how big your hemispheres are, I would guesstimate you'd need at least 10 kiloamps to even consider what you're talking about. The cables going to the electrodes would be about an inch thick, and the electrodes would be a couple inch thick solid copper. You'd probably need to servo your electrodes to get an even weld without deforming it.

Unless you want to fixture it up and run a rolling seam weld around it like they do tubing. That'd be doable too and a fair bit less current than smashing them all at once, but the fixturing and handling gets more involved.

Resistance welding beyond the basic pinch unit for round welds in sheet metal isn't hard, exactly, but it takes a fair amount of care, a fair chunk of cash and often a few iterations of experimentation. Worth it if you need 100k pieces. For 100, just TIG em with some sort of rotary positioner.

Resistance welding a large area and length like than would be a frustrating process. Once contact is made in one spot, that spot will hog the current. Massive overheating in one area, no weld in another. As noted, machine requirements would be beyond your small welder.

Tom

To start you would need thousands of pounds of force on a joint like that. You would also need a lot bigger power supply than what you have. Best to tig the parts. Id invest my time and money in a positioner.

The general number is 100,000 Amps/sq inch of weld. The weld time and pressure varies depending on the material and thickness.

Spot welding is good for just that - spots.

You can seam weld with resistance welding, but it's done between wheels and one spot at time.

Meritus Resistance Seam Welding Machine For Sale at Westermans - YouTube

A key detail missing is the diameter of the spheres. If they were 1/2" diameter by 1mm wall it would be around 1900 Amps, and it's stainless which is the best thing to spot weld. Still I'm also dubious on evenness grounds and if it was me I'd make up a little electric motor jig and laser weld them. We've done that in the past on small scale stuff with great results.

Thank you all for the feedback. The spheres are 2.5" so looks like it won't work. I'll just tig them.

As uniform as the parts are, it would be easy to rig a motorized rotary fixture with a holder for the TIG gun. Plop a couple of hemispheres in clamp them and turn of the fixture motor and TIG. Have a couple sips of coffee or hire a high school kid to monitor and change parts.

Tom

Can I ask what the end use of these thingys are? Tig might be the best choice given the nature of the 400's due to heat input. being 1mm thick you shouldn't have to preheat but the heat input from tig might be enough to help prevent issues.
If these are an art project, go for 304/316 unless you have them already formed in the 400's...

Resisiance Welding

bobinoregon said:

Thank you all for the feedback. The spheres are 2.5" so looks like it won't work. I'll just tig them.

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To weld this job you're looking at a Three phase welder.
Resistance welding is more than sticking two pieces of whatever material together. The electrode material is not the same for aluminum as for steel nor is the machine selection. Your making the right choice for so few parts.
Roger

rogertoolmaker said:

To weld this job you're looking at a Three phase welder.

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Why not expand on this a wee bit for us, the unknowing.