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Quick-n-dirty resistance welding?

Gentlemen,

I need to join a handful of short (18mm long) stubs of 6mm diam. stainless bar to another longer piece of bar - i.e. make a load of little butt joints. Elsewhere in the project I've made do with mig welding, but it's too rough for this - I'm sick of filing welds down, and holding in place will be really awkward.

So, I'm thinking of using the mig welder as a current source to resistance-weld these stubs on. A copper receptacle could be made to screw onto the torch end: this would hold most of a stub, allowing me to manually press the protruding end onto the other bar while passing a huge current through; no filler wire would be used. Hopefully the two would fuse together without too much distortion. It's not a structural joint but must be secure.

Before I give it a go, has anyone tried something similar, or got a trick for welding a nasty little joint like this?

thanks Guy

Reply to
Guy Griffin
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When spot welding it is important to be able to switch the current on and off easily and quickly. A foot switch is very useful. A switch on the mig torch might work okay though.

In theory a tig or stick welder would work better than a mig - I haven't tried it.

Reply to
Peter Fairbrother

Resistance welding needs a LOT of current at a few volts. A meaty low voltage transformer based on a rewound stick welder would be a better starting point.

The usual trick is light pressure for initial joint heating immediately followed by substantial pressure to complete the weld.

A short sacrificial 3mm stub would reduce the necessary current a bit.

Jim

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Reply to
pentagrid

This is a totally uninformed suggestion, but was wondering if you could have a go at rotary friction welding, the parts sound small enough that you might be able to do it in a lathe?

Stephen.

Reply to
Stephen Woolhead

This takes me back some 25 years. We did some experiments using some old Student lathes for a Thesis in about 1971 and 3/8" dia steel. If I remember you need to develop a surface speed for steel between 350 -

650 sfm. It won't work below 350 but can go much higher than 650 up to about 2000 sfm if you can generate it. The pressure that needs to be applied was a problem for us and is approx 1.5 tons psi for pre-heat and then 4 tons psi for heating and about 10 tons psi for forge (post weld). Our problem was getting repeatable parameters for reliable welding. Initial trials using a torque wrench on the tailstock were to say the least hit and miss. Occaisionally a superb weld would be produced but more often than not it would fail. Maintaining the pressure during the upset stage was a problem. Welds also produced a "flash" around the joint. Later trials using a hydraulic arrangement to load the unlocked tailstock were more successfull.

If you are prepared to do a fair bit of trial (and error) and have a reasonably powerfull OLD lathe could be worth a try.

Best regards

Keith

Reply to
jontom_1uk

Having just tried the setup I described I can confirm it doesn't work: Jim is quite right, not enough current by a long way. I reckon 400-600A would be more like it, so perhaps 4v instead of the 20v produced by a mig welder. Fortunately it only blew a fuse :)

I did manage to get one trial piece to stick by bringing in into contact with the power on, making a violent arc between the two parts; but a very weak, bubbly weld.

Back to the welding & filing! Friction welding is a great idea, but out of the question as I'm joining rods of the same size (rather than a thin rod to something nice and solid). Guy

Reply to
Guy Griffin

Gentlemen,

When I worked with industrial robots the customer would have a stud gun fitted so that M6 threaded studs could be welded to car panels, I don't know what current was used but it would take three of us to fit the device to a robot and most of it was a transformer.

Mart>> Resistance welding needs a LOT of current at a few volts. A

Reply to
campingstoveman

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