spotweld Titanium

Search the internet for microwave oven spot welder. The transformers from a Microwave oven can have the high voltage winding removed and a high current low voltage winding installed. I am assuming this is a hobby application not a commercial situation.
Dan

I have a 500VA 12v transformer, might that do?
Do I need argon or anything?

Greetings Peter, The way a microwave oven transformer (MOT) is constructed makes them very easy to modify into a high current, low voltage xmfr. The two windings are not wound one around the other the way conventional transformers are. The secondary high voltage winding is next to the primary low voltage winding. So removing the secondary winding and putting just one or two turns of the heaviest wire you can get into the space will turn that MOT into a spot welder. I have done this and it is easy. Use Dan's suggestion to look on the internets for examples. Eric

Peter,
I have a spot welder and argon if you can get over here to try it. Might need a grooved tip made to support the wire. A quick look on the internet indicated that sheet can often be spot welded without shielding due to the close proximity of the surfaces. I would guess the wire might need shielding though as the sides will be exposed.
David Billington

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Unlikely - that's only 40A. It would be more into the short circuit that a weld is, but not that much more as the core would saturate (?).
My MOT spotwelder ( ) delivers about 2000A. That's for a 1/4" diameter weld in steel. It would take much less for the tiny welds you want to do. How much less? - I duuno.
Bob

. A quick look on the Before I got some Argon, I would try using most anything to exclude the air. I suspect plain water would work. The voltage is very low so no concern about the water shorting out the current. I would probably mix some borax and boric acid with the water so you would be using something that is a flux. Mostly because I have some on hand , and with a bunch of borax in the water it will make a paste and that will be easy to cover the joint. Now I have never done this, but it would be easy to try. Over here you can find borax in some grocery stores and boric acid in some drug stores.
If you try that let us know if it works.
Dan

=A0 =A0 =A0 =A0 =A0 =A0 =A0Dan
A quick search on the internet found one site saying fluxes can not be used and several places that sell flux for titanium brazing.
Dan

Try your TIG welder.

I haven't got an AC ammeter, but my newly-built MOT spotwelder just blew a 13A fuse at 240 V primary on short circuit; I think it needs at least 30 A primary to blow a 13A fuse that quickly, = 1800 A secondary (60:1 turns ratio), and probably more.
Medium-size MOT. 4 turns of 35mm^2 copper, direct to the electrode holders. 4.1V no load.
Used 2m of a 455x0.3mm 35 mm^2 ultraflex cable which I stripped and then untwisted the major twists of, after taping the ends of the major twists, then covered with good 12.7mm heatshrink (you need good-but-not-best heatshrink, the cheap stuff doesn't work, damhikt).
Threaded it unshrunk through the transformer holes, than squashed it down flat (that's why I untwisted it) before threading the next turns, and managed to get 4 turns in, which was what I wanted :) - with the original round cable and insulation I could only get two turns
Anywhoo, I haven't built the clamp system or electrode holders or whatnot yet, waiting for a SSD relay and stuff, nor tried spotwelding titanium.
Have some copper rod for electrodes (and lathe to turn them on etc), but I hear that it's better to use tungsten/copper or tungsten/silver electrodes for Ti.
So, anyone got a couple inches of copper/tungsten rod, about 1/8"-3/16" dia, available at a not-silly price? There is some on Ebay, but the postage to the UK is horrendipilous.
Tia,
-- Peter Fairbrother
the cuervo gold - the fine co-lumbian ..

Before you punt or kick yourself - look at your drawing.
You have two secondary in parallel.
You might have them out of polarity so they are the dead shorts.
If you really have 4v open circuit - you are likely ok.
Unless there is 4 volts differential.
Those bars are over 200 amp capable bars without much heat.
I had a commercial unit that was 1000 amp that used 1" soft copper bars.
Martin