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I need help, how do i tig weld MMO anodes with straps?


matchstick

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Heres the info

i have 1.5mm titanium plates to use as straps, but i might go and buy some thin walled tubes too
i have 1mm expanded mesh, about 8x15cm per unit

i have a tig welder with 1.6mm lanthanum electrodes specifically for this task (bought them with alu welding in mind also)

I will NOT employ the use of a spot welder by either buying, renting or improvising one together, no matter what

 

I am probably going to improvise a gas chamber to do the weld in, if its really neccesary

 

I have never tig welded titanium before, only steel.

The desired weld will essentially be the equivalent of spot welding it, so, just enough to keep it secured.
My concern is that the likely 8 second weld will destroy the titanium, converting it into a glass like fragile poor conducting oxidic mess. given the extent to which i need to weld, which is essentially Tacking it, it shouldnt, but i have no idea what will happen and i dont have any titanium to practice on.

so, how should i go about using the tig to do this weld, again, given it must be done with the tig no exceptions.

This is a process i need to be able to repeat, to produce reliable anodes at home (shed)

 

 

please help

 

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Matchstick,

 

All alloys of Titanium are exceptionally finicky about cleanliness, any plating, dissimilar metals, dirt, oil, oxygen etc will foul the puddle. Welding in an environment with the shielding gas (typically argon) be not less than 99.995 percent purity with not more than 5 to 20 ppm free oxygen and have a dew point better than –50 to –76°F is about the only way to lay an exceptional bead.

 

Since you have TIG welding experience already, you know that is best done close to your chest for stability, welding in a box of any type will reduce your ability to keep the electrode out of the puddle and keep the filler in the middle of the puddle. Be prepared for that and consider getting a cheap sandblasting cabinet that you can evacuate and fill with Argon for a shielding chamber instead.

 

For welding titanium use a 2%-ceriated tungsten sized to carry the required welding current: 1/16-in. or smaller for welding at <125 amps; 1/16- to 3/32-in. for 125 to 200 amps; and 3/32- or 1/8-in. for welding >200 amps. Use a gas lens to evenly distribute the gas and create a smooth gas flow, and use a cup with a diameter of at least 3/4- to 1-in. A larger cup will enable you to make a longer weld. There is no advantage to using the lanthanum electrodes unless you are running high currents, you will likely run a low current so use 2%-ceriated tungsten instead.

 

I pulled some of the above information from the Miller website, you may find the color charts to be very handy.

 

The reason why spot welders are used so much is that they are cheap and reliable, the bond will last the service life of the bonded materials and don't leave titanium dioxide (embrittlement) in the weld cracking as it cools.

 

Good luck but be prepared to spend lots of money and have lots of scrap Ti.

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Sorry but there is a proven and well (enough) documented method with spot welding, why do you need to do it the hard way. Rewind a MOT is the cash cheap way, bribe the local welding shop is the easy way. Anyone who does MIG welded titaniun for the aircraft industry probably can't do cash jobs.

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I have seen some novel MIG welding with Ti wire in a closed bubble environment but I am unaware of anybody outside of aerospace running a MIG welder for Ti. The conditions would be cost prohibitive for most shops.
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If you just need to attach it and don't need much strength I wouldn't even worry about adding any filler material. I would be inclined to crank up the gas to really push the air away and to heat the base material to get it hot and then walk the arc onto the edge of the strap so it melts the thin edge to provide the filler to bond to the base. It should also get pulled into the gap between pieces and just a little puddle fills quite a bit when the gap is small/pieces are flush.

 

You could also drill a hole and do similar to let the puddle fill in the hole.

 

Just what I would try though I have never welded Ti and it's been a long time since I've welded. Might not hurt asking the local welding shop if they have a small scrap of Ti laying around. You only need a small piece to play with. That and get it as clean as possibly using a solvent. I would also lay a wet rag on the anode to keep the plating cool as possible. A fairly damp rag will pull out quite a bit of heat as the water turns to steam.

 

And actually if I was real worried about damaging an expensive anode I would probably look into hard soldering it first and see if it will hold. A lot of flux and clean surfaces will bond a lot of different metals. You can always clean it off and then use the TIG.

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Sorry but there is a proven and well (enough) documented method with spot welding, why do you need to do it the hard way. Rewind a MOT is the cash cheap way, bribe the local welding shop is the easy way. Anyone who does MIG welded titaniun for the aircraft industry probably can't do cash jobs.

Ive given it some thought and i think i maybe i will build one.

 

I just realized i have very easy access to some old junked stick welder transformers. but now its a matter of do i need any special current control or anything? or can i just quickly flick a switch on and off and thats it?

 

of course ill eventually get a fancy timed solid state relay, but for now, immediate use ill do it figuratively by hand.

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Swede's blog has his manufacture of a MOT spot welder, Youtube has several tutorials on making a rewound microwave oven transformer for a spot welder.

 

Spot welding is usually done with a very high current at low volts. 2 volts at 1000 amps would be typical for a professional spot welder. A home built one using a MOT rewound with 0 gauge wire should yield 2v 500a easily, and usually a pressure switch is used to control the primary current in the transformer.

 

Added; search youtube for "MOT spot welder"

Edited by Arthur
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Ive given it some thought and i think i maybe i will build one.

 

I just realized i have very easy access to some old junked stick welder transformers. but now its a matter of do i need any special current control or anything? or can i just quickly flick a switch on and off and thats it?

 

of course ill eventually get a fancy timed solid state relay, but for now, immediate use ill do it figuratively by hand.

 

You should google the mods needed for a stick welder transformation, there are some interesting things you need to do. For the price, I would rather go on Craigslist for a broken one.

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this MOT welders sounds really dangerous, 500Amps is plenty enough to fry you if im remembering this right ....

 

Stay Safe and Stay Green

 

~Steven

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Can you link me to swedes instructions to making a mot spot welder?

I looked but all I found was an entry with a picture of it.

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I believe the electric chair that was in use here in a prison here in Florida about an hour down the road was only 15 amps. It doesn't take much juice if it gets to your heart to get it fluttering out of sequence and no longer pumping.

 

A spot welder is just causing both surfaces to melt and mix. A quick tack should be plenty and can be done in just a few seconds with current equipment.

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Welding Titaniun comes with it's own problems, but spot welding minimises these. My first choice would be to take the job to a weld shop that would do the job for cash, second choice would be hire a spot welder for half or a day and weld it myself, third choice would be a rewound MOT transformer.

 

When the electrodes are 2 volts apart there is no chance that you would get problems with the human body, the 500amps are only available into a very short metallic conductor. -You'd happily hold the terminals of a truck battery and that's 12 volts.

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Welding Titaniun comes with it's own problems, but spot welding minimises these. My first choice would be to take the job to a weld shop that would do the job for cash, second choice would be hire a spot welder for half or a day and weld it myself, third choice would be a rewound MOT transformer.

 

When the electrodes are 2 volts apart there is no chance that you would get problems with the human body, the 500amps are only available into a very short metallic conductor. -You'd happily hold the terminals of a truck battery and that's 12 volts.

 

Shop prices around here (Midwest) run in excess of $95 an hour, "hiring" a spot welder (I assume you meant rent?) would be a lot more than simply buying a Harbor Freight one. They do work but you HAVE to get the 220V unit, the 110V is crap.

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I'm in Australia so, harbor freight is gonna cost me more than its worth just to get here, plus its all 120v and no way I'm buying such a huge stepdown lol.

 

I'll give a shot at rewinding the mot or stick welder xformer, whichever I can get more easily, do you think itle be OK to switch it with a pressure switch?

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IIRC Swede used five spot welds to hold each electrode to it's stem. So for a pair that's ten spot welds and a couple of tests, The cheapest way will be the most viable. First I'd see whether there is a welding works near you that would do the job for you. Realistically you need 2.5v so that side isn't particularly hazardous. The fat wire should permit short bursts of 500+amps and the two metals to be welded should fuse under pressure.

 

Your pressure switch idea is a good one if the switch you use is rated for your mains and has the contacts and connectors covered. Unless you are a serial cell maker you are only going to need 20 welds max in it's lifetime!

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Be 100% sure the HV capacitor is completely discharged before removing the transformer from a microwave. They store lethal voltages and the internal 10M ohm resistor designed to bleed off the charge can fail without any outward signs ;)

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Your pressure switch idea is a good one if the switch you use is rated for your mains and has the contacts and connectors covered. Unless you are a serial cell maker you are only going to need 20 welds max in it's lifetime!

Actually I am. Making many anodes and cathodes.

 

But if I ever come across a cheap proper one I'll snatch it up.

 

 

Also I've noticed a general lack of spot welders in workshops. Actually I can't recall ever having seen any ever in any of the workshops i frequently go to

Edited by matchstick
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Actually I am. Making many anodes and cathodes.

 

But if I ever come across a cheap proper one I'll snatch it up.

 

 

Also I've noticed a general lack of spot welders in workshops. Actually I can't recall ever having seen any ever in any of the workshops i frequently go to

 

Spot welders are made for sheet metal, they are useless on thick metals where MIG welding can be accomplished without burn through. You will need to look at weld shops, not machine shops.

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If you intend to make lots of electrodes, then either look around for a specialist welding workshop which does offer a spot welding service, or buy or make a cheap spot welder of your own. Swede's findings were that his DIY spot welding machine worked but his commercial one worked slightly better.
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Yeah I assumed as much.

 

But I won't buy one unless I can get it for $150 or less, because otherwise I'm paying for too high/unnecessary quality. I think swedes one was also a cheap portable one.

 

Anyway, I've got a mot, and I'll go about making it into a spot welder but I'll still keep an eye out for a proper one.

 

After all the one swede made had a proper timed relay and decently engineered parts, opposes to me who will go all improv and 3d printed where possible

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As long as you carry the current on FAT copper it's up to you what design you chose. A PRO spot welder uses about 1000 amps, A good DIY cheapy from A MOT should give you 350 - 500 amps which works fine just takes a second longer. It's best that the pressure goes on before the current and the current goes off first. A pressure switch running a timer would be a great plan.

 

You do need five good welds to get the current from hanger to the MMO mesh or Ti plate.

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