Spot welders for TC/RTD

[Personwithhats]

Hey there,

I'm looking into making some custom RTD cartridges, possibly TC 's as well, and as part of the process I'm going to need to find a spot welder.
Unfortunately nearly everything I see is some kind of battery pack setup.
I'm also not sure if I need argon for the welds? Would the lack of argon compromise the sensors? Some will be used up to 500 celcius.

I've started looking into stuff such as used HotSpot II, Unitek resistance welders, orthodonic welders, Miyachi TC welders, etc.
Not entirely sure what to go for here, any advice is welcome

Budget would be $500 or lower, I've looked into kweld but it seems massively overpriced for what it is at first glance. I might be wrong though

Maybe an Orion clone with retractable electrode?
https://www.aliexpress.us/item/3256805987367586.html?

[David Hess]

I would not mind seeing an answer also.  I would probably end up hacking something together.

[jpanhalt]

First off, my homemade capacitor-discharge welder is mains powered.  It works fine for welding nickel strips to batteries.  I added a winding to a store-bought toroid to give me logic-level voltage for the MCU.  I tried it on type K TC's (not super thin,but fairly fine wire), and the weld was not reliable.  Much finer wire than I used might be OK.  I don't think argon would help in a plasma.

For TC, I set my TIG welder about as low as it will go to  give a stable arc (it has HF start and foot control),  strike the arc on a copper plate, and carry it across the twisted TC wires. Very little dwell time over the wires is needed.  I use a standard W electrode and DC polarity for steel  It uses argon, as do most, but that is for protecting the weld zone. I found the type of stipper shown works best for Teflon insulated TC wire.

Pictures attached.  For the photo with two TC's: the top is a Fluke made TC; the bottom is one I made.

[Personwithhats]

I've been reading and it looks like CD welders would run too hot, and modify the TCR of the resistor?
And that I'd need some kind of pulse-arc-welder similar to the Orion welder series.....not too clear on this.

[jpanhalt]

My TIG welder is a 1983-vintage Miller that was bought for an entirely different purpose (structural steel and aircraft mufflers).  It has so many uses, it is hard to imagine not having one.  I also have a smaller Linde MIG that I got for sheet metal and "red iron."  If I could have only one, it would be the TIG.

[jpanhalt]

I've been reading and it looks like CD welders would run too hot, and modify the TCR of the resistor?
And that I'd need some kind of pulse-arc-welder similar to the Orion welder series.....not too clear on this.

TIG is quite hot, of course, but the heat zone is small, and the copper plate with a slot, which I use to fixture the wires, reduces it even more.   That is evident in the pictures.

[Personwithhats]

On further review I don't believe the KWeld will work, it just seems to be a single pulse capacitive discharge. Likely will heat up the target area too much.

Contacted Orion clone makers, and they say they can only go down to about 3J with a 0.8mm wire limit or the spot weld will run too hot
Considering RTD leads are 32 AWG (0.2mm) or thereabouts doesn't seem serviceable. Per some Orion videos I think it needs around 1.5J to 2J.....

I'm left considering an actual Orion. Unfortunately they seem to, arbitrarily, limit output in the lower models.
A model from 1-30J with 1J increments is cheaper than a model with 3-30J with 0.5J increments.
The only model that goes low enough is limited to 15J, awfully limiting for a device that's several thousand.
Due to the ridiculous 'Permanent jewelry' craze can't even find any used at reasonable prices.

I'm left with trying to come up with ideas to justify such a purchase, these RTD's are mostly for some research/ad-hoc work and are unlikely to generate any profit for me.

Maybe I can snag some kind of linear DC welder on the used market.....

[jpanhalt]

@tatus1969
I thought KWeld originally had a short cleaning pulse followed by the weld pulse.  It's developer might want to respond.

[Personwithhats]

@tatus1969
I thought KWeld originally had a short cleaning pulse followed by the weld pulse.  It's developer might want to respond.

As far as I can tell it's a variation on a capacitor discharge that does constant voltage (similar to some linear DC welds I suppose?)
It still struggles with small wires and it's one pulse not two, it works fine for batteries then again many resistance welds work fine for that

[CaptDon]

O.K. guys, try not to laugh, but this really works well. I have an Eico 20 volt 20 amp variable power supply. No regulation, just one of those transformers with the sliding tap, a full wave bridge and big filter caps. Here's the process, Twist the bared T.C. wires together about two full twists. Connect one end of the power supply to the pair of untwisted T.C. wires at the far end of your wire. Take a mechanical pencil replacement lead about 1.5 inches long. Jumble wrap some bare wire-wrapping wire around one end of the pencil lead covering about 1/4" of the lead. This forms a place where you can connect the remaining end of the power supply via gator clip and inject current into the lead without burning up the lead at this end. Set the power supply to about 15 volts and use the free end of the lead as your welding 'electrode'. The capacitance in the power supply will give you the energy to perform the weld and the power supplies continued output can maintain the arc if need be. This also works well using the old Sorenson supplies like the 40-10 or 80-15. No joke, not only does it work but when you need to make about 50 T.C.'s for doing thermal tests and have the T.C. wire prepped and ready for welding I can do at least two per minute! I have done hundreds this way (since we use at least 20 per test) and usually because the T.C.'s are epoxied to the U.U.T. we snip them off at the end of the test. We have a commercial T.C. welder but my welds look better and are more uniform. The pencil leads give me a nice smooth sustained arc to complete the weld.

[Personwithhats]

Well the point would be to not have a sustained weld, otherwise you heat the nearby material and alter TCR.
This sounds good for welding mesh together with a wheel or other AC/Transformer based welder tasks.

[jpanhalt]

There are a lot of TIG welders for way <$500 (your budget).  With the extra money, you  need a cheap helmet, single stage regulator, and small tank of argon (about $40 locally).  I assume a few electrodes and torch come with those welders.  Just think of the fun you will have welding razor blades together. With a little practice, advance to aluminum foil. 

I don't think I would try one on a Li battery.

[Personwithhats]

Yea TIG will blow a hole straight through. If you can't use it on a battery I wouldn't use it on an RTD sensor lead.
At this point I'm just going to have to sit until maybe an Orion 100c comes out used or I get a promotion deal on the mPulse or something.
A few thousand but at least it will work and I can use it for some other projects, mostly small parts so mini-tig sounds useful.
Heat sinks, honeycombs, vacuum flange seals, heater/RTD cartridges, etc.

Discussion with some manufacturers gives comments on the micro-tig weld lack of porosity + purity of the weld (which resistive welding has issues with) for long term sensor measurements.

[p.larner]

what is rtd tc etc?

[coppercone2]

I think its possible to use a tig on this with power resistors and low current settings if you have a fixture. A current divider. You need a beefy resistor to split the current but it might work. In parallel to the work, not limiter.

[jpanhalt]

@Personwithhats

I have not mentioned this, nor has anyone.  If budget for TIG is not sufficient, in grad school, we used a hydrogen-oxy torch to make TC's.  The flame is very hot and clean. Heat-affected zone is very small. Our usual reason for using one  was to work with quartz, as in glass blowing. The added cost for a tank of hydrogen is trivial.

A hydrogen flame is different from a methane-oxygen torch.  It is essentially invisible until it heats something.  Because flame propagation is very fast (backfire), with reasonable care, they are safe.  Most important, you can use a simple, single aperture lab torch that is often used for glass blowing.  Just don't be foolish.  I didn't use TIG until more than 40 years later.

[coppercone2]

also IMO k-weld is not over priced. I think its well made and works well.

Cheaping out on welding equipment is never a great idea.

If you save scrap metal (thin brackets, sheet, etc) you can build impressive prototypes for various things using it to quickly make its moneys worth. And it can do some impressive things like weld stainless steel screens to things, for vent screens, etc.

Its literally how you can use literal scraps to make something like in a RPG video game (alien isolation, etc)

Like once you realize you can build something from old steel computer bay rails using nothing but tin snips and a file, its impressive. Basically any thin steel bracket can be repurposed to mount basically anything using a spot welder and a dremel. That weird half arch thing from a dell computer... can now be used for something.

And its strong as hell and has actual electrical properties (unlike 3d printers).

I will literarly go out of my way to harvest esoteric sheet metal parts from whatever now so long they are reasonable because it can be used in conjunction with the spot welder to mount basically anything in a sturdy way. and also there is no CAD involved. Caliper scrapes are enough to mark out anything. Transfer screws are useful too.

There is so much structural bullshit you can take out of equipment that can be reused for high quality prototypes using a spot welder to join it with minimum work. It actually feels like tinkering, not machine shop, not cad-jockey, not automation machinery technician. literal tinkering.


You might think what makes it any better then solder? The answer is speed, ease and greater parts utility. You could solder alot of steel stuff together but the fact is, you have annoying prep to do. Alot of it. And you need to fixture to solder properly, plus there is often thermal problems. With the spot welder so long you have flats you use the electrodes to fixture and its like playing GMOD irl. How about small bolts? well you have tons of crap to do, that is locate, drill, deburr, tighten. With spot welding its way less work. That means easy to make complex structures without sitting around all day figuring about how to drill things. And, if you have a esoteric joint that needs solder or braze, the welds you made for the majority of the structure can hold easily.
 

[Personwithhats]

also IMO k-weld is not over priced. I think its well made and works well.

The Canada reseller makes me think otherwise. The base price for a K-Weld + its various charging components/etc. is already on the higher end.
Then add a 30%+ markup, it's nowhere near reasonable. The $13 programmer is $19, the ultra-caps go from $140 to $200 

Cheaper to get an acquaintance to buy and ship from EU. Save a few hundred......

On another note - Got a pair of tin snips/etc. to recommend? Looking for stuff to cut, well, basically what you're cutting.
Thin metal, stainles/aluminum/copper/etc., scraps, figure out some way to cut PCB board,  etc.

[jpanhalt]

I didn't spend much time searching, but can you beat this price for a simple torch + tanks for O2 and H2?

https://www.aliexpress.us/item/3256802797368055.html?src=google&src=google&albch=shopping&acnt=708-803-3821&slnk=&plac=&mtctp=&albbt=Google_7_shopping&albagn=888888&isSmbAutoCall=false&needSmbHouyi=false&albcp=19108282527&albag=&trgt=&crea=en3256802797368055&netw=x&device=c&albpg=&albpd=en3256802797368055&gad_source=1&gclid=EAIaIQobChMI4bXBupLjhAMVkElHAR3XXAqjEAQYBSABEgJi9fD_BwE&gclsrc=aw.ds&aff_fcid=53ac252541fd490cb78c64a206d8836f-1709848623887-06195-UneMJZVf&aff_fsk=UneMJZVf&aff_platform=aaf&sk=UneMJZVf&aff_trace_key=53ac252541fd490cb78c64a206d8836f-1709848623887-06195-UneMJZVf&terminal_id=ef690b8ad8a745578aa2c5cb4395b034&afSmartRedirect=y&gatewayAdapt=glo2usa

[coppercone2]

also IMO k-weld is not over priced. I think its well made and works well.

The Canada reseller makes me think otherwise. The base price for a K-Weld + its various charging components/etc. is already on the higher end.
Then add a 30%+ markup, it's nowhere near reasonable. The $13 programmer is $19, the ultra-caps go from $140 to $200 

Cheaper to get an acquaintance to buy and ship from EU. Save a few hundred......

On another note - Got a pair of tin snips/etc. to recommend? Looking for stuff to cut, well, basically what you're cutting.
Thin metal, stainles/aluminum/copper/etc., scraps, figure out some way to cut PCB board,  etc.

I used my own super caps + bus bars, I just use the control board and electrodes. it was more expensive though but I like the design.

A typical engineering design is 400% of parts cost BTW, for complex machinery like that. Power tools have incredible mass production that allows for lower costs but its still pretty steep markup. I think its a fair deal especially if its soldered right (good reflow profile).

[p.larner]

so what on earth is rtd rc,some form of welding?why cant folks use the full words and not abreaveations in cases like this?,ive been a professionall welder for 30 yrs and dont know what the op is on about.

[Personwithhats]

I used my own super caps + bus bars, I just use the control board and electrodes. it was more expensive though but I like the design.

A typical engineering design is 400% of parts cost BTW, for complex machinery like that. Power tools have incredible mass production that allows for lower costs but its still pretty steep markup. I think its a fair deal especially if its soldered right (good reflow profile).

I understand why the base part is marked up, obviously R&D carries its own costs and small volume production is never cheap.
I'm not fine with the importer jacking up the price just because.

so what on earth is rtd rc,some form of welding?why cant folks use the full words and not abreaveations in cases like this?,ive been a professionall welder for 30 yrs and dont know what the op is on about.

RTD = (platinum) resistance temperature detector
TC = Thermocouple

I didn't spend much time searching, but can you beat this price for a simple torch + tanks for O2 and H2?

I have a torch already lol
It's fine, I found a welder albeit expecting to pay a lot more than I'd care to. At least I can use it for other projects.

[Retirednerd2020]

I needed 30 or so thermocouples for a thermal test a few years ago.  I hooked up a lab power supply up to charge a big electrolytic cap through a resistor, maybe 47000 uf, 60V?  I forget.  Grasped both TC leads near the working end with alagator clip and wire to + and touched the two wires to -.  Zap, done.  I just played around with voltage until the TC ball was about right.

I tested the TC's all together at 0C and 100C and all but one or two were well within their TC wire published specifications.  My range of use was up to 150C and these worked well.

[richnormand]

Sorry to be a bit late at the party.
One pix shows the two types of TC I usually deal with.
The second pix is what I use.

For the small TC it is a cheap ebay jewelry "sparkle" welder (on the right). The active goggles were bought separately but are a must under magnifying glasses to protect you from UV if you do a lot.
It is a kind of TIG welder in air with a tungsten tip held close to the work.

The bigger TC one setup is on the left. An old 6/12V battery charger with big caps... Works well when you get the hang of it. Pretty powerful.

In both cases make sure the TC is disconnected from the reader when welding !!!!!

Also of note, make sure the TC is the only joint at the junction. You might twist the wires to prep them for solder but make sure they are untwisted after, as the many spurious junctions will change the reading while heating. You want to deal with only one TC point.