Micro welder

[Pip]

Hi Folks,I am attempting to find a simple way to send a single timed pulse to be able to tack weld small silver components.There is a unit on the market (puk 2)Which is well beyond my means. So I have a power supply 3.2v. DC capable of providing about 40amps.The time period of the pulse I need to supply is going to be trial & error so is the amperage,as it will depend on the depth of weld produced.The pulse will be delivered to the parts to be tacked via a tungston tip.Please note my knowledge of required values for electronic componants is hopeless.I am able to fabricate circuits from simple diagrams (usually).I ought to clarify the power suppy is a 240v transformer 3.2v out via a couple of hefty diodes. I would be really gratefull for any help.
Kind Regards, Pip.

 

[jpanhalt]

I have never welded pure silver. But, I have done spot welding of battery tabs (usually nickel) and SS tubing. To that end, I tried two types of spot-welder designs. The first used a modified microwave oven transformer (MOT) with a re-wound secondary to deliver a few volts at lots of amps. The second was based on capacitor discharge.

I ran the MOT using a timer and zero-crossing switch, so I could get welding times based on the number of cycles of 60Hz. I used periods that gave on the order of 10 cycles (1/6 second). It worked for thin sheet, but gave a larger heat-affected zone than capacitor discharge.

My CD project is described elsewhere and is what I use for battery tabs and thin-wall SS tubing prior to hard soldering the latter.

I never wrote up my experience with the MOT. You can search on MOT spot welders and get some good designs.

Again, I have never tried spot welding silver, so your results may be quite different from mine with nickel or ferrous alloys.

John

 

[Pip]

Hi John, thanks for your fast reply,you mentioned capacitors got 2x 20v 80,000 mfd, any way I could use these?

 

[jpanhalt]

My total capacitor bank is a little less than 0.5 F. I need about 16V to weld 0.003 nickel and 20V to weld 0.005 nickel well. I don't think just 160,000 microfarad at 20 V would be enough. An even larger bank than what I have should be even better.

One other difference to consider is that battery tabs are welded from just one side to a relatively thick substrate. If you clamp the pieces between the electrodes, as in conventional spot welding, the MOT or lower CD capacitance might work better.

I have to run now, but will see if I can find my notes on the MOT experiments that I did and will post something more helpful later, I hope.

John

 

[jpanhalt]

It was a good exercise to look up my notes. I should have done that a long time ago. Must be getting lazy

My MOT welder was very similar to the one described by 5bears: 5 bears - Spot Welder

The transformer was scavenged from a 1000 or 1200 W microwave. The secondary and control windings were removed in the usual way. A new secondary was wound using 6-1/2 wraps of #4 welding cable. Welding cable was used for flexibility. O.C.V. was 6V with 120V input. Nylon ties were used to keep everything in place and tight. Copper welding crimp fittings were used for termination.

A typical 555-based one-shot timer was used (see: any 555 datasheet) and operated at 5V. I could vary the timing as needed. Most experiments were done with 170 mS for the pulse.

The solid state relay was a Continental S505-OSJ410-000, which was scavenged from a old refrigeration unit. The Crouzet equivalent is 84134000. The datasheet is a bit hard to find, so here is a link to it. The relay is zero crossing.

Good luck.

John

 

[Pip]

micro weld

Hi again John,thanks for all your input,I've followed your links and noted your comments.It would seem that the best path to follow would be a capacitor based unit as there will be less chance of heat transfer to close components gemstones etc
Kind Regards Pip

 

[jpanhalt]

If it were me, I would give your DC transformer a first shot, or even AC without the diodes. You already have it, and all you need is a solid state relay and timer to switch it on and off. That is quick and very cheap, if you can get a used relay.

Both methods require that the electrodes be in good contact with the wire being welded. If the contact is at all loose, the CD welder will blow the end of the wire off. I don't know whether the conventional welder is less sensitive in that regard. Also, a bank of capacitors can be quite expensive, if you buy them new. If you buy them used, and they have been sitting a long time, you will need to condition them before putting them at full voltage. That is easy to do. It is just a matter of charging them to a lower voltage and ramping it up over time.

Lastly, I also experimented with car audio capacitors to get even more capacitance for my bank. They work fine, but are more limited in voltage compared to the 35V or more that you can use with regular capacitors.

John

 

[Pip]

Hi John,Take your point will work with what I've got first.
Thanks Pip

 

[dougy83]

I had a look at the puke2 operating instructions, looks like the voltage to go for is 20-38VDC; it also provides current up to 25A for up to 1.7 seconds. Sounds like overkill for tack welding.

You could also use a few 12V lead acid batteries connected in series, with an appropriate control (current + timing) circuit. Even SLA can provide up to 60A for short bursts.

 

[Pip]

Hi Dougy,Agree with you 1.7 secs is a long time to be heating up small silver components.Sorry but my knowledge is limited when it comes to components SLA ?Like your spelling for "puke 2" most apt when I looked up the price.
Kind Regards, Pip

 

[dougy83]

Sorry, SLA -> Sealed Lead Acid. They're the batteries you'll usually find in e.g. motorbikes, emergency exit signs, small UPSs, etc.

 

[tcmtech]

Given the lower voltages and moderate currents this type of spot welding needs simple Ni Cad or Ni MH cell put in combinations of series and parallel can easily produce a working output of several volts at a few hundred amps for a short burst of several seconds with out any problem at all.

If some lower voltage High current Mosfets are used for switching each set of cells its possible to make a very accurate timed spot weld with simple battery cells as the power source.
Add in some PWM and current feed back and you can have a small portable self contained spot welder with a good range of function and versatility.

Just a thought.

 

[Sceadwian]

I'm going to guess that to get even a halfway decent weld even for spot welds you're going to want to provide an inert gas shield.

 

[jpanhalt]

I'm going to guess that to get even a halfway decent weld even for spot welds you're going to want to provide an inert gas shield.

That is generally not needed for spot welds, even with 2024 aluminum. First, you have occlusion of air by the pressure. Second, you have rarification by the heat, maybe even the plasma, if one is formed (I don't know).

With steels, an inert atmosphere is not needed even in regular welding using oxy/gas. I suspect the same holds true for silver, except it is probably a more difficult metal to fusion weld. But, that is another subject.

John

 

[Sceadwian]

jpan, why are spot welds almost always followed up by full flow welds unless a tenuous joint is warranted? I'm guessing what's wanted isn't actually a 'spot' weld but a sustained micro weld. Might have something to do with the topic =) Spot welding is VERY different from controlled high precision welding and scale is a big problem, at least as far as I know. I've found virtually jack for useful information for micro welding, regardless of the metal, I haven't spent an incredible amount of time on it though.

 

[jpanhalt]

jpan. Then why are spot welds almost always followed up by full flow welds unless a tenuous joint is warranted?

I think we are headed on a tangent from the OP's original question. In fact, I responded initially, because I have used such spot welds for fixturing SS tubing before hard soldering, which seemed analogous to his use, except he is using silver.

As for the strength and integrity of spot welds, spot welds are entirely satisfactory as the FINAL weld for batteries and other purposes. Your car has numerous structural spot welds, as do airplanes, instrument cases, cooking pots, electronic devices (including IC's), etc.

John

 

[Sceadwian]

I just noticed the original poster said 'micro weld' and specified absolutely no final dimensions anywhere in this thread =\ So lets get back on topic then.
EXACTLY What two points are you trying to weld?

 

[Pip]

micro weld

Hi Folks,
Thank you all for your input,I need to clarify my question somewhat.I often need to silver solder 2 or 3 small prongs (5mm long x 1mm round) to a ring setting.The hard part is holding all 3 prongs in position while soldering them.If a tack weld is applied with just enough strength to hold them in position whilst the soldering process can take place its job done.The professional units (read expensive) appear to use a timed pulse, applied vai a hand held tungstone tip which retracks into the handle the moment the tack has been applied.Hopefully will be able make that ok.My problem is a suitable circuit and components that are capable of handling the 20 or 30 amps required with an option to vary the pulse time ie.25msec--1 sec.
Kind Regards, Pip

 

[jpanhalt]

Hi Pip,

Is this like the commercial device you mention:

**broken link removed**

One US company is MicroMark

Based on your description and if the MicroMark device is like what you need, I would lean even more to using the conventional (i.e., not capacitor discharge) spot/resistance welder.

Do you need a circuit for a 555-based one shot?

John

 

[Pip]

John,Thank you,I've never seen seen one of those,looks like a pair of 1950's electric scissors! I have heard of the Co. though.The unit I was describing is a Puk 2 by Lampert Tools inc. your side the pond I think.And yes please for your kind offer 555 one shot circuit,I 've looked at the solid state relays so could you show how I might connect trigger pulse to the relay.I intend to use the 3.2v supply I already have first as you suggested.Again many thanks for your time & patience. Pip