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Making a micro-welder?

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lewstherin

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There is a special tool I need which is basically an arc welder but on a much smaller scale. It uses DC current and you basically short the positive/negative to create an arc and transfer material from the positive(anode) to the negative(cathode) in the plasma that forms. The anode is vibrating to constantly short, then pull away from the material breaking the connection then short again..several times a second.

My problem is traditional welders are too strong, and the inexpensive machine sold for doing this task is slightly too weak. The more expensive version is out of my price range (and overpriced imo).

So...I thought I would try making one. In fact I did make one by simply using a 12v 13amp car battery charger. It works ok but it is too strong for very thin sections of metal...it tends to overheat them. Also it only has about a 50% duty cycle.

I *think* my problem is that the arc welders and battery charger are too high in amps and too low in volts. I would like to make one(or modify the battery charger) that is adjustable voltage and a 100% duty cycle would be great. The problem is I am a complete novice with electronics.

Btw we use 220v here.


So here is my question:

What would it take to make a DC power supply that is adjustable voltage (5-50v?) and will not burn out when shorted? Can I simply use a variac with a bridge rectifier or would it burn out/pop a fuse when shorted constantly?

Thank you for any insight you can offer.
 
I'd say a triac control, or variac on a hacked microwave transformer wound to suit your purpose. U can use it with ac or rectify 'pre stepdown' and use pulsed dc.
 
I think if the battery charger is to "hot" try the variac in front of it.
Tell us more about how it works. How do you turn it on and off. What material and thickness what does the clamp look like?
 
Mosaic, unfortunately microwaves are rare in this country so surplus parts are hard to find...the used ones sell for as much as new ones in the US. I will research triac controls...I'm not familiar with them.

Ronv, To turn it on an off right now I am just using the on/off switch on the battery charger. Clamps are typical automotive battery charger type. The material I am having trouble with is .040" thick titanium(cathode) and 3/32" or 1/8" tungsten carbide or titanium carbide for the anode. Using this setup on .060" and thicker steel it deposited the tungsten as desired.

Here is a video (not mine) of the commercial model in operation so you can get an idea of whats going on. https://www.youtube.com/watch?v=Ww-scla1r0s . I would simply buy one of these but I've read from others its on the weak side. The next model up starts at 10 times the price...which is not in my budget any time soon.

The idea of using a variac before the charger is a good one. Now I just have to track down a variac locally... Using reduced voltage to a car battery charger shouldn't hurt it should it? I wonder how wiring a rheostat(dimmer switch) before the charger would work? Probably just fry the rheostat wouldn't it?

Sorry for my ignorance on the subject. I'm decent at the mechanical end, but I have very limited experience with electronics.

Thanks for the suggestions.
 
There is a special tool I need which is basically an arc welder but on a much smaller scale.

....and the inexpensive machine sold for doing this task is slightly too weak. The more expensive version is out of my price range (and overpriced imo)....
It usually helps to tell the whole store. What device are you trying to replicate?


Ken
 
It usually helps to tell the whole store. What device are you trying to replicate?


Ken

Ken, the tool is called a "carbidizer". As far as I know there are only 2 suppliers making them. If you are familiar with hardfacing in welding it is basically that except on a much smaller scale. The machine basically deposits a very thin layer of very hard material. Good for restoring slightly worn shafts, holes, etc in machinery.
 
Well I had a dimmer switch just sitting here saying "please try to fry me!" so I hooked it up between the automotive battery charger and the wall socket. To my amazement it actually worked. I was able to turn down the rheostat and create a much smaller tungsten deposit without burning the material. It also lengthened the duty cycle from around 50% to 90%..which was nice. Its not an ideal setup but it is getting the job done.

Thank you "ronv" for the suggestion of limiting the current before the charger...it saved me a lot of hassle.

Some day soon I will pick up a transformer and rectifier and try the dimmer switch idea with it to see how it works since I have other plans for the battery charger.
 
From what I could find on the subject you are looking for an output of around 1.5 - 3 volts with a 40 - 60 amp current behind it and ideally a variable duty cycle.

Sounds pretty simple to me! :D
 
Actually Lews...the dimmer IS a triac control and not a rheostat, that's why u have control.
 
Dimmers designed for incandescent lamps tend to be a simple design that doesn produce equal triggering either side of the mains waveform, this is seen by the transformer as dc which is bad for a tranny, however in this application the load time of the transformer will be very small so it'll probably work fine, if you were going to use a dimmer switch to control a transformer primary on load for a period of time you'd have to make sure or adapt the dimmer so that it didnt produce dc.

My ex made jewellery, and I considered making a welder for gold and silver, my idea was to use a current source to charge up a super cap, when the cap was charged its energy was dumped into the workpiece via a fat mosfet, the output power being controlled by the charge time, the more charge time the higher the supercap voltage so more current dumped into the load.
I tried a crude setup and it seemed to work, a shame the relationship didnt last out long enough to complete it.
 
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About 50yrs ago my Dad built a small arc welder that was used to assemble skin friction gauges and the like. I recall it having a big capacitor, but my one remaining brain cell operating on all 8 can't dig up anything else.
Around the same time, he made a "water welder". It electrolyzed water and took the H2. The flame was about 3/32" OD and had no trouble poking holes through Buffalo, NY phone books.
Both of those devices were/are commercial items, maybe there's info out there somewhere about them.
 
Strange that this should come up; I was just commenting on something about this on the Arduino forums. Anyhoo...

About 6 months back Electronic Goldmine was selling booster caps (in fact, right now they're having another sale on similar ones); as an experiment, they ended up charging a few up, hooking them together, and seeing what they could do with them. They made some youtube videos as I recall; in one of them, they showed how they welded some small bits of steel together with an arc they produced. So...

I though maybe you could build such a small arc welder, but use a tungsten tip - and you might even have to introduce argon into the mix as shield gas; basically a very tiny MIG/TIG welder (?) - put the caps in a box or something to keep safe in case something blows (and/or add some kind of "fuse" or something to trip in case of a shorting of the tip?).

In their demos they said that even after doing their experiments and such several times, the caps had plenty of voltage/current capacity left (they were also saying you should make sure to drain them fully, because they could give you a helluva jolt otherwise if you didn't).

Thought it was an interesting idea to try, even if it didn't work, as sometimes you do want to do small scale welding on material too thin for larger welding processes (your only other real choices would be to solder or braze the material - or epoxy).
 
Jagjoe, interesting comment about the hh0 welder, I've never seen one of these in action, they say that the cone from the flame is inverted and only the tip of the flame is hot the cone itself is cold, is this true?
 
I would have no idea. Two days after he finished building and checking it, he took it to work at Cornell Aeronautical Laboratory.

I can't speak for every flame, but I thought the cone was always the coldest.
 
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