DIY Wire EDM

[Cody henry]

Saw this on the CNC coverage of Rocky Mountain Rep Rap Festival, thought it was pretty cool: 

https://rackrobo.io/products/BWV1

[Brad Freese]

I'm embarrassed to ask this, but what exactly does it do? I'm assuming it doesn't make Electronic Dance Music or do Educational Data Mining. 

Is it Electrical Discharge Machining?

[Kirk Nelson]

Hello,

EDM is Electrical Discharge Machining. It takes an electrode and burns through the metal to put it simply. It can make some amazingly detailed parts and works better cutting hard material.

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[Cody henry]

Yeah Electrical Discharge Machining with a wire. Essentially one of those hot foam cutters but for metal. But this company sells kits to convert a 3D printer into a cnc wire EDM 

On Thu, May 23, 2024 at 4:25 PM Brad Freese <bradley...@gmail.com> wrote:

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[Charles Mullerup]

YES

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[Ray Scheufler]

I believe it is electric discharge machining. My understanding is that you have a plate of material and a wire that you put electricity through and it controllably arcs to the plate of material machining it away. It is a very precise form of machining because the tool is rather thin and because there is very low tool pressure (you don't have to worry about rigidity of the machine / tool allowing deflection which messes with tolerances). My understanding is that it is relatively slow or relatively limited in work volume. My understanding is that it is a lot like a laser cutter in terms of the type of design rules but while you may be impressed by a laser kerf the wire EDM kerf is like an order of magnitude better.  All of this is recollection and her say. I've never worked with one so someone with more experience can chime in with real details.

Ray Scheufler 

On Thu, May 23, 2024, 4:25 PM Brad Freese <bradley...@gmail.com> wrote:

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[Brad Freese]

I’m guessing the downside of this would be very toxic fumes? You’re essentially vaporizing the metal, right?

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[Ray Scheufler]

Main downsides I'm aware of are speed and 2d only.  A hot wire cutter for metal is a pretty decent analogy.

Ray Scheufler 

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[Brad Freese]

If it’s 2D, why do they call it a 4-axis machine?

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[Ray Scheufler]

There is an XY gantry above the material to be worked and an XY gantry below the material to be worked.  In theory this means that if you had a way of dynamically controlling the wire length you could do fancy things like angles by not having the top wire holder at the same position as the bottom wire holder.

Ray Scheufler

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[Charles Mullerup]

Work is done in a fluid.

Not much of a smell.

That I remember. 

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[Caroline Longnecker]

A 4 axis wire can do 2.5D machining, or roughly 3D if you have a rotary axis. The reason it's 4 axis is so the top and bottom wire guides can be moved out of alignment with each other to cut a taper. Typically the top wire guide has a second XY motion system attached to the same XY motion system that the bottom one is on. On really fancy machines like the Mitsubishi wire I used at DMACC the machine will actually automatically move them slightly out of alignment to help cut straighter (on straight cuts it leads with the top slightly iirc).

A wire generally has no fumes. The machining is generally fully submerged with flushing jets around the wire to remove the "chips". A wire typically uses deionized water as a dielectric, which means there may be some water vapor from the sublimated metal cooling, but there are no metal fumes since the flushing/water tank cool them back down again very rapidly. They reform into small spheres of metal and are supposed to be filtered out. This will also progressively ionize the water. The wire at DMACC (and most other wire EDMs) have a deionizer setup to to maintain a specific water conductivity level.

There are a few other types of EDM machines. The original one rack robotics built was basically a sinker/plunge/ram EDM, though it could be sorta used like an EDM drill (we called it a hole popper at DMACC). Normally sinkers use a stronger dielectric such as mineral oil (the new one at DMACC used a special green dielectric). The dielectric needs to be stronger due to the much larger surface area typical in this process. Electrodes are typically graphite or copper. This is the process that can make large cavities, occasionally entire mold cavities are machined into prehardened toolsteel using this process. This is how I made both halves of my mold cavity at DMACC, as well as the runner.

An EDM drill is generally a pretty crude machine. I'm sure some relatively fancy ones exist, but the one we had at DMACC was really only meant for putting small holes to feed the wire through into already hardened materials. It could also clear out a small broken drill in a hole, and if you got good you could cut a blind hole to a relatively accurate hole depth (I burned a subgate from my runner into my cavity with the hole popper for my mold at DMACC). The one at DMACC had a literal small drill chuck that you put a brass tube into, with a diamond guide on the opposite end to help the tube move straight. It pumped deionized water through the hole in the tube for flushing. Due to the highly manual nature of the machine at DMACC, there was a ton of electrode wear relative to the sinker. I think a 50mm hole would burn off around 10mm of the electrode, vs a 20mm pocket would burn around 0.2-0.5mm off a roughing electrode on the sinker.

There's at least one other form of EDM, but I can't even remember the name, nor do I have experience with it. It's basically like using a really small piece of wire as an endmill though. I believe Accumold has at least one. I know nothing else about the process.

Caroline

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