Wire EDM machine

[Neale]

This thread is under the "Other Machines..." heading as it doesn't have its own category - yet?

I know that some forum members will be aware of the Society of Model and Experimental Engineers (SMEE), a old-established society with mainly UK but also international membership. A small group of members of the SMEE Digital Group have been collaborating on a wire EDM(*) machine for the last couple of years. For those who haven't come across wire EDM, think of a hot-wire cutter as used for foam, but this time using a spark between the wire and the (metal) workpiece. Enough sparks for a long enough time, and the workpiece gets cut away, leaving a cut around 0.1mm wider than the wire used for "cutting" - and this machine uses 0.25mm wire, so that's a pretty fine cut. Move the wire under CNC control, and you can cut intricate and accurate shapes out of difficult-to-cut materials, including hardened metals that are next to impossible to cut otherwise. Wire EDM sits alongside laser and water-jet cutting as a go-to technology for tricky jobs. If the principle sounds easy (which it is), the practice is a bit more tricky. The wire has to keep moving as it gets eaten away as well, while maintaining tension; the spark voltage has to be accurately controlled by adjusting the position of the wire and thus the spark gap - too close and you need to back off, too far away and there's no spark; the whole thing is working in an incredibly noisy electrical environment as all the electronics is running a few centimetres from this spark transmitter.

If you do a bit of googling on "wire EDM", you will find plenty of big - and I mean pretty big - commercial machines and companies offering wire EDM services. Look hard and you will find a few, a very few, "home-built" wire EDM machines. We now have a working wire EDM machine that is totally self-contained and small enough to go into the back of a car, and as a small demonstration of its capabilities, here are a couple of sample pieces I cut on it earlier this evening:

The letter E is about 8mm high, the star about 4-5mm across. In fact, I had difficulty in finding the star in the tank (the cutting operation happens submerged in distilled water with a jet directed at the cutting area to flush away cutting debris).

I know that there are people who have made claims to fabulous machines on this forum but have offered little proof of their existence. Well, you will be able to see this machine in the flesh at the Bristol Model Engineering Exhibition next week, where with a bit of luck and a following wind, I shall have it running on the SMEE stand for all three days of the show. Forum members are cordially invited to come along, and if you can't find me, just ask anyone on the stand. If you are also a wire EDM user, then you are even more welcome to come along and compare our efforts with your commercial machine!


(*) Electrical Discharge Machining