One thing we do far too much of is turning round holes into square holes. Typical size is between 1/8" and 1/4", multiple parts stacked 1-3" high. We generally undersize the drill by ~20 thou and our 10 thou wire makes 3 passes around the square. However, the corners fall through and cause problems about 75% of the time.
We have read https://edmproud.com/the-most-effective-methods-for-holding-and-retaining-slugs/ but our parts and slugs are too small for glue, clamps or magnets. I am interested in the “Slug Ejection via Programmable Flushing” - Does anyone have any experience doing this on a Makino U3 or similar?
We have also tried roughing passes that make an X shape to cut into the corners first and remove material but it isn’t always successful either. Seems like dealing with “Backward movement exceeds limit during machining” errors is faster than any additional roughing passes.
Any other suggestions anyone? Thanks in advance!
I’ve been reading The Complete EDM Handbook by Carl and Steve Sommer, and they recommend a smaller start hole and only dealing with one slug. You would also have the wire fully engaged all the way around the cut instead of having the “thin” spots where the diameter meets the square walls. Just my thoughts—— John
I think you should be asking what you are trying to optimize for here; Simplicity or Time?
If you just want a simple option with fewer headaches from slugs dropping I would program a coreless cutting path for each square. It might take a little longer but given that these holes arent that big my guess is that it would only be slightly longer if you run the most aggressive cutting parameters for the coreless roughing passes (this would also allow you to run “lights out” with less supervision)
The quickest option to me would be to have someone stand there when the slugs drop which it sounds like you’re doing. You could always program 4 “Tabs” or “Gluestops” into each of the four corners so that you can make one long rough pass around most of the square, put a mo, then go through and cut them all off at the same time. I’m imagining one X shape like you said but instead of cutting into the corners, you could rotate it 90deg and go into the middle of the sides and make a T at the end, stopping just before you hit the corner to leave a tab, then reverse and cut your way down to the next corner on that line. Like an X made out of 4 T’s.
Why don’t you just drill a smaller hole though… If you drill a small hole then you only have one large slug that is much more manageable. We have a hole popper at our shop and we make 0.06" starter holes for all internal features, running 0.01" wire. Starting with a larger hole just means you have more little slivers and smaller slugs that cause problems with almost no decrease in runtime.
Either drill a smaller hole to begin with, making it all one solid slug, run the square program coreless (will take longer), or cut it as you have been but add 3-4 passes and increase the offset on the first few so that they do not create a slug (basically making the first few passes run coreless, but avoiding a path that takes the entire square).
In the shop I’m at that is something they always ask about before a piece comes to the wire, what drill size is going to avoid problems, but your answer definitely depends on personnel, and how much you’re wanting the machine to run without any operator input.
Just an additional thought - If you are doing enough of these size holes and drilling a small enough start hole is an issue, you may want to consider getting an EDM hole driller. Doing a 1/8" hole through 3" material can be a challenge. With a hole driller, you could drill a start hole with a .5mm electrode and get about a .023" start hole.
Best bet is like others have suggested, either nocore it out or a smaller start hole will take care of your issue. If you don’t want to worry about slugs at all, nocore is where its at. You can do different nocore patterns so you wouldn’t have to waste time cutting air in your start hole.
I agree with the smaller start hole. Sometimes, I’ll stop before the slug drop and tie the slugs with EDM wire to hold them together.