EDM types and uses

Could someone please explain to me the basics on which EDM types do which kinds of work. I'm EDM ignorant.

Wire, sinker... usefulness of a manual edm vs CNC... etc.

Many Thanks
Sean

Okay, hope I can explain this without getting too wordy. Sinker EDM, also called Plunge, Ram or Conventional EDM. Generally 3 to 4 axis. X and Y are like on a mill, Z would be the quill and C would be the spindle. This type of machine uses either graphite or copper for the electode. Electrode is in the shape of the detail you want to burn into your workpiece. Machine uses a dielectric fluid to keep the atmosphere from the burning area, in sinker EDM this is usually petroleum based. No the spark from the electrode to workpiece will not catch the dielectric oil on fire, dielectric is keeping the atmosphere(oxygen) away form the spark. Advantages to this type of machine, tap a hole in a hardened part, do blind pockets, do fine details on mold inserts, drill holes that were forgot before the part was hardened. Machine come in both Manual and CNC, each one has it special place. CNC is great for when you need to make 100 mold inserts with the same details, with an electrode changer you can run un-attended. We have both in our shop, 2 manual, 2 CNC. One CNC with a 90 station electrode changer robot. Wire EDM Generally 5 axis machines X and Y as on a standard machine. Z is generaly programable for height on and stays set when machine is cutting. U and V axis these correspond to the X and Y axis, and can move independentily allowing you to cut tapers and 3D shapes. By 3D I mean square opening on top of workpiece and round hole on bottom of workpiece, as an example. Instead of dielectric oil these machine use water as the dielectric fluid. This water has been filterd and de-ionized. The electrode in this case is a wire generaly brass, sometimes coated or not. Size ranges from .001 to .012 in diameter, its a one shot use and is discarded after that. Machines are all CNC controled. Some uses for this machine are, cutting openings in plates for dies, stack cutting many parts at one time, die inserts that need angular relief, also carbide is no problen to cut. Machines can cut and thread the wire by themself, great when doing a plate with many openings. Can run a high degree of automation with these machines, nights and weekends. We have 2 of our machines runing over the Thanksgiving weekend unattended. Hope I didn't confuse you too much or get too long winded. Mark

Thanks Mark.
The machine shop class I took didn't have an EDM. I'm sure I'd get it if I could see them running.
My mind is set on the idea of having a cutter.

The concept of the sinker makes sense to me, although I cannot imagine the speed at which it errodes away the metal.
I see manual machines of this type and it seems rather amazing that it could errode fast enough that the operator could turn the handwheels *slow* enough.

Wire I imagined was for cutting only...as you would with a water jet or laser. When you say "3D shapes" how does it do this...with the "tip" of the wire?

In threading... with the sinker, I can picture a carbon "tap" slowely making it's way through the material, but how is this done with a wire?

I often need to own something before I completely "get it", but this is useful so I know what sort of thing to get.

I really appreciate it.

Sean

Sean,
Forget conventional feed like you are thinking about. Even the "ancient obsolete, totally worthless sinkers" you find at auctions a lot had a short circuit reverse feature. It was a kind of fuzzy logic feed feature that decided for itself how fast to cut. Kinda hard to visualize without seeing one run. You don't run handwheels on a sinker to cut, you run the handwheels to position the electrode, then the automatic fuzzy logic powerfeed takes over. Wire edm's have the same thing, they have an adaptive feedrate control that goes faster or slower as it senses cutting conditions. Pretty wild stuff. The power settings are kinda a black art to most people, including me. You'd have to have a phd in electrical engineering to understand the circuitry involved. The only way to learn edm is to do it....

Sean: on a manual sinker machine you don't turn the cranks like on a mill, the table is used for positioning only. Z axis is controled to burn to desired depth with the electode. On a wire machine the wire is more like on a band saw it cuts with the side not the end, and it is impossible to tap with it. God I wish we could do graphics on here I am horrible at explaining things. The two companies we deal with in our shop are AGIE and Charmilles both Swiss companies. They have literature available and their own web sites. AGIE has one section called "What is EDM". Hope this helps ask me more, most I can do is confuse you. Mark

[This message has been edited by Space (edited 11-28-2002).]

Thanks guys.. I did some research on the net as well (EDM for dummies).
I found some diagrams and explanations that when combined with your posts, really help.

The two types are pretty much as I thought, but those handwheels were really throwing me off. I had no idea that the machines had some time-warp, slo-fuzzy-elecronics to control the feed, and I couldn't possibly imagine them eroding fast enough for manual feed.

I pretty much get it...in concept now.
For reference though... let me ask....

If you were sinker EDM'ing say... the sole of a hiking boot for a mold, how long would it take to complete, and how many units could you produce with the carbon (or whatever would be used)?

Thanks Again
Sean

This looks lioke the easiest thread to post this in. We have a Charmilles 610 Robofil at work that we got from a sister plant. The diskette drive only takes 3.5"720k floppys. Any ideas were we can get some. I've been surfing and I can't seem to find them at any of the computer supply houses.

Boy this is a tough one, when we find a 720k floating around we grab onto it. Have you tried taping over the square hole opposite the write protect window, then formatting the disk? I have an older drive on my computer and this seams to work. Is your machine new enoughto update to a 1.44 disk drive? Call Charmilles and ask, only drawback might be the cost of parts. Good Luck Mark

Sean, in answer to your estimated time for the " boot sole mold": More than likely you would have 3-4 electrodes. As you burn away material, the electrode also deteriorates somewhat, so for best definition you have to burn it several times. Generally sinkers will be rated at cubic inches per hour. My guess ( I am not a sinker man...) is if you get 6-8 cubic inches per hour you are flying. I would expect more like 2-3 cubes per hour. Wire speeds are rated in square inches per hour. You figure the length of cut x the thickness/ machine rating. Generally if you get actual rate of 1/3 machine rating ( including skim cuts and rethreading) you are doing good on a manual thread wire machine. To do a boot sole mold like you are talking would be more than a 24 hour job in my opinion, depending greatly on the machine.
Leo

Thanks Space, thats one thing we havn't thoight of yet. The normal opperator is pretty sharp, he even writes his own Autolisp routines for AutoCAD and I don't think that he's tried that one yet.

Sean: I have to agree with willieo6709 on number of electrodes and burn time. Something the size of a sneaker mold is out of my league, most of the cavities we make are fairly small. We are burning inserts for one of our bigger molds right now, these cavities are .25 X .187 X .75, Later Mark

Ok... now this is all making more sense.

Thanks much guys... EDM, a good movie, a trip to ocean, some sleepy tea and a Prozac.

I think I'd need to become a lot more patient before aquiring one of these machines.

Cheers!
Sean

Sean: It's not that bad, I think the strongest thing any of the people in my departmnet are on is Busch Light. One thing not mentioned is the fact that while the machine is running, even a manual machine, you or your people can be doing other jobs. It gets a little hectic, but when managment wants to see cost savings, it's not a problem. I also have to admit just sitting watching one of these machines run is like watching paint dry, it's good to have something else to do to keep you busy. Later Mark

See, that's the problem.... I *HAVE* to watch paint while it's drying.
This is why I don't garden

Heck, I'll see if I can pick up an obsolete cheap sinker that works to play with.... maybe it will distract me from the paint

Sean

www.quala-die.com

hey sean check out the link above this is the
shop i work in by day we have 10 ram edms
and 7 wire edms. go to the facilites page of the site above about half way down you can see a gear die i was burning on a cnc ram im the big guy at the far end of the picture

Im building a falling block rifle,if I run into problems cutting a rectangulr slot through a block of 4140HT and it needs accurate smooth surfaces can it be cleaned up with a wire edm and how much material would I leave for the machine to work with,in other words if I get to a place where I cant use my shaper can I bail out and save the piece with edm.Are there job shops that will take on a small piece of work, and or is it to expensive to consider.Any and all input will be appreciated----Tim Smyth

Tim, if you run into a problem contact me. I can wire e.d.m. the part(s) for you. [email protected]

I have a small amount of PocoGraphite material that can be used to make electrodes. I will flip a coin with the first 10 people who send me an e-mail wanting it and let you have it for the shipping.