What kind of EDM should I use?

[gakare]

I need some help with this one.I don't know much about EDM's. I build small high speed stamping dies. I want to EDM hardened punch blanks of CPMM4 material. The punches are max. size of 1.5" wide x .75" thick x 3.0" long. They need a profile cut across the 1.5" at one end only thru the .75" thickness. I want cut a piece of the coil I will run and scan
the profile into the program, I may need to make some small adjustments to it( opening up vertical walls a few thou.)Then cut my punch shape out of the blanks so I have an exact fit with my punch to strip. What kind or type of machine will I need? Model #'s would be great! I will need to stay under $50,000, used is okay too.
Thanks in advance for any help if I am unable to answer.

 

[ornerynorsk]

The first thing you need to do is learn more about EDM before you go blowing your budget on a machine. Check out wire edm's, I believe this is what you are looking for.

 

[is2634]

I agree with ornerynorsk, you probably need a Wire EDM. We do the type of cuts you are describing on a Charmilles 2030. On the used market my guess is they run around $75,000, but they may be more accurate than you need. Keep an eye out for additional costs when you buy, such as filters, deionization bottles, chillers, programming software, work holding, etc. Those costs add up in a hurry. It can cost up to 20% of the purchase price just to get the machine installed and running.

 

[JMarv]

Have you looked into getting custom "made to print" punches from a supplier such as Dayton? Dayton Progress

Joe
SW Office 2008 SP5.0
P4 3.0Ghz 3GB
ATI FireGL X1

 

[gakare]

The accurancy I need hold is +/- .0005. Made to order punches will not work. We custom fit every cutoff punch we run to the coil that is running. Each coil is different. If it varies by more than .005" , The cutoffs will not make the part.

 

[MikeHalloran]

There are basically two kinds of EDM machine: 'wire' and 'plunge'.

One of my employers had a plunge machine. Making a cut required first producing a copper or graphite electrode in a milling machine. The electrodes were slowly consumed as workpieces were cut, so deep holes or repetitive work might require producing many electrodes. Ours had a borderline magical and hideously expensive set of tooling called 'System 3R', which allowed you to remove electrodes for modification and reinstall them to the exact same position, within fractions of a tenth. It was ideally suited for making a cavity in one face of a part, less so for making a profiled edge as I think you want. Note also that you need a fully tooled milling machine nearby, and most of them don't much care for machining graphite.

A wire EDM machine does not require a milling machine to make electrodes, because the electrodes come on a spool. It's not good at all at making blind cavities, but excels at profiles. I think it's commmon now for such machines to be able to produce a punch, a stripper, and a die with back taper/clearance, all from the same shape description, with adjustable clearances and drafts, and to do unattended piercing of a blank for cutting holes.

EDM is inherently a slow process, so unattended operation is a critical basic requirement; set it up, go home, and retrieve your finished part in the morning. It gets much slower than the usual claimed speeds when you need a good finish or tight tolerances.



Mike Halloran
Pembroke Pines, FL, USA

 

[gakare]

It appears from all the experts on this forum and from what I've read,I need a wire edm. There is no plunge cutting involved. Just a side to side cut at one end of the punch.
As for surface quality, we cut our punches on a linear surface grinder. So what type of finish would that be and how many passes of EDM would it take to achieve that? Also, could I have a warping issue cutting CPMM4.
One source I found said to use cryogenics to control it. (sounds a little far out to me).
How long does it take to make one cut across a 1.5w x .75 thick stock?

 

[MikeHalloran]

EDM produces heat at a very localized level, one tiny spark at a time. At the part level, it doesn't produce warping at all.

As you try to push the speed, the finish gets rougher and rougher. At the lowest speed you can stand, you get a satin finish.

Talk to your dealer about the metal removal rate you can expect, and ask for some sample pieces to show the finish.

One important way in which EDM differs from grinding is that it doesn't leave behind any locked-in stresses. ... which is actually not good for fatigue life of cut parts.



Mike Halloran
Pembroke Pines, FL, USA

 

[is2634]

Regarding finish, our typical surface grinding yields a 6 microinch Ra. This will vary with wheel grit, machine quality, process, etc. To achieve that finish in WEDM, you will have to buy a machine less than 5 years old. However, since your stamping, surface finish of profiles may not necessarily be your priority. It sounds like you want guiding (mating profile surfaces to be flat and fit with tight tolerance). The portion of the punch that stamps can usually be surface ground or hand polished. A 5 to 20 year old Wire EDM will accomplish that with a surface finish of ~12 Ra and will require about 6 passes. In .75 inch thick material, a 6 pass with .010 inch diameter wire will cut approximately 2 inches per hour. This varies with make and model so ask your dealer.

Regarding cryogenics...When heat treating metals, quenching gives a desired structure change to the metal. Often quenching to room temperature accomplishes this. Some tool steels, however, do not have 100% structure change at room temaperature. Cooling these metals further (say ~-100°F), completes the 100% transformation. If you don't do this there is some residual stress left in the material. Your application will dictate if this residual stress is a problem. If you wire edm a very thin section out of a larger block, the work piece may move due to the residual stress. It is very application specific, so I suggest you try it without the cryogenics until you see a problem.

 

[jbel]

Ours had a borderline magical and hideously expensive set of tooling called 'System 3R', which allowed you to remove electrodes for modification and reinstall them to the exact same position, within fractions of a tenth.

I think you are really minimizing the cost of 3R tooling. Hideously expensive is the understatement of the week!!

But it's darn repeatable and fun to work with if you can swallow the price.

But back to the question at hand. This could be completed with either sinker or wire EDM. You would just need the appropriate sized electrode for the sinker and the size of the cutoff blade.

Before you spend the ~$50K i would develop a process with a local supplier. Then you would know what type of machine works for you application and what doesn't. This also helps to prevent you from purchasing a very expensive boat anchor.

 

[KevinJon]

You could send out a punch to a wire edm shop to cut for you to see if the process will work for you with minimal investment.

Repectfully

Kevin
Intelligent Design and Services. Inc.

http://www.IDandS.com

 

[gakare]

That's a good idea sending it out as a test. We use about 600 cutoff punches per year at a cost of $100,000. And we spend a lot of time hand grinding.