OT-sinker opinions/adivice sought/burning with copper

[El Scotthead]

Hey all.

 

I'm seeking opinions, advice, experience, or whatever other wisdom you sinker gurus wish to share.

 

I'm pretty capable running the sink, when burning with graphite. However, now we're getting into medical molding and our designer(my boss?) wants to start using copper for mirror finishes in the cavities. I have virtually no experience with copper. He's really being a pain in my you-know-what about this. Mitsubishi has told me that to keep the accuracy that our customers are demanding(+/-0.0002 in most mold cavities), we're better off using graphite and maybe polishing the electrodes a little. I've also called some other shops around the state that help us out from time to time, and NONE of them use copper.

 

I'm going out on the web to try to get some data now, but would greatly appreciate what you guys/gals may have to offer. Tips, tricks, burn settings, edm fluid, milling data, anything. I'm trying to keep an open mind here, but am about ready to grab ahold of him just go to town over this. Wouldn't be the first time I've had him by the neck

 

Thanks

scott

[El Scotthead]

Sorry, might help you to know what machines we're working with. I'm getting really frustrated over this.

 

Mitsubishi EX-8 CNC sinker, Hangsterfer's Crystal Brite EDM fluid

Eltee Pulsitron manual plunger(1990-ish),

Defiance Innovations 3 axis CNC electode mill, 45K spindle, air blast, no coolant, biggest tool = 0.375

[Lucky]

Copper electrodes will produce a finer finish but the difficulty in electrode machining is much greater and electrode accuracy is likely to suffer. Make sure you have exhausted the possibilities of graphite before considering copper. I have obtained impressive finishes using premium grades such as Poco EDM-3, Poco EDM-C3, and Poco AF-5. These graphites have much finer grain structures and can approach the finishing capabilities of copper. Similar grades may be available from other manufacturers.

 

We use Agie sinkers here so I can't help you with specific erosion parameters. The guys at Mits should be able to give you something that will produce a good result with super-premium graphite.

[Kevangel]

I have never seen copper used for mold cav. in my travels. I only have (a lot of) manual sinker experiance, BUT in manuals, whatever finish you have on the electrode is what you will have in the cavity,eventhough to the naked eye all burns to the same settings ,look the same. If you mill an electrode in the Bridgeport or grind the same electrode in the surface grinder, then burn there will be a big difference when you go to polish...between the milled electrode and the ground electrode. I used to put a good grind finish on then lightly polish with 600 paper when required. I agree with Mits. people. my opinion. I can't imagine making precision molds with copper electrodes.

[Accu-Molder]

We use copper here 90% of the time burning with a mits EA12 machine. the reason being the size of the parts the small graphite trodes will erode bad and the copper will hold up very well. We use copper telerium or for better wear resistance coppper tungsten is even better but this is harder to machine . You will find if you are wanting to burn to a mirror finish the edm time will greatly increase and erosion of trode will increase. If we can polish our cavity we burn to a 1 or 2 mat finish and polish by hand.

[Lars Christensen]

I agree with everyone, with the fine grain of graphite they have now a day's it does cost more to burn with copper. I use copper tungsten but only when I have to burn carbide. The only problem with graphite can be that your spindle on your mill dies premature, if you do not have the proper vacuum.

Try to call your graphite reseller and get some info on finish they can get with there product, and hand it to your boss, facts my change his mind.

 

Lars

[BernieT]

I've used a fair amount of copper for electrodes - more so than graphite. If you use Telco (telurium copper) it machines almost like aluminum. I can't comment on holding +/- .0002. I never needed better than +/- .0004-5.

 

I suggest giving telco a try, you have nothing to lose and will learn something new!!

[El Scotthead]

Thanks guys. That's the kind of info I was looking for. Most people I talked to yesterday agreed that an EX-8 is not a machine for mirror finishing and that the finish I do get with copper won't be worth the extra time involved. Customer wants it shiny and dead nuts on tolerance, but doesn't want to pay the $$ for it?!?

 

I'm going to order some Poco 3, copper, and some Telco(thanks Bernie) and set up a test. That way I can document everything, and hand him the results. Plus, Bernie, you're exactly right. I'm gonna learn a thing or two

[BernieT]

Another comment on copper for electrodes - I had problems with the copper 'moving' when machined due to stresses in the raw blocks. Easily solved by stress releiving before machining (600 deg F. for 1/2 hour - as I remember) Also solved when we switched to 3R Tooling and soldered the copper to the shank. The heat from soldering eliminated the stresses.

[Kevangel]

Bernie, this is intresting, I hace used silver tungsten, and some copper for general EDMing. How many electrodes per burn with copper? also was this only for smaller cavities, this stuff must be expensive? thanks!

[Kannon]

cant chat much, sitting in pro e class, but what I would suggest is contact Intech and they sell edm3 graphite. Its copper inpregnated and burns very nicely, holds up much better then the straight grahite, and leaves a nice finish, not to mention much easier to machine.

Maybe it will make the boss happy if he finds out the graphite is inpregnated with copper and he will leave you alone

back to class, and talk to you guys in a few days!

 

If you are forced to go with copper, get copper tungsten, much easier to machine, cuts cleaner and dosent roll over such nasty burrs

[BernieT]

quote:

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Bernie, this is intresting, I hace used silver tungsten, and some copper for general EDMing. How many electrodes per burn with copper? also was this only for smaller cavities, this stuff must be expensive? thanks!

---

I found that usually only one copper electrode was needed to finish a cavity. Sometimes two if tol were close. Most cavities were less than 2 inches dia. But one 4" x 6" job 1" deep I made 2 trodes but was able to finish it with the 1st one. (Sodic and Mits machines with orbit capability)

 

As for expense, the last time I priced Telco and graphite the copper was cheaper by almost half for the same size stock. (8 - 10 years ago)

 

HTH

[Kevangel]

thanks Bernie, I will check this al.copper out!

[El Scotthead]

Ok, one more question here....

 

how does Telco compare to copper tungsten, as far as milling/grinding it and burning with it?

[Accu-Molder]

Personally with tungstun I will grind it With a 120 grit wheel and use wd-40 on the wheel to remove and keep copper from building up. Same stategy when grinding telurium but I would rather mill it and yes it does roll burrs so you may need to take a dry pass to remove or deburr after milling. . Copper is still much cheaper today than graphite. Oh and we 99% of time use telurium over tungsten. 3trodes per burn and detail is perfect and within tenths of size.

[Lars Christensen]

Accu-Molder,

Don't you loose you money in the mill department when you are using Copper Vs. Graphite?.

 

Lars

[Müřlıń®]

+/- .0002 If you could grind the copper maybe you could hold those tolerances if you managed the dilethric temp.

 

I have ground aluminum before but have never tried copper.

 

I have used copper on Ram type EDM's and it is alot cheaper to use when you are building multi cavity molds that must be burned.

 

+/- .0005 was about as close as I got tough since we wern't in controlled environment or didn't controll dilethric temp....bout all we did was just rough one day and finish the next, after the workpiece and oil cooled off...

[Midwest]

 

 

Here is a sample of the tiny parts Accumold makes, they are in a whole different world with the size of parts they make.

 

Just felt like patting you guys on the back for the type of work you do. I have also heard it is a great place to work and is a growing company.

 

(1.) quick question have you ever sneezed or someone next to you and lost your part.

 

 

[Kevangel]

.0002 mold shop standard or .0002 gage shop standard?...I have done both, gage shop, if your out 10 millionths it will come back. Molds can be out some if cavities are all the same and molder "packs out" cavity to make the parts come in. just what I have seen.

[Müřlıń®]

10 millionths that's .00001....

 

I have held +/- .00005 before but its tuff, and that was only for grinding work that we were checking with a 50/1 comparitor in controlled environment..

 

kevangle you are correct. I have seen packing/cycletimes/and mold temp vary a part as much as .02 on 2" poloypropelene parts...

[El Scotthead]

Murlin, good point on controlling the temp. There is a chiller that keeps the fluid temp pretty constant. I usually let the fluid circulate for a while first thing in the morning to get some initial heat into it. Another Mits guy(who was a sinker guy for longer than I've been alive) told me to do that when I first started running the thing 4? years ago.

 

Kev,

.0002 mold shop. And IMHO, there's nothing we mold that needs to be THAT tight on the cavities, not even the medical stuff. Alot of times, I think it's our designer over engineering. The processing department, as you said, can usually make up for a few tenths or even a thousandth, as long as the cavities are uniform.

 

BTW, Midwest,

our molds look comparable(in size anyway) to those you showed. And, yes, one time our grinder guy had a bunch of tiny inserts on his surface plate when he sneezed. We spent the whole morning on our hands and knees, with a magnet finding them all

 

Thanks again guys.

scott

[Müřlıń®]

quote:

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Alot of times, I think it's our designer over engineering.

---

LOL you said it pal.....most enjuneers don't have a clue....

 

I was grinding some core pins on one occasion and the print had a +/- .0001 on the dia.

 

The guy would run them across the street in a Texas sun to the CMM (holding them in his hands of course ) And by the time he got there the pins had already grown out of tolerance by the heat in his hand....

 

 

Man, we went round and round that day

[Accu-Molder]

Lars if we use graphite we have to make more trodes than with copper to get the definition we need so I think the mill time is a wash. Our medical and fiber optic parts are done in a seperate clean room. The tool room is controled temp when the chiller goes down in the summer wich it has a few times it effects the wire machine and edm quiet abit so we shut it down but our mill doesnt grow and move much. As far as tolerances goes I hold .0002 all day long on our mill. Midwest your right you dont want to sneeze any were near parts if you do get lucky and find them on the floor they are probably junk anyway being dirty or damaged from hiitting the floor. It makes you sick when you drop a core pin or a ablock with a lot of grinding on it that took all day to make 1 good one and it hits floor you pray its not damaged.