Radio Frequency Waves from Ram EDM affecting CNC performance?

Yvonne · May 31, 2013

Hi,
We have 3 small sinker EDM machines we use to machine stamping dies for our engraving business. This past couple of weeks we have been very busy (yay!) but have noticed a strange phenomenon with the way our CNC is cutting our carbon/graphite electrodes. We have been experiencing uneven cuts -the variance on the letter heights on 1 stamp die we did is over 0.010"! Some of the part numbers come out looking like they had a wild party (not lined up...crooked, just plain "goofy" looking).
Since we have not had this type of problem before (probably because we never had all 3 EDM's running at the same time), we were wondering if the radio frequency waves from the EDM's could be affecting the encoders on our CNC.

If this is the case, would grounding each EDM to Earth be a solution for this problem?

Any insights would be greatly appreciated.

Thanks!

Yvonne

Brian Pfluger · May 31, 2013

Yvoone,

Have you checked and confirmed the incoming voltages at the transformer for each machine? Since this is the first time you have run all 3 machines at the same time, it is quite possible that your incoming power capacity is not sufficient.

-Brian

Yvonne · May 31, 2013

Hi Brian,
No we have not checked that yet...but we certainly will. We are looking into everything we can to try and figure this out.

Thank you for the suggestion Brian.

Yvonne

dinosaur · May 31, 2013

All of your machines should be earth grounded. Do not have it earth grounded and simultaneously grounded through the bus bar. You will create ground loops. Your EDM machines may not be properly shielded as well and might be generating some electrical noise. Take an AM radio if you can find one and tune it in between stations. Bring it close to your machines and listen for any change such as an increase in static or hissing. That would tell you that there is some electromagnetic radiation being emitted.

It is a better practice not to have an EDM, an ultrasonic cleaner, an induction heater or a welder near a CNC machine or tied into the same bus bar.

However, since you are cutting graphite, another possible issue is the graphite dust getting into the servo and spindle amplifiers or the power supply. Graphite is conductive and will cause these drives to go flaky. Turn off the CNC power and take a shop vac and suck out the drives. You might want to blast some clean compressed air into the drive on one side and suck the dust out on the other.

I hope this is helpful to you.

Yvonne · May 31, 2013

Hi Dinosaur

(I love your name)
All of our machines are earth grounded through the bus bar. We had just thought maybe adding a dedicated ground to each machine might be helpful. I am pretty sure our machines are not properly shielded because we have an old FM radio that we just put in the shop about 8-10' from the EDM's, and when the EDM's are running full bore we get terrible static. The guys in the shop next door have a problem with static on their radio too....and that's through 12" thick concrete block! If you know what we need to do to shield the machines that would be extremely helpful.

Our CNC is located about 35' from the EDM machines and it is on a separate bus bar from the EDM's, but you are right about the graphite dust. The machine manufacturer told us to do exactly what you said and from now on, vacuuming the CNC will be part of our PM program. Although, when we opened the covers on the drives there was a small amount of dust...not packed or anything, but it is still a good habit for us to get into.

Your post has been extremely helpful to us and we appreciate it.

Thank you,

Yvonne

dinosaur · Jun 1, 2013

If the machines are grounded through the bus bar do not add a dedicated grounding rod as well. It needs to be one or the other.

You might try to fabricate some sort of metal cover around the power supplies on your EDM machines. That might provide enough shielding.

Red James · Jun 2, 2013

dinosaur said:
If the machines are grounded through the bus bar do not add a dedicated grounding rod as well. It needs to be one or the other.

You might try to fabricate some sort of metal cover around the power supplies on your EDM machines. That might provide enough shielding.

Electrostatic shielding works the other way around. . .what happens INSIDE a conductive box still affects things outside. Instead, make sure the CNC case is grounded to form a "shield" around it. HTH!

Yvonne · Jun 3, 2013

Thanks much Dinosaur! We will try your suggestions.

Yvonne

Yvonne · Jun 3, 2013

Thank you Red....we will try your suggestion as well!

Yvonne

Zahnrad Kopf · Jun 3, 2013

You're in Wisconsin, so it's most likely a Mitsubishi or a Fanuc. If it's a Mitsi, there's a WHOOOOOOOLLLLLE section in the books about shielding.... I have my doubts about it being necessary though. I run mine 10 feet away from a machining center AND a turning center without ill affects on any of them.

XD341 · Jun 3, 2013

We run a sinker within 10 feet of cnc mills and lathes and have never had a problem. We also run a 75Kva spot welder in the shop, that thing will dim the lights in the whole place and I have often wondered if it would somehow screw up fine tolerances on a cnc, never has.

toolmaker76 · Jun 3, 2013

I worked on wire EDM's at a machine shop for a time, at the time the only CNC machinery in the place. We kept having goofy things happen with the machinery, always seemed that a reset (cycle power off/on) took care of things.

What finally helped was driving a ground rod into the ground beside the CNC cabinet and grounding the cabinet to the rod. I don't think we changed anything else, but this took care of the majority of our trouble.

The phenomenon at the time was called electrical noise. CNC controls use a low voltage to run, and there may be lots of wiring in the cabinet, which sets up a condition that acts like a radio receiver. Get some nearby interference, such as a welder striking an arc, relay contacts, any NUMBER of things, and it plays havoc with your low voltage commands in the CNC. Grounding the cabinet itself took care of most of the goofiness, shields the CNC from outside "electrical noise."

As someone posted earlier, grounding the cabinet of the CNC would be more effective than the EDM's. If you have several cabinets (our machines did) if you have to choose which, then the one you want to ground is the one that has all the circuit boards that control movement (X,Y,Z) and function. Another cabinet might house the power supply, that one will not be as critical.

Yvonne · Jun 10, 2013

Hello Zahnrad,
We are located in Milwaukee too! We actually have a small Tiag desktop CNC that works well for engraving carbon electrodes for stamping dies. I sent an e-mail into the Tiag support team, but have not heard back...possibly the e-mail went into spam. I am going to give them a call.

I apologize for taking so long to get back to this forum...but we have been BUSY...life is good!

Thank you,

Yvonne

Yvonne · Jun 10, 2013

Hi XD,
We have asked other shops if they have experienced this phenom...and most have not. That's what makes this kinda like fixing an intermittent electrical problem

Thanks,

Yvonne

mfgbydesign · Jun 10, 2013

Stranger things have happened...
Australian News - Beer fridge knocks out mobile network in Australia

Yvonne · Jun 10, 2013

Hi Toolmaker,
Your experience sounds a lot like what we were experiencing. Currently we have a small Tiag desk top CNC to engrave the carbon electrodes for stamp dies and it is on a 120V circuit, grounded to the busbar. What we have been doing lately is cutting our carbons first thing in the morning before we turn on the EDM machines and this seems to have taken care of the problem. However, when we get rich and famous and buy a real CNC, we will likely have to either ground or shield it as you suggest.

Thank you...I appreciate your advise!

Yvonne

Yvonne · Jun 10, 2013

Well, people lost their phones for a good cause at least

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