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Achievable surface finish EDM vs ID grinding

M

M. Roberts

Cast Iron
Joined
May 11, 2021
Guys,

I hope everyone is well. This was a tough question to figure out the correct location to post; if I made the wrong choice, my apologies. So, quite simply, the question has arisen as to by what process produces the best, highest quality hole between wire EDM, and ID grinding; roundness and surface finish. The material in which the holes are to be finished is a silicon carbide based ceramic; so regarding the tooling for the ID grinding operation, it would be diamond. The proposed CNC is a Yasda. Hole size: 0.250" x 0.625" thru. IMO, the wire wins hands down across the board for a multitude of reasons including but not limited to cost, maintenance, repeatability....Please chime in...

Thanks in advance,
Mark
 
I should think as far as a finishing operation ID grinding would be far quicker. Other than that it would probably come down to the machines and processes used. I don't think either would win hands down.
 
What type of dielectic are you using in your WEDM? Kerosene would probably be best for this, as it creates a carbon layer to help with conductivity. It might be a headache dialing in your settings to cut this on an EDM. I haven't cut any of this stuff before though. I know that pure SiC can't be machined on an edm and the lower surface area of the cut, the better. Might be worth a try.
 
Guys,

Thanks for the replies. I still say that the EDM is the better choice, I guess I am a little biased. The wire would have deionized water. My concern is how finicky the grinding nibs would be; adjusting for wear and all that rot; the wire is much simpler...again, I guess that I am biased.

Mark
 
From what I've read, to make wire edm of SiC more conducive, the silicon carbide is doped with extra silicon to make it more electrically conductive.

As far as speed or being subjectively "better" goes, in your shop the "better" way may be different than in Bob's shop, which may be different than Joe's. This will depend on what machines you are most familiar with and have the most experience using.

If you want to compare a shop that is aces on ID grinding vs a shop that is aces on wire EDM you might find one or the other has the edge. But I bet it wouldn't be a very large deficit either way. The wear on a diamond wheel when grinding a simple finish cut out of SiC should be pretty minimal, and dressing is pretty quick anyway. Unless you are using an electroplated wheel or grinding point, in which case you just change the point when it's dull... As you can imagine, the variables and options can get pretty convoluted pretty rapidly.
 
implmex said:
Hi All:
Are you certain the silicon carbide ceramic is even conductive?
If it's not there will be no wire EDM.
If its conductivity is low there might be wire EDM in the mix but it'll be a hair tearing exercise for the poor bugger who has to try.

I am not hopeful, from the bit I've Googled.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
Click to expand...

I was waiting to reply until I was able to research SiC a bit more. It seems that wire edm is probably not going to work for this application.
 
Last edited:
OP, can you explain your bias towards EDM, is it based on experience with sample runs or just conceptual?

Your post title asks about the best surface finish achievable. In tool steels at least, grinding is able to produce a much better surface finish than even the best edm process. Geometry should be better too. So do you need the best possible or what do you really need?

I work with parts that often have small wired holes that I often lap to hit final size with the mating components. One feature on wired holes is the common start/end point of the wire path can have a distinct geometry variation of a shallow groove. It is probably sub 50 millionths deep, but you can see it if you are careful lapping and checking.

Given that these are straight through holes, I would look at a honing process. A manual Sunnen hone for small quantities. A single pass honing setup will be the ticket for millions. Engis Single-Pass Honing/Bore Finishing Systems - YouTube
 
M. Roberts said:
.... IMO, the wire wins hands down across the board for a multitude of reasons including but not limited to cost, maintenance, repeatability....Please chime in...
Mark
Click to expand...
Agree that 0.250 5/8 deep is pain to grind in this stuff.
Even with stock that is wireable I do not see the speed or accuracy anywhere close to grind but that is just my opinion and we know how that goes.
Silicon carbide based ceramic is sort of a generic callout and so many variations and grades.
Bob
 
I have honed this stuff before. It's tough but hones well with diamond stones. ceramic is easy to hold size with a hone and almost no size change from heat. In that small a hole I don't think grinding would be a good choice.
 
Grinding is going to give a better surface than edm, while you can get pretty good surfaces after the recast is removed it's still not as good as grinding. Considering it's made from sand and carbide heated to over 4000°F I doubt edm would easily touch the stuff.

I found an article talking about using wedm with kerosene as the dielectric and wrapping the SiC in foil. This is extreme and dangerous. Diamond cutters with simple water flush seems to be the method of choice.
 
Guys,

I was out for the Holidays...nice to see some interesting viewpoints on this subject. Yes, this material is very EDMable...I do it on a daily basis. My biased towards the EDM process? Again, it is based on having experience working with this stuff. It is tough to machine; tooling wise the only thing feasible to use is diamond abrasive. To ID grind the hole to size, I don't think that I would take the full depth of the hole and slowly interpolate out to the final diameter; but probably take shallower cuts, and still step it out to final. This would still require a secondary operation to finish the hole; I am picturing the hole having an irregular profile due to uneven wear on the tool. With the EDM process, I see it as a much simpler, way to go...no concerns with tool wear, or changing tools...yes, a second or third cut may be required, but I see it as a much more repeatable process. I am thinking out loud now; I guess it is possible to have a probing routine set up on a mill to check the holes after the operation is done??? But isn't there issues with checking the work on the same machine that the part was machined on?? I guess the probing (if possible) could take multiple hits throughout the depth of the hole to check "profile".....still not convinced that EDM inst the better option....keep going..
Thanks,
Mark
 
M. Roberts said:
Guys,

I was out for the Holidays...nice to see some interesting viewpoints on this subject. Yes, this material is very EDMable...I do it on a daily basis. My biased towards the EDM process? Again, it is based on having experience working with this stuff. It is tough to machine; tooling wise the only thing feasible to use is diamond abrasive. To ID grind the hole to size, I don't think that I would take the full depth of the hole and slowly interpolate out to the final diameter; but probably take shallower cuts, and still step it out to final. This would still require a secondary operation to finish the hole; I am picturing the hole having an irregular profile due to uneven wear on the tool. With the EDM process, I see it as a much simpler, way to go...no concerns with tool wear, or changing tools...yes, a second or third cut may be required, but I see it as a much more repeatable process. I am thinking out loud now; I guess it is possible to have a probing routine set up on a mill to check the holes after the operation is done??? But isn't there issues with checking the work on the same machine that the part was machined on?? I guess the probing (if possible) could take multiple hits throughout the depth of the hole to check "profile".....still not convinced that EDM inst the better option....keep going..
Thanks,
Mark
Click to expand...

How about some basic info? What are the volumes, tolerances (ID, circularity, concentricity), and minimum surface finish requirements? The right answer will be highly dependent details.

Are these always one size? Air gaging will be the way to go with if the sizes are limited.

Honing in likely to win if high volume or very tight tolerance and surface finishes are required.
 
Hi M.Roberts:
Well if you can get it to cut on the wire, and it's a through hole, why not wire it?
I can't think of a good reason to even have the debate if you've got the gear and the experience to wire it and you know it works.
Grinding or honing "might" get you a better hole...maybe.
Will it be enough better to make a difference?

I assume the cylindricity and tolerances of the hole are well within the wire EDM range... Is that correct?

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
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