Sinker EDM vs Wire EDM for Fine Features and Thin Walls

[KaminKevCrew]

I’m working on a design, and figuring out the best way to manufacture it has been making me think more and more about EDM machining.

Basically, the part in question has the overall nominal dimensions of 210mm x 68mm x 6mm. I need to put a bunch of holes (~150) that go through the 6mm dimension of the part, so the holes would be 6mm deep. Nearly all of the holes are very close to each other, and have a ~0.5mm wall thickness between them. The holes need to have as sharp of corners are possible, ~0.05mm radius would be ideal.

I have 3D printed some prototypes, and I have had another couple of prototypes laser cut from acrylic, as well as aluminum. The 3d prints aren’t consistent enough for what I need. The laser cut acrylic is pretty close, but the black acrylic I had cut is not opaque enough for this project, and bleed too much light. The laser cut aluminum had issues with the thin walls melting during the cutting process and is completely unusable.

I need all of these walls to be completely opaque to visible light, which is why I’m thinking that making this out of metal would be ideal.

Wire EDM - at least from what I can find online - doesn’t appear to work with wire that is as thin as I would need.

Sinker EDM seems like it might have the capabilities that I need. All of the walls of the part will be normal to the face of the part, so angles won’t be an issue. Ideally, I would like to have an electrode machined that can cut a large portion of this part (or all of it) in one operation, but I don’t know how feasible that is. Do sinker EDM machines have the capability to cut an entire part whose top surface is 210mm x 68mm, to a depth of 6mm? I have seen used sinker EDM machines up for sale for relatively low prices around me, but I don’t know that those machines would be capable of making all of these cuts without my having to line up each of the ~150 holes manually.

Additionally, if anyone knows of a better way of manufacturing this part (maybe water jet?) I’m all ears.

 

[pcd]

Have you considered using metal honeycomb?

 

[nlancaster]

What is the Diameter of the holes you are making?

The shop I work in we routinely do .020 holes with wire EDM. These parts have a zero blemish rule on the ID of the hole.

And for large numbers of small holes consider EDM drilling, it can make lots of holes within very tight tolerances.

 

[KaminKevCrew]

Have you considered using metal honeycomb?

I haven’t - of the ~150 holes in this part, there are over 80 that are unique, and the shapes are very different from each other. I’m not sure how a metal honeycomb would help me with that (though if there’s a way that might work, I would be open to the idea).

What is the Diameter of the holes you are making?

The shop I work in we routinely do .020 holes with wire EDM. These parts have a zero blemish rule on the ID of the hole.

And for large numbers of small holes consider EDM drilling, it can make lots of holes within very tight tolerances.

I may have mislead you when I called them holes - while they are holes, in that they are cavities in a solid part which go from one side to the other, only four of the holes in total are actually round (and those four could pretty easily just be clearance drilled as they’re just mounting holes that M3 bolts will pass through). Other than those, two of these ‘holes’ are about 1mm wide, 175mm long on an ~800mm radius bend, and have several sections that stick out perpendicular to the tangent of the radius by between 3 and 10mm depending on the section. Most of the other holes are close to being parallelograms, but the top and bottom follow that same 800mm radius with an offset, if that makes sense.

The majority of the holes are about 1.5-1.65mm wide, and between 5 and 20mm long, and need to have extremely sharp, defined interior corners.

 

[implmex]

Hi KaminKevCrew:
Yes you could wire EDM these parts out of metal, but IMO that would be an exceptionally poor way to go about it.
You could also sinker EDM your parts...that would also be a poor way to go about it but for different reasons.

Starting with the sinker:
You need to make an electrode with cylindrical features spaced so there is 0.5 mm between them.
Your electrode will have 150 little cylinders sticking up at least twice or even better 3 times the height of the throuh holes you want to burn.
Milling a copper or graphite electrode 18 mm tall with a 1/2 mm endmill is a non-starter IMO.
Next you need to get flushing around every cylinder and it must reach every part of every cylinder.
This is a tall order...you have 150 of them.
Defective flushing in even the smallest corner of your entire workpiece stalls the entire burn.

Moving on to the wire...you'd need to pre drill start holes for every location where you intend a final hole to be and they must be big enough to accept an EDM wire, so for most machines they must be bigger than 0.015" to accept an 0.010" wire with clearance all around it.
Every hole needs to be threaded with the wire and then cut to final size and then the wire needs to be cut and the next hole threaded.
This is time consuming and expensive.
Depending on what the final hole diameters are (you didn't say) the wire start holes might be small enough to be hard to drill.

So as I said, EDM is not a good way to make something like this...you could hole pop them one at a time with what's called a hole drilling EDM or "hole popper", and if this part was to be made of something unmachinable, I'd make the recommendation, but not for this.

IMO these are CNC machined parts and not that hard to do.
Here's a picture of a Delrin part I made recently:

The part is smaller than yours, but the holes are spaced much closer together too...0.25 mm instead of 0.5 mm.
They also have steps and chamfers and other features.

You could choose black Delrin for your parts and with 1/2 mm webs between the holes it's going to be opaque... not like acrylic.
My gut tells me also that if you were almost successful with 3D printed and laser cut parts these are low tolerance parts and you may well be able to just drill peck them in one shot with a stubby carbide drill in seconds per hole.

So that's where I'd pin my hopes.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

Whoops...lots of other posts happened while I was typing.
I'd still mill them out of black Delrin though and if you have holes where you need to pick out the corners with a tiny endmill to get the corners sharp enough, and then broach the corners to get them dead sharp, I'd figure out a way to do that.

BTW, 0.05 mm corner radii is dreaming in sinker or wire EDM unless you are good with dropping a LOT of money, like thousands per part.
MC

 

[SeikiCorp]

Will a corner rad of .004" be acceptable? Most wire shop will handle that with ease.
.003" or .002" corners is more specialized. Not all shops are prepared for that wire size.

If there is a multitude of shapes, it will drive up the cost of a sinker process with electrode costs.

 

[nlancaster]

Other than those, two of these ‘holes’ are about 1mm wide, 175mm long on an ~800mm radius bend, and have several sections that stick out perpendicular to the tangent of the radius by between 3 and 10mm depending on the section. Most of the other holes are close to being parallelograms, but the top and bottom follow that same 800mm radius with an offset, if that makes sense.

The majority of the holes are about 1.5-1.65mm wide, and between 5 and 20mm long, and need to have extremely sharp, defined interior corners.

If I am reading that properly you have various sized and shaped slots cut thru the material all over it?

Can you post an image without dimensions, as that may help some of us understand exactly what you are asking for.

We routinely wire slots that are .25mm wide with our Wire EDMs, and repeat to within .01mm for all the parts in a given operation.
With inside corner radius of around .10mm.

To get below .10mm corner radius you would have to go to some very fine wire, which would slow down the entire process.

This sounds exactly like something Wire EDM is meant for, but it will be an expensive part. That is a lot of hours of cutting.

One possible way to lower cost, if you are making more than one, wire edm can cut thru a stack of raw parts without significantly increasing cut times in many cases.

To get this sinker cut you would have to invest in alot of machined electrodes that will wear out and have to be replaced.

Something else to consider, with walls that thin between the openings you will have movement of the material, your best bet would be to use stress relieved material.

 

[KaminKevCrew]

Hi KaminKevCrew:
Yes you could wire EDM these parts out of metal, but IMO that would be an exceptionally poor way to go about it.
You could also sinker EDM your parts...that would also be a poor way to go about it but for different reasons.

Starting with the sinker:
You need to make an electrode with cylindrical features spaced so there is 0.5 mm between them.
Your electrode will have 150 little cylinders sticking up at least twice or even better 3 times the height of the throuh holes you want to burn.
Milling a copper or graphite electrode 18 mm tall with a 1/2 mm endmill is a non-starter IMO.
Next you need to get flushing around every cylinder and it must reach every part of every cylinder.
This is a tall order...you have 150 of them.
Defective flushing in even the smallest corner of your entire workpiece stalls the entire burn.

Moving on to the wire...you'd need to pre drill start holes for every location where you intend a final hole to be and they must be big enough to accept an EDM wire, so for most machines they must be bigger than 0.015" to accept an 0.010" wire with clearance all around it.
Every hole needs to be threaded with the wire and then cut to final size and then the wire needs to be cut and the next hole threaded.
This is time consuming and expensive.
Depending on what the final hole diameters are (you didn't say) the wire start holes might be small enough to be hard to drill.

So as I said, EDM is not a good way to make something like this...you could hole pop them one at a time with what's called a hole drilling EDM or "hole popper", and if this part was to be made of something unmachinable, I'd make the recommendation, but not for this.

IMO these are CNC machined parts and not that hard to do.
Here's a picture of a Delrin part I made recently:
View attachment 437373
The part is smaller than yours, but the holes are spaced much closer together too...0.25 mm instead of 0.5 mm.
They also have steps and chamfers and other features.

You could choose black Delrin for your parts and with 1/2 mm webs between the holes it's going to be opaque... not like acrylic.
My gut tells me also that if you were almost successful with 3D printed and laser cut parts these are low tolerance parts and you may well be able to just drill peck them in one shot with a stubby carbide drill in seconds per hole.

So that's where I'd pin my hopes.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

Whoops...lots of other posts happened while I was typing.
I'd still mill them out of black Delrin though and if you have holes where you need to pick out the corners with a tiny endmill to get the corners sharp enough, and then broach the corners to get them dead sharp, I'd figure out a way to do that.

BTW, 0.05 mm corner radii is dreaming in sinker or wire EDM unless you are good with dropping a LOT of money, like thousands per part.
MC

Thank you for the detailed information! Milling out some Delrin and using a super small endmill or broach to get the corners as tight as I need them is something I hadn’t considered and is a great idea. I haven’t tried Delrin, but if it will still be opaque with a wall thickness of 0.5mm, that would be great. I might see if I can get some laser cut in that case, as the laser cut acrylic did have tight enough corners.

You are correct that these parts do not require extreme precision. As long as they hold up to a close visual inspection, that’s basically all I need.

It’s also good to know that such tight corners may not possible with EDM without spending a huge amount of money. If the laser cut Delrin doesn’t work out I’ll look more into machining it. It looks like there are at least 0.004” endmills that might still be small enough for the visual effect I am in need of.

Will a corner rad of .004" be acceptable? Most wire shop will handle that with ease.
.003" or .002" corners is more specialized. Not all shops are prepared for that wire size.

If there is a multitude of shapes, it will drive up the cost of a sinker process with electrode costs.

It may very well be - for what I have as a reference, I need the 0.002", but because it primarily needs to hold up to a well illuminated visual inspection, a 0.004" radius may work.

If I am reading that properly you have various sized and shaped slots cut thru the material all over it?

Can you post an image without dimensions, as that may help some of us understand exactly what you are asking for.

We routinely wire slots that are .25mm wide with our Wire EDMs, and repeat to within .01mm for all the parts in a given operation.
With inside corner radius of around .10mm.

To get below .10mm corner radius you would have to go to some very fine wire, which would slow down the entire process.

This sounds exactly like something Wire EDM is meant for, but it will be an expensive part. That is a lot of hours of cutting.

To get this sinker cut you would have to invest in alot of machined electrodes that will wear out and have to be replaced.

Something else to consider, with walls that thin between the openings you will have movement of the material, your best bet would be to use stress relieved material.

Yes, stress relief is definitely a consideration. So far in my testing with plastics it hasn't been too much of an issue, but obviously plastic and metal behave differently. I've attached a couple of examples of what I'm talking about - hopefully they give a better idea of the kinds of shapes I'm trying to achieve.

 

[plastikdreams]

Do we advertise beds here now? We sure get a lot of dreamers these days...

 

[KaminKevCrew]

Do we advertise beds here now? We sure get a lot of dreamers these days...

I’m not entirely sure what beds have to do with anything. I am definitely a dreamer - that’s a fair assessment. But the point of this post is literally that I’m trying to figure out how make my ‘dream’ a reality.

So, is there something wrong with being a dreamer, or trying to learn about the possibility of using a certain manufacturing method to produce the thing I’ve been ‘dreaming’ about?

 

[???]

The information that you are posting is insufficient to give you considered options. Go and see a shop with CNC, wire and sinker EDM and ask them to quote you on the job and also advise you whether what you are wanting to do is even feasible.

 

[bob]

You might have started with what your budget is for these. I figure that would end the discussion pretty quick.

 

[KaminKevCrew]

You might have started with what your budget is for these. I figure that would end the discussion pretty quick.

My budget for these is anywhere up to ~$1,200 per part. Maybe that’s way too low - if it is, that’s fair enough. However, in my area there is currently a sinker EDM machine for sale for $1,500, and a wire EDM machine for $1,800. Supposedly they are both fully functioning machines, one of which is currently under power so I can check it out.

I am mostly curious about the feasibility of using either sinker EDM or wire EDM for this project because there’s no point in me buying machines that can’t do the thing I need them to. That’s why I’m asking here.

So, is my budget unreasonably low?

 

[implmex]

Hi again KaminKevCrew?
I just gotta ask...what sort of budget have you allocated for this?
I ask because all of the options that have been considered so far will cost a good chunk of cash and you need to know that up front.

Those ambitious corner radii are the principal problem.
With the variety of shapes you've shown in post #8, every corner will also be different from the others so you cannot make a single broach that can get them all with a single form if you want to do one hit per corner.
The tiny radius means you cannot simply run a tiny endmill into the corners.
The tiny radius means you cannot just run a standard 0.010" diameter EDM wire.
The tiny radius means you cannot just laser them or waterjet them with common machines using common settings.
The tiny radius means you cannot just 3D print them on a standard printer.

So IMO, your least expensive but still pricey options are:
a) Make it out of metal and wire it with 0.004" wire or smaller and accept that the last time I had fine wire stuff cut, it cost roughly 10 times what it would have cost with regular 0.010" wire and that's because the fine wires are fragile and cannot take much power.

b) Make it out of Delrin or some other opaque plastic that machines easily and stuff down the smallest cutter you can that will allow a reasonable L ratio...that might be a 0.8mm or 1/32" endmill which will be necked down for a stick out of 7.5 diameters.
Once all the pockets are cut, you can use a custom ground slotting blade that has an included angle that's as acute as the most acute angle in any of your pockets.
You then walk the slotting blade into the corner, orienting it as needed using the M19 spindle orient command and skive out each corner in small 0.001" bites, so the slotting blade acts almost like a single tooth sawblade.

All this is not simple to set up but if your vendor grits his teeth and beats his way through all the code it needs it will get you the sharpest corners of any process I can think of.

Another way forward to get nice sharp corners is to make it out of metal, mill it as close as you can as with the Delrin parts but then make a separate sinker electrode for every pocket (makes them easy to make and flush) and drop the trode into the proper pocket, then swap out the trode, orient to the next pocket location, and go at it again.
This approach is a lot simpler code wise and is more foolproof but you said there are 150 pockets so 150 electrodes...also a lot of expensive work.

Don't expect to get away with spending 50 bucks on this.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

Well, looks like I'm late to the party again...I started writing when post #10 first appeared.
MC

 

[Orange Vise]

The holes need to have as sharp of corners are possible, ~0.05mm radius would be ideal.

How did you come up with this number?

You are correct that these parts do not require extreme precision. As long as they hold up to a close visual inspection, that’s basically all I need.

It would be beneficial for you to see sample WEDM cuts in person and determine how sharp of a corner you actually need.

Even 0.200mm is going to look pretty damn sharp to the naked eye.

The reason why your 0.05mm is so prohibitive is because it's smaller than what the average WEDM can cut.

Open up your corner radius requirement and the job becomes pretty straight forward. You can even stack several plates and cut them at the same time.

 

[implmex]

Hi yet again KaminKevCrew:
Those machines you have an eye on are not going to get you there without a lot of pain.
I say so because you cannot make this project work with these two toys alone even if both are in perfect working order (HIGHLY doubtful given the price)

You need at least a VMC as well in order to make trodes for the sinker or start holes for the wire.
You need some sort of metrology to know if what you made is going to work as you intended.
You need a place to put the toys and you need to power them up and you need to buy a few grand worth of stuff and etc etc.

Also, I would be very surprised if any vendor you contact will quote this for you except maybe a wire shop, because the job is all about screwing around until you can make it work (unless you wire it).
I wouldn't...I'd demand cost plus best effort.

Unless you REALLY want to start a machine shop of your very own I recommend putting those old beater EDM's out of your mind.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

 

[precisionmetal]

KaminKevCrew

To me, this could be doable in wire edm. I regularly ran 100µm wire in my Agie (170HSS) with excellent reliability and consistent results. I even dropped to 70µm wire for the occasional tiny features/parts.

Using 100µm wire, I would probably cut one part at a time, though two (12mm stack) might be OK with that wire size. I'd drill all the start holes in the cnc mill.

However... the real time-sucker will be the ~150 threadings the machine has to do, and I gather some/many would be through a .020" start hole. That probably means babysitting the machine through this job, which could add significantly to the cost.

However, that said: I think Marcus's idea of just machining (and broaching) them out of plastic might be the right approach (or definitely the one to try first). A relatively small investment to attempt.

PM

 

[implmex]

Hi precisionmetal:
If you were going to wire these skinny slots would you rough them with a slugless strategy using 0.010" wire first and then pick out the corners with fine wire?

I'd hate to try to manage those tiny slugs and I sure wouldn't want to run them slugless with fine wire.
So now I'd be looking at 300 threadings...150 for the roughing and another 150 for the finishing.
This is not gonna be a cheap part.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

 

[precisionmetal]

Marcus,

Since we only have a verbal description of the part, it's difficult to say. I gather from the description that some of the drops would be very "narrow", but long, so I would probably try and drop those out with the small wire. You are absolutely spot-on though: no-core could likely be the best method on at least some of the features.

My only apprehension would be how accurately a machine could pick back up on the geometry after a wire swap, especially since KaminKevCrew mentioned how "thin" the walls may be in places. Do we have any tolerances on this part? It would be interesting to see the model.

Regardless... any methods used would probably require a ton of time keeping an eye on the machine!

PM

 

[Nmbmxer]

What process did you use when you had it 3D printed? Seems like SLA could hit your tolerance and resin can be opaque.