Wire EDM small Titanium washers
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    Default Wire EDM small Titanium washers

    My company is being asked by a customer to make some tiny titanium washers.

    4.5mm x .61mm and they have a very tight flatness and parallel tolerance range, .005mm.

    On our Sodick AG600L, as far as I know a general purpose machine, we are running into a tiny amount of curve while cutting.

    The wire enters at one side of the blank, and as it cuts to the center of the cylinder the kerf is shrinking on the order of .002mm.

    This of course is making it tougher, not impossible, to hit the flatness and parallelism tolerance.

    Any tips on reducing that curve that results from the change in thickness of the part while cutting?

    I am already running the current and voltage down as low as I can and still cut for a decent single pass surface roughness of the part.

    And the tension is already near the maximum the machine can tolerate with .010 brass wire.

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    If it is critical, I would not be trying to limit it to a single pass. At all. This is where the rubber meets the road in WEDM. Finishing passes often employ lots of fiddly tricks for exactly this reason. playing with flushing pressure, multiple tool paths with varied entry/exit points, and special fixtures of very creative nature are all part of that repertoire. I don't think you will ever get the belly out from a single pass, in every place.

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    Quote Originally Posted by nlancaster View Post
    My company is being asked by a customer to make some tiny titanium washers.

    4.5mm x .61mm and they have a very tight flatness and parallel tolerance range, .005mm.

    On our Sodick AG600L, as far as I know a general purpose machine, we are running into a tiny amount of curve while cutting.

    The wire enters at one side of the blank, and as it cuts to the center of the cylinder the kerf is shrinking on the order of .002mm.

    This of course is making it tougher, not impossible, to hit the flatness and parallelism tolerance.

    Any tips on reducing that curve that results from the change in thickness of the part while cutting?

    I am already running the current and voltage down as low as I can and still cut for a decent single pass surface roughness of the part.

    And the tension is already near the maximum the machine can tolerate with .010 brass wire.
    Well... if they want those tolerances they shirley (hah Ox) can't be "washers"?? But I get the description.

    In inches, they want flat and parallel to .00019" !! Yikes! And you're seeing a variance of pretty much half your tolerance, .0001" Hmm sounds like a royal PITA, hope they are making money for you anyways... If you are trying to get that last tenth or so of flatness I would try a couple things

    1) cut them .0002" or so oversize and lap them?
    2) if material/previous machining is not too expensive, just cut and sort them and throw out the ones out of spec? .61mm = .024" plus your kerf of roughly .012" wouldn't seem like wasting much material

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    Good morning nlancaster:
    Both Zahnrad Kopf and Mike 1974 have the right of it; it doesn't matter what machine you put it on, you will have stress release in the material and wonky parts (technical term) as a result if you're slicing them like bologna slices from a tube.

    Zahnrad Kopf's recommendation is the traditional one, but it's going to be the devil's very own to try to find a way to fixture it.
    The best way I've ever found is to make a fixture that's like a fork with tines of the part thickness.

    So, you wirecut a hole in your fixture, open on one side like a "C" shape that that will allow a tube of the correct diameter to be forced into it.
    You make relieving cuts in the fixture so it's springy and the tube can be gripped solidly but still be pushed in and out with moderate finger pressure.

    Now you can flip the fixture and blank assembly 90 degrees and cut your fork tines into it so each tine is your part thickness.
    Since the cuts are made into the fixture with the tube already in it, you can rough cut and skim cut all the faces, then unload the fixture and begin again.
    Your parts will be as accurate as the machine is, and the modern Sodicks are as good as any other decent brand out there.
    Obviously if you hope to grip all the washers in the fixture, the OD of the tube must be cylindrical within close limits.

    If you have lots to do, resist the urge to pretend you can re-use the fixture.
    At only 0.61 mm wide, the tines will bend hopelessly if you try to push a new tube in.

    I've found the best material for fixtures like this to be...wait for it...Inconel 718 of all things.
    It seems to have just the right amount of springiness to make a great fixture, so I keep a bit of it around for when I have to cut off short, small diameter tubing that's impossible to hold any other way.

    Now, given all that farting about, I really like Mike's idea of just slicing them oversize and having them lapped to thickness...it's going to be so much less work and they'll be dead nuts accurate and right on size with no pain on your part whatsoever but you need a decent quantity to justify farming out the lapping.

    Cheers

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

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    Don't forget to slap the person who quoted/accepted that job!!

    I did something similar years ago. Wired off slice of something around 5/8 diameter stainless. The thickness tolerance wasn't nearly so tight, but they wanted the surface finish on the faces to be something stupid like a 4 or 6ra. Don't remember the exact material, but was not magnetic so surface grinding was out. Each piece had to be lapped on both faces with diamond paste (multiple grits). Not sure what qty we made, but it was too many for that crap!

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    All good solutions.

    We are currently looking at cutting off of a tube of material like slice balogna.

    We are going to have to lap them because I only get one pass.

    At the low settings I am using I get a 90ish RA finish, and the spec from the customer is 16-25RA.

    So yes they will have to be lapped, was just hoping to reduce any belly as much as possible.

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    Quote Originally Posted by nlancaster View Post
    All good solutions.

    We are currently looking at cutting off of a tube of material like slice balogna.

    We are going to have to lap them because I only get one pass.

    At the low settings I am using I get a 90ish RA finish, and the spec from the customer is 16-25RA.

    So yes they will have to be lapped, was just hoping to reduce any belly as much as possible.
    Hey nlancaster,
    Just an idea to help limit the belly as much as possible, if it is a tube your cutting these off of you can put some round stock in the OD to make it as a "SOLID" piece.


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