Wire Edm not picking up centre
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  1. #1
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    Default Wire Edm not picking up centre

    Currently using an AC Classic V2 Wire Eroder and its been working fine for a while but this morning I done the usual maintenance/wire alignment and I wired a form in a carbide die. The form ended up being 4 thou out of concentricity. Normally its within a few tenths. Cant understand why it didn't pick up the centre accurately. wonder if anyone has any suggestions as to what can cause this, thank you.

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    Hi mootrix:
    When I've had problems like this it's almost always been things like my block's not square or there are burrs on my touch-off surfaces so I'm touching a corner, not the whole surface.

    Next most common is rough touch off surfaces that abrade the wire and rub a bit of brass onto the surfaces while shaving the wire
    These fall in the wire transport system and mess up the touch-off.
    They also build up on the touch off point, shifting it a little more with every successive touch.

    Next most common is insulating contaminants on the block or on the wire and eventually on the power contacts.

    Least common is an electronic fault with the wire touch sensing circuitry.

    I always run my touch offs at least twice and check for consistency.
    Most often it's within a tenth or so.
    Sometimes it's a mile off which means I got a bad touch on one of the attempts.
    The root cause has always been one of the above.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    www.vancouverwireedm.com

    Oh yeah, one I forgot: a wet touch especially if the filters are dirty or the DI resin is used up.
    MC

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  4. #3
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    Mootrix,

    Did you pick-up the part from a center hole, or did you pick-up from the outside of the part?

    Are you able to determine which direction the profile was cut incorrectly off by 0.004”? Knowing if the 0.004” error is off in one or both axes might identify other items to look.

    You might also want to consider the following beyond Implex's excellent suggestions:


    Work Piece Related:
    - Verify there is not a burr on the edges of the pick-up surface from grinding, milling, other
    - Verify that the pick-up surface is CLEAN or lapped (oil, dirt, debris will cause inaccuracies, and any heat treat scale on steel parts can also cause pick-up issues)
    - Verify that the work piece was setup flat, level, and securely clamped (did the part move during machining)
    - Verify that the start hole was drilled properly (non-perpendicular holes or holes on angles will pick-up as elliptical egg-shaped features)


    Machine Related:
    - Verify that the machine contacts were indexed to a new fresh position
    - Verify that wire tension is set properly (very low wire tension will not pick-up accurately)
    - Verify that the water quality is within proper levels (filters & resin)
    - Inspect the machine Power Cables and Gap Box are in proper working order, as these items can cause issues if they are damaged (usually other symptoms and issues occur with this)


    Wire Related:
    - Verify that the wire used is clean and of good quality (what type of wire did you use, as some coated or stratified wires do not pick-up accurately)
    - Verify that the wire itself is also not looped underneath itself coming off the spool, as this can cause pick-up inaccuracies and also cause wire lines on the part


    Pick-Up Process:
    - Does your machine run and advance the wire slowly during pick-ups?
    - Did you pick-up the part dry or submerged? (submerged pick-ups will be more accurate)
    - Always run your pick-ups twice to verify repeatability of location (2nd opinions are a good thing)


    Slug Investigation:
    - If the part pick-up was from a center start hole, you can do some investigative work and measure the position of the Start Hole in the slug
    - If the Die Cavity was a simple square, the Start Hole edges should be equal distant to the X/Y outsides of the slug
    > If you see equal distant/correct values, then the pick-up was good and the part didn’t move = Start Hole was off location to the outside of the final work piece
    > If you see unequal distant/incorrect values, then the pick-up was bad or the work piece moved during machining

    - Brian

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    Thanx alot for getting back to me MC and Brian

    I always run one centre find program. normally never do it twice and I know my V block is square. ran another job in the same V block straight after and it was perfectly in centre. I think I will do 2 measure finds from now on, they weren't no burr on edges but the finish wasn't the best but was round within 1 tenth.

    when you mention contacts do you mean the pick up pads? I did clean them and moved both top and bottom along.

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    Hi again mootrix:
    You wrote:
    "and I know my V block is square".

    Of course the obvious next question is: but is your wire square too??
    In your case, since you ran a successful job immediately after the goobered one, you can say with confidence: "Yes it is".

    However, wire out of square has cost a few people some real grief (me included when I was young and cocky).
    One poster here (I can't remember who) had a great idea to manage that particular problem.
    He has a dead nuts square block that he clamps directly to the table and wires a dowel bore into it.
    He then pushes in a dowel or a gauge pin and inspects it for squareness off the machine with a tenths clock and a surface plate.
    The block gets used over and over again until it's Swiss cheese and then he makes another block.
    Fast, simple and accurate...the best kind of process check there is!!.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    www.vancouverwireedm.com




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    Quote Originally Posted by implmex View Post

    However, wire out of square has cost a few people some real grief (me included when I was young and cocky).
    ONE POSTER HERE (I can't remember who) had a great idea to manage that particular problem.
    He has a dead nuts square block that he clamps directly to the table and wires a dowel bore into it.
    He then pushes in a dowel or a gauge pin and inspects it for squareness off the machine with a tenths clock and a surface plate.
    The block gets used over and over again until it's Swiss cheese and then he makes another block.
    Fast, simple and accurate...the best kind of process check there is!!.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    www.vancouverwireedm.com
    [/COLOR]
    As Marcus stated, we always prove our wire to be square by cutting a dowel in a square block after using the squaring jig. It has saved me a lot of money over the years. Does it cost time and money to wirecut a hole and check it for square? You bet. But not as much as ruining a customer's steel and that customer not coming back.

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    I almost always check a hole twice, ones at 90° and once at 45°

    Btw it's center, maybe that's your problem

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    If you are trying to wedm a bore and maintain concentricity/cylindricity to the od of the part and relying on a pre-drilled start hole for your location you need to ...

    1. Make sure your start hole IS on center ... at both ends of the part.

    2. Make sure the id finish lends itself to being center-found. Rough drilled holes are not suitable.

    3. Make sure the od of your part is NOT tapered. Way too many times we have received customer parts with tight tolerances for size, concentricity and cylindricity only to find their parts had too much taper on the od to hit the tolerances they want.

    4. Do a wire alignment.

    5. Then check for all of the previously mentioned problems.

    In addition to all the above, I use a shop made vee-block and skim the vee every time it goes back in a machine.

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    [QUOTE=implmex;3076754]Hi again mootrix:
    You wrote:
    "[COLOR=#333333]and I know my V block is square".

    Of course the obvious next question is: but is your wire square too??
    In your case, since you ran a successful job immediately after the goobered one, you can say with confidence: "Yes it is".

    However, wire out of square has cost a few people some real grief (me included when I was young and cocky).
    One poster here (I can't remember who) had a great idea to manage that particular problem.
    He has a dead nuts square block that he clamps directly to the table and wires a dowel bore into it.
    He then pushes in a dowel or a gauge pin and inspects it for squareness off the machine with a tenths clock and a surface plate.
    The block gets used over and over again until it's Swiss cheese and then he makes another block.
    Fast, simple and accurate...the best kind of process check there is!!.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    www.vancouverwireedm.com

    I did run 2 more jobs after the first successful attempt and both were fine so I guess it may have been a bad contact for that particular job. Have taken on board on everyone's feed back and will do things different from now on.


    Cheers

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    Hi Mootrix,

    You mentioned that you were cutting a carbide die in a Vee Block. Was this by any chance a header die which was already pressed into its casing? These dies are assembled with a tremendous amount of press-fit, and depending how much material you remove from the I.D., can shrink enough during machining to cause the positional error you describe.

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    Quote Originally Posted by EDM AE View Post
    Hi Mootrix,

    You mentioned that you were cutting a carbide die in a Vee Block. Was this by any chance a header die which was already pressed into its casing? These dies are assembled with a tremendous amount of press-fit, and depending how much material you remove from the I.D., can shrink enough during machining to cause the positional error you describe.
    it was indeed pressed into a casing prior to wiring and what I think which also didn't help was i didn't clean the bit of molly which was still attached to it.


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