Strange buildup in the slot
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  1. #1
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    Default Strange buildup in the slot

    Good morning All:
    I had a weird new problem this morning I've never seen before.
    I'm wire cutting a simple rectangular cutout in a 4140 round shaft.
    All went well for the first 0.050" then I started getting wire breaks occasionally, then the cut stalled and I got wire shorts.

    I look at the slot and it's welded shut!!
    I can't even get a skinny shim in or run a piece of wire through.

    So I cut the offending chunk away from another direction, cut through the welded bit, and then popped out the slug.
    Attached is a photo.
    Look at the funny little lump glued to the side of the slug at the top of the photo

    I've never seen this before.
    The wire was recently maintained, water conductivity is good, power contacts have been indexed: it ran like a bunny yesterday.

    Any one seen anything like this before?
    Any theories as to why?

    It's running just fine now...noodling along as expected and I'm totally stumped.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining
    Attached Thumbnails Attached Thumbnails dscn5001.jpg  

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    Marcus,

    It sounds like you encountered a non-conductive "goober" in your block!

    It appears that the machine was trying to cut thru it, and you probably had some secondary discharging happen from the wire being pushed around by flushing.

    It looks like that build-up might be the result of the brass wire brazing itself back on top of the part from secondary discharging?

    Does this sound like what you're are seeing?

    - Brian

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    Yeah Brian it sure does!
    Thank you for responding...as I said, I've never seen this before and I was frustrated and puzzled by the fight I was having trying to get through this.
    It's cutting just fine now; I'll be very curious to see how it skim cuts in that area.
    Cheers

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

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    Damnedest thing I've ever seen...ive had wire pushed off from flushing being redirected by airfoils on multi blade vanes but never had that result. I've had the "there's something non conductive in there somewhere" happen plenty of times but again nothing even remotely close to that.


    Bet you couldn't do it again lol

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    Hi again all:
    The rest of the cut went completely uneventfully.
    The skim cut went completely uneventfully too.
    I have NO idea what happened, but Brian's theory is the best I've heard so far.

    Plastikdreams you wrote:
    Bet you couldn't do it again lol"
    I tried...I did try...really hard, but no joy.
    All is good though...my customer still loves me!

    Cheers

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

  6. #6
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    Quote Originally Posted by implmex View Post
    Hi again all:
    The rest of the cut went completely uneventfully.
    The skim cut went completely uneventfully too.
    I have NO idea what happened, but Brian's theory is the best I've heard so far.

    Plastikdreams you wrote:
    Bet you couldn't do it again lol"
    I tried...I did try...really hard, but no joy.
    All is good though...my customer still loves me!

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining
    Hah perfect storm I ghess

  7. #7
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    We have had similar thing happen, and concluded the same thing, something non conductive in the material. Did the same thing, cut from the other direction to get through it. Had some glass bead stuck in the bottom of a tapped hole that must have melted during heat treat. PITA

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    I believe the term is "recast"...?

    I've seen it when cutting very large/tall parts where the burn was extremely slow (13-14-15" in Z). Not sure what the root cause is though.

  9. #9
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    Can you polish that offending section up too see any differences in the material?


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