Is this part suitable for Sinker EDM?
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  1. #1
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    Default Is this part suitable for Sinker EDM?

    Hello friends.

    I am attaching a few pictures of a part we are currently manufacturing by machining from 0.025" sheet stock.
    material - 1075 carbon steel
    General tolerance +- 0.003" (see some dimensions are within +- 0.0004")
    Machining this part is challenging due to it's abrasive and dulling effect on the cutting tools.
    Tools get dull quickly and we lose the tolerance. also there is a lot of optional stops required to change bolts and clamps...around 15 minutes cycle time per part.
    Maching the 45 degree chamfer in particular is pretty difficult.

    Eversince Ive seen this part I always thought it suits sinker EDM but we dont have the equipment in house so I would like to ask -
    Is this a sinker EDM part?
    Is this a wire EDM part?

    if not - why?

    what is the lifecycle of a sinker electrode for this type of material ? 1075 crs steel?
    If possible - erosion will be to a depth of the thickness of the part - 0.025" - so how long should this take per part?

    Thank you!
    drawing1.jpgdrawing1.jpgdrawing2.jpgdrawing3.jpg

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    MULTUSB200,

    This part IS EDM-able by both Wire or Sinker EDM, and your tolerances are easily achieved by EDM. Are you just talking about EDMing the (x3) rectangular cavities? Will the outer holes be Drilled? How many of these parts do you make per month or per year?

    In general, Sinker EDM will be faster than Wire EDM, as all (x3) cavities would be machined at the same time on (x1) electrode with SEDM. On the plus side, either EDM method will not produce any burrs on the part.

    I would suggest using SEDM and perform machining with an electrode that has (x2) locations...(x1) location will have the straight rectangular geometry, while the other location would have the 45 degree angle feature. You would SEDM the straight rectangular detail first, and then position the electrode over to machine the 45 degree lead-ins.

    For SPEED, I would recommend using a Graphite Electrode for this. If you use current Sinker EDM technology that provides good low-wear electrode technology, you will be able to machine 20~30 parts before the electrode needs to be redressed. The straight electrode detail will last longer, but the 45 degree lead-in feature will see more wear and set the interval for redressing.

    Wire EDM could also be used to machine the (x3) cavities complete, but you would need to have a pre-drilled start hole inside the feature. Wire EDM is capable of cutting both the straight section and 45 degree lead-in, but the total cycle time will be longer than the Sinker EDM approach, as each cavity will be machined individually. On a positive note, Wire EDMing would also allow you to cut the outside shape too (eliminate milling of this feature), so you could setup and machine many parts from a simple pre-drilling sheet of material. This approach would also allow the Wire EDM machine to run unattended (overnight) for an extended period of time, as the key to any EDM operation is maximizing unattended machining time!

    Your Part Print does not contain all the dimensions of the internal features, but I’ve SWAG’ed the cycle times below.

    SEDM Pro: Will provide the fastest cycle time
    SEDM Con: You will need to continuously manufacture and redress electrodes
    - Cycle Time Est. = 10~15 minutes (x3 Inner Features)

    WEDM Pro: Will provide the lowest cost of manufacturing (no electrodes are needed), and the part inner and outer features can be machined
    WEDM Con: Will provide a longer per-part cycle time
    - Cycle Time Est. = 30~40 minutes (x3 Inner Features)
    - Cycle Time Est. = 50~60 minutes (x3 Inner Features & Outside)
    - While the 50~60 cycle time is longer for the complete part, all machining is performed unattended and you will only consume about $4.00 in wire per part, so the manufacturing cost is VERY low.

    I hope this helps!

    - Brian

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    We stack parts like this 10 at a time on our wire edm, takes about 1 hour to process the entire stack.

    Chamfer is done later on a cnc mill.

    If they are magnetic, you could use a magnetic chuck while cutting the chamfer and it will be as close to perfect as possible.

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    nlancaster,

    That is also a great way to process parts! With Wire EDM, creating a stack-up around 2.0" thick will yield the optimum cycle time per part.

    As an alternative process method, we could start with a 3.0" diameter round bar stock that is 4~6" long (or taller) and perform the following:
    - Mill the flat on the one side to complete the part OD geometry
    - EDM Drill all the start holes (x9 in total)
    - Wire EDM all (x9) features (minus the 45 degree chamfer)
    - Perform a 2nd setup in the Wire EDM and Bread Slice the parts off at 0.025” thick
    - Machine the 45 degree chamfer by Milling or Sinker EDM

    - Brian

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    Stacking and wiring is quickest way for sure. Sinker would work too, but sinker slows down as it breaks thru. Especially thin like that.

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    Thanks everyone. Brian in particular for the detailed post.
    I imagined making a male electrode with all the features to erode the square openings+chamfers+outer shape. Maybe just drill the holes after?
    Machining the chamfers by milling after edm is problematic and bows the windows.
    Stacking to WEDM several parts is smart. I guess we can do that and only SEDM the chamfers as well one by one. BTW if the wire has to stop cutting when it moves from one window to another and also cut the holes and outershape does that happen automatically on the machine - i.e by the threading process?
    I'm just not familiar with plunge drilling with Wedm and then wire cutting the shape?
    What about laser cutting the outer shape and SEDM the chamfers? What's the tightest tolerance we can achieve by laser cutting ?

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    Hi MULTUSB200:
    While I agree there is something to be said for stacking and wire cutting the blanks and then putting on the chamfers and maybe putting in the holes afterward, you need to focus on the overall processing time and here's how it breaks out for me:
    To wire cut the blanks:
    1) make a stack: 2" tall 3.5" x 8"....30 min (will make 160 pieces)
    2) holepop wire start holes....15 min
    3) setup on wire....15 min
    4) Wirecut stack....3.5 hr at 0.100" IPM single pass precision and finish (makes 80 pieces)

    Some wirecut notes:
    a) If you try to wirecut all the holes too you will fuck around forever with the slugs unless you cut them slugless which adds another 2 hours to the cut time (slugless cutting for those who are unfamiliar with the term refers to eroding the entire center bit away by spiraling from the center outward for each hole, leaving no slugs to fall free and short the wire or break it.)
    b) slug and part management will still be a concern you need to manage, so this is not going to ever be a "fire and forget" kind of operation.
    c) The stack prep must be good enough so the stack acts essentially as one single lump otherwise the wire cut time goes up drastically.
    Many operators will stick the stack in a hydraulic press, squeeze the bejabbers out of it and then TIG weld beads across the edges of the stack to hold it together.
    So the plates must be flat and smooth...preferably but not necessarily surface ground on both sides and CLEAN CLEAN CLEAN.
    A tiny bit of non conductive crap trapped in the layers of the stack and she won't cut...no way, no how if the wire path crosses it.

    What you get for your trouble is parts well within tolerance even with single pass cutting and the HAZ is miniscule.
    There's no dross, the edges are perfectly square and smooth and you can fixture from them with confidence.
    Since it's a high carbon steel alloy, I'm guessing that the presence or absence of a significant HAZ will be important.

    The big benefit which makes it competitive to laser and waterjet is the ability to stack the parts.
    A yield of 80 parts per 3.5 hr of run time is not bad at all; under 3 min per part if you don't include the holes.
    If you can holepop the holes right to size or within 1 wire diameter of size you can get them in too, in the same setup you use to put in the wire start holes avoiding the slugless strategy above at the expense of having to screw around with varying sizes of electrodes during the holepop phase.

    I'm guessing a laser can make one of these in well under one minute...so if you can live with the HAZ and the looser tolerances you're still better off with the laser.
    Maybe ditto for waterjet; but I'm betting laser will be cheaper and make a WAY better part than waterjet.
    I'm guessing you can hold your tolerances if your laser guy is really good and has a top end machine...the stock is nice and thin and not too reflective so ideal for laser.
    The thin webs between the rectangular cutouts would be my big concern but a test is cheap and will tell you everything you need to know.

    Last thing you gotta do is put in the chamfers...sinker is not a bad way because you can fixture the parts on a mag chuck to keep them flat and the trode is simple.
    Wirecut blanks are the best because they're most accurate and there is no dross, so the parts will lay nice and flat.
    As you know, if the blanks are off even a little bit, the chamfers will look like crap.

    Cheers

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


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