Cutting multiple stacked sheets at the same time
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  1. #1
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    Default Cutting multiple stacked sheets at the same time

    Hello,

    My company is interested in using a Wire EDM cutting process, but we have no experience in this area.
    We are interested in stacking a number of thin silicon steel sheets and cutting them with a Wire EDM process. If we try to cut multiple sheets at once, will the Wire EDM process melt the metal and fuse the sheets together as it cuts?
    Any comments on the possibility of the Wire EDM melting material as it cuts would be a great help.
    Thank you,
    Eddie

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    No, they will not weld together due to the wire EDM process. I cut thin materials stacked together all the time. In fact, I find that stacking the thin work pieces under 1/8" up give me less trouble than trying to cut a single thin piece. My perception is that square inches of cut per hour seem to peak when the workpiece thickness is approaches 1 inch.

    A few things you really want to try to do is have clean good quality tool steel materials like A2 and D2. Preferably a ground to thickness with plenty of stock margin(extra material) around the finished part to allow for clamping to the work table. Debure the edges and stack the up and clamp tightly together. We put them in a hydraulic press and then TIG weld several fusion beads in several places around the perimeter. Not too much heat as to warp the stock though.

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    If you have a preferred EDM in mind. Ask the dealer for a test cut in your material.
    The will be happy to develop a turnkey system for your needs.

    Regards,
    John

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    How thin are we talking?

    The only time we've found this to be problematic is on .001" or thinner shim stock.

    From there on up they're easily seperated.

    Depending on the sheet size and stack height you will need to use stiffener plates top and bottom.

    If you are cutting multiple thicknesses in the same stack it sometimes helps to seperate them with a stiffener
    too.

    We used to weld our stacks, but thats more trouble than it's worth.

    Stack 'em, get some kant-twists on 'em, drill your start holes, get 'em in the machine, take the kant-twists off and cut 'em.

    I highly recommend an edm hole-popper for "drilling" your start holes.

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    Default Here's one application

    .010" thick Inconel 600, 50 pieces,

    picture223-299.jpg
    picture223-318.jpg
    Attached Thumbnails Attached Thumbnails picture223-300.jpg  

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    Eddie,

    What you are asking is 100% possible using Wire EDM, but as KilrB and Roysol have pointed out requires some different processing techniques. Depending on the size and thickness or your material, you might have to create some specialized work holding fixture to hold the stack and keep everything flat. If your sheets are very thin, you will need to create some form of a "Sandwich" fixture that has a rigid plate Top and Bottom to compress and hold the stack together. I've done this in the past, and if the size of the geometry you are machining is large, you might also see some delamination of the stack as you are machining (think of fanning out a deck of playing cards). This is pretty normal, and might require the addition of a Kant Twist clamp on the completed cut section during operation.

    This type of operation is 100% do-able, but is purely application and process driven. Since this would be your 1st Wire EDM, you might want to ask your OEM vendor for a Turn-Key or Share-Key process where the machine tool OEM would provide some engineering service and process support. I'm not sure what your internal shop capabilities are, but you might consider these OEM engineering services to help design and build a work holding fixture for you to get you up and going.


    -Brian

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    Not familiar with silicon steel, is it 100% conductive? If so , no problem as others have said. Screw it together between 2 sacrificial plates or weld the edges.

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    Eddie,

    I am also one of those that's had the best luck when sandwiching a stack of thin material between sacrificial plates (typically 1/4" or so top and bottom -- even thicker if the parts are large). If the parts to be cut are thin, then I won't weld the edges of the stack -- rather I TIG weld on some small "bars" that connect the top sacrificial plate to the bottom one. I squeeze the stack either in a hydraulic press or in a big vise... usually with some really thick flat plates on both sides so the stack stays very, very flat while welding.

    Sometimes, I'll make one of the two plates "long" on one edge so I have something to hold onto.

    The one major PITA when cutting stacks is when part(s) break free. If I'm cutting a stack of thin material, I'll hole pop my start holes and then will also hole pop in the center of what will be a drop. The first thing I do is no-core cut a hole in there large enough to get a screw/bolt through there so I can *also* clamp the stack in the center (outside being held together by the welded plates.

    (sidenote) My "trick" for getting an extra clamp bolt in is to drill and countersink one of the sacrificial plates exactly where I'll want to install that extra clamp bolt -- I do this *before* I ever assemble/weld the stack. Then what I do after my stack is welded is I'll use the hole popper to touch off on the inside diameter of that drilled and counterbored hole, and I hole pop dead center there. After I no-core this hole out, I install a flathead bolt/screw that drops into the counterbore, and put a 1/2-thickness nut on the other side. Now I flip the stack over the other way (flush surface where the flathead went in is now on the bottom so I can run the stack down right on top of the lower nozzle).

    This was my method to save a lot of grief, as I found that an instant before an inside cut is finished, you will start seeing a few parts of your stack break free (but not all simultaneously). This makes an endless "start and stop" routine as you try and pick parts out that have broken free and then restart the machine (and sometimes break the wire a few times in this process).

    Oh... for what it's worth: If the parts I was making had small holes in them, I **ALWAYS** no-core cut those holes. The machine can run this process unattended, whereas if you're creating a drop it inevitably requires a lot of attention. Don't forgot to change your flushing to pressure on the top nozzle and suction on the bottom nozzle if your stack is down on the Z -- I've found this to work much better for no-core cutting "small-ish" holes.

    Doing whatever you can to bolt together the stack anywhere that there is going to be a drop has always been a HUGE timesaver in the long run -- well worth the time to no-core cut that extra bolt hole or holes in there to do some additional clamping.

    Don't hesitate to ask more question, as big stacks of fine material definitely caused me a lot of grief until I figured out the little tricks. And as mentioned by other, do NOT drill any start holes in thin material! Always hole pop.

    PM

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