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  1. #1
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    Default Precision Die Punch

    Hello All,
    If I am wanting to hold a die punch clearance of 0.0002" per side on a die cutting tool what types of materials would you consider using and at what Rc hardness's would you consider for the upper punch and lower die shoe. This is a four posted die tool by the way using precision ball cages, posts and bushings. Just wanting to see what others do (processes, materials, hardness, matching, etc.) when having to hold ultra tight tolerances on fine blanking die punches. Don't consider the thickness of the material for this post.

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    I'd want to know what the actuating mechanism is, you could easily deflect your die set if you have a press that's got an imprecise motion or contact face.

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    ^ agree'd. Nearly all of my die accuracy issues have had zero to do with material or tolerances and everything to do with the post placement in relation to the die and how much slop there is between them and their bearings. Granted, my dies have all been small bend/shear operations with the old 2 post fixtures held in mechanical press's, but in general your material will have more to do with how long the die lasts.

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    You've not stated the material thickness so I'll presume that this is an academic question rather than questions with a job in mind. Fine. But asking questions about what the upper/lower components are made of and the relative hardness (Rc) do call for the material to be known. Working low carbon steel is a whole lot different than BeCu, spring steel, or any number of problematic materials. You've also not stated whether this is perforating, forming, half-punching, embossing/coining, or a combination of any/all of the above. The quantity of the run and the expected life of the die makes a big difference too, even if it's just a general opinion of long/short life. How do you intend to capture the punch? Is it secured to the upper shoe or does it float? Is a spring/box/guided stripper to be used? I'm not trying to be a jerk here, all of these questions have to be factored into the design of a die IMO or you're just asking for a re-work of the design. Holding .0002 PS is certainly doable, it's done every day in shops. I suspect you're not a diemaker and have come here to double check what you've been told, nothing wrong with that either. But if I told you that it's important to use a wire EDM (WEDM) in creating upper/lower plates would you know the methods employed that are so critical to achieving .0002 accuracy in line-up? Probably not. Is this a "fine blanking" type of process? Is the die going into a high speed press like a Bruderer or a low speed OBI press? So I don't come off as a complete jerk here's my short list for general die work (which is NOT what you're asking about) Die section- D2(Rc 60-62) Perforators- A2(Rc 58-60) The choice of these is VERY dependent on the material being worked and the process involved. All of this can be easily found on the internet. I hope I've encouraged you to do some reading and report back with what you've found. Asking questions here after researching is just fine, spoon feeding is not. My intent is not to slight or insult but rather to help you learn to educate yourself. My apologies if my words have offended.

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    OBTW- I haven't discussed the M,T,S, or PM groups of steels that are used in stamping dies because there are specific reasons for selecting any of these. I also have not mentioned coatings for the same reasons.

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    Suspect that with a clearance of 0.0002" per side the OP is punching shim, but what?? Insufficient data ..

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    If the OP is truly speaking of fine blanking, that's another wrinkle.

    Tom

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    Oops! The OP DID mention fine blanking .. my mistake. Hide the shimstock!

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    I always order a "lamination grade" die set, if I don't make my own.

    When it arrives, I check the parallelism at the desired shut height. if you are truly running that close of cutting clearance, you may need to send the die set back a few times before they get it right. ( I use Superior, Lamina just can't get it right.)

    It also may require a "bump" style press operation. This is where the top of the die set is NOT bolted to the ram, the ram simply "bumps" the top in the middle, and springs are used to retract the punch from the bottom.

    This keeps the alignment in the hands of the die set.

    You didn't mention the size of your project, I usually work with very small products, so some of this can scale up, but not too far up.

    Good luck and be patient.

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    Quote Originally Posted by TDegenhart View Post
    If the OP is truly speaking of fine blanking, that's another wrinkle.

    Tom
    Well, the fineblanking process WILL take out any wrinkles eh ?

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    Material thickness is 17.8mil (0.0178"), it is a plastic laminate of 15mil polyproylene/COC/polypropylene/2.8mil Polyethylene/EVOH/Polyethylene. The tool is blanking the plastic laminate out drops are the final product. These tools are meant to last at least 1 million cycles. The tool is 4 posted using the highest precision ball cage bearings that Fibro has to offer. The tool is then placed into a 4 posted press/station. The tool consists of a lower die plate that is hardened, upper punch locating plate (holds the punches with dowels and fasteners), punches that are hardened and a stripper plate with die springs to help hold the material in place. The punches are pined to the upper punch plate and fastened with socket head cap screws. We typically use D2(punch and die Rc60-62). The issue I am having is that one of the thin layers in the laminate is stretching and not cutting. i have been told that the clearance needs to be 0.0002" per side but if we go tighter i fear the life span of the tool will be greatly reduced and or damage will occur when trying to cut the 0.0178" material. Let me know you thoughts.

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    I am not a die expert, but if I were looking at this I'd be examining the punch and die edges with a microscope, looking for signs of abrasion or edge breakdown. I'd also wonder if you should change the punch to another material, perhaps a carbide, due to tribology of similar materials in a rubbing environment being more likely to gall against each other.

    Lastly, perhaps redesigning the P/D to include DLC coatings will be a worthwhile effort, done right it may give much longer cut life.

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    Quote Originally Posted by FrankTartaglia View Post
    Material thickness is 17.8mil (0.0178"), it is a plastic laminate of 15mil polyproylene/COC/polypropylene/2.8mil Polyethylene/EVOH/Polyethylene. The tool is blanking the plastic laminate out drops are the final product. These tools are meant to last at least 1 million cycles. The tool is 4 posted using the highest precision ball cage bearings that Fibro has to offer. The tool is then placed into a 4 posted press/station. The tool consists of a lower die plate that is hardened, upper punch locating plate (holds the punches with dowels and fasteners), punches that are hardened and a stripper plate with die springs to help hold the material in place. The punches are pined to the upper punch plate and fastened with socket head cap screws. We typically use D2(punch and die Rc60-62). The issue I am having is that one of the thin layers in the laminate is stretching and not cutting. i have been told that the clearance needs to be 0.0002" per side but if we go tighter i fear the life span of the tool will be greatly reduced and or damage will occur when trying to cut the 0.0178" material. Let me know you thoughts.
    The laminate is going to be a problem.

    .0002 per side is probably a must. With that tight of cutting clearance, anytime you demount either the punch or die for service, you'll need to blue in the clearance. If the edges were wire EDMed, there may be some wearing of the surfaces occurring. When you sharpen, be sure to deburr all edges carefully. A piece of brass and an optivisor are more than sufficient.

    Then BEFORE you put the die in the press, can you test it on the bench with maybe .003 plastic shim stock? If this looks good, then you know it's you press that's the problem.

    If this fails to work, you may want to try a few non-conventional ideas:

    Can you freeze the material?

    Have you tried any lubricant Tap free, or WD-40 work wonders on thin nickel.

    Hope this helps.

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    Quote Originally Posted by FrankTartaglia View Post
    Hello All,
    If I am wanting to hold a die punch clearance of 0.0002" per side on a die cutting tool what types of materials would you consider using and at what Rc hardness's would you consider for the upper punch and lower die shoe. This is a four posted die tool by the way using precision ball cages, posts and bushings. Just wanting to see what others do (processes, materials, hardness, matching, etc.) when having to hold ultra tight tolerances on fine blanking die punches. Don't consider the thickness of the material for this post.
    Frank - are you sure you understand FINE BLANKING? FINE BLANKING is done on metal. Fine blanking dies use a "STINGER" around the part to be blanked. I am not aware of any FINE BLANKING on plastic. May be I can learn something new.

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    Quote Originally Posted by juergenwt View Post
    Frank - are you sure you understand FINE BLANKING? FINE BLANKING is done on metal. Fine blanking dies use a "STINGER" around the part to be blanked. I am not aware of any FINE BLANKING on plastic. May be I can learn something new.
    Well, if the part is dropping out (as I think the OP described) the "waste" is the outer edges, so any fineblanking stripper plate with heavy preload (and the aforementioned stinger capturing details) will be done on the waste product ?

    How about a steel rule die ?
    I don't know if one could be made to such tight tolerances.

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    Quote Originally Posted by digger doug View Post

    How about a steel rule die ?
    I don't know if one could be made to such tight tolerances.
    I was actually thinking the same thing last night.

    You only need the punch for a steel rule die. And with the material being a laminate, it would probably perform better than his settup now.

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    Despite the attempts of the OP to include details there just aren't enough. Die design, especially at .0002 PS cut clearance isn't a casual conversation around the water cooler. No info on the shape of the blank (multi-toothed profile?) the type of die (compound, multi station prog die) the basic type of stripper (spring, box, guided) is there even a pressure pad involved? The timing of the components, influence from the next station due to no idler station or insufficient carrier. Fine Blanking? Due to critical profile tolerance or flatness? On plastic? How has alignment been checked? Is the top bolted to the Ram or is it used like a "bump" type of die. What kind of press? Are heel blocks used in the die to locate? What cut clearance has been used already? The only issue I hear is a stretched laminar layer. Top or bottom? When does it happen in the strip? I'm no die expert either but there's something odd about this thread.
    Last edited by AD Design; 07-10-2019 at 03:14 AM.

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    Default Tooling Engineer?

    I had presumed that the OP had not included a more descriptive account of all this due to being unfamiliar with the nomenclature and/or the intimate details of die stamping and was a desk jockey. Checking the profile of the OP the occupation is listed as "Tooling Engineer". It makes me pause to wonder what sort of Tooling Engineer cannot provide those details even if that background was in cutting tools and tool paths. How long on the job before one picks up on being able to discuss the process? If your vocabulary is lacking, mine often is, wouldn't some homework/research be in order? Something about this thread doesn't have the ring of authenticity.

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    Quote Originally Posted by AD Design View Post
    I had presumed that the OP had not included a more descriptive account of all this due to being unfamiliar with the nomenclature and/or the intimate details of die stamping and was a desk jockey. Checking the profile of the OP the occupation is listed as "Tooling Engineer". It makes me pause to wonder what sort of Tooling Engineer cannot provide those details even if that background was in cutting tools and tool paths. How long on the job before one picks up on being able to discuss the process? If your vocabulary is lacking, mine often is, wouldn't some homework/research be in order? Something about this thread doesn't have the ring of authenticity.
    \
    These days, a "tooling engineer" is one that can "google" and find their way thru a "catalog".....

    Not one sitting at a drafting board/CAD station.

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    Quote Originally Posted by digger doug View Post
    \
    These days, a "tooling engineer" is one that can "google" and find their way thru a "catalog".....

    Not one sitting at a drafting board/CAD station.
    -Apparently common courtesy is not a required skill set when a college degree is all that matters.....Frank I'd like to thank you for wasting my time.... Baka. My own fault for taking the bait.


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