Punch and die clearance...fail
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  1. #1
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    Default Punch and die clearance...fail

    I built a progressive punch and die set. I tested it today and it didnt work. I calculated the tons required and it was 16 tons of shear. 3/8" 6061 aluminum is the material. I have a no. 3 Niagara punch press that's good for 19 tons. The books said clearance constant for aluminum over 1/8" is 8, so .375 divided by 8 is about 48 thousandths, divide that by two so my clearance is 24 thousandths per side. I have that built in the die set. Running it in a commercial danley die shoe set on leader pins. The half inch hole and pilot worked good, when it got to the big blank out operation it stalled the press and just slightly indented the material.

    Not sure if I got the right category of forum. Any ideas what I'm doing wrong? I'll try to get some pictures uploaded here.

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    You are ignoring AREA to be sheared. The hole has a tiny area - its circumference times its thickness. The big hole has FAR MORE area to be sheared. If it has - say - ten times the area of the round hole, you will need ten times the tonnage

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    Whats the "circumference" of the larger profile? I don't think you have enough tonnage to punch that profile at 19 tons. You can add shear which will help but you will still probably be under powered as far as your punch press goes.

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    Quote Originally Posted by johnoder View Post
    You are ignoring AREA to be sheared. The hole has a tiny area - its circumference times its thickness. The big hole has FAR MORE area to be sheared. If it has - say - ten times the area of the round hole, you will need ten times the tonnage
    Hmmm ok so I rechecked my math, I came up with 18 tons now. But still under the 19 ton cap. The book uses a blanking force formula, which is shear strength of material times the perimeter of cuts times the thickness.

    Here is a page out of the book and my math, howd I do? I'm referring to die design fundamentals book.

    20191117_191259.jpg - Google Drive

    20191117_191307.jpg - Google Drive

    20191117_192245.jpg - Google Drive

    The black line would be the shear perimeter.

    Whaddya think?

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    I think too close on capacity for comfort. You should never be running that close to capacity. Did you also take into account the other operation going on simultaneously in your calculation? That puts you even farther in the red.

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    I assune your round hole punch is on the same plane as your blank? I calculate your same 18ish tons for the blanking operation but when you add the hole (3 tons) you are over capacity. Add shear to your die on the blanking operation and you will reduce your tonnage by up to 30%. If you add it to just your blanking operation, in theory you should be a little bit north of 15 tons.

    Press Dies Tutorial | Technical Tutorial - MISUMI

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    Quote Originally Posted by eKretz View Post
    I think too close on capacity for comfort. You should never be running that close to capacity. Did you also take into account the other operation going on simultaneously in your calculation? That puts you even farther in the red.
    I did accommodate for the simultaneous operation of the .548" hole that's being punched.

    I understand that I shouldn't be running near capacity...but it still should work which makes me think I'm doing something wrong...

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    Quote Originally Posted by bigjon61 View Post
    I assune your round hole punch is on the same plane as your blank? I calculate your same 18ish tons for the blanking operation but when you add the hole (3 tons) you are over capacity. Add shear to your die on the blanking operation and you will reduce your tonnage by up to 30%. If you add it to just your blanking operation, in theory you should be a little bit north of 15 tons.

    Press Dies Tutorial | Technical Tutorial - MISUMI
    Yes same plane, large punch, and small punch hit at same time.

    Ya I guess I could add shear to the die... but it should work as is, unless I'm calculating something wrong, or my clearance is wrong...

    A few people have told me a rule if thumb for clearance is 10% of material thickness...but I wanted to go by the book. Which is how I got to .024" per side.

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    Quote Originally Posted by winklershop View Post
    9.112" perimeter of the larger profile

    1.722" perimeter of the hole

    9.384" total perimeter of shear
    X
    10,000 shear psi aluminum
    X
    .375 thickness
    =
    35,190/2000= 17.6 tons
    9.112+1.722= 10.834

    Using 10.834 I come up with 20+ ton. Honestly adding shear should be pretty easy and then you won't have to worry about tonnage.

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    Oh wow I did screw up some math there...herez another formula out of a different book, using the correct 10.8 perimeter it comes up with 9 tons...

    20191117_205417.jpg - Google Drive

    20191117_205451.jpg - Google Drive

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    Quote Originally Posted by winklershop View Post
    9.112" perimeter of the larger profile

    1.722" perimeter of the hole

    9.384" total perimeter of shear
    X
    10,000 shear psi aluminum
    X
    .375 thickness
    =
    35,190/2000= 17.6 tons
    What flavor of 6061 aluminum are you punching?
    My book shows shear strength of t-0 as 11,000 psi and T-6 as 30,000 psi.
    You may be short of tonnage by a factor of 3.

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    Quote Originally Posted by Dennisrech View Post
    What flavor of 6061 aluminum are you punching?
    My book shows shear strength of t-0 as 11,000 psi and T-6 as 30,000 psi.
    You may be short of tonnage by a factor of 3.

    6061 aluminum T6

    One of my books says 10,000 for "aluminum"
    Another one says 15,000 for "aluminum"

    You have a book showing T6 6061 as 30,000 psi?

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    I can honestly disagree with that formula. Even the text that you provided says there is a controversy with tonnage calculations. I understand where the .3 comes from but that should be factored into the shear strength in the formulas. I believe the machinery's handbook lays all this out fairly well, if I remember I will take a picture of it tomorrow.

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    Quote Originally Posted by bigjon61 View Post
    9.112+1.722= 10.834
    Using 10.834 I come up with 20+ ton. Honestly adding shear should be pretty easy and then you won't have to worry about tonnage.
    What would be the best way to add shear to the die? Want to make sure the blanks stay flat. Would I have to make a new stripper plate?

    What are your guys thoughts on the clearance. All the charts I have only show up to 1/4" thicknesses... the one piece of information I found in a book said use 8 as a constant over 1/8" for the clearance....well how for above 1/8" does that apply...

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    Quote Originally Posted by winklershop View Post

    You have a book showing T6 6061 as 30,000 psi?
    yes that is about how high it is. tensile strength of 42,000 psi. ratio of sheer to tensile strength is .5 to .7 depending on material.

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    Even Google says 6061 is 30,000 psi

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    More die clearance means less force needed.

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    all good info here, thanks for your input.

    so i used an auto cad program to come up with the perimeter (i cant do math when im tired, it shows, LOL, sorry)

    perimeter of all areas to be sheared is 8.440"

    and if we use the 30,000 6061 t6 shear number...its not looking good

    8.440 x 30,000 x .375 / 2000 = 48 tons....EKKK, even if we add shear i dont think we are gonna make it

    sounds like i will have to order in some softer aluminum, like the T0 al.... i think i have heard this referred to as "oh" condition aluminum

    so if we go with oh condition aluminum we would be looking at

    8.440 x 11,000 x .375 / 2000 = 17.4 Tons ......... thats mo better

    i guess when those wrote those books they didnt have terminator grade aluminums?

    thanks, signing off for the night




    20191117_222404.jpg - Google Drive

    20191117_213409.jpg - Google Drive

    20191117_213415.jpg - Google Drive

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    You can bring forces down by giving the punch a slant. Make the tool enter the stock not on the entire line of cut but increasingly along it. Would presumably need to pass the cut pieces between rectifying rollers afterwards. That’s the way they used to stamp blanks like that:

    Aluminum sheet, thickness 0.118"
    Attached Thumbnails Attached Thumbnails p1010421.jpg  

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