Punch Press Calcs?

I'm building a shearing and piercing die for a customer and I want to figure out the approximate force neccesary for this die. It's got four
3/8" piercing punches and one 6" wide shear blade. This is using 1/8" thick AL stock.
So he's got a 20T press and I'm thinking we need a bigger press. So how do I figure out the tonnage needed for this die?
Bob
rbi4t5t@soft6home.7net
(remove the 4567 and it'll get to me)
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Generally, cutting length times thickness times shear strength of the material will result in cutting force required. 3/8 dia x PI x 4 =2.356 inches; 2.36 plus 6 times .125 x 26,000 ',170 lbs.58 tons more or less Put some 2 time thickness shear on the 6" cut and you could cut the force to about 17,420 lbs=8.71 tons. R. Wink

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rwwink wrote:

"V" notch, or an angle on the punches would drop the tonnage on those also.
Best, Steve
--


Regards,
Steve Saling
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In article

Thanks for the info. Of all the books I've read, not one has had a good formulae for figuring punching forces. Also thanks for the idea of using angled or rooftop shearing. I know this reduces shearing forces but I've never known how to calculate the forces.
Bob-
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First thing an apprentice toolmaker learns is cutting/punching forces.
Periphery of hole x thickness x 25 = tons in steel
Use 17 for aluminium.
Your four 3/8" holes would need a shade over 10 tons.You didn`t say what width you were shearing. Other thing to bear in mind is that press tonnage is only fully developed a short distance from bottom dead centre and some presses will run happily full time at maximum rating and some makes will not.
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