Finding PSI on a press brake die. BRAIN RATTLER

Sunny 5 acres · Jun 4, 2011

One of the engineers at work says that finding PSI on a round or half round surface such as a top punch on a press brake is impossible. I fail to believe it because as long as there is a contact point there must be someway to measure the psi. anyone wanna jump in?

Ken Macfarlane · Jun 4, 2011

It is extremely complex to do but it can be done using finite element analysis.

If the round surface is the same a one of the brinnell hardness testing ball scales, you can measure the impression and there are tables which tell you an average psi of the tensile strength. They don't tell you the actual though.

The problem is there is compressive force squeezing, and mixed tensile and friction forces from it trying so slide sideways. For flat faces this is well documented from "upset" calcs for forging. You can calc for various lubricants on the flat face, different temps etc.

You could calc an average psi, but what it is at each point is the tough part.

Jerry/MT · Jun 4, 2011

Ken are you a manufacturing engineer? I have never heard of anybody speak of finite element analysis on any of these forums. We used it in my former job for fluid dynamic calculations and also for structural problems. Never heard anybody mention it on these forums before, however.

Anonymous-0 · Jun 4, 2011

For mild steel they have some idea how much because the smallest round hole you can punch is the same as the thickness of the steel you're punching. IE/ you can't punch a 3/8" hole in 1/2" plate. There are similar formulas for other materials as well and special punches with scalloped edges are also made to make punching easier. Because of the design of the punches, it would be very difficult to get an actual measurement.

Jerry/MT · Jun 4, 2011

Correction: I meant to say we used finite difference analysis on our fluid problems.

Ken Macfarlane · Jun 4, 2011

Mech eng with a manufacturing option. Work in the fire protection field now doing fluid calcs, fire and smoke modelling, sprinkler systems etc.

I'll admit, I read his question wrong, I thought he was trying to indent something. The scalaped punch is complex too, they give a bit of room for the material to move into so it can more cleanly shear the face. If I remember right, poisson's ratio is part of the calc for how thick you can cleanly punch. The forces in the steel near the edge of the punched hole are very complex.

What pressure is he trying to figure out? Its not the same everywhere on the punch face.

Sunny 5 acres · Jun 4, 2011

Say you have a 1000 ton press brake with at 20 foot top punch that is half round. How do you figure the psi on the surface of the half round? Since a round surface contact point on a piece of flat stock is not constant that is from front to back of the punch head

Anonymous-0 · Jun 5, 2011

You aren't making sense. A press brake bends steel and doesn't use punches. You'd need to know the type and thickness of the steel and they do know how much tonnage it takes to punch holes in specific steels. By putting center points, scalloping or modifying the punches, they can lessen how much force is required to punch holes. Thicker steels need a larger die in the bottom to give enough relief when punching as well. I'm sure the makers of punches and punch presses would know how to figure these things out.

Sunny 5 acres · Jun 8, 2011

yes i am. if a half round surface has a 1/8th inch contact patch the center of the half round punch will have more psi than if u measure a 1/32nd out from center. so psi will be less

JHH · Jun 8, 2011

Does this question have some practical application or is it like the question "Can a wind driven vehicle go straight down wind faster than the wind?"
Maybe that is not a good analogy but it generates a lot of discussion.

Finding PSI on a press brake die. BRAIN RATTLER

Sunny 5 acres

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Ken Macfarlane

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Jerry/MT

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Anonymous-0

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Jerry/MT

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Ken Macfarlane

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Sunny 5 acres

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Anonymous-0

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Sunny 5 acres

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JHH

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