Piercing Sheet Metal Formula

[richg1]

Hi all,

Does anyone know of, or have a calculation to estimate the force required to pierce sheet metal, either with a conical point, or a tapered knife edge?

(Have looked in all the usual places and come up blank)

 

[CorBlimeyLimey]

http://www.precisionsheetmetal.com/home/forces.htm

http://www.efunda.com/processes/metal_processing/stamping.cfm

from (the City of) Barrie, Ontario.

I tried sniffing Coke once, but the ice cubes got stuck in my nose

 

[richg1]

Thanks CorBlimeyLimey,

I had already looked at the Efunda stuff, but the calculations are for punching (ie shearing the metal about the shapes' perimeter) rather then piercing with a point or edge. Maybe there's no real difference in the loads required?

It has been a while since I last dealt with sheet metal, and I had forgotton about the DSM website.

Cheers

 

[notnats]

I am only guessing, but I think a conservative value for the force required would be the ultimate compression stress of the material being punched multiplied by the projected area of the blade at the maximum penetration.

ie. If the taper is 1 in 10 and the material to be cut is 1mm thick, then the projected width of the blade would be 0.1mm and if the blade is 100mm long then the projected area is 10mm^2. If the UCS is 200 mPa then the force required is 2000N.

Intuitively that looks a bit low to me. I am thinking about cutting a 30mm dia hole in copper with a wad punch.

But I am only guessing. Someone might actually know.

Jeff

 

[loquillo]

Check for manufacturing processes books or references.

 

[steve1]

I think there is more to this than first meets the eye.

If the perimeter of the supporting surface exactly matched the perimeter of the conical point, than the failure mode would be punching shear.

As the supporting perimeter gets further away from the point of application of the load than other forces come into play. I imagine that there is some sort of transistion zone as the plate begins to see bending forces and again as direct tensile forces develope.

I don't think there is a simple equation that will give you the answer you seek.

 

[richg1]

Steve,

My thoughts too. But thought that there may be some emprical data available. Haven't found it yet though.

I would assume that it more closely relates to tearing through the material rather than basic shearing.

Rich

 

[steve1]

Rich

Why not try to set up your operation to force the failure mode to be punching shear?

For example if you used a conical point and had the sheet metal placed over a pipe (or formed surface) with id approximately equal to size of hole you want to make?

This could be extended to an array of conical points and a die with circular holes cut into it.

Steve

 

[notnats]

Are we talking about a cookie cutter type of punch here?

The carton industry uses "steel rules" set into a plywood matrix to punch out the blanks for cardboard boxes. Stationary printers use a more sophisticated version to make fancy invitation cards in batches 40-50mm thick. Is this the type of application we are considering?

Jeff