The OP asked about both punching and forming. Suppose in your first
stage you take out a "U" shaped piece leaving a nice little tab that you
want bent at 90 degrees to the main piece. In the second stage you have
a ram that bends the tab over. For minimum press tonnage, you would put
the ram edge 3x to 5x metal thickness over from the corresponding edge
in the base die. Of course this may or may not wind up with the tab at
90 degrees and the bend edge will be quire rounded. So ironing is a
third step where the ram comes down with very little or no clearance
(after the metal thickness is deducted) to smear the edge and give a
precise bend. Lots of friction here.

Coining is the next step: you set it up with negative clearance, the ram
actually moves some metal around on the edges in a forging operation.
Cleans up the burrs very nicely, VERY hard on the press.

Brian Lawson wrote:

Hey Roy,

Very interesting rules of thumb. (rule of thumbs??) I don't
understand "ironing" an edge though. Wuzzat??

Take care.

Brian Lawson,
Bothwell, Ontario.
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On Wed, 29 Jun 2005 12:56:24 GMT, RoyJ wrote:


The old rules were "25 tons per inch per inch" for straight lines and
"80 tons per inch per inch" for holes. These are based on 50,000psi
shear strength for mild steel and mechanical presses that have a weird
tonage versus position curve. Example: for a 1" hole in 1/4" plate it
would be 80x1"x1/4" = 20 tons. These also assume reasonable die clearances.

You can get by with less tonage if you put some shear on the various
cutting edges. Works great on hydraulic presses, you can effectively
punch several dozen small holes in sequence, each one taking only a
small pessure. Same thing on a mechanical may stall it, NOT a good thing.

The forming part is trickier. For soft bends you can use the beam
calculator formulas. When you try to "iron" a edge, the tonage required
is very much a function of the clearance.

wrote:

Anyone have the formulas for tonage for a stamping die handy? I need to
start on the design of a two stage, progressive blanking and forming
die for a project, but don't have my handbook or die design book where
I can get to them right now. I know my material, the hole diameters and
the total length of the part perimeters. What I need to do now is
calculate the press tonage so that we can start the search for a press.

Craig C.