BEND ALLOWANCE & OVERALL FLAT PATTERN LENGTH

[PUMPMANPLEE]

Greetings,

i need to work out the overall
Flat pattern length of my sheetmetal.

i will be bending my sheetmetal material
at each end into 90 degrees bend, ie; there
will be two 90 degree bends, one at each
end of the sheetmetal material.

i am bending sheetmetal material
of 0.5 mm thickness
which has a Bend Allowance of 0.2 mm.

after bending, the overall length is
300 mm,
the two 90 degree bends ( one at
each end) will have a length of 20mm
each.

how do i work out the
overall Flat pattern
length of my sheetmetal material ?

any assistance appreciated....

PUMPMANPLEE

 

[MikeHalloran]

I find that whole 'bend allowance' technique confusing and conducive to argument, misinterpretation and inaccuracy.

I figure out the length of the neutral surface instead. The most important data that you need and can't find on the Internet is the actual radius that your bender can achieve. Easiest way to find it is go out in the shop and measure it. For a box & pan brake or a press brake run down hard, it's pretty easy to measure. For air bends, you have to guesstimate it.

Then, assume that the blank length at the midpoint of the thickness doesn't change during forming, and work out the geometry. In AutoCAD, you can just construct a polyline through that neutral surface, and query its length. That will get you close enough for government work.

If you need better precision than that, you have to know the material hardness. The real location of the neutral surface that neither stretches nor shrinks is somewhere between 35 and 45 pct of the thickness from the inner surface, depending on the hardness. That you can look up on the Net.





Mike Halloran
Pembroke Pines, FL, USA

 

[CDBatAMW]

hmmm, not a very active forum....
one moment while I break out my calculator.
ok
0.5mm = .0196 inches
BA = .0078 inches
overall = 11.811 inches
ends (flanges) = .787 inches

11.811 + .787 * 2 - .0078 * 2 = 13.369
(300 mm + 20mm * 2 - 0.2 mm * 2 = 339.6)

Your BA and the resulting flat dimension are all dependent on the inside radius of your punch and the 'V' opening of your die.