SHEETMETAL

Can someone give me a formula to calculate a sheetmetal flat pattern.

Thanks,

 

Add the outside dimensions of adjoining flanges and subtract the bend
deduction. The bend deduction is the difference between the outside
dimensions (to a point coincident to both outside surfaces of the
sheet metal) and the actual length of the material required to make
the part. The radius in the formula below is the inside radius.

BEND ALLOWANCE = (.01745 X RADIUS) + (.0072 X THICKNESS) X DEGREES IN
ANGLE
OSSB = RADIUS + THICKNESS
ISSB = RADIUS X TAN 1/2 DEGREES IN ANGLE
BEND DEDUCTION = (2 X OSSB) - BEND ALLOWANCE

The radlius will be somewhat different for press brake work than
stamping, and bottoming bending or air bending parts. So there is
variation depending on your process, but the formula is pretty close
for general fabricating.

Hope this helps. Diego

 

I think in my drafting class we used a line at 1/3 the thickness from the
outside length of the bend to compensate for the stretching of the metal.
But, it will vary with the material, thickness and bending method.
dimensions for sheet metal are usually given to sharp corners and the die
maker usually deals with it.

Bob

 

Yeah, in most cases, flat patterns should be avoided on product
drawings. You are specifying the final condition of your product to
you vendor, and it is up to them to match it by whatever means, per
current ASME Y14.5M.

Matt Lorono
http://sw.fcsuper.com
http://www.fcsuper.com/swblog

 

For any given material the length along the "neutral axis" remains
constant no matter the bend. The "neutral axis" gets no tension
or compression during a bend & remains of the same length.
You just need to know where it is for your material & thickness
then calculate it (from the proper side) for each bend. Bent or
unbent it's the same length. Not hard to work it backwards
from there, as needed.
Search for "sheet metal" "neutral axis" bending.

Ignore jb <G>.

 

http://www.sheetmetalguy.com/bend-calculator.htm


Bob

 

This is going to be a dumb question, but if you're doing it in
SolidWorks, why not let it do the calculation for you? Unless you
just want to verify what it's giving you. I can certainly understand
that.

 

Actually, the CAD systems use the neutral line approach AFAIK.
Which may not always work well in some cases, such as for materials
that work-harden.

Perhaps the very first sheet-metal fold/unfold/flat pattern program came
out of the Indiana/Kentucky ComputerVision user's group (written in
Varpro II). GE In Appliance Park may have had something to do with it.