loft - bending tables

Hello,

I'm a new user of solidwx. I've got a problem with the bending tables,
working with the loft feature in sheet metal mode.
I've just prepared my excel work sheet, and I tried to work with it.
When the cad asks for it, I tell the directory (my docs) where it is.
But the developed lenghts are still wrong.
For example: for a cylinder with a diameter of 1000 mm, I get a devoloped
lenght of 12000 mmm.
To be complete, the equation I used is:

Lb = alpha ( R + kT )

where:

- alpha is the bend angle in radians
- T is the sheet thickness (usually bigger than 8 mm)
- R is the bend radius
- k is a costant value.

Are there other equations to describe and get the correct lenghts?
Where is my problem?

Waiting for a positive reply, thank you very much.

Vanessa

 

You might want to have a look at this link.

http://files.solidworks.com/Support/html/KBTechTips/SheetMetalLengths/SheetmetalCalc.html

You will probably have to log into subscription service first.

 

This is not a fault of SolidWorks. There is not a CAD program in
existence that can accurately unfold a loft by means of simple
neutral-axis equation. The equation is only valid for simple bends.
You may get a result, but it will not be accurate.

Unfolding non-gaussian geometry is a task fit for FEA-based specialty
software. Many stamping toolmakers have such software.

 

Gaussian geometry basically is any surface which can be unfolded
without distortion (conversely, any surface that can be made from a
flat piece of paper without kinks). As far as sheet metal and CAD
goes, planes, cylinders, cones, and untapered extrusions are Gaussian.
Almost everything else is not.

I got into this some years ago when I was tasked to sculpt surfaces
that could have labels applied without wrinkling. Unigraphics actually
has a special surface analysis tool to check Gaussian curvature.

 

I also figured out how to do this in SW. It is a lot of work though.
The better you want the approximation, the more work it is.

 

So should we request SW add a Gaussian curvature plot to it's surface
shading capabilities.

Looking at the definition of Gaussian curvature one might quickly
determine whether a surface is developable and how to unbend it by
using TOOLS/SKETCH TOOLS/SURFACE CURVES. Turn on curvature combs for
two intersecting face curves. If one of the face curves doesn't show a
comb then there is the possibility that the Gaussian curvature at that
intersection point is 0 or close to it. However, the curvature combs
don't seem to be very good at representing principal curvature values
so results should be taken with a grain of salt. Two perpendicular
planes and intersection curves might also be useful.