how do I apply curvature to flat object

Hi,

I have a large extruded object -- say 600 x 200mm, 1mm thick. How do
I curve it so the middle of the long dimension is -- say -- 60mm above
the orginal plane. I can do this easily if I start with the curve,
ie. make it sheet metal and flatten it. I need to start with the flat
version.

It is actually a large PCB, and the part is complex ie. it has
components exteruded on one surface. In the real assembly it is
curved in one plane only. I have tried starting with the curved
part, but getting the dimensions correct has proved difficult, as I
only know the correct positions of the holes etc. in the flat state.

Any bright ideas ??

 

Sorry, no bright ideas, but how the heck can you expect to deform a
600mm x 200mm PCB by 10% of its length and not cause solder failures
everywhere? Is this thing soldered AFTER deforming? And if so, it
better not be allowed to un-deform even for a moment or you'll have
major problems. Maybe I'm stating the obvious, but I just can't imagine
.. . .

 

Metalwork accurate -- better than deform is from early tests.

I would live with a thin feature that I could apply the curve to, and
I would drill holes in it before applying the curvature, so I could
find where those holes ended up after doing so. I can apply the
components after curving the board, as long as I can carry through
some kind of mark (point, hole etc) to show the position. The
components with real height end up normal to the curve anyway -- they
don't deform like the fiberglass does.

Fairly good. Even allowing elongated holes it has to be accurate
within 1mm or so over 600mm

 

As long as all components are "bent" across their short dimension we
have no problem with it. The actual deflection is quite small -- the
PCB fits on a 1.9m radius. We have tested them with far more
curvature and even capacitors (probably the most delicate) have no
problems.

 

This method will work if it's OK if your holes are normal to the sketch
plane rather than the curve:

1) draw your curved object and extrude it
2) create a plane which is normal to the curve at some convenient point
(probably an end)

3) Use a little math--the dimension on the normal sketch plane is
geometrically related to the dimension in the flat. The dimension is a
function of the hole's angular distance from the normal that defines your
plane

A little nomenclature:
X is distance in the flat
S is distance along the curve
Theta is angle (in radians)

From geometry, we know the S=R*Theta, and X=R*sin(Theta)....
doing a little algebra, we get:
Theta=S/R (eqn 1)
S/Theta=X/sin(Theta), or:
X= S*sin(Theta)/Theta (eqn2)

For any given point, you know S & R
Use eqn1 to calculate Theta
Use eqn2 to calculate X
dimension your hole (with value X) on the normal sketch plane

This method can be extended to apply to curvature on two axes.

PS--This'd be a great use of a design table....

 

oops--the sketch plane should be tangent, not normal....

 

Thanks Michael,

I had thought of that -- although I do have 91 objects to get the
correct position for.. Still possible, just less fun than it looks.

Of course I really need to do this the other way around -- I have the
flattened object, and want to get the curved one.

Have been experimenting with gentle bends in sheet metal objects -- it
looks like it won't work. It would be really nice if I could flatten
the part, make some changes, and bend it again.

 

(Gavin Melville) wrote in

I may be mis-understanding but....

If I create a flat sheet metal panel a little longer than I need (say .25"
on each end in the direction of eventual curvature), punch all my holes in
it and then use a sketched bend to get the curve I want, I then have my
PCB curved with all its required holes dimensioned in the flat.

Then bring it into an assembly and add components.

Zander

 

Gavin, Have you tried the Deform feature in 2004? You can deform using
an initial curve and a target curve and do it after all the feature
are in the board. Perhaps, I'm barking up the wrong tree here, but
sounds like what you want to do.