Why Can't SWks Fold Plastic Hinges

SolidWorks is set up to be able to fold sheet metal, so why can't & why
shouldn't SolidWorks be able to automatically bend a flat plastic hinge
about a defined center by a user specified angle.

Hinged plastic products are so common, I am surprised this isn't
available (or wasn't last time I checked). I can honestly say I have
not looked in SWks 2005 beyond the help menus where "folding" and
"hinge" turns up no topic. "Flex" command appears to flex the whole
solid body, which is NOT what is needed with hinged parts.

In the past I have modeled parts with up to 5 hinges by modeling each
part in the open and closed positions, in an assembly drawing so I
could illustrate the different finished part assembly and use
conditions. That is painfully slow.

Anyone have better solutions for SolidWorks. We are NOT talking rocket
science, just an adaptation of what is already done in sheet metal with
Fold-Unfold.

All I know for sure, is that a BendHinge function would save one heck
of a lot of time.

Bo

 

You didn't get the memo?

www.dezignstuff.com/fold.zip

 

No, but I have now seen the .avi run.

Bo

 

In a word, plasticity. In sheet metal the behavior of the bend zone is
well characterized by a single parameter which allows SW to make bend
allowances for the plasticity that occurs. In a plastic hinge there are
many parameters involved that depend on geometry and materials. In
addition, plastic hinges typically have a geometric nonlinearity which
causes snap through. SW wouldn't have a clue how to deal with that.

 

Umm, you can do it with flex - I have myself with good success. It
takes some monkeying around because the interface is GOD AWFUL, but if
you make your own co-ordinate system to set the axis of the bend it can
be done with good precision. The trim planes are what limits the bend
region to just the hinge area and not the whole solid body.
Tip - try to model in the 'as-molded' condition and just use flex to
fold it up to check the interface. The model geometry can be seriously
messed up with flex and though you will get a good visual you might not
be able to export it for the CAM system.

If the hinge is simple like in matt's avi, its even easier. I will
tend to model the base as one part, the cap as another, and the hinge
as a third. Through the hinge I will define an arc not by radius but
by arc length (click on the ends of the arc and the body of the arc to
make the arc-length dim) of a construction arc somewhere in the middle
fof the hinge so it realistically stays the same length. The ends of
the arc are then set by an angle (click the endpoints and the
centerpoint of the arc when making that dim) Then I mate the
compoenents toghether, and I can move them around by just changing that
angle dim. Join to get the final part, OR have all three componenets
actually just configurations of a single part file.

-Ed

 

Ed, you're 2nd paragraph is basically what I am doing now, & I use the
centroid arc length, at least when my hinges are non-deforming (of
course I immediately start designing some parts by exceeding the yield
limit so I can preload things, but I can't expect SolidWorks to model
that).

I found Flex to be unusable because I couldn't get it to do anything
but flex the whole part. That is inexcusible on SolidWorks part as a
good user interface is one of their mantras.

My whole point here is that it should be terminally easy to allow
software to bend and unbend specific areas, as they already do it for
sheet metal.

Guess I continue to do it the hard way. What a waste of time.

Bo

 

quote Bonobo: "My whole point here is that it should be terminally easy
to allow
software to bend and unbend specific areas, as they already do it for
sheet metal."

Not really. Sheet metal lends itself to easy bending in CAD because
the bending fairly predicatable and can be quantified with a few
generic parameters. Bending plastic is almost inherently nonlinear,
with immediate permanent deformation, creep, and depency on speed
(hyperelasticity). The math just isn't simple enough to put into a CAD
feature with a simple user interface.

Even so, the best sheet metal die builders I know don't waste time
building a tool based on a customer's unbending calculation and CAD
work. They ALWAYS double check against their own programs and
standards.

 

But...for the simple 90 to 180 degree thin plastic hinge which is
nearly elastic bending, without permanent yield, it ought to be easy
for SolidWorks to allow that type of bend.

I did a specialty box with all six sides hinged along with another flap
and some snap fits about a year ago. It would have taken maybe 1/3 the
time if I had the ability to fold and unfold those little 90 degree
bends easily during the design process.

As it was, each panel had a hinge or some times two, which had
configurations for as molded and as bent, and then an assembly drawing
to put it all together to iron out the difficulties.

Bo

 

Here are links to models using the flex feature and sheetmetal
features.

www.dezignstuff.com/swparts/flexhinge.SLDPRT
www.dezignstuff.com/swparts/sheetmetalhinge.sldprt

They "work". They may not be perfectly analytically accurate, and the
sheetmetal technique certainly requires a lot of conditions, but both
techniques can create both flat and bent hinges.

Maybe you would like to post your model to get some help with it?

matt

 

woops,

That second link should have the extension in caps...


www.dezignstuff.com/swparts/sheetmetalhinge.SLDPRT

 

Matt, thanks for the comments.

I get the job done, but it would be much easier if the SolidWorks CEO
spent the time to direct the crew to make SWks do this relatively
simple task easily for us designers.

Bo

 

" found Flex to be unusable because I couldn't get it to do anything
but flex the whole part.".

That's what the trim planes do - they limit the flex to just a small
region. My part was 14 inches long and I limited the flex to just the
..5" of hinge that I wanted to fold -everything outside of the hinge
region stayed board straight. I snapped the planes to sketch points
(the same sketch used to predict the radius of the flex and set the new
co-ordinate system where it needed to be to be accurate)
Like I said,the interface is AWFUL, AWFUL,AWFUL, but it can be worked
out and forced to do what you want it to.

 

Thanks Ed. I will have to investigate flex further.

Bo

 

Hi Ed,
In some cases, in fact all the cases inwhich I wanted to use Flex, the
planes will intesect geometry you dan't want to be deformed... The
planes limits the distance in their "Z" but they are still infinite, so
they may intersect your part further away...

-Marc

 

Hmmm, I haven't ever had a part that bent in one area while other areas
on the same plane didn't bend. Kind of like having your arms at your
side and bending at the waist, eh? The arms stay straight.
Sounds like a job for split part. I'd split the arms off into seperate
bodies, bend the waist of the 'torso' body,then combine them back
together. Being lazy I'd try to leave the upper torso stationary and
just move the hips/legs, but if that wasn't an option the mate-like
moving of bodies in 2006 is pretty decent.
Interesting case - I might want to mess with it to see if the theory
works.

 

Have you tried splitting out the hinge as a separate body, flex only
that body, then putting them all back together again? Using the 2006
body mates might make that feasible.

matt

 

Ed and Matt,
Thanks for your response. That's something to try. I haven't installed
2006 yet.

-Marc

 

I asked the original question in this thread, hoping to spur some
opinion on this board, & maybe inspire SolidWorks corporate to do
something substantive, and indeed we see there are some partial
solutions, and then the "old" way.;

In the end for now, I will just rely on constructing two versions of
hinges, Open & Closed and doing the final SolidWorks Assemblies in the
various positions I need.

But somehow, SolidWorks must provide a better way to flex hinges, and
if you think about it, flex wires, tubes, etc.

The design of things that flex and bend at specific places is so
common, SolidWorks deserves a better faster way.

Bo

 

One of the ultimate goals I dream of is being able to design a hinged
assembly and then have SolidWorks' Animator show the animated assembly
& closure of such a flexible hinged part.

I don't know how many times I've tried to show a 'non-engineer' how a
part folds up in words, but they just don't get it, without a real part
in their hands.

I can fake it in SolidWorks right now in various ways, but that is not
like just telling solidworks:

Animate Hinge 1 from Position 1 to Positions 2 about Axiz 3...etc for
each hinge