Why Can't SWks Fold Plastic Hinges

You didn't get the memo?

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.

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...

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

-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