Flatten a Sticker

It’s interesting sometimes the lengths you have to go to solve a little problem. I frequently get emails or calls from folks who maybe I’ve met once upon a time, and maybe not. A lot of them ask me to solve some sort of a problem they’ve got. Sometimes the problems are interesting. The other day I got one that should have been easy to solve, but wasn’t. Or maybe I was just looking for the complex solution. Anyway, here it is. Maybe you can learn something, and maybe you can teach me something. I’m sure there were other ways to solve this, but this is the way I did it.

This particular problem boiled down to the fact that this fellow had a curved face, and he wanted to know what the shape of it would be if it were flattened. He wanted to put a sticker on the face, and needed the shape of the cutting die. It took me a couple of emails to understand just what he was talking about. The blue face above was the one the sticker needed to go on.

We know from the exercise with the bottles earlier that stickers have to be limited to curvature in one direction, because they don’t stretch, and you don’t want them to pucker when applied.

This one’s simple, right? The curvature of the face is just an arc. PPppphhhbbt! that’s simple. Right? You can just use sheet metal to flatten it. Wrong. The curvature is just an arc, but in order to get a SolidWorks part to flatten, you have to have a straight edge, and this part is all curves. You might have been able to fake it with a tiny straight edge, but I thought this could be done without cheating.

Well, you could take measurements and just remodel it flattened and call it done. Yeah, well, this is a different age. We would have done that 10 years ago, but these days, we have to get an answer from the computer, whether the computer is right or not, and whether it saves time or not. Keep looking.

Maybe you could put a split line down it and use Deform to deform the split to a straight line. Yeah, but Deform is awfully… approximate.

Um, Rhino? Rhino could do it, but giving up and using tools that are meant to do that sort of thing seems terribly… defeatist. Doesn’t it?

Ok, so all the obvious stuff doesn’t work. Let’s try combining a few things.

First, Lets make something we know we can flatten. So I took the profile of the sticker and used it to make a sheet metal base flange. But you have to play some tricks because SolidWorks Sheet Metal and multibody functionality don’t mix well together. (I played some trix to get them to show up here together for display purposes).

Then cut it to get the oval shape. But what with? Ah! a Ruled surface. Check. That’s always perpendicular to the surface, at least you can make one that way. I just made the outline of the sticker a spline shape just to give it a random shape that didn’t look too much like a simple oval.

But… if I cut away the outside, I don’t have any straight edges left to flatten the part. Drat.

So cut away the inside instead, leaving the outside. This better reflects the cutting die anyway.

And that’s something you can flatten…

Anybody want to take a crack at showing a different method?

So did that answer the question, or is that cheating? I just modeled the part of the material that the cutting die will discard, not the part to keep. But with a little boolean work, it’s not hard to get the negative of that part.

I just thought this was interesting because the original part started out as a shelled plastic part, and we went through surfacing, multibodies and sheet metal to get to the shape of a cutting die for a sticker.