Rivets

This is a picture of a mock up section of a helicopter tail boom I did. The design criteria were that it take 1 day of engineering and 1 day of assembly to make it. It's about 5' wide. I didn't meet the design goals.

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Another design goal was to demonstrate fixtureless matched hole assembly. That worked out ok. I can't remember how I did it, but I know it was unpleasant.

It boils down to putting thousands of holes in curved flanges and lofted bends. When you do that, they aren't round holes anymore, which means you can't find their centers which means it's really, really hard to locate (thousands of) holes in mating parts.

What I'd like to do is not use holes, but put an array of points on the surface and have them unfold with the sheet metal.

Since I can't do that, can anyone offer any suggestions? Anyone else doing something like this?

Reply to
JKimmel
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We do a lot of this.

What you do is create the sheet metal part, unfold it, put your desired hole pattern into the part in the flattend state (try and use the hole wizerd)then fold the part up again. If you can't select the hole edge in the folded part to mate a rivet then you can select the axis of the hole to use as a mate. Using this method gives you a flat pattern with round holes that you can then use to send to laser cutters etc to produce the parts and get your "fixtureless" asembly.

A word of caution when unfolding, double check your flat pattern dimensions especially with cones etc to be sure that it is correct. You may have to play with the K factor to get it exactly right. SW must be calculating a stretch allowance when unfolding but with the sheet

Steve R

Reply to
Steve Reinisch

To complete what I was writting....

..... and just rolling it there really is no tradational stretching so you may find that your flat is not quite correct. The flat result also depends on what modeling method you are using to create the formed part.

Reply to
Steve Reinisch

"Steve Reinisch" ha scritto nel messaggio news:g4ednURVD_tEyzDZnZ2dnUVZ snipped-for-privacy@magma.ca...

Just for curiosity; I tried doing what you wrote, but when I fold up the sheet the holes go into suspended mode.

Reply to
secdef

This works for holes on flat flanges, but aircraft skins, ribs, formers etc have rivet holes on curved surfaces. If you make a simple "L" bent part with a large bend radius, unfold it, insert some holes *in the bend* and fold it up again, you'll see that the holes within the bend zone lose their temporary axes because they're no longer cylindrical.

The best I could do to locate "bent" holes was to insert a ref point using the "Center of Face" option while selecting the punched surface of the hole (the surface that would be cylindrical in the flat state). That locates the hole center approximately halfway through the sheet thickness. (The depth of this point varies with hole diameter and bend radius.

Then another point can be placed using the "Projection" option while selecting the first point and one of the part faces. This puts the second point on the surface also at the hole center. A ref axis between the points defines the hole centerline.

Unfortunately, these are "bogus" ref points and axes (for the OPs purposes) because they're left hanging in space when the part is unfolded. I suppose they're tied to the surface IDs in the folded state, and these surfaces don't exist when unfolded.

Might be a nice enhancement request to have hole axes transfer between flat and folded states.

Art W.

Reply to
Art Woodbury

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