CAD to CAM best methods for sheet metal

Monty

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Jul 15, 2010
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Fayetteville, AR / USA
I started this in response to a post in the CNC plywood aircraft thread because the question and response were specific to metal construction and I thought it would be a good idea to have a metal specific discussion.

I need a good sheet metal design package so I can design my own matched hole airplane. Solidworks? Anyone have definete preferences?

I'm doing this right now. I gave up on matched hole construction. Even with a sheet metal package, you are going to have to guess at the bend allowances. Unless you are going to build multiple prototype parts and tweak things to get it to be "matched". I concluded this was too much trouble for a one-off.

My solution is to layout the rivet holes on the skins. The flanges on the bulkheads and ribs will not be pre-punched. That way all you do is line things up with clamps. Then start the drilling/cleco routine. There is enough slop in the flange to soak up slight errors in bend allowance.

I'm using Rhino. I use the offset surface, and unroll developable surface command to generate my flat patterns. Rivet lines can be made by splitting the surface along the line and unrolling it in pieces. Then you can use the divide curve command to place the desired number of rivets along the rivet line. Make sure all your tab and cut radii are larger than your cutter bit dia. and its easy to export a .dxf and generate your tool paths.

I have Solid Works at work, it is a very capable package and has become a sort of industry standard in the mid range space. I have used a LOT of cad packages and I do not find Solid Works to be as user friendly as something like Alibre...which will do 90% of what SW will do. I find that Solid Works is Similar to Solid Edge in trying to "help" you by dictating workflow....well that's fine unless you don't like to work the way they think you should. I much prefer an open ended programming structure.

I have the sheet metal package for Alibre......I wouldn't even think of using it to design an airplane.

It's much better to understand conic lofting, and developable surfaces and use a package like Rhino than to try to rely on some cumbersome software tool that gets you all tangled in your underwear.

I'll post some examples of flat pattern generation later.
 
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