Solidworks - Lofted Bend Flat Pattern
Solidworks - Lofted Bend Flat Pattern
(OP)
Does anyone know how Solidworks determines the flat pattern length for a Lofted Bend? Or can anyone verify its validity? It doesn't seem to take any material properties or bend allowances into account. It doesn't seem to simply "unroll" the perimeter either. Somehow it depends on the thickness though. If I create a simple half cylinder and flatten it, the flat length ends up being something that I can't predict mathematically - using inner radius, outer radius, or neutral axis.






RE: Solidworks - Lofted Bend Flat Pattern
Unfolding non-gaussian geometry is a task fit for FEA-based specialty software. Many stamping toolmakers have such software.
We don't even make flat paaterns anymore. Even if we did, our toolmakers would just make their own.
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RE: Solidworks - Lofted Bend Flat Pattern
BTW: Why do you want to predict what SW is going to give you? Why not just measure the flat pattern? Is this a real requirement or just for you own amusement? I think the only way you could verify it would be to do a real test or ask the vendor to tell you what the flat pattern length should be for your part and compare. They must be able to figure it out since they do it all the time.
I suspect that in practice there may be some variation due to exact process or machine as with bending.
We have the luxury of not having to do flat pats. We just give the vendor the finished part drawing and let them figure it out - heck, they are the experts. The few formed parts we use are hyro-pressed.
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RE: Solidworks - Lofted Bend Flat Pattern
We have also had problems with the lofted bend and you're right, it does not take bend allowances, k-factors, etc. into consideration. I agree with the others that the shop guys should make thier own flats, but that is another battle. We have reported the issue and I suggest you do also.
If you must make the flat, here is the work-around we have found:
Modifying the initial sketch used to create the loft can solve the problem. If you take the thickness of the metal and multiply by the k-factor for that metal, and then add that number to the radius in the sketch, this should result in a correctly flattened part. An example would be a lofted 16-ga. stainless steel part with a 1/2" initial radius and .37 k-factor. Instead of the .5 for the radius, use [.5 + (.0598 x .37)], or .5221.
This works for our shops with our tooling (which is where the .37 came from)and an initial sketch which is an arc.
Of course this is a bad idea since it makes your formed part wrong. Create different configs so you can use the correct formed part where needed.
Michelle
RE: Solidworks - Lofted Bend Flat Pattern
I need to design a complex 3D part that can be molded (yes molded) economically in the flat state and then ROLLED into the 3D form. The material in this case is not metal, but plastic and/or foam (therefore, no yeilding). If SolidWorks Sheetmetal doesn't even use material properties to flatten a Lofted Bend (unlike edge flanges, etc. where bend allowances seem to be taken into account), then I figure that I just might be able to apply the technique to non-metal materials. Even if it does somehow take material properties into account, such as bend allowances, then perhaps I can give it the right inputs to neglect yielding.
The reason that I can't use simple hand calcs to determine the flat shape is because the pattern is complex. It's not just a simple rectangular sheet formed into a cylinder. But if I could get Solidworks to unfold something that simple into a predictable flat pattern, then I might trust it to do a more complex shape.
Thanks.
RE: Solidworks - Lofted Bend Flat Pattern
Forming plastic is a whole different ball of wax anyway as you say, so I don't think SW will probably ever get to that point. So your parts are flexible and do not remain in the formed state on their own - only in the assembled configuration? How about using a design table to edit the flat pat configuration using some Excel calcs? Maybe not if your shapes are pretty complex.
BTW: I suppose you know you can do anything Excel you want in a DT whether embedded or external. You just leave a blank column or row at the bottom or right edge of the DT proper and the rest of the worksheet is yours to mess with. So you can do data entry, links, calcs, even check-boxes, etc. and just link the results into the DT cells. Actually you can do calcs in the DT cells themselves, but I find it cleaner the other way if things get complex.
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