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What is the best way to handle flat patterns of curved sheet metal parts?

Question asked by Michael Gera on Mar 1, 2019

A frequent (enough) part that I have to model and ultimately have fabricated is the curved sheet metal part. 


Traditionally, I've done it via the method exemplified in the attached "radiused_part_A.SLDPRT". 


This method is certainly easy and direct enough, but it has one major drawback: when the flat pattern is generated, holes are not circles.  Rather, that are multi-faceted approximations of ellipses and such.  This causes problems when the sheet metal fabricator tries to generate laser toolpaths with their CAM software.  Often times, their engineer will have to make a .DXF from my flat pattern, then open it in AutoCAD and manually replace the ellipses with circles.  Needless to say, this doesn't make me a very popular person with them...


More recently, I switched to the methodology exemplified in the attached "radiused_part_B.SLDPRT".  The advantage of this is that my flat pattern woes go away and the CAM software is happy.  The disadvantage is that it's a bit of a convoluted way of doing things and it's not suited to all curved part jobs, rather only to those where the "wrap" in its flattened state is known up front.  Designing the cylindrical section of a tank with many exterior penetrations, for example, would require doing all sorts of math on the front end to figure out the effective linear distance between holes.  Changes or even simple tweaks to the tank later or during the initial design process would be a lot of work.


So the questions is: what is the best way to design curved sheet metal parts, taking a clean, usable flat pattern into account?


Thanks for any replies.  Any help would be much appreciated, as always!