Lofted Sheetmetal Part ??

[tmalinski]

I have a .030" thick part made with a loft along most of its curved length. My part looks like this:
Take a sheet metal ruler hold it by both ends and bow it into an arc, then twist one end slightly.

I need to be able to unfold this part to establish the flatblank shape. Is there a way to loft a sheetmetal part? Or is there some other totally different approach?



Tom Malinski
Sr Design Engineer
OKay Industries
New Britain CT

 

[tmalinski]

Foolish me, I just found the lofted bend in the sheetmetal menu, I'll play with this

Tom Malinski
Sr Design Engineer
OKay Industries
New Britain CT

 

[CorBlimeyLimey]

Just remember that the loft is an approximation of "real life" parts. The flat may not be 100% accurate, so you may have to do some tweaking depending on the precision you need.


Helpful SW websites FAQ559-520
How to get answers to your SW questions FAQ559-1091

 

[tmalinski]

I created my lofted part, but the flattened pattern is not the correct length. The arc in this part is so subtle that the K factor is set to .5 no stretching or compressing of the material.

My part is .030 thick, When I make a drawing of the part and offset the inside geometry to the center of the material thickness (.015) and measure its overall length it should be the same as the flat pattern with .5 K factor... but my flat pattern is .010 shorter, thats a mile for this little part. Just for the heck of it I changed the K factor to .3 but hte flat pattern did not change. Is there a possibility that a lofted sheetmetal part does not unfold correctly because the bend is part of the loft geometry rather than an actual sheetmetal bend? If so, where is the flat pattern length comming from?
Thanks for any help in advance...

Tom Malinski
Sr Design Engineer
OKay Industries
New Britain CT

 

[CorBlimeyLimey]

Like I said, the algorithm used in the Loft only approximates "real life". It ignores any plastic deformation which occurs during actual manufacturing processes. It does not use the K-factor or bend radii.


Helpful SW websites FAQ559-520
How to get answers to your SW questions FAQ559-1091

 

[tmalinski]

Thanks CBL. I guess I'm SOL to use the flat pattern then. Its to bad that the loft bend command won't let me specify a mid-plane point for the thickness similar to the extrude command. Then I could just set it for my K factor and everything would work..

Tom Malinski
Sr Design Engineer
OKay Industries
New Britain CT

 

[CorBlimeyLimey]

Correction ...

NOTES:

When a lofted bend is represented with a lofted surface (B-spline), as is created by a square to circle profile, it cannot use K-Factor or Bend Allowance in the sheet metal calculations.

When a lofted bend is represented as a conical or cylindrical bend, such as a loft between concentric circular arcs, then it behaves in the same way as a cylindrical or conical bend in that it uses K-Factor or Bend Allowance to calculate the bends.

Helpful SW websites FAQ559-520
How to get answers to your SW questions FAQ559-1091

 

[tmalinski]

CBL thanks for your help. Here is a pic of my Lofted Part. Do you think this should work with a K-Factor? as you noted? As I stated earlier, I tried different K-Factors and the flattened part did not change its length. Maybe I'm just doing something wrong.
In my history tree, I RMB on the Sheetmetal Icon / Edit Feature and change the K-Fator value, then go to my drawing and update the view. But the Flat pattern does not change!!!



Tom Malinski
Sr Design Engineer
OKay Industries
New Britain CT

 

[CorBlimeyLimey]

I've just been lofting between two concentric arcs and I found that the flattened loft has the same dimensions as the outer surface of the formed loft. So, to get the correct flat, you may be able to adjust the thickness of the lofted part to allow for actual material stretch/compression.

eg. If the inside surface size of the formed loft is critical, make the part very thin (say .001" or less) so that the outer & inner surface sizes are almost the same.

I'm not sue if that actually helps in your case though.


Helpful SW websites FAQ559-520
How to get answers to your SW questions FAQ559-1091

 

[tmalinski]

Thanks, CBL it sounds like I'll need to apply your approach as a work around for flat blank development only. I will construct the part using geometry that represents the neutral bend position. In my case its simple, I will just add .015" to the rad sizes for the lofts and then loft it at .001 thick and the flat blank should be correct. But I will still need to create the actual part with the correct geometry because I am building other fixtures and tooling in context that needs the actual part to build off of. A little extra work but at least it should give me an accurate flat blank.

Thanks for your help...

Tom Malinski
Sr Design Engineer
OKay Industries
New Britain CT

 

[CorBlimeyLimey]

A perfect scenario for a configuration.


Helpful SW websites FAQ559-520
How to get answers to your SW questions FAQ559-1091