Internal vs. External Flanges

General Composites Discussions Composites Talk
#1

I am trying to understand the cost and complexity impact of external vs. internal (returned) flanges. In the conceptual images below the red shell has an external flange and the yellow has a returned flange. The approximate dimensions are 90” long x 60” wide and 30” high. The flanges are about 1”. The outside surface is polyester gel coat and the overall layup (CSM and cloth) is about 1/8” thick. Corner radii are about 1/2” max.

http://i250.photobucket.com/albums/gg272/robrien24/ExternalFlange.jpg
http://i250.photobucket.com/albums/gg272/robrien24/InternalFlange.jpg

The external flange is simpler to make but would be far less attractive than the returned flange. I’m not really sure how the returned flange would be made although I assume the flanged portion of the mold would be a separate piece so the part can be released from the mold. Is it better to attach the flange surface to the mold and then mold the part and flange as a single piece or is it preferable to mold the shell w/o the flange first and then add the flange as a secondary operation.

Any insights would be appreciated.
Thank you
Rick OBrien

#2

Mostly the flange is laminated together with the part. Indeed the flange mould is a seperate piece.

#3

Any idea of the relative costs if I were planning to outsource this?

Thanks
Rick

#4

No idea. Some producers are not used to internal flanging, and are likely to charge more. In any way, expect a surcharge.

#5

I dont think the extra cost will be that great.

I would think you would need to make a mould with the outside flange first either way as the outside flange would be needed to secure the mould part for the inside flange onto. This could be just some thin alloy or pvc sheet bolted to the outside flange but overhanging to the inside to create your inside flange. It looks an easy enough shape to mould from the pics.

#6

I visited a local shop and that’s pretty much what they told me. Price wise, it would turn a roughly $400 part into a $500 part using CSM and chopper.