Spray on "hardcoat" , foam tooling 1

[ncprogrammer]

We currently build most of our master tools for composite
parts from different density's of foam depending on the
required tolerances. Mostly we use 10-15lb yellow foam.
If we need "hard" tools we pull a "splash" off of the foam
tool and then make our parts from that. I am looking for
a spray on or roll on coating that would harden up to a
density of something like Renboard that we could then
do a finish machining operation on. This would allow us
to pull parts right off the master without making splashes.

If anyone has used or hear of such a thing I would greatly
appreciate the information to be passed along.

Thank you.

 

[Compositepro]

Renshape and others make frozen, one-part, room-temp. curing syntactic foam "patties" that you can use to coarsely build your tool. After cure you machine to shape. If the tool profile requires more than 1" in thickness you use aluminum honeycomb for a back-up structure.

Boeing Helicopter in Philadelphia uses this tooling method and they have published papers in SAMPE Symposia.

 

[donvai]

Thank you for this tip. It should work on some of my projects as well.
I was just on the Renshape site and found no syntactic foam. I am trying to source an epoxy-based w/glass microspheres syntactic foam also to use as a core in radomes. Do you have any leads there?

 

[Compositepro]

Both Dexter Hysol and Cytec make uncured syntactic foam films. Cytec supplies a cyanate ester/glass micro balloon film that is used on the F-22's radomes. Cyanates resins have a lower dielectric constant and loss tangent than epoxies and make much higher performance radomes. Few are willing to pay the higher price however. Finding the right contact at these companies can be difficult.

Go to

http://www.nfgsales.com/LCTC Procedure.htm

for info on tooling.

 

[bmeyers]

In boats , some of the tooling shops use a syntactic foam to develop a machineable surface. The foam is a mixture of glass or plastic spheres in polyester resin.This is applied and machined prior to application of tooling primers and topcoats. Spraycore is one brand.

 

[divergent]

I have a pretty good amount of experience with the Spraycore tooling topcoat. Great stuff, machines well, but you will still need to do some hand finishing to get a good mold surface.

One thing to consider is the thermal issues with the topcoat and the base material. If you are using prepreg or cooking the molds for other reasons then you will need to consider using a denser foam base. Anything less then 6-8lb foam will cause the topcoat to crack and distort after the first cure.

Also, I have found that usless you plan to do a substancial amount of rework between uses the molds are only really good for 5 parts maximum.