What would be the most common (best) material used when cnc forming a plug?
Foam?
It’s for a large scale epoxy/graphite tooling.
I’ve been calling around for just this and it seems like closed cell foam and wood are the two most popular options. Ask for a large wood cnc since those are designed to deal with sawdust/foam dust as opposed to metal chips.
If you have luck with finding a good machining company would you mind if I asked for the details. I’m currently looking for company to machine a nose cone for our Formula Hybrid team.
It depends if your going to post cure on the plug or free stand it in a oven. There are many styles of tooling boards available. Foams and wood are also common to used like canyon said. It really depends on your application
Many types indeed:
MDF
Tooling board
Tooling foam
EPS foam, undercut, then 1 layer of polyester (the EPS safe version) over it, sprayable polyester putty, then mill to size.
Or the same as above, with epoxy laminate and PU paste. Less heat distortion temperature, though.
PU foam with above options.
EPS with Acrylic material on it.
Or even doing a negative mould in high density EPS, then pull a stretchy vacuum bag in (with vacuum), and use that as tooling.
In making their plug for the USF1 racecar monocoque, a video shows them using Advanced Composite Group’s acg tb 720 tooling foam. They call it a “epoxy syntactic tooling board”, with a density of about 45 lb/ft^3 (.75 g/cm^3). The pores are sealed with an epoxy sealer and gaps with an epoxy filler. Temp rating is only 212°F (100° C).
I’ve been using General Plastics polyurethane Last-a-Foam. The FR6700/3700 series are available in various densities, and have a Continuous Service Temp of about 250°F. I’ve heard of people using this foam in autoclaves and ovens up to 250°F. In 10-12 lb/ft densities, the foam pores need to be filled and sealed, but at higher densities only priming/sealing is necessary. Obviously, if supported post-curing of the tool is necessary, every component of the plug has to handle the heat.
Fiberlay distributes the Last-a-Foam. A 4" x 48" x 96" sheet of FR-6712 (12 lb/ft^3) costs about $1000.
Yes, the tooling will be post cured in an oven at 130°C (266°F) with the plug.
Would a polyurethane foam be suitable? Data sheet maintains the it has a service temp of 150°C (302°F). Seal with an epoxy filler and finish with a 2 pack polyurethane paint.
I was also refereed to a company in the US called CFOAM. They make carbon foam blocks. Looks pretty good. Has any had used this stuff? Looks like it can be used an tooling, would save a fair bit of $$.
See post above yours…
Cfoam is very nice for tooling, has a low CTE. You can either buy the blocks from them and machine and laminate them, or have them do it for you.
Hi hojo,
Do you know the approximate cost of the Cfoam?
Its fairly expensive, chearper than Invar. I suggest giving them a call for pricing.
Expensive, even for aerospace. 
Ouch, thanks for the warning! Do you use it, TET?
A little off topic but Canyon make sure that the radius on the nose cone is not too small for the rules.
We have, and it’s great. Strong, light, and temperature stable. Used it to make some plugs to lay up molds, and even made a short run production mold with it (using their surface coating.)
Wouldn’t use it again though, unless customer asks for it and covers the cost. Urethane and epoxy tooling blocks work fine for most jobs.
Yep Yep. 1.5 inche radius ±45 from leading edge. It’s not going to be as perfectly sharp as it is in the model. Thanks for the reminder!
What are you planning on using for your impact attenuator?
We’re using a sheet metal box with stacked Nomex honeycomb with CSM between the layers to avoid the layers cutting into each other. We wanted to use aluminum honeycomb or aluminum foam but it turned out to be too expensive.