CNC cut plug to prepreg tool recommendations?

I've got a CNC and an autoclave, 130C prepregs (that can be cured at 85C with a long cycle), what's the easiest way to get from drawing to prepreg tooling, without a lot of distortion or expense?

Currently using vinylester tooling, but they move around too much at elevated temperature.

The real issue is how to make a plug that can take the heat, or a RT master that can. I've considered using the vinylester as a master to make the jump, but I'll still get the distortion.

Most RT epoxies won't do better than 80C, but my experience is limited here. Perhaps I just need the right epoxy?

I'm aware of SP sytems tooling blocks and LTM prepregs, but don't like the price. I'd like to use more common materials. The following materials are readily available to me:

Extruded and expanded polystyrene
Polyurethane foams(PUR,PMI)
MDF
DICY/Accelerator based prepregs and epoxies(gel coat)
polyester/vinylester/epoxy resins - various hardeners.

What do you think?

 

http://www.reichhold.com/composites/products/product.cfm?ID=60&processID=25
I have build several large tools using filled resin tooling,,,,,,I have often thought of using this tooling for oven cured small parts as it can handle great temps.Replace the balsa core with a high temp core and give it a shot.
Most of my oven/clave cured parts are Graphite(carbon fiber) and require a tool made of same for expansion reasons............
If you are curing carbon,you need a carbon tool.........If not a carbon part,then there seems no reason for excessive heat......
Reichold has great tech support,I would bet they can tell you how if their filled resin will work your.

Hope this helps....
Peter Ross

 

I konow some Volvo boats have been constructed over male tooling, in an oven (120degrees C). The plug was MDF framing, with MDF strips over it, coated with a couple of layers of epoxy. This worked without shifting too much.

However, the plugs were only used for 1 or 2 parts. (depending on the part)

For more durable molds, one can make those on the same type of plug, with epoxy types that are compatible with the high temperatures. Those epoxy types need postcuring definately, and the most important factor is the ramp rate at which to elevate the temperature. Do not go over 5 degrees C per hour, or 10 if your adventurous. (I recommend 5, better safe than sorry).
Ramp down should be not too shocking as well.

Good story about influence of temperature on composite parts:
A customer of mine makes carbon arrows, using a pultrusion machine. These arrows are checked by laser, for straigthness, and automatically sorts in 4 categories: A: for the top of the bill bow and arrow specialists, B for the sports player, C for the novice, D is useless.
In normal production, almost all arrows end up in A and B. When someone opens a door, causing a draft, the production shifts to B, C and even D...

 

I could form a better understanding of your problems and potential solutions if you could give us an idea of the size of your CNC machine and the number of axes it has together with the size of your autoclave or the largest part you intend to make.I have worked with moulds that were laminated over MDF/wood at ambient temperatures and then subjected to a post cure process that allowed the use of 85 degree cures.You can either buy ambient cure prepregs or use a suitable epoxy resin with the fabric of your choice.
Your post does not refer to the fabric you intend to work with.Would it be carbon?If so avoid glass tools as the difference in thermal expansion makes life interesting when the tool cools.
If you intend to produce a mould at elevated temperature you really are obliged to use an epoxy tooling block as most other materials will distort somewhat,a situation that can be mad worse by the addition of pressure.At the very least,expect all glue lines to show if you use MDF or polyurethane tooling block.You may also have problems if some of the constituents of these materials outgas and react with the tooling resin.It can be worth subjecting the plug to the same temperature and pressure conditions it will be exposed to while encased in a vacuum bag and prior to paint.The bag will collapse any voids that may be lurking beneath the surface.
You should also be aware that tooling block is a very good insulator,as is MDF, and you may not find it easy to progress through the heating cycle at the rate the resin supliers recommend.Before committing to a large component,try a small part first.
I have skipped past the CNC aspect of the job I now realise.My limitation in this respect is that I am only familiar with Mastercam so if you need advice on other systems you could try the machining forum at practicalmachinist.com or CNCzone.The knowledge is almost certainly there.Good luck.

 

My autoclave is 8 meters long, and 1.5 meter diameter. The CNC is 3 axis, very simple, envelope is 1.5 x 1 x 18 meters. The hulls are 7 meters.

I am working with carbon, and glass. My current molds are glass, and I have experienced some of the thermal issues, but nothing too serious. I understand the thermal expansion issues, but I think the carbon tooling will have to wait until I've made successful glass prepreg tools.

The machining is no big deal, my inexperience has to do with the materials and the temperature.

My thinking has evolved a little since the first post. It seems that the way to go may be to:

1) Use polyurethane blocks, supported on a flat steel frame
2) Mill the foam about 3mm undersized.
3) Apply several layers of prepreg, bag and cure in the autoclave
4) Apply a coat of filled epoxy resin
5) Mill to final dimension and finish.
6) Layup with prepreg, and back into the autoclave.

 

I may not have understood your post correctly as it seems that you intend to do quite a lot of work in order to be able to make tools from prepreg material.What I had imagined that you were after was tools with which to make prepreg components.The simplest method in terms of number of operations is :
1)Machine epoxy tooling block to shape and finish
2)Layup prepreg

I would have serious doubts about the use of polyurethane foam if it is to be exposed to both temperature and pressure while encased in a vacuum bag.It may well collapse.If you have the chance to try a test piece with your intended process you should do so as it will either verify the process or fit into the bin more easily than a 7 metre disaster.
An alternative would be to use steps 1&2 of your proposal although I would be more comfortable with a 5mm thickness of filler,rather than 3mm for prepreg.I would apply 8-10mm in order to achieve this and then go for a moulding finish.The mould could be made with wet laid glass or carbon in a resin suitable for elevated temperature post curing.There are several epoxies which can be successfully used for this application but they may be sold under different names in different regions.I would suggest that in addition to the names already mentioned you talk to your nearest Huntsman distributor and research Axson resins.The mould should be released and well supported before post cure and avoid the temptation to use pressure.Again,I would recommend a test piece first.