I have been working on a hybrid vehicle project for my university, we are looking at using Twintex (continuous fiberglass reinforced polypropylene) as our primary material, one of the biggest problems we have been running into is cost effective tooling. Since twintex is a thermoplastic it has to be processed above the melting temp of polyproplyene (around 360 F) so the molds have to be able to withstand high heat and thermal cycling. All the options for tooling are extremely expensive (high temp epoxies or aluminum/steel tools) i have been investigating plaster as a possible low cost tooling option, i understand that the molds wouldn’t have the longevity or durability of a more traditional tool, but since the vehicle is a “one off” prototype they probably wouldn’t have to be used more than a couple times. I have heard of people using plaster tools for fiberglass layups. I have access to machining/plastics labs and a 3 axis CNC router which i was thinking i could use to make matching foam plugs that i would then pour plaster into to make tools with constant wall thickness of about an inch. I’m thinking a constant wall thickness mold reinforced with 10-15% short length glass or carbon fibers would be resistant enough to cracking to use as prototype tooling. Does anyone have any experience with making plaster tools for fiber composites? or any other advice on a cost effective, high temp tooling options?
I only have a very limited amount of customers using twintex, and tooling (especially epoxy) always is a pita.
No experience with “high temp adventures in plaster tooling”
[LEFT]TWINTEX® R PP is a roving made of commingled High Performance Glass and polypropylene filaments. TWINTEX® R PP is suitable for filament winding, pultrusion, reinforcement of extruded profiles and weaving. Consolidation is done by heating the roving above melting temperature of PP matrix (180°C–230°C / 360°F-450°F) and applying a pressure before cooling step under pressure.[/LEFT]
I was curious on some questions to the above. found a sweet link describing basically a ‘How to’ manual to use this item. I can see some benifits in it, especially for what you are doing.
From this link:
Vacuum molding tools
The choice of material to make the mold will depend on economic factors such as the cost, tool life, the number of parts to be produced and the cycle time. The final surface appearance of the part will also depend on the quality of the mold finish. There are five general types of mold:
• High temperature epoxy composite molds
• Ceramic matrix composites tools
• Electroformed nickel skin molds
• Aluminum molds
• Welded metal molds
And the info i was looking for at the end: Curing Time: 90 min (from the entrance to the exit of the tool) in a hot air oven set at 210°C
In short, you need a mold that can withstand 210C min for 90 minutes. I must admit I would be skeptical about having ANY foam.
I am a novice at most of the stuff on here for the application of laying up the part but have made lots and lots of molds using MDF. In truth, I dont know to what temp MDF would be considered safe to use. Sure, it likely wont catch fire unless it gets real hot but I am not sure at what temp the glues may present issues. I knew for very short periods 350ish F wasnt a problem but that was just on the surface for just a couple minutes at most before we would make tooling out of it. I nshort, I dont know if you can use MDF for extended periods. Next to foam this about the cheapest thing I know of. If you go this route, use MDF Wheat Board. It does make a very hard surface. Down side to MDF is 2 fold. Large heat sink and unknown if stable at 210c. I would put more money on the MDF than the foam though.
Do I think plaster would work? Sure why not. Is there potential issues with it? Yes there it. Plaster is porous and you will need to seal it. Plasteralso has poor thermal conductivity (as does Twinex and they dont recommend more than 5mm thickness due uneven curing). You run the risk of the outside of twinex ‘going off’ while the inner layers are kept cool by the plaster. You also run the risk of the foam melting or going into gasous form. The foam (if unit is fully bagged) may go gasous INSIDE the vacuum bag. Not only do you loose vacuum, the chemicals could react very very bad. How I dont know but it is a potential problem for sure.
Now if your foam is FULLY encased in plaster it may work. Mostly on the hope it never gets quite that hot inside the plaster but then again if its not 210C at minimum o nthe outside of the plaster, the part will not cure properly. Its a gamble.
In truth, make the negative of the mold you want to use. lay it up with high temp fiberglass. This gives you the opportunity to sand and make a very good surface also.
Just my thoughts. How big is the part you are making?
I would not bet on MDF, especially for the reason of fire, and moisture, which potentially can ruin the fiber, or alter the shape. (plaster also holds a pretty decent amount of water, which only comes out at high temperatures.)
My best guess is that for one-off production, I would stick to epoxy.
But if you want to go ahead with Twintex, you could opt for a mould made of ultra high temperature tooling epoxy gelcoat, and laminate plaster behind it.
tooling board!!! Some will withstand high temps. That, or you have to invest in high-temp tooling gel and epoxy, or metal molds.
Why use Twintex for one-off production? Twintex is designed for a higher production environment. Going through all the tooling to produce a one-off with Twintex seem crazy to me. In fact building a mold for a one-off doesn’t seem warranted unless it’s an hollow structure that needs a lot of internals. Tooling board is far from a cost effective alternative. If the part is thick then stacks of tooling board can be very expensive.
If you are determined to use it then a plaster mold could work. You could also fabricate a plastic faced plaster mold. Most epoxy surface coats that are designed for PFP usage are designed for high temp use. You need to bake the moisture out of the plaster before it will reach it’s full strength. On thick slabs this can take days.
Plaster bonds pretty poorly to glass and carbon. Most plaster molds are reinforced with sisal fibers because they facilitate a much better bond. Whatever process you use with plaster has to be pretty quick. You don’t have much working time.
Wyo is correct…especially on working time with plasters. My limited experience was with making a high temp tool for Acrylics. Like anything …there is a learning curve getting it right. The worst part with that curve and plasters is the waste if it goes wrong.
There is indeed more control with a full epoxy tool…cost too. But that control is money as well in the end.
Hi,the hand lay mould could use wood or fiberglass master mould to get fiberglass body mould and then do mold for production.if you have any questions you could ask again
we use plaster molds at those temps and also mill the blanks with cnc. the challenge would be in release as well as moisture considerations. the plaster also oxidizes so its repeated use is limited