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Hi guys I'm new here and new to making my own composites! I am a third year Mechanical Engineering student in Canada. What I want to do is make some carbon fiber parts for my truck which include; Intake tube, Turbocharger tube, and Intercooler tubes to start. I have began making my intake tube plug utilizing the following materials: Foam - Floracraft Dry Foam from michaels craft store Basic hot glue Bondo Gold body filler Filler primer Duplicolor engine paint I just received my prepreg carbon fiber from Composites Canada (196gsm and 670gsm) and I attached the spec sheet they sent me. My plan was to make the mold from the prepreg as it will cost me the same as to do a wet layup fiberglass mold vs prepreg. Do I need a gelcoat for a prepreg tooling mold? My vacuum pump will only get about 17 inhg at sea level, will this be sufficient? Will my plug hold up to curing the mold in an oven? I will need to make an oven, any suggestions? Sorry about all the questions guys I have spent about 2 months researching and am getting really excited! The pictures are of my plug installed in my truck to verify fitment. Thanks guys!
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Hi Mitch Is always good to use gelcoat for molds. It gives a nice, smooth surface making demolming from plug easier. Reach a prefect surface on your mold. Wetsand and polish if needed, to reach a mirror finish. I use to wetsand to 800 or 1000 and then polish. The better the mold, the better will be your part and mold's life. The vac pressure is an aditional help. There's not a minimum. It´ll improve adaptation of fiber to edges, radius, corners and will also improve adhesion between layers, it's main goal. So, better as higher. But there's not a minimum. For the plug and the oven.... the foam may collapse (depending of material) under a high temperature and pressure. I don't know about floracraft. If is it a PVC there may be degassing problems over aprox 90ºC. If a polyestyrene, the combination pressure + high temp will almost sure collapse the foam. Just make a test. Make your oven and then try your foam under curing conditions.. You can use wood, cheapboard or any foam especific for high temperature use. Even PVC for high temp or PU for plugs. I would use a good poliurethane 2 comp. panit for the plug with a nice smooth shiny surface. For a cheap oven, you can use any commercial thermal isulator as poliurethane or polyestyren foams and thin wood to protect it, making edges, etc. The isulating capability depends on the material itself and thickness. I´ve done simple ovens with 50 mm polyestyrene + 3mm wood. If volume is small you can easyly reach 80ºC with a domestic heater. Remind to isulate also the oven´s floor. Try to put a thermocouple inside the oven to know what's going on inside without the need of opening it (use an external temp display) and loosing your temp. If can´t reach your minimum temp, try recirculating the hot air (closed air circuit, driving the hot air to the heater again). You can use any tube for the recirculated air by isulating it with glass or mineral wool, for example. For prepregs, follow carefully manufacturer´s temp ramp. Make as much tests as you need to reach your ramp. Then cook the part. Vacuum may be a bit messy, but if you are carefull to details, it´ll be fun ! Mind specially mold´s surface and temp ramp. Remind that vac bag, tacky tape, release, etc mut withstand curing temp properlly (pay attention if you use wax, must be high temp resistant) .... and good luck !
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Wow thanks for all the info! I will make an oven this weekend. It will probably be 3ft long, 2ft wide, and 2 ft high. I was thinking of using 4 100W light bulbs as this would allow me to turn some off if needed. Build the frame from steel studs and Ruxol fire proof insulation with some fire guard drywall on the inside. Do you think this will work? I will try a small test with the foam I used in a vacuum bag. I really hope it works as I already have about 20 hours into the plug. If it doesn't work what would be a good alternative for the complex shape? CNCing aluminum moulds is way out of my price range unfortunately. How many layers would you recommend for making the mould out of prepreg? I have 196gsm and 670gsm. Would a casting resin be a better option vs prepreg for the mould? Thanks again!
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I PREFER wood for the oven´s structure as absorves less heat than steel or aluminium and for me is easyer to make. Steel is also valid, but need to be well isulated. 4 x 100 W will probabilly be not enough. Try a domestic heater. I would suggest 2 x 1000 W. In case you need medium power, you could add a potentiometer to one of the 1000 Ws line. (Or better with electronic control !) If you don't reach your requested temp, insist on isulation. seal edges and corners with mineral wool, fiberglass or similar. Increase wall thickness. recirculate your air and by last, increase heating power. For the mold / plug.... if foam collapses on your test, I would suggest to make the mold epoxy wet layup room temp a few plyes. This will create a sufficent strength to support next prepreg layers vacuumed + heated. Once cured, maybe poscure it to resist prepreg´s curing temp. And then add the prepreg + high temp + vacuum as higher as possible. Mold´s thickness.... I use to make about 6 mm for room temp wet layup. Made with glass. Up to 10 mm for big parts. If part is big, flexion under vacuum is more "able" (?). Less probable on small parts => thinner mold. As the parts are not too big, you can use "thin" molds. Using carbon for the molds gives stifness.... I would go to about 5 or 6 mm. Maybe 2 x 200 gr + 7 x 670 gr ? I would use gel coat to avoid fabrics's crosses marks on the surface. If you´ll make many parts, give a few extra plyes, to about 8mm as high temp + vac is a pain for molds (contraction, pressures, dilatation, on each part .... I woul not use casting resin. Fabric gives dimensional stability, avoid torsions or other deformations... That all is a fast recomendation... I´ve probabily missed any points... Pay attention to details and think before making. Is not complicate !!
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