I have been working on producing these 1/24 scale slot car bodies out of 1 layer of 8.3oz carbon and bagging. The good news is the weight is the same or lighter as the thin polycarbonate bodies they are replacing with considerably more stiffness. At 140mph this added stiffness is helping but overall the layup results have been inconsistant as getting the fabric to lay down perfectly everywhere has been challenging as might be imagined. I have been using an existing clear poly body as a mold so that allows me to see the problems through the mold. I can see that just a little more pressure would solve the problem of fabric conforming so of course my next thought is that an autoclave can do that. I am in the process of building a good tool and a small autoclave but my question is will the added 20,40,60…psi of pressure fix the asthetic issue of resin voids in between the fiber weaves. a lower resin content with a nice finish would be ideal.
You might try a double bag. Be advised that autoclaves do not yield perfect consolidation. Proper resin ratio at impregnation does. What’s even harder is to get that right with a wet layup. If you go autoclave… You might consider switching to pre preg.
Have you at least tried a double bag setup. That can help get added consolidation.
whats a double bag? I am putting the entire tool into a bag so there is bag against internal and external surfaces. I have tried several pleet arrangements, perforated release, fabric type release, silicone pressure pads (which make the problem a moving target). It just seems it needs a little more pressure. keep in mind this is a very small part, 8"x 2 1/2"x 1 1/4". thanks
if you infuse you will not get pits in the carbon
I had thought about infusing but was concerned about weight. The body is 9grams and every gram counts. FYI total car weight is 50g. They cover the 55’ track in .45sec @ 140mph +. Am I off on the thought of ending up with too much resin? I’m sure surface finish would be nice.
If you do infusion correctly the weight difference should be very close if non existent. It might be worth it to accept a .5 to gram hit on the body but reduce it somewhere else, such as different fabric or even lower density resin.
is there a good thread here on how to go about infusing a part like this. I have heard about degasing the resin prior to infusion but not sure the best way to go about this. also info on resin ports and materials used. I would like to stay with the 4x4 cuz I really like the look and also need a source for the correct, thin resin I can buy by the gallon.
RTM, VaRTM, RTM lite, what ever you want to call it. I think would fix this problem because you will be “infusing” to get the good finish without voids and because you have a closed mold you control the thickness of your final part so added weight shouldn’t be an issue. Check out John Moores webpage/youtube page to get a better idea. He has GREAT videos and info on RTM. I’m surprised we don’t see more people on here doing this process. Is anyone??
http://www.rtmcomposites.com/ Website
http://rtmcompositestv.com/ Web TV
http://www.youtube.com/user/jhmtechrtm?blend=23&ob=5#g/u Youtube videos.
And that is just CRAZY 0-140+ mph in .45 sec. hehehe I guess the only replacement for displacement is volts/amps 
I think that it will not work in RTM to reach the minimum weight. May be a negativ Form with a Stamp made from silicone will work very good. Make a hand laminate and press it for example with srew clamps.
Infusion will work, but you need some experience to make a good and light infusion with 1 layer of carbon, 2 layers will work a lot easyer, but I´m sure than the part weight will be bigger than 9gr.
Take a look at the MTI thread in the products talk, there i have shown how to make an infusion.Degasing the resin is very important for a good surface, at least if you have a thin laminate and a small part.
The ambient pressure is always the same, it makes no difference if you work with one or two bags. Two bags are used to eleminate leaks in the first bagging film.
Two bags can be contraproductive for consolidation if there is space between the first and the second bag. At that place the abient pressure does not work on the laminate.
I’m just thinking out loud. Since I have the ability to machine a aluminum tool I could make one so it was a cavity then wet the prefitted fabric lightly (as I have been) and add the bagging components but instead of pulling a vacuum a plate could be screwed to the top and add compressed air. my concern about VARTM, RTM, etc is the complexity of materials, resin porting and possibly pressure plates just to introduce 4 or 5grams of epoxy.
I think with aluminium tooling (top and bottom tool) you could either do a full scale RTM (with lots of pressure), preferably even heated, but you could also be press moulding: Just add the right amount of resin in the middle of the mould, add the fabric, and close the mould. Then press it down firmly.
The edge design is crucial. It needs points which ensure the right cavity thickness, and around the perimeter you need cut-off points, which basicly is a relatively sharp edge pointing upwards, leaving a very small cavity which clamps the fabric when closed completely. This way the resin will fill the complete cavity, instead of pouring out the shortest route, and the part will be extremely thin at that point, making the cleanup of the part very simple (just break of the excess fiber, do a quick sand). Next to the cut-off ridge you need a resin gutter (small) to catch excess resin.
Your parts will be very consistent, and are quick to produce. The tool is costly though, but you do not need extra expensive machinery. I even have clients that do not use a press, but just large C-clamps. (use gloves when tightening the clamps, this needs to be done a couple of times over a short period of time, to get the right pressure)
If all else fails, you can convert the tool to RTM by drilling a small hole in the middle.
you can get higher fiber content in infused parts if done correctly. Something that small you could infuse with no mesh. Worth trying atleast before going a more expensive route.
I agree with DD on the silicon inner “plug” method. Yes the pressure would be the same as regular bagging. But the distribution of that pressure is the key. Using this process you can establish the exact amount of resin that’s needed, pre-impregnate the cloth with spreader then place in mold. Very little additional cost associated with this method.
If increase the weight of only 5 grams is so dramatic, why don’t you change the fabric type ?
I’m not used to english sytem but (correct me if i’m wrong), 8.03 oz = 227 grams. You can go down with weight using carbon fabric 1K-67 tex ( 67 grams/m2) .
excellent advice guys. I appreciate the experts chiming in. The part has zero draft on the sides so matched metal molds are out but a rubber die might be possible. Seems like several good ideas. maybe I should machine the metal female mold first allowing for the ability to explore various techniques presented here. I guess the order of importance here is.
1- push fabric tight against mold surface
2-avoid resin bridging in between fiber bundles
3- Keep resin low but as long as excess was to the inside that would be fine because it could be sanded away if the end user wanted absolute minimum weight.
4-keep labor to a minimum.
Wings, the fabric is about 230 grams per square meter. Total weight of the bodies I have made so far are 9-10 grams. somewhere around half that being resin. Going to lighter fabric could drop a few grams but I am in love with 4x4 twill:rolleyes: Plus the added strength/stiffness we are at now over polycarbonate body is good and still same or slightly lighter weight than poly body
Yep as Herman says compression mould is the go. Will take some pics of some parts I did last week tomorrow.
so going back to my initial idea of wetting out the fabric, laying down some bagging material then bolting a plate on top and adding air pressure is basically compression molding? the male mold just happens to be the bagging film? Here is a few pics of a chassis i made using compression molding a while back. I have used that process in the past and it has been great
That is beautiful! GREAT work Busted blade!
Incorrect.