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9/17/2020 5:59:48 PM
Posted: 3/1/2010 5:35:06 PM EDT
Has anyone here ever had experience with making composite structures? If so, are there any recommendations you can provide for a first timer? I'm thinking of two possible routes for the car chassis I'm trying to build:
1) Make the core of the structure out of high density foam and wrap the foam in carbon fiber.
2) Pay a company to make a plug (negative mold), and lay my own carbon fiber sheets.

Any recommendations, resources, or references would be appreciated.
Link Posted: 3/1/2010 6:06:27 PM EDT
You could build the various components from wood and seal them. Then sand those "plugs" smooth and coat liberally with wax. Lay your carbon sheet and vinylester resin over the top and sides being careful to roll out all the air bubbles. Let it cure and "pop" your part off the plug.



Be sure to taper the sides slightly to aid in removing the parts from the plug/mold.



You could fabricate a one piece, c-channel  automotive frame in this manner. If you wanted to box the frame rails you could flip it over and fill the channels with 8# pour foam and sand flush. Then glass it over the same as before.
Link Posted: 3/1/2010 6:11:32 PM EDT
Originally Posted By OFFSHORE:
You could build the various components from wood and seal them. Then sand those "plugs" smooth and coat liberally with wax. Lay your carbon sheet and vinylester resin over the top and sides being careful to roll out all the air bubbles. Let it cure and "pop" your part off the plug.

Be sure to taper the sides slightly to aid in removing the parts from the plug/mold.

You could fabricate a one piece, c-channel  automotive frame in this manner. If you wanted to box the frame rails you could flip it over and fill the channels with 8# pour foam and sand flush. Then glass it over the same as before.


Dude, you are the man. That is exactly the kind of shit I was looking for. Thanks.
Link Posted: 3/1/2010 6:39:09 PM EDT
Glad to help. I was a sales rep for a composite distributor. Spent a lot of time with boat mfgs.



Do a lot of research on fiberglass lay-up before you buy materials. Then do more research on carbon fiber lay-up. Carbon fiber is not nearly as user friendly as traditional glass. The experts in your area (MA) are most likely firms building light weight sailboats for racing. They will know more far more about carbon lay-up than I do.



Reichold Chemical makes a Vinylester resin called Hydrex-100. It was the industry standard for high end lay-ups 5 or 6 years ago but I have no experience with automotive applications.



Good luck!
Link Posted: 3/1/2010 6:42:52 PM EDT
Now that I think about it, epoxy might be a better resin for your application.
Link Posted: 3/1/2010 6:46:07 PM EDT
Originally Posted By OFFSHORE:
Now that I think about it, epoxy might be a better resin for your application.


this, plus vaccum bag it
Link Posted: 3/1/2010 7:01:08 PM EDT



Originally Posted By cterrebonne:



Originally Posted By OFFSHORE:

Now that I think about it, epoxy might be a better resin for your application.




this, plus vaccum bag it


Bingo!



 
Link Posted: 3/1/2010 7:23:20 PM EDT
Originally Posted By OFFSHORE:

Originally Posted By cterrebonne:
Originally Posted By OFFSHORE:
Now that I think about it, epoxy might be a better resin for your application.


this, plus vaccum bag it

Bingo!
 


Yep, I saw that recommended. I was thinking about using a pre-preg but couldn't find a large enough heat source. Thanks again to both you guys for the great advice. Keep it coming if you think of anything else.
Link Posted: 3/1/2010 7:31:57 PM EDT
You'll find all the supplies you need here:



http://www.aircraftspruce.com/index.html



I'd recommend west system epoxy, it's what we always used to repair Predator with.  You'll also want 3M peel ply, and you can get all your vacuum bagging supplies from aircraft spruce as well.  To cure it for high strength use you'll really need to find a way to bake it.  You don't have to have an autoclave, but a large paint drying booth such as that used for car painting might work if it gets hot enough.  You might want to check with powder coating places, some of them have ovens large enough to bake entire car frames with.  



There are books about composite building available as well.  For low strength stuff you don't really need to worry about vacuum bagging and autoclaving, but for high strength applications like a vehicle frame you do.  You can lay up mutiple layers of CF, fiberglass, and kevlar to suit your needs for strength and flexibility.  the west system resins are compatible with all three.  
Link Posted: 3/1/2010 7:34:45 PM EDT
Originally Posted By Chairborne:
You'll find all the supplies you need here:

http://www.aircraftspruce.com/index.html

I'd recommend west system epoxy, it's what we always used to repair Predator with.  You'll also want 3M peel ply, and you can get all your vacuum bagging supplies from aircraft spruce as well.  To cure it for high strength use you'll really need to find a way to bake it.  You don't have to have an autoclave, but a large paint drying booth such as that used for car painting might work if it gets hot enough.  You might want to check with powder coating places, some of them have ovens large enough to bake entire car frames with.  

There are books about composite building available as well.  For low strength stuff you don't really need to worry about vacuum bagging and autoclaving, but for high strength applications like a vehicle frame you do.  You can lay up mutiple layers of CF, fiberglass, and kevlar to suit your needs for strength and flexibility.  the west system resins are compatible with all three.  


I'm glad you recommended that site, because I fell on it from someone else, and that makes me feel confident in the supplier. Thanks for the resin recommendation too. It's funny you say that because my buddy was talking to me about the affects of adding kevlar to the composite mix (oddly because I told him when we race, he is building one as well, that I was going to shoot his frame and shatter it!)

Thanks again guys, keep it coming if you can think of anything else.

Link Posted: 3/2/2010 3:48:54 AM EDT
Messy messy stuff. Plan on lots and lots of screw ups. If I were to do this I would recruit a pro for help.
Link Posted: 3/2/2010 6:03:04 AM EDT
Make sure you have a decent design for crash worthiness.

Unlike metal that continues to absorb energy as it is deformed, composites tend to go from adequate strength to close to zero after the material fractures.
Link Posted: 3/2/2010 1:37:43 PM EDT

There is another method that is often overlooked. But regularly used in certain composite aircraft structures.


Making or purchasing CF sheets. Then joining them using carbon angle, epoxy and rivets/fasteners. The trailing edges of certain Gulfstream aircraft are made this way. Top skin, bottom skin and forward section (like a spar). It results in an easy to assemble complex shape.


As you probably know, there are plenty of vendors selling CF stock. In a way, the method I describe can be thought of as manufacturing a precision part out of veneer plywood. (like the old boats).


I wish I had a pic to show you, I had a trailing edge sitting around for years. I finally chucked it out.


The method uses no foam, but, there is no reason that a CF and foam board could not be used with this method.







Just an FYI, I worked in a shop manufacturing very high end composite cars (race cars). While, I'm not the worlds leading expert on CF, I did work with it extensively. Cutting and grinding it really is bad for your health. Use extreme caution and fantastic safety procedures. You'll thank yourself later.







Laying up CF sheet yourself can be done on a large section of plate glass, such as an old glass window pane. The bagging is quite easy here, as the edges are simply taped down to the glass. However, each sheet takes a full day to make. It's simply better to purchase it, IMHO.

Link Posted: 3/2/2010 1:41:19 PM EDT
I have often thought about making a car using the flat CF sheet method. The floor pan would be structural and angular. The exterior body would be the only curved sections. This would cut down fabrication time to a fraction of the time necessary to make molds and pull parts off. Plus each section could be computer designed and cut, to fit perfectly. Making life easy.
 
Link Posted: 3/2/2010 1:43:53 PM EDT

Another thought. Bimota is now making a motorcycle with CF tubing. They claim it's stiffer than the steel tube it replaces by simply making the CF tubing 0.5 mm thicker than the steel.


The ends are joined in lugs, with epoxy holding the tubes in the sockets. Much like a tube and lug bicycle.

Link Posted: 3/2/2010 3:00:11 PM EDT
Originally Posted By cujet:
Another thought. Bimota is now making a motorcycle with CF tubing. They claim it's stiffer than the steel tube it replaces by simply making the CF tubing 0.5 mm thicker than the steel.

The ends are joined in lugs, with epoxy holding the tubes in the sockets. Much like a tube and lug bicycle.



I saw that! Freaking sweet. I like your sheet idea, I'm going to have to mull that around. Thanks.
Link Posted: 3/2/2010 3:08:04 PM EDT
Originally Posted By makabi24:
Originally Posted By Chairborne:
You'll find all the supplies you need here:

http://www.aircraftspruce.com/index.html

I'd recommend west system epoxy, it's what we always used to repair Predator with.  You'll also want 3M peel ply, and you can get all your vacuum bagging supplies from aircraft spruce as well.  To cure it for high strength use you'll really need to find a way to bake it.  You don't have to have an autoclave, but a large paint drying booth such as that used for car painting might work if it gets hot enough.  You might want to check with powder coating places, some of them have ovens large enough to bake entire car frames with.  

There are books about composite building available as well.  For low strength stuff you don't really need to worry about vacuum bagging and autoclaving, but for high strength applications like a vehicle frame you do.  You can lay up mutiple layers of CF, fiberglass, and kevlar to suit your needs for strength and flexibility.  the west system resins are compatible with all three.  


I'm glad you recommended that site, because I fell on it from someone else, and that makes me feel confident in the supplier. Thanks for the resin recommendation too. It's funny you say that because my buddy was talking to me about the affects of adding kevlar to the composite mix (oddly because I told him when we race, he is building one as well, that I was going to shoot his frame and shatter it!)

Thanks again guys, keep it coming if you can think of anything else.



I build epoxy and wood boats with some Kevlar for abrasion resistance and would recommend using System Three Silver Tip Laminating Epoxy. It wets out just about better than any other epoxy I've used and leaves no blush. Also helpful is its straight forward 2:1 mix ration.  Check it out System Three

Link Posted: 3/3/2010 5:51:24 AM EDT

Check this out.


I've been looking up prices of pre made panels. They are very expensive. Making it yourself is much cheaper.



Link Posted: 3/3/2010 8:25:05 AM EDT
http://forums.corral.net/forums/showthread.php?t=660756



A lot of the pics are gone but there is a ton of info on using molds, release agents and actually laying out the fiber.  He was just making body panels but I'm sure the steps are pretty close to what you would do.
Link Posted: 3/3/2010 5:47:48 PM EDT
Link Posted: 3/3/2010 6:19:24 PM EDT
Hey, I wanted to throw in my 2 cents.

I'm a mechanical engineer. I was somewhat involved with a project that basically made a race car from scratch for the College I went to. The body/frame of the race car was made of carbon fiber. It competed against many vehicles that used a more traditional aluminum tubular chassis with a plastic or fiberglass body over the top.

Well, the "carbon fiber monocoque" that our team used was strong, but a little more flexible then a traditional frame. It was also very heavy- 2 to 3 times heavier than aluminum. It was designed using 3D cad programs and tested for strength with Mechanica.  The crash-worthiness was actually quite good, as we found out when some idiot crashed at about 60 mph. The body/frame was completely destroyed, but he only got minor injuries. It turns out the carbon fiber body/frame did a great job of absorbing the energy of the crash.

That being said, I would highly recommend you use tubular (round or square cross-section) aluminum for your frame. A car is too important to just try and design. Oh, and with carbon fiber, it's best to make it a "one piece" design. It doesn't do well making many parts out of it and trying to join them.
Link Posted: 3/6/2010 3:41:55 PM EDT
Thanks for all the answers guys, I'll keep you posted.
Link Posted: 3/6/2010 6:47:26 PM EDT
Originally Posted By djkest:
Hey, I wanted to throw in my 2 cents.

I'm a mechanical engineer. I was somewhat involved with a project that basically made a race car from scratch for the College I went to. The body/frame of the race car was made of carbon fiber. It competed against many vehicles that used a more traditional aluminum tubular chassis with a plastic or fiberglass body over the top.

Well, the "carbon fiber monocoque" that our team used was strong, but a little more flexible then a traditional frame. It was also very heavy- 2 to 3 times heavier than aluminum. It was designed using 3D cad programs and tested for strength with Mechanica.  The crash-worthiness was actually quite good, as we found out when some idiot crashed at about 60 mph. The body/frame was completely destroyed, but he only got minor injuries. It turns out the carbon fiber body/frame did a great job of absorbing the energy of the crash.

That being said, I would highly recommend you use tubular (round or square cross-section) aluminum for your frame. A car is too important to just try and design. Oh, and with carbon fiber, it's best to make it a "one piece" design. It doesn't do well making many parts out of it and trying to join them.


I'm going to have to agree.  Even working in the multi million dollar composites lab at school, we still have a hell of a time with carbon fiber just making simple parts like seats and clutch covers.  To do the job correctly you need a lot of equipment that isn't at all cheap and a lot of safety equipment or you'll have itchy lungs.  It's not like fiberglass where you can lay down the mat and slather resin over it and be good to go.  If you want to make a car chassis that is safe and structurally sound there will be a ton of planning and preparation to be done.  I agree with making something simple first, it will give you an idea of the complexity of making something out of carbon fiber.
Link Posted: 3/7/2010 9:00:53 AM EDT
[Last Edit: 3/7/2010 9:04:27 AM EDT by djkest]
I think for some people they are in love with the concept of carbon fiber, but the reality isn't the same.

I guess it really just depends on what you want. If you want carbon fiber at any cost, it can be done. If you want the best bang for your buck or highest performing chassis, I'd go with tubular aluminum. If you are going to race it, prepare to (not win). Our car had some of the highest horsepower, but never placed higher than 18th in the races. We were one of 2 teams who used a CF chassis. I'm getting in contact with one of the suspension engineers who was heavily involved in it, and I'll see what he thinks.

They also did some composite type framing with a lightweight fiberglass honeycomb sandwhiched between layers of carbon fiber. This has a higher str/weight ratio that pure CF.

ETA: another problem with a hand-built custom CF chassis is it's hard to be extremely consistent , and that makes your mechanical simulations a little less reliable in predicting performance.
Link Posted: 3/7/2010 9:53:13 AM EDT

I spent some time driving a Ferrari Enzo (for my boss). It's essentially a CF chassis with metal attach points. Other than the fun factor, I found it to be less than ideal as as car. I hit a big, sharp bump in a construction zone. The "crack" was deafening. Harsh and uncomfortable feeling. While, that was mostly due to tires with sidewalls the height of rubber bands and 1.2 mm of suspension travel. I can't stop wondering if I actually did crack something on the chassis. Come to find out, my experience is common among Enzo drivers and is likely "the nature of the beast".


Today, chassis design and structural floor pan design are so common, a novice can do a fairly good job of getting it right. Do your research, but don't be turned away by those saying "you can't do that". One thing composite aircraft engineers understand, is the age old saying "one you've made composites stiff enough, they are way too strong". In other words, don't worry too much about ultimate strength, once it's stiff enough. Make sure to take design clues from successful composite cars and use metal for structural attach points.


Think about fiberglass boats for example. They were commonly built with a just few 2x4 wooden stringers and simple fiberglass. Once stiff enough, they were incredibly strong too. In fact, much stronger and lighter than a competitive metal boat.


Remember this too: CF is conductive and will foster galvanic corrosion on metal, wherever metal attaches. Stainless steel and Ti are good choices here.

Link Posted: 3/7/2010 4:42:06 PM EDT
Link Posted: 3/7/2010 4:44:02 PM EDT



Originally Posted By AeroE:


I'll add a couple of suggestions while you're learning this building method.  Practice basics with polyester resin, and consider using vinylester resin instead of epoxy.  Polyester is cheap and easy to find at Walmart and auto parts stores.  Vinylester is less sensitizing than epoxy.



Sensitivity to epoxy is nothing to blow off.  Some persons may work for years without problems, and then have a sudden onset of dermatitis that is so severe it's debilitating and the person can never work near the material again.  Other people become sensitized quickly.  I've seen a couple of cases after long term exposure that were so severe that they couldn't enter a hangar size room where layups were being assembled.



And don't wash your hands in MEK.





No shit!  That stuff not only causes cancer when absorbed through the skin, but dries your hands out something awful.  I know several people with dermatitis caused by use of MEK and PD680 without gloves.



 
Link Posted: 3/7/2010 5:33:45 PM EDT
Originally Posted By cujet:
I spent some time driving a Ferrari Enzo (for my boss). It's essentially a CF chassis with metal attach points. Other than the fun factor, I found it to be less than ideal as as car. I hit a big, sharp bump in a construction zone. The "crack" was deafening. Harsh and uncomfortable feeling. While, that was mostly due to tires with sidewalls the height of rubber bands and 1.2 mm of suspension travel. I can't stop wondering if I actually did crack something on the chassis. Come to find out, my experience is common among Enzo drivers and is likely "the nature of the beast".

Today, chassis design and structural floor pan design are so common, a novice can do a fairly good job of getting it right. Do your research, but don't be turned away by those saying "you can't do that". One thing composite aircraft engineers understand, is the age old saying "one you've made composites stiff enough, they are way too strong". In other words, don't worry too much about ultimate strength, once it's stiff enough. Make sure to take design clues from successful composite cars and use metal for structural attach points.

Think about fiberglass boats for example. They were commonly built with a just few 2x4 wooden stringers and simple fiberglass. Once stiff enough, they were incredibly strong too. In fact, much stronger and lighter than a competitive metal boat.

Remember this too: CF is conductive and will foster galvanic corrosion on metal, wherever metal attaches. Stainless steel and Ti are good choices here.




I know what you mean. Great advice. Also, good call on the Galvanic reation; I did not even think of that. I would probably try and use Ti attachments or sleeves if I could anyway due to weight. I agree while it may be difficult and trying, I do not foresee it as anything impossible. Just need space, patience, and some dollars to spend. Thanks again for the advice and information.
Link Posted: 3/7/2010 6:09:39 PM EDT
Link Posted: 3/8/2010 2:58:42 AM EDT
[Last Edit: 3/8/2010 2:58:50 AM EDT by makabi24]
Originally Posted By AeroE:

Use barrier plies of glass where galvanic corrosion is a problem.



I'll have to look into that. Seems like a good idea. Thanks. Man, the level of knowledge around here is awesome...I swear if we could just get some $$$ together, ARFCOM could setup a heck of a consulting firm or manufacturer of some sort!
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