Hey there, I am fairly new to composites and molding in general and VERY new here to the forums! I did a couple of searches on how to lay up a thick laminate of carbon fiber to make a flat piece. Here is an example of what I mean
I am not certain how strong this would be, but it sure gets the job done! The piece I am trying to duplicate is a small aluminum handle. (home made hood release on a race car) It is 3/8" thick. Any suggestions on this? Thanks in advance and thanks to all who make a forum like this work! So much to learn here.
Not quite sure how the guy in the link would of accomplished this and be 100% carbon all the way through as he has mentioned without a fixture to form the carbon around.
You can take a foam core of an item, be it whatever, either shaped by hand or machine cut and wrap it with carbon and then pour a solvent in it to melt the foam away. At that point, someone could continually lay-up layer after layer of carbon to achieve the desired thickness.
To be honest, if you want something which would also be structural and in carbon you need to vacuum it. The piece shown in the link looks nice but structurally, it would not be equal to a vacuum’d piece, unless he put vacuum to it. He does not want to provide any details on how he did it which is fine, ideally, anything we build has not only be asthetically pleasing but also provide structural integrity, otherwise, whats the point…
It has been posted here before, but at atmospheric pressure every square inch of a mould will see 14.7 lbs of pressure. A 144" total volume mould is getting 2,118 lbs of pressure on it, compression is what makes good composites…
For additional help from many members here, you would need to post some pics of the handle so we can see how organic of a shape it is, from there many of us can provide some guidance on which way to build it.
What SLS said but times 3 literally. The strongest most sound parts are nearly always cured in autoclave with pressures that are normally between two and three times atmospheric pressure
I guess I have a different take on the whole compaction/vacuum bagging issue.
A few thoughts:
The suggestion that only highly compacted composites are structurally functional is inaccurate. There are many fully functional structural parts that are fabricated without the use of a press, vacuum bag, or autoclave. In fact, I’ve tested some pretty poor quality laminates that were made using a vacuum bag. The advantage to using a compaction process is that you can get more fiber into a structure for less weight. This isn’t necessarily a “quality” issue but a design requirement issue - maximized specific strength. If stringent weight requirements aren’t a major component in the design then compaction may not be necessary.
Voids within the laminate can be it’s downfall. The purpose of the matrix (resin) is to transfer the loads from fiber to fiber. If you have voids within the laminate this load transfer is halted and the fibers are not adequately held together. I’ve seen many vacuum bagged prepreg laminates, especially the new OOA pregregs, that performed pretty poorly because there were many voids between the fibers.
Recently, I had to do a problem solving issue with a UAV manufacturer. They were pre-wetting their fiber with resin, laying into the mold, and then vacuum bagging it. The structure kept on failing even though the fiber volume was adequate. I did the same layup in the shop by wetting the fibers in the mold to ensure that there was no trapped air. This structured tested 38% stronger simply because there weren’t voids trapped within the fiber from the pre-wetting and placement process. Moral of the story:vacuum bagging won’t give you much of advantage if there are voids in the laminate.
Compressing a laminate can sometimes make the structure weaker The misnomer is that 3 compacted layers of woven carbon performs better than 3 layers of non-compacted carbon (assuming that voids don’t exist in either). The compacted layup will be lighter but thinner. The thinner laminate will have a lower flexural modulus due to it’s thinner state. The lower flexural modulus will make the laminate more prone to buckling under compression…which is the downfall of most structures.
I did a round of test samples. All the samples used the same resin and used the same volume of fiber. The only difference was one half of the samples were vacuum bagged and the other half was just a simple unassisted hand lay-ups. The test was an impact drop on a nose cone. The strongest samples in every drop were those that were uncompacted/non-vacuum bagged. The reason: the non-compacted samples had a greater wall thickness which reduced the materials propensity to buckle. The downside to the non-compacted layup is that they were heavier than the compacted lay-up. The downside to the compacted layup is that the wall thickness was thinner. Moral of the story: compacted layups can perform worse than those than that are not compacted (assume an equal volume of fiber).
If you are going to compact a layup you often need to add more fiber to a structure to perform as well as non-compacted layup (although you end up being lighter). On recent project I had to create a very light structure that had to meet a stringent strength requirement. Through testing I found a layup that consistently met the strength tests. I then started increasing the compaction level of the laminate which resulted in a thinner laminate. The parts then started to fail due to buckle failure. Moral of the story: if you are going to boost your compaction level you often need to add more fiber to keep the wall thickness at an adequate level to prevent buckling.
If you have a structure that demands the most strength for the least amount of weight then compaction is must. With compaction you can compress the fiber closer together. This means that less resin is needed between the fiber to transfer the loads from fiber to fiber. This means that you can put more fiber into a structure for equal or less weight than a non-compacted laminate.
The expectations of the laminate dictate the process. Again, many structures can be made to meet the expectations without the use of a vacuum bag, press, or autoclave. A 3/8" thick carbon laminate seems very excessive for a handle. A 3/8" thick 1/2" wide unassisted hand layup could make a handle that had a tensile strength of 12,000 pounds. If you need to increase the strength or reduce weight then some form of compaction could be used. The compaction would allow you to put more fiber into the structure (increase the fiber volume fraction). The increase in the fiber volume fraction would make the handle stronger which would allow you to build a thinner laminate (weight reduction).
I would make a thick laminate with a press to create a consistent thickness. Vacuum bagging will do a poor job at creating a part with consistent thickness and nice finishes on both faces. The pressure applied to the press would dictate the fiber volume fraction. The average clamp torqued to 35 in/lbs will generate 450 lbs of pressure. If your part has an area of 60 sq. in. then a vacuum bag could only generate 880 lbs of pressure. 4 clamps on press with stiff back could give you 1,500 lbs. or more. If weight isn’t a big issue then doing half the layup on a piece of glass, then doing other half on another piece of glass, pressing the two halves together and putting a brick on the top could meet or exceed the requirements. As long as there aren’t to many voids in the laminate due to poor layup practices then the laminate would perform well.
I guess I lied a little bit on the handle. It is actually for a parachute on a drag car. I will post pics tomorrow. (currently traveling home from work away) By all means this thing does not need to be very structural at all! The cable pulls very easily to release the chute. It would mostly be a made in carbon to please the eye. I have no problem vacuuming the part if need be.
I was thinking i could lay up a bunch of layers of carbon in the ruff shape of the piece, then vac. Once cured maybe use the original as a guide for a router, and trim it up to match. I have done similar things tracing like that with a router and a wood template to make a “machined” piece out of aluminum.
Again I will post pics of the piece tomorrow, and look forward to continuing to learn my new found hobby!
With these thick parts, if price is no issue, you could infuse a large number of layers of carbon (I suggest multiaxial instead of woven, except for the outer layers) and either route or waterjet shapes out of it.
The other option is to use a large amount of glass inside. With black coloured resin you will hardly see the difference. Much cheaper though…
Keep in mind that routing carbon with electric tools has a drawback: the carbon dust can short the motor of the tool.
HAHAHAHAHAHAHAHAHAHA Holy crap hojo, that is the EXACT piece I was going to try to replicate! so crazy! well for 45 dollars looks like I wont be trying to make my own, still any guesses on how this piece is made? im guessing its a bunch of layers than water cut or whatever.
Making a part like that is not difficult even without vacuum. I made the first dropouts for a prototype bike frame by making an 8mm plate. I took a steal plate laid up many layers of CF (I think about 30). Wet out every layer before adding the next. Place a second plate on top and squeeze. I put it under my car for pressure. Cut the shape out of the plate with a scroll saw.
Mine are still going strong after 5 years. Here’s a pic before clean up:
The Kevlar was a bitch to cut. I went through at least 20 blades for those two.
^^ Very good post Adam, lots of good info in there, my opinion is a slight bit different but only because of symantics…I think it is healthy for discussions about how and why things are made as each person can take away something from it, so I am not questioning you, just shooting my take on it out there.
In the post above you mention producing a composite piece, lets say a panel with 3 layers hand-laid, wetted out versus 3 layers bagged. You are 100% accurate in your comparison but I would go another direction. If a client proposed a scenario like this I wouldn’t build to a “layer” basis, always to a thickness comparison.
If the laminate is 1/4" thick hand laid, wetted out and not bagged or closed mould infused and a comparison panel was created, 1/4" thick either bagged, LRTM or some other closed mould scenario the compressed panel would out perform the non-compressed. Working to a comparison of compression to non-compression composites should be done on laminate thickness, not how many layers, provided both are void free. This is where the testing comes into play, the question would be how many layers are required to produce a panel less than 1/4" thick while still equaling the structural strength or integrity of the composite non-compressed. Does it make sense to produce it this way, how much stronger will it be? That is usually the scenario we would see in an example you highlighted. Obviously, there are a variant of other factors which can increase or decrease the final result, be it resin type, fiber selection, laminate bulker, etc…etc…
I also agree with your points on vacuum bagging for consistent thickness and surface finish on both sides, however, vacuum bagging is not intended to serve that function. If a required laminate must meet a specific thickness with a +/- ratio tight enough to question a bagged process than a closed mould is the only option to maintain that uniformed thickness through-out. That is not say the vacuum’d version won’t produce the thickness, just not uniformed. The requirement of a double surfaced part is something vacuum’d based moulds cannot accomplish unless a male/female method is introduced which both must have structure to compress.
Regardless, each process has its place, I for one prefer bagged & closed mould methods because of the process integrity versus open moulding.
Agreed. Composites is an interesting science because the processing, fiber orientation, and void content of the laminate will dictate it’s final properties. As long as we create products that meet the design requirement and expectations then everyone is happy.
We have different approaches which is just fine. I start by determining how much fiber it takes to generate the ultimate tensile and compression strength + the safety margin. I’m not looking a total laminate thickness but rather total fiber volume. Then I use various techniques to alter the thickness to generate the required stiffness and buckle prevention.
Extra pressure = More compaction. Compaction is the only way to improve the fiber volume fraction without leaving voids. About the best that you can get with one atmosphere is 50% unless you are using UD materials. If you need to get above that you need more pressure via bladders, presses, or an autoclave.
I used aramide for looks and to give a little more abrasion resistance. This is the contact area for the axle. It also provides a bit of insurance because it won’t fail as easily as carbon. That was important because it was for an experimental bike and I wanted to keep my teeth
I start by determining how much fiber it takes to generate the ultimate tensile and compression strength + the safety margin. I’m not looking a total laminate thickness but rather total fiber volume. Then I use various techniques to alter the thickness to generate the required stiffness and buckle prevention.