Carbon fiber bicycle manufacturing method?

How are carbon fiber bike frames made?

I found the following patent, which indicats that an inflatable blow-molded bladder is used to force the material against a mold. Is this typical?

Ahh nevermind, here’s an even better description from a Trek patent:

The frame for a Trek OCLV 5500 bicycle, for example, is formed by joining a set of composite fiber tubes to a set of composite fiber lugs. The tubes are those portions of the frame that form the top tube, down lube, seat tube, chain stays and seat stays. The lugs are the irregularly shaped portions of the frame that form the head lug, seat lug and bottom bracket lug. The lugs are preformed and pre-cured articles fabricated from a composite fiber material comprised of overlaid layers of unidirectional carbon fibers embedded in an epoxy resin. Several layers of material are stacked on top of each other so that the fibers of adjacent layers cross over one another. The stacks of unidirectional fibers are cut into shapes called preforms for molding into a particular lug. The preforms are placed in a mold and arranged around an inflatable bladder. The assembly of preforms is then heated and cured, with the bladder pressurized for urging the respective preforms into the shape of the mold. This method of fabrication provides a high laminate compaction having low voids, which results in a strong, uniform, thin walled, tubular lug. The composite fiber tubes may be formed by a similar method. The separate tubes and lugs are then glued together to construct the frame. Further details of this method of making an all-composite bicycle frame are disclosed in U.S. Pat. Nos. 5,624,519 and 6,270,104 assigned to the Trek Bicycle Corporation.

Kestrel, Look have been making monocoque frames via the layup - close mold - inflate bladder - heatset for decades.

My Orbea Orca frame sparked my curiosity. The unpainted areas reveal the carbon fiber beneath. Nice quality and very form-intensive.

wow…that bike LOOKS fast.

speaking of bike stuff… anyone had any experience getting AL parts prototyped? It would def need to be CNC’d, but what alloy? Grade?
Is it even worth the bother?

I’m thinking of designing a new chain ring and possibly crankarms for my fuji track.

speaking of bike stuff… anyone had any experience getting AL parts prototyped? It would def need to be CNC’d, but what alloy? Grade?
Is it even worth the bother?

Its Possible, but expect to pay more money than you will ever want to. Unless you know someone in a machine shop.

If you’re really going to go after it, 6061-T6 or even 7075 if you can get it are the most common as far as chainrings, etc goes. Other things that are cast might be a slight variation, but you can get plates from almost any major metal supply house. I’ve posted this before, but I’ve always enjoyed this crankset as far as the CNC style goes…

Evidently they’ve delayed the release because it didn’t meet their performance parameters. Something like $900 for the thing, minus rings.

My biz partner says that the problem is that they are CNC as opposed to forged, so they aren’t as strong.

Im not going to go into technobabble here but

The carbon question

Trek technology is old i wont go into details

The aluminium question

a forged part is stronger intrinsically provided it is a part which has been designed to be forged no sharp radii etc added to this you must ensure that the correct alloy is used Just because its 7075 the supposed strongest alloy does not mean that it will be stronger forged 7000 SERIES ALLOY suffer SCC.

There are special alloys with properties geared toward forging that although on paper they seem slightly weaker are much stronger when forged in terms of fatigue.Fatigue or stress corrosion is what makes very high tensile aluminiums fail

The other thing is that most suppliers have little access to so called aerospace alloys and by this i do not mean certified i mean altered metallurgy, only slight in some cases ut it makes them unique.they do vary from commercial alloys.

on top of that you have post processing ,you think anodizing is good? think again it allters surface properties in a way that can induce failures ,most companies claim they know how to manufacture good alloy parts but in truth their post processing is far behind the techniques used in aerospace or even high performance motorsports

Unfortunately if most of these good techniques were applied the part, cost would spiral to a point meaning commercial products were out of our reach.

most companies claim they know how to manufacture good alloy parts but in truth their post processing is far behind the techniques used in aerospace or even high performance motorsports

But have you seen Trek’s current designs? The 08 Madone?

Their carbon process out performs aerospace standards, in fact they buy carbon fiber from US suppliers that also supply sheet to weapons manufacturers and military aircraft manufacturers.

Not many, if any, manufacturers can say that.

Yes I have seen the madone its a lovely shape which has one or two things going for it in the technical advantages department none of it is in the carbon layup processing though.

Their carbon specification/marketing hype says it is better than aerospace standard for void content which is a completely different thing to the actual quality of the final laminate.

Any manufacturer that goes to a carbon supplier can buy aerospace materials again more marketing hype

I think you may find a lot of manufacturers buying carbon from Hexcel

Hello Enthusiasts,
I’m in the market for a carbon tri-bike but I have reservations about the lay-up methods used by many of the popular and even highly regarded brands that I feel are worth sharing with other like-minded enthusiasts.

In the past 10 years or so I have built several carbon fibre sailboat masts and various other components including honeycomb core carbon panels and hollow bladder-molded structural shapes. Through my experience, training as a materials engineer and guidance from friends in the aerospace industry I have learned many of the finer points of building components with carbon and other fibres.

A bicycle frame is primarily a stiffness critical structure which essentially means that additional material beyond the amount required for adequate strength must be added until the structure achieves the desired rigidity. While it is true that damping and other properties are desirable, they are secondary to the requirement of delivering the rider’s power through the transmission with minimal loss – and this means minimal flex at the bottom bracket.

After the shape has been addressed fibre orientation and placement is critical to optimizing stiffness. The object of the engineering exercise is to align the fibres with the direction of the forces that are applied by the operating loads. For example to resist bending a structural shape like a tube requires fibres that are aligned perpendicular to the load applied along its axis; to resist torsion a tube needs fibres aligned axially at +/- 45 degree angles.

Uni-directional prepreg tape is specifically designed to provide optimum fibre orientation for stiffness critical structures. Of course it also offers the lowest possible resin content - in the range of 40 % by weight. Indeed technologies such as pultrusion and filament winding were also invented for this purpose and most simple cylindrical shapes are made using either or both of these.

Woven fabrics on the other hand are not used in stiffness critical structures because their ‘under-over’ weave causes the fibres in each direction to adopt a “wave” profile which makes them initially “stretchy” - up to the point where the fibres have been pulled straight.

The problem with the techniques that so many carbon bike builders use is that they start their lay-up with a layer of cosmetic fabric which creates that black woven appearance you see so often these days. When the frame has cured and is released from the mold very little additional finishing is required other than a coat of clear enamel. After the cosmetic fabric they add various layers of uni-directional prepreg tape cut into different patterns to create the stiffness critical structure. What happens when the mold is closed, heated and the bladders inflated? As you might expect, the bladder compresses the various layers of fibre against the inner face of the steel mold while the thermo set resin melts and fuses them together…but what about the bumpy fabric layer? Again, as you would expect the inner layers of uni-directional tape are forced down over all the little “hills” and “valleys” in the weave of the cosmetic fabric layer. Needless to say, they become anything but “uni” – directional by the time the cure is complete. If you cut open a tube made this way and examine it under a microscope you can clearly see the wavy profile in many of the fibres especially those immediately adjacent to the fabric.

With this procedure, the finished product despite all its ‘high’ modulus hype is considerably less rigid than it would otherwise be had the job been done without the cosmetic fabric layer. Of course, an outer layer could be added afterwards but this would increase the cost – and lower margins - significantly.

At the end of the day I suspect that many carbon bike frames built using this lay-up schedule are adequately stiff owing to other factors such excess material and oversize tubes, but they certainly don’t meet my personal requirement for proper engineering and best construction practices. I will continue to look for a builder who knows his technology and/or won’t allow his commercial interest to compromise his engineering.


have you done that piece of art!? wowwww!!! that s amazing!! congratulations!! what else do you got ! do you have more pictures!!??

Bulldog UK - Sheet metal machinery supplier

Being a materials engineer you are probably way more enthusiastic and critical about your gear than 99% of Tri-geeks who are THE MOST hyper critical riders I know… Please note: that in no way should be construed as an insult.

To add to your comment above, the techniques used in 90% of carbon bike building only allow a 2-3 year shelf life for a CF frame before the $5000 investment starts cracking and “going dead”. But by that time the builders count on you to upgrade to their next $5000+ offering.

Even though companies like Trek and Orbea will claim “Aerospace Grade” fibre, what they cannot claim is that the weave is aerospace grade as most of aerospace companies who use CF have specially designed purpose woven weaves for specific applications.

But back to bikes. You may want to look at Time Bicycles. They buy carbon in spools and weave it in house (as well as Kevlar and Vectran), pull it over steel mandrills and use RTM to form it up.

They do use aluminium lugs for the BB on some of their frames. Aside from the expense i have heard nothing bad in regards to them.

Isn’t carbon fiber technology just over hyped paper mache with fancy materials?
check out this post on bicycle design blog and you’ll see what I mean. 301 moved permanently

I took a look at the Time marketing blurb. They actually say " Unidirectionnal braids offers excellent flex characteristics." I agree, but you might as well use black fibreglass or Kevlar which is far more flexible! Moreover a braid is always bi-directional.

As I mentioned in my initial message, woven materials are not desirable in stiffness-critical structures.

The resin/fibre ratio with RTM is lower than prepregs. This means they are heavier.

Most industry people consider Bob Parlee’s frames the best carbon fiber bikes made in the US.

Outside the US, a tremendous number of frames are made to very high standards.

Basically, it comes down to how much marketing do you want to believe. I 100% guarantee, your local bike shop has been fed a large amount of aerospace “blah blah”. It is your choice to believe it or not.

The bike industry is incredibly small, If you are an inseder, you will hear hundreds of stories. " did you hear the _____ bikes are made in the same factory as the _____" Yes it is true.

being a materials engineer, aside from the marketing hooey. is Time’s RTM lay up “better” than a normal cloth with a higher resin fiber ratio?

I have heard that it is and typically lasts longer before it goes dead…

I ask in all sincerity as someone who is looking for new frame but not interested in “lightweight and stiff” for racing but “compliant, strong and efficient” for longer distance riding and longer life of the frame.

My preference would be Titanium, custom by Tom Kellog, but I have an eye on a certain pre-owned ride…

I’ve ridden many of Trek’s carbon frames, and the new Madone is pretty spectacular. Especially considering I ride a 62cm frame. I’ve heard their sales pitch countless times (working at a dealer) and I’ve heard many others from the likes of Scott, BMC, Titec, Look, and Colnago. None so far have matched the ride quality as Trek in my opinion. Believe me, the last thing I want to do is ride a Trek because everyone has one, but they ride way too nice to ignore.

Here’s a small blurb on their process. Its much more in depth than this though.