How TIME Makes Carbon Reinforced Bike Parts

TIME Sports in France makes carbon fiber bike products. They have been a leading brand since the early 90's. Time's forte is that they weave their own carbon fiber, instead of buying flat pre-preg sheets from someone else like the rest. They did this by mastering Resin Transfer Moulding, a type of moulding process that enables the manufacture of high performance and complex fiber reinforced composite parts with two moulded surfaces. 

Some characteristic features of this method differentiates it from other processes :

1)  A two part, matched metal mold is filled the pre form of the part (a fiber reinforced skeleton of the actual part) and is closed before resin is injected to fill the inter-fibre spaces. While this produces components with superior dimensional tolerances on one hand, it also reduces the dangerous emissions that workers will otherwise face in traditional methods such as spray or hand layup. Note that the heat curing of the resin for polymerization requires the use of a metal mold.

2) Low viscosity resin (200-600 centipoise typically) is injected into the mold at moderate pressure (50-100 psi typically) which ensure wetting of all reinforcing surfaces and filling in all voids.

3) A longer range of flow of resin through the fiber tow or fabric as opposed to the shorter range from other manufacturing methods. 

All this high tech allows TIME to charge a premium for its bikes. Hence, its not cheap. Some of the higher end bikes are in the 6000-7000 dollar price range. Mamma mia!

A month back, a video was posted on the internet describing how Time makes carbon reinforced composite parts. It was very interesting, to say the least.

From a technical standpoint, I found the information on Time's website not bad for learning about this technology. Other carbon bike makers hardly have the time to provide you with this kind of literature.

Enjoy the video (courtesy ucallrt), and the supplemental reading from TIME's website.

I. MAKING THE BRAIDS AND POSITIONING

TIME uses two types of tubular braids for its carbon products: unidirectional and bidirectional. The threads kaleidoscope into an unending tubular weave that is later cut according to the required dimensions. The weaves of the tubular braids differ in both the direction of the weave and the threads used.

1) Bidirectional braid : Tubular weaving of the carbon strands, varying the weave angle between 15 and 60°  depending on the desired dynamic flexural and torsion properties. This type of braid offers very good crack resistance and carbon fibers can be mixed with other type of fibers such as Vectran or Kevlar. 

The mechanical properties of a tubular braid depend on 4 parameters :

a) Quality of the actual fiber: HM, HR, Vectran, Kevlar, …
b) Number of filaments: 3000, 6000, 12000
c) Number of threads in a braid : 24, 48, 96, 120, 144, …
d) Angle of the weave : The mechanical characteristics of the braid vary depending on the angle of the weave, vary between 15 and 60°. The closer to 45°, the better the torsion properties of the braid. The smaller the angle, the better the resistance to flex.

2) Unidirectional braid : Tubular weaving of the carbon fibers in which the carbon strands are parallel. This type of braid offers excellent flexural properties and can be fully customized according to the desired mechanical properties. Polyamide fibers with special shock absorbing properties are incorporated in some of these braids. These filter out the imperfections of the road.

The mechanical properties of a tubular braid depend on 3 parameters:

a) Quality of the actual fiber: HM, HR, Vectran, Kevlar, …

b) Number of filaments: 3000, 6000, 12000

c) Number of threads in a braid : 24, 48, 96, 120, 144, …

The manufacture of unidirectional and bidirectional tubular braids from pre-selected fibers allows TIME to accurately position them on the basis of the properties sought without disturbing their continuity. 

This is the first stage of TIME’s Resin Transfer Molding (RTM) technology, a three-step process that enables TIME to fully control the content and quality of its carbon fiber tubing.

II. MANUAL FIBER LAY-UP

The second step of RTM technology is manual fiber lay-up. Fiber lay-up starts with either steel or wax mandrels which act as the molding components that form the interior shape onto which the carbon braids will be cast, specific to the tube or joint being produced. The most complex designs use wax mandrels, which are melted out, after the carbon-setting process.The mandrel is sheathed with 5 to 8 layers of carbon fiber weave. The final layer is bonded with adhesive powder that stops it from moving against the other layers and prevents distortions of the weave pattern, despite the complex nature of various joints, including the bottom bracket. This guarantees the cosmetic appearance of the carbon fiber, visible through the clear finish.

III.  MOLDING

Molding is the third part of the RTM process. It is done with a two-part epoxy resin that is injected into the mold and left to harden. This phase is named polymerization and lasts approximately 30 minutes. 

A standard carbon fiber molding process using an inflated bladder to form the interior shape of the part tends to produce a part that looks perfect from the outside but can contain inconsistencies within. TIME’s RTM process prevents this because the resin penetrates completely into the fibers throughout the mold, with the part's design shape strictly controlled by the use of both outer and inner molds. This technology is extremely useful because, unlike steel and other metals, the carbon fiber is stronger where it is thinner and where all layers have achieved ideal fiber compaction, rather than thicker, where they haven’t.

IV. MACHINING

After the three-phase RTM process, TIME’s head tubes, lugs and bottom bracket shells are then sent out to be machined. Machining guarantees total dimensional precision and the flawless surface of all the parts prior to the bonding stage. Both the carbon parts and the aluminum alloy parts are machined. The machined tubes and lugs are then laboriously and meticulously hand sanded.

V. BONDING

The different machined parts and tubes are then bonded by hand. Latex gloves are used all times to ensure that even the smallest amounts of grease that might affect bonding are not transferred across onto tubes and lugs. Tubes and lugs are bonded using an aeronautical quality epoxy adhesive. Each tube is produced based on its specific position and the stresses the entire frame is subjected to. Temperature is kept at a constant 23°C in the bonding shop so that the adhesive used by TIME remains at the right level of viscosity to ensure an ideal bond.

Once bonded, the tubes and lugs are installed onto a pressurized jig and stored for a minimum of eight hours. This process both results in completely secure joints and the perfect alignment of the frame.

After bonding, we are left with a crude version of the final frame. Until 2006, TIME had used aluminum dropouts on all of its models, Carbon Matrix technology (CMT) has been introduced to the top of the range models. CMT is also used for other small parts such as screws.

VI.  PAINTING AND DECALS

After bonding, all that remains in the production is painting and the application of decals.

The paintwork, application of stickers and varnish is what gives the TIME modules their identity, a combination of toughness and refinement, responsiveness and sensuality. All of the details that make up this aesthetic racer are applied in a crucial and time-consuming operation. During the last stage of finishing and testing, of production, TIME conducts rigorous and comprehensive checking of the finish quality of the module and its components.

The final parts are also attached (front/back derailleur hangers, housing stops, seat collar, seat clamp…) and the module is assembled (fork, stem, seat post).

Additional Reading : Lecture C6 : Resin Transfer Moulding , Composites And Design Manufacturing Course Taught by John Summerscales, UK.