A Step-By-Step Guide
To FACT Carbon Manufacturing
Step 1: Tooling
The first step is for us to create a custom-made steel mold that defines the exact outside shape and surfaces (the part of the frame you can see) of the frame. Depending on the part it’s being created for, a steel mold may take 8-12 weeks to make. Why so long? Because it’s a big chunk of steel that’s precision CNC’d, weighs a few hundred pounds, and must be accurate to within a few thousandths of an inch in every aspect. A finished frame section or part comes out weighing just a tiny fraction of the tool. Assuming the mold is made correctly, the finished part will have the same level of accuracy as the mold.
Step 2: Layup and Pre-form
In this important step to the manufacturing process, flexible sheets and pieces of prepreg are wrapped over a pre-form mandrel and assembled into the shape of a frame, fork, or part according to a heavily revised Layup Schedule Development. Arguably, a pre-form can be anything; a round tube, the nylon bladder used to mold the frame, or even just a piece of wood. But in the case of our highest end bikes, we want the pre-form shape to mimic the shape of the mold cavity as closely as possible. So we take the time to engineer a mold for all of our pre-forms and invest in the tooling required to make some of the most advanced mandrels used in the composites industry. These super accurate pre-forms allow us to mold very complex shapes (like the Shiv’s seat tube or the bottom bracket of the Tarmac SL3) and optimize fiber alignment, which is key to achieving the ultimate in stiffness.
Next, we place an air bladder made of pressure-resistant nylon inside the flexible composite layup structure. Its function is to internally pressurize the composite material in the layup against the tooling surface to eliminate internal voids in the composite structure. By using silicone lining in conjunction with the bladder during molding, we can ensure adequate compaction in areas with complex geometry. Still pliable, the entire prepreg assembly, including the bladder, is placed inside its big steel mold. The multi-piece mold is closed and locked down, and the bladders are connected to pressurized air fittings.
Step 3: Molding
The closed mold moves on a conveyor into an electric hot press where its temperature is raised to 155°C (that’s 311°F or 428.1 K.) The high temp allows the resin in the prepreg to liquefy and spread uniformly in the composite layup. To help aid in the process, the bladders inside the prepreg assembly are pressurized to 150 psi. This mixing of resin in the carbon fabric is called “wet out”, a critical component to the integrity of the molded structure. Too little pressure in the bladder and the composite won’t wet out effectively, leaving high-resin areas that add useless weight and low-resin areas that weaken the structure. Too much pressure and the resin gets squeezed out of the composite altogether. Correct wet-out pressure forces between 4% and 8% of the resin out of the prepreg. Note: Some manufacturers claim “ultra-low” resin content. This is not good!
The mold stays at this temperature for about 30 minutes depending on its size, then it must cool down. Due to the size and mass of the steel tooling, this takes another 20-30 minutes. Once the frame inside the mold has cooled enough, the resin is cured and cannot be changed. If there is even a minor defect or issue with alignment, the entire frame must be scrapped. These types of unchangeable composite structures are called thermoset; structures made with a different matrix that can be re-heated and changed are called thermoplastic.
Details on our Layup Schedule Development (LSD)
The anisotropic (directional-specific) nature of advanced composite materials allows Specialized engineers to use weaves and ply designs to create carbon structures that are stiffer in one or more axes, while remaining more compliant in others. Engineers can also tune the weave structure, ply angles, fiber alignment, and layup patterns of a particular frame or component to optimize performance characteristics for its intended use. The resulting pattern of layers of carbon fibers is called a layup. The overall protocol we use at Specialized for developing layups is called Layup Schedule Development or LSD.
The major layup in the top tube and down tube of our frames is composed of multiple layers of uni-directional carbon sheets in different angle orientations. Some fibers run fore/aft (i.e. along the “axis” of the tube) and are referred to as “zero” fibers. These fibers give the frame a lot of strength for in-line impacts and loads and make the frame resistant to bending. Some fibers run at angles of plus or minus 45°, 30° or 22.5°. These fibers give the frame its torsional (twisting) stiffness.
Each frame has a detailed laminate schedule. The tubes have five or six main plies, but there are over 100 pieces of carbon fiber in a frame’s layup—precisely why LSD is such an involved process. Placement of smaller pieces of carbon fiber at tube junctions minimizes overall weight and helps the joints handle loads. From the largest to the smallest, every sheet or piece of carbon is cut and placed by hand, making staff training and quality control a top priority. Once completely assembled, the carbon fiber layup is called a pre-form. At this state, it’s pliable and ready for molding and curing.
Proprietary Manufacturing Methods
Once the individual monocoques for a FACT frame are molded, they must be assembled into a finished construct. We could use any number of different manufacturing methods for accomplishing this, but after years of refining thousands of frames, we’ve settled on two advanced and precise methods: FACT IS (Integrated Structure) and Triple Monocoque.
FACT IS our most advanced carbon construction method. By separating the frame into four large monocoque structures—head tube/top tube/down tube, seat tube, seatstays, and one-piece bottom bracket chainstay—this method allows the carbon fibers to run continuously from tube to tube, offering advantages in weight, stiffness, and strength.
FACT IS frames include:
ROAD — S-Works, Pro, and Expert models of Tarmac, Roubaix, and Ruby; all Amira and Shiv models
MOUNTAIN — Epic S-Works, Marathon, Expert, and Comp models; Era S-Works and Expert models; Stumpjumper FSR S-Works, Pro, and Expert models; Enduro S-Works and Pro models
Triple Monocoque is a balanced approach to frame assembly that minimizes seams and redundant materials. The main triangle, chainstays, and seatstays are each created as a single monocoque structure and then joined together at the dropouts, bottom bracket, and seatstay/seat tube junction using aero-space adhesives and a final carbon wrap.
Triple Monocoque frames include:
ROAD — Tarmac Comp and Elite models; Roubaix Comp, Elite, and base-level models; Transition S-Works, Pro, Expert, and Comp models; Ruby Comp and Elite models
MOUNTAIN — Stumpjumper HT S-Works, Marathon, Expert, and Comp models; Stumpjumper HT 29er S-Works and Expert models