The manufacturing of carbon tubes for bicycle frames involves the use of specialized molds and a process called molding or lamination. We have already discussed the difference between a monocoque frame and a hand-wrapped one. Now, let’s delve into the specifics of the molds, which, in the case of the monocoque frame, represent the entire shape of the frame, whereas in the case of the hand-wrapped frame, they are used to produce the tubes that will later be joined together through gluing and layering.
Here are the main steps in preparing molds for carbon tubes or for junctions and other parts of the frame.
The molds are made in two parts and are often constructed from materials such as aluminum or steel. Before the process begins, the molds need to be thoroughly cleaned and prepared to receive the carbon fiber material.
Cutting Carbon Fabrics
Carbon fiber fabrics are cut into specific shapes based on the tube design. These fabrics can be unidirectional, bidirectional, or in honeycomb weaving, depending on the required properties for the tube.
The resin, acting as a binder for the carbon fiber, is carefully prepared by mixing catalyzing agents, additives, and possible reinforcements if needed.
Laminating Carbon Fabrics
The carbon fiber fabrics are placed into the prepared molds. Several layers of fabric are layered to create the desired thickness and properties for the tube. During this phase, resin is applied to the fabrics to fully impregnate them. A skilled craftsman inserts additional layers of carbon fiber at points under higher pressure, providing the best orientation based on the specific area.
Mold Closure and Pressing
Once the fabrics are positioned in the molds, the two sides of the mold are joined and sealed tightly. Then, the material undergoes pressing, often using a combination of heat and pressure, allowing the resin to polymerize and solidify, thus creating the shape of the tube. All of this occurs under vacuum.
Curing and Hardening
After the pressing phase, the tube inside the molds is left to rest to allow the resin to completely harden. This process can take several hours depending on the type of resin and working conditions.
Extraction and Finishing
Once the material has solidified, the tube is extracted from the molds. It then undergoes finishing processes, which may include removing excess material, trimming edges, and checking measurements and specifications.
This detailed process is essential for producing high-quality carbon tubes that are subsequently assembled to create lightweight, strong, and high-performance bicycle frames. The quality of work done on the molds not only affects the yield of the frame but also significantly impacts its robustness and durability.
The quality of the molds also significantly impacts the final result. An old and worn-out mold will create carbon parts with a few tenths of a millimeter of error. This discrepancy – seemingly minimal – cannot be rectified or smoothed during the frame manufacturing process and will result in a difference in the frame’s final ability to flex and withstand stress.