Design of a Carbon Fiber Bicycle Stem Using an Internal Bladder and Resin Transfer Molding

摘要

The goal of this research is to design, analyze and manufacture a carbon fiber bicycle stem that maximizes the use of carbon fiber composites. The stem is the part of the bicycle that connects the handlebar to the fork. The design is difficult due to the small size and complex geometry of the part, thus not obvious to conceive with a standard composite manufacturing approach. The major problems are: the integrity of the part, the fastening method, the injection process and the post-molding operations. This project is the result of several design iterations. Early prototypes allowed identification of the basic structural, aesthetic and manufacturing problems. In conjunction with a bicycle manufacturer, essential features (e.g., length, weight) were defined. With all the required specifications and the experience of the early prototypes, a general manufacturing plan was devised. Work began with a concurrent design and analysis process, where shapes would be designed on a 3-D CAD system and sent to finite element analysis software to find weaknesses and allow modifications. The machining and preparation of the prototyping molds followed the design stage. The molds were used to experiment with the injection and curing processes where several matrix systems were evaluated. After a limited production of prototypes, a set of jigs was designed to perform the post-machining operations and a series of tests was run to detect any possible flaws in the design. The resulting design was successful in terms of weight, stiffness, strength and aesthetic properties. Finished parts weighed below 125g and demonstrated sufficient torsion and bending stiffness values. Even though the process is here applied to a composite part for the sports industry, the manufacturing techniques developed in this project can be applied to many other fields such as aerospace or automotive. The techniques can be used anywhere where a small, complex, hollow composite part is designed, especially where existing manufacturing methods prove difficult.