Structural composite Beam Crank - A Design to Manufacture Case Study
Project Overview
As part of the development of a modular composite footbridge, Structural Evolution was tasked to design and develop the tooling and manufacturing strategy for a critical structural component known as the beam crank.
The beam crank forms a key transition node within the bridge structure, connecting the horizontal deck to a stair section descending at approximately 20.3°. The component was required to integrate seamlessly within the bridge’s modular structural system, where pairs of beams sit within prefabricated modules to create a continuous structural base for the deck system.
To satisfy these geometric and structural constraints, the beam crank was developed as a trapezoidal hollow composite section, allowing it to fit within the modular frame envelope while efficiently transferring loads between the deck and stair structures.
Design Strategy
The component geometry presented several manufacturing challenges due to its complex curvature, varying section geometry, and closed structural form. To address these constraints, Structural Evolution designed a multi-part mould system and resin infusion strategy capable of producing the component as a fully closed, single-piece hollow structure.
The mould system was designed as a two-part base and lid assembly incorporating integrated vacuum ports, sealing interfaces, and locator systems, enabling controlled resin infusion across the entire component length of approximately 2.5 m. The tooling itself weighs approximately 285 kg and was engineered to produce structural composite components with an approximate finished mass of 200 kg.
The beam crank components were manufactured using E-glass multiaxial non-crimp fabrics (NCF) infused with a bio-based (InfuGreen 810 / SD4771) epoxy resin system, providing a high‑performance structural laminate suitable for civil infrastructure applications while supporting more sustainable material choices.
Structural Evolution was responsible for the design of the mould tooling and infusion methodology, as well as leading and overseeing the manufacturing process with the factory, ensuring that the component could be produced reliably using vacuum infusion techniques.
The overall design approach and customisation provided a robust tooling solution capable of delivering repeatable quality and dimensional accuracy while accommodating the complex geometry and sealing requirements associated with a single-shot hollow infusion process.
A key aspect of the beam crank project was the integration of additive manufacturing techniques into the composite tooling development process.
Custom Seal Development
Maintaining vacuum integrity across a multi-part mould assembly is essential for successful resin infusion. Structural Evolution utilised in-house 3D printing to produce moulds used for casting bespoke silicone seals tailored specifically to the mould interface geometry. These custom seals provided reliable vacuum sealing in areas where conventional sealing solutions were unsuitable.
3D Printed Seal Formers
Additive manufacturing also supported the tooling lay-up process. Seal formers were produced using 3D printing to create precise recesses in the mould surfaces that house the silicone seals. This allowed highly complex geometries to be produced rapidly and accurately while reducing manual fabrication and improving repeatability.
Digital Design Integration
The use of CAD-driven design and additive manufacturing allowed tooling components to move directly from digital models to physical parts. This approach reduced development time while improving tooling accuracy and enabling rapid iteration during the mould development process.
Single-Shot Hollow Infusion
The beam crank was required to be manufactured as a fully enclosed hollow section, eliminating secondary bonding operations and improving structural continuity. Achieving this through single-shot vacuum infusion required careful planning of resin flow paths, internal consumables, and vacuum control to ensure complete fibre wet‑out and avoid void formation.
Sealing Complex Mould Interfaces
The multi-part mould assembly included numerous sealing interfaces between removable mould sections. In vacuum infusion processes, maintaining a fully sealed mould is critical because any leakage can disrupt resin flow and compromise laminate quality. The geometry required bespoke sealing solutions tailored to the mould interface.
Tooling Precision and Repeatability
(Despite the relatively small production run of four structural components,) the tooling needed to deliver consistent dimensional accuracy and repeatable manufacturing quality. Locator systems, controlled bolt clamping, and integrated vacuum ports were therefore incorporated into the mould design.
Project Outcomes & Lessons Learned
The beam crank tooling programme successfully demonstrated how design-for-manufacture principles, advanced composite engineering, and additive manufacturing techniques can be combined to produce complex structural components for civil infrastructure applications.
The tooling system enabled the successful production of four fully enclosed hollow composite beam crank components using a single-shot infusion process. The approach eliminated secondary bonding operations while delivering the dimensional accuracy and structural integrity required for the bridge structure.