In the rapidly evolving world of electric vertical takeoff and landing (eVTOL) aircraft, a pragmatic shift is taking root as Original Equipment Manufacturers (OEMs) refine their production forecasts for 2025. While initial projections may have skewed optimistic, the industry is now diligently aligning these figures with the practical challenges of certification, building infrastructure & scaling production. Nevertheless, this recalibration does not undermine the industry’s resolve to establish robust high-rate manufacturing facilities, pivotal for future growth and sustainability as originally promised during their public debuts via SPACs.
Leading this endeavor are aviation pioneers Archer Aviation and Joby Aviation, each channeling substantial investments into their production infrastructures. Archer has laid the groundwork at its new site in Covington, Georgia, marking the commencement of an ambitious manufacturing journey. On the other hand, Joby Aviation has revitalized a brownfield site in Dayton, Ohio, with plans to invest $500 million and generate around 2,000 jobs to support an annual production target of 500 vehicles. Archer sets its sights even higher, with aspirations to achieve an annual output of 650 vehicles by 2028, while the site is supposed to be support 2,100 vehicles annually after potential further extensions.
These facilities are not mere assembly lines; they are the epicenters where innovative technology meets decades of automotive industry expertise. Archer benefits from significant financial support and manufacturing insights from Stellantis, while Joby has entered into a strategic collaboration with Toyota, leveraging their renowned lean manufacturing processes.
Despite the optimism, significant hurdles remain, particularly in the realm of composite manufacturing, which is critical for eVTOL production. The traditional reliance on aerospace-grade thermoset materials and autoclave processing struggles to meet the demands for high-rate output and sustainability. In response, industry titans like Airbus and Boeing are pioneering alternative methods in preparation of the next single aisle airliner.
Airbus’s investment in its "Wing of Tomorrow" program explores out-of-autoclave technologies, and Boeing’s Truss-Braced Wing (TBW) concept, developed in conjunction with NASA’s HiCAM (High-Rate Composite Aircraft Manufacturing) initiative, seeks to quintuple the production rates of large components like wings and fuselages.
Source: NASA (2023)
The pursuit of alternative processes for high-rate composite output is crystallizing around innovative uses of both thermoset and thermoplastic materials, as long as they can be produced out-of-autoclave to minimize equipment investment cost and long curing cycle times (8-10hrs).
Thermosets:
Probably not as attractive from a sustainability and circularity perspective, but most likely will still be dominantly used especially for bigger structural components.
For smaller components, companies could utilize the advantages of press processes coupled with fast curing resin systems may be revolutionary as we already see them mostly for manufacturing of cabin interiors components. These systems, which can achieve remarkable 5-15-minute cycle times, are a boon for high-volume production environments where efficiency is paramount. The press process typically involves placing fiber-reinforced polymers in a mold which is then subjected to heated presses that facilitate quick curing of the resin. Fast curing resins are specially formulated to react and set within minutes under the influence of heat and pressure, significantly cutting down curing time compared to traditional methods. This rapid curing not only enhances efficiency but also reduces energy consumption and increases throughput.
However, the approach has its limitations:
Size Limitations: The dimensions of the press restrict the size of components that can be manufactured. Larger presses, while capable of handling bigger components, are exponentially more expensive and require substantial space, making them less feasible for many operations.
Investment Cost: The initial capital investment for high-quality, large-scale press equipment can be prohibitive, especially for small to medium enterprises.
When it comes to manufacturing larger components like aircraft wings and fuselage sections, the Automated Fiber Placement (AFP) lay-up process offers a scalable solution. AFP involves the precise placement of pre-impregnated fibers by robotic arms, allowing for intricate designs and optimal fiber orientation that enhances the structural integrity and performance of the composite.
While AFP is already widely in use and on its way to incrementally replace the manual hand-lay-up process the actual time / cost saving starts with the curing process, removing these long-lasting autoclave cycles.
Room Temperature Cure: Here, some advanced composites are given the time to naturally set and harden at ambient conditions. It’s a slower process, a waiting game that demands patience as it can extend production timelines.
Oven Cure: More dynamic and considerably faster, this technique involves placing components into a giant oven. Controlled and intense heat works to accelerate the curing process, dramatically shortening the cure cycle. More importantly, it ensures a uniform transformation across the component, a crucial factor for maintaining the mechanical properties essential for flight.
But our narrative doesn’t end here. To achieve the zenith of manufacturing excellence, particularly at the very joints and interfaces of these composite behemoths, automated bonding solutions play a crucial role:
Automated Shot Blasting: This process prepares the bond lines by roughening the surface area of the components to be joined, which is crucial for achieving a strong and durable bond. The automation of this process ensures consistency and quality, reducing human error and increasing the reliability of the end product.
Automated Adhesive Applications: Precision in adhesive application is key to maintaining the strength of bond lines. Automated systems ensure consistent spread and thickness of adhesives, crucial for structural integrity, especially in safety-critical applications like aerospace.
RTM & Resin Infusion
Both technologies (RTM and resin infusion) are already widely used for manufacturing composite parts in aerospace applications. RTM typically involves injecting resin into a closed mold under pressure, offering precise control and suitability for complex parts, while resin infusion uses vacuum to draw resin into the mold, making it more suitable for larger, less intricate components and offering potential cost savings. While RTM is suitable for highly complex parts it has limitations in terms of dimensions as once again bigger presses are exponentially more expensive. The choice between the two methods depends on factors such as part complexity, part dimensions, production volume, and cost considerations.
The most common catch with either technology is, to save time during the curing process but if companies do not automate the time-consuming stacking of the dry fiber, also called “pre-forming, only half of the battle is won. In either scenario using an AFP and Pick`n`Place equipment is paramount to automate the pre-curing processing”.
Thermoplastics:
Thermoplastics are becoming increasingly favored for their circularity benefits as eVTOL companies are trying to make their sustainability appeal to the public. Unlike thermosets, which cannot be re-melted after curing, thermoplastics can be recycled and reshaped, supporting a sustainable lifecycle for eVTOL components. This recyclability reduces waste and diminishes the environmental impact of manufacturing processes. As demand for eVTOLs grows, spurred by the expansion of urban air mobility markets, the costs associated with thermoplastics are expected to decrease, enhancing their cost-effectiveness and appeal. To clarify, currently the demand remains quite low, which results in high material costs, offsetting the potential cost savings from the post-curing / assembly process. The business model is only viable if economies of scale can significantly lower the cost of raw materials.
Speaking of post curing / assembly processing, thermoplastics allow for various welding techniques that replace traditional mechanical fastening methods like drilling, riveting, and bolting, thereby enhancing production efficiency and contributing to weight reduction. Key welding processes include induction welding, ultrasonic welding, laser welding, and hot plate welding.
These methods not only eliminate the need for holes and fasteners, which can compromise structural integrity but also reduce labor costs and processing times, significantly enhancing manufacturing efficiency.
Welding processes in summary:
Induction Welding: Utilizes electromagnetic fields to generate heat, melting the thermoplastic material to form a bond. This process is highly controlled and quick, ideal for large-scale production.
Ultrasonic Welding: Uses high-frequency ultrasonic acoustic vibrations to create a solid-state weld. This method is best suited for joining small to medium-sized parts and is valued for its speed and energy efficiency.
Laser Welding: Involves using a laser beam as a concentrated heat source to fuse thermoplastic components. This technique is precise and allows for complex joint geometries.
Hot Plate Welding: Where parts are pressed against a heated plate to melt the contact surfaces, which are then pressed together to form a bond upon cooling. This is effective for larger and irregularly shaped components.
While these technologies hold promise, they must yet be fully certified for use in airborne vehicles. Finding the “sweet-spot” for implementing these technologies is crucial, as OEMs and suppliers seek to avoid substantial investments in soon-to-be-outdated technologies such as procuring hundreds of autoclaves or, conversely, premature investment without sufficient demand and rate justification.
Joby’s last year`s agreement with GKN to produce moveable parts like spoilers or ailerons from thermoplastics for their next-generation aircraft represents a strategic, incremental approach to integrating these materials. Starting with high-part-count components like moveables, doors, and propellers allows for a gradual transition to more sustainable materials, setting a precedent for the industry’s forward march toward innovation and environmental stewardship.
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