Stirling Dynamics’ approach to AM application spotting
Aerospace engineering company identifies AM use cases like customizable seat blockers
While the integration of additive manufacturing for aerospace applications largely brings benefits like reduced lead times, customization opportunities and enhanced performance, there is still the question of when to use the technology. In other words, when will it have the greatest impact. Stirling Dynamics, an EASA 21.J-certified design organization specializing in aerospace and aviation engineering, has developed a reliable process for this that enables its clients to really make the most out of additive technologies.
“Our core offering is design and certification, but the fun part comes when we start developing products,” explained Henryk Bork, Head of Aviation at Stirling Dynamics. “This is what you can touch and feel. It’s where we can delight our customers because we are experts in niche and bespoke product design. Whenever they are unhappy with the performance, lead time, or cost of an OEM part, we love taking on the challenge of improving this—it’s what drives us.”
Bork and his team are distinctly skilled at finding use cases for additive manufacturing and have created an internal process for evaluating every application. “We developed this process for several reasons. Not everything becomes a 3D printing project, and we have to be very careful. Developing a part and bringing it up to an EASA Form-1 approval is a very time-consuming process for all involved,” he added. “We first need to check whether 3D printing is applicable, then consider our internal policy of never copying a part.”
The first step in the application spotting process involves a root cause analysis, which seeks to identify why the original component was a pain point (this can be anything from lead times to performance failures). From there, the Stirling Dynamics team can conduct a feasibility study which evaluates whether the application makes sense from a business perspective. Notably, the company’s partnerships with Materialise and aircraft part distributor Proponent, often enable it to bring its certified solutions to a broader range of customers, which can actually improve the business case. “Finding customers with similar needs gives us a clear indication that there’s potential, there’s a pain point worth solving, there’s a niche to produce this part and bring it to a wider audience,” Bork said.
To date, the company has developed a range of aircraft products that leverage additive manufacturing, including a repair kit for a decompression panel (dado panel) for the Boeing B737 and a multi-functional seat blocker. Seat blockers were developed during the pandemic in order to remove seats from the schematics for social distancing purposes. Now, these products are being repurposed to “offer extended comfort”. 
With a focus on comfort, the newly designed seat blocker integrates a number of features, like document pockets, cup holders and detachable 3D printed slots for chargers and devices. “We worked on a new design, put it through the testing phase, and began manufacturing,” said Sergey Gettinger, Chief Design Engineer at Stirling Dynamics. “The shape is roughly the same as the original, but we improved the inserts and the cupholders.”
The 3D printed components are designed for easy integration into a foam base, resulting in an overall weight of just 1.5 kg. The design had to be strong enough to maintain its shape and function while also be light enough that it wouldn’t hurt someone if they fell on it. The seat blocker, which is secured in place using the seatbelt, is finished in handcrafted leather, which can be customized in terms of color. The 3D printed inserts can also be customized to include the aircraft company’s logo.
“It would be impossible to balance the tooling costs with any other method,” Bork said of this application. “There are no other options if we wanted to bring this part to market because the costs are reasonable for the recurring part. Otherwise, we would need a minimum order quantity, and that’s very difficult when you start within a niche.” Moreover, Materialise is certified to make the product and other flight-ready ready parts with a lead time of just three weeks.
As the final stage in Stirling Dynamics application spotting and product development process, the company makes a point to involve the customer. Specifically, the company has a three-stage trial process for obtaining feedback. “We send prototypes to make sure fit, form, and function are guaranteed and meet their expectations,” Bork added. “Because it’s 3D printed, we can easily adapt whatever needs adapting and do another loop, then agree on a trial period of one to three months. That trial series provides us both with information we don’t have: how will it handle fatigue and in-service performance, such as yellowing from exposure to sunlight, for example? We’ll go through all of that before we finalize the part, taking away some of the risk of adopting a newer technology like this.”
To date, Stirling Dynamics has applied this approach to low-criticality parts for commercial airlines, leveraging polymer 3D printing technologies to produce a range of replacement parts and helpful products like the seat blocker. In the future, the company is also interested in exploring more uses of additive manufacturing for aircraft, including exploring metal additive manufacturing for more critical applications like structural repairs.
