Full-flight qualification for F-16 aircraft additive manufacturing spare part in just 30 days

Engineers from nTop, Origin, and Stress Engineering Services collaborated to redesign a family of F-16 aircraft hydraulic tube clamps for Additive Manufacturing. The final part was 2x stiffer than the legacy design, was easier to assemble, and was manufacturable on-demand.

Within 30 days the team completed the project and passed the full-flight qualification criteria set by the US Air Force’s Rapid Sustainment Office.

They used a design-optimize-build-test approach with cutting-edge design tools and manufacturing technologies and delivered a proposal that exceeded the US Air Force’s requirements.

The result was a reusable methodology for qualifying new components. What’s more, the team was awarded 1st place in the US Air Force’s competition and received $100k in prize money.

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Technical takeaways

• Follow a design-optimize-build-test approach rapidly qualify additive manufacturing components for aerospace applications
• Develop reusable design workflows to perform more iterations and accelerate your simulation, testing, and development processes
• Apply automated post-topology optimization smoothing to reduce the peak concentration of stresses by up to 50%

Business value

• Time advantage: Accelerate your tried-and-tested engineering design process by leveraging cutting-edge engineering software
• Digital supply chains: Manufacture spare parts on-demand and on-location bypassing legacy restrictions and cutting overall costs
• Highest-performing products: Apply the latest engineering product development techniques to exceed design requirements and win more contracts

Key statistics

• Part strength: 2x stiffness
• Weight reduction: -5% weight
• Design cycle: 30 iterations in 30 days
• Peak stresses: -50% after smoothing
• Manufacturing process: Programmable Photopolymerization (P³) by Origin
• Material: FST photopolymer

Introduction

The U.S. Air Force’s Rapid Sustainment Office (RSO) held an advanced engineering competition where teams were presented with some of the Air Force’s most pressing technical problems. Solving them helps the Air Force maintain and modernize its aircraft fleet. This year’s challenge in the Approval Sprints category: produce a stronger, more durable hydraulic line clamp for the U.S. Air Force’s fleet of F-16 aircraft.

Engineers from nTop, Origin, and Stress Engineering Services teamed up to tackle this challenge. They combine their unique expertise in engineering design, analysis, advanced manufacturing, and optimization to redesign the C3175-9J hydraulic line clamp. By following a design-analyze-optimize-print-test methodology, the team managed to exceed RSO’s design requirements to win 1st place in the RSO’s challenge.

In this case study, we will focus on the design methodology that the team followed to arrive at the final design. This is just an example of what can be achieved by combining proven and trusted approaches to engineering with cutting-edge design and manufacturing technologies.

The design challenge

The US Air Force has thousands of hydraulic tube clamps in service across its fleet. These clamps fail after a certain amount of time due to exposure to vibrations, chemicals, and heat. For this reason, replacement parts must always be in stock. The assignment given by the Air Force’s RSO was to redesign and qualify a family of clamps that are used throughout the F-16 aircraft for Additive Manufacturing.

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By updating and digitizing its supply chain, the Air Force can eliminate the shortcoming connected to traditional manufacturing processes. In this case, the legacy design was either CNC machined from a material that produced toxic fumes, or injection molded with long lead times and at high storage cost.

The new design must exhibit the same level of performance as the legacy and should be able to be rapidly deployed to sustain the operations of an F-16 Fighter Jet. The list of design requirements given by the RSO to the eight competing teams can be found below.

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The new hydraulic clamp

The new design consists of three parts: two clamp halves and a flexible tether. The two clamp halves were designed and optimized to maximize their performance. The clamp is able to carry double the load of the legacy design while being 5% lighter.

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One of the most innovative features of the design is the flexible “lanyard” tether that holds the two clamp components together. It allows the clamp to be stored as one piece, enables fitting with one hand by the technician, and it is tearable after the installation.

The clamp halves were 3D printed using Loctite 3955, a flame-retardant, chemically resistant thermoset material. The tether was manufactured using the elastomeric IND402. Both materials were developed by Henkel and were specifically formulated for applications in the aerospace industry.

For the purposes of this design challenge, the team 3D printed a batch of 27 clamps. Production took 24 minutes followed by a 20-minute post-processing UV radiation step. All told, over 1,200 clamps can be manufactured in one day at a cost of $1.25 per part. Taking into account the increased part performance, it is easy to understand how this on-demand manufacturing process greatly outperforms its legacy counterparts.

Every part is serialized to ensure part traceability, provenance, and inventory management. This is yet another way in which additive manufacturing combined with design automation can greatly improve the efficiency and reliability of the manufacturing supply chain.

The design methodology

When evaluating proposals, the RSO gave a big emphasis on the qualification strategy — 50% of the judge’s score. The Air Force was particularly interested in identifying processes that can reduce the time, cost, and risk associated with qualifying new designs.

For this reason, the team focused on developing a methodology that could be easily replicated and reused to create libraries of high-performance 3D printable parts that are manufacturable on-demand. The team followed a design-optimize-build-test approach to reach the final result:

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Here’s a breakdown of the steps they followed:

• First, they reverse-engineered the legacy clamp design to determine the loading conditions. The material properties and technical specifications of the original design were unknown, so conservative assumptions were made to catch all cases.
• Then, they used the nTop’s topology optimization tools to determine and visualize the load paths. Based on these results and their engineering intuition, they drafted possible solutions in CAD and evaluated their performance using FEA.
• To further improve the performance of the part, the team used nTop’s smoothing functionality. This step had a significant impact on the final result as it reduced the peak stresses by more than 50%.
• Finally, test samples of the candidate geometries were 3D printed in two different materials and tested in the lab under different conditions. The results of these tests were then used to further improve the performance of the design and validate the material properties of the manufactured part.

When new information became available (for example, experimental results) or when fundamental changes needed to be made to the design (for example, a new material or new loading conditions) the design engineers were able to generate new geometry simply by altering the inputs of their workflow in nTop. This enabled the team to kickstart a new iteration of analysis, evaluation, and testing at a speed that would be impossible if they’d used only traditional CAD software.

The team evaluated over 30 designs in a short time frame of 30 days. This was only possible due to the reusable design workflows that the team created using nTop.

The optimization process

One of the key steps that set the team apart from other submissions to the competition was the method they used to optimize their design.

In addition to using topology optimization to identify the loading paths, the team took advantage of nTop’s automated smoothening capabilities to post process the geometry. The result: 50% reduction in peak stresses. This important design post-processing step was enabled by nTop’s unique core modeling technology and was carried out without user input.

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The team also took advantage of an extensive simulation package to test the candidate solutions for fatigue strength, grip force, pull-out breaking force, and behavior during take-off and landing. These simulations enabled them to limit the experimental validation steps to a minimum, accelerating their development process.

The next steps

The hydraulic tube clamp design and manufacturing approach is currently under detailed examination by the US Air Force for further implementation. Upon approval, the team will proceed with applying the same process to redesign the other members of this part family. Because of the work done, the redesign qualification will be even faster, as a robust methodology has been already established.

If you want to learn more about this project, we hosted a webinar in collaboration with Stress Engineering Services and Origin. The engineers that lead this project dove into the details on all aspects of the design, manufacturing, and qualification steps. The webinar recording is available to watch on-demand.