Metal-printing a flight-ready radio frequency filter

Edited by Elizabeth Engler Modic

Direct metal printing (DMP) may have reached the tipping point in aerospace, jumping beyond prototyping in the past two years to production parts and flight-ready assemblies.

During that time, Airbus Defence and Space worked with 3D Systems to achieve a breakthrough: the first 3D-printed radio frequency (RF) filter tested and validated for use in commercial telecommunications satellites. The project built upon research funded by the European Space Agency for optimizing waveguide components using additive manufacturing.

Metal RF waveguide filters act like traffic cops, allowing selected channel frequencies to pass through while rejecting frequencies from signals outside those channels and date to the first space communication systems nearly 50 years ago. An industry trend is to increase the capacity for multiple beams within a single satellite. A high-capacity satellite, such as the Eutelsat KA-SAT manufactured by Airbus Defence and Space, carries nearly 500 RF filters and more than 600 waveguides. Many of these are custom-designed to handle specific frequencies.

Meeting critical mandates

Sending a telecommunications satellite into a geo-stationary orbit can cost as much as $20,000 per kilogram, emphasizing the need to reduce weight. Continuing design innovation and reduced production time are also major priorities, as most satellites are designed for a 10-to-15 year lifetime.

These priorities make telecommunications satellites an ideal candidate for direct metal printing (DMP). The 3D Systems ProX DMP 320 used in the Airbus RF filter project enables manufacturers to:

• Consolidate parts
• Improve functionality with shapes and surfaces not possible via traditional manufacturing
• Reduce production time and lower costs for customized designs
• Decrease weight while maintaining or improving material strength

RF application

3D Systems in Leuven, Belgium, has been using the 3D Systems ProX DMP 320 since the machine was in beta development. Successful projects include topological optimization, weight reduction, and parts consolidation for spaceflight-validated parts such as brackets and strut end-fittings for telecommunications satellites. The Airbus Defence and Space project was 3D Systems Leuven’s first foray into RF filters.

The ProX DMP 320’s architecture, designed for heavy-duty metal parts production, simplifies setup and can produce part geometries in titanium, stainless steel, aluminum, nickel-chromium, and other alloys.

Exchangeable manufacturing modules increase versatility and reduce downtime when moving among different part materials. A controlled vacuum build-chamber prints every part with verified material properties, density, and chemical purity.

Disruptive design

The Airbus Defence and Space RF filter project demonstrated 3D printing’s ability to enable design innovation for aerospace parts that haven’t changed appreciably in decades.

RF filters traditionally have been designed based on libraries of standardized elements, such as rectangular cavities and waveguide cross-sections with perpendicular bends. Shapes and connections are dictated by manufacturing processes such as milling and spark eroding. As a result, cavities for RF filters typically need to be machined from two halves and bolted together, increasing weight, adding an assembly step, and requiring extra quality assessment.

Designing the parts for 3D printing enabled Airbus Defence and Space to explore complex geometries without increasing manufacturing cost. Engineers used CST MWS, a standard 3D electromagnetic simulation software tool, to design the RF filters for 3D printing, The design features a depressed super-ellipsoidal cavity to channel RF currents and delivers the required tradeoffs between Q factor – a measure of a waveguide’s efficiency based on energy lost – and rejection of out-of-band signals.

“The disruptive innovation lies in the fact that pure functionality, not manufacturability, now determines how the hardware will be designed,” says Koen Huybrechts, project engineer for 3D Systems Leuven. “This project is a classic example of ‘form follows function.’”

“The main benefits of a monolithic design enabled by 3D printing are mass, cost, and time,” says Paul Booth, the RF engineer for Airbus Defence and Space in Stevenage, United Kingdom. “The mass is reduced because there is no longer the requirement to have fasteners. With direct metal printing, there is also the no-cost bonus to have the outer profile more closely follow the inner profile, so only the necessary metal needs to be used. The cost/time benefit comes from the reduction in assembly and post-processing.”

Rigorous testing

At its Stevenage facilities, Airbus Defence and Space tested three aluminum samples printed on the ProX DMP 320 using different processing paths. Tests mimicked conditions the parts would face during launch and orbit, including vibration, shock, temperature extremes, and vacuum conditions. All three samples met or exceeded requirements, with the best performance coming from a filter that was silver-plated via an electrolytic process.

Beyond 3D printing, 3D Systems Leuven certified powder handling, providing process control for material density, post-processing, and quality control.

Booth recognizes that this added expertise played a key role in the project’s success: “We realize that this is not just down to using a good machine to manufacture the part but also the result of a good understanding by 3D Systems Leuven of the manufacturing process.”

ROI potential

Now that the process has been validated and the parts have met Airbus Defence and Space’s standards, the company can consider the return on investment (ROI) potential for 3D metal printing from faster turnaround time, reduced production costs, and weight reduction of 50%.

“Mass was reduced without spending any time on optimization, and it can be reduced further with more aggressive mechanical design. The reduced mass saves costs by requiring less propellant in the rocket and puts fewer demands on support structures, allowing further mass reduction,” Booth says. “The success of this project opens up the possibility of much greater integration of RF filters with mechanical and thermal components to reduce part count and overall mass. We will also look at integrating more functionality, such as test-couplers, as part of the filter or directly integrated into waveguide runs.”

Airbus Defence and Space

www.airbusdefenceandspace.com

3D Systems Corp.

www.3dsystems.com