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Within the aerospace industry, 2016 and onwards could be looked upon as the tipping point for direct metal printing (DMP), as the technology increasingly made the jump beyond prototyping to production parts and assemblies ready for flight.

Metal 3D printing enabled Airbus Defense and Space to design and build a new RF filter based on a super-ellipsoidal cavity that efficiently channels RF currents.

During that time frame, Airbus Defense and Space worked with 3D Systems (Rock Hill, SC) to achieve a major 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.

Metal RF or waveguide filters date back to the first space communication systems nearly 50 years ago. The filters act like traffic cops, allowing frequencies from selected channels to pass through, and rejecting those from signals outside those channels.

A major industry trend is to increase the capacity for multiple beams within a single satellite. A high-capacity satellite such as the Eutelstat KA-SAT, manufactured by Airbus Defense 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

Telecommunications satellites exemplify the aerospace industry's relentless emphasis on reducing weight — sending a vehicle into a geostationary orbit can cost as much as $20,000 per kilogram. Continuing design innovation and reduced production time are also major priorities, as most satellites are designed for a lifetime of 10 to 15 years.

These priorities make telecommunications satellites the ideal candidate for direct metal printing. 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 to manufacture via traditional means, reduce production time and lower costs for customized designs, and decrease weight while maintaining or improving material strength.

The unique internal structure of the 3D-printed RF filter based on depressed super-ellipsoidal cavities.

3D Systems’ facility in Leuven, Belgium has been using the 3D Systems ProX DMP 320 since the machine was in its beta stages. 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 Defense and Space project was 3D Systems Leuven's first foray into RF filters.

The ProX DMP 320 is designed for heavy-duty metal parts production. It uses a totally new architecture that simplifies setup and provides the versatility to produce all types of part geometries in titanium, stainless steel, aluminum, nickel-chromium, and other alloys. Exchangeable manufacturing modules deliver increased applications versatility and less downtime when moving among different part materials. A controlled vacuum build chamber ensures that every part is printed with proven material properties, density, and chemical purity.

Disruptive Design Innovation

The Airbus Defense and Space RF filter project demonstrated the ability of 3D printing to enable new design innovation for aerospace parts that haven't changed appreciably in decades. RF filters have been traditionally designed based on libraries of standardized elements, such as rectangular cavities and waveguide cross-sections with perpendicular bends. Shapes and connections are dictated by typical manufacturing processes such as milling and spark eroding. As a result, cavities for RF filters typically need to be machined from two halves bolted together. This increases weight, adds an assembly step to production time, and requires extra quality assessment. Designing the parts for 3D printing enabled Airbus Defense and Space to explore complex geometries at no additional manufacturing cost.

CST MWS, a standard 3D electromagnetic simulation software tool, was used to design the 3D-printed RF filters, with little time spent on optimization. The increased manufacturing flexibility enabled by 3D printing led to a design using a depressed super-ellipsoidal cavity. The unique shaping helped to channel RF currents and deliver 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,” said Koen Huybrechts, project engineer for 3D Systems in 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,” said Paul Booth, RF engineer for Airbus Defense 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 really necessary metal needs to be used. The cost/time benefit comes from the reduction in assembly and post-processing.”

Eliminating Surface Concerns

Initially, the different surface topology in 3D-printed metal parts was thought to be an issue, but extensive testing by Airbus Defense and Space eliminated those concerns.

“The microscopic topology is different in the 3D-printed part than in a machined part,” said Booth. “Machined surfaces have sharp peaks and troughs, while the 3D-printed surface is spheroids melted together so there is less sharpness.”

The metal 3D-printed RF filter designed by Airbus Defense and Space integrated into the satellite payload. The new filter reduces weight by 50% over the previous design.

“The spherical shape of the powder particles used in 3D metal printing leads to a certain waviness rather than steep transitions,” said Huybrechts, “but the ability to shape a part for more effective signal filtering more than overcomes any concerns with surface topology.”

“We were very pleased with the work that 3D Systems did for us, and many inside Airbus have commented on how good the surface finish is,” said Booth. “We did some X-ray CT scans and have been impressed with the density of the part and the general surface quality.”

Passing Rigorous Tests

Three aluminum samples printed on the ProX DMP 320 using different processing paths were tested by Airbus Defense and Space at its Stevenage facilities. Tests mimicked conditions the parts would face during launch and orbit, including vibration, shock, and thermal situations such as 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 delivered added value that is critical to this kind of project, including certified powder handling, process control for superior material density, proven post-processing, and reliable 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 of the manufacturing process.”

The metal 3D-printed RF filter designed by Airbus Defense and Space consolidates two parts into one and reduces overall mass. 3D printing enables faster production and lower costs.

ROI Potential

Now that the process has been validated and the parts have met the highest spaceflight standards Airbus Defense and Space has in place, the company can begin to consider the return on investment (ROI) potential for 3D metal printing. The project delivered faster turnaround time, reduced production costs, and a weight reduction of 50 percent.

“Mass was reduced without spending any time on optimization,” said Booth, “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.

“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,” Booth added. “We will also look at integrating more functionality such as test-couplers as part of the filter, or directly integrated into waveguide runs. There is a huge potential for reducing mass while cutting production time and costs.”

This article was contributed by 3D Systems, Rock Hill, SC. For more information, Click Here.