Direct Metal Laser Sintering (DMLS)
Stratasys Direct Manufacturing
NASA’s Marshall Space Flight Center is currently leading the development of the Space Launch System (SLS) program, which is building a heavy-lift launch vehicle to carry human explorers and science payloads to new frontiers. Today, one important technology being explored by the team at Marshall is additive manufacturing, or 3D printing, as it relates to manufacturing hardware and propulsion for the SLS rocket. The center dedicated resources to materials and technologies research, using their latest liquid rocket injector development as one optimal project for testing out the capabilities, costs, and benefits of additive manufacturing processes. One goal of additive manufacturing is to consolidate parts to reduce labor and weight, and create an overall more efficient part with increased complexities that help optimize injectors for future applications.
Marshall is taking additive manufacturing to the next level by advancing the technology readiness level of additive manufactured parts. One of the primary objectives of the SLS program is to evolve engine hardware. Part of achieving that objective involves advancing and vetting out the Direct Metal Laser Sintering (DMLS) additive manufacturing process to determine the role of metal additive manufacturing and its suitability for making rocket hardware, comparing it to traditional manufacturing, and pushing the limits of current additive manufacturing applications. Advancing the technology readiness level and viability of DMLS began with a headfirst dive into the design and materials capabilities of the technology, and one of the first rocket engine parts to be built and tested was an injector.
DMLS is an additive process that uses many of the same metals the aerospace and medical industries rely upon heavily. Titanium, Inconel, stainless steel, cobalt chrome, and aluminum are all metals that can be built up, layer by layer, with this 3D printing technology. Stratasys Direct Manufacturing was one vendor tasked with manufacturing the injector for Marshall’s additive test program. The company has eight DMLS manufacturing platforms in two Texas facilities, ISO 9001 and AS 9100 certifications, and years of experience working with DMLS.
Marshall required 3D printing to execute their hydrogen-oxygen injector due to the complicated internal design. There are three basic conventional methods used to create the flow pattern within injector inlets. Traditionally, manufacturing methods would require holes drilled into each element of the inlet. A fitting would be machined with unique flow features, and then welded to the first element. This method required multiple pieces to be welded, machined, cast, and otherwise bonded together to create the injector. DMLS allowed the complicated, unique swirl pattern to be built directly into the inlet of the injector in one print or build. Prior to utilizing DMLS, the injector was a less complex part manufactured through casting and other machined units.
Manufacturing the injector the traditional way took six to nine months. Stratasys Direct Manufacturing worked to combine features and incorporate complexity for more efficiency and still deliver the part faster. What began as a unit of more than 150 individual pieces that required months to manufacture was transformed into a two-part 3D-printed unit that eliminated extensive touch labor and could be built in 10 days.
Parallel to 3D-printing injector components, Marshall conducted materials research to determine the success of DMLS metal units when subjected to stressful environments. Another challenge of 3D-printing a metal part for an injector on a rocket is that there isn’t currently precedence for this process in this application. At the forefront of the project has been the evaluation of metal additive manufacturing consistency and repeatability from one completed part to the next, compared to conventional manufacturing. Controlling repeatability falls to the hands of the 3D printing service provider. Before attempting the injector, Stratasys Direct Manufacturing built half a dozen different parts to show the interior complexities, and allow for extensive mechanical property testing. The results helped to both accelerate development for the injector, and provide insight on optimal designs and materials for similar applications.
The DMLS injectors underwent hot fire testing earlier this year, and continue to undergo evaluation as the Marshall teams expand into the additive manufacturing territory.
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