A team at Marshall Space Flight Center is exploring additive manufacturing (3D printing) for NASA’s Space Launch System (SLS) rocket. The team is looking into the capabilities, costs and benefits of using additive manufacturing on their latest liquid rocket injector.
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. The Marshall team is exploring how this manufacturing process might replace or enhance current manufacturing methods for faster, more cost-effective production.
One of the primary objectives of the Space Launch System program is to evolve engine hardware. Thus, the team is investigating Direct Metal Laser Sintering (DMLS) to determine its suitability for making rocket hardware, comparing it to traditional manufacturing and pushing the limits of current additive manufacturing applications.
Direct Metal Laser Sintering (DMLS) is an additive process that uses many of the same metals the aerospace and medical industries rely heavily upon. Titanium, Inconel, stainless steel, cobalt chrome and aluminum can all be built up, layer by layer, with this 3D printing technology. Despite decades of development behind this particular additive process, its true viability is only just being tested by major aerospace players – such as NASA, GE Aviation, Space-X – to discover what it can and cannot do.
Stratasys Direct Manufacturing was one vendor tasked with manufacturing the injector for the test program. This company has fourteen DMLS manufacturing platforms in its two Texas facilities, ISO 9001 and AS 9100 certifications and years of experience working with DMLS. Phillip Conner, DMLS Manager at Stratasys Direct Manufacturing, headed the internal team working on the injector. Conner had worked previously in the casting industry; he’s an expert in both the conventional and the new metal manufacturing technologies. “We realized the work with Marshall Space Flight Center would benefit research into DMLS manufacturing in its entirety, not just in terms of aerospace capabilities,” said Conner. “We learned a lot from the project in terms of how much farther we could push our DMLS technology to succeed in more areas.”
Printing complex design
Marshall Space Flight Center required 3D printing for 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 singular print or build.
Prior to using DMLS, the injector was manufactured through casting and other machining operations. Manufacturing the injector this 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 with 150+ individual pieces, requiring 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 the exploration of 3D printing injector components, Marshall researched materials to determine the success of DMLS metal units when subjected to stressful environments. Conner confirmed that across the board DMLS parts exhibit stronger mechanical properties than cast parts. “When you’re evaluating a part cut from a solid chunk of metal to a cast part, the cast part will always have less strength,” said Conner. “But DMLS parts are typically only 5 – 10% less strong than cut metal, which means DMLS is consistently stronger than cast parts.”
Consistency and repeatability
One of the challenges of 3D printing a metal part for a rocket injector is there is no precedence for this process in this application. The team needed to evaluate the ability of metal additive manufacturing to build consistent and repeatable parts in comparison to conventional manufacturing technology. Controlling repeatability falls to the hands of the 3D printing service provider. “Before attempting the injector we built half a dozen different parts to show the interior complexities and allow for extensive mechanical property testing,” said Conner. The results helped to accelerate development for the injector and gave insight to Stratasys Direct Manufacturing on optimal designs and materials for similar applications.
The current benefits of DMLS don’t necessarily equate to revamping the entire production line, however; a simple part without these complicated interior features would be perfect for traditional manufacturing. Metal additive manufacturing excels with challenging units – that’s where it positively impacts product cost, time and labor, by cutting these elements in half and resulting in more efficient production development and parts. Generally, the response to the project has been encouraging with excitement over what its success might mean across a range of industries.
The DMLS injectors underwent hot fire testing in August and continue to undergo evaluations as the Marshall teams expand into the additive manufacturing territory. In other areas of the Space Launch Systems program, Marshall recently unveiled the largest, most powerful solid rocket booster ever built for a NASA rocket. It underwent a two-minute static test on March 11, 2015. The SLS program continues to reach new milestones for rockets, science and the future of space exploration.
Edited by Leslie Langnau