NASA Explores NDE Options for Evaluating Additively Manufactured Parts
Although Additive Manufacturing (AM) has been around for decades, increasing awareness of the significant benefits of flying 3D printed parts and using 3D printers in space has pushed NASA and the aerospace industry to take a close look at how to evaluate and certify AM parts to assure safety and mission success.
“[With 3D printing], you can print an entire part,” explained LaNetra Tate, principal investigator for NASA’s Space Technology Mission Directorate. “With traditional methods you can build, inspect, build, inspect, but with 3D printing, you’re doing it in one swoop. We need to understand how we are going to verify and qualify and certify these parts.”
AM has the potential to produce lighter parts, enhance the strength and reliability of materials, create less waste, reduce up-mass, and ultimately result in cost savings. However, there is a significant challenge in utilizing these promising parts — the most readily performed methods for evaluating 3D printed parts are destructive, and because NASA builds a lot of high-value, one-of-a-kind parts, destructive tests aren’t a practical choice. To address this issue, NASA’s Office of Safety and Mission Assurance has turned to the NASA Nondestructive Evaluation (NDE) Working Group, or NNWG, for insight.
“The unique nature of AM parts leads to correspondingly unique product qualification challenges, and this is where NDE fits in,” said Dr. Jess Waller, material scientist at NASA with Jacobs Technology Inc. “You have parts with complex geometry that are difficult to inspect through traditional means. NDE is uniquely suited to inspect AM parts with all the unique inspection requirements.”
The NNWG has outlined a series of near- and long-term NDE goals for AM parts in their recently published Nondestructive Evaluation of Additive Manufacturing State-of-the-Discipline Report. In the near-term, the goal is to develop NDE methods for the certification and qualification of AM parts to be used in launch applications. In the long-term, the NNWG will be applying NDE methods to AM parts to be used in the space environment.
The NNWG also is working with ASTM Committees E07 on Nondestructive Testing and F42 on Additive Manufacturing Technologies to create and advance government-industry technical standards. A new standard under the jurisdiction of Committee E07 is being developed that will serve as a guide for NDE of AM parts used in aerospace applications.
“It will be the first of its kind — a standard for AM parts — and NASA is taking the lead on that,” said Waller.
In addition to NASA, a number of other institutions are taking a proactive role in what has become a world-wide collaborative effort to qualify AM parts. NASA currently is sharing ideas, information and best practices with the European Space Agency, U. S. Air Force, National Institute of Standards and Technology, Boeing Company, SpaceX, Lockheed Martin, Aerojet Rocketdyne, and Aerospace Corporation, among others, to gain a mutual understanding of what each is doing.
“We are also trying to develop relationships with NASA’s commercial space partners,” said Waller. “They are going to be a key team player on developing the standards. We are here as much to learn as we are to lead.”
Evaluating AM Parts
There are two options for when to use NDE to test AM parts: During the manufacturing of parts with in-situ process monitoring or after the manufacturing of parts with post-manufacturing inspections.
This technology offers the opportunity to create a detailed record of each layer of the part during the build.
“It’s a unique opportunity we have with additive that’s not available at all with traditional methods,” said Waller. “You can develop an NDE build record of your part that tells you what the properties of that part are, layer by layer.”
NASA also is using structured light to verify AM part dimensions to ensure in real time that the part is being built to the right dimensions.
For post-manufacturing inspections, NASA is exploring x-ray Computed Topography (CT). The technology can detect inaccessible, internal features and deep or embedded porosity, but it is limited by its ability to reliably detect cracks because cracks that are oriented perpendicular to the x-ray beam may not be detected.
“It’s not the end-all-be-all, just one of the tricks of the trade,” explained Waller.
NASA also has had some success using eddy-current testing and penetrant testing, but the rough surfaces often encountered in as-built AM parts can pose challenges for these methods. As a result, the parts must be polished before these methods can be used.
Although there is a still a lot to learn, NASA is not alone in its quest to expand the applications of AM parts — industry and the agency’s commercial partners are using the technology to support aerospace designs. Earlier this year, SpaceX flew its first 3D-printed part, a main oxidizer valve body in one the engines in the Falcon 9 rocket. The company also is testing a 3D-printed SuperDraco engine chamber as part of its Dragon V2 capsule.
“They [commercial partners] are facing the same challenges that NASA is in trying to figure out how to use this new technology and the parts made from it safely and reliably, so we can learn together,” said Waller.