Metal Additive Manufacturing for Aerospace Hardware

Process families

Two families cover most aerospace metal AM. Laser powder bed fusion (LPBF, also written PBF-LB) melts thin layers of powder with a laser and suits complex, fine featured parts such as injector bodies, manifolds, brackets and heat exchangers. Directed energy deposition (DED) feeds wire or blown powder into a melt pool created by a laser, electron beam or arc, and suits large near net shapes, features added to forgings, and repair. Electron beam powder bed fusion exists too, but NASA-STD-6030 excludes adaptive processes where heat input changes during the build, citing electron beam powder bed fusion as an example.

Material standards

ASTM has issued material specifications for common powder bed fusion alloys, plus a thermal post processing standard that they reference.

As an example of how these documents are used, one published fatigue study on powder bed fusion 718 selected a HIP temperature of 1185 °C based on ASTM F3055-14a, ran HIP at 100 MPa, then solution annealed and double aged. HIP closes internal porosity and also helps homogenize chemical segregation in as built material. Take actual cycle parameters from the current revision of the standard your drawing invokes, not from a paper. Alloy background is on the nickel superalloys and titanium alloys pages.

NASA-STD-6030: classes and the qualified process

NASA-STD-6030, baselined in April 2021, sets AM requirements for spaceflight hardware. It applies in full to crewed systems, and Appendix B gives guidance for tailoring to robotic missions. Many commercial launch and spacecraft programs borrow its structure even when it is not contractually required.

Classification. Parts are classed by consequence of failure, then sub-classed by structural demand and AM risk:

Subclasses 1 to 4 for Class A and B come from two assessments. Structural demand is low only if the part meets the margin, fatigue and environmental criteria in the standard tables. AM risk is scored from a checklist covering items such as inspectability and build sensitivity: a total under 5 is low risk (subclass 2 or 4), 5 or more is high risk (subclass 1 or 3). An A1 part, high demand and high risk, carries the heaviest controls, including witness articles where inspection is incomplete.

Process control. The backbone is an AM control plan plus the supplier quality system. Foundational controls cover a qualified material process (QMP), equipment control, personnel training and material property development. Part controls cover design assessment, a part production plan, preproduction articles and production controls. The QMP locks the feedstock specification, machine parameters and post processing, and feeds the material property suite used for design values. Witness specimens built with production parts are tested and evaluated with statistical process control.

The companion NASA-STD-6033 covers equipment and facility control through an Equipment and Facility Control Plan: machine qualification, maintenance and calibration, and facility controls such as feedstock powder storage and handling.

Powder control

Powder condition drives porosity and properties. Expect a supplier to control and record lot chemistry, particle size distribution, flow, and oxygen and nitrogen pickup, especially for titanium. Reused powder must be tracked, sieved and tested against limits set in the QMP. Storage in controlled humidity and inert containers is part of facility control under NASA-STD-6033. Ask the supplier how many reuse cycles its process allows and how it is verified, and require powder lot traceability to each build. For DED with wire feedstock, the equivalent controls are wire chemistry certs, spool traceability and cleanliness of the wire surface.

Design for AM and inspection

The design rules that matter most for flight parts are about inspection, not printability. If a feature cannot be inspected, the part is high AM risk under 6030 and needs more witness testing and process control. Practical points:

• Provide powder removal paths for every internal cavity, and a way to verify they are clear
• Avoid unsupported down facing surfaces in fatigue critical regions, because as built down skins are the roughest
• Leave machining stock on sealing surfaces, bores and threads. Printed threads are prohibited for Class A and B
• Plan where tensile, fatigue and density witness coupons sit on the build plate
• Assume CT will be needed for internal features, and size the part so the CT system can resolve the flaw size of concern

Surface condition dominates fatigue in as built AM metals, so specify machined or polished surfaces where fatigue margins are small. NDT methods for AM are covered on the nondestructive testing page.

What to require from an AM supplier

• Machine and parameter set identification, frozen per the qualified process
• Powder or wire lot certs and reuse history
• Build log with plate layout, interruptions and any anomalies
• Stress relief, HIP and heat treat certs with cycle records
• Witness specimen results per the agreed test plan
• CT or other volumetric inspection results where required
• Dimensional report and, for new parts, an AS9102 first article

Most of these feed Form 2 of the first article report, covered on the inspection and metrology page.

Get additive parts quoted

If you have LPBF or DED parts to build, or need HIP and heat treat on parts you already have, send the model, drawing and part class. We source from qualified AM suppliers, flow down the material, process control and witness test requirements, check build records and certs before shipment, and a person replies within one business day. Mutual NDA before files. Controlled data goes through the process on controlled programs, never the website. Back to the processes hub.

Questions

Related

• Aerospace Heat Treatment: Pyrometry, Process Specs and Callouts
• Nondestructive Testing for Aerospace Parts
• Inspection and Metrology for Aerospace Parts
• 5-Axis CNC Machining for Aerospace Parts

Sources

• NASA: NASA-STD-6030 Additive Manufacturing Requirements for Spaceflight Systems (PDF)
• NASA Technical Standards: NASA-STD-6030 status
• NASA: additive manufacturing standards support human spaceflight
• NASA NTRS: NASA-STD-6030 training on qualification of AM hardware
• ASTM F3301 thermal post processing of PBF metal parts
• ASTM F2924 Ti-6Al-4V with powder bed fusion
• NIH PMC: static and fatigue properties of rhenium alloyed PBF 718 (HIP per F3055-14a)
• ANSI Webstore: SAE AMS 2774G