In recent years, the US Army aviation community has made great progress in utilizing metal additive manufacturing (AM) technology to fabricate individual structural components needed to repair aircraft. Now the Army wants to advance metal AM manufacturing capacity to produce primary structure and mission-critical parts.
“This CTMA project, Additive Material Property Evaluation, and Demonstration (AMPED), will accelerate the use of AM for Army aviation,” says Colton Butcher, the NCMS Project Manager for this collaboration. “The initiative will assess and transition knowledge of commercial metal AM airworthy technology and processes to additively design, develop, and certify hard-to-source parts.”
Launched in September 2021, and scheduled for completion in March 2023, AMPED brings together experts from US Army Aviation and Missile Command; US Army Combat Capabilities Development Command, Aviation & Missile Center; and industry partner GE Additive.
Currently, the aviation community uses titanium—in particular the titanium alloy Ti6Al4V—for a number of additive manufacturing applications. Ti6Al4V is an excellent lightweight material for aerospace structures because of its high strength, high fracture toughness, low density, low coefficient of thermal expansion, and high corrosion resistance. Because of the high-performing mechanical properties of Ti6Al4V at elevated temperatures, commercial aircraft manufacturers utilize Ti6Al4V for additively manufactured turbine blades.
To leverage AM on a larger scale, the aerospace community requires detailed process work instructions to ensure that future AM parts meet the Federal Aviation Administration’s (FAA) stringent certification protocols for airworthiness. The FAA applies the same level of rigor to approving AM parts as to those built with conventional manufacturing (CM) techniques. Inspection techniques for metal AM parts must account for highly complex geometries, hidden internal features, textured material microstructures, anisotropic properties, and rough surface finishes, all of which may impact not only the parts’ airworthiness but also the ability to inspect parts using existing non-destructive inspection (NDI) methods. The FAA is currently working with industry, academia, government agencies, and standards development organizations to review NDI methodologies for suitability in detecting key defects, anomalies, and flaws relevant to metal AM parts.
To help ensure that these metal AM parts meet FAA airworthiness standards, AMPED is establishing new procedures for designing and assembling AM parts. As a testbed, the team is creating AM parts for the CH-47 Chinook helicopter. Project participants jointly selected part numbers to additively manufacture that will promote the sustainment and readiness of Army aircraft. The team will use the Ti6Al4V alloy and advanced AM printers to produce parts and will also document additively manufactured technical data (AMTD) for parts that meet Army requirements.
The AMPED team began by designing, printing, and evaluating AM component prototypes. This evaluation involves post-processing inspection for final additive casting dimensions and material characteristics. Next, the team will manufacture near-net components and supporting documentation to assist with Army-performed testing and qualification. This AMTD documentation consists of material property data for AM-fabricated components, especially the fatigue properties that are vital for military aircraft safety. This data will also incorporate information about microstructures, mechanical properties, powder, and consolidated material specifications, design approach, process qualification, work instructions for key printing process parameters, and a component quality plan.
“AMPED leverages modeling and simulation tools, along with commercial engineering best practices, to determine the optimal material solutions, processes, and tools to ensure that AM is consistent, repeatable, and reliable,” says Butcher.
The AMPED team will provide engineering support for preparation and airworthiness reviews, including a product analysis and evaluation report. AMPED aims to accomplish the technology transfer of one airworthy component, along with completing the AMTD.
If successful, the AMPED initiative can be used to improve sustainment for aircraft and weapon systems across the entire DOD enterprise. This project will transmit cutting-edge industry knowledge to military engineers and technicians so they can manufacture hard-to-source parts. Because AM can allow repair parts to be produced on-demand—and in some cases at the point of need—it lowers the transit time and cost of delivering parts to the operational theater. Moreover, the project’s metal AM process can be employed with other optimization tools to find more opportunities to replace heavier components with lighter parts, which will lessen wear and tear, extend useful life, and boost fuel efficiency. Because AM parts made with titanium outperform parts made with conventional materials, they will require less maintenance and therefore conserve tax dollars.
This initiative demonstrates how AM is accelerating next-generation product design, which will have a long-lasting impact for many commercial product sectors as well as the maintenance, repair, and overhaul (MRO) sector. AM allows metal parts to be fabricated quickly, and with savvy suppliers, on-demand. As a result, AM can help to establish a more efficient and responsive supply chain—especially for hard-to-source parts that are no longer mass-produced. Ultimately, in the aerospace industry, AM is expected to lead to safer air travel, upgraded system performance, less waste, higher fuel efficiency, and lower costs.