SAE International Celebrates its 10th Anniversary of AM Aerospace Standards

Ten years into SAE’s AMS AM standards work, Bill Bihlman examines progress, pain points, and the path to wider aerospace adoption.

This summer, SAE celebrated its 10th anniversary of its additive manufacturing committee. Its rather successful journey – along with key developments within additive manufacturing (AM) – is recounted below. SAE AMS AM extends a long tradition of material specification excellence dedicated to aerospace. This is consistent with the 120-year-old organization’s mission of “connecting and educating engineers” for the advancement of the mobility industry globally.

SAE Aerospace Material Standards

The genesis of aviation involves some of the most intriguing chapters of our eternal quest for technology – experiments in France by the Brazilian engineer Santos-Dumont, in Germany by Lilienthal, and in the United States by the storied Wright Brothers. It was there in an Ohio bicycle shop that Orville and Wilbur cleverly deployed their engineering talent. They combined the fundamentals of mechanics with a rudimentary understanding of aerodynamics to build a wooden heavier-than-air flying machine. Alas, the first flight only lasted 12 seconds. But aviation was born. The year was 1903.

Nearly a decade later, Wilbur, in failing health, asked his brother to actively engage the fledgling aviation community to promote this new technology. In 1916, Orville organized a meeting in Philadelphia with other well-known aviation pioneers, such as Elmer Sperry, Jimmy Doolittle, and Glenn Martin, to form the Aviation Division of the Society of Automotive Engineers (SAE). Around that same time, the US Government formed the National Advisory Committee for Aeronautics (NACA) – the predecessor to NASA.

SAE was founded in 1905, shortly after the Wright Brothers’ first flight. The Society’s ambitious goal was to facilitate the open exchange of information amongst engineers. At that time, there were over 40 automobile original equipment manufacturers (OEMs) in the United States. Many struggled to solve common design problems. One solution was technical consensus standards. Consequently, SAE published its first standard in 1912, and within a few years, followed with its first aeronautical standard. SAE International has since grown to become one of the world’s largest (and oldest) technical standards development organizations (SDOs).

A few additional milestones from the last century:

* 1926 – The US Government passes the Air Commerce Act to ensure the safety of the flying public

* 1927 – SAE awards the Wright Brothers medal for the best technical aviation paper

* 1939 – SAE issues its first Aerospace Material Specification (AMS), helping to reduce bespoke company standards

* 1950s – significant advancements in aerospace alloys, namely aluminum, precipitated hardened steels, super alloys, and titanium

* 1961 – AMS exceeds 1000 documents, a consequence of the rapid development during the previous decade

* 1990s – SAE inherits many US military standards (via Perry Reform), now exceeding 1500 documents

The Dawn of Additive

Since its inception in the 1980s, additive manufacturing has evolved from rudimentary light-cured resin stereolithography systems and single-nozzle polymer filament extruders – both used for rapid prototyping – to multi-laser metal powder bed machines that can produce topologically complex production parts.

In the context of aerospace, additive manufacturing provides an exceptionally optimized tradeoff between part performance (i.e., strength, stiffness, and durability) and weight. Naturally, properties are determined by part chemistry and microstructure, ultimately dictated by processing conditions. Thus, both material and process standards are essential.

The use of new materials for flight-critical parts requires extensive empirical substantiation. This can be cost-prohibitive. For example, creating a Federal Aviation Administration (FAA)-approved “design allowables” (bulk material) database for an alloy can cost millions and require years of testing and analysis. Material qualification for the gas turbine is even more costly due to testing at elevated temperatures and the need to understand creep and low-cycle fatigue.

This lack of a well-defined manufacturing process and feedstock characterization has greatly impeded the adoption of additive manufacturing. Meanwhile, the FAA and its European counterpart, EASA, have increasingly turned towards industry consensus standards to support regulation via Means of Compliance (MoC). The SAE AMS AM committee was created to convene a broad range of stakeholders needed to address these emerging issues.

SAE AMS AM

In 2015, SAE International responded to an FAA tasking letter for AM material guidelines and standards, establishing the SAE AMS AM committee. The committee has over 600 members from 27 countries. Members represent airlines, aerospace OEMs, and various organizations throughout the AM supply chain required to develop, manufacture, test, and maintain aircraft. Furthermore, the FAA, US Department of Defense (DoD), NASA, and EASA are actively engaged.

AMS AM addresses material and process specifications for metals, non-metals, and repairs. This broad array of documents includes details such as machine qualification, metal powder reuse, and in-situ process monitoring. Each subcommittee has dedicated working groups that meet regularly to debate the merits of relevant engineering and/or production quality criteria. Indeed, this consensus process is robust, benefiting from broad stakeholder agreement.

To date, AMS AM has published 43 documents for PBF, DED, cold spray, and polymer FFF. This includes six revisions as the committee incorporates timely feedback from industry. There are an additional 60 documents in process.

The committee also works closely with the Metallic Materials Properties Development and Standardization (MMPDS) handbook for metals, and the Composite Materials Handbook-17 (CMH-17) for composites. Additionally, SAE coordinates closely with its affiliate, the Performance Review Institute (PRI), to ensure quality and efficiency throughout the production ecosystem via Nadcap.

SAE AM Ecosystem

For aerospace manufacturing, major suppliers are effectively required to maintain an industry quality management system (QMS), such as SAE’s AS9100 and AS13100, and/or Nadcap. In most cases, there is significant overlap between the membership of these popular programs and the SAE AMS AM committee.

Within the past two years, Nadcap has created facility audit criteria for metal PBF and DED. These consensus checklists are intended to drive efficiencies and lower costs for accredited suppliers. Twenty-five OEMs are already involved in this task group.

Lastly, SAE and its partners are evaluating a supplier registry to help guarantee part pedigree. A longer-term goal is a qualified producers list (QPL), similar to SAE’s carbon-fiber composites program.

Looking Ahead

Consensus standards provide a vital contribution to aircraft quality and safety. They can also significantly reduce costs and increase efficiency by aligning disparate company frameworks and codifying industry best practices. Standards are even more crucial in today’s regulatory environment as governments continue to rationalize aviation-related R&D spending.

SAE International has been an important partner within aerospace for over a century. Its industry-led AMS documents are the de facto standard for aviation materials, known for their empirical rigor and technical integrity. Developing (and maintaining) adequate guidance is non-trivial, though, especially as additive manufacturing continues to evolve.

The AMS AM committee is just one of SAE International’s 180-plus technical committees, each working diligently to create quality specifications that endure. It is a formidable challenge in a swiftly changing world. The organization, however, is poised and committed to maintaining AMS as the global standard of excellence.

About the author:

Bill Bihlman has served as a volunteer member of SAE AMS AM for over a decade. Over the past five years, he has served as a consultant to the committee. Bill has worked in aviation for nearly 25 years, with a focus on advanced materials and manufacturing.

Note: The views expressed are those of the author and do not necessarily reflect the positions of SAE International or any affiliated organizations.