Metal Additive Manufacturing Standards
Metal additive manufacturing has evolved from being limited to prototyping into a disruptive technology capable of fabricating parts flying on jet engines today.
Today we are at the starting line of the digitization of manufacturing. This digital, technological revolution that we are witnessing is often referred to as the fourth industrial revolution, with the integration of cyber physical systems, where parts, machines and systems communicate with each other, and can predict failure and autonomously trigger a process change or preventative/predictive maintenance. Additive manufacturing (AM) is one of the core technologies within the decentralized smart manufacturing ecosystem of Industry 4.0.
AM, also known as 3D printing, has come a long way since 1986 when stereolithography (SLA) was first patented to form objects layer by layer using photo-curable resins (liquid photopolymers). The technology has advanced at a rapid pace to form objects using a wide variety of materials including metals, ceramics, glass, composites, biomaterials, and electronic materials. Metal AM has evolved from being limited to prototyping into a disruptive technology capable of fabricating complex, functional parts flying on jet engines today. There are multiple metal AM technologies available including powder bed fusion (PBF), directed energy deposition (DED), and binder jetting.
The PBF process uses a high-power laser or electron beam, which impinges directly on the powder bed so that only selected portions of the target material are impacted. The beam selectively melts and fuses powdered metal by scanning 2D cross-sections (of the 3D part file) on the surface of a powder bed, enabling complex objects with intricate internal structures to be produced. After each cross-section is scanned, the powder bed is lowered by one layer thickness (typically 20 to 60 µm in L-PBF). Then a new layer of material is applied on top, and the process is repeated until the entire part is printed. This layer-based process is therefore additive (i.e. generative) as opposed to conventional manufacturing which is subtractive and requires eliminating unwanted material during or after processing.
All the above-mentioned AM technologies rely on technical standards. Industry standards affect all aspects of life, ensuring the quality and reliability of products that we use daily. The use of standards saves resources and optimizes outcomes by providing unified methodologies and frameworks for harmonized collection, analysis, and implementation of data among AM stakeholders. Standards may also serve to mitigate risks involved in various aspects of AM including workplace safety, the manufacturing process, and information/data security.
Several ASTM technical committees have written standards related to the fast, growing field of AM, including the ASTM F42 Committee on AM Technologies. The F42 Committee was formed in 2009, with the objective of knowledge promotion, research stimulation, and technology implementation via development of AM standards. The F42 Committee have developed standards that support feedstock materials, process and equipment, finished AM parts (including post-processing methods, testing and characterization), and application-specific standards (e.g. automotive, aerospace, medical).
ASTM F42 Committee is unique amongst ASTM Committees because of its close working relationship with ISO Technical Committee 261 on Additive Manufacturing (ISO TC261), which was formed in 2011. The F42/TC261 partnership has helped the technical community interact and cooperate within the same framework, facilitating the adoption and use of AM technologies. Such streamlining through harmonized, international standards will reduce duplication of efforts, and allow the community to fully leverage AM technologies by focusing on continual quality improvement rather than incompatibilities among standards.
In June 2018, SAE International announced the release of their first four AM materials and process specifications. “The Aerospace Material Specifications (AMS) additive manufacturing specifications will support the certification of aircraft and spacecraft critical parts by providing a framework to protect the integrity of material property data and provide traceability within the aerospace supply chain,” noted the SAE International’s AMS-AM Committee, officially supported by the Federal Aviation Administration (FAA) for this effort. The new specifications are focused on L-PBF feedstock, process, and alloys.
AM standardization efforts in Europe have also been increasing. The German Institute for Standardization (DIN) has founded a new AM Steering Committee (NA 145-04 FBR). This effort is a part of NA 145-04 FB “Section Additive Manufacturing,” operating under “NA 145 DIN Standards Committee Technology of Materials.” The Steering Committee is tasked with coordinating efforts within NA 145-04 FB, which is comprised of four working committees focusing on metal and polymer standardization efforts.
America Makes and the American National Standards Institute (ANSI) have also jointly published the Standardization Roadmap for Additive Manufacturing (Version 2.0) in June 2018, which lists 93 gaps in current AM standards and specifications. This Additive Manufacturing Standardization Collaborative (AMSC) body is comprised of worldwide AM stakeholders, from various backgrounds (OEMs, academia, government, standards organizations). The AMSC was chartered to identify existing gaps in standards (where no published standard or specification exists), and to make prioritized recommendations for areas where there is a need for additional standardization and/or additional pre-standardization research and development needs.
The landscape of AM standards and specifications developed by various organizations described in this article has helped define fundamental guidelines required to fabricate AM quality parts through a repeatable and fixed process, but for AM to morph from being a niche into a largely adopted manufacturing business model, a continuous effort to update existing standards and develop new ones to bridge gaps is crucial. The additive processes developed to fabricate engineering components not only have more process variables to control when compared to conventional (subtractive) manufacturing, but the interaction between those process variables is also more complex. For example, in L-PBF of metal powders, the variables that should be considered in quality standards include feedstock variables (powder size and size distribution, inter-particle cohesive strength, laser absorptivity, environmental conditions such as humidity), process variables (laser energy density, laser mode (continuous vs pulsed), scan pattern, protective atmosphere, machine and model), and post-process variables (heat treatment, machining, surface finish). The advent of Industry 4.0 and digitization of manufacturing poses significant challenges for the continued adoption of AM.
An ongoing, holistic standardization approach to develop a comprehensive set of technical standards will address those challenges by ensuring that high-quality AM components with repeatable and reproducible properties are produced, especially over larger-volume production runs.