SAE releases ARP7302 standard for closed-loop AM powder sampling
SAE International, the global standards organisation based in Warrendale, Pennsylvania, USA, has released ARP7302 – Sampling, Conformance Strategies, and Recommended Practices for Closed Loop Processing of Powder for Additive Manufacturing, addressing powder control in closed-loop metal Additive Manufacturing machines.
The Aerospace Recommended Practice (ARP) establishes methods for sampling powder feedstock circulating within closed-loop Additive Manufacturing equipment to demonstrate conformance to a defined powder specification.
The difficulty is that powder within the entirety of closed loop equipment cannot be represented by sampling and testing of discrete, in-process lots. Because powder processing (reconditioning, conveyance, and storage) is asynchronous with a build cycle, individual samples and their associated tests do not represent the totality of powder committed to a machine.
Also, powder consumed as part of an individual build cycle may only represent a subset of feedstock in circulation within such equipment. Therefore, regular testing to substantiate conformance to a powder specification is required to assert conforming feedstock was consumed during individual build cycles of the AM workflow to fabricate parts or preforms.
ARP7302 provides guidance on how to sample and test this circulating powder to support conformance. This is particularly relevant in cases where control frameworks based on key process variables (KPVs) are not implemented or monitored.
The standard outlines recommended approaches including the treatment of powder top-off strategies in closed-loop machines, guidance on sampling both from the machine and from individual build cycles, and terminology intended to support consistency across future SAE standards.
The standard also recognises that, in the absence of defined and controlled KPVs, regular testing is required to substantiate that conforming feedstock has been used during each build cycle. In such cases, evidence of conformance may be required for every build when producing parts.
While other specifications may define control frameworks to maintain powder characteristics – such as atmosphere control and its effect on reactive elements – these approaches are outside the scope of ARP7302.
“ARP7302 is a stepping stone,” explained Tyler LeBrun, PhD, who led the SAE working group responsible for the standard. “AMS7052 is reserved and in drafting as the requirements-laden process specification for continuous closed loop powder reuse, analogous to how AMS7031 governs batch processing of reused powder. A future document covering powder lifing and tracking for closed loop machines, similar in practice to ARP7044, is anticipated but has not yet been reserved as a project.”
The ARP7302 standard is available here.
