Materials Standards for Additive Manufacturing

This project provides the measurement science for the additive manufacturing industry to measure material properties in a standardized way.  Determining the properties of the powder used for metal-based additive manufacturing, as well as the resulting bulk metal material, is a necessary condition for industry to be able to confidently select powder and produce consistent parts with known and predictable properties.

By 2014, develop and deliver enhanced measurement techniques that support new, standardized methods for quantifying the material properties of both the powders used for additive manufacturing and the resulting manufactured products.

Currently, the additive manufacturing (AM) industry does not have the confidence, and is unable to rigorously verify, that nominally identical metal powders used in AM are in fact identical, resulting in unconfirmed powder properties.  This lack of confidence in material properties is also true for parts produced by AM.  The new idea is to develop enhanced material characterization test methods for the raw powder materials used in additive manufacturing as well as the final products fabricated by the process. Current test methods used for the determination of properties of materials made through conventional processes may not be suitable for materials made through additive manufacturing techniques. This is due, in part, to the anisotropic build patterns inherent to the layer-wise nature of additive manufacturing processes, but also to the quality and characteristics of the powder material used in the additive process. The powder batch could consist of an assortment of all virgin, unprocessed particles, a collection of reused particles that have already been subjected to the build environment, or a mixture of both. Another challenge to material property characterization of parts made via additive manufacturing processes is the fact that each AM equipment vendor makes available their own, proprietary set of powders which are to be used in their specific machines. Therefore, if a user purchases Ti-6-4 powder from one OEM and additional Ti-6-4 powder from a different OEM, there is no guarantee that the two batches of powder are identical, nor is it assured that parts made with the two different powders will have the same material properties.

The research plan is to first assess the current state-of-the-art testing methods for determining properties of both bulk metal materials and raw metal powder, including those methods used in powder metallurgy. These methods may include mechanical testing (including indentation and fracture testing to determine tensile strength), non-destructive techniques (to determine porosity and modulus), and mass spectrometry (to determine powder composition).  For powder characterization measurements of particle homogeneity, size distribution and morphology will also be examined.  These methods will then be evaluated and enhanced for use on additively manufactured parts and raw additive powder. NIST’s new Direct Metal Laser Sintering (DMLS) machine will be utilized to make parts, and these new methods will be rigorously implemented. Using these enhanced methods, the sensitivity of part material properties to variations in initial powder properties will be determined.  This is a critical step necessary for the production of AM parts with consistent properties.  This project will provide the technical foundation and required leadership necessary to develop new consensus-based standards.  This will be done via ASTM Committee F42 on Additive Manufacturing Technologies and the newly formed ISO TC261 on Additive Manufacturing.

As this is a new project, none of the recent results have a focus on the materials aspects of additive manufacturing. However, the following recent outputs and outcomes laid the foundation for this project: 

• Outcome: In 2009 EL personnel helped form ASTM Committee F42 on Additive Manufacturing Technologies, and continues serve as members of that committee.
  
• Outcome: EL staff helped develop the 2009 Roadmap for Additive Manufacturing
  
• Output: EL staff has contributed technical papers to both the 2010 Solid Freeform Symposium (Cooke and Soons, Variability in the Geometric Accuracy of Additively Manufactured Test Parts) and the 2011 International Solid Freeform Fabrication Symposium (Cooke and Moylan, Process Intermittent Measurement for Powder-Bed Based Additive Manufacturing.)
  
• Output: Recently EL staff have provided technical comments and feedback on ASTM F42 work item WK30522 - New Standard Additive Manufacturing Titanium-6 Aluminum-4 Vanadium with Powder Bed Process.

Currently there are no consensus-based standards in this area, except for those pertaining to terminology and data file formats.  This project, in conjunction with the Fundamental Measurement Science for Additive Processes project, will provide the technical foundation and required leadership necessary to develop new consensus-based standards.  This will be done via ASTM Committee F42 on Additive Manufacturing Technologies and the newly formed ISO TC261 on Additive Manufacturing.