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- Quality in metal AM
This chapter focuses on quality aspects of raw material used for AM and the recyclability of metal powder. The chapter subsequently describes (1) metal materials available for AM, (2) the properties of metals available for AM, (3) powder handling guidelines, (4) studies on powder recycling and material characterisation, (5) standardisation for AM materials and (6) sources for further reading.
Keywords: Metal powder for AM, feedstock, powder handling, recyclability
- Material identification
- Material properties of feedstock
- Powder handling
- Powder recycability and feedstock studies
- Standards for material qualification
- Further reading
1. Material identification
The following metals can be used in powder bed fusion (Tapia 2015):
- Titanium alloys
- Nickel alloys
- Stainless steel
- H13 tool steel (M300 Maraging Steel)
- Cobalt chrome alloys
- Aluminium alloys
- Copper alloys
The powder materials used for AM are classified as pure metal, pre-alloyed, metal matrix composites powders. The material development process for any metal AM process powder characteristics (e.g. particle size, shape, flowability) and processing parameters (laser power, scan speed, scan spacing and layer thickness) play major role in defining quality.
2. Material properties of feedstock
- Chemical composition (including residual elements)
- Thermal process (stress relaxation/heat treatment)
- Residual stress
- Surface roughness
- Powder Morphology (and particle size distribution)
Raw metal powder is the most important aspect considering quality of an AM manufactured part, and when obtaining certifications for medical applications, extensive testing is required, both on of fresh raw material, as already processed material, which can be recycled.
3. Powder handling
Powder handling encompasses the following topics, which are described in the full document:
- Fresh powder reception
- Powder management
- Storage of fresh powder
- Storage of recycled powder
4. Powder recycling studies
The ManSYS project performed three powder recycling studies, thereby benchmarking SLM and EBM technology.
- The first study on feedstock control is a validation of recycled powder and correlation between powder and bulk material in terms of chemical composition.
- The second study is an as built (bulk) material characterisation into the critical element limits.
These two studies can be downloaded HERE.
3. The third study is on the oxygen uptake of recycled titanium powder using EBM technology.
The full 'materials' document extensively describes this study.
5. Standards for material qualification
This chapter encompasses both the structure of material specific standards and a standard specification database.
Standards incorportating material requirements are the following:
- Standard Specification for Additive Manufacturing Titanium-6 Aluminum-4 Vanadium with Powder Bed Fusion
- Standard Specification for Additive Manufacturing Titanium-6 Aluminum-4 Vanadium ELI (Extra Low Interstitial) with Powder Bed Fusion
- Standard Guide for Characterizing Properties of Metal Powders Used for Additive Manufacturing Processes
6. Further reading
- NISTIR 7847 assessed current state-of-the-art for material property testing of bulk metal material properties, Slotwinski, Cooke, Moylan, 2012
Determining the properties of the powder used for metal‐based additive manufacturing, as well as the properties of 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. This report assesses the current state-of-the-art methods for determining the mechanical properties of bulk metal materials. Emphasis of this assessment was on existing internal standards that cover the measurement of mechanical properties of metal parts. This assessment will later be used as the basis to develop standardized test methods that are appropriate for metal parts made via additive manufacturing.
- Presentation on standards of materials for AM, John A. Slotwinski, 2013
- NISTIR 7873 assessed current state-of-the-art methods for characterizing metal powder. (Cooke, Slotwinski)
This project provides the measurement science for the additive manufacturing (AM) industry to measure material properties in a standardized way.
LPW Technology are the global market leader in developing, manufacturing, and supplying cutting-edge metal powder solutions for Additive Manufacturing.
- Materials KTN, Shaping Our National Competency in Additive Manufacturing, 27th ed., Additive Manufacturing Special Interest Group for the Technology Strategy Board, UK, 2012
Report on additive manufacturing the UK, launched by Materials KTN, which is an overarching network of networks in Materials.
- insidemetaladditivemanufacturing.com on materials
This review includes: "Material discontinuities resulting from well understood processes are explored and the case for in-situ monitoring is made".