Characterization of metal powders along the reuse in Additive Manufacturing

We investigate characteristics of metal powder along the reuse cycles and identify impact of the Selective Laser Melting process on powder characteristics and its suitability for further processing. Particle characterization- and rheological technologies highlight the impact of powder reuse on its properties and show how to test it.

Currently, the most versatile and the most commonly adopted 3D printing technology used for metal components is Laser Powder Bed Fusion (L/PBF) also known as Selective Laser Melting (SLM). It’s high-tech and high-end applications often require cutting-edge quality of 3D-printed components. This, mostly is dependent on quality of feedstock (1). Therefore, the quality of metal powders is a paramount for quality-stable additively manufactured components and thus identifying if powder characteristics along its life and reuse cycles is of utmost importance. The microscopic properties of metal powders are of central importance in order to guarantee high quality of the final product (2). To assure it, typical powder analysis methods such as particle sizing and powder rheology, are used for assessing the physical properties of these powdered materials.

Additive manufacturing processes, also known as layer-based processes, make it possible to create products of nearly any complexity. This method is used in variety industries including:

  • aviation and space industries,
  • automotive industry,
  • medical implants,
  • machine building.

The heating chamber of the Anton Paar Convection Temperature Device 600 MDR is a model example for the need of additive manufacturing. In case of this component it enabled formation of tightly formed hollow air channels within the 3D-printed shells.

Anton Paar offers a versatile toolbox for characterization of impact of reuse on powders’ characteristics: Laser diffraction measures particle and aggregate sizes, powder rheology enables characterization of their flow and mechanical behavior, while the Streaming Potential allows to track qualitative changes occurring directly on the surface and surface of particles. 

Laser diffraction is the ideal technique for finding out the particle size distribution of powders in this size range. It enables fast and reliable measurements for deciding whether the present powder fulfills the required manufacturing criteria and when combined with comparative method also enables deeper insight to phenomena influencing the feedstock. The Particle Size Analyzer (PSA) allows powder dispersion in a liquid where agglomerates can be broken down by sonication, as well as with compressed air in the Venturi in dry mode. Very coarse particles of up to 2.5 mm can be measured in the free-fall mode. With the robust design of the PSA and the easy to use software Kalliope, this instrument is ideal for quality control in metal powder production.

Powder rheology can characterize powders using two unique powder cells on rheometers: the powder flow cell and the powder shear cell. These two cells provide the means for comprehensive characterization of powder properties such as flow behavior, fluidizability, cohesion strength, permeability, compressibility, tensile strength and more. With these parameters, the powder behavior can be characterized under the conditions closely reflecting every step of the application. In the powder shear cell, it is even possible to control the ambient conditions with a humidity range from 5 % RH to 95 % RH and an extensive temperature range from -160 °C to 600 °C.

The relatively high costs of metal-based additive manufacturing pose a strong limitation to its widespread adoption. High costs of powdered materials consist a considerable factor and limiting it by powder reuse offers an opportunity to both expanding the business getting closer to full sustainability of this technology. 

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