In powder bed fusion processes a powder layer is applied to a building platform and a laser or electron beam is used to selectively melt or fuse the powder. After melting, the platform is then lowered, and the process repeated continually until the build is complete. The unfused powder is removed and either reused or recycled depending on its condition.
Metal powders are the most commonly used materials although ceramic and polymer powders can also be used. Where an electron beam is used, the process is called Electron Beam Melting (EBM) and when a laser beam is used it referred to as Selective Laser Melting (SLM) or Selective Laser Sintering (SLS).
Particle size and shape
The efficiency of powder bed additive manufacturing processes and the quality of finished components is largely dependent on the flow behavior and packing density of the powders. Particle size directly influences these properties and hence is a key specification for powders used in this process with the optimum particle size being 15-45 μm for SLM and 45-106 μm for EBM for example. Particle shape and particle shape distribution are also known to influence how powders flow and pack and is another key indicator of powder quality.
Laser diffraction is an established technique for determining the particle size distribution of metal powders (ASTM B822) and works by measuring the angular variation of light scattered as a laser beam passes through a dispersion of the metal powder. Laser diffraction assumes that all particles are spherical so while providing high resolution size data (based on an equivalent sized sphere) it does not give any information about shape. A complementary technique to laser diffraction is morphological imaging or automated imaging, where individual particle images are captured and analyzed to determine their particle size, particle shape and other physical properties.
Crystal structure and elemental composition
In addition to particle characterisation techniques, Malvern Panalytical also supply X-ray techniques such as X-ray diffraction (XRD) and X-ray fluorescence (XRF) for determining the crystal structure and elemental composition of metal and alloy powders, and their fabricated components. Crystal structure and elemental composition can affect sintering behaviour of the powders and also the chemical and physical properties of fabricated components so their analysis is important.
What can our solutions do for you?
By measuring particle size, particle shape, crystal structure and elemental or phase composition powder manufacturers, suppliers and end users can:
- Ensure a consistent powder supply and prevent variations in product quality
- Identify suitable powders for machines with different spreader or rake designs
- Optimize atomization conditions to achieve the desired powder characteristic
- Predict and optimize powder packing density, flow characteristics and sintering behavior
- Follow changes in powder properties during processing and recycling and identify potential contaminants