What is powder usage efficiency?
In Selective Laser Melting, material efficiency, or powder utilisation rate, is defined as the ratio of the total powder used (as part or as support) or recycled over the quantity of powder wasted during the process or the powder cycle. Material utilisation rate is a direct indicator of process efficiency and ongoing materials costs.
Supports are included in this definition as the powder used to melt these volumes is taken into consideration and should ideally be minimised at the digital processing stage.
Waste is defined as what is inherently lost during standard machine functioning and during the whole production cycle (see below).
What is ‘usable’ or ‘reusable’ powder?
- to keep flowing in the machine; factors measured to assess this aspect can be particle morphology, Hall or Carney flow, …
- to retains its chemistry composition; factors measured cam be moisture, oxygen levels and elemental composition…
- to produce stable, repeatable properties of the solidified material; factors tracked in each build can be fatigue and tensile, hardness, optical density…
Data so far – recycling efficiency vs powder utilisation rate
In a study regarding polyamide powders, the powder utilisation rate varies around 45%, in tune with the recommended ‘refresh’ rate (= ratio of virgin versus used powder). [1, 2, 3]:
As for metal recyclability, in one study, researchers report 20% waste for a 409g component  based on five consecutive batches of the same metal. In other words, manufacturing a product weighing 1 kg produces ~200g of waste such as filter residue, aerosol emissions and remaining substrate stumps. Recycling efficiency is not mentioned.
The variance is thought to be due to differences in LBM machines, machine efficiency (laser processing and gas flow across the bed) and material properties (aluminium=light metal). In this study, overall material efficiency, or powder utilisation rate (=net part mass/mass of powder used), stands at ~61% to ~63%.
Why is so little data available?
Technology still maturing
Lack of definitions
- Powder utilisation rate: describes the actual quantity of powder used to produce a component;
- Recycling efficiency: defines how much un-melted powder retains its original physical properties and can be returned to the process;
- Powder refresh rate: defines the optimum quantity of virgin/new powder that is added to recycled powder to minimise the mechanical properties variations in the finished product.
Little demand, lack of customers’ awareness
 EOS e-Manufacturing Solutions:,
 Dotchev, K., Yussof, W., 2009, Recycling of Polyamide 12 Based Powders in the Laser Sintering Process, Rapid Prototyping Journal, 15(3), pp. 192-203.
 K. Kellens, et al, Eds, Energy and Resource Efficiency of SLS/SLM Processes, 22nd ed, 2011.
 C. Gebbe, M. Lutter-Günther, B. Greiff, J. Glasschröder, and G. Reinhart, “Measurement of the Resource Consumption of a Selective Laser Melting Process,” AMM, vol. 805, pp. 205–212, 2015.
 M. Lutter-Günther, A. Hofmann, C. Hauck, C. Seidel and G. Reinhart, Quantifying Powder Losses and Analyzing Powder Conditions in Order to Determine Material Efficiency in Laser Beam Melting, Applied Mechanics and Materials Submitted: 2016-07-17Vol. 856, pp 231-237 Revised: 2016-08-11