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An introduction to metal powder atomisation
How to make metal powders. Part 1: An introduction to atomisation, process fundamentals and powder characteristics The rise of metal Additive Manufacturing has resulted in renewed interest in metal powder production. A market once dominated by a small number of specialist powder producers has now seen the arrival of a diverse range of competitors, all hoping to capitalise on the promised opportunities of metal powder-based part production. As many are discovering, however, making powders with the required characteristics, to the necessary standards, and profitably, is far from easy. Here, in the first instalment of a four-part series, two masters of metal powder atomisation, Joe Strauss and John Dunkley, introduce the process.
This portion of our series on atomisation is an overview to provide the reader with some understanding of the general science and attributes of the various methods of atomisation. The overall influence of the melt properties on the resultant powder particle properties will be presented along with the effect of the powder particle features on the bulk powder characteristics. Subsequent sections will provide greater detail on the individual atomisation processes. There are numerous industrial and commercial uses for metal powder. Most of these applications remain invisible to the end user, because the powder has been transformed to a solid by sintering or fusion, contained in paints and coatings, consumed as a fuel or in a chemical reaction, or as an ingredient in food. Visible or not, metal powder production exceeds 1,500,000 tons per year globally. In the Powder Metallurgy sector, the main applications for metal powders include the manufacture of structural and machine parts, cutting
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tools, and bushings and filters; two examples are shown in Fig. 1. All of these PM technologies process the powder via sintering, either in the solid state or with a partial formation of liquid. This includes the new sinter-based Additive Manufacturing technologies such as Binder Jetting. Laser and Electron Beam Powder Bed Fusion (PBF-LB and PBF-EB, respectively) Additive Manufacturing technologies produce threedimensional parts by binding the
powder using direct melting. Melting, or fusing, is also the mechanism used to process metal powders for solders and brazes, welding, thermal spray, and dental amalgams. In these examples, the powder becomes a three-dimensional object, film, coating, or an amalgam. Fig. 2 shows a brazed joint that used a paste containing powder as the filler material. Other uses of metal powder include the current carrier in conduc-
Fig. 1 PM porous bronze filter, Capstan California (left); PM worm gear, ARC Group (right) (Courtesy Metal Powder Industries Federation)
Winter 2021
Powder Metallurgy Review
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