| contents page | news | events | advertisers’ index | contact |
Metal Powders for AM
An introduction to metal powders for AM: Manufacturing processes and properties As the AM industry grows, so does the number of metal powder suppliers and the range of different powder types that are available. In the following article Toby Tingskog presents a beginners’ guide to understanding metal powders for AM. Topics include powder manufacturing processes, spherocity, chemistry and measurement technologies, as well as considerations in relation to heats, lots and batches. As such, it is hoped that this review will allow for a clearer understanding of powder properties and reduce confusion among end users.
Metal powders have been used in a wide range of industrial applications for over a hundred years; Additive Manufacturing is just the latest sector to benefit from a technology that has evolved throughout this time. Metal powders are used from the most mundane applications such as oxygen getters in food packaging to the most advanced applications such as nickel-cobalt superalloy gas turbine discs. The major manufacturing processes for AM powders are Gas Atomisation, Induction Melted Bar Atomisation (EIGA), Plasma Atomised Wire (PAW) (Fig. 1) and Plasma Rotating Electrode Atomisation (PREP). There are, of course, many other methods for the manufacture of metal powders. Additional powder production routes which can be used for selected AM processes include water atomisation, crushing and spheroidising, and precipitation from chemical solutions and gas phases. The advantages and disadvantages of the major processes are shown in Table 1.
Vol. 4 No. 2 © 2018 Inovar Communications Ltd
Metal powder production processes for AM Gas Atomisation In Gas Atomisation, a molten metal stream is disintegrated into droplets by a high-pressure gas stream. The drops free fall inside a tower and solidify before collection. During free fall, the surface tension of the metal
has time to pull the drop into a sphere. To protect the metal from oxidation, the atomising gas is usually nitrogen or argon. Melting of the starting material, or charge, can be performed in an open atmosphere, under cover gas or in a vacuum (Fig. 2). The melting method and atomising gas have a significant influence on powder
Fig. 1 Highly spherical titanium powder produced by Canada’s AP&C using the plasma atomisation process (Courtesy AP&C)
Metal Additive Manufacturing | Summer 2018
111