(448l) The Application of Powder Rheology for Evaluating the Flow Behaviour of Powders for Additive Manufacturing Applications

Many Additive Manufacturing (AM) techniques require powder to be distributed in a uniform manner and are therefore sensitive to minor variations in the properties of feedstocks. Particle size alone is often used to define the suitability of a particular feedstock, however, to suggest that any single parameter or test method, e.g. particle size analysis, Hall Flowmeter or Hausner Ratio, can reliably describe a powderâ??s suitability for a particular process is a simplified approach to a complex issue. The ability of a powder to perform in a desired manner in a specific piece of equipment is not an inherent material property. Successful production demands that a powder is compatible with the process and it is not uncommon for the same powder to perform well in one unit operation, or machine, but poorly in another. This means that multiple characterisation methods are required, the results from which can be correlated with process ranking to produce a design space of parameters that correspond to acceptable process behaviour.

The increasing application of AM processes in an expanding number of industrial sectors is due to the ability to manufacture complex components quickly and precisely. While the main application has historically been prototyping, typically for biomedical, aerospace and automotive industries, there is an increasing emphasis on higher volume manufacturing. In order to manage the costs associated with larger production scales, manufacturers may look to evaluate alternative suppliers of feedstock materials as well as consider the re-use of powder that did not become part of previous components.

This study investigates the flow behaviour of samples of a commonly used titanium alloy sourced from different suppliers and produced using different manufacturing methods. The data show that despite similar physical specifications, the flow behaviour of the samples varies significantly resulting in inconsistent final build quality and requiring adjustments to be made to machine settings in order to achieve the necessary throughput and desired properties of the finished part. A further study demonstrates how the measurement of dynamic flow properties can be applied to optimise the re-use of metal powders.

The paper illustrates how a multi-variate approach to powder characterisation can help optimise AM processes by identifying powders that are conducive to successful manufacture, enabling machine settings to be defined to handle variations in feedstock, as well as enhancing efficiency through the re-use of unused material.