The Spreading Behaviour of Stainless Steel Powders for Additive Manufacturing

Additive manufacturing (AM) is a rapidly developing technology that transforms the manufacturing toolbox and operation of industrial companies. In this technology, material is selectively added layer-by-layer in order to create a complex part that is not easy to be produced in subtractive methods. Physical and chemical behaviour of powders used in additive manufacturing is a key element in industrial applications. Hence, it is necessary to accurately control and optimise the processing techniques with precise powder characterisation. There has been a considerable attention to the bulk powder behaviour in different fields of powder technology, but there is a lack of extensive research on the spreadability of powders in additive manufacturing (AM). To date, no prediction in spreadability of AM feedstock has been established hence no feasible powder spreadability metrics is achieved so far. While quantifying powder spreadability is a vital step for AM, there is no standard strategy for this purpose. Lack of a generally agreed definition for spreadability in AM might be related to the heterogenous nature of the powders which may differ by powders types, method of AM application and processes conditions. Therefore, precise monitoring of the spread behaviour of powders seems to be very challenging since powders may change their spreading dynamics at any period of time during the experiments and results to uncertainty. In other words, one spreadability metric may perfectly fit with a specific type of powder or process condition, while for a different choice of material or application it may not be relevant. Hence a parallel investigation on powder properties and processes parameters may be a suitable approach to develop the understandings in powders spreadability.
However, expanding of the current understandings regarding the spread behaviour of powders may help to establish a standard measurement method for spreadability.

In this project the combined effect of powder characterisations and processes parameters such as gap size, spread velocity and environmental conditions on the spreadability of stainless steel powders has been investigated. The samples are two different batches of 316L stainless steel and their particle size distributions are both in the range of 15-105μm. Series of experiments are conducted through using an in-house spreading rig to quantify the spreading behaviour of two different samples. This work investigates the spread quality of powders through obtaining the bulk density of spread layer on the build plate and form a comparison to the initial bulk density of the respective powders.