(173e) Influence of Relative Humidity on the Spreadability and Triboelectric Properties of Powders in Additive Manufacturing Processes

Metallic and polymer powders are widely used in Additive Manufacturing (AM) processes, with for example Selective Laser Melting (SLM) and Selective Laser Sintering (SLS). During such operations, successive thin layers of powder are created with a ruler or with a rotating cylinder and then partially sintered with an energy beam. The layer thickness defines the vertical resolution, and the spatial homogeneity of the layer is a key parameter to ensure good and consistent quality of the built parts. Consequently, assessing the spreadability/flowability of powders is required to ensure good and consistent quality of the additively manufactured parts. The flowability of powders depends not only on their intrinsic properties (grain size, shape, etc.) but also on the measurement/processing conditions. Therefore, it is crucial to investigate the influence of the measurement conditions.

In this work, we investigated the influence of the relative humidity on the spreadability, packing dynamics and triboelectric behaviour of several common metallic powders (AlSi7Mg, Inconel, and SS316) used in additive manufacturing applications. The spreadability/flowability of the powders was characterized using the rotating drum method, to reproduce the recoating conditions (flow field and stress state) encountered in an additive manufacturing process. The packing dynamic was measured with the GranuPack instrument to study the bed density. Finally, the triboelectric behaviour of the powders was measured with a GranuCharge.

We show that the relative humidity modifies significantly the cohesiveness, the packing dynamics and the tendency to create electrostatic charges during a flow. The modification of the flow properties and triboelectric behaviour has a direct influence on the spreadability of powders in additive manufacturing applications. This study demonstrates the influence of the environmental conditions on the flow properties of powders used in additive manufacturing applications.