Metal powder characterization for 3D printing

摘要

In 3D printing of metals, dry powders are spread into thin layers prior to the exposure to ink jet printing for component shape definition. The performance of the specific powder in this process is critical and depends upon a number of properties such as particle size distribution, particle shape, specific surface area and surface chemical properties. The sum of these properties determines the flow and packing behaviour. Recent development of advanced rheometers for dry powders characterization has opened opportunities to accurately determine a variety of powder properties to be related to the function in specific powder processes. In this study, stainless steel, copper and titanium powders aimed for 3D ink jet printing (Digital Metal) were characterized regarding particle size, specific surface area and rheological properties in term of basic flow ability and shear yield stresses using a powder rheometer. The results showed that different batches of the same quality of stainless steel (316L) powders, with similar particle size distribution, vary significantly regarding the dry flow properties with critical impact on the function in 3D printing. In similarity, a modified copper powder showed a clear retardation in flow performance versus the as-received version. Differences in specific surface area indicated variation in particle shape or surface texture that could be correlated to the rheological data. Low shear resistance related to low degree of powder cohesivity and high bulk density was identified as favourable characteristics. Hence, powder rheology has been concluded to provide a powerful tool for powder quality control for ensuring adequate processing performance in 3D printing.