Quality Control of Metal Powder Feedstock for Additive Manufacturing

The term “Additive Manufacturing” describes a process in which digital 3D design data, typically generated by CAD, are used to build a component layer by layer by depositing material. Additive Manufacturing, also widely known as “3D printing”, is a red-hot topic for R&D departments and small-scale production companies alike. Many manufacturers offer 3D printers or systems for Additive Manufacturing based on a variety of technologies and materials, for example in automotive, aerospace, defense, food, jewelry, medicine, and many other industries. Some of these methods have matured from a development tool for rapid prototyping to a standard production method. The basis for most of the above-mentioned processes is a powder bed on which material is sequentially deposited. Depending on the desired specifications of the 3D components, different types of powders are employed in the printing process. The particle size distribution and shape of the powders is a critical parameter for the operating conditions of the printer and for the properties of the final product. The size distribution (average size, as well as the amount of dust and the number of oversized particles) but also the shape of the particles has a strong influence on the flow behaviour of the powders. Generally, round particles within a narrow size range are preferred as they flow more easily and can be deposited more homogeneously. On the other hand, if the size range is too narrow, the packing density of the powder decreases which can generate voids and inhomogeneities in the final component. Oversized particles may cause defects in the thin layer of the powder and in the structure of the finished component. Small particles, for example, melt faster than larger particles but contain more oxide due to their relatively large surface area. The oxide content changes the material properties which characterize pure metals, for example melting temperature, conductivity etc.