Polymer powders for laser-sintering: Powder production and performance qualification

The capacity of industrial parts manufactured by additive manufacturing (AM) has increased in the recent years considerably. More and more industrial sectors recognize the potential AM can deliver with regard to amplified part complexity, function integration, product personalization and many other encouraging aspects. Parts produced with Laser-Sintering (LS), one technology of the AM-basket, have been identified early to provide high potential for industrial applications. However, as of today, polyamide 12 (PA12) covers over 90% of the commercial and industrial relevant LS-materials. To ensure a reasonable growth of the LS market, new materials must be established to enlarge the material portfolio. But the design of novel LS materials is not an easy task, as they need to succeed several specific criteria. Besides appropriate intrinsic properties of the basic polymer like correct thermal, rheology and optical behavior, the distribution of the powder and even more the particle shape and structure (extrinsic properties) are crucial for a successful LS-processing. Especially the single powder particles as well as the particle size distribution are remarkably dependent form the particular powder production method. Understanding the pros and cons, particles exhibit in dependence of their creation raise the question how to qualify the particle shape correctly and how to correlate it with powder behavior during LS part production. With this work an approach is described to qualify single powder particles in a semi-automatic procedure with optical microscopy. The core value of the calculation is the so-called “elliptic smoothness” (E_S). This is the comparison of the contour of a single particle with the contour of a barycentre ellipsis having the same area as the 2D-silhouette of the said particle. E_S, as a novel form factor, gives an impression of the evenness of a particle surface. The combination of E_S with other features like particle diameter (p_d), aspect ratio (a_r) and solidity (s) improves the information about particles and their applicability to LS-processing. Several commercial and LS-research powders was investigated regarding this approach in order to gain more insight how the form factors should look like to be promising for successful LS-processing.