With the increasing use of laser sintering for the production of end-use parts, there is considerable interest in developing new and improved polymer materials for this technique. Due to the complexity of the process, however, materials are subject to very specific requirements in order to be easy processable. To gain a better understanding of these material requirements, this study investigates the currently most widely used material family: polyamides. Four commercial polyamide sintering grades, including two polyamide-12 grades, one polyamide-11 and one polyamide-6 grade, are characterized, using a new screening approach that encompasses all material properties essential for laser sintering. These include powder characteristics, melt flow, and solidification behavior of the polymer. The study reveals several particular characteristics of polyamides that explain the current popularity of this material family for laser sintering, and may be used as a guideline for finding new materials for the process.

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A need exists for techniques to assess flow properties of powders intended for laser sintering (LS).Although several powder flow measurement techniques are available, the flowability of a powder is strongly dependent on the nature of the applied flow field and none of the currently availably techniques adopt the flow field of LS. Therefore, this paper proposes a new technique, which mimics the flow in an LS machine, allowing a more appropriate powder flow evaluation for this particular process. The set-up provides qualitative assessment of powder layer smoothness, as well as a quantitative determination of the packing density of the deposited layer. Measurements on PA12, spherical PS and PMMA, and cryogenically milled TPU powders demonstrate the set-up's capability to evaluate powder flow with regard to LS.

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As the material market for laser sintering (LS) is currently dominated by polyamides, this research aims to widen the material pallet by investigating the feasibility of PB-1 for the application. Due to the polymorphism of PB-1, different thermal treatments were applied to obtain powder with a different crystalline structure. Lab tests on DSC, WAXS, rheology and TMA showed problems with the thermal window for the untreated, twinned hexagonal powder, mainly originating from the powder stickiness at temperatures in the melting onset, but the thermal treatments were able to improve the thermal window, by sharpening and shifting this onset to higher temperatures. Small-scale sintering tests validated the applicability of the treated powders via the creation of sintered multilayers. Higher bed temperatures were possible due to the thermal treatments, thus confirming the lab experiments. High shrinkage was, however, seen post cool down, as the crystal structure transforms from the tetragonal to the twinned hexagonal structure in a timespan of several days.