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The use of Selective Laser Sintering (SLS) of polymers evolved from a pure prototyping into an additive manufacturing technology within the last 30 years. It enables the production of complex parts made out of high performance polymers that can be directly implemented in industrial environments. SLS is a complex two-step process composed of the powder recoating to form homogeneous, dense powder beds and also the laser processing leading to the coalescence of particles in order to obtain components showing a dense microstructure. Unfortunately, as of today, 95% of the SLS materials sold worldwide is based on polyamide 12 (PA12). In order to enlarge the SLS material portfolio and make it available to a wider industrial application field, the basic understanding of the basis powder material needs to be improved. Laser Sintered surfaces have always shown inhomogeneous and rough features inherent to the process. No surface characterization method was found to reliably measure such surfaces due to their rough features coupled to reflective optical properties. A novel surface characterization system, the Gelsight™, is examined to determine its suitability for SLS surfaces. It turned out that this new method achieves better results than the established stylus profilometry, delivers highly qualitative and quantitative data that easily help differentiate and compare SLS surfaces processed out of various materials. Finally, the mechanisms of surface texture formation on SLS components could be unveiled through Fourier analysis for various materials and surface orientations. The formation of dense and homogeneous powder beds is limited by the recoating process. Experimental work was coupled to statistical regression to unfold the complex interrelations between intrinsic and extrinsic particle properties during flowing and packing of microsized powders. Statistically sound and quantitative models were identified to help predict the flowing and packing behaviour of powders that corroborate with SLS processability of the investigated powders. Besides, a screening methodology was presented to design novel composite SLS powders. The effect of filler nature, size and shape on both thermal and flowing properties of the new SLS powder was identified and could be meaningfully implemented to optimize the thermal conductivity of SLS powders in an industrial application. Furthermore, the impact of both powder particle size and shape on the SLS processing of polyamide powders was thoroughly investigated. The linear regression models issued from this experimental work are not only statistically relevant but also deliver precise prediction tools for the sintered density, tensile mechanical properties and surface roughness of SLS components. Finally, the findings of this work based on material design according to size, shape, flowability and packing of powders are used to develop ceramic granulates for Laser Partial Melting (LPM) of ceramics. Through design of oxide ceramic composite granulates in addition to the development of process control, the direct processing of stiff but macroporous oxide ceramic parts was achieved. The present work sets the basis for a fundamental understanding of the SLS materials and their impact on the SLS process. Moreover, it provides quantitative screening tools and the fundamental understanding to design new SLS materials in order to expand the SLS material portfolio.

DDMC 2014 : Fraunhofer Direct Digital Manufacturing Conference : proceedings, ISBN:978-3-8396-9128-1