Polyolefiinien selektiivinen lasersintraus

Selective laser sintering (SLS) is a powder based additive manufacturing method especially equipped to produce small batch sizes of products with customized properties. However, the limited raw material availability restricts the production of functional parts with SLS. The purpose of this master’s thesis is to investigate the usability of polyolefins, namely polypropylene and polyethylene, as possible materials to be used in the SLS. The theoretical part of this thesis includes basic information about selective laser sintering and its requirements. In addition, possible powder production methods are investigated including mechanical and physiochemical methods. Furthermore, some general information about polyolefins is discussed. The experimental part investigates injection moulding grade polypropylene and polyethylene as well as two different commercial polypropylene powders. The material properties of these polyolefins were investigated to determine their suitability to be used in the SLS. Grinding was employed to pulverize materials in granulate form. Furthermore, the flowability of the powders was evaluated with a SLS machine and tensile specimens were produced with the SLS for the tensile testing. In addition, the fracture surfaces of the tensile specimens were investigated with SEM to evaluate the sintering quality and porosity of the specimens. Thermal analysis showed that all the investigated polypropylenes had adequate thermal properties, however, the investigated polyethylene did not. Rheological properties were superior for the commercial polypropylene powders compared to the injection moulding grade. The commercial powders had a relatively spherical morphology and sufficient particle size. However, grinding did not lead to the desired extrinsic properties. The flowability evaluation showed that the grinded polypropylene could not be spread evenly enough to be able to use it in the SLS. However, both of the commercial powders showed promising flowability and the tensile specimens could be manufactured with one of the commercial powders. The tensile specimens were produced with the different energy density levels to determine the optimal value for the specific material. According to the tensile tests, increasing the energy density level increases the tensile strength. However, all the SLS specimens showed very brittle behavior and quite low tensile stress at break. The sintering quality evaluation with SEM showed that the powder particles were not completely coalescence and the individual powder particles could be seen quite clearly in the structure. Using higher energy density levels could lead to lower porosity and better tensile properties