Marius Sachs

Increasing flowability and bulk density of PE-HD powders by a dry particle coating process and impact on LBM processes

Purpose – The purpose of this paper is to demonstrate the processability of cohesive PE-HD particles in laser beam melting processes (LBM) of polymers. Furthermore, we present a characterization method for polymer particles, which can predict the quality of the powder deposition via LBM processes. Design/methodology/approach – This study focuses on the application of dry particle coating processes to increase flowability and bulk density of PE-HD particles. Both has been measured and afterwards validated via powder deposition of PE-HD particles in a LBM machine. Findings – For efficient coating in a dry particle coating process, the PE-HD particles and the attached nanoparticles need to show similar surface chemistry, i.e. both need to behave either hydrophobic or hydrophilic. It is demonstrated that dry particle coating is appropriate to enhance flowability and bulk density of PE-HD particles and hence considerably improves LBM processes and the resulting product quality. Originality/value – At present, ...

A novel process route for the production of spherical SLS polymer powders

Currently, rapid prototyping gradually is transferred to additive manufacturing opening new applications. Especially selective laser sintering (SLS) is promising. One drawback is the limited choice of polymer materials available as optimized powders. Powders produced by cryogenic grinding show poor powder flowability resulting in poor device quality. Within this account we present a novel process route for the production of spherical polymer micron-sized particles of good flowability. The feasibility of the process chain is demonstrated for polystyrene e. In a first step polymer microparticles are produced by a wet grinding method. By this approach the mean particle size and the particle size distribution can be tuned between a few microns and several 10 microns. The applicability of this method will be discussed for different polymers and the dependencies of product particle size distribution on stressing conditions and process temperature will be outlined. The comminution products consist of micropartic...

A novel process for production of spherical PBT powders and their processing behavior during laser beam melting

Additive manufacturing processes like laser beam melting of polymers are established for production of prototypes and individualized parts. The transfer to other areas of application and to serial production is currently hindered by the limited availability of polymer powders with good processability. Within this contribution a novel process route for the production of spherical polymer micron-sized particles of good flowability has been established and applied to produce polybutylene terephthalate (PBT) powders. Moreover, the applicability of the PBT powders in selective laser beam melting and the dependencies of process parameters on device properties will be outlined. First, polymer micro particles are produced by a novel wet grinding method. To improve the flowability the produced particles the particle shape is optimized by rounding in a heated downer reactor. A further improvement of flowability of the cohesive spherical PBT particles is realized by dry coating. An improvement of flowability by a fa...

New approaches towards production of polymer powders for selective laser beam melting of polymers

The opening of new fields of application of powder-based additive manufacturing methods like selective laser beam melting of polymers (LBM) is hampered by the limited choice of materials showing good processability. So far, basically only polyamide-based materials are available as optimized powders for LBM. Two innovative methods for production of spherical polymer microparticles for LBM polymers are presented: wet grinding with subsequent rounding in a heated downer reactor and melt emulsification. Moreover, the possibilities of dry coating to tailor particle properties are illustrated. The influence of particle and powder properties, like bulk density, shape or flowability on the LBM processability and properties of devices obtained from the powders are outlined. The first approach, stirred media milling and rounding, is applicable for a variety of polymers with a quite high breakage elongation. The second approach, melt emulsification, allows for spherical polymer microparticles in a single process ste...

Design and scale-up of a semi-industrial downer-reactor for the rounding of irregular polymer particles

The recent development of rapid prototyping technologies towards additive manufacturing reveals some major drawbacks of processes such as laser beam melting (LBM). This contribution focuses on the lack of suitable polymer material with a fine particle size and good flowability. Polymer particles obtained by a wet grinding process 1 are treated in a heated downer reactor. This treatment changes the particles’ morphology from a chiselled state towards a spherical form by surface tension forces in a molten state 2 and leads to an improved flowability. To reach the required amount of rounded polymer powder, a downer reactor in semi-industrial scale has been established and will be characterized in this article. For the purpose of particle rounding it is necessary to avoid contact of molten particles with each other and with the hot reactor walls. Furthermore, the heat distribution has been investigated as one of the key parameters of the process. Finally, a proof of concept by rounding wet grinded PBT materia...

Functionalization of polymer powders for SLS-processes using an atmospheric plasma jet in a fluidized bed reactor

Recently additive manufacturing processes such as selective laser sintering (SLS) of polymers have gained more importance for industrial applications [1]. Tailor-made modification of polymers is essential in order to make these processes more efficient and to cover the industrial demands. The so far used polymer materials show weak performance regarding the mechanical stability of processed parts. To overcome this limitation, a new route to functionalize the surface of commercially available polymer particles (PA12; PE-HD; PP) using an atmospheric plasma jet in combination with a fluidized bed reactor has been investigated. Consequently, an improvement of adhesion and wettability [2] of the polymer surface without restraining the bulk properties of the powder is achieved. The atmospheric plasma jet process can provide reactive species at moderate temperatures which are suitable for polymer material. The functionalization of the polymer powders improves the quality of the devices build in a SLS-process.

Neue Ansätze zur Herstellung gut fließfähiger Polymerpartikelsysteme zum Einsatz im Laserstrahlschmelzen von Kunststoffen

Wahrend generative Fertigungsverfahren bis vor einigen Jahren nahezu ausschlieslich im Prototypenbau eingesetzt wurden, stellen sie heute eine Fertigungstechnologie zur Herstellung spezieller Endprodukte dar. Der Erschliesung breiterer Anwendungsfelder und dem ‘rapid manufacturing‘ stehen unter anderem noch die eingeschrankte Auswahl an gut verarbeitbaren, kommerziellen Materialien entgegen: momentan ist praktisch nur Polyamid-12 als optimiertes Strahlschmelzmaterial erhaltlich. Im Folgenden wird eine Prozessroute zur Herstellung von Pulverwerkstoffen fur das Laserstrahlschmelzen von Kunststoffen fur Polybutylenterephthalat (PBT) vorgestellt. Die Prozesskette umfasst die Teilschritte Nasszerkleinerung, Verrundung, sowie das trockene Beschichten. Gut fliesfahige, im Laserstrahlschmelzprozess verarbeitbare Mikropartikeln werden erhalten. Der Einfluss von Partikeleigenschaften auf die resultierende Bauteilgute wird aufgezeigt.

Funktionalisierung von Polymermaterialien für Laserstrahlschmelzverfahren

Es werden zwei Prozessrouten fur eine Funktionalisierung von partikularen Ausgangsmaterialien fur das Laserstrahlschmelzen (LSM) prasentiert. Der erste Prozess stellt eine Adharierung von nanoskaligen Additiven auf Polymerpartikeln dar. Die Adharierung erfolgt rein uber physikalische Wechselwirkungen. Hierbei wird der Einfluss der Oberflacheneigenschaften der Polymere auf das Beschichtungsergebnis diskutiert. Neben einer Untersuchung mittels Rasterelektronenmikroskopie konnte die Fliesfahigkeit unter prozessnahen Auflasten mittels eines Zugspannungstesters gemessen werden. Im zweiten Prozess wird die Oberflachenenergie der Polymerpartikeln mittels eines atmospharischen Plasmas erhoht. Diese chemische Funktionalisierung erfolgt in einem Wirbelschichtreaktor.