Andreas Wegner

Understanding the decisive thermal processes in laser sintering of polyamide 12

Due to the advancements during the last decade, the laser sintering process has achieved a high technical level, which allows parts being used for Rapid Manufacturing applications. However, the processes still show a poor reproducibility of part quality. Furthermore, process interruptions or defective parts still occur regularly. The know-how and expertise needed to avoid these kind of problems is still insufficient. The temperature increase in the powder bed during laser exposure is the driving force in laser sintering of plastics. The resulting part properties strongly depend on the interaction of melt temperature and melt viscosity caused by the laser power input in the powder bed. Additionally, cooling conditions and temperature gradients in the powder bed significantly influence the accuracy and especially the warpage of parts. However, literature provides only little information on these decisive thermal processes. Therefore, additional information is necessary to improve process understanding as we...

Comparison of long-term properties of laser sintered and injection molded polyamide 12 parts

Abstract Selective laser sintering (SLS) of polymers is on the edge from a pure prototyping technique to a small-scale production. For this transition, characteristic values such as long-term properties, and thus the degradation mechanism, are crucial factors for enabling a series application. Due to the specific characteristics of SLS parts like porosity and rough surfaces, a direct transfer of known mechanisms and models for injection molded (IM) parts is not or just to a limited extent possible. This leads to the aim of this paper, which is to investigate and compare the degradation behavior of polyamide 12 parts produced by SLS and IM.

Cross-linking of laser sintered polyamide 12 and polyethylene parts by gamma irradiation

Laser sintering gets more and more importance as a small series production technique. However, there is only a little number of materials available for the process. In most cases parts are build up using polyamide 11 or polyamide 12. Therefore, parts produced with laser sintering sometimes do not have the required part properties for intended applications. Especially temperature stability or chemical resistance is sometimes not sufficient for parts made by polyamide 12.Cross-linking by gamma irradiation is a well-established process for the post-processing of plastic parts in a cheap and fast single step treatment. It offers the possibility to improve temperature stability, the mechanical properties and the chemical resistance of parts. Therefore, it offers also great potential to improve part properties of laser sintered parts. However, there is only very limited knowledge on use of cross-linking for those parts.Within the performed work cross-linking by gamma irradiation is used to post-process parts ma...

Optimale Energieeinträge für die Verarbeitung unterschiedlicher kommerzieller Polyamid 11 und 12-Pulver sowie eines neu entwickelten Polyethylen-Pulvers beim Laser-Sintern

Das Laser-Sintern gewinnt zunehmend an Bedeutung als Kleinserienfertigungsverfahren. In den meisten Fallen werden die Bauteile aus Polyamid 12 (PA 12) gefertigt. Alternative Materialien kommen aufgrund der schwierigeren Verarbeitung kaum zur Anwendung, obwohl sie teilweise bessere Bauteileigenschaften aufweisen. Andere Kunststoffe sind uberhaupt nicht verfugbar. In beiden Fallen fehlt oftmals ein ausreichendes Prozessverstandnis, um Bauteile mit optimalen Eigenschaften zu erzeugen oder neue Materialien fur das Laser-Sintern zu qualifizie-ren. Im Rahmen der Versuche werden kommerzielle PA 11- und PA 12-Materialien sowie ein Polyethylen-Pulver hinsichtlich der Einstellung optimaler Verarbeitungsbedingungen untersucht. Ziel ist es, Zusammenhange zwischen dem Energieeintrag und wichtigen Bauteileigenschaften aufzustellen. Auf Basis der Versuchsergebnisse werden optimale Energiedichtefenster fur die verschiedenen Materialien abgeleitet, innerhalb derer mit guten Eigenschaften gerechnet werden kann.