Friedrich-Alexander-Universität Erlangen-Nürnberg

Processing Strategies for Selective Beam Melting of Polymer Powders

Processing Strategies for Selective Beam Melting of Polymer Powders

When producing components by melting polymer powders layer by layer, complex issues referring to the application of material and energy, and to material consolidation, arise. Models for these sub-processes are highly idealized at present, failing to comprehensively describe the real processes taking place in component generation. For example, there is the idea that semi-crystalline thermoplastics can form a mixed two-phase area that remains over the entire period of component generation.

Figure 1: There is both polymer melt and powder in the build chamber of the SLM unit, at the same time

In preliminary investigations, scientist used thermoanalytical methods to show that the question whether there is such a mixed section is highly dependant on time and temperature. This affects the crystallization kinetics of the component in its molten state, and thus its final properties. In fact, the respective space- and time-resolved states during processing in existing plants can hardly be described. This is why process control can be correlated only to some extent to the formation of structures within the component, and thus to the final properties to be expected in these components. As a result, it is impossible today to control or monitor the specified characteristics (e.g. mechanics and surface quality) of these plastics components generated by beam melting.

 

This project is due to conduct experimental investigations to look into the sub-processes of component generation mentioned (application of material and energy, material consolidation with space- and time-resolved cooling and crystallization), in addition to their interactions (between e.g. packing density and energy coupling). Phenomenological description of sub-processes will result in profound investigation of the overall process, thus enabling modelling and simulation of the process, along with other sub-projects. Thermal effects are of particular significance here, because they influence component generation, as well as the properties of powder and material. For this purpose, it is necessary to analyse the mechanisms of interaction in the individual states of melting and sintering under variable conditions of processing. This investigation is due to provide the data for modelling and simulation of the (thermal) conditions in a beam melting unit, in order to enable the prediction of the geometrical and mechanical component properties resulting, in the long term. Manufacturers of commercial systems (EOS GmbH or 3D-Systems) have blocked their units, thus making it impossible for the operator to intervene in process control. To enable close consideration of the individual processes in this sub-project, scientists will design and build test set-ups (to analyse e.g. material application and beam-powder interaction), and they will also obtain a beam melting plant that can be freely parameterized.  By specially furnishing this equipment with appropriate measuring units, it will moreover be possible to conduct very profound analysis of the thermal processes, and thus of the melting and crystallization behaviours of the various materials, which is impossible at present.

Publications:

  1. D. Drummer, D. Rietzel, F. Kühnlein: Development of a characterization approach for the sintering behavior of new thermoplastics for selective laser sintering, Physics Procedia 5 (2010) Part 2, S. 533-542.
  2. D. Drummer, D. Rietzel, F. Kühnlein: Influence of temperature fields on the processing of polymer powders by means of laser and mask sintering technology. In: International SFF Symposium – An Additive Manufacturing Conference; 08-10.08.2011, Austin, Tx (USA)

Mission

SAOT provides an interdisciplinary research and education program of excellence within a broad international network of distinguished experts to promote innovation and leadership in the areas

Optical Metrology
Optical Material Processing
Optics in Medicine
Optics in Communication and Information Technology
Optical Materials and Systems
and Computational Optics.