Fundamental investigation and modeling of filament extension atomization for the production of polymer powders for selective laser sintering

• Applicant: Dr.-Ing. Steffen Jesinghausen
• Subject Area: Mechanical Process Engineering
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 550670348

Selective laser sintering (SLS) is an established additive manufacturing process for plastic components that is already widely used in low volume production. However, further development is currently hampered by a severely limited choice of materials, as the powder material must also have very specific disperse properties. While an established process for the production of SLS powder exists for PA12, other polymers can usually only be produced via energy- and cost-intensive processes (e.g. cryo-grinding and subsequent rounding). Therefore, Filament Extension Atomisation (FEA) will be fundamentally investigated as an alternative manufacturing process for finely dispersed, spherical polymer particles allow for a modelling of the process and to develop an understanding of which new materials can be processed into SLS powder using this procedure with suitable process parameters. FEA is a new method for dispersing difficult-to-spray liquids - primarily polymer solutions - at room temperature. In simplified terms, the process consists of two rollers rotating in opposite directions, which convey a liquid across a small gap so that individual filaments form as it emerges, which then break up into individual droplets. The great advantage of this method is that strain hardening and very high viscosities, which generally make spraying processes impossible, are beneficial for filament formation. Up to now, there has been no theoretical modelling of the process, which would allow, for example, a prediction of material suitability or the size of the droplets that are formed. However, this is essential for the further development of the method. In this research project, the breach between the modelling, the process and the material selection are to be closed and the method further developed to process polymers at suitable temperatures. The focus is on modelling the drop formation process and predicting the material as well as the powder properties. To achieve this, targeted extensional rheometric investigations will be carried out on partially self-developed experimental set-ups, in order to be able to observe the fundamental processes in filament and droplet formation individual. In addition, a laboratory-scale apparatus (FEA) will be set up that can precisely vary previously identified parameters such as roller spacing and geometry or rotational speed and temperature. In parallel, the processes are described theoretically and simulatively. A comparison at the different levels should make it possible to customize the models and determine appropriate material parameters so that a simulation of the overall process is possible with sufficient accuracy. Finally, the production of small quantities of powder in a specially modified SLS plant for small quantities of powder is planned.

• DFG Programme: Research Grants