SIM-AM 2023

Prediction of process windows for PBF-LB/P using dimensionless characteristic numbers

  • Bierwisch, Claas (Fraunhofer IWM)
  • Mohseni-Mofidi, Shoya (Fraunhofer IWM)
  • Grünewald, Moritz (German Plastics Center SKZ)
  • Rudloff, Johannes (German Plastics Center SKZ)
  • Bastian, Martin (German Plastics Center SKZ)

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Laser irradiation and thermo-viscous flow during PBF LB/P are analyzed both theoretically and by transient numerical simulations using the smoothed particle hydrodynamics (SPH) method to spatially resolve individual powder particles. Taking into account the strongly different time scales of laser motion, thermal diffusion and viscous flow, normalized master curves for the transient melt pool temperature and the surface temperature are presented. Infrared camera measurements of the surface temperature confirm the validity of the theoretical framework [1]. Based on these master curves a novel ratio of laser energy input and energy required to melt the polymer – the attenuation melt ratio (AMR) – is introduced, which puts material properties and process parameters into relation. Based on the AMR, normalized process diagrams, which relate depth and temperature of the melt pool to the laser energy input, are constructed [2]. The process diagrams include process windows for optimal part properties. The predictive quality of the process windows is confirmed by the assessment of mechanical properties of manufactured parts made of different polymers (PA12, PP, PEEK). The division of the PBF LB/P process into the temporal regimes of laser motion, thermal diffusion and viscous flow is furthermore exploited by implementing a one-dimensional process simulation solver, which only considers the building direction but also takes the crystallization kinetics into account. The reduction of dimensionality of the system enables fast simulations which are used to investigate, e.g., the influence of the time between subsequent layers in the PBF LB/P process. [1] M. Grünewald et al., Experimental, numerical and analytical investigation of the polyamide 12 powder bed fusion with the aim of building dimensionless characteristic numbers. Materials and Design (2021) 201:109470. [2] C. Bierwisch et al., Universal process diagrams for laser sintering of polymers, Materials and Design (2021) 199:109432.