Numerical and experimental investigations of dimensionless material parameters in the generative manufacturing of polymers using laser sintering for accelerated material development and process optimization – Phase 2: Expansion of the field of application

Project description

Numerous research groups are currently working on the development of new powder materials and manufacturing processes. Compared to other manufacturing processes for plastic components, only a few materials are available for laser-based powder bed fusion (PBF/LB). The overarching goal of the DFG Priority Program “Materials for Additive Manufacturing” (SPP 2122) was to overcome this limitation.

The complexity and material requirements of PBF/LB make the development of new powders difficult. To accelerate powder development, a better understanding of the process is needed. Of particular interest is the influence of material properties on processing behavior. A better understanding of material-process relationships should enable the reproducible manufacture of components with improved mechanical properties.

The LaserSintering2 project is a continuation of the project “Numerical and experimental investigations of dimensionless material parameters in the generative manufacturing of polymers using laser sintering for accelerated material development and process optimization” from phase 1 of DFG-SPP 2122.

In the first funding period, theoretical considerations and numerical simulations led to a better understanding of material-process relationships. However, further investigations were necessary to take into account previously neglected material parameters. In addition, effects that occured during multi-layer application were to be investigated in greater depth.

The main objective of the LaserSintering2 project was to develop dimensionless parameters that can realistically represent the PBF/LB process and enable the definition of stable process windows depending on the material.

The first sub-goal was to investigate the relationship between other intrinsic and extrinsic material parameters and the PBF/LB process. As extrinsic material parameters, the influences of the shape and size of the polymer particles, with particular focus on the coalescence behavior in the PBF/LB process, were investigated. Intrinsic material parameters whose influences were investigated are viscoelastic properties and crystallization kinetics. In addition, the optical penetration depth of the laser in various polymers or polymer blends was analyzed in detail. Since there were no established measurement methods for this yet, an analysis method was developed. Numerical simulations were used to investigate the influence of all the material parameters mentioned and to determine their respective relevance for processability.

The second sub-goal was to validate the process windows derived from the dimensionless key figures using other materials. For this purpose, the simulation tools developed were made available to cooperating groups. In addition to validation, this also allowed newly developed powders to be examined for their processability.

The third sub-goal focused on the influence of applying several successive layers. The stationary melting and coalescence behavior of ten layers were investigated, which presumably depends on the time interval between the application of the layers. It was shown that the waiting time between the application of the individual layers influences the density and mechanical properties of the components produced.

Fraunhofer IWM subproject:

• Investigation of the influence of particle shape and particle size distribution
• Consideration of crystallization behavior in material modeling
• Development of a fast 1D solution method for simulating multiple powder layers
• Investigation of the influence of the waiting time between powder layers on component density