Abstract

Powder bed additive manufacturing (AM) is comprised of two repetitive steps: spreading of powder and selective fusing or binding the spread layer. Powder-bed AM can be sub-categorized as fusion-based where electron beams or laser beams are used to fuse the spread powder layer and binder-based where a liquid binder is used to bind the spread layer at areas specified by the governing CAD model. The latter process, commonly referred to as binder jet additive manufacturing (BJAM), outperforms fusion-based methods with respect to cost, build time, and material suitability; however, the parts are prone to shear-induced deformation during the powder spreading stage. Unlike fusionbased AM, the strength of BJAM parts is not fully developed until sintering and infiltration during postprocessing. This results in BJAM parts being more susceptible to deformation or even breakage due to the shearing action of the spreader. This shear-induced deformation can affect the precision and thereby performance of 3D printed parts. The binding step in BJAM is a complex function of binder viscosity, density, droplet size, impact speed, and drying time. The spreading step is a complex function of spreader speed and spreader shape, topography of spread and bound layer, and the rheology of the AM powder. This study presents a first-order model to simulate BJAM using a weak concrete-like, non-local, multilayer bonded DEM model. The DEM model has been parallelized using the massive parallelism offered by GPUs. An industry-grade metal powder is used to print physical cuboids at varying spreader speeds. The model is qualitatively verified against experiments on a real 3D printer. The model can be used to provide layer-wise spreading process control to minimize spreader shear-induced deformations.

Abstract

In terms of environmental, health and explosion protection, it is important to assess the extent of diffuse dust emissions. In addition to standardized dustiness tests and measurements under field conditions on real dust emissions, numerical methods such as the Discrete Element Method (DEM) coupled to Computational Fluid Dynamics (CFD) are promising approaches for the prediction of the latter. Thereby the DEM calculates the bulk solid particle motion and the CFD provides information about the flow parameters of the fluid phases in terms of location and time. Due to computing time restrictions when simulating larger processes, each dust particle is usually not modelled in detail, but rather described using so-called dust detachment functions. In this study, detachment functions are adapted and developed based on a benchmarking with dust-resolved DEM simulations. Therefore, the adhesive contacts of fine dust particles attached to coarse bulk solid particles are modelled with an adhesive contact model (JKR approach). Depending on the bulk particle velocity, impact angle, material properties and bulk particle rotation in the case of single particle-wall and single particle-particle contacts, a good match between dust-resolved DEM and DEM with integrated detachment functions can be provided. For the further derivation and verification of the method, it is planned to compare numerical results also to experimental investigations. Therefore, the fine dust particle amount is reproducibly applied to coarse bulk solid particles by a well-defined calcium carbonate powder. The adhesion of the powder phase is then analysed before and after an impact.