Influence of particle shape in additive manufacturing: Discrete element simulations of polyamide 11 and polyamide 12
Graphical abstract
Introduction
Parts of arbitrary complex shapes can be manufactured by melting sequentially deposited layers of fine particles [1]. This technique is called selective beam melting additive manufacturing and has become more and more important for many industrial sectors in the last years. However, restrictions such as processing speed and product quality in beam-based additive manufacturing processes still limit the technology from a broader range of applications [2].
Improvements in the quality of finished parts and reduction in manufacturing time requires a broader understanding of the mechanical behavior of fine particles composing the layers of powders deposited during the manufacturing process [3]. Particle-based numerical simulations are a valuable tool to predict the mechanical behavior of powders and have been recently employed by several authors to obtain crucial information to understand the role of powder in additive manufacturing process [4], [5], [6], [7]. In [6] it is investigated the influence of the shape of the blade used in the recoating step in the quality of the recoated powder layer. The formation of jamming and empty patches is investigated using numerical simulations of non spherical particles in [5]. In [4] mechanisms like shear induced dilation were identified to have a direct influence in powder bed quality during the investigation of process parameters such as recoating speed and layer thickness. In [7] realistic particle-based simulations were performed for different recoating velocities, and an expression to describe powder bed roughness as a function of the recoating mechanism velocity was derived.
Particle shape have a large influence in the behavior of granular material. Some distinct outcomes such as particle alignment and interlocking are only observable when dealing with non-spherical particles [8], and some granular properties such as angle of repose and packing fraction are highly dependent on particle shape [7], [9], [10], [11]. The role of shapes of different polymeric powders used in the additive manufacturing is still poorly explored. The goal of powder layer deposition is to obtain homogeneous powder layers with high density and low roughness to improve part quality and process speed. Particles of irregular shape are known to have poorer flowability compared to spherical particles [12], however packing fraction increases for shape anisotropic particles when compared to spherical particles [8]. As reported in [13], ellipsoids can randomly pack up to ϕ = 0.68 for aspect ratios near 0.6 (oblate shapes) and ϕ = 0.71 for aspect ratios 1.5 (prolate shape), and even approach ϕ = 0.74 for ellipsoids with other aspect ratios. Randomly packed spheres, as comparison, reach a maximum pack of ϕ = 0.64.
In this work we investigate the role of particle shape in the quality of the powder layer. For this task, we developed a method to generate optimized multisphere representations of real particles, obtained through X-ray tomography. These particles are reconstructed in the proposed multisphere framework, retaining the form factors of the original particles while using a relatively low number of spheres for multisphere representation, allowing us to investigate multiple scenarios involving hundreds of thousands of particles.
Section snippets
Multisphere method
The discrete element method (DEM) is a particle-based numerical technique that describes the translational and rotational motion of N individual particles by means of integration of Newton's equation of motion [14], [15], [16]. Collisions between particles are described by a physical model which relies on inter-particle parameters, particle size and shape to simulate realistic granular behavior [17], [18], [19], [20], [21].
The complex shape of the particles are modeled here by means of the
Effect of particle shape on the roughness of the powder bed – experimental validations
To validate the numerical simulations of the recoating process, we measured the surface roughness of a recoated layer of virgin PA12 powder. The evaluation of the powder roughness has been proved by a surface measurement of several single layers of PA12 powder. The recoating blade dispenses the powder with a thickness of 120 μm and a recoating speed of 100 mm/s. As shown in Fig. 14, the surface measurement is done by a projection of a planar, periodical and equidistant structured pattern on the
Conclusions
We developed a multisphere reconstruction approach followed by an optimization step to reduce the number of spheres used in the multisphere representation. The optimized representation preserves the original form factors with errors not larger than 5% and also the original volume with errors smaller than 6%. Additionally, the optimization step reduced the average numbers of spheres used for a multisphere representation from the range of 102–103 to 101, which allowed us to investigate different
Authorship contribution statement
Daniel Schiochet Nasato: DEM simulations, data processing, discussion of the results, draft of the manuscript.
Thorsten Pöschel: literature review, model development, mathematical description, discussion of the results, manuscript preparation.
Conflict of interest
The authors declare no conflict of interest.
Acknowledgments
We thank the German Research Foundation (DFG) for funding the Collaborative Research Center 814 (CRC 814) – Additive Manufacturing, sub-project B1. We thank Martin Heinl, Lehrstuhl für Fertigungsmesstechnik, Friedrich-Alexander-University of Erlangen-Nuremberg for providing the experimental measurements.
References (40)
- et al.
A novel process route for the production of spherical LBM polymer powders with small size and good flowability
Powder Technol.
(2014) - et al.
Jamming during particle spreading in additive manufacturing
Powder Technol.
(2018) - et al.
Particle-based simulation of powder application in additive manufacturing
Powder Technol.
(2016) Calibration of the discrete element method and the effect of particle shape
Powder Technol.
(2016)- et al.
Particle shape matters – using 3d printed particles to investigate fundamental particle and packing properties
Powder Technol.
(2020) - et al.
Discrete particle simulation of particulate systems: theoretical developments
Chem. Eng. Sci.
(2007) - et al.
Review on the influence of elastic properties on DEM simulation results
Powder Technol.
(2015) - et al.
Discrete particle simulation of particulate systems: a review of major applications and findings
Chem. Eng. Sci.
(2008) - et al.
Dem validation using an annular shear cell
Powder Technol.
(2013) - et al.
Investigation into calibration of discrete element model parameters for scale-up and validation of particle–structure interactions under impact conditions
Powder Technol.
(2011)
Multi-sphere approximation of real particles for DEM simulation based on a modified greedy heuristic algorithm
Powder Technol.
A new Voronoi-based surface reconstruction algorithm
Comput. Geometry
Production of polyamide 11 microparticles for additive manufacturing by liquid–liquid phase separation and precipitation
Chem. Eng. Sci.
Morphology of polymeric powders in laser sintering (LS): from polyamide to new peek powders
Eur. Polym. J.
Additive manufacturing (3d printing): a review of materials, methods, applications and challenges
Compos. Part B: Eng.
Additive manufacturing: rapid prototyping comes of age
Rapid Prototyp. J.
Dem simulation of particles of complex shapes using the multisphere method: application for additive manufacturing
AIP Conf. Proc.
A DEM study of powder spreading in additive layer manufacturing
Granular Matter
Discrete element simulation and experimental study of powder spreading process in additive manufacturing
Powder Technol.
Granular materials composed of shape-anisotropic grains
Soft Matter
Cited by (27)
Review of the types, formation mechanisms, effects, and elimination methods of binder jetting 3D-printing defects
2023, Journal of Materials Research and TechnologyIn-situ monitoring of powder bed fusion of polymers using laser profilometry
2022, Additive ManufacturingSimulation of the thermomechanical behavior of discrete particles in the laser directed energy deposition process
2022, Powder TechnologyCitation Excerpt :Dao and Lou [14] developed a SPH model for detailed 3D simulations of L-PBF and L-DED processes, including the powder flow, laser-powder interaction, heat transfer, solid-liquid phase change, solid-solid-liquid interactions, interfacial forcing at air-liquidand, and melt-pool dynamics. Nasato and Poschel [15] investigated the role of particle shape in the quality of the powder layer. The authors developed a method to generate optimized multi sphere representations of real particles.
A review of powder deposition in additive manufacturing by powder bed fusion
2022, Journal of Manufacturing ProcessesCitation Excerpt :However, their choice to use 2D particle traces obtained via SEM in order to create a 3D model of particles is controversial, since the reconstruction of a 3D object based on 2D data induces unwanted uncertainty into the simulations and might cause non-realistic results [40]. There are also studies that optimize this process by managing to achieve acceptable resemblance of powder particle models with the real particles by using a minimum of spheres [48], which do not necessarily only have contact points with each other, but might overlap to create a complex shape with the minimum amount of spheres [49]. This is incredibly important, since, even though it is easy to use a large number of spheres to combine them together and develop the model of the real particle with high dimensional accuracy, the more the spheres, the more the computational cost, hence the more time necessary for the simulation to run to completion.