Influences of powder morphology and spreading parameters on the powder bed topography uniformity in powder bed fusion metal additive manufacturing

The powder bed fusion (PBF) process is widely adopted in many manufacturing industries because of its capability to 3D print complex parts with micro-scale precision. In PBF process, a thermal energy source is used to selectively fuse powder particles layer by layer to build a part. The build quality in the PBF process primarily depends on the thermal energy deposition and properties of the powder bed. Powder flowability, powder spreading, and packing fraction are key factors that determine the properties of a powder bed. Therefore, the study of these process parameters is essential to better understand the PBF process. In our study, we developed a two-dimensional powder bed model using the granular package of the LAMMPS molecular dynamics simulator. Cloud-based deposition was adopted for pouring powder particles on the powder bed. The spreading of particles over the substrate was mimicked like a powder bed system. The powder flowability in the proposed study was analyzed by varying the particle size distribution. The simulation results showed that a greater number of larger particles in a power sample results in an increase in the Angle of Repose (AOR) which ultimately affects the flowability. Two different kinds of recoater geometry were considered in this study: circular and rectangular blades. Simulation results showed that depending on the recoater shape there is a change in the packing fraction in the powder bed. Cross-sectional analysis of the power bed showed a significant presence of voids when a greater number of larger particles existed in the powder batch. The packing fraction of the powder bed was found to be a strong function of particle size distribution. These analyses help understand the influence of particle size and recoater shape on the powder bed properties. Findings from this study help to provide a guideline for choosing particle size distribution if the spherical particles are considered. While the present study focuses on the spherical powder particles, the proposed system can also be adapted to the study of powder bed with aspherical particles.

Powder bed additive manufacturing (AM) processes, including binder jetting (BJAM) and powder bed fusion (PBF), can manufacture complex three-dimensional components from a variety of materials. A fundamental understanding of the spreading of thin powder layers is essential to develop robust process parameters for powder bed AM and to assess the influence of powder feedstock characteristics on the subsequent process outcomes. Toward meeting these needs, this work presents the design, fabrication, and qualification of a testbed for modular, mechanized, multi-layer powder spreading. The testbed is designed to replicate the operating conditions of commercial AM equipment, yet features full control over motion parameters including the translation and rotation of a roller spreading tool and precision motion of a feed piston and the build platform. The powder spreading mechanism is interchangeable and therefore can be customized, including the capability for dispensing of fine, cohesive powders using a vibrating hopper. Validation of the resolution and accuracy of the machine and its subsystems, as well as the spreading of exemplary layers from a range of powder sizes typical of BJAM and PBF processes, are described. The precision engineered testbed can therefore enable the optimization of powder spreading parameters for AM and correlation to build process parameters in future work, as well as exploration of spreading of specialized powders for AM and other techniques.

Experimental analysis of powder layer quality as a function of feedstock and recoating strategies

Powder spreading precedes creation of every new layer in powder bed additive manufacturing (AM). The powder spreading process can lead to powder layer defects such as porosity, poor surface roughness and particle segregation. Therefore, the creation of homogeneous layers is the first task for optimal part printing. Discrete element methods (DEM) powder spreading simulations are typically limited to a single layer and/or small number of particles. Therefore, results from such model configurations may not be generalized to multiple layer processes. In this study, a computationally efficient multi-layer powder spreading DEM simulation model is proposed. The model is calibrated experimentally using static Angle of Repose measurements. The adhesion model parameter, cohesive energy density is related to adhesive surface energy and strain energy release rate parameters. The model results show that interaction between particle and the powder spreading rake leads to noticeable variation in packing density, surface roughness, dynamic angle of repose (AOR), particle size distribution, and particle segregation. The powder model is experimentally validated using a recoater spreading rig to measure the dynamic AOR at spreading speeds consistent with recoating speeds and layer heights used in AM processes.

Laser powder bed fusion (LPBF) is an additive manufacturing technique whose efficiency and quality depend largely on a consistent and precise powder spreading procedure. This article examines the crucial role of powder spreading in influencing the quality of 3D-printed parts. Through case studies and experimental results, the article demonstrates in detail the impact of parameters such as: powder flowability, spreading speed, layer thickness, and recoater type on powder uniformity during spreading. In addition, the paper presents a comparison between types of recoaters in order to obtain optimum surface finish, mechanical properties, and reduced defects. This paper reviews the most appropriate powder spreading techniques to maintain the flowability and uniformity of the powder. Therefore, the primary objective of this work is to present an in-depth review of the impact of powder spreading dynamics in LPBF. In addition, it aims to demonstrate to the reader the various factors influencing powder spreading and the methodologies employed to optimize this crucial process.

Is high-speed powder spreading really unfavourable for the part quality of laser powder bed fusion additive manufacturing?

Lunar surface additive manufacturing with lunar regolith is a key step in in-situ resource utilization. The powder spreading process is the key process, which has a major impact on the quality of the powder bed and the precision of molded parts. In this study, the discrete element method (DEM) was adopted to simulate the powder spreading process with a roller. The three powder bed quality indicators, including the molding layer offset, voidage fraction, and surface roughness, were established. Besides, the influence of the three process parameters, which are roller’s translational speed, rotational speed, and powder spreading layer thickness on the powder bed quality indicators was also analyzed. The results show that with the reduction of the powder spreading layer thickness and the increase of the rotational speed, the offset increased significantly; when the translational speed increased, the offset first increased and then decreased, which resulted in an extreme value; with the increase of the layer thickness and the decrease of the translational speed, the values for voidage fraction and surface roughness significantly reduced. The powder bed quality indicators were adopted as the optimization objective, and the multi-objective parameter optimization was carried out. The predicted optimal powder spreading parameters and powder bed quality indicators were then obtained. Moreover, the optimal values were then verified. This study can provide informative guidance for in-situ manufacturing at the moon in future deep space exploration missions.

A literature review on powder spreading in additive manufacturing

Powder bed additive manufacturing (AM) processes, including binder jetting (BJAM) and powder bed fusion (PBF), can manufacture complex three-dimensional components from a variety of materials. A fundamental understanding of the spreading of thin powder layers is essential to develop robust process parameters for powder bed AM and to assess the influence of powder feedstock characteristics on the subsequent process outcomes. Toward meeting these needs, this work presents the design, fabrication, and qualification of a testbed for modular, mechanized, multi-layer powder spreading. The testbed is designed to replicate the operating conditions of commercial AM equipment, yet features full control over motion parameters including the translation and rotation of a roller spreading tool and precision motion of a feed piston and the build platform. The powder spreading mechanism is interchangeable and therefore can be customized, including the capability for dispensing of fine, cohesive powders using a vibrating hopper. Validation of the resolution and accuracy of the machine and its subsystems, as well as the spreading of exemplary layers from a range of powder sizes typical of BJAM and PBF processes, are described. The precision engineered testbed can therefore enable the optimization of powder spreading parameters for AM and correlation to build process parameters in future work, as well as exploration of spreading of specialized powders for AM and other techniques.

Powder bed additive manufacturing (AM) processes, including binder jetting (BJAM) and powder bed fusion (PBF), can manufacture complex three-dimensional components from a variety of materials. A fundamental understanding of the spreading of thin powder layers is essential to develop robust process parameters for powder bed AM and to assess the influence of powder feedstock characteristics on the subsequent process outcomes. Toward meeting these needs, this work presents the design, fabrication, and qualification of a testbed for modular, mechanized, multi-layer powder spreading. The testbed is designed to replicate the operating conditions of commercial AM equipment, yet features full control over motion parameters including the translation and rotation of a roller spreading tool and precision motion of a feed piston and the build platform. The powder spreading mechanism is interchangeable and therefore can be customized, including the capability for dispensing of fine, cohesive powders using a vibrating hopper. Validation of the resolution and accuracy of the machine and its subsystems, as well as the spreading of exemplary layers from a range of powder sizes typical of BJAM and PBF processes, are described. The precision engineered testbed can therefore enable the optimization of powder spreading parameters for AM and correlation to build process parameters in future work, as well as exploration of spreading of specialized powders for AM and other techniques.

Electrostatic powder spreading for metal powder bed fusion applications

Powder bed fusion (PBF), a subset of additive manufacturing methods, is well known for its promise in the production of fully functional artefacts with high densities. The quality of the powder bed, commonly referred to as powder spreading, is a crucial determinant of the final quality of the produced artefact in the PBF process. Therefore, it is critical that we examine the factors that impact the powder spreading, notably the powder bed quality. This study utilised a newly developed testing apparatus, designed specifically for examining the quality of powder beds. The objective was to analyse the influence of various factors, including the recoater shape, recoater gap size, and the different powder flow properties, on the powder bed relative packing fraction. Additionally, the study aimed to assess the variation in the particle size and shape across the build plate. The results indicated that all of the variables examined had an impact on the relative packing fraction, as well as the size and shape variations observed across the build plate.

Role of gravity magnitude on flowability and powder spreading in the powder bed fusion additive manufacturing process: Towards additive manufacturing in space

Powder bed-based additive manufacturing processes such as laser powder bed fusion, binder jetting, and electron beam melting are commonly utilized in various critical areas such as medical, aviation, and energy. Common to all these operations, the powders are first spread onto the build platform in a layer-by-layer fashion and selectively fused or bound with a suitable method. The quality of the process depends on several parameters, including how the powders are spread onto the build platform. The powder spreading operation, which involves spreading powders on a powder bed with a roller or spreader, is an important step in these operations and can affect various process outputs. In this study, powder spreading is numerically investigated using the discrete element method to determine the effects of layer thickness, rotation, and translation velocities, selected as parameters with a powder spreader roller. To account for the relationship between powder spreading parameters and the powder volume packing fraction, as well as the interactions between particles themselves and between the particles and the build plate, the Hertz-Mindlin contact model, including normal tangential forces, as well as the Johnson-Kendall-Roberts (JKR) contact model, including the effects of surface energy, were added to the numerical model. A Design of Experiment combined with analysis of variance (ANOVA) was utilized to gain a broader understanding of the relationship between process parameters, green density, and dynamic angle of repose.

Dynamic investigation on the powder spreading during selective laser melting additive manufacturing