Powder Spreading Process Research Articles

Numerical Studies of Influencing Factors on the Homogeneity of the Powder Mixture during the Powder Spreading Process of Powder Bed Fusion–Laser Beam/Metal

Recent studies have focused on the alloying of nitrogen (N) in high‐alloy stainless steels by powder bed fusion–laser beam/metal (PBF‐LB/M). However, N‐induced pore formation remains a challenge. To overcome this, a combined PBF‐LB/M and hot isostatic pressing (HIP) process is developed. AISI 304L stainless steel powder was mixed with silicon nitride (Si3N4) powder and processed by PBF‐LB/M, allowing partial retention of Si3N4. This helps to maintain sufficient N content while reducing pore formation. The microstructure is then homogenised by HIP. A major challenge of this process is to maintain the homogeneity of the deposited powder mixture on the powder bed to ensure a consistent N content in the final products. This study combines experimental and numerical methods to address this issue: scanning electron microscopy is used to characterize the microstructure and map the local N content, while various numerical studies based on the discrete element method are carried out to investigate the effects of layer thickness, substrate surface roughness, and powder properties on the intermediate product. The numerical approach effectively predicts the N content distribution and homogeneity on the powder bed. The models are validated with experimental data and optimal process conditions for PBF‐LB/M are identified.

Accelerating Laser Powder Bed Fusion: The Influence of Roller-Spreading Speed on Powder Spreading Performance

The powder spreading process is a fundamental element within the laser powder bed fusion (PBF-LP) framework given its pivotal role in configuring the powder bed. This configuration significantly influences subsequent processing steps and ultimately determines the quality of the final manufactured part. This research paper presents a comprehensive analysis of the impacts of varying spreading speeds, which are enabled by different roller configurations, on powder distribution in PBF-LP. By utilizing extensive Discrete Element Method (DEM) modelling, we systematically examine how spreading speed affects vital parameters within the spreading process, including packing density, mass fraction, and actual layer thickness. Our exploration of various roller configurations has revealed that increasing spreading speed generally decreases packing density and layer thickness for non-rotating, counter-rotating, and forward-rotating rollers with low clockwise rotational speeds (sub-rolling) due to powder dragging. However, a forward-rotating roller with a high clockwise rotational speed (super-rolling) balances momentum transfer, enhancing packing density and layer thickness while increasing surface roughness. This configuration significantly improves the uniformity and density of the powder bed, providing a technique to accelerate the spreading process while maintaining and not reducing packing density. Furthermore, this configuration offers crucial insights into optimizing additive manufacturing processes by considering the complex relationships between spreading speed, roller configuration, and powder spreading quality.

Effect of blade geometry on the powder spreading process in additive manufacturing

In powder-bed-based additive manufacturing, the quality of the powder bed is closely related to the geometry of the blade used during the powder spreading process. In this study, the spreading process with the vertical blade, inclined blade, and round blade with different radii was performed by discrete element method to investigate the effects of blade geometry on powder spreading. The results show that at the same spreading parameters, the round blade caused the highest density than inclined blade and vertical blade. Increasing the round blade radius can improve the packing density of the powder bed, but it has little effect on the uniformity. The increase in packing density is related to the transitional smoothness of the blade surface at the entrance of the powder bed. The smoother the shape transition of the blade surface at the powder bed entrance, the powders enter the powder bed more gently, so more powders enter the powder bed, resulting in higher packing density. The results may provide suggestions for improving the laser melting process.

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

Understanding powder spreading under low gravity conditions is essential for optimizing final products using additive manufacturing in space. In this study, we investigated the role of gravity on flowability and spreading mechanisms through combined experimental and discrete element method (DEM) studies. Three powders with different theoretical densities were used to reenact low compressive conditions resembling those in a low-gravity environment. The influence of low compressive conditions on flowability and spreading behavior was examined using the Hall flowmeter, rotating drum, and spreading experiments. In the experimental result, the static flowability was primarily affected by the presence of elongated particles rather than the compressive conditions. The dynamic AoR of TD_4 powder increased compared to that of TD_8 powder, despite the presence of spherical particles with a smooth surface finish. A DEM simulation study was conducted using TD_8 powder to investigate the impact of different gravity levels on dynamic flowability. The DEM studies revealed that the dynamic flowability under rotation was decreased under low gravity owing to the promoted cohesive interactions. The powder spreading experiment was performed using the three powders with different theoretical densities. The in-situ observation with particle image velocimetry analysis revealed that kinetic energy dissipation in the spreading process was accelerated in the TD_8 powder pile, despite its high interparticle friction and cohesive force. The powder spreading simulation was conducted using TD_8 powder to clarify the effect of low gravity on the powder spreading process. In TD_8 powder under 1 G, particle supply was facilitated by a synergistic effect of free-falling and deposited particles. However, increased cohesive interactions under 0.5 G and 0.16 G restricted particle supply via free-falling, consequently reducing the powder bed density by about 2 % and 6.2 %, respectively. These findings prove that the cohesive force predominantly controls dynamic flowability and powder bed quality in the spreading process under low gravity conditions.

Powder spreading process monitoring of selective laser melting manufacturing by using a convolutional Takagi–Sugeno–Kang fuzzy neural network

Powder spreading process monitoring of selective laser melting manufacturing by using a convolutional Takagi–Sugeno–Kang fuzzy neural network

Dynamic simulation of powder spreading processes toward the fabrication of metal-matrix diamond composites in selective laser melting

A novel method for the integrated production of structural and functional metal-matrix diamond composites is provided by selective laser melting (SLM) in the field of diamond tools. However, the uneven distribution of diamond particles and loose packing density in the powder bed can easily result in poor performance of diamond tools. In this work, a discrete element method model of diamond/CuSn composite powders is developed to simulate blade-spreading processes. It investigates how powder bed quality and particle dynamics are affected by diamond powder physical properties and powder spreading process parameters. The findings reveal that coarse diamond particles exhibit strong force chains at low velocities, whereas contact force chains are weak for fine CuSn particles at high velocities. It shows that diamond particles with irregular shapes have poor diffusivity and spreadability due to the large friction and mechanical locking forces, which causes diamond particles segregation. Therefore, the packing density and uniformity of the powder bed are both improved by reducing the volume fraction and particle size of diamond particles. In addition, the powder bed quality is improved by increasing the powder layer thickness and decreasing the translational speed of the blade, which weakens the shear expansion and jamming of diamond particles. The results have some significance for optimizing powder spreading processes toward the production of metal-matrix diamond composites in SLM.

Transient jamming of granular flow by blade spreading

This work focuses on a new kind of jamming of particle flow through constriction, which occurs in the powder spreading process in additive manufacturing, i.e. a powder heap is spread onto a rough surface by a moving blade. This work shows the experimental evidence of transient jamming by blade spreading at the first time. The jamming repetitively forms and collapses under the combined effects of narrow gap and blade shearing action. Angular particles with weak cohesion are more prone to mechanical jamming, with longer survival time of jammed state and stronger jamming strength. Besides mechanical jamming, cohesion-induced jamming is also responsible for the formation of empty patches within the spread layer. A regime map is deduced from physical experiments for the transient jamming by blade spreading in additive manufacturing, depending on the gap size, particle shape, and particle cohesion.

Effect of cohesion on structure of powder layers in additive manufacturing

Producing a consistent layer quality for different raw-materials is a challenge for powder-based additive manufacturing. Interparticle cohesion plays a key role on the powder spreading process. In this work, we characterise the structure of deposited layers in the powder-base additive manufacturing process by numerical simulations using the discrete element method. The effect of particle cohesion on the quality of powder layers is evaluated. It is found that higher interparticle cohesion lead to poor spreadability, with more heterogeneous powder layer structure and enhances particle size segregation in the powder layer. We also compare the powder layer quality deposited on a smooth substrate with that on a powder layer. Deposition on a powder layer leads to inferior layer quality of powder layer with higher heterogeneity and higher particle size segregation effects.Graphical abstract

Wear of blade spreader during powder spreading in Additive Manufacturing

The wear of blade spreader in powder spreading process in Additive Manufacturing is explored by experiment and numerical simulation using Discrete Element Method. The results identify a new mechanism for the wear of blade spreader, i.e. transient jamming of particles. Significant wear of blade spreader could be observed when the gap between the spreader and base is less than 2 times of particle diameter D90. The wear depth is more sensitive to particle interlocking than particle cohesion. Large wear depth or a long scratch could be induced by bumps or spatters on the base. The wear mainly occurs at the front bottom surface of the blade spreader. A simple method is proposed to reduce the wear of the blade spreader.

Powder flowability characterisation at preheating temperature in additive manufacturing

ABSTRACT The powder spreading process is usually performed at preheating temperature in powder-bed-based additive manufacturing (AM). Thus, the powder flowability characterisation at preheating temperature is important for powder spreading processes. However, devices for traditional powder flowability characterising methods are mainly designed for specific conditions at room temperature and cannot consider the effect of temperature on powder flowability. In this work, an experimental platform with a heated rotating drum was set up and a high-speed camera was used to record powder avalanche processes in a heated rotating drum for the powder flowability characterisation at preheating temperature. Nylon and stainless steel powder flowability at different temperatures was assessed by the statistical analysis of avalanche angle, avalanche time, arithmetic mean deviation and surface linearity of powder surface profile. Four parameters provide a good characterisation of powder flowability. The results can provide guidance for the powder flowability characterisation method at preheating temperature in AM.

Study on the Powder-Spreading Process of Walnut Shell/Co-PES Biomass Composite Powder in Additive Manufacturing.

Powder laying is a necessary procedure during powder bed additive manufacturing (PBAM), and the quality of powder bed has an important effect on the performance of products. Because the powder particle motion state during the powder laying process of biomass composites is difficult to observe, and the influence of the powder laying process parameters on the quality of the powder bed is still unclear, a simulation study of the biomass composite powder laying process during powder bed additive manufacturing was conducted using the discrete element method. A discrete element model of walnut shell/Co-PES composite powder was established using the multi-sphere unit method, and the powder-spreading process was numerically simulated using two different powder spreading methods (rollers/scrapers). The results showed that the quality of powder bed formed by roller laying was better than that formed by scrapers with the same powder laying speed and powder laying thickness. For both of the two different spreading methods, the uniformity and density of the powder bed decreased as spreading speed increased, although the spreading speed had a more important influence on scraper spreading compared to roller spreading. As powder laying thickness increased, the powder bed formed by the two different powder laying methods became more uniform and denser. When the powder laying thickness was less than 110μm, the particles were easily blocked at the powder laying gap and are pushed out of the forming platform, forming many voids, and decreasing the powder bed's quality. When the powder thickness was greater than 140 μm, the uniformity and density of the powder bed increased gradually, the number of voids decreased, and the quality of the powder bed improved.

Effect of powder morphology on flowability and spreading behavior in powder bed fusion additive manufacturing process: A particle-scale modeling study

Improving the quality of the powder bed is of great interest in the powder bed fusion-based additive manufacturing (PBF-AM) process to reduce micro-defects in the final product. We investigated the influence of particle morphology on flowability and spreading behavior using a discrete element method (DEM) simulation with multi-sphere modeling. The addition of non-spherical particles effectively decreased the flowability under gravity and rotation, resulting in a transition from rolling flow to cascading flow in the rotating condition. In the powder spreading process, the quality of the powder bed was decreased by adding elongated particles, owing to the frequent force-arch formation and additional wall effect caused by strong particle interlocking. Furthermore, the high spreading velocity facilitated loose powder packing owing to the frequent force arch and wide rearrangement area. In conclusion, spherical particles with a low spreading velocity are desirable for improving the quality of the powder bed, such as packing density and surface roughness, in the PBF-AM process.

Smart recoating: A digital twin framework for optimisation and control of powder spreading in metal additive manufacturing

We present a new framework for learning novel operational strategies and dynamically controlling the layering process in metal additive manufacturing. Metal additive manufacturing technologies such as powder bed fusion (PBF) are generally constrained by a fixed action powder spreading process. At every layer, the print platform is lowered by a fixed amount, and the same recoating action is performed. Ideally this would lead to consistent layering and identical properties each time, but frequently process variability disrupts this procedure, leading to inconsistent layers. This can be mitigated by intelligently controlling the powder spreading process, which we achieve via a shift to digital methodologies that can reveal new process strategies and dynamically update the printer commands. We employ Bayesian optimisation as a method to build and train surrogate models for real-time control. We then demonstrate the utility of this Smart Recoating approach within an integrated simulation framework driven by realistic Discrete Element Method powder spreading simulations. Our results inform new strategies for controlling the recoater and print stage displacements, and demonstrate the potential of a digital twin control system to mitigate process variation and achieve consistent print quality in each layer.

Simulation Research on the Effect of Spreading Process Parameters on the Quality of Lunar Regolith Powder Bed in 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.

Powder Spreading Mechanism in Laser Powder Bed Fusion Additive Manufacturing: Experiments and Computational Approach Using Discrete Element Method.

Laser powder bed fusion (LPBF) additive manufacturing (AM) has been adopted by various industries as a novel manufacturing technology. Powder spreading is a crucial part of the LPBF AM process that defines the quality of the fabricated objects. In this study, the impacts of various input parameters on the spread of powder density and particle distribution during the powder spreading process are investigated using the DEM (discrete element method) simulation tool. The DEM simulations extend over several powder layers and are used to analyze the powder particle packing density variation in different layers and at different points along the longitudinal spreading direction. Additionally, this research covers experimental measurements of the density of the powder packing and the powder particle size distribution on the construction plate.

Numerical modelling of SS316L powder flowability for laser powder-bed fusion

This work aims to improve the powder-bed spreading process for laser powder bed fusion additive manufacturing by gaining a greater understanding of metal powder flowability through numerical modelling and in-situ experimentation.Using the Discrete Element Method (DEM) to study the flowability of the powder and its intrinsic properties. A high-fidelity particle-scale model was developed to capture the dynamics of metal particle interactions in a virtual Hall flow meter based on a modified Beverloo law. The results are validated experimentally using the Hall flow static powder characterisation technique.For SS316L powder alloy with the hall-value of 29s/50g and with an angle of repose (AOR) of 32, the modelled powder that exhibited the same flow behaviour was found using 0.5 for both rolling and sliding coefficients resulting in simulated Hall value of 28.55s/50g with a simulated flow rate of 0.571 g/s, which is validated by AOR of the simulated powder [31.2-32.6]. However, rolling friction had minimal effect on the mass flow rate but increased the angle of repose. Sliding friction significantly decreased the mass flow rate and increased AOR.DEM is an ideal method to study flowability. However, there are certain constraints imposed on the computational power by a number of simulated particles and simulation time-step. Future research may involve investigating other dynamic flowability characterisation techniques.Enabling a better understanding of powder particle flow at a micro-scale by modelling powder flowability. This leads to simulating a more realistic powder bed and improving the powder spreading process, leading to better AM parts quality.This paper provides a unique approach for modelling the flowability of SS316L powder using a Beverloo law-based design of the Hall flow meter. This will improve the modelling of the spreading process needed for metal 3D printing.

Discrete element analysis for effects of recoating blade and surface morphology of substrate on powder spreading quality

A discrete element method model was established to simulate 316L stainless steel powder spreading process in selective laser melting. The effects of recoating blade speed, assigned gap width and substrate surface morphology on the powder spreading quality was studied. The results showed that lower recoating speed and larger gap width benefited the quality of powder layer. When the angle between the moving direction of recoater and laser scanning direction was greater than 45 °, the density level of the powder layer on the SLM processing surface was higher than that of the flat substrate and more uniform. The quality of the powder layer on the milled surface varied with position obviously, and the maximum density was between the other two types of surfaces, while uniformity of the powder layer was worse than the other two surfaces. This study shows that the quality of powder layer can be controlled by adjusting the setting parameters of the recoater and the surface morphology of the substrate.

Influence of layer thickness and substrate bed on the void fraction of powder layers for laser powder bed fusion

The spreading powder layer plays a vital role in determining the quality of Laser powder bed fusion (LPBF) -manufactured samples. In this study, the effect of layer thickness is investigated numerically and experimentally. It was determined that the void fraction at a certain height is higher than that of the entire layer, especially for thicker layers, because of gravity. The former is consistent with the experimental result for powders of the same thickness. The void fraction of the sintered part was also measured to confirm their relationship. Furthermore, the dynamics of spreading particles on a particle bed were numerically studied to investigate whether support powders around the sintered part affect the powder-spreading process. The powder layer on a particle bed is denser than that on an adjacent solid bed, suggesting that support powders will affect the powder-spreading of the sintered part, especially its borders, and contribute to the surface topography.

Raking Process for Powder Bed Fusion of Ti–6Al–4V Alloy Powder Analyzed by Discrete Element Method

In order to avoid the formation of defects in additive manufacturing (AM) by powder bed fusion (PBF) process, it is crucial to understand the relationship between the quality of powder bed and a powder spreading process. In this study, the influences of conditions of powder raking process on the densities and homogeneity of powder bed have been examined by computer simulation using Discrete Element Method (DEM) and experiment of powder bed formation using a blade-type spreader for Ti–6Al–4V powder by way of example. The results were analyzed with a special focus on the effects of the relative size of powder particles with respect to the gap between the blade and the build platform. It has been clearly shown that the gap needs to be larger than the upper bound of the distribution of powder particles diameter to obtain a high-density powder bed. The DEM simulation indicated that the blade can sweep even powder particles that are not in direct contact with the blade when the powder particles are in a close-packed tetragonal configuration. This is the probable reason for the experimental fact that powder particles smaller than half of the gap are suitable for PBF.

Preparation and properties of CoCrMo-Ni@Al2O3 composite by selective laser melting

In this study, nickel coated alumina (Ni@Al 2 O 3 ) particles were prepared via electroless plating, and ball milled with CoCrMo alloy powder in the proportion of 0 wt% to 2 wt%. Then the Ni@Al 2 O 3 reinforced CoCrMo alloy were manufactured by selective laser melting (SLM) process. The microstructure, mechanical property and wear resistance performance of the CoCrMo alloy were characterized. By increasing the content of Ni@Al 2 O 3 particles from 0 wt% to 1.0 wt%, the CoCrMo alloy kept flawless with the highest hardness of 435 HV 1 and best abrasion performance, which could be attributed to the pinning dislocation slip effect of Al 2 O 3 phase and the metallurgical bonding of Ni phase with CoCrMo alloy during the SLM process. When the content of Ni@Al 2 O 3 increased to 2 wt%, the inconsistent fluidity between Ni@Al 2 O 3 and CoCrMo powders has led to the uneven distribution of mixed particles during the powder spreading process, which resulted in the lowest compressive strength and wear resistance. • In the field of joint replacement surgery, the SLM-processed CoCrMo alloy implants are gaining more popularity for their excellent mechanical properties. In order to promote the wear resistance and prolong the service life of implants, small amounts of ceramic particles can be added into the alloy matrix. • In this work, we have fabricated the uniformly core-shell structure of Ni coated Al 2 O 3 particle by electroless plating, and the CoCrMo composites with different amounts of Ni@Al 2 O 3 particles were prepared by SLM technology. As the Ni phase acted as a bridge during the melting process, the surface of CoCrMo-Ni@Al 2 O 3 composites were smooth without obvious cracks. Moreover, the CoCrMo composites demonstrated better wear resistance and stable coefficient of friction for the introduction of Al 2 O 3 .