The Effect of SLM Spreader Structures on the Powder Spreading Dynamics Mechanism of Diamond Tools
ObjectiveSelective laser melting (SLM)technology provides a new approach for the integratedmanufacture of metal-matrix diamond tools with structural and functional integration, which has drawn alot of interest from the academic and technicalcommunities. The powder spreading process is the keyprocess...
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| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Editorial Department of Journal of Sichuan University (Engineering Science Edition)
2025-01-01
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| Series: | 工程科学与技术 |
| Subjects: | |
| Online Access: | http://jsuese.scu.edu.cn/thesisDetails#10.12454/j.jsuese.202400658 |
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| Summary: | ObjectiveSelective laser melting (SLM)technology provides a new approach for the integratedmanufacture of metal-matrix diamond tools with structural and functional integration, which has drawn alot of interest from the academic and technicalcommunities. The powder spreading process is the keyprocess of SLM technology, which is very important toobtain a dense, flat and uniform powder bed. However,there are defects such as pits, scratches, loose packing ofpowder bed, uneven distribution of powder layer, andparticles segregation in the powder spreading process.Further research is required since the powder spreadingprocess of metal-based diamond composite powdermaterials entails intricate scientific and engineeringissues such as non-spherical particles and multicomponentpowders. In this work, three blades of linear,circular, and parabolic as well as roller spreaderstructures are selected to explore the influencemechanism of spreader structures on the powderspreading quality and particle dynamic behavior.Research results have guiding significance for theoptimization of powder spreading processes of metalmatrixdiamond tools in SLM.MethodsIn order to achieve the aforementionedobjectives, the diamond/CuSn powders were utilized asthe research object to build the three-dimensionalgeometry of two types of powders. In this work, theadhesion force was introduced into the particle contactdynamics model, which was based on the Hertz-Mindlinmodel and Johnson-Kendall-Roberts (JKR) theory. Adiscrete element model (DEM) describing the microforceof two kinds of powder particles was established.The DEM of powder spreading process was constructed,and three blades of linear, circular, and parabolic as wellas roller spreader structures were selected. Parametricequations were used to alter the spreader's geometricshape. It has been investigated how the spreaderstructural factors affect the powder bed's density and thediamond distribution's homogeneity. The particledynamic behavior and the mechanism of powder beddensification in the powder spreading process wereexplored. Furthermore, the physical mechanism ofparticles segregation and jamming in the process ofpowder spreading were revealed.Results and DiscussionsFirst, the influence ofspreader structures on the powder bed quality wasexamined. When the structural coefficient angle θ of thelinear blade increased from 0° to 90° , the powder spreading quality changed slightly. As the angle θincreased from 90° to 150° , the powder spreadingquality was significantly improved. The powderspreading quality was significantly improved as thestructural coefficient c of the circular blade increasedfrom 0.25 mm to 1.25 mm. When the structuralcoefficient p value of the parabolic structure increasedfrom 0.1 to 2, the relative bulk density decreased from0.36 to 0.29, and the standard deviation increased from0.031 to 0.041. Increasing the diameter of the roller canimprove the powder bed quality. Under the condition ofthe structural parameter optimization given in this work,the influence of spreader structures on the powder bedquality was comprehensively considered. The resultsshowed that the powder spreading quality of parabolicblade and roller spreaders was relatively good, thecircular blade was the second, and the linear blade wasrelatively poor. Second, the flow behavior of particleswas analyzed. With the translational motion of thespreader, the upper part of the powder pile was shearedand moved forward under the action of the spreader. Theparticles in the lower part of the powder pile passingthrough the gap between the spreader and the substratewere similar to particles flowing through the orifice ofthe conical hopper. In addition, the particles underwentcomplex diffusion and cyclic movement inside thepowder pile due to the complex movement of the roller.While the diffusion movement of particles inside thepowder pile was relatively weak during the blade'spowder spreading process. The structure of the bladespreader had a slight effect on the trajectory of particles.The trajectories of diamond and CuSn particles showedsimilar flow patterns. The particles driven by thespreader moved horizontally and rose, fluctuating adistance at a high position. Particles then avalancheddown the powder heap's slope as a result of gravity.Ultimately, the particles through the gap between thespreader and the substrate were deposited on thesubstrate. Then, the particle contact force chains wereexamined. With the increase of θ value and c value, andthe decrease of p value, the blade exerted an obliquedownward pressure on particles, increasing their normalcontact force and lessening the blade's shear effect onthem. This would improve the powder bed quality. Forthe roller spreader, increasing the diameter of the roller would increase the area of interaction between the rollerand the powder pile, which would increase the normalcontact force of particles, strengthen the compactioneffect of the roller and improve the powder bed quality.Finally, the volume fraction of diamond particles wasanalyzed in terms of its spatial distribution. There wasno significant difference in the effect of spreaderstructures on the volume fraction of diamond particles inthe X direction, but the volume fraction of diamondparticles first increased exponentially along the Xdirection before fluctuating about the predeterminedvalue. This demonstrated that there was particlessegregation due to the low concentration of diamondparticles close to the front of the powder bed. Theprimary cause was that the fine CuSn particles weremore likely to pass through the gap between thespreader and the substrate, and deposited on the front ofthe powder bed. While the coarse diamond particleswith irregular shapes created strong force chains that caused particle jamming.ConclusionsWith the increase of the linearstructure angle θ value and the circular structurecoefficient c value, the decrease of the parabolicstructure coefficient p value and the increase of theroller diameter d, the oblique downward pressure of thespreader on particles is enhanced which will increase thenormal contact force of particles. And the shear effect ofthe spreader on particles is weakened, therebyimproving the powder bed quality. The results show thatthe powder spreading quality of parabolic blade androller spreaders is relatively good, the circular blade isthe second, and the linear blade is relatively poor. Thevolume fraction of diamond particles first increasedexponentially along the X direction before fluctuatingabout the predetermined value, resulting in the diamondparticles segregation during the powder spreadingprocess. |
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| ISSN: | 2096-3246 |