The quality of parts manufactured by laser powder bed fusion is closely related to the uniformity and density of the powder bed. In this work, the discrete element method is used to simulate the powder spreading process by different spreader geometries with rough substrate surfaces. The results indicate that reducing the spreader inclination angle significantly increases the number of force chains, enhances compaction, and consequently improves the quality of the powder bed. Studies also show that optimizing the bottom structure of the spreader can effectively reduce exposed areas. An arc-shaped structure promotes particle packing and filling, improving the powder distribution characteristics. A narrow spreader significantly affects the packing density of the powder bed at low layer gaps, whereas a wide spreader is relatively less constrained. At high spreading speeds, the spreader with an inclination angle of 135° produces the highest quality of the powder bed. R1000 performs excellently at larger layer gaps. The above findings provide valuable guidance for optimizing powder spreading strategies in the laser powder bed fusion process.

Controlling the quality of the powder bed is critical for guaranteeing component quality in laser powder bed fusion (LPBF). In this work, the discrete element method is used to examine how substrate surface morphology, including the roughness and texture angle, affects powder bed quality. The results indicate that the bed quality is more sensitive to changes in surface roughness than texture angle. Powder coverage can be improved by increasing the texture angle. The force analysis reveals that on rough surfaces, the contact force acting on the substrate has strong fluctuations. The particle-substrate contact force under the piles has an increasing-decreasing trend with the distance from the scraper increasing. In addition, the in-situ re-coating technique at a proper gap increment can effectively fill the depressions generated from the rough surface, achieving more uniform and dense powder beds. The findings provide a theoretical basis for optimizing powder-spreading strategies in LPBF process.

Powder bed fusion additive manufacturing has been applied to the fabrication of functionally graded materials. A new design that allows the material composition to change along the direction perpendicular to the powder spreading has been reported in the literature. Based on this design, this work examines the quality of the graded spread powder layer with two powders, which have a large difference of density. The results reveal that during the spreading of graded powders, the volume of particles on the heavy powder side is deposited less than that on the light powder side, indicating that heavy particles diffuse to the light powder side. This diffusion is affected by the spreading speed, but not much by the layer gap. Large spreading speed causes more significant deviation. The results also show that particle size affects diffusion, indicating that decreasing the particle size of the heavy powder may be a solution to reduce diffusion. [Figure not available: see fulltext.]

The shape variation of the laser beam is evidently observed in the laser powder bed fusion (LPBF) process because of changes in laser incidence angle and misalignment between the build plate and the laser focus plane. This issue is particularly relevant in large-scale LPBF systems where the laser beam needs to scan a large build area. However, most LPBF modeling studies assume vertical laser radiation. The heat transfer, melt pool, and solidification evolution due to the laser shape variation have not been well addressed and quantified. In the present study, the temperature distribution, melt pool geometry and flow dynamics are captured via numerical modelling, and the grain morphology is characterized under various laser incidence angles. The results show that the melt pool depth becomes shallower, and the width is near the beam size as the laser beam becomes more elongated. The beam shape variation can affect the liquid flow pattern with increasing incidence angle, resulting in a larger vortex at the front of the melt pool and a smaller vortex at the rear of the melt pool. The thermal gradient increases and the solidification rate decreases as the laser incident angle becomes larger. The present study enhances the understanding of multi-physics in the LPBF process.