Spreading of highly cohesive metal powders with transverse oscillation kinematics

TL;DR

This work investigates a new powder spreading approach for highly cohesive metal powders using transverse oscillation kinematics. It combines an integrated DEM-FEM computational model with an experimental spreading testbed and X-ray depth imaging to evaluate spreading quality. The key finding is that transverse oscillation (above ≈200 Hz) can achieve high packing fractions ($\bar{\Phi} \approx 0.50$–$0.60$) and robust layer uniformity, especially for thicker layers, suggesting practical potential for producing thin, consistent powder layers in LPBF/BJ when machine design is optimized. The study advances the understanding of kinematic spreading strategies for cohesive powders and highlights directions for hardware improvements to enable reliable multi-layer deposition.

Abstract

Powder bed additive manufacturing processes such as laser powder bed fusion (LPBF) or binder jetting (BJ) benefit from using fine (D50 $\leq20~μm$) powders. However, the increasing level of cohesion with decreasing particle size makes spreading a uniform and continuous layer challenging. As a result, LPBF typically employs a coarser size distribution, and rotating roller mechanisms are used in BJ machines, that can create wave-like surface profiles due to roller run-out. In this work, a transverse oscillation kinematic for powder spreading is proposed, explored computationally, and validated experimentally. Simulations are performed using an integrated discrete element-finite element (DEM-FEM) framework and predict that transverse oscillation of a non-rotating roller facilitates the spreading of dense powder layers (beyond 50% packing fraction) with a high level of robustness to kinematic parameters. The experimental study utilizes a custom-built mechanized powder spreading testbed and X-ray transmission imaging for the analysis of spread powder layers. Experimental results generally validate the computational results, however, also exhibit parasitic layer cracking. For transverse oscillation frequencies above 200 Hz, powder layers of high packing fraction (between 50-60%) were formed, and for increased layer thicknesses, highly uniform and continuous layers were deposited. Statistical analysis of the experimental powder layer morphology as a function of kinematic spreading parameters revealed that an increasing transverse surface velocity improves layer uniformity and reduces cracking defects. This suggests that with minor improvements to the machine design, the proposed transverse oscillation kinematic has the potential to result in thin and consistently uniform powder layers of highly cohesive powder.

Figures (15)

• Figure 1: Simulation setup with roller, fully extended powder reservoir piston with 42,000 particles and powder reservoir
• Figure 2: Calculated force required to oscillate at varying frequencies and an amplitude of $50 \, \mu m$ for each combination of springs explored
• Figure 3: Exemplary discretization of a sine wave with 1 kHz frequency with the maximum sample rate of the voice coil motor controller
• Figure 4: Mechanized powder spreading testbed equipped for transverse oscillation using a voice coil motor (a) CAD model including pre-loaded springs, and (b) annotated side-view of implementation
• Figure 5: Oscillation mechanism detached from spreading testbed