Abstract

Binder jet additive manufacturing (BJ) offers unique advantages, including the ability to produce complex geometries and utilize a wide range of materials, but faces challenges related to part quality and defect formation. This thesis investigates the effects of process parameters on droplet-powder interaction, powder relocation, and line formation in BJ printing. A custom BJ test platform was developed to enable precise control over key process parameters and in-situ monitoring. High-speed synchrotron X-ray imaging revealed modes of powder relocation above and below the powder bed surface. Testing revealed that parameters that increase moisture in the powder bed, such as lower droplet spacings, printing adjacent to previously printed geometry, and pre-wetting, reduce powder disturbance. Powder ejection above the powder bed surface was found to be affected by powder material, density, pre-wetting, previously printed geometry, and droplet spacing. Powder relocation below the powder bed surface was found to be largely independent of binder infiltration behavior, suggesting that powder relocation below the powder bed surface is driven by the kinetic impact of the droplet. A novel approach for analyzing printed lines demonstrated the sensitivity of line formation to various parameters, including droplet spacing, inter-arrival time, volume, and velocity. Lines were found to ball more readily at lower droplet spacings when printing at lower droplet velocities, although other coupled droplet parameters such as droplet volume and formation of satellite droplets also play a role. In printing conditions susceptible to balling, the droplets at the beginning of printed lines were observed to agglomerate, relocating powder and introducing error to the starting position of the line. Pre-wetting the powder bed with a water/TEG mixture significantly reduced balling and increased the range of droplet spacings and inter-arrival times resulting in successful line formation. Printing with low droplet velocities on moisture treated powder beds further increased the range of inter-arrival times that successfully formed lines. Reducing the kinetic energy of droplet impact by reducing droplet velocity and reducing the impact of balling by pre-wetting presents a set of process print process parameters that show promise to reduce powder relocation during the printing process. These findings provide valuable insights into the fundamental mechanisms of droplet-powder interaction, modes of powder relocation during printing that may contribute to porosity defects seen in final parts, and print process parameters that mitigate powder relocation due to droplet-powder interaction.

Degree

MS

College and Department

Ira A. Fulton College of Engineering; Mechanical Engineering

Rights

https://lib.byu.edu/about/copyright/

Date Submitted

2024-05-10

Document Type

Thesis

Handle

http://hdl.lib.byu.edu/1877/etd13231

Keywords

binder jetting, inkjet, droplet-powder interaction, balling

Language

english

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