Search for: All records

Binder Jet (BJ) additive manufacturing creates parts by binding powder particles together with inkjet-printed droplets. BJ shows promise as an industrial process, but poor final part properties often limit applications. Prior work has shown that there is significant powder rearrangement from the kinetic impact of binder droplets that may contribute to the formation of defects in the final parts. This study builds upon previous research by studying the effects of print parameters, including droplet spacing and inter-arrival time, and droplet parameters, including droplet volume, velocity, and satellite formation, on the formation of lines. A new method, using an adhesive film, for extracting single-layer parts is described which allows for study of smaller, more sensitive primitives. The results show that pre-wetting the powder bed expands the feasible design space and allows printing with larger droplet spacings, smaller inter-arrival times, and slower droplet velocities. This enables up to 50 % faster print rates and the potential for reduced powder relocation due to droplet impact. Results from this work can be used to inform the selection of optimal process parameters and the design of new BJ systems to produce higher quality parts. 

Binder jetting (BJ) is an additive manufacturing process that uses a powder feedstock in a layer wise process to print parts by selectively depositing a liquid binder into the powder bed using inkjet technology. This study presents findings from high-speed synchrotron imaging of binder droplet-interaction during the BJ printing process. A custom laboratory-scale BJ test platform was used for testing which enabled control of relevant process parameters including powder material, print geometry, spacing between droplets, powder bed density, and powder moisture content. Powder ejection was observed above the powder bed surface and powder relocation due to droplet impact was observed below the powder bed surface. Powder relocation was observed to be sensitive to powder material, powder bed density, powder bed moisture, droplet spacing, and print geometry. Increasing powder bed density was found to increase particle ejection velocity but reduce the total number of particles ejected. Process parameters that increase binder / moisture content in the powder bed were found to reduce powder ejection. The number of ejected powder particles was reduced for lower droplet spacings. Both powder ejection and powder relocation below the powder bed were reduced by treating the surface of the powder bed with a water/triethylene glycol (TEG) mixture before printing. Results from this study help to build understanding of the physical mechanisms in the BJ printing process that may contribute to formation of defects observed in final parts. 

The Binder Jetting (BJ) process is capable of producing parts at high speeds from a variety of materials, but performance is limited by defects in the final parts. An improved understanding of fundamental phenomena in the printing process is needed to understand the source of these defects. This work presents initial findings from high-speed imaging of the BJ process using synchrotron X-rays. High-speed X-ray imaging allows for direct observation of key physical mechanisms in the printing process that may introduce defects including binder droplet impact on the powder bed, powder rearrangement below and above the powder bed surface, and balling formation. Testing was performed with multiple materials and droplet spacings to compare the effect on observed phenomena. Multiple lines were printed on packed and loose powder beds to further explore factors that affect defect formation and to better simulate industrially relevant conditions. 

Although commercial binder jetting (BJ) printers are available, they typically do not allow sufficient control over process parameters needed to study fundamental process characteristics. This work presents an overview of the design and construction of a custom BJ system used to observe fundamental phenomena in the BJ process. CAD models for the design and information on the software of this system is also given. This system will help elucidate the mechanisms that introduce part defects and other challenges unique to the BJ process. The BJ system was designed for both laboratory-scale experiments with a 100 x 100 mm build box and high-speed synchrotron X-ray imaging with a 500 μm thick powder bed, requiring high-accuracy motion stages and a controller with precise timing. The printer includes functionality for depositing and rolling powder, printing multi-layer parts, and direct observation of the jetting nozzle. This BJ system has enabled experiments that provide insight into the printing process that will aid future efforts to mitigate challenges associated with BJ.