Search for: All records

Binder Jetting (BJ) has increased in popularity and capability since its development at MIT as it offers advantages such as fast build rates, integrated overhang support, low-power requirements, and versatility in materials. However, defects arise during layer spreading and printing that are difficult to remove during post-processing. Many of these defects are caused by particle rearrangement/ejection during binder deposition. This study explores methods of reducing particle rearrangement and ejection by applying small amounts of moisture to increase the cohesive forces between powder particles. A moisture application system was built using a piezo-electric disk to atomize water to apply a desired liquid to the BJ powder bed without disruption. The moisture is applied after spreading a new layer. Lines of binder were printed using varying droplet spacings and moisture levels. Results show that the moisture delivery system applied moisture levels across the entire application area with a standard deviation under 23%. The moisture levels delivered also had a single position test-to-test uniformity standard deviation under 21%. All tested levels of moisture addition showed mitigation of the balling defects observed in lines printed using dry powder under the same parameters. Moisture addition decreased effective saturation and increased line dimensions (height and width), but lines printed using the smallest amount of moisture tested, showed similar saturation levels and line widths to lines printed in dry powder while still partially mitigating balling.

 

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.