Experimental investigation on ultrasonic hopper dispensing system in powder bed additive manufacturing

In powder bed additive manufacturing, feedstock powder can be dispensed onto powder bed through a hopper. The hopper dispensing system assisted by ultrasonic vibration is effective, especially for powder with small particle sizes (e.g., <10 μm). However, the ultrasonic hopper dispensing system does not dispense powder at a constant rate. The current remedy for this issue is to dispense more powder than necessary to ensure there is sufficient powder to cover the powder bed. However, this practice often results in longer dispensing time and larger amount of dispensed powder than necessary, and hence, higher manufacturing cost of printed parts. Therefore, it is desirable to understand powder dispensing behavior of the ultrasonic hopper dispensing system. This paper reports an experimental study on powder dispensing behavior of an ultrasonic hopper dispensing system equipped on a commercial binder jetting 3D printer (Innovent+, ExOne, PA, USA). Dispensing variables investigated are ultrasonic mode, ultrasonic intensity, and initial feedstock amount loaded into the hopper. In addition, the effects of cumulative number of dispensing cycles are also investigated. Results show that dispense rate changes as ultrasonic mode changes; it decreases when vibration intensity decreases, initial feedstock amount increases, and cumulative number of dispensing cycles increases. Based on the findings from this study, several approaches can be proposed to minimize the variation in dispense rate during printing, for example, to increase ultrasonic intensity as cumulative number of dispensing cycles increases.