Drop penetration tests were performed using a single droplet of
water-based binder (ZB7, Z Corporation, UK) falling and subsequently
penetrating on to the powder bed.To facilitat the mimicking of a typical
test powder bed, each powder bed was prepared by running the actual
3DP process. After the process, the reservoir in the build area was
removed from the 3D printer and subsequently used for the drop pene-
tration test. A digital syringe was positioned 8 mm above the powder
bed to minimize the occurrence of droplet impact on the powder bed
and also allow the droplet to fully discharge from the syringe. A droplet
volume of 30 μL was used and five replicates were preformed for each
composite powder. Thepenetration site for each droplet on the powder
bed was carefully chosen to ensure that there was no interference from
other pre-formed granules or reservoir walls. A high-speed particle
image velocimetry system (LaVision, Germany) was used to track the
complete drop penetration process (Fig. 1). The image velocimetry sys-
tem recorded each test at a rate of 60 frames s −1 . Following each test,
the drop penetration process was studied frame by frame to determine
the drop penetration time. The starting point was denoted as the in-
stance when the droplet first came into contact with the powder bed
surface, and thereafter the end point was defined as the time when all
the liquid was drained below the surface of the powder bed.