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Materials Science in Additive Manufacturing Thixotropic metal 3D printing

resolution, the actuator’s maximum and minimum
movement capabilities limit printing effects. When the
extrusion speed is set within a specified range, another
significant parameter that can be adjusted is the X-Y
platform movement speed. Two motorized linear actuators
provide X- and Y-axis movement for the printing system.
The moving stage’s parameters can be configured through
CNC control software. Acceleration along both axes was
the first parameter considered in this study. Based on
the motor movement profile, the CNC control software
selected an acceleration value of approximately 50 mm/s .
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As illustrated in (Figure 13A), when the acceleration was
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lower than 50 mm/s , a significant amount of material
was deposited at the initial point, increasing the risk of
the nozzle tip becoming blocked. In contrast, when the
acceleration was >50 mm/s , the extruded thread spun, Figure 13. Extrusion results with different substrate moving acceleration.
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necessitating an extended preparation area to eliminate the (A) Acceleration lower than 50 mm/s and (B) acceleration higher than
50 mm/s .
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spinning lines.
The second part of the test was to determine the effect Table 4. Setup of printing parameters for studying the effects
of printing parameters at the same acceleration of on-axis of distance between nozzle and platform.
moving speed. As specified in Table 5, the reservoir was Printing parameters Values
heated to 83°C and maintained at that temperature
throughout the tests. The distance between nozzle tip and PID set value (°C) 83°C
substrate was set to 15 mm, two nozzles with diameters Nozzle diameter (mm) 1.5 mm and 1 mm
of 1.5 mm and 1.0 mm were compared, and the extrusion Extrusion speed (mm/s) 7.87 mm/s
speed was set to 7.62 mm/s for the two nozzles. X-Y platform moving speed (mm/s) 4 mm/s
The printed line width with the 1.5 mm nozzle reaches
an average of 2.5 mm at the slowest moving speed and Table 5. Setup of printing parameters for studying the effects
then decreases dramatically as the moving speed increases of X-Y platform moving speed.
to 3.5 mm/s, as shown in Figure 14. When the moving Printing parameters Values
speed is increased from 4 to 8 mm/s, the average line width
measured on the substrate decreases gradually until the PID set value (°C) 83°C
moving speed exceeds 8.5 mm/s. The results obtained with Nozzle diameter (mm) 1.5 mm and 1 mm
the 1 mm nozzle are consistent with those obtained with Extrusion speed (mm/s) 7.62 mm/s
the 1.5 mm nozzle trails. The smaller-diameter nozzle, Distance between nozzle tip and substrate (mm) 15 mm
however, showed a limited adjustable moving speed range;
discontinuous lines were detected and impacted the print alloy was conducted with the following process settings: PID
quality at speeds >6.5 mm/s. The best printing resolution set value to 83°C, actuator extrusion speed to 7.62 – 7.87mm/s,
for the 1.5 mm nozzle was 1.61 mm, which is 7.33% larger distance between the nozzle tip and the substrate to 15 mm,
than the initial outlet diameter. Meanwhile, the 1.0 mm nozzle outlet diameters to 1.0 and 1.5 mm, X-Y motion speed
nozzle can print a line with a width of 1.15 mm, which is to 4 mm/s, and X-Y platform acceleration to 50 mm/s . As
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15% wider than the 1.0 mm outlet. illustrated in Figure 15C, the thixotropic bismuth alloy was
4.2.5. Printing results with optimized process heated to 70.5°C and then extruded through a single-piece
parameters nozzle. In Figure 15A and B, printed sample lines with nozzles
of various diameters are shown. The printing system was
The printability study not only provided us with knowledge examined to demonstrate the entire printing process using
on the effects of major process parameters, but also enabled a 1.5 mm nozzle. As illustrated in Figure 15D, the printing
us to optimize the process and create good printing results. process included a material preparation step in which heated
For the Bi-Pb alloy, we have accordingly conducted extensive material was tuned to deposit as a stable line. The nozzle was
calibration and configuration to develop an optimized able to print the desired geometry using CNC software after
printing procedure. The final printing trial with the Bi-Pb material preparation.

Volume 1 Issue 1 (2022) 10 http://doi.org/10.18063/msam.v1i1.5