SAMPE Journal - July/August 2022 - 35

end of the nozzle itself will cool to 220.5°C (Figure
10).
The extended nozzle analysis was conducted
using the same base boundary and material
conditions as the stock nozzle, with the 50.8 mm
extension modeled with two material assignments
(Figure 9), first being the stock 304 Stainless Steel
nozzle and second a custom brass fitting with the
same material properties of the stock nozzle (Table
3). This will allow us to see the effects of adding
an extended nozzle by how the material's cooling
behavior changes. The goal is to where on the
extended nozzle the material will cool to 180°C.
The stainless-steel nozzle showed a temperature
drop from 212.2°C to 180°C over a 0.917 mm length
(Figure 11a). The brass nozzle showed a drop in
temperature from 212.7°C to 180°C in 2.205 mm
(Figure 11b). It is important to note that these are
results during steady-state operation, meaning
the extruder is heated, but not pushing material
through the nozzle. During the Z-pinning process,
this will occur during a movement diagonal across
the length of the structure after a layer of pins has
been deposited. The analysis indicates that during
a steady state process the maximum length of a
304 stainless steel extended nozzle can only be
0.917 mm for a stainless-steel design, while the
brass extended nozzle can be 2.205 mm in length.
It is important to note that the layer height for the
Z-pinning process is 0.25 mm, so to fully deposit
a 20-layer pin (largest previously studied) the
penetrating nozzle must be able to reach 5 mm in
length. Factoring in the results from the thermal
analyses, the 304 stainless steel nozzle will only
be able to fully penetrate 3 layers (specifically
3.668). The brass extended nozzle would be able
to fully penetrate 8 layers of material (specifically
8.82 layers), which is the full pin length of the
smallest pin parameter that has been studied (4-8).
Limitations on this analysis can be seen through
the material properties being the average or
general case for these parts, as well as the geometry
of such a large gauge needle (in this case designed
as a 22-gauge needle). Meaning that there is heat
loss to the outside due to such thin walls. Another
form of limitation in the study is determining how
far the nozzle needs to penetrate to deposit a clean
pin,
Further analysis will be conducted determining
if the penetrating nozzle needs to fully penetrate
for the entire pin length. This will affect what
materials can be used to construct the nozzle. For
example, in the case of a 20-layer length pin, if
the nozzle only needs to penetrate up to 10 layers
than the brass nozzle might be good enough with
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JULY AUGUST 2022
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SAMPE JOURNAL |
35
Figure 11. Thermal analysis of 304 stainless steel (A) and brass (B) extended
nozzles.
small modifications to increase the outer diameter
or choosing a small needle gauge. Additionally,
different materials outside of brass and stainless
steel will be investigated. While brass and stainless
steel are the most common nozzles, nickel plated
copper nozzles for example have better thermal
properties than either.
CONCLUSIONS
Initial research in the Z-pinning printing process
has concluded that the novel process is effective
at increasing the ultimate tensile strength of
Z-axis samples. By introducing pins into a 35%
infill sample the Z-axis ultimate tensile strength
of the printed structures was increased by over
3.5x11
. Further research in Z-pinning established
that as pins got longer defects during the pinning
process effected the overall strength (in both X and
Z axis) of the printed part27
. To alleviate the defects
found during the pinning process, a penetrating
deposition nozzle was proposed. This penetrating
nozzle would incorporate standard FFF printing
abilities as well as the ability to extend into the pin
cavities creating during the Z-pinning process. The
goal of the penetrating nozzle proposal is to allow
the Z-pins to penetrate deeper into the printed
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