Medical Design Briefs - February 2025 - 22

Design Briefs
a
ser cutting, etc., as final steps in component
production is dependent on the
quality of the workpiece, whatever preform
configuration is used.
b
Additive Manufacturing Process
To produce the PtIr powder, no ingot
is necessary for atomization. Platinum
and iridium are placed into the crucible
at the specified ratio of the materials
and the molten material is fed into a gas
atomizer to produce PtIr powder. Upon
cooling, the powder is sieved to separate
the specified particle diameter
range. Any particles that fall outside the
specified range can be easily returned
to the powder production process and
serve as input material for the next
batch of atomizing, for high efficiency
of metal use. This is highly cost-effective
if the atomizing is done at the same facility
as the AM process.1
The chosen AM process was selective
laser melting (SLM) because it produces
fine, uniform, and denser microstructures
compared to selective laser
sintering (SLS). SLM has faster cooling
rates, which helps to produce the
superior microstructure, especially important
for applications that have miniaturized
features or demanding mechanical
performance.
Schematic showing SLM process (a) and an example of an AM produced blank with CNC milling (b).
crostructure and to prevent or minimize
formation of gas pockets. The microstructure
of the material, i.e., the arrangement
of atoms, the grain size and/
or the presence and the number of defects,
such as porosity, will affect results
of the fabrication processes. The bulk
material key features of microstructure
and porosity will affect the resulting mechanical
properties of a drawn wire, as
well as its surface finish.
Shrinkage porosity and surface inconsistencies
are known to be highly likely
defects when casting Pt alloys. While
80/20 is the most difficult to cast of the
three approved PtIr alloys, including being
the most susceptible to gas pocket
formation, 90/10 and 95/5 have the
same concerns. To ensure consistent
product quality, manufacturers use several
complex postprocessing technologies
including, for example, hot forging.
After casting, the cooled PtIr ingot
can be subjected to hot working by rolling
or forging, which refines the grain
22
structure and improves the mechanical
properties. The alloy is further processed
through cold working techniques that
can include drawing or rolling to achieve
the desired wire form. Cold working, i.e.,
drawing or rolling without heat treatment,
changes the crystalline structure
which increases the strength and hardness
of the alloy. Annealing, i.e., heating
the material above its recrystallization
temperature and maintaining temperature
for an appropriate amount of time
and then cooling, can be used, if or
when needed, to relieve internal stress
and recover ductility to make the wire
easier to draw into finer diameters.
The challenges of conventional manufacturing
of PtIr semifinished products
by vacuum casting requires extensive
and tight process control
throughout the entire process chain to
produce a homogeneous grain structure,
100 percent density, and uniform
properties. Finally, the efficiency of fabrication
using CNC milling, turning, lawww.medicaldesignbriefs.com
PtIr
alloys manufactured by SLM exhibit,
moreover, a finer grain structure
than in conventional production. The
extreme fine grain structure of SLM
parts is achieved by rapid cooling after
laser melting and not by forming and
heat treatment processes, as with conventional
manufacturing. This means it
will produce both higher yield and ultimate
strength. Wall thickness can be
printed to 0.012 in./0.3 mm and holes
down to 0.02 in./0.5 mm diameter. Ongoing
developments in the SLM process
should be able to reduce the as-printed
feature dimensions in the near future.
The AM equipment used has a high
level of built-in process control and monitoring
capabilities. The powder bed is
automatically monitored by a high-resolution
camera, which can also image the
continuous state or form of the component,
layer by layer. Other sensors produce
a real-time display of conditions,
with alarms preset if there is, for example,
a layer of powder that is not consistent.
Multiple lasers can improve features and
throughput in some instances, if needed.
Through the described process control
Medical Design Briefs, February 2025

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Medical Design Briefs - February 2025

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