Medical Design Briefs - January 2022 - 22

Extruded Silicone Tubing
power up the extruder and input a
screw RPM does the machine react
accordingly? This is all documented in a
protocol established by the SiMEDEx
engineering group, and in some in -
stances, is also reviewed by the customer.
Additionally, any preventative
maintenance steps must be established
in this step when bringing on a piece of
equipment online.
OQ - Operation Qualification. This is
the verification that the installed equipment
is working properly. It is also in
this step of the validation that engineering
studies must be performed for
process development. Die and mandrel
sizes are selected based on historical performance
of the raw material specified.
Questions to ask include:
* How much die swell do we anticipate
for this particular raw material?
* How much draw down do we anticipate
for the processing of a particular
raw material?
* It is at this point that tooling is modified
to ensure a stable manufacturing
process?
Once tooling dimensions are determined,
it is time to begin a series of engineering
studies to establish processing
windows (minimums and maximums) for
the critical processing variables. Some
customers have referred to these processing
windows as the worst case for manufacturing
product that meets dimensional
and visual specifications. For silicone
extrusion, those key variables are processing
temperature (to ensure proper vulcanization)
and line speed.
PQ - Process Qualification. The
process qualification is really where the
rubber hits the road (yes, pun intended).
Building on the previous engineering
runs, these runs are performed at
the nominal settings for the process.
For example, if the worst case OQ runs
showed that product could be manufactured
at 25 ft/min and 15 ft/min, a
good setting would be 20 ft/min as the
feed rate for the process qualification
lots. In most cases, it is best to perform
a minimum of three different setups
with two distinct lots of raw material.
This shows repeatability of the process
setup while also accounting for lot-tolot
variability.
It is becoming more and more common
for manufacturing engineers to
look at statistical process control to
ensure that a manufacturing process is
stable. A minimum CpK value of 1.33 on
the critical dimensional attributes illustrates
that the process for extruded silicone
tubing is in control.
This statistical work is typically performed
on a minimum of 30 samples,
and the CpK is calculated from this
data set. At SiMEDEx, a report summarizing
the findings is presented to the
customer showing that the process
meets the minimum CpK requirements
and is routed with for appropriate
signatures.
References
1. Medical Devices Regulation (Regulation
(EU) 2017/745), https://www.ema.
europa.eu/en/human-regulatory/
overview/medical-devices.
2. FDA Quality System Regulation (21 CFR
Part 820), https://www.fda.gov/medicaldevices/postmarket-requirements-devices/
quality-system-qs-regulationmedical-devicegood-manufacturing-practices.
This
article was written by Paul Mazelin,
President of SiMEDEx, Paso Robles, CA. For
more information, visit http://info.hotims.
com/82317-341.
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22
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Medical Design Briefs, January 2022

https://www.ema.europa.eu/en/human-regulatory/overview/medical-devices https://www.fda.gov/medical-devices/postmarket-requirements-devices/quality-system-qs-regulationmedical-device-good-manufacturing-practices http://info.hotims.com/82317-341 http://info.hotims.com/82317-713 http://info.hotims.com/82317-803

Medical Design Briefs - January 2022

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