medical device molding technology july 2010
TRANSCRIPT
mddionline.com
July 2010
PREMIEREISSUE
a A Canon Communications LLC Publication
From the publisher of
Complex Molding PracticesGaining Design Freedom and Process Efficiency p. 20
Simulation TrendsCan Finite Volume Models Increase Accuracy?p. 24
Validation for DevicesGlobal Requirements Are Intensifying for Molded Components p. 12
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Contents
2 | JULY 2010 mddionline.com
JULY 2010 | Vol. 32, Number 7
28
24
20
Features12 Need A Little Validation?
Validating the injection molding process is no longer limited to
medical device components.
Ed Stockdale
17 When Molders Need to Be Choosy Medical devices often have to be molded in a cleanroom
environment. But which cleanroom option is best?
Stephen Moore
20 Using Complexity as a Competitive Advantage Complex injection molding can reduce costs and improve function
and aesthetics.
Dave Robinson
24 How Finite Volume Models Improve Accuracy Some commercially available tools have eschewed the finite element
method for the finite volume method.
John Cogger
28 So Fresh, So Clean A few analytical methods can help manufacturers keep residual
material product contamination away from their devices.
Tina May and Brent Shelley
31 Getting Up to Speed with Hot Runners Hot runner systems are boosting their importance to the medical
device industry thanks to speed and precision.
Craig Kovacic
Departments 4 Editor’s Page 6 Contributors 8 Molding News36 Molding Directory37 Advertisers Index
Cover images courtesy of Eastman Chemical Co., Fraunhofer IZM, Innova
Engineering Inc., Mack Molding, Kaysun Corp., and Nelson Laboratories.
17
MD+DI would like to extend a special thank you to its sister publications Modern Plastics Worldwide and Injection Molding Magazine for their contributions to this issue.
MD100702_002 2MD100702 002 2 7/2/10 8:37:43 AM7/2/10 8:37:43 AM
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FROM THE EDITOR
4 | July 2010 mddionline.com
W hen putting together a team for prod-
uct development, everything from the
material to the manufacturing must be
considered, and molding is just one of those pieces
of the puzzle. Recently, DD Studio put together a
team that included Eastman Chemical, Phillips Plas-
tics, and PolyOne to design and develop a mobile,
wireless, continuous vital signs monitoring system.
The ViSi Mobile by Sotera Wireless Inc. is composed
of a wireless device that straps to a patient’s arm
to monitor vital signs, such as blood pressure and
heart rate; a monitoring device to keep clinicians
connected to patients’ information; and a charging
station.
But according to Michael Swartz, growth strate-
gist, DD Studio, the result would not have been pos-
sible without a team pulled together from these four
companies. Swartz spoke at a press conference at
MD&M East in June.
Having the right material only works if
it can be manufactured successfully.
“When Sotera Wireless approached us with this
medical device design concept, it wanted the look
and feel of a small, user-friendly consumer product,
but had a number of specific demands. The device
had to be chemical resistant, durable, easy to clean,
and submersible under water. We weren’t sure the
design was possible,” said Swartz. “But, by working
with Eastman’s technical experts, we were able to
specify Eastman Tritan copolyester as a material
solution to make the innovative design a reality and
meet the device’s performance requirements.”
The device’s lens, housing, printed circuit board
assembly, and connectors are made with Eastman
Tritan copolyester MX711. The cold-swaging ability
of Tritan allows for fit and press assembly of the de-
vice, which offers a tight, smooth, continuous fit be-
tween parts; allows for joining parts without the use
of chemicals, adhesives, or mechanical fasteners;
and saves energy. By utilizing Tritan, Swartz said,
the device features superior resistance to chemicals
used in disinfectants and cleansers without crack-
ing or crazing. He said the material also exceeded
durability requirements, which he said was par-
ticularly valuable in mobile devices that are used
frequently or could be dropped or damaged should
a patient fall.
To protect the device from water and fluids found
in the hospital environment, it had to meet IPX7 re-
quirements of withstanding water
submersion for 60 minutes at a
depth of 1 m. DD Studio worked
with compatibility samples and
testing results from PolyOne to
select the thermoplastic elasto-
mer GLS Versaflex OM 3060. Ac-
cording to PolyOne, the material
adheres to the Eastman Tritan
copolyester substrate to seal the
device housing, including the
speaker port and microphone,
from water seepage and protects
internal electronics.
Having the right material only
works if it can be manufactured successfully. To en-
sure the manufacturability of the design, DD Studio
and the product development team worked with
Phillips Plastics Corp., which took the designs DD
Studio created and conducted a detailed design
for manufacturability exercise and created market-
entry prototype tooling.
“Contemporary plastic materials, such as East-
man Tritan copolyester, are well-positioned to re-
spond to the trend in the healthcare industry toward
durable, reliable wireless devices that enhance pa-
tient safety and comfort,” said Scott Hanson, global
industry leader, medical market segment, Specialty
Plastics Business, Eastman. “Development of the
Sotera Wireless device is an example of how early
and ongoing interaction between material suppli-
ers and designers is truly effective to bring next-
generation devices to the marketplace.”
Sherrie [email protected]
Molding: Just One Piece of the Manufacturing Puzzle
MD100702_004 4MD100702 004 4 7/2/10 8:40:42 AM7/2/10 8:40:42 AM
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6 | JULY 2010 mddionline.com
John Cogger is president of
Innova Engineering Inc. (Irvine,
CA), a full-service engineering
firm specializing in nonlinear
analysis of plastics. Cogger
originally formed the company
as Leading Edge Design in 1987. Reach him at
Craig Kovacic is global
manager of hot runner systems
for DME Co. (Madison Heights,
MI), an essential mold
technologies resource to
customers worldwide. Reach
him at [email protected].
Tina May is the chemistry
section manager at Nelson
Laboratories Inc. (Salt Lake City).
She has been with the company
since 2004. May previously held
the position of quality manager
of a certified EPA laboratory. Contact her at
Dave Robinson is vice
president of engineering at
Kaysun Corp. (Manitowoc, WI)
and brings a focus to tool
design. Robinson has worked in
the plastics industry since high
school, when he was a part-time machine operator
during school breaks. Reach him via e-mail at
Brent Shelley is a study
director at Nelson Laboratories
Inc., where he directs the
quantification of extractable
residue test. Shelley has been
with Nelson Laboratories since
2006 and is an ASTM committee member. Contact
him at [email protected].
Ed Stockdale is a process
engineer at MackMedical/Mack
Molding, (Arlington, VT) where
his responsibilities include the
development and validation of
injection molding processes and
programs. He can be reached at ed.stockdale@
mack.com.
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8 | JULY 2010 mddionline.com
MOLDING NEWS
Bioplastics: The Proof Is in the Isotopes 9 | Elastomer Grades Tailored for Medical Devices 10 | Eastman Opens Expanded Tritan Plant 10 |
OTHER STORIES
R esearchers from a
consortium of Eu-
ropean universities
and small-to-large medical
device developers and man-
ufacturers are using plastics
in various forms to create
tiny lab-on-a-chip devices.
Such devices could, for ex-
ample, enable consumers
to quickly analyze the risk of
blood clots in their legs prior
to a long-distance flight, or
warn pacemaker patients
when electric smog levels
approach dangerous levels.
One of the project’s goals is to use high-volume
printing and plastics processes to ensure that
such devices can be made and marketed at a price
attractive for consumers.
Not yet commercial but in an advanced testing
phase is the measuring device to ascertain the
danger of blood clots during long flights. The Eu-
ropean Union–supported project is called DVT-
Imp, and one of the active project members is the
Fraunhofer Institute for Reliability and Microin-
tegration IZM in Munich, Germany. The lab-on-
a-chip, which is the core of the diagnostic device
for deep vein thrombosis, was built and tested at
IZM. It is a small single-use cartridge, made of a
polycarbonate plate measuring 3 × 22 × 70 mm,
that acts as a tool for the biochemical analysis of
a drop of a passenger’s blood. The cartridge unites
two critical components in one device: a film
150 μm thick on which a filigree network with con-
ductor lines and gold sensors for blood analysis is
attached, as well as a 120-μm-deep fluid channel
for bringing blood to the analysis elements. Inside
the sensor chamber, antibodies are integrated on
electrodes that enable the analysis of the concen-
tration of blood-clotting markers. If the number is
elevated, then the risk of a thrombus (blood clot)
is forming.
“This example shows clearly the possibilities for
polytronics...In order to build up the infrastruc-
ture necessary for this, electronic systems have to
be produced in large quantities, in a cost-effective
manner on large substrates. And with polymer
electronics, this would be perfectly possible,” says
Karlheinz Bock, head of the Polytronic Systems
division at IZM. Polymer electronics combines
functional materials and electronics; for instance,
one technique involves dissolving polymers and
then recapturing them through a printing pro-
cess, structured on flexible sheets. The EU proj-
ect on the feasibility of the system runs until the
middle of 2010.
The sensor wristband (photo), which also was
engineered at IZM, is used for the long-term mon-
itoring of various body functions of older patients
or even athletes. Lighting elements, sensors,
and polymer resistors printed on films are con-
nected into one system with integrated circuits
made of silicon. A 0.003-mm-thin resonance cir-
cuit with an etched coil records electric smog. A
0.030-mm-thick interdigital capacitor attached
to a film detects skin moisture. Comb-shaped,
narrowly interlaced meanders made of copper
bands 0.5 μm thick measure body temperature.
—Matt Defosse
Lab-on-a-Chip Project Counts on Plastics
DuPont Expands Healthcare Off erings DuPont (Wilmington, DE) has
launched 10 new engineering
polymers targeting the healthcare
products and equipment market.
The company reports that its
healthcare offerings comply
with FDA, USP Class VI, and ISO
10993-5 and -11 regulations.
Sixteen of the products are
available as special control
grades that meet the standards
of manufacturing consistency
required of many nonimplantable
medical products, with 12 grades
available in even more stringent
premium control versions.
Masterbatch Squelches Smells and BacteriaFrom Polyvel (Hammonton,
NJ) comes two new series of
masterbatches. The first of the
developments, the VA-series of
masterbatches, contains silver,
trichlosan, or proprietary agents
that effectively kill microorganisms
such as fungus, E. coli, and
salmonella. These masterbatches
are suitable for inclusion in
most thermoplastics and can be
injection molded and extruded.
Because bacteria can emit
unpleasant odors, antimicrobials
are often used as a method of
controlling unwanted scents.
When the source of the smells is
not bacteria, Polyvel’s ZO-series of
odor-managing masterbatches help
end-product scent improvement.
PolyOne Distributes Dow SiliconesPolyOne and Dow Corning jointly
announced in June at the Medical
Design & Manufacturing East
show in New York City that
PolyOne is now distributing Dow
Corning’s silicone products to
healthcare device manufacturers
and fabricators in the United
States, Canada, and Mexico.
Imag
e co
urte
sy o
f FR
AU
NH
OFE
R I
ZM
Shown here is a sensor wristband with an electroluminescent display.
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MOLDING TECHNOLOGIES JULY 2010 | 9
Bioplastics: The Proof Is in the Isotopes
B ioplastics continue to get a lot of press,
and are one of the fastest-growing seg-
ments of the plastics and packaging indus-
tries. More and more consumer packaged
goods companies have announced cam-
paigns to integrate bioplastics into their
packaging to reduce their carbon footprint,
and thus attract eco-conscious buyers. But
how can processors be certain that the
amount of bioplastic content that is promot-
ed in a material actually exists in the resin?
Picarro Inc., a Sunnyvale, CA, technology
company can help make that determination
with its Combustion Module-Cavity Ring-
Down Spectrometer (CM-CRDS) device for
stable carbon isotopic analysis. According
to Picarro’s CEO Mike Woelk, the CM-CRDS
makes analysis push-button simple for com-
panies to verify the bioplastics composition
of polymers or finished materials throughout
the supply chain, whether on the factory floor
or at the distributor’s warehouse.
There are two massive cycles going on,
explains Woelk—the carbon cycle and water
cycle, and both CO2 and H
2O are very dynam-
ic molecules. “You can determine how CO2
moves in the universe and where it originat-
ed—shale gas, coal, [and] natural gas all have
a distinctive isotopic pattern. We measure it
as a family of molecules based on the carbon
that is in it,” Woelk says.
Previously, this type of measurement re-
quired expensive and disruptive testing in
specialized labs, but Picarro’s method gives
both plastic consumers and suppliers a tool to
ensure that bioplastics content claims can be
verified in minutes without disrupting ongo-
ing production.
To determine whether a material is bio-
plastic or “petroplastic,” the material is
burned, and the composition of the CO2 is
measured to determine where it originat-
ed. “There are very distinct signatures for
CO2—soy, corn, rice, etc.,” Woelk says. “We
make it easy—shop ready—so that you can
put a piece of plastic into the device and im-
mediately determine the material’s integrity
throughout the supply chain.”
Woelk agrees that there’s a lot of hype sur-
rounding bioplastic products, and added that
the manufacturers of medical devices, “regard-
less of their philosophical point of view,” want
to support their consumers’ buying preferenc-
es with respect to being eco-friendly. “How do
you know the truth? That’s what we provide
and it’s as simple as you can get,” Woelk states.
“What we’re talking about is analytical-grade
results as good as any technology in the world
can produce, and you don’t need to be a scien-
tist to do the work.”
This material analyzer helps companies determine whether packaging actually contains the bioplastic specified.
[See Bioplastics, page 11]
Where innovation takes flight
email: [email protected] call: 866-216-8808 219-989-3297
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MD100702_009 9MD100702 009 9 7/2/10 8:48:05 AM7/2/10 8:48:05 AM
10 | JULY 2010 mddionline.com
Underlining its ongoing commitment to the
medical device industry, Arkema (Colomb-
es, France) now offers specialized grades for
medical devices marketed as the Pebax MED
series of resins.
According to the supplier, these grades rep-
resent the highest quality of Pebax polymers for
medical applications, including devices exposed
short term to bodily fluids (<30 days). Effective
January 1, 2011, Arkema will no longer offer
standard-grade Pebax SA resins for any medical
applications. Pebax is a polyether block amide
thermoplastic elastomer that can be injection
molded or extruded.
Pebax resin has been a preferred material
in medical devices, such as minimally invasive
catheters for angioplasty, since the mid-1990s.
It has gained recognition over other elasto-
mers for its excellent flexibility, kink resistance,
torque transfer, low coefficient of friction, and
resistance to softening in the body.
Over recent years, however, the functional
and processing requirements for polymers have
become more rigorous. Arkema is introducing
this new Pebax grade as part of an ongoing
commitment to the medical industry, offering a
range of grades specifically intended for today’s
devices. “Our highest-quality Pebax MED resin
will be instrumental in helping OEMs meet
the growing demands of minimally invasive
and intravascular devices by improving product
performance and manufacturing yields,” says
Basker Lalgudi, Arkema’s North American medi-
cal market manager.
All Pebax MED resin grades have passed
USP Class VI biocompatibility testing and are
sterilizable by EtO, gamma, and steam, key
requirements for minimally invasive devices.
Pebax thermoplastic elastomer is manufac-
tured in the United States by Arkema Inc. (Phila-
delphia, PA) and marketed in North America
through its strategic partner Foster Corp., a
PolyMedex Discovery Group company (Putnam,
CT).—Stephen Moore
Elastomer Grades Tailored for Medical Devices
Eastman Opens Expanded Tritan Plant
pursue the new monomer and polymer, a
team led by Rutstrom pushed forward in
2005 with the simultaneous creation of the
monomer and polymer production tech-
nologies, as well as market development.
The goal was to commercially launch the
material by 2007 at the triennial K show in
October in Düsseldorf, Germany. The com-
pany reached that goal and announced its
intention to expand production, with those
plans coming to fruition in the form of the
newly inaugurated line.
Making all of this possible was the work
of a handful of researchers, building from
an investigation of a new monomer, tetram-
ethyl cyclobutanediol (TMCD), that began
in the late 1950s. At the time, Eastman
felt that the research could present a path
to a high-heat material. That work, led by
Robert Hasek, was eventually abandoned.
But in 2001, Emmett Crawford, a recently
hired research scientist, saw promise in the
monomer that Hasek had studied. Work-
ing with fellow researcher David Porter,
he started Eastman on the path that, after
much trial and error, would eventually lead
to Tritan.
Some 60 years prior, Crawford said a num-
ber of companies investigated TMCD, look-
ing for a method to produce polycarbonate
(PC) from it. Eastman’s interest stemmed in
part from how well the chemical fit within
its technology footprint. “The reason [East-
man] looked at it in the 1950s,” Crawford
said, “is it’s a great fit for our company,” on
the basis of the chemicals and intermedi-
ates Eastman produces in Kingsport. The
company has capacity in all of the elements
that make up Tritan, helping it better con-
Eastman Chemical Co. (Kingsport, TN)
marked another important milestone
in the whirlwind development of its Tritan
copolyester material with the May 13 open-
ing of a dedicated Tritan production plant
at its Tennessee headquarters.
“I’ve been in R&D most of my career, and
taking something from lab scale to com-
mercial scale when you have to simulta-
neously develop a new monomer, a new
polymer, and the market, it’s just…we had
no right to believe we could actually do that,
but we did,” explained Dante Rutstrom, vice
president and general manager, specialty
plastics business, at the plant opening.
Eastman officials hosted trade and area
press as well as local and regional govern-
ment officials to mark the occasion, show-
ing visitors the new production line, as well
as the array of now-commercial products
Tritan is used in. Including the original de-
velopmental line, Eastman now has more
than 30,000 tn/yr of capacity for Tritan co-
polyester, all in Kingsport. The supplier has
plans in place to double that capacity by
2011 should demand continue to expand
at its current pace. Eastman said that in the
past 12 months, Tritan business has qua-
drupled in dollar and volume terms, with
applications expanding beyond the initial
markets of reusable sports water bottles,
house wares, and small appliances, to now
include medical, infant care, bulk water,
and signage. Eastman did not disclose its
investment to date in the material’s launch.
Company officials said that technology
development began in earnest in 2004. After
presenting a plan at the corporate level to
Eastman’s dedicated Tritan production plant opened in May.
MD100702_010 10MD100702 010 10 7/2/10 8:49:19 AM7/2/10 8:49:19 AM
MOLDING TECHNOLOGIES JULY 2010 | 11
trol costs and production.
Pushing past the reluctance of some to
pursue TMCD on the basis of past failures,
Crawford successfully found a route to cre-
ate the monomer and a new copolyester
from it. He would eventually share his work
with Hasek, who had toiled with the mol-
ecule decades before.
Mark Costa, Eastman’s executive vice
president, specialty polymers, coatings, and
adhesives and chief marketing officer, said
Tritan’s rise has been fueled by concerns
about the safety of PC, and more impor-
tantly, its chemical forerunner, bisphenol
A (BPA). In the past, where its heritage
copolyesters could compete with acrylic,
vinyl, and some styrenics, Tritan’s proper-
ties enable it to target PC—a market that
has a global annual volume of 700,000 tn by
Eastman’s estimation. “So, 60,000 tn out of
a 700,000-tn/yr market leaves a lot of room
for additional build for us,” Costa said, “but
PC is a huge market, and lots of things like
optical media, we have no interest in and
won’t be pursuing.”
In order for Eastman to target PC replace-
ment, it understood early on that its con-
sumer safety credentials would need to be
well established. To that end, in addition to
its own testing for endocrine disruption and
estrogenic and testosterone activity, it has
completed independent third-party testing
of the material. “Even when we began, we
had a sense that we really want to go the
extra mile here in understanding the safety
of our materials and the monomers that go
into them,” Rutstrom said. Motioning to a
spot on the conference table, he added, “if
the letter of the law stops here, we want to
stop here,” dropping his hand farther along
the surface. —Tony Deligio
Bioplastics [continued from page 9]
The CM-CRDS is a tabletop unit that per-
forms a bulk specific isotope analysis and de-
livers isotopic carbon measurements of plas-
tics and other packaging materials in roughly
10 minutes. The CM-CRDS is designed to run
up to 147 plastic samples consecutively with-
out operator intervention, and with minimal
training and setup time. Woelk notes that
Picarro is in the very early stages of commer-
cialization of its technology, even though it
has been around for several years.
Picarro sees the regulatory environment
evolving as a result of the green movement,
“More regulations will evolve by hook or by
crook,” Woelk says. “I think people think that
these bioplastics markets are all big estab-
lished markets, but they’re not. There are
very few companies that are making any
money in the green space. And there are is-
sues surrounding bioplastics, such as com-
mingling bioplastics and petroplastics, that
contaminate the resin stream. It will be im-
portant for manufacturers to produce scien-
tific results to match the suppliers’ claims.”
—Clare Goldsberry MT
The company’s copolyester material has a surprisingly long history.
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A successfully validated process is
stable, dimensionally centered
within the required tolerance, and
minimizes rejects with significantly fewer
adjustments from run to run. The adop-
tion of process validation principles and
disciplines has proven beneficial for both
new and existing programs. It is essential,
however, to first establish an agreed-upon
procedure for the validation, known as the
installation, operation, and process qualifi-
cations or IQ/OQ/PQ. This should be done
in conjunction with the customer.
Early interaction identifies and resolves
areas of concern between the two parties. It
also details the equipment needed to manu-
facture, test, and measure product, and it de-
fines dimensional tolerances, molding tech-
nique, engineering studies, the substance of
the qualifications themselves, and the quali-
fication approval and acceptance criteria.
Typically, the desired acceptance criterion
for critical dimensions is a Cpk of ≥1.33 (see
the sidebar “Definitions“ on p. 13).
The IQ/OQ/PQ procedures are outlined
below. It’s important to note that the use of
all or any of these disciplines has proven ben-
eficial for process and dimensional control.
Installation QualificationThe purpose of IQ is to demonstrate that the
equipment and facility used to manufacture,
measure, or test the product is maintained
and calibrated as required. Additionally, it
affords the opportunity to benchmark spe-
cific installation and process conditions that
can prove valuable over the life of a mold-
ing program. For example, if a process isn’t
yielding the same dimensional stability after
months of run time, the problem could be
attributed to a number of circumstances,
including restricted water circuit flow, a dif-
ferent style of nozzle body or tip, the use of
similar but different equipment, etc.
All of these and other deviations can con-
tribute to process and dimensional varia-
tion, as well as instability. By documenting
the initial installation settings, fewer per-
sonnel will be needed to investigate and de-
termine the root cause of the rejects. More
importantly, satisfying customer delivery
and quality requirements will be much more
consistent.
When selecting the molding machine of
choice, keep in mind the following criteria:
■ Real-time closed loop technology (electric
molding machines have recently demon-
strated more consistent repeatability and
reduced cycle times).
■ The shot size of the screw should utilize
25–75% of barrel capacity (ideally, 33–
66%) to avoid minimal or excessive resi-
dence time, either of which can influence
process variation.
■ Machine tonnage should provide enough
clamping pressure to keep the mold fully
closed and prevent flash; typically 5–10
tn/in.3 of the projected area of the molded
part is adequate.
Cooling circuits in the mold should be
adequately sized to satisfy the Reynolds
equation for turbulent flow for good ther-
mal coefficient (typically 1.0 gpm of flow
for each 0.5 in. of cooling line is adequate.
See the sidebar, “Definitions.”). Additionally,
the cooling lines should be sized equally to
achieve balanced cooling.
The inspection area of the molded prod-
uct should be benchmarked for location
and lighting influence, as well as cleanli-
ness attributes, e.g., lumens, particulate in
ppm, etc. The equipment and techniques
used to inspect and accept product must be
calibrated and documented. Additionally, all
equipment used in the direct manufacture
of the product needs to be calibrated in ac-
cordance with ISO and GMP guidelines.
Operation Qualification OQ is at the heart of evaluating and defin-
ing the injection molding process. Through
the use of analytical processes, engineer-
ing studies, and statistical and dimensional
evaluations, one can identify areas of con-
cern that need to be addressed early in the
program. Examples might include a small
runner system that would limit pressure,
a part that won’t fill evenly, or less-than-
desirable aesthetics that might result from
shear, dimensional concerns, and so forth.
In these cases, the mold can be modified to
address the concerns before building a pro-
Medical Molding: How to Validate the Process Validating the injection molding process is no longer limited to medical device components. It is increasingly becoming a requirement throughout global industries.
ED STOCKDALE
A metrologist conducts first article inspections, which consist of the measurement of all dimensional calloutson the molded product part print.
VALIDATION
MD100702_012 12MD100702 012 12 7/2/10 8:52:05 AM7/2/10 8:52:05 AM
MOLDING TECHNOLOGIES JULY 2010 | 13
duction tool, thereby minimizing lead times
to production.
For a new molding program, it is benefi-
cial to perform process development and a
design of experiments (DOE) with a proto-
type mold prior to building a production
tool. The purpose of performing process de-
velopment is to minimize areas of the pro-
cess that cause variation, e.g., pressure limi-
tations, shear rates or viscosity variations,
inadequate changeover definition, proper
pack and holding pressures, and time. The
DOE defines which process attributes affect
specific dimensional responses, the influ-
ence on the response, and the interactions
between them. From the two studies, one
can confidently define an ideal process with
a predicted dimensional outcome.
Process development consists of a short-
shot study, in-mold rheology, a stability or cav-
ity-to-cavity balance run, gate-seal analysis,
and a pack-pressure study, as well as a DOE
and first article inspection (FAI). As a starting
point for these studies, use the resin manufac-
turer’s recommended process settings.
The short-shot study demonstrates that
the cavity or cavities fill evenly or balanced,
the injection pressure required to fill the part
approximately 95–99% (used for velocity-to-
pressure-changeover definition) is not lim-
ited due to the runner system in the mold,
and there are no mechanical issues that pre-
vent the mold from successfully cycling.
In-mold rheology defines the best shear
rate (injection rate) to minimize variation
during fill. This rate varies from one resin to
another and is influenced by the geometry
of the mold and cavities. A level shear rate
slope is more desirable and will exhibit less
variation than one on a sharp incline or de-
cline (see Figure 1).
A stability or cavity-to-cavity balance run
demonstrates that the process to the point
of velocity-to-pressure changeover is stable
and balanced. It also validates process capa-
bility through the use of Cp and Cpk relative
to the molding process itself (see the side-
bar, “Definitions”).
A gate seal or freeze study (holding and
pack time) confirms when the influence of
injection within the cavity and runner system
is complete. An improper gate-seal or freeze-
time setting can cause process variation or
add unnecessary additional cycle time.
The pack-pressure study identifies the
influence that the pack and holding pres-
sure have on dimensional characteristics. It
defines a proper pack-pressure process win-
dow and evaluates how the mold operates
under these conditions. Dimensional studies
are then necessary to evaluate these progres-
sive influences on the molded product.
Once the process window for each pro-
cess attribute has been defined, these set-
tings can be used to define the DOE. The
DOE defines the optimum process win-
dow and its respec-
tive influence on
each dimensional
response. A series
of experiments are
run, and the influ-
ences are evaluated
statistically. A DOE
prediction is made,
and an additional
run confirms that
the DOE predic-
tion is accurate and
defines the optimal dimensional process
window. These process limits will then be
challenged and evaluated. The challenges
consist of three different runs: low, high,
and nominal process challenge runs. Each
run is equal in run time and evaluated for
dimensional, functional, and cosmetic
considerations in relation to the product
specifications and tolerance. The results
may demonstrate conditions that do not
meet the desired acceptance criteria, in
which case the process, tolerance, mold,
or specification needs to be modified and,
if necessary, the processes rerun to verify
conformance.
Beyond process development and DOE,
an in-mold cavity pressure transducer
equipped with a temperature sensor can
also be beneficial. This equipment illus-
trates and defines proper velocity-to-cavity
pressure settings and cooling time (see Fig-
ures 2 and 3, p. 14). The sensor and transduc-
er combination minimizes the difference in
cavity pressure between the beginning and
end of fill, thereby reducing in-mold stresses
while enhancing dimensional and product
stability. Recent studies comparing process
variation both with and without the use of a
sensor and transducer demonstrated a pro-
cess and dimensional stability improvement
A measuring machine is adjacent to its medical molding cell to minimize the time required for first article inspections on new medical molding programs.
HighProcess
Limit
Ap
pa
ren
t Vis
co
sity
PA
.S
0.5 0.6 0.7 1.0 1.1 1.20.3597264726972747279728472897294729972
1197210472
119721247212972
0.4 0.8 0.9
Low
Normal
Shear Rate, 1/s
Figure 1. Defining proper In-mold rheology process window.
DefinitionsThe following terms are commonly used in
validating molding processes.
4.1 Cp: Estimates what the process would
be capable of producing if it could be centered
in tolerance. Assumes that the process output
is normally distributed. Cp demonstrates that
the process is in control without respect to the
present dimensional tolerance, so tolerance
can be adjusted with confidence.
4.2 Cpk: A globally recognized measure-
ment of the process capability index or sta-
tistical prediction of potential product at risk
that could be out of dimensional tolerance.
Based on (4) sigma (standard deviation), a
Cpk of ≥1.33 is the commonly recognized ac-
ceptance specification for medical devices.
This means that 63 of every million parts
produced (ppm) are at risk of potentially being
out of dimensional tolerance (99.99%). A Cpk
of ≥1.67 based on (5) sigma potentially yields
a process that is at risk of producing one part
out of tolerance specification for every ppm
or 99.9999%. The benefit of these disciplines
is realized through the reduction of potential
risk of out-of-tolerance product, fewer assem-
bly issues with mating components, and less
scrap and down time due to rejects.
4.3 Reynolds number equation: The
measure and calculation of turbulent flow,
which translates into thermal heat transfer
or cooling.
MD100702_013 13MD100702 013 13 7/2/10 8:52:10 AM7/2/10 8:52:10 AM
14 | JULY 2010 mddionline.com
VALIDATION
of greater than 50% over time when the sen-
sor and transducer combination was used
(see Figure 3).
First Article Inspection An FAI consists of the measurement of all di-
mensional callouts on the molded product
part print. Typically two samples are taken
from the nominal process run or from the
DOE conformation run and submitted to
metrology for measurement. The dimen-
sional results are evaluated by the customer
and for conformity.
It is common to find out-of-specification
conditions, which need to be evaluated for
significance, followed by corrective action.
Usually this requires a dimensional change
on the part print or a tooling modification.
Once the FAI is approved by the customer,
process qualification begins.
Process Failure Effects and Mode Analysis (pFEMA)Depending on the end-use of the product, a
pFEMA may be conducted to identify poten-
tial areas of concern. There may be specific
critical dimensions, for example, that need to
be monitored closely, because if even one is
out of specification periodically, it may cause
significant failure or risk with the product.
Potential risks and safeguards are there-
fore assigned to these areas, e.g., special
measurement devices or equipment, 100%
inspection, etc., to ensure that product of
this nature is appropriately rejected.
Process QualificationPQ demonstrates that the process is stable
and dimensionally capable and that it produc-
es a molded part that meets the customer’s
expectations. Typically, PQ is accomplished
by running the defined or nominal process
through three separate runs. These runs are
a simulation of three separate production
runs and should be a minimum of four hours
in length for each run with a shutdown pe-
riod between each run. Additionally, three
different lots of resins should be used dur-
ing the PQ, which represents actual molding
conditions and variation over time. Samples
should be taken at even intervals through-
out each run, labeled sequentially, and then
submitted to metrology for measurement
and conformity. Once the PQ and FAI have
been approved, these samples should be kept
for the life of the program for reference. This
retaining policy helps with answering ques-
tions as programs develop and transition.
If the PQ is unsuccessful and the molded
part does not meet customer expectations,
the root cause needs
to be evaluated
and the two parties
must work together
to define and accept
a resolution.
The qualification
of spare mold or
tooling components
directly related to
the molded part,
e.g., spare core pins,
lifters, etc., should
be evaluated and
validated so that they are readily available
if needed. Typically, the spare part or com-
ponent validation process consists of one
similar PQ run that demonstrates accept-
able capability.
Other ConsiderationsDocument Control and Process Docu-
mentation. The ongoing documentation of
the process needs to be maintained in a con-
trolled environment in accordance with ISO
13485 standards. This is essential in main-
taining and ensuring that the same process
is run from one run to another.
Variation versus Profitability. The use
of these analytical and engineering concepts
will stabilize process and dimensions, as well
as profitability. It’s worth noting, however,
that sufficient resources and specific equip-
ment are necessary to successfully incorpo-
rate these concepts into a business strategy.
Resource requirements include management
staff; process, quality, and tooling engineers;
process technicians; metrologists; and tool-
ing personnel experienced in Cp/Cpk disci-
plines and tight- tolerance molding. Specific
equipment needs include well-maintained
peripherals and molding machines, check
ring and barrel assemblies capable of hold-
ing a molding process to a tight tolerance,
coordinate measurement machine and vi-
sion system equipment for measuring tight
geometric dimension and tolerance profiles,
and tool room equipment.
The business approach that integrates
process validation touches many areas of the
company, so the company’s commitment to
the process is essential to its success. And
while significant investment is required, it is
recouped through stable molding programs
where profitability is maintained over time.
Ed Stockdale is a process engineer for Mack-
Medical/Mack Molding Co. (Arlington, VT). 2
A technician defines the optimal dimensional process window for a DOE.
46.75
44.7
5 A
ng
le
Serial #
43.75
42.75
44.75
45.75
1 6 11 16 21 26 31
With Psi Tranducer
Upper Control (UCL)Lower Control Limit (LCL)
With out Psi TranducerNominal
Without Transducer
Poor Cpk (.683)
WithTransducer
Good Cpk (8.75)
Figure 3. Typical cavity pressure transducer (with and without a sensor ).
80
70
30 1-1
17-1
40
90
100
50
60
CavityTemperature
CavityPressure
CavityTemperature
Stable
Gate SealedY1-1
Y17-2
Sca
le (%
)
Figure 2. In-mold pressure transducer and temperature sensor application.
MD100702_014 14MD100702 014 14 7/2/10 8:52:16 AM7/2/10 8:52:16 AM
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MOLDING TECHNOLOGIES JULY 2010 | 17
CLEANROOMS
C leanroom molding is essential
for serving the medical segment,
and various options exist for
manufacturing anything from discrete
components to complex assemblies in
a pristine environment. So what clean-
room alternative should you choose?
It very much depends on your application
and business strategy.
What may appear to be the simplest so-
lution to medical molding is to locate the
entire machine in a cleanroom. This is best
suited for molders that are operating several
machines under cleanroom conditions and
need to integrate large assembly systems
into the cleanroom concept, according to
Jochen Hirt, application department man-
ager at Arburg (Shanghai) Co. However, this
solution can only obtain ISO 7 standard at
best, which is essentially equivalent to the
Class 10,000 U.S. federal standard typically
required as a minimum for cleanroom mold-
ing. Good manufacturing practice (GMP)
standards are generally also required for
cleanroom molding, and these specify maxi-
mum bacterial count in addition to particle
count. GMP Level C equates to ISO 7.
One issue with the fully integrated ap-
proach is, “If the cleanroom malfunctions
and air quality is adversely affected, you
have to shut down all your machines,” says
Jack Liu, application engineering manager
at Demag Plastics Machinery (Ningbo) Co.
Ltd. A more flexible and lower-cost method
is to enclose only the mold space in a clean-
room environment by installing a laminar
flow element on top of the machine’s clamp-
ing end. The clean air module is mounted on A laminar flow box mounted over the mold area keeps molded parts clean while removing many contaminant sources from the clean area.
Robotic part placement onto a covered conveyor
enables transfer of fragile parts to a
separate cleanroom for postprocess operations.
Keeping It Clean Which cleanroom
option is best? Well, that depends.
STEPHEN MOORE
MD100702_017 17MD100702 017 17 7/2/10 8:54:40 AM7/2/10 8:54:40 AM
18 | JULY 2010 mddionline.com
CLEANROOMS
a traveling frame above the clamping unit,
allowing easy mold installation from above.
In its simplest form, parts are molded in
this miniature cleanroom area and dropped
onto a covered conveyor that then trans-
ports them to a cleanroom attachment for
robotic or manual assembly and packing.
“Being much smaller, ISO 5 is attainable in
this attachment,” says Liu.
With this modular clean air hood tech-
nique, the ambient air is drawn in via radial
fans and clean air is produced via a prefilter
and a suspended matter filter (HEPA H14).
An integrated ionization module produces
ionized air, which ensures the neutraliza-
tion of electrically charged components.
This reduces electrostatic charging of the
molded parts. Through the permanent air
flow, a high level of air circulation is ensured
within the clamping unit. The fan also cre-
ates an overpressure in the interior of the
mold, which effectively prevents the pen-
etration of particles from the ambient air.
Needless to say, for fragile parts that
might be damaged by free-fall and a sorter
flap, robotic takeout is essential. The clean-
room area must therefore be expanded to en-
compass the robot and conveyor placement
area. Arburg’s offering for this situation is a
cleanroom production cell with its Multilift H
horizontally operating robotic system.
KraussMaffei Technologies GmbH (Mu-
nich) has a different take on this option in
that the robot accesses the mold space from
an adjacent cleanroom. The overpressure in
the white room causes the clean air to flow
through the tunnel and flow out through
the chute on the injection machine. The
production area is isolated from the rest of
the machine. This solution achieves ISO 6/7
standards.
Room in a RoomKraussMaffei also offers a room-in-room
option whereby the clamping end of the
machine protrudes into a sealed clean-
room. This option can cater to cleanliness
up to the ISO 5 standard. For mold chang-
ing, service, and repairs, the machine is
retracted on rails until the clamp is in the
gray room area and the white room is com-
pletely sealed off by a second metal plate at
the front of the clamp end.
This option was adopted by Rexam
Pharma GmbH (Neuenburg, Germany) for
molding vials from cyclic olefin co polymer
(COC) with TPE closures for injectables.
The ready-to-fill vials leave the cleanroom
closed and packed. Thomas Hörl, who over-
sees product and technology management
at KraussMaffei, notes that when mold-
ing takes place under GMP Class B (ISO 5)
conditions, the surrounding gray room area
should be at least GMP Class C (ISO 7). Pro-
duction in a Class 5 cleanroom makes post-
mold cleaning or sterilization unnecessary
in many applications, although it may be
stipulated by end-users.
Demag’s decentralized method for in-
corporating an injection machine plus
automation into a cleanroom is dubbed a
cleanroom cabinet with roof construction.
Takeout, assembly, and packing are carried
out under an ISO 7 environment. The ma-
chine may also be enclosed in the cabinet
in its entirety.
Using a decentralized approach, Arburg’s
Hirt says that newcomers to cleanroom
molding can benefit in that they can start
with just one machine and add cleanroom
capacity as they go. “If individual machines
are temporarily not required for cleanroom
production, they may be undocked to pro-
duce standard parts,” he adds.
Cleanroom-Customized MachinesWorkers are the main source of particulate
contaminants, accounting for around 40%
of emissions in a cleanroom, and removing
them from the equation, or at least minimiz-
ing their presence, goes a long way toward
eliminating particles. The next largest source
on the list is the injection machine itself, and
here, various techniques exist to minimize
contamination. While Demag’s Liu says
that fully hydraulic machines are capable of
achieving ISO 7 standards when contained in
cleanrooms, all-electric machines can oper-
ISO 7-standard cleanrooms can be sufficient for medical molding tasks.
KraussMaffei’s room-in-room approach minimizes the volume of work area held at high cleanroom level, while facilitating machine servicing and toll changes.
MD100702_018 18MD100702 018 18 7/2/10 8:54:46 AM7/2/10 8:54:46 AM
MOLDING TECHNOLOGIES JULY 2010 | 19
ate at up to ISO 5 standards if water-cooled.
“Fan cooling is not as good for cleanroom
environments, although ISO 6 is technically
achievable,” says Liu, who adds that direct
drive is also preferable over belt drive. An-
tistat metal coatings and PVC coatings for
mobile elements are also employed, while
use of perforated metal sheet minimizes air
turbulence in the mold space.
“During production under cleanroom
conditions, it is very important that the [hy-
draulic] machine can be cleaned easily,” says
Arburg’s Hirt. “For this purpose, the dis-
tributor manifolds of the hydraulic circuit
can be contained in a powder-coated sheet
metal housing located at the machine base.
This allows the injection molding machine
to be kept clean much more effectively.” Fur-
ther, raising the machine by 100 mm using
antivibration pads makes cleaning under
the machine considerably easier.
Closer to the tool, multiple cooling cir-
cuits can be routed directly to the fixed or
moving mold platen for the mold cooling.
“This tidy routing prevents unnecessary
trailing of the hoses,” says Hirt. Powder
coating is also used throughout Arburg ma-
chines for wear and scratch resistance. Hirt
insists that a properly configured hydraulic
machine can run in a cleanroom equally as
well as a hybrid or all-electric machine.
KraussMaffei recommends its EX Series
all-electric machines for medical molding
applications. The Z-toggle has only eight
pivot points, all of which are lubricated
with completely encapsulated circulating
oil. All drives are water-cooled, and plas-
ticating and injection are driven by two
coupled direct drives.
Stephen Moore is senior editor of Modern
Plastics Worldwide. MT
In this cleanroom variant, parts are molded in a laminar flow clean area, and then drop onto a covered conveyor for transport to a separate cleanroom.
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MD100702_019 19MD100702 019 19 7/2/10 8:54:55 AM7/2/10 8:54:55 AM
20 | JULY 2010 mddionline.com
COMPLEX INJECTION MOLDING
C omplex injection molding repre-
sents a direct route to competi-
tive differentiation. It provides
the design freedom and process efficiency
required to create new features and incor-
porate new technologies as quickly and
cost-eff ectively as possible.
Complex injection molding is defined
by simultaneous complexity in four criti-
cal areas: part design, mold design, mate-
rial selection, and process control. To make
successful medical products, OEMs should
choose a molding partner that can offer
them expert guidance in these areas. This
article explores when to address pertinent
molding considerations in complex injec-
tion molding.
Why Use Complex Injection Molding?With complex injection molding, additional
materials—from dissimilar polymers to
metal components and other nonplastics—
can be integrated during molding. These
materials and features are combined in
the molding process to facilitate assembly
by adding metal inserts, threading for fas-
teners, and incorporating elements such
as lenses. Such features can also optimize
function by creating waterproof seals and
increasing durability.
Improving aesthetics can also drive the
decision to use complex molding. For ex-
ample, some OEMs may want to color a
polymer to make the device more appealing
to patients—notably in pediatric applica-
tions—or, they may want to integrate deco-
rative elements such as metal flake, gloss, or
some other proprietary pattern. Such visual
uniqueness can differentiate products with-
in a manufacturing line or separate them
from the competition.
In addition to streamlining production
and reducing costs, incorporating a deco-
ration or functional item into the injection
process improves quality. Machine-paced
production always yields higher quality
product by eliminating or greatly reducing
human involvement and inconsistency. It
also reduces potential process variances
introduced by secondary machining or
joining operations. Just as important,
complex molding yields more predictable
quality because manufacturers are able to
maintain consistency no matter how many
units are produced, ensuring that tight
tolerances are met and sterility is always
maintained.
Furthermore, the medical market is sub-
ject to regulatory compliance demands
from organizations such as FDA that dic-
tate the validation requirements for all
physical, chemical, and compositional
aspects of medical products. Regulatory
control of implanted devices is especially
critical, for example, because these types of
products carry the greatest risks. Complex
injection molding addresses the design and
production challenges posed by such strict
controls.
Part Design ConsiderationsMany of the crucial decisions involved in
complex injection molding should be made
as early as possible in the design phase,
when adjustments can be made without
a significant effect on the total costs and
product timeline. For example, the place-
ment of ejector pins and gating—the point
where the plastic enters the mold—is
Complex Injection Molding for Competitive AdvantageWith careful planning, complex injection molding can result in reduced costs, optimized function, and improved aesthetics.
DAVE ROBINSON
Decisions regarding each part’s unique cosmetic, functional, and volume characteristics should be made as early as possible in the design phase.
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MOLDING TECHNOLOGIES JULY 2010 | 21
critical aesthetically and stylistically. A vis-
ible knit line, where the flow fronts of the
molten material meet, may be objection-
able to the customer. If such marks cannot
be strategically located to a place on the
part where they will not be visible, they can
sometimes be disguised by texturing the
mold. Either way, the part designer must
plan for them.
If multiple materials are to be used, the
polymers must be chosen carefully for com-
patibility to ensure a permanent chemical
bond. Different plastics undergo thermal
expansion at different temperatures, and
any incompatibility can become a serious
issue. For example, polysulfone, a polymer
commonly used in medical applications,
will not bond with polypropylene, which in
turn bonds weakly with nylon, styrenic, and
urethane-based elastomers.
Process complexity is added when a part
requires metal inserts or pass-through cor-
ing. For example, the metal elements being
added to a mold often require preheating to
reduce thermal shock, improve retention
properties, and prevent flash—thin, sharp,
or unsightly areas that can form in the pass-
throughs due to stress (e.g., molten plastic
meeting cold metal fasteners) during the
molding process. The presence of flash can
have an adverse effect on the performance
of the product or require secondary opera-
tions to be removed.
All of these issues highlight the impor-
tance of a robust part design that antici-
pates possible problems with complex in-
jection molding and prevents them through
thoughtful planning. A careless part design
can lead to weak points, aesthetic flaws, or
overall part failure.
A robust part doesn’t just meet the origi-
nal requirements its designer intended; it
also stands up to the wear and tear—or
even abuse—it is subjected to during daily
use. For example, many medical devices
are moved often, from room to room or
even between ambulances and hospitals,
so they must be designed and built to with-
stand the jostling and bumping that ac-
companies such use. Aesthetically, a device
must maintain its appearance. This means
no fading, hazing, or yellowing of the plas-
tic after exposure to sun, fluorescent light-
ing, chemicals, or other potentially harsh
elements.
Mold Design Considerations The development of the mold or tool is the
heart of the injection molding process, the
stage from which everything else flows. The
ultimate success of the part is determined
when the engineering team designs, cre-
ates, and maintains the mold—accounting
for the materials to be used and the quan-
tity of the item to be produced. Poor choices
in any aspect of the mold development pro-
cess ultimately results in poor products, re-
gardless of part design, material choice, or
process control.
The type and durability expectations for
a mold determine which material is used to
make it. For example, aluminum is relatively
inexpensive and easily machined but it of-
fers limited longevity. Therefore, it should
be used only for small and finite produc-
tion runs—a rare case in medical device
applications. As a result, molds for medical
applications are nearly always steel. They
can range from soft steels used for simple,
single-cavity prototype molds with smaller
runs to hardened steels used for complex,
multicavity molds to support greater pro-
duction volumes.
Because medical device production leans
toward high volume and high complexity,
these requirements increase the importance
of selecting the proper steel for building the
tool. The determining factors are based di-
rectly on the goals and expectations of the
project, ranging from total quantity sought
to the finish quality needed. Budgets for
both time and cost can influence material
choice as well (see Table I).
Softer metals, such as P20 steel and
aluminum, are easily machined and there-
fore less costly to mold. However, because
they are prone to wear faster, they are
less commonly used in medical device
manufacturing.
Stainless steel is an appropriate tool steel
for medical applications because it resists
corrosion, pitting, and wear while sup-
porting the smooth finishes required for
cleanliness in a medical setting. In general,
the harder the steel, the more effort and ex-
penditure is required. Each additional step
used to create the mold drives up time and
cost. But these harder steel molds also last
An OEM’s evaluation process for a complex injection molder should include a site visit to assess the quality of the plant’s environment and personnel.
<10,000 10,000—200,000 200,000—1 MM
Aluminum X
P-20 X X X
Tool steel (various grades) X X
Table I. Rules of thumb for material choices are based on project volume requirements.
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22 | JULY 2010 mddionline.com
COMPLEX INJECTION MOLDING
considerably longer and return high-quality
parts with consistency.
Other steels used for complex injection
molding medical devices and equipment
include high-carbon varieties, such as
H13. These varieties contains a negligible
amount of impurities—an important fac-
tor in heat treating—and are economical
to purchase in larger sizes. See Table II
for a breakdown of types of steel and their
characteristics.
Corrosion resistance in a mold is es-
pecially important with the use of ma-
terials that have a high degree of acid-
ity. These materials include resins in
the PVC family or those with certain
added agents, such as flame retar dants,
which are often required to meet the
UL standards for resins used in medical de-
vice manufacturing.
Materials ConsiderationsJust as important as selecting the
material for the mold is choosing
the material for the part. Deter-
mining the proper material for
a complex injection molding
application should begin with
a discussion between the plas-
tics engineer and the OEM.
This decision requires informa-
tion about five defining factors
(outlined below), as well as any
outstanding special needs, such
as the frequency and method of
sterilization.
Physical Load. The impact
expectations of the part must be
determined so that it will stand
up to the conditions of everyday
use without fatigue. Any degrada-
tion can lead to life-threatening
part failure.
Mechanical Function. The
particular polymer must be right for its ap-
plication. For example, a part of a surgical
device that holds a blade must be made
from a polymer with appropriate stiffness.
Thermal. Exposure to fluctuating and
extreme temperatures must be accounted
for. Most medical devices are kept indoors,
but some portable devices or ambulance
equipment may be exposed to extreme heat
or cold. Polymers must be chosen to endure
such conditions.
Environmental. Consider whether the
device will be implanted or used in direct
contact with bodily fluids. If so, the poly-
mers must be biocompatible in accordance
with FDA regulations (as well as further
testing requirements depending on the
device).
Chemical. Exposure to chemicals is also
a factor. Most hospital-grade disinfectants
are strong formulas, often in an alcohol
base. Plastics chosen for the exposed parts
of a device must stand up to their composi-
tion without breaking down. Certainty that
a part will be exposed to chemical steriliza-
tion will limit the list of polymer options,
as will applications in which medications
will be transmitted via plastic parts and
tubing.
Sterilization is another factor to con-
sider. Many medical devices must with-
stand regular sterilization treatment by
radiation, chemicals, or the high heat and
steam of autoclaving. Table III shows some
common material choices that steriliza-
tion requires.
The need to mold dissimilar plastics also
plays a role in material selection. One of the
most common complex injection molding
techniques used in medical device manu-
facturing is the multishot method, which
is required to add soft polymers for ergo-
nomic and waterproofing features (such
as keypads, grips, protective bumpers, and
seals) over a hard plastic substrate, as in an
impact-resistant device body. Other times,
overmolding of silicone tubing may be
required.
By accomplishing these steps during
molding, manufacturers eliminate costly
and inefficient secondary steps from the
production process. It can also result in
higher quality because the material it-
self can be monitored during production
through cavity pressure feedback—a pres-
sure reading of the resin as it is going into
the mold. The feedback provides data on
the consistency of the pressure and where
correction is needed. Causes for inconsis-
tent pressure include a change in the vis-
cosity of the molten material.
The mold and the process must be de-
signed to suit the part and materials. No
medical OEM would tolerate a soft-touch
keypad separating from one of its handheld
monitoring devices during use. Nor would
it accept a waterproof seal failing because
materials were improperly selected or the
process to manufacture it was not expertly
designed.
The last material concern of importance
is whether a project requires high-heat
resins. The high-heat resins such as poly-
sulfone, which are required to withstand
autoclaving, have their own set of process
considerations. These materials are more
difficult—and therefore more costly—to
work with, mainly due to their high melting
points, which complicates everything from
safety concerns to the molding process.
Type of Steel General Use Criteria
S-7 General all-purpose, heat-treatable tough steel. Normal wear resistance.
A-2General all-purpose, heat-treatable hard steel. Higher wear resistance and less
toughness.
D-2 High-wear applications.
420 SS Medium wear resistance, high polish, corrosion resistant, not as hard.
H-13 Medium wear resistance. Can be nitrided for surface lubricity with flex strength.
Table II. A profile of the different types of steel that can be used to make a mold.
The high-heat resins required to withstand autoclaving require specialized oil heating equipment to bring the molds to temperatures in excess of 325°F.
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MOLDING TECHNOLOGIES JULY 2010 | 23
As an example, polysulfone has a melting
point of 700°F versus 500°–550°F for typical
resins. Oil, rather than water, must be used
to control mold cooling, requiring a longer
molding process and different equipment—
with different risks involved. Heating oil
also takes longer and metal-braided hosing
must be used as opposed to rubber. These
higher demands mean higher risks for both
safety and deviation. Because the mold
itself can reach 325°F (whereas a water-
heated mold typically reaches 180°F), it is
subject to higher levels of thermal expan-
sion, which adds complexity to the overall
mold design process.
Supplier Considerations The importance of selecting the right
manufacturing partner increases in di-
rect proportion to the complexity of the
task at hand. With all that is at stake in
the medical device industry, the OEM’s
evaluation process should be rigorous.
The process should cover every aspect
of a partner’s operations, equipment,
personnel, track record, culture, and fi-
nancial health. A site visit should also be
part of this process because it provides
the best method for assessing the quality
of the supplier’s plants environment and
personnel.
ConclusionComplex injection molding can provide a
medical device and equipment manufac-
turer with competitive differentiation, but
it requires highly specialized equipment,
skills, and engineering expertise. OEMs
that take advantage of the complex injec-
tion molding process can enjoy the ben-
efits of high-quality parts and devices with
optimal efficiency and low total production
costs.
Dave Robinson is vice president of engi-
neering at Kaysun Corp. in Manitowoc,
WI. MT
Method Amorphous Polymers Semicrystalline Polymers
Autoclaving
Polyphenylsulfone (PPSU) offers best resistance.Polycarbonate and polysulfone can withstand finite
number of cycles.Acrylonitrile butadiene styrene (ABS) and polyester
should not be autoclaved.
Polyether ether ketone (PEEK) offers best resistance.Polyamides and polypropylene can withstand finite number of
cycles. Some polyethylenes can withstand shorter cycles at lower
temperatures. Polyethylene terephthalate (PET) should not be autoclaved.
Chemical (ethylene oxide) Withstand very well. Withstand very well.
Radiation Most withstand well; polycarbonates will discolor. Most withstand well.
Table III. Certain polymers are better suited for specific sterilization treatments.
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24 | JULY 2010 mddionline.com
SOFTWARE MODELING
M ost modern mold filling simu-
lation software uses some type
of solid or shell element mesh to
define the part geometry. These range from
simple midplane element models meshed
with 2-D shells to 2 ½-D surface meshing
strategies.
Increasingly, some of the high-end soft-
ware packages are using full 3-D elements.
With few exceptions, these codes almost
exclusively use four-noded tetrahedral el-
ements—not always the best choice when
modeling fluid behavior.
As the fundamental physics of mold fill-
ing simulation is really a fluid flow problem,
several codes are now commercially avail-
able that use the finite volume method as
opposed to the more common finite ele-
ment method.
Finite Element versus Finite VolumeMost mold flow simulation is finite ele-
ment based, a technology made popular in
structural analysis codes. Some of the newer
codes, such as Moldex3D, are finite volume.
There is a significant difference in how these
tools work.
The finite volume method differs in that
the mesh grid nodes and integration points
are fixed, and the fluid moves within the
fixed mesh grid. In the finite element meth-
od, the mesh grid points actually move,
simulating the flow behavior.
There are pros and cons to both ap-
proaches, the main practical advantage
of finite volume codes being the accuracy
of the solution for fluid flow and the speed
with which you can get a solution. Finite ele-
ment codes tend to be computationally ex-
pensive, as a large mesh can create inordi-
nately large numbers of nodes, all of which
must translate to simulate the flow behav-
ior. Typically, the finite element method is
more stable, and provides better results for
those primarily interested in stress tensor
outputs, such as in structural analysis. Fi-
nite volume codes are useful for fluid and
gas flow problems, and are used extensively
in CFD codes.
The speed advantage inherent in finite
volume codes is significant for simulating
thermoplastic flow when using full 3-D ele-
ments, because it is necessary to create large
numbers of elements to accurately capture
the part geometry. For example, a good rule
of thumb is to provide a mesh density of at
Using Finite Volume Models in Mold Filling SimulationsFinite volume simulation can increase accuracy in models.
JOHN COGGER
Figure 1. 2 ½-D element filling simulation.
Figure 2. High-order 3-D element filling simulation.
Figure 3. High-order 3-D elements with gate modeled.
Figure 5. A cutaway shows inner mesh resolution.
Figure 4. High-order 3-D elements, hybrid mesh hexahedrals with tetrahedrals.
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MOLDING TECHNOLOGIES JULY 2010 | 25
least three 3-D elements spanning the cross
section of a wall thickness. Propagated over
even a small part, this can create element
counts in the hundreds of thousands, which
can make it difficult to get timely solutions.
Larger parts can and do create 3-D element
counts in the millions.
The use of finite volume technologies
can substantially reduce the solution
time to run these types of mold fill simu-
lations. These jobs are very large, and the
Moldex3D solver allows for parallel pro-
cessing (we typically use an eight-core
machine) to get a solution of a model this
size in a few hours. Such a large model may
not even run on a finite element solver,
and many mold filling codes do not sup-
port parallel processing.
High-Density 3-D Elements. Armed
with a high-performance finite volume
solver, we can now use high-quality 3-D el-
ements to model plastic f low, and get solu-
tions in minutes or hours instead of days,
with high-fidelity results. Figure 1 shows
a mold filling analysis using typical 2 ½-D
fusion elements, while Figure 2 shows the
Figure 6. High-order boundary layer elements used with solid tetrahedrals.
Figure 7. Predicted results in the simulation.Figure 8. Actual molded part results (short shot).
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26 | JULY 2010 mddionline.com
SOFTWARE MODELING
same part using high-order 3-D elements in
a finite volume solver. The differences are
dramatic. With computationally efficient
finite volume solvers, we can also expand
our element library to include higher-order
elements, such as hexahedrals, to capture
much more accurate fluid flow behavior.
Drilling into the mesh resolution, we can
see a typical high-order mesh in Figures 3,
4, and 5 (p. 22). Note that these mesh struc-
tures are a hybrid of several element types.
In addition to using these types of hybrid
meshes, we can combine these methods
into a boundary layer strategy, allowing
higher-order elements to be used on the
part bounding surfaces and lower-order
3-D elements to be used in the part interior
for better resolution of temperature effects
on the critical boundary layer. An example
can be seen in Figure 6 (p. 23).
Gate/Runner Modeling. One of the
most important parts of mold filling sim-
ulation is the gate and runner modeling.
This is an area that is often overly simpli-
fied by software applications, and poor
accuracy here can negatively influence
results. Best results can be achieved using
high-order 3-D elements in the gate and
runners as well as in
the part geometry.
Results Correla-
tion. One of the best
ways to validate the pre-
dicted results of a mold
flow is to compare with
a short shot study after
the fact (Figures 7-9).
Fiber Orientation
and Postprocessing.
One of the more inter-
esting aspects of this
type of analysis is the
ability to import mold
filling analysis results
into structural analysis software for more
realistic loads analysis. Most structural
finite element analysis uses the flawed as-
sumption that thermoplastics are isotropic
(uniform material properties) and therefore
cannot accommodate the effects of molding
on structural part performance. This can
lead to unanticipated part failures when
weld lines, material flow lines, and part den-
sity changes occur in highly loaded areas.
When the mold filling solver runs the
warp load case in a typical molding simu-
lation, we (automatically) convert to the
finite element method, as we are now inter-
ested in finite strains and residual stresses
to predict warp accurately. This output file
can then be used as an initial condition for
a structural FEA, bringing along the follow-
ing attributes:
■ Fiber orientation.
■ Material density variations.
■ Residual stresses (f low and thermally
induced).
■ Initial strain.
ConclusionThese attributes are critical to under-
standing the part performance when
structural loads are applied. When cou-
pled with orthotropic or anisotropic mate-
rial data, accurate structural FEA can be
performed on injection molded parts. Fig-
ure 10 depicts a cross section of a molding
simulation showing fiber orientation of a
glass-filled part, while Figures 11 and 12
show the warp prediction with and with-
out consideration of fiber orientation.
John Cogger is president of Innova Engineer-
ing Inc. (Irvine, CA). MT Figure 12. Typical fiber warp results plot without fiber orientation.
Figure 11. Typical fiber warp results plot with fiber orientation.
Figure 10. Typical fiber orientation plot.
Figure 9a (left) and 9b. Predicted results versus actual short shots.
MD100702_026 26MD100702 026 26 7/2/10 9:19:52 AM7/2/10 9:19:52 AM
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28 | JULY 2010 mddionline.com
MATERIALS ANALYSIS
M ost medical device manufac-
turers know the importance
of putting a product through
rigorous cleaning and testing before it is
released into the market. Standard sterility
and biocompatibility tests are an essential
part of manufacturing protocols. However,
some manufacturers may not fully under-
stand the different ways a product can be
contaminated during the production, pack-
aging, and cleaning processes. To avoid
detrimental contamination, manufacturers
should test their devices, including those
made via injection molding, using residual
manufacturing materials (RMM) analysis.
The Basics of RMM AnalysisAny contaminants such
as oils, lubricants, releas-
ing agents, and detergents
transferred to the product
during the manufactur-
ing or cleaning process are
RMM. From extracting the
device out of the mold to
cleaning and packaging,
device contamination can
occur just about anywhere
along the production pro-
cess. Those residues that
remain on a product can be
potentially cytotoxic and
harmful, particularly for de-
vices implanted inside the
body. For example, a metal
device may be designed
to integrate with a patient’s bone, but oils
remaining on the metal could reduce new
bone growth or inhibit integration, causing
the device to be ineffective or unsafe.
RMM analysis quantifies the residuals on
the device and identifies them. It establishes
a baseline against which manufacturers can
discover if the amount of residuals changes
as they improve their assembly process.
Manufacturers can use RMM analysis
as a tool to monitor the cleanliness of pro-
duction at any point, including the final
product. Knowing how much residue is on
a device or component allows for the estab-
lishment of effective cleaning procedures
that are crucial to the release of clean and
safe medical devices.
RMM analysis uses three methods to
evaluate the different phases of manufac-
turing and cleaning—gravimetric analy-
sis, total organic carbon (TOC) analysis,
and detergent residual analysis by ultra-
violet/visible (UV/VIS) spectroscopy. All
three tests are quantitative and designed
to remove surface contamination but are
not intended to remove or assess leachable
components from a device. The assess-
ment from these tests can be used to de-
termine cleaning efficiency as well as aid
in the validations of cleaning and rinsing
methods.
Gravimetric Analysis
(ASTM F2459-05). Quantify-
ing extractible residue by gravi-
metric analysis involves using
aqueous and nonaqueous sol-
vents to extract contaminants
such as oils, salts, and other
materials from the surface of
medical devices.1 After the de-
vice is extracted, the solvent
is evaporated and the remain-
ing residuals are weighed and
quantified. Gravimetric analy-
sis does not determine the
specific elements making up
the residue, but it measures the
quantity of the total amount of
residue coming off the device.
If the analysis quantifies
significant residue, the labo-
ratory may also identify, or
qualify, residue by Fourier
transform infrared spectros-
copy. A general analysis or
Analyze This: Device Cleanliness TestingThree analytical methods can help manufacturers avoid residual material product contamination.
TINA MAY AND BRENT SHELLEY
Scientists are shown weighing a crucible for gravimetric analysis. Im
ages
cou
rtes
y of
NEL
SO
N L
AB
OR
ATO
RIE
S
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MOLDING TECHNOLOGIES JULY 2010 | 29
interpretation of the sample
spectrum can reveal the pres-
ence of certain types of com-
pounds such as hydrocarbons
and amines. The laboratory can
also identify the compounds by
comparing the sample spectrum
to the spectra of target com-
pounds. Identifying the residue
may be important when a manu-
facturer is trying to control the
source of residue production.
TOC Analysis. TOC analy-
sis is the most sensitive of the
RMM series of tests. The analy-
sis is quantitative and detects
carbon-based materials such as
oils, adhesives, and detergents on a prod-
uct, but does not pick up inorganic residue
such as metals and salts.
TOC analysis involves extracting devic-
es in USP-purified water by sonicating or
shaking, to remove surface contaminants.
An aliquot of the extraction solvent is ana-
lyzed on a TOC instrument to determine
how much organic carbon is on a device or
component. Alternatively, the manufac-
turer can use swabs to evaluate clean-in-
place components and equipment. After
swabbing the targeted component, the
swab is sent to the lab to be immersed in
USP-purified water and analyzed.
The manufacturer must evaluate the
results and determine how much residual
material is allowable based on the device’s
designed use. For example, if a device is
designed to be implanted in the body, it
needs to carry fewer organic residuals
than if it is a smaller, functional part of a
bigger device used outside the body, such
as a gear in a machine.
Detergent Residual Analysis. Manu-
facturers use a variety of cleaning agents
to clean their devices. Unfortunately,
these cleaning agents can leave behind po-
tentially harmful residual material. Deter-
gent residual analysis detects detergents
by UV/VIS spectroscopy.
Because each detergent absorbs UV
light differently, the laboratory validates
each one for accuracy, precision, linearity,
limit of detection, and limit of quantita-
tion. For this validation method, manufac-
turers must provide a full-strength sample
of detergent that is used in the cleaning
process. Detergent residual analysis also
uses water extraction and sonication to
identify the detergent left on a device. The
lab compares device extracts to the deter-
gents calibration curve for quantification
(see Figure 1).
Detergent residual analysis confirms that
devices are being adequately rinsed. Manu-
facturers, including molded de-
vice manufacturers, should con-
sider having this analysis method
performed on each type and size
of device because different devices
may require different or addition-
al rinsing to completely remove
detergent residuals. For example,
rinsing a smooth artificial knee is
much easier than rinsing a device
with grooves, pockets, lumens, or
mated surfaces.
Why RMM Analysis is EssentialSeveral critical reasons why
medical device manufacturers
should perform RMM analysis include the
following:
■ Cleanliness of device: RMM analysis
helps manufacturers determine wheth-
er they are producing a clean and safe
device.
■ Cleanliness of manufacturing process:
RMM analysis can determine cleanliness
throughout the manufacturing process.
Without this series of tests, manufactur-
ers may not know whether they are over-
cleaning their devices and molds and
therefore wasting time and money on
unnecessary rinses and cleaning cycles.
The analysis also informs the manufac-
turer whether its cleaning processes are
working by showing how much residue is
left behind on the products.
■ Designing cleaning processes: Manufac-
turers design their cleaning processes to
remove residue from a device, but clean-
The manufacturer must evaluate the results and determine how much residual
material is allowable based on the device’s designed use.
280250 270260230 240210 220190 200
0.6
0.8
1
1.2
0.4
0.2
0
Ab
sorb
an
ce
(AU
)
Wavelength (nm)
Figure 1. An example of a detergent residual analysis U/V printout.
A scientist loads samples on a TOC analyzer.
MD100702_029 29MD100702 029 29 7/2/10 9:21:15 AM7/2/10 9:21:15 AM
30 | JULY 2010 mddionline.com
MATERIALS ANALYSIS
ing agents can add additional contami-
nants to a device and render it unclean
and possibly cytotoxic. In some cases,
the cleaning process can makes the de-
vice more cytotoxic than before cleaning.
RMM analysis can help manufacturers
ensure that cleaning and rinsing process-
es are effective and producing a device
that is safe and patient ready.
■ Increased FDA involvement: FDA is in-
creasingly examining the cleanliness of
medical devices. RMM analysis provides
substantiated proof that products have
undergone meticulous cleanliness test-
ing. This documentation can be extreme-
ly useful to support a regulatory submis-
sion or in the event of an FDA or notified
body audit.
■ Mold-release agent transfer: Manufac-
turers often use mold-release agents
to remove devices from a mold, which
can leave residue on the device. RMM
analysis ensures that the device is not
picking up unexpected residues or that
these residuals are at acceptable levels
postproduction.
■ Creating a baseline measurement: RMM
analysis creates a baseline or a gauge for
a cleaning process. This can serve as a
useful validation criterion to ensure con-
sistent production of a safe product.
ConclusionThere are no established regulatory limits
of cleanliness for residual analysis. Manu-
facturers should perform a risk assessment
to determine acceptable levels of residue
based on the application and patient-con-
tact duration. They should also establish
limits for the cleanliness and safety of their
medical products.
Medical device manufacturers can save
time and money down the road if they ana-
lyze their devices, including those made
in molds, for RMM. The analysis method
streamlines and enhances process efficien-
cy to ensure safety while reducing product
and regulatory liabilities. Conducting such
analysis can prevent manufacturing from
halting when a problem or changes in the
process arises.
References1. ASTM F2459-05. 2005, “Standard Test Method
for Extracting Residue from Metallic Medical
Components and Quantifying via Gravimetric
Analysis” (West Conshohocken, PA: ASTM In-
ternational, 2005).
Tina May is chemistry section manager at
Nelson Laboratories (Salt Lake City). Brent
Shelley is study director at the company. 2
Manufacturers can use RMM analysis as a tool to monitor the cleaniness of production at any
point, including the final product.
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MOLDING TECHNOLOGIES JULY 2010 | 31
INJECTION MOLDING
M old makers, mold designers, and mold-
ers in industrial manufactur-
ing have used hot runner
technology for at least 40 years. The
systems are becoming especially im-
portant within the medical products
industry. Hot runners may help de-
vice OEMs reduce costs, improve
part quality, and increase speed
to market.
Hot runner systems are well-
suited for molding medical prod-
ucts for multiple reasons. The tech-
nology opens the door to a variety of options for molders, all
of which provide reduced material use and faster cycle times.
Recent innovations in technology can also provide power and
speed in cleanroom environments, which are required for pro-
ducing many medical products.
Hot Runner BasicsA hot runner system is an assembly of heated components used
in plastic injection molds that inject melted plastic into the cavi-
ties of the mold. A hot runner system usually includes a heated
manifold and a number of heated nozzles. The main task of the
manifold is to distribute the plastic entering the mold to the vari-
ous nozzles, which then meter it precisely to the injection points
in the cavities.
By contrast, a cold runner is simply a channel formed between
the two halves of the mold, for the purpose of carrying plastic from
the injection molding machine nozzle to the cavities. Each time
the mold opens to eject the newly formed plastic parts, the mate-
rial in the runner is ejected as well, resulting in waste.
Hot runner systems consist of a steel block, machined with an
internal passageway for molten resin. Heaters affixed to the pe-
rimeter of the steel block heat the manifold from the outside in,
enabling an even heat inside the block. Melt is then distributed
throughout the heated manifold block, fed into a heated nozzle,
then sent into the final gate well—or bubble—just prior to passing
into the part cavities. When designed properly, the system achieves
maximum material processing capability while eliminating resin
waste per injection cycle.
Hot Runners for Medical ProcessingThe primary benefit of hot runner systems is speed. Fractions of
a second in cycle time add up quickly and can significantly affect
the bottom line.
Hot runners also cut cost by reducing waste. The technology
eliminates runner waste and any costs necessary to regrind or dis-
pose of scrap. The technology also enables a variety of increased
process efficiencies, as well as the capability for extreme precision.
An example of how exact hot runner systems can be is the electric
valve gate. This machine has variable pin positioning in 0.001-in.
increments, giving a significant level of control to molders.
Top Considerations for Selecting a Hot Runner System Hot runner systems were created out of a need to mold plastic parts
fast and at a low cost. When they are selected, installed, and work-
ing properly, these systems can improve part quality, as well as en-
able fast processing speeds, low scrap, low labor costs, high-volume
production, and efficiency. But achieving the maximum potential
requires proper knowledge, planning, design, and execution.
The primary consideration for selecting a hot runner system is
to determine whether the product needs to be molded in a clean-
room. A contaminant-free environment is often a prerequisite for
producing medical products, especially Class II and Class III medi-
cal devices. Producing these types of items outside a cleanroom can
create serious risks for both patients and medical staff.
There are products, however, such as bedpans or food trays, that
do not require cleanroom standards. These types of items can often
Hot Runners and the Evolving Medical Industry Hot runner innovations may be able to provide speed and precision for medical molding.
CRAIG KOVACIC
An electric valve gate system provides technology for precision molding while also reducing waste.
MD100702_031 31MD100702 031 31 7/2/10 9:25:44 AM7/2/10 9:25:44 AM
32 | JULY 2010 mddionline.com
INJECTION MOLDING
be sanitized after the standard molding process due to advance-
ments in gamma radiation and other sterilization procedures.
Once you’ve established whether the application requires clean-
room molding, the next step is to determine the tolerance for gate
vestige based on the nature of the part. From there, you can ulti-
mately choose which nozzle, and therefore which system, is the
most appropriate for the application.
Preparation for Hot Runner Systems
Before starting a project, meet with
the materials supplier, the toolmaker,
and the hot runner manufacturer to
determine how each will contribute.
Working together from the beginning
allows the OEM to consider options
and ensure that all parts of the pro-
cess will fit together.
The most important recommenda-
tions should come from the material
supplier. The residence time of the ma-
terial is important. The supplier should
provide information on how much sheer
the material can take and on the proper flow
materials. Figuring this out first is especially
important for producing medical products,
because the resins used for medical devices
are typically highly engineered with specific processing parameters.
In medical applications, it’s also important for a material’s sur-
face to be as nonporous as possible to prevent bacterial growth.
Producing this type of resistant surface usually demands highly
engineered machines. This is also common when producing parts
for the food industry.
With the material supplier, determine whether a hot runner sys-
tem is even an option. Due to residence time, a highly engineered
resin may need to be injected right into a part once it comes out of
the molding machine. If a particular material only has a short amount
of time it can be fluid, a hot runner system might not be viable.
All of the specs provided by the material supplier will ultimately
determine which nozzle is selected. And knowing everything you
can about a material will help you “think like a pellet” when design-
ing the hot runner system for optimal operation.
Hydraulic, Pneumatic, or ElectricHot runner equipment comes in three varieties: hydraulically pow-
ered, pneumatically powered, and electrically powered. Whether a
cleanroom is required dictates which of these options is used.
Hydraulic systems provide powerful valve gate shutoff, contrib-
uting to maximum part quality. However, due to the risk of oil leaks
and contamination, they are unsuitable for use in cleanrooms.
Pneumatic systems, a much cleaner option, have long been the hot
runner of choice, but these also have a downside. Their relatively
weak shutoff force is less than ideal for the high speeds and preci-
sion the market demands.
Electrically powered hot runner systems are a relatively new
innovation. These systems provide more power, speed, and pre-
cision than pneumatic or hydraulic options. And they use power
that doesn’t require hoses, oil, or other potential contaminants. The
electric technology is suited for cleanrooms.
Thermal Gate versus Valve GateOnce the power source has been chosen, molders must determine
whether to use a thermal gate or a valve gate. This decision is based
primarily on whether the final part has any tolerance for gate ves-
tige, the mark a gate can create on the part.
Although gate vestige can be undesirable for many plastic prod-
ucts, it’s particularly problematic in the medical field. Surgical gloves
prevent the spread of disease within medical facilities and are a criti-
cal part of overall safety for patients and medical staff. Plastic parts
produced with any sharp or jagged edges, as a result of gate vestige,
can potentially tear through thin gloves and pose an assortment of
safety risks. Vestige points can be trimmed off of plastic items if nec-
essary, but these secondary processes reduce efficiency.
Thermal gates are generally the more common and less expensive
gate option. They are particularly suited for high-cavity-count molds
with close cavity pitch dimensions. With thermal gates, plastic hard-
ens in the gate area as it cools, creating a barrier between the molten
plastic and the cooled part, and leaving a small vestige point. The
molder must take this into consideration ahead of time and accom-
modate accordingly. It is not uncommon for molders to put a dimple
in a part so that the vestige is below the surface and not easily felt.
Valve gates, the other type of gate option, typically do the best job
eliminating vestige and producing suitable medical products. They
function by shutting off the flow of plastic mechanically, with a
physical barrier between molten and cooled plastic. They are good
for superior gate cosmetics, sequential part filling, and eliminating
the potential for sharp edges.
Some circumstances exist in which plastic parts are too small to
use a valve gate. In those cases, use a hot-to-cold runner technique
to feed a tiny runner into the small part. When the part ejects from
the mold, it makes a clean break from the cold runner, leaving no
sharp edges.
Selecting NozzlesThe appropriate nozzle for a hot runner
system is determined by the type of mate-
rial going through the flow channels. If the
nozzle is too small, sheer is created. If it is too
large, the system cannot be flushed out through
the manifold or the nozzle.
When choosing a nozzle, it is important to
consider how many shots of material are in the
manifold. Typically, it is standard to have within
three shots of material between the machine
barrel and the part. Sometimes this changes due to high cavitation
(the formation of vapor bubbles of a flowing liquid). Resin can only
be heated for a certain amount of time before losing its properties.
Because all material has this residence time, it is important that the
nozzle be small enough to constantly contain fresh material.
Reusing Hot Runner SystemsThere are situations in which a processor can use the same hot
runner system for different parts that are within the gram weight
capacity of the system’s nozzles.
Thermal gates are a common option that can accommodate high-cavity molds.
Choosing nozzles and manifolds depends on the individual needs of the part.
MD100702_032 32MD100702 032 32 7/2/10 9:25:49 AM7/2/10 9:25:49 AM
MOLDING TECHNOLOGIES JULY 2010 | 33
For example, a part may be 5 g, but the same nozzle can also han-
dle a part that is 10 g. If the molding is within the same limitation of
that nozzle itself, A-plates and cavities can be pulled off and placed
on other A-plates and cavities, as long as they match the capacity of
the nozzles that were chosen first.
Reusing hot runner systems generally requires forethought on
the part of the mold maker to design molds and part cavities that
are spaced appropriately for a specific hot runner system. A mold
maker can put small cavities into a large footprint, which is an im-
portant planning consideration.
If one part can work in a 1-in. pitch, but the other part requires
a 1.5-in. pitch, the drops must be 1.5 in. apart. That way, the larger
spacing is run first, and it becomes the reference point before run-
ning the smaller part. A molder can always go large to small, but
not the other way.
Tip Style SelectionOnce the nozzle type is selected—which also determines the hot
runner model provided by the supplier—an OEM should select the
nozzle tip style. A variety of tips are designed for different types of
hot runner applications.
Sprue gate tips are used for situations in which gate vestige is
not a concern. They offer minimal flow resistance and handle most
resins effectively. Extended styles of sprue gates provide additional
stock for machining runner profiles or part contours. Sprue gate
tips can be used with either valve gates or thermal gates, but gener-
ally go from thermal to a cold runner. They keep the sheer of the ma-
terial down until it goes into the part, which prevents plastic from
degrading before it has achieved a fully fluid state.
Point gate tips are used only for thermal gate systems and are
suitable for direct part gating. They’re generally used for applica-
tions needing optimal gate cosmetics and can run a wide range of
resins. As a general rule, point gate vestige will be one half of the
gate diameter. If a 0.04-mm gate is used, up to 0.02 mm of material
could stick up. That excess can be removed, if necessary, depending
on where it is on the part.
Through-hole tips, also used for thermal gating, have nothing in
the tip to split material molecules. Their gate vestige is equal to the
gate diameter. A 0.04-mm gate will produce a 0.04-mm vestige.
Many preforms use through-hole tips. They’re also commonly
used for parts with secondary operations, like blow molding, when
the processor doesn’t want to sheer the material and wants to mini-
mize gate vestige as it moves to a secondary operation.
Valve gates eliminate vestige completely, leaving only a witness line
where the part is sealed off, similar to those left by an ejector pin. This
makes valve gate tips essential for many delicate medical molding ap-
plications in which surface quality and precision are critical.
Sourcing the ManifoldsOnce the nozzle type and tip style are determined, they need to
be housed in a manifold, which takes the melt from the molding
machine and distributes it evenly to each of the hot runner system
nozzles. Often, manifolds are sourced from the nozzle supplier as
part of a nozzle and manifold system due to the precision machin-
ing required. However, some mold makers may have the capabilities
needed to do this in-house as well.
Manifolds are generally made of P20 or stainless steel for the
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34 | JULY 2010 mddionline.com
INJECTION MOLDING
part of the design. This is helpful if the part requires a screw hole or
similar element. The pin can be set to open at 0.0001-in. increments
along its 0.75-in. stroke range. All other hot runner options are ei-
ther open or closed, without the ability to stop the pin midway.
Besides design benefits, variable pin positioning also enables
even filling of a family mold in which one cavity may be larger than
another. Without this level of control, the mold may become out of
balance in the filling process or uneven pressure buildup may be-
come a problem.
Electric valve gate machines provide faster mold changeovers as
well. With these systems, a molder merely hooks up the electric from
the hot runner system to the control box. Air
and hydraulic require hooking up hoses and
cables and make the process much more
time consuming.
Electric valve gate hot runner systems
also have variable speed capability, which
is perfect for coinjection and family molds.
This capability helps balance the mold and
allows for sequencing on larger parts. When the molder wants to
move the knit line across, the machine enables the plastic to flow
from one nozzle to the next as they open and close in sequence.
Most molding requires the pins to all open or all close at the same
time within a mold. However, there are times when a molder might
want to partially open one gate while another is fully open to help
balance out the mold as it fills. The electric valve gate is the only
machine that can accomplish this.
Limitations of the Electric Valve GateBecause the electric valve gate is still fairly new technology, there
may be some applications for which it is not the right solution. This
is often due to the 3-sq in. size of the motors that currently operate
each valve gate. The measurements are somewhat large for close
center-to-center distances.
That means that three pins share the same plate if a molder needs
one inch of distance between pins. All of the pins have to fire at the
same time. That isn’t generally a problem for small, high-quantity,
high-cavitation parts. But it does create limitations for larger parts
with multiple gates.
ConclusionThe benefits of hot runner technology, specifically the electric valve
gate, are only getting better. The future of this technology includes
faster and smaller motors. In addition, the cost of the machines is
also anticipated to come down in the coming years.
Hot runners are an extension of a molding machine nozzle, but
they offer a unique opportunity for efficiency and cost savings. They
offer problem solving for complex applications.
Craig Kovacic is global manager of hot runner systems for DME Co.
(Madison Heights, MI). MT
medical industry. It is crucial that they be properly extrude honed,
a process by which flow channels are rounded and highly polished.
This eliminates friction and removes any spots where materials
could potentially get stuck or degrade.
Because extrude honing is an advanced and critical process,
medical molders or mold makers rarely build their own manifolds.
By buying an entire hot half (defined later), or a whole system from
a manufacturer, molders know the manifolds have been extrude
honed to the highest specifications.
The final step in creation of a hot runner system is developing
what is called a full hot half. This includes the nozzles, the manifold,
the mold plate that houses the manifold so that it can fit into a mold
base system, along with all of the wiring. Again, the level of sourc-
ing for a full system versus in-house development depends on the
capabilities of the molder or mold maker and the best use of their
resources and core competencies.
The Electric Valve GateGiven quality and contamination considerations in molding medi-
cal products, it’s no wonder the industry is moving toward electric
machines—both electric molding machines and electric valve gate
hot runner systems. Hydraulic-powered hot runner systems are not
an option for cleanrooms, and the cylinders in pneumatic systems
cannot match the speed or the 35,000-psi shutoff power of an elec-
tric valve gate.
Pneumatic systems have a moving solenoid, which takes time to
move. A mechanical process has to occur before the machine can
send air to the valve gate cylinder. With the electric valve gate, it
takes mere nanoseconds for an electric signal to fire a valve.
Another downside is the common maintenance and performance
issues of pneumatic systems caused by poorly tightened air or water
lines that don’t properly cool the plates. When this happens, the O-
rings can bake on the cylinders, lose their integrity, and cause air
leaks that contaminate the parts and decrease system pressure.
Since a motor moves the cylinder on an electric valve gate, there are
no O-rings that can dry out or that need to be maintained.
Eliminating leaks reduces scrap as well. A fast, precise, and power-
ful closing force reduces the gate vestige into which scrap can enter.
With oil or air, leaks can occur, which change the viscosity of the
material. The change in viscosity prevents the valve from opening or
closing all the way, creating a nub on the parts. Electric valve gate hot
runners have such a great closing force that they will close up on the
material flow as programmed even if the viscosity of the material has
changed. This results in better part quality and reduced scrap.
The electric valve gate and its variable pin-positioning feature can
also make design elements easier. The molder can control how far
the pin sticks out. This means it can even protrude into the product
if desired, allowing the valve pin to make a hole in the product as
Given quality and contamination considerations in molding medical
products, it’s no wonder the industry is moving toward electric machines.
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Company Listing
Crescent Industries Inc.70 E. High St.New Freedom, PA 17349717/[email protected] Industries is a single-source pro-
vider of custom injection-molded plas-
tic components using high-performance
thermoplastics in a variety of molding
services. The company’s medical molding
division, Crescent Medical Plastics, oper-
ates in a 10,000-sq-ft cleanroom facility. It
has the ability to produce Class I, II, and III
medical devices, surgical equipment, and
disposables.
Donatelle501 County Rd. E2 Ext.New Brighton, MN 55112651/[email protected] helps OEMs from concept
through production. Services include
molding of engineering grade thermoplas-
tic and elastomeric materials, micromold-
ing, liquid silicone injection molding, insert
Molding Directory
RY
MD100702_036 36MD100702 036 36 7/2/10 4:27:38 PM7/2/10 4:27:38 PM
MOLDING TECHNOLOGIES JULY 2010 | 37
AD INDEX
molding, and overmolding. The company’s
facilities house more than 40 molding ma-
chines ranging from 5- to 300-tn capacity.
The company is FDA compliant as well as
ISO 9001 and 13485 certified.
Micro140 Belmont Dr.Somerset, NJ 08873732/[email protected] is a full-service contract manufac-
turer of precision medical devices and
components, injection and insert mold-
ings, and fabricated tube assemblies. It
offers product development and design
capabilitie from prototyping and validation
to full-scale production. The company’s
modern facilities are ISO 9001, ISO 13485,
and ISO 14001 certified. Micro maintains
an ISO Class 8 cleanroom for surgical in-
strument assemblies.
Minnesota Rubber and Plastics1100 Xenium Lane N.Minneapolis, MN 55441952/[email protected] Rubber and Plastics is a custom
molder of components and assemblies,
specializing in high-performance materi-
als. Services include product development,
tool design and fabrication, prototyping,
insert molding, silicone overmolding, as-
sembly, and Class 10,000 and 100,000 clean-
rooms and packaging.
Plastics One Inc.6591 Merriman Rd.Roanoke, VA 24018540/[email protected] One specializes in custom injection
molding of medical device components
with complex requirements and unique
specifications. It provides a range of servic-
es including design and research, in-house
tooling, prototyping, and assembly.
PolyMedex Discovery Group45 Ridge Rd.Putnam, CT 06260860/[email protected]
www.polymedexgroup.comPolyMedex Discovery Group serves medi-
cal device manufacturers with comprehen-
sive development and manufacturing ser-
vices for intravascular, minimally invasive,
and implantable applications. It supports
its customers with polymer distribution,
custom compounds, bioresorbable and
drug delivery formulations, thermoplas-
tic and thermoset tubing, and custom
components.
Proto Labs Inc.5540 Pioneer Creek Dr.Maple Plain, MN 55359877/[email protected] Labs through its First Cut and Proto-
mold services uses proprietary computing
technologies and automated manufactur-
ing systems to provide prototype parts and
short-run production services. All compo-
nents are made by standard production
methods and can be shipped in as fast as
one day.
Vesta 5400 W. Franklin Dr.Franklin, WI 53132414/[email protected] is a manufacturing services com-
pany that provides molding, extrusion, and
assembly for the medical device industry.
The company provides expertise in design
assistance, material selection, and quality
standards within ISO-certified facilities. It
offers a range of molding capabilities in-
cluding liquid injection, transfer, and insert
molding of medical-grade silicone. 2
Look for the following upcoming directories in MD+DI :
■ Who’s Who in Contract Manufacturing■ Outsourcing Showcase* ■ Packaging and Sterilization Showcase*■ LitPak*
*advertisers only
Contact your local sales representative to see whether your company qualifies.
Canon Trade Events ...............................30, 35
310/445-4200 • www.canontradeshows.com
Crescent Industries Inc. ..............................33
717/235-3844 • www.crescentind.com
Donatelle .......................................................... 7
651/633-4200 • www.donatellemedical.com
Foster Printing ...............................................25
866/879-9144 • www.fosterprinting.com
Medical Extrusion Technologies Inc. .....11
800/618-4346 • www.medicalextrusion.com
Plastics One Inc. ...........................................25
540/772-7950 • www.plastics1.com
PolyMedex Discovery Group ....................15
860/774-1559 • www.polymedex-possible.com
Proto Labs Inc. ................................................. 3
877/479-3680 • www.protolabs.com
Saint-Gobain Performance Plastics ........19
800/236-7600 • www.medical.saint-gobain.com
Sil-Pro (Silicone Professionals) ................. 5
763/972-9206 • www.sil-pro.com
Smiths Medical OEM .................................... 9
866/216-8808 • www.smiths-medical.com/oem
Vesta Inc. ........................................................23
414/423-0550 • www.vestainc.com
Wacker Chemical Corp...............................27
888/922-5374 • www.wacker.com
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