Equipment Innovations Give Silicone
Molders a Shot in the Arm
Multicomponent systems, waste-reducing
cold runners, and specialized tooling enable
molders to cut assembly costs and increase
productivity
While liquid silicone rubber (LSR) injection
molding is a mature process, emerging
technologies are changing the face of the
old workhorse. As manufacturers increasingly mold
medical products such as valves, seals, and implants
from LSR, they are turning to multicomponent, or
2K, molding equipment to perform multimaterial,
multicolor, and multidurometer processing. At the
cutting edge of this 2K trend is the emergence of
single machines that perform multiple molding
steps and the proliferation of cold-runner units that
prevent premature LSR curing and waste.
separate the hot tool from the
cold runner more effectively. This
technology enables sequenced or
profiled filling to each cavity and
minimizes gate vestiges or cold
slugs in finished parts, thereby
reducing waste.
According to Vassallo, whose
company employs European
tooling equipment, the tooling
is the mold itself. “It has the
cavities in it for the part that
you’re going to make…. You can
have a one-cavity tool, you can
Simtec’s overmolded components and parts are manufactured using two-shot
have a 16-cavity tool. It produces
LSR molding systems.
one part at a time, or 16 parts
at a time.” Today’s tools can
comments Camacho. “Several parts that are made
as single, separate units from LSR and a plastic
substrate are integrated into a two-shot component
with the assistance of the two-material injection tool.
This process eliminates the need for several injection
units for the production of single parts.” According
to Camacho, this technology reduces validation costs
and enables the production of complete components
that are easily assembled into end devices.
Taking advantage of another breakthrough
in LSR 2K processing, the company employs
medical-grade self-adhesive materials to
overmold components for such products as
temperature-measuring devices, feeding devices,
and diaphragms. Camacho emphasizes that
“the imagination is the limit for the inception
and development of two-shot-made devices.”
Typical examples of such products include
couplings, septums, needleless valves, connectors,
thermometers, and drug-delivery devices.
Two Shots, One System
Injection molders are constantly striving to
implement technological improvements that reduce
production costs, increase cost-effectiveness, and
lower the unit price of the products they sell to
their OEM customers. Simtec Silicone Parts
(Madison, WI; www.simtec-silicone.com) is no
exception. With its recent acquisition of European
8+ 8 two-shot systems for LSR molding, the
company is providing continuous lights-out serial
production of integrated components and thereby
lowering validation costs.
Injection molding of LSR has been available in
the United States for more than 10 years, remarks
Simtec president Enrique Camacho. But in recent
years, manufacturing innovations have advanced
the technology. For example, overmolding using
two separate machines has enabled producers to
mold LSR onto plastic or metal substrates.
New Tools of the Trade
Building on this multicomponent molding Equipped with two small-shot European
strategy, European machine and tool builders have micromolding presses and specialized tooling
developed two-shot systems—the first of their kind, technology, Helix Medical (Carpinteria, CA; www.
according to Simtec—that perform what Camacho helixmedical.com) molds a variety of LSR products
for the medical device market,
including voice prostheses for
the ear, nose, and throat market;
bariatric surgery products; drug-delivery parts; neurosurgical
shunts; silicone joint prostheses;
and micromolded parts such as tips
for catheters less than 3 French
in diameter. According to Helix
president Tom Vassallo, “Some
parts are small enough to fit into
the tear duct of an eye.”
While Vassallo sings the
praises of single-machine 2K
molding, he stresses that tooling
advances are also changing the
face of the industry. “If you can
mold plastic and silicone in the
Standardized cold decks from D-M-E Co. are used for elastomer processing. same system, what you do is reduce
the labor because you don’t have
to assemble [a part] by hand,” he
notes. “But European tooling technology is also
important, because tooling is the second half of
being able to produce a product. You’ve got your
press and you’ve got your tooling.”
The LSR tooling business is a niche specialty
dominated by Austrian firms. Tooling developments
are being propelled by molders’ demands for higher
cavitation, flash prevention to hinder low-viscosity
LSR from shooting through gaps in the molds as
small as 0.0002 in., and cold-runner valve gates
for tight part tolerances. While open-nozzle designs
are preferred over valve-gate nozzles, the latter
contain up to 256 cavities and produce hundreds of
thousands of parts per day. As for Helix’s systems,
Vassallo remarks, “Our cold-runner cavities range
from 1 cavity to 16 cavities. The throughput
becomes relative, since we produce less engineered
waste—scrap from runners—and we make parts
that have flash tolerances within exacting medical
device specifications.”
dubs ‘truly two-shot LSR/substrate injection
molding’ using a single piece of equipment.
“The two-shot injection molding unit enables the
integration of several parts into one component,
thereby reducing the cost of production, validation,
and assembly,” he explains. The technology
enables the production of parts with complex
geometries and designs and also optimizes part
performance—a feat achieved by combining raw
materials with complementary properties.
“The integration of several parts that go into
one component takes place in the design phase,”
Waste Not, Want Not
Injection molding equipment supplier
D-M-E Co. (Madison Heights, MI; www.dme.net)
knows all about reducing waste. Runner systems
waste liquid silicone material because they begin
to cure it before it reaches the molds, explains
Michael Kreitner, the company’s business manager
for quick-change mold systems and emergent
technologies. To prevent this undesirable effect,
“The material must get to the cavities and cores
of the mold before any of the curing starts to take
place.” To address that challenge, the company is
marketing a new cold-deck cold-runner-type system
for molding materials such as LSR and other
elastomers.
While hot-runner technology delivers hot
plastic to the cavities and cores of molding
machines, cold-deck technology is based on the
same method, only in reverse: “We need to keep
the liquid silicone cool or at room temperature,
then have it injected into heated cavities and cores
where it is cured to make the silicone part itself.”
Kreitner notes that while excess thermoplastic
material can often be reground or reused after it is
molded, “liquid silicone, once it is cured, cannot be
reused for anything. It is 100% waste.” Silicone
molding operations that do not use cold-runner
systems can generate waste in the form of runners
or sprue residue. “That, of course, is the waste
portion we’re looking to eliminate,” notes Kreitner.
“You’re striving to get a finished part out of your
mold without any secondary trimming or steps like
that—especially when it comes to medical, because
the more you touch it, the more you have to handle
it, the more sterilization steps may need to happen
down the road.”
Besides achieving an obvious cost benefit by
lowering silicone consumption, manufacturers that
use cold-deck technology can also contribute to
environmental sustainability, according to Kreitner.
“It’s not like you can ship [silicone waste] off
like a used milk bottle and have it recycled into a
park bench or some other reprocessed product. It
basically has to go to landfill, and that’s what we
want to avoid at all costs.” —Bob Michaels
For more articles and
information on molding for
medical applications, visit www.devicelink.com/mpmn/molding
