the molds and have the capacity
to handle large, multi-mold projects. The company’s largest CNC
machine has a build envelop of
100” x 60” x 28” and a 28 station
robotic tool changer. “It can run
for days on its own when everything is working properly – which
is all the time,” adds one enthusiastic machine operator.
In contrast to high-pressure injecting molding, RIM is low-pressure, around
50 to 70 psi, and low-temperature, reaching
anywhere from 150° to 170°F. These factors
allow for aluminum molds, rather than steel,
because the conditions lead to a lower mold
One advantage to aluminum molds,
is cost. “If you have a huge part with a
huge mold, it’s going to cost hundreds of
thousands of dollars with steel. But with
aluminum, it’s about a third of the price,”
Besides the cost savings, RIM parts don’t
require secondary operations to machine
vent-slots or to glue-in bosses. These features are molded into the part, and result
in precise tolerances, and batch-to-batch
“You don’t have someone trying to drill
holes after the fact,” says Boettcher. “It
saves [our customers] time and money,
and they aren’t buying multiple tools.”
The Injection Process
Once the custom molds are machined,
“first article” parts are molded and sent to
the customer for verification. After approval, they are ready for production. The mold
is then placed in a press which is tilted at
an angle specified for each part. Tilt orientation ranges from 25° to 80°, and helps to
Two liquid components, a polyol (the resin)
and an isocyanate (the reactant), wait in separate holding tanks until they are released
by the dispensing unit and impinged in the
mix-head attached to the mold.
The mixed components are now called
the “resin system,” which is injected from
the bottom of the mold (at the gate) to flow
through the mold toward the vent area. “The
resin flows in with the viscosity of skim milk.
As a result, you can fill out really large and
complex parts,” explains Boettcher.
The resin system fills the mold in a
few seconds, and then the curing process begins. On average, RIM parts cure
in three to eight minutes depending on
the size and complexity of the geometry.
Because these are urethane thermoset resins, the part is fully cured in the mold.
One drawback is that RIM is not suitable
for high volumes. “Our set up times are
low, but the actual cycle time can take a
while,” says Boettcher. Typically, RIM parts
are used when a customer needs between
100 and 2,000 parts-per-year. The parts are
produced in small batches, usually 25 to 50
After the molding process, the next step
is to get rid of the mold release, which is
essentially petroleum jelly that keeps
the product from sticking. “We sand
blast [the part] with calcium chloride.
It is good for the environment, gets
recycled after use, and takes off the
mold release. It also prepares the part
for optimal paint adhesion,” Boettcher
When the base coat is established,
the paint is cured in an oven. A second
coat is applied which determines the
texture and gloss of the product by con-
trolling the spray of the droplets, specifically
the frequency and thickness. The part then
goes back through the paint curing oven to
complete the process.
Drying the paint takes around 45 min-
utes, as the product makes its way through
the paint-drying oven. Kept at around
140°F, Boettcher describes it as “a slow
In addition, Premold maintains UL rec-
ognition to apply top quality electromag-
netic shield coatings (EMI) to their custom
molded plastic parts. The EMI coated parts
provide a highly effective EMI shielding for
enclosures, and can eliminate the need for
In line with the company’s quality standards, every part must have a Class A
finish, meaning that it must be visually perfect from a distance of 18”. With
this requirement, and an additional ISO
9001:2008 certification, attention to detail
is pertinent. To ensure that everything is
performed to specifications, a “job traveler” document accompanies each batch of
products throughout its time in the facility.
The document details the customer information on the product, and provides product description, quantity, and history. All
processes are barcoded so employees can
scan them to receive visual work instructions. “If there is a problem, it’s easy to
look back at the job traveler, so there is a
lot of accountability,” explains Boettcher.
Securing a Market Niche
With a path towards commercialization
in the industry, the Premold process offers
customers a chance to differentiate themselves from their competitors. Custom
covers and silk screens are easily achieved
through the RIM process, and with vertical
integration in the facility, the customers
have many options.
“I think that if you aren’t evolving and
staying hungry, there is always competition that is going to want to fill your market niche,” says Boettcher.
Above: An employee works to release
the mold from the part after finishing
the injection process. Below: A robotic
CNC system machines a custom mold.