By Mike Roberts
President & Co-Founder
Microplastics, Inc.
Insert Molding
Solutions for Efficiency in Producing
Electromechanical Components and Interconnections
Microplastics
Insert Molding Engineered for Quality
Insert Molding:
Solving Component Design Challenges
oday’s component design engineers are challenged to reduce the size,
weight, and costs of electromechanical components and interconnections while increasing part reliability. However, achieving these goals is
often difficult with conventional production methods using soldering,
fastening, or adhesives.
T
Insert molding can be an optimum solution. Insert molding offers an
efficient process for combining multiple discrete parts into a single
component, joined by a lightweight molded thermoplastic.
This White Paper will provide an examination of insert molding, its
origins, the steps involved, the equipment, the advantages, design
considerations, and applications. The purpose of the paper is to help
you evaluate insert molding as you plan your next component.
Overview
Insert molding defined
Insert molding is a process by which discrete parts
such as stampings, bushings, or electromechanical
components are joined by thermoplastic to create a
single component.
The parts, called inserts, are loaded into a custombuilt mold, whereupon thermoplastic is injected, and
the inserts become encapsulated within the plastic.
How insert molding evolved
One of the earliest applications of encapsulating a
metal part within a molded elastomer was the nowuniversal wire-plug connection on the electrical
cord. Metal prongs were inserted into a mold, and
an elastomer was injected around them in a manner similar to the injection molding process.
Another early application of the process was the
screwdriver handle.
Two of the earliest insert
molding applications.
Around the mid-20th century, this encapsulation
process became known as insert molding.
Coinciding with the proliferation of engineering
resins that offered a great many characteristics, from
the ability to withstand extreme temperatures to
insulating and conductive properties, insert molding
found a broad spectrum of uses.
Today, insert molding is widely used for applications
ranging from electronic circuitry to automotive
components to appliances. Yet numerous applications for which insert molding is well suited, such as
wire harnesses and filtration mechanisms, still
employ more traditional production and assembly
methods. From a cost and quality standpoint, many
of these applications could benefit considerably
from a conversion to insert molding.
The insert molding process
The insert molding process begins with the placement of inserts in precise positions within a mold by
an operator or robot. For exact placement, the
inserts are positioned on small metal support pins,
or locating pins, within the bottom tool of the mold.
Typically, the support pins leave small holes. In
some cases, overmolding is used to fill these holes.
In other applications, retractable pins are used, and
the pressure of the incoming plastic pushes the pins
out of the mold, allowing the pin holes to be filled
during injection.
Once the mold is loaded with inserts, the mold
closes, and plastic injection takes place. When
the plastic is sufficiently cooled—generally within
seconds—the mold opens and the component
is ejected.
Benefits of insert molding
Insert molding can be a highly efficient alternative
to the assembly of discrete parts using soldering,
connectors, fasteners, or adhesives. Its benefits over
such methods include:
Reduced assembly and labor costs. Because insert
molding joins numerous components with thermoplastic, assembly and labor costs are greatly minimized.
For example, a single stamping can be overmolded,
then perforated to create multiple circuit paths.
This single insert
molded part replaced a
12-component assembly.
Reduced size and weight. By eliminating fasteners
and connectors, and by combining the physical
strength of resin and metal inserts, insert molding
yields smaller and lighter components.
Increased reliability. With every part tightly secured
in thermoplastic, an insert molded component
prevents part loosening, misalignment, improper
terminations, and other problems. The thermoplastic
resin also provides improved resistance to shock
and vibration.
Increased design flexibility. Designers appreciate
the virtually unlimited configurations that insert
molding allows. For example, in creating a 3-D
circuit board, overmolding permits circuitry to
move freely through the part, from inside to
outside, up walls, down in holes—and the plastic
ties it all together.
More rapid cycle times. Insert molding cycle times
are generally faster compared with injection molding cycle times, because the multiple-bottom mold
concept allows molding to take place virtually
continuously during a run.
Cycle times range from 15 seconds to one minute,
from loading through molding and packaging.
Within this span, shorter cycle times will generally
involve robotics, while longer times will generally
involve manual operations and may have parts with
larger size or heavy wall sections.
Materials
The materials used in insert molding may be divided
into two major categories: the plastic resins to be
injected, and the inserts. Below is an examination of
both categories, followed by material considerations.
Injection resins
Virtually any plastic material may be used in insert
molding, from general purpose formulations to engineering grade materials for high end applications.
They can include:
• Polyolefins
• Polystryrene
• Liquid crystal polymer (LCP)
• Glass-filled PBTs
• Glass-filled nylons
• Polycarbonates
• Acetals
• Acrylonitrile-butadiene-styrene (ABS)
How insert molding differs from
standard molding
There are several clear distinctions between insert
molding and standard injection molding. As we
have seen, the major distinction is the need to
support the inserts within the mold using the
aforementioned pins.
Other important distinctions include:
Insert materials and types
Inserts may be metal or plastic parts, including fine
meshes for filtration applications. While insert types are
only limited by the imagination, a typical list follows:
• Metal stampings
• Bushings
• Filters
• Terminals
• Pins
Vertical presses are
commonly used for
insert molding.
Vertical press equipment. Rather than the standard
horizontal press configuration, insert molding press
equipment employs a vertical rotary press design
to accommodate the easy loading of inserts. While
a horizontal press mold has a top and a bottom,
each vertical rotary mold has one top and several
bottoms. This facilitates high volume runs, since a
complete mold can be filled while other mold bottoms are being loaded with inserts, and completed
components are being removed from others.
• Electromechanical components
• Plastic parts
• Filter material—comprised of polyester,
polypropylene, nylon, stainless steel, or brass
Material considerations
Shrink rates. Designers should be mindful that
the presence of inserts will change shrink rates
from those given by plastics manufacturers. The
shrinkage will vary, depending on the amount of plastic displaced by the inserts. Once the quantity and
thickness of the inserts are determined, the insert
Insert Molding Capabilities
Design Capability
Example
Benefits
Allows numerous components to be
combined into a single component
Overmolding a single stamping and
then perforating the stamping to
create multiple circuit paths
• Reduced assembly
• Reduced labor
Elimination of fasteners
and connectors
Overmolded plastic holds inserts
in position, not screws or rivets
• Smaller and lighter parts
Thermoplastic allows inserts
to be securely joined
Wires, solder, or connectors that
can vibrate loose are eliminated
• Increased reliability
• Prevention of loose connections
• Prevention of improper terminations
Ability to design
in three dimensions
In circuit board designs, circuitry
can move freely through the part,
up walls and down in holes
• Increased flexibility
molding manufacturer should be able to provide the
designer with adjusted shrink rates, if required.
Plastic inserts in plastic. When using plastic inserts,
the insert material should have a higher heat resistance than that of the surrounding material, so as to
maintain total part integrity.
Filtration media in plastic. When filter inserts are to
be incorporated, the insert molding manufacturer
should be informed of the following criteria: 1) what
will be flowing through the filters, e.g. air, gas, or
liquid; 2) how robust the force of the flow will be;
and 3) which direction it will be flowing in. This
will help the manufacturer in supporting the insert,
to prevent it from dislodging or delaminating.
An insert molded
dishwasher filter
assembly.
Secondary operations and testing
As with assembly, secondary operations may be
available from the insert molding manufacturer.
They may include:
• Separation of inserts using hydraulic blanking
dies or presses
• Precision gel dispensing - for dampening parts
to resist vibration
• Oven curing of epoxies and gels - to provide
optimum characteristics
• Part serialization and tracking
• 100% end process testing (including electrical
testing of lighting fixtures, etc.)
• 100% testing of all parts
Applications
Extending the capabilities of
insert molding
Assembly
While insert molding often replaces assembly, further assembly can favorably extend its functionality.
When assembly is desired, designers will be best
served by single sourcing the insert molding and
assembly process, as some insert molding manufacturers offer in-house assembly services. Assembly
steps may include:
Applications for insert molding continue to grow.
As of today, insert molding has been used for the
following functions and markets:
Functions
Markets
• Connectors
• Appliance
• Electromechanical
• Automotive
• Filters
• Communications
• Housings
• Computers
• Bonding
• Lighting
• Controls
• Two-part epoxy
• Mechanical
• Electrical
• Microsoldering
• Sensors
• Electronic
• Variable tune assembly
• Switches
• Industrial
• Pre-forming and post-forming of inserts
• Trimming of inserts
• Manual assembly of switches, shields, bulbs,
bulb sets, and many other part sets
• Application of pressure-sensitive adhesives
Design Considerations for
Insert Molded Components
hile the primary design focus of any component will always be its function within a
total product or system, designing a component
that will be insert molded gives the designer two
additional sets of considerations. These are meeting
the requirements of the insert molding process,
and maximizing the potential benefits that insert
molding can provide.
W
Preventing voids. Void prevention is an important
consideration in the engineering and tooling stage
of an insert molded application. Proper gate design
and venting holes, that allow air and gas to escape,
are critical. Adding multiple gates during the tooling
stage is one way to prevent voids. Raising the temperature of the mold or the plastic, or increasing
flow, can also be effective. But avoiding heavy wall
sections in part design is the best prevention.
Functional considerations
The function of an insert molded part is defined by
the inserts, the molded plastic, and the interplay
between the two.
Specifying inserts. A design engineer can often
approach a component project by considering the
same group of discrete parts, whether the component is to be manufactured by traditional assembly
methods or insert molded. But greater benefits are
usually derived when the inserts are specifically
designed to be overmolded. For example, a single
stamped insert, that is overmolded and then perforated can provide all of the circuit paths required in
a component, eliminating the need for numerous
wires and terminations.
Specifying plastics. The plastics used in an insert
molded component give design engineers the opportunity to meet a wide range of mechanical, environmental and dielectric requirements. Mechanical
characteristics include tensile and compressive
strength, flexural modulus, impact resistance and
hardness. Environmental considerations include heat
resistance, chemical resistance and U. V. stability.
A wide range of engineered thermoplastics are
available to meet virtually any application.
Process considerations
Locating the inserts. One unique requirement of
the insert molding process is the need to support
the inserts while injecting the thermoplastic.
Determining where the inserts and support pins
should be located, so as to minimize insert movement under pressure, is an important decision
affecting both component and tooling design. One
consideration is the injection of plastic in a profiled
manner—minimizing movement by leaving an open
area around an insert that eventually fills in as more
plastic comes in. Gate design and gate location (where
molten plastic enters the mold) is another factor in minimizing insert movement. Finally, injection molding typically occurs at lower pressures (700 to 1500 gauge psi)
than does conventional injection molding.
Maximizing the benefits
Extending functions. One way to get more out of
insert molding is by adding or modifying inserts to
extend the functionality of a component. For example, bushings can be inserted into a component to
provide a secure mounting method. Or a currentcarrying stamping can be extended to provide circuit and interconnect in a single part. Extending the
functions of an insert molded component to include
mounting and interconnection reduces assembly
and labor costs.
Enhancing material performance. The interplay of
insert parts and plastics provided by insert molding
can enhance material performance beyond what
can be economically achieved with either material
alone. Combining the physical strength of resins and
metal inserts can allow for a reduction in the size
and weight of a component. In other applications,
environmentally sensitive metal or electronic parts
can be protected against corrosion, vibration and
shock by being encapsulated in chemical-resistant
and impact-resistant plastic. Insert molding can also
be used to secure terminations. These capabilities
all result in increased component reliability.
Designing in three dimensions. Traditional manufacturing and assembly techniques often lead a design
engineer to conceptualize a component as a series
of flat planes that are then stacked or joined at
angles to provide the finished product. Insert molding provides an opportunity to design in three
dimensions. Circuitry can move freely through the
part, from inside to outside, up walls, down in
holes, and the plastic ties it all together. This allows
virtually unlimited design configurations and
increases design flexibility.
Making the Decision
s we have seen, many multi-part components,
especially those requiring extensive assembly,
may be candidates for insert molding. In most cases,
insert molding will reduce or eliminate many
assembly steps and secondary processes.
A
systems to ensure no project elements and steps
are overlooked?
Materials. Can the supplier offer a full array of materials including high end engineering grades? Do they
offer materials assistance and recommendations?
Assessing potential suppliers
Once you have decided upon the insert molding
process for your component, it is important to select
the right manufacturer to meet your requirements.
Following are some qualities to consider:
Mike Roberts, president and co-founder of
Microplastics, Inc., has been involved in the design
and production of insert molded components for
more than 20 years.
Engineering and tooling capabilities. Does the
potential supplier provide in-house engineering and
tooling services? Can they recommend cost-effective
solutions for component optimization? Do they use
3-D and CAD tools to facilitate designs? Are molds
guaranteed and maintained by the supplier?
About Microplastics
Molding and assembly. Does the supplier have the
capability to produce complex components in high
volume? Do they utilize robotic and manual insert
molding resources? Ask for an equipment list and be
assured that they have state-of-the-art press equipment.
Is the supplier able to meet assembly process
requirements like microsoldering, adhesives application, and forming? Do they provide secondary
processes like curing and part serialization?
Quality and testing. Is the supplier ISO/QS 9000
certified? Do they have an accredited quality laboratory? Do they use Advanced Quality Planning
(AQP) or other quality tools? Are they committed
to zero ppm defects? Do they offer 100% product
testing?
Prototyping. Does the supplier develop prototypes
utilizing the same material that will be used for full
production?
Microplastics has been a world class insert molding
manufacturer since 1989. We are committed to
producing high volume, highly engineered electromechanical interconnections and components in the
most efficient and reliable way possible.
Serving automotive, computer, appliance, telecommunications, medical, and electronics customers,
Microplastics offers a wealth of applications experience. Switches, relays, lighting components, connectors, timers, sensors, filters, and disk and tape
drive components are among the many products
we have manufactured in our dedicated insert
molding facility.
Microplastics controls the entire process, from
engineering and tooling to molding and assembly,
under one roof. Our quality system is ISO/QS 9000
certified, our quality lab is accredited by General
Motors, and we work with our customers to achieve
zero defects.
For more information on insert molding, or to
discuss your component requirements, contact
Microplastics today.
Project support. Does the supplier offer a methodology for taking your project from conception through
testing? Are you assigned a dedicated team to
facilitate projects? Do they use computer-networked
Microplastics
Insert Molding Engineered for Quality
406 38 th Avenue
St. Charles, IL 60174
Phone: (630) 513-2900
Fax: (630) 513-2901
www.microplasticsinc.com
Copyright Microplastics, Inc. 2001