What is insert molding?
Typically insert molding, or overmolding, requires
accurately placing part(s) made from metal or
other suitable materials (referred to as the insert)
into the mold, closing the mold and then injecting
the plastic into and/or around the insert(s).
A typical application would be electrical connectors
that incorporate machined metallic pins or sockets
into a molded plastic housing. Most insert
moldings utilize metal parts, including handles,
threaded inserts or electrical contacts. At
Rebling Plastics, insert molding can be done with
any of our molding processes, including thermoplastic
injection molding and thermoset
molding. Rebling Plastics uses both vertical
clamp and shuttle type plastic injection molding
presses for insert molding applications and has
experience overmolding circuit boards, wires and
harness assemblies, as well as connectors.
Plastics materials insert molded at Rebling Plastics
such as epoxy, phenolic
and DAP and thermoplastics
such as nylon, acetal
, PBT, polycarbonate,
Polyphenylene oxide, Polyphenylene
sulfide and others.
We also specialize in wire
overmolding, where we have molded plugs and
strain reliefs over bare and insulated wire of
Special design considerations
for insert molding
The design of both the insert and the end product
are critical for successful insert molding. At
Rebling Plastics, we have several engineers
on staff to help our customers with product design
and material selection. For example, the suitability
of non-metallic parts for overmolding must be
evaluated from a temperature and stress standpoint.
A solder joint using standard 60/40 Tin/Lead may
not be able to withstand the high mold temperature
needed for processing a thermoset or high temperature
thermoplastic injection molding material.
Since the part will be subjected to high pressure
caused by the flow of plastic material in the
cavity, it is important that the insert be restrained
from movement. Rebling Plastics has implemented
several innovative mold designs to accomplish
Undercuts, thru holes, and knurling on the insert
are common ways to rigidly secure the insert in
plastic. However, it is important to avoid sharp
corners on the inserts when molding with notch-sensitive
plastic materials such as acrylic.
For thermoplastic injection molding, the plastic
part must be designed with a uniform wall thickness
to avoid sinking and warping. It is important
to balance the wall thickness with the adhesion
of the plastic to the insert.
Mold design is particularly important for this type of molding. All of the toolmakers used by Rebling Plastics have extensive experience designing tools for insert molding. Whenever possible, we mistake-proof the insert and mold designs to prevent press operators from incorrectly installing parts in the mold. Our mold designers take into account the maximum material conditions of the insert on one hand and still insure a flash-free molding when inserts are received at less than the maximum material condition. Frequently, Rebling Plastics uses its molding experience and expertise to make recommendations and incorporate them into the product design.
In some cases, the tooling and labor cost associated
with insert molding may not be as efficient as assembling
the insert as a secondary operation. Rebling Plastics
also offers ultrasonic
assembly as a cost saving alternative.