| Threaded Insert Installation Methods |
Insert
Molding: Molding a threaded insert into a plastic
assembly increases the total molding time because extra
time is
needed to
load the insert. Molded-in inserts may also cause sink
marks. They are widely used with thermoset (non-meltable)
plastics.
|
| Post-molded: Post-molded
inserts eliminate the downtime associated with
molding a thread or an insert into a plastic part, such
as die
damage caused by improper placement. Advantages include
faster assembly, reduced open press time and no sink marks. |
| Ultrasonic: The
most common method for installing threaded inserts into
thermoplastic materials, ultrasonic installation provides
fast, positive anchoring. An insert
is placed in a molded or drilled hole which guides it and
provides resistance. An ultrasonic horn contacts the insert
and delivers ultrasonic vibrations which travel through
the insert during the "weld cycle." Frictional
heat is immediately developed which melts the plastic as
the horn drives the insert into position. After the vibrations
cease, the equipment applies clamp pressure until the plastic
cools, preventing back-out. |
Thermal: During
thermal/heat insertion, the threaded insert is placed
into a molded or drilled hole. Pressure is applied with
a
heated
probe
that contacts the top surface and minor thread diameter
of the insert. Localized melting takes place, and plastic
flows in and around the knurls and serrations. When the
proper depth is reached, the probe is removed and the
plastic re-solidifies, locking the insert in place. Upon
removal of the probe, a minimal amount of withdrawal
(back-out) of the insert may occur. Thermal/heat insertion
provides a good alternative to the ultrasonic method,
but it is a slower process. Some benefits include:
• Multiple
inserts can be installed simultaneously, even on different
levels
• Quiet when compared to ultrasonic
• Thermal equipment is less expensive than ultrasonic equipment
• Excellent for larger inserts |
| Cold
Insertion: Some inserts can simply be pressed
in after molding. However, pressing inserts into cold
plastic may create unwanted stress. A larger boss (or
wall thickness) is required to prevent stress fracture.
Pull, torque and jack-out strengths are significantly
lower compared to thermal or ultrasonic installation. |
| Variables to consider |
| Lubricants,
Fillers or Glass in the Plastic: If the plastic's
filler or glass content exceeds 40%, assembly or performance
problems may result. |
| Molded
Versus Drilled Holes: Molded holes provide better
performance than drilled holes because a strong skin
of denser material is formed around them during molding.
This is particularly true with structural foam plastics
which are porous under the skin. |
| Plating
and Color-coding: We offer a full range of plating
and/or color-coding services. The most common metal finishes
include nickel, tin and zinc. Inserts of similar size
and configuration are often color-coded to prevent inadvertent
mixing (inch threads vs. metric threads). |
