Read an informative article on using induction heating for heat staking metal inserts. The article was written by Dr. Girish Dahake, Senior Vice President of Global Applications for Ambrell Precision Induction Heating.

1. he development of glass-filled
plastic materials is undeni-
ably the major cause for this
increase. Manufacturing and
other related processes must differ from
conventional lower-temperature thermo-
plastic manufacturing methods due to
higher melting temperatures.
In addition to the glass-filled plastics,
there are many other components that use
regular thermoplastics. Thermoplastics
are still too soft to sufficiently hold a
thread, so brass- or steel-threaded inserts
are commonly used as anchors. Post-
molded installation is more cost effective
than molding in place, and induction is a
proven way to preheat these inserts prior
to installation.
For heat staking, the insert is preheated
withinductionandthenpressedintoahole
in the plastic part. This is accomplished
by positioning the induction coil over the
hole and then holding the insert in the
coil for a short period of time. When the
correct temperature is achieved, the insert
is pressed into the plastic (Fig. 1). A narrow
zone of plastic then melts and flows into
the knurls of the insert. The plastic re-
solidifies, resulting in a complete assembly
that often has much better mechanical
properties than inserts implanted with
other techniques.
The insert material is usually brass or
steel; each has advantages and disadvan-
tages. Brass is non-magnetic and will not
corrode as easily as steel. However, brass is
a softer material and will anneal at tem-
peratures as low as 450˚F (232˚C). Steel
starts to anneal at 1200˚F (650˚C). Glass-
filled plastics require inserts to be heated
to 700˚F (371˚C) for correct installation,
so the brass inserts must be heated and
inserted quickly to prevent thread an-
nealing. Brass has lower electrical resis-
tivity than steel and, therefore, requires
more power to heat with induction. The
selection of the insert material is depen-
dent on the specific application require-
ments, but brass is most commonly used
in the industry.
Induction Heating
A basic induction heating setup is shown
in Fig 2. It consists of a high-frequency
power supply that takes the input from
the AC line mains. This power-supply
unit converts regular line frequency (50
or 60 Hertz) to a high-frequency signal,
which operates between 10 and 400 kHz.
This high-oscillating signal is then fed
to a tank circuit that feeds the water-
cooled induction heating coil. The signal
generates a high-frequency magnetic field
Heat Staking Metal
Inserts by Induction
Girish Dahake – Ambrell, an Ameritherm Co.; Scottsville, N.Y.
Injection-molded plastic parts are used increasingly in industry,
particularly automotive, because of their strength and reduced weight
when compared to metal.
Fig.5. Four-position insert heating coil
h
p
TT
Fig.1. Typical heat insertion process Fig.2. Basic induction heating system
Feedback control system
Coil
connection
Coil
Part
Fixture
Water
Air-operated
cylinders Coil
Insert
Insert
Plastic part
Non-magnetic
stainless-steel push rods AC line
Tank
circuit
Power
supply
Smaller sources of variation Larger sources of variation
Featured in Industrial Heating May 2014

2. FEATURE | Induction
Heating
inside the induction coil. The insert is
placed inside this induction heating
coil. It generates eddy currents due to
the high-frequency magnetic field and
produces heat. An optional noncontact
temperature controller can be used to
measure the temperature of the insert. Its
output can then be fed to the induction
heating power supply to control the
temperature of the insert for each cycle.
Here are the critical parameters for a
consistent induction insertion process.
• Tuning frequency: The frequency of
operation of the power supply should
be chosen to deliver efficient energy
based on the size and material of the
part. Care must be taken to ensure that
this frequency is above the critical fre-
quency of the part for efficient heating.
• Repeatability of the induction power
supply: This is the cycle-to-cycle
repeatability of the induction power
supply in manufacturing given standard
incoming voltage variations and other
tolerances.
• Heat-on time: This should be the
same every cycle to reach the same
temperature on the insert.
• Positioning of the insert in the coil:
This is dependent on the fixturing
and handling device. Varying
placement of the insert inside the
induction coil will result in inconsistent
temperatures of the insert.
• Insertion pressure: The location of
the insert in the hole of the plastic
part is determined by insert pressure.
Lower pressure leaves the insert
above the required location, whereas
higher insertion pressure may cause
undesirable “flash” of the plastic
material.
• Fit of the insert in the thermoplastic
material: The diameter of the insert
hole must be the correct size to allow
the plastic to flow around the insert. If
the hole is too small, extra plastic will
be displaced.
• Cool-down time: Cool down following
the insertion cycle is needed to anchor
the insert inside the plastic part. If the
cool-down time is too short and the
insertion pressure is removed quickly,
inserts will often be pushed out of the
plastic part.
• Insert temperature: The installation
temperature of the insert is a key factor
in the success of the staking process.
Each insert must be heated to the
same temperature in the same time to
achieve a consistent process.
Single-Position vs. Multiple-
Position Coil
The simplest system consists of a single-
Non-magnetic
stainless steel pushrod
Air-operated
non-magnetic steel
push rod
Computer-
controlled "X"
and "Y" table
Remote
heat station
with coil
Plastic
Part
X Y
Remote
heat
station
3-position
multiturn coil
Steel inserts
Induction Heating Benefits/Advantages
Unsurpassed reliability: 100% solid-state RF power and control circuitry.
Process repeatability: With advanced microprocessor control, power supplies are
extremely accurate and repeatable.
Maximum deliverable power: High-frequency range and continuous auto tuning of
the power supplies track the resonant frequency of the system to continuously deliver
power at resonance.
Convenient coil placement: Remote heat stations can be located on the production
line, up to 200 feet from the power supply (application-dependent).
Easy system integration: Quick and easy integration manufacturing control with
PLC and analog inputs.
Fig.3. Single-position heating system Fig.4. Multiple-position heating system

3. position heating coil to heat one insert at a
time. Depending on the number of inserts
in the plastic part, either the plastic part
can be indexed under the induction coil or
the heating head can be moved to each in-
sert location. An x-y positioning table can
be used in conjunction with a single-posi-
tion coil when multiple inserts need to be
installed in a single molded part. The posi-
tion of the coil is held constant, and the
x-y table moves each insert location under
or above the coil. This technique provides
for a flexible manufacturing tool that can
be changed by software programming
rather than hardware tooling changes.
A second option for a single-position
coil is the use of a robotic arm. The plas-
tic part is held in a fixed location while
the coil and indexing mechanism can be
moved to each insert location. Location
of the coil relative to the heat station is
custom-designed for each application
(Fig. 3).
A multiple-position coil makes it
possible to install more than one insert
at a time into a single plastic part (Fig.
4). Three- and four-position coils have
been used for this application. The coil
is normally in a fixed position, and the
plastic part is placed under the coil.
The inserts for each location are heated
simultaneously and then pressed into the
plastic. The multi-position coil requires a
higher power than a single-position coil.
However, the production cycle time is
significantly shorter.
Case Study
A four-position induction heating coil
(Fig. 5 - intro) is used to heat four brass
inserts of 8 mm diameter to 550˚F (290˚C)
using the Ambrell EasyHeat 7590, a 7.5-
kW induction heating power supply. The
inserts are heated to temperature within
four seconds before they are pushed into
the plastic part. The induction coil is
designed to allow for adjustment of each
heating location so as to heat the four
inserts to exactly the same temperature.
The temperature variation between the
four positions of the induction coil, once
adjusted, is locked to ensure good product.
Figure 6 shows the thermal image of the
four inserts at the end of the heating cycle.
Conclusion
Whether applied directly in an initial
design or incorporated into an existing
process or industrial heating operation,
induction heating has become more
and more desirable because of its ability
to contribute to lean-manufacturing
setups. It is easy to justify a good value
proposition for the induction heating
setup. Its flexibility, small size, versatility
and efficiency represent an indispensable
adjunct for a number of process heating
applications in manufacturing processes
worldwide. IH
For more information: Dr. Girish Dahake,
Ph.D.,istheVP,GlobalApplicationsforAmbrell
Inc., an Ameritherm Co., 39 Main Street,
Scottsville, NY 14546; tel: 585-889-9000 (X
121); fax: 585-889-4030; e-mail: gdahake@
ambrell.com; web: www.ameritherm.com
Fig.6. Thermal image of the four inserts at the end of the heating cycle

4. staking.ambrell.com
411-0170-00 Rev A
Ambrell Power Supplies
Ambrell manufactures a wide range of power supplies,
both low and high power for an array of applications. For
heat staking, the EASYHEAT (1-10 kW) and the low
power end of the EKOHEAT (10-15 kW) product lines
are most popular.
Ambrell power supplies have movable workheads so the
coil can be placed a distance from the power supply, a
high power factor to ensure efficient heating, significant
versatility with multiple capacitor and tap configurations,
and repeatable, reliable heating with agile frequency
tuning. Additionally, systems are compact and easy-to-
integrate into manufacturing processes.
Systems are manufactured at Ambrell’s ISO 9001:2008
certified facility at its headquarters in Scottsville, NY
USA.
Complimentary Applications Testing
You can send parts to Ambrell’s Applications Laboratory
for a free half-day of testing. Testing is recorded and parts
are sent back to you for inspection. Additionally, you
are welcome to visit during testing to see induction heat
staking live.
After testing, you will receive a tailored system
recommendation. The recommendation will be based on
your process requirements, including process time, cycle
time and temperature.
Heat staking is a common application at Ambrell. So take
advantage of that expertise and send in your parts for risk-
free applications testing today.
As a pioneer in solid-state induction heating technology,
with over 25-years of innovation, Ambrell provides industry-
leading heating solutions. We pride ourselves in making it
easy for you to implement an efficient, safe, rapid induction
heating process by applying our knowledge of the science
and art of induction to your heating application. Ambrell
is headquartered in the United States with worldwide
operations including Ambrell Ltd. in the United Kingdom,
Ambrell SARL in France and Ambrell B.V. in the
Netherlands.
About Ambrell
Ambrell Corporate
39 Main Street
Scottsville, NY 14546
tel: +1 585 889 9000
fax: +1 585 889 4030
sales@ambrell.com
Ambrell B. V.
Holtersweg 1
7556 BS Hengelo
The Netherlands
Tel: +31 (0)880 150 100
Fax: +31 (0)548 659 010
saleseu@ambrell.com
Ambrell, Ltd.
Phoenix Works, Saxon Way
Battledown Industrial Estate
Cheltenham, Gloucestershire
GL52 6RU
tel: +44 (0)1242 514042
fax: +44 (0)1242 224146
salesuk@ambrell.com
Ambrell SARL
Tour Sébastopol
3 quai Kléber
67000 Strasbourg
France
Tel: +33 970 440 335
Fax: +33 38 9748533
saleseu@ambrell.com