Induction Brazing
Inductive heating
Induction brazing uses inductive heating to bring having to heat the whole assembly. This can be espe-
the components up to the brazing temperature in a cially favorable for large components with only a few
controlled manner. In induction heating processes, braze joints, where in many cases induction brazing can
eddy currents are induced in metallic materials when have a cost advantage over continuous belt furnace
they are exposed to the alternating electromagnetic brazing. As the process is quick, and introduces heat
field of a coil (inductor). locally in the area to be brazed, negative effects on the
base materials such as sensitization and grain growth
Due to the electrical resistivity of the metal, these
can be minimized. With suitable control systems in
currents generate precise and localized heat without
place, the induction brazing process has a very good
any direct contact between the part and the coil. The
repeatability, enabling high production rates and consis-
heating effect is largest on the surface of the compo-
tently good product quality. Turnkey induction brazing
nent being heated, called the skin effect. The depth of
solutions are available from the equipment suppliers.
penetration of the induction heating is a function of the
base material and induction frequency. For most induc- Induction brazing is a commonly used brazing techni-
tion brazing processes equipment operating at medium que in industries such as the tool industry and the
range frequencies (1 to 50 kHz) are used. High frequen- automotive industry. For example, automotive fuel rails
cy range (50 to 400 kHz) equipment is typically used for are often brazed by induction brazing. Normally the
small parts or very small brazing areas. The equipment brazing filler metal is applied as preforms, but for some
controls automatically adjust the frequency to give the applications it might be favorable to use brazing paste.
most optimal heating. However, for successful induction brazing using brazing
paste, some changes are required compared to when
Brazing process brazing with preforms.
Induction brazing enables the brazing process to be
performed very quickly compared to other heating met-
hods. Induction heating enables a heat input up
to 30.000 W/cm2, compared to around 1.000 W/cm2
for torch brazing. Heat is applied locally, which avoids
Considerations for induction brazing
with brazing paste
• Close temperature control is required to control the
binder burn-off stage. This is normally controlled by
including an additional, low-temperature pyrometer.
With too fast heating in this temperature range,
excessive outgassing can cause the paste to blow
off the joint. The brazing paste can ideally be placed
Figure 1: inside the component for more controlled drying and
Schematic induction brazing profile with brazing paste binder burn-off, due to heat convection through the
base material.
• A protective atmosphere such as N2, H2 or vacuum
is recommended to prevent oxidation of the base
material and filler material during brazing.
• Selection of a brazing paste with proven performance
for induction brazing is required, as not all brazing
pastes will give good results with induction brazing.
Höganäs have brazing pastes in the BrazeLet®
product range that have proven to give good results
and little or no residues during induction brazing.
Induction brazing profile
Figure 2: The main difference between the brazing profile when
Schematic furnace brazing profile with brazing paste doing induction brazing and conventional furnace
brazing is the brazing cycle time. While furnace brazing
cycles take hours, the induction brazing cycle can be
completed within seconds or a few minutes depending
on the component. For induction brazing with paste,
a controlled drying and binder evaporation stage
with lower heating rate is required to avoid excessive
outgassing. For induction brazing with solid filler metal
preforms, this is not required and the assembly can be
2312HOG
heated directly up to the brazing temperature.
© Höganäs AB (publ.), August 2018.
Figure 3:
Schematic furnace brazing profile with brazing
filler metal preforms
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