SAMPE Journal - January/February 2017 - 42

Feature Article
P. Mitschang, D. Maurer
Institut für Verbundwerkstoffe GmbH (IVW), Kaiserslautern, Germany

Quality Controlled Induction Welding by
Adapted Process Parameters
Abstract

In this paper the continuous induction welding of carbon textile reinforced thermoplastics is introduced and investigated
regarding optimized process parameters and quality control. The resulting overall bonding quality of welded joints shows the
capability to replace other mechanical joining methods like bolts. Therefore, the process has a high potential for the aerospace as
well as the automotive industry. During induction welding, the heating of the material is generated by induced eddy currents
and joule losses. Due to their electrical conductivity, carbon fiber reinforced thermoplastic composites can be inherently heated.
To prevent delamination (void growth) of the laminate, the part surface is cooled by an air jet. To implement a quality controlled,
automated welding process the surface temperature is monitored and a thermal simulation is used to calculate the temperature
in the joining area. The thermal simulation model is explained and process diagrams are calculated. These process diagrams can
easily be changed by a user interface. For different welding speeds, optimum coil settings are found to gain bonding strength
at autoclave quality with high welding speed and reproducibility. Overlap specimens were produced and tested to verify the
simulated optimum parameters and to show the capability of the quality control concept.
Introduction
The continuous induction welding
process consists of three steps
(Figure 1). First, the joining area of
two thermoplastic partners is heated
until the polymer melts. Second,
the joining area is consolidated
by cooling the joining area below
solidification temperature. To get
an excellent bonding this cooling
has to be supported by joining
pressure (roller). In the third step the
adherends are cooled down to room
temperature by the surrounding.

Because the heating of the
joining partners is generated by
induction, the laminate is inherently
heated. But due to the magnetic
field intensity the part surface
which is closest to the coil has the
highest energy absorption and the
highest temperature. To hinder the
delamination or degradation of the
surface, an active surface cooling by
an air jet is used1.
Figure 1 shows the temperature
development of the laminate surface
and the joining area as a function

of time. First, joining area is heated
above melting temperature and
below degradation temperature
while the surface temperature stays
below the melting temperature of
the laminate. Then, after leaving
the
consolidation
roller,
the
laminates temperature is below the
solidification temperature and a
successful welding is reached. The
most significant process parameters
are the generator power, coupling
distance between coil and laminate
surface, the distance between coil

Figure 1. Schemata of the continuous induction welding and temperature development in the joining zone and at the laminate
surface.
42

SAMPE Journal, Volume 53, No. 1, January/February 2017

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