JEC COMPOSITES MAGAZINE - Issue #101 - November/December 2015 - 41

Fig. 3: Simulation test-bed setup for the continuous induction welding of two materials and their corresponding physics interactions developed at the Institut für Verbundwerkstoffe GmbH

process speed all affect one another mutually. In addition, the welding process is influenced by the design of the induction coil and the
laminate structure which is determined according to its application.

Advance through process simulation
Due to this host of crucial parameters, a huge amount of experimental investigations is needed to identify the suitable parameters for an
efficient process. Therefore, two approaches were taken to simulate
the process. The first approach considers highly detailed modelling of
the process in order to understand the nature of the physics involved,
while the second aims at developing a simplified simulation tool that
is easy to handle for end-users.
To capture and study in detail the most important physical phenomena encountered during the process, a multiphysics finite element
(FE) code was used for the first approach. The 3D-FE modelling
approach sets the stage for more complex investigations (as shown
in Figure 3) using moving coil cases where the steady-state temperature patterns are different to that of a static case and are far more

Fig. 4: Full weld width surface temperature plots for the top surface without (a)
and with (b) air jet cooling and for the joint interface surface without (c) and with
(d) air jet cooling, welding speed 0.18 m/min, fixed coil coupling distance 2 mm,
coil to roller offset distance 60 mm, and volume flow of air jet cooling 304 litres/
min (based on data from Rudolf [4] and Moser [2])

difficult to predict and measure experimentally. Using this process
simulation tool, the effects of the consolidation roller as well as an
impinging air jet were incorporated in order to show the effect on the
temperature developed on the top surface of the laminate stack with
and without surface cooling. Fig. 4 a) and b) illustrate the impact of
the modification as simulated by Duhovic et al. [3], where the only
difference in parameters is the application of an air jet with a flow
rate of 304 l/min. As can be seen, the top surface temperature can be
significantly decreased. A different but also advantageous effect of the
top surface cooling can also be visualized for the joint interface (Fig.
4 c) and d)), whereby a steeper temperature drop over a short time
period can be achieved.

Process simplification for the end-user
In order to ensure a constant joining quality, the power input from
the generator has to be governed according to an implemented
control signal. Since the temperature in the joining area cannot be
measured from the outside, the laminate surface temperature has to
be used as the control signal. A second simulation approach using
a simplified 3D-FE model dataset yields the temperature in the
joining zone referring to the control signal. To gain reliable process
conditions and to get a fast feedback of the control signal, the control
temperature is defined as the average temperature within the surface
area between 0 mm and 10 mm directly after the coil.
Furthermore, process diagrams were calculated by means of the
thermal 3D-FE simulation model of the second approach in order to
optimize bonding quality (Fig. 5). The process diagram shows the

Fig. 5: Process diagram for a coil-roller distance of 35 mm

No101 November - December 2015 /

jec composites magazine 41

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #101 - November/December 2015