JEC COMPOSITES MAGAZINE - Issue #103 - March 2016 - 73

Tab. 3: Parameters of the laser joining process

GF/PA6 + aluminium
Sand blasted and SB+LST

Fig. 4: Induction joining machine equipped with a roller for continuous joining

to heat a metal part (e. g. steel or aluminium), which then melts the
polymer of the adjacent TP-FRPC by heat conduction. Induction
heating can be used for discontinuous and continuous joining processes. Discontinuous joining requires a stamp that applies pressure
after and/or during heating, while continuous joining uses a roller
that follows the coil along a joining seam. The set-up currently used at
IVW is shown in figure 4.
With the material combinations considered in this study, both
continuous and discontinuous joining is possible. For continuous
joining, process speeds of up to 1 m/min can be reached and a discontinuous joint can be manufactured in approximately 30 seconds,
depending on its size. All the specimens were manufactured using a
discontinuous joining process because it ensures stable and benign
process conditions. The process parameters are listed in table 2.
Laser joining (LJ) usually uses a coherent (single phase) light of a
single wavelength (monochromatic) with a low beam divergence and
high energy content that quickly heats up the irradiated surface. Like
in IJ, the beam is applied directly to the metal specimen, which melts
the polymer that is in close contact with the metal by heat conduction. To optimize the heat distribution and the joint, the shape and
size of the laser beam can be adapted using different optics (spot
shape, line, area...) and quasi-simultaneous joining can even be
achieved with the help of a scanner head. The process parameters are
listed in table 3.
The laser joining set-up currently used at Tecnalia is shown in figure 5.
Tab. 2: Parameters of the induction joining process

GF/PA6 + steel

GF/PP + steel

Sand
blasted

Laser
structure

Sand
blasted

Laser
structure

Generator power [%]

Heating time [s]

Consolidation pressure
[MPa]

0.32

0.96

0.32

0.96

Consolidation time [s]

Coupling distance [mm]

Power [%]

Close loop temperature control

Temperature set point [°C]

420

Joining time [s]

Consolidation pressure [MPa]

0.94

Spot diameter [mm]

It includes closedloop temperature
and pressure
controls to ensure
the quality and
repeatability of the
joint. The joint for
a flat specimen can
be produced in six
seconds.

Fig. 5: Laser joining machine

Performance
The influence of a surface structure on the joint strength was verified
by lap shear tests according to the EN 1465 standard (specimen
width: 25 mm, length of each joining partner: 100 mm, overlap: 12.5
mm). The results obtained with IJ are shown in figure 6. The joint
strength of the laser-structured specimens is compared with a SB reference. In the case of GF/PA6, specimens with a degreased (acetone)
surface were also manufactured. However, this was not possible with
GF/PP due to PP's low surface energy. Figure 6 shows that the lap
shear strength of GF/PA6 and steel can be increased by 20% compared with the SB specimen. The influence on the joint strength of
GF/PP and steel is even more impressive since it can be improved by
176%. The results obtained with LJ on GF/PA6 and aluminium are
shown in figure 7. In this case, the lap shear strength can be increased
by more than 50%.
As explained before, other surface texturing methods did show the
same favourable results. However, it is certain that a textured surface
is required to obtain promising results by IJ and LJ, and the selection
of the suitable surface texturing method mainly depends on the part
requirements (performance, cost, productivity, flexibility...).

Conclusion
IJ and LJ have proved their potential for the manufacture of hybrid
components consisting of composites and metals. Both technologies also perfectly complement each other. While IJ is capable of
manufacturing large areas in a cost-effective way due to its efficiency
and the simplicity of the required equipment, LJ can be patterned
spatially with good resolution and is able to access extremely complex
and tiny areas with great accuracy at high speeds. These technologies also complement each other regarding the metal material: IJ
showed better results on steel specimens while LJ is more advisable
No103 March 2016 /

jec composites magazine 73

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #103 - March 2016