SAMPE Journal - November/December 2021 - 28

FEATURE / LASER-SINTERING PROCESS
Figure 2. Selected concept and process flow for fibre integration in the
CFRP sintering process.
insertion was investigated to draw conclusions
for the automatability of the process. Based on
the findings in12
integration were developed in13,14
concept is shown below.
, two concepts for automated fibre
. The selected
Concept of Integration Continuous Fibres
The concept of integration can be seen in Figure 214
the curvature K
of the front surface of the nozzle, the
surface condition e as well as the nozzle distance dD
have an influence on the shape of the HAZ (width
wHAZ
and depth dHAZ
). Furthermore, the adjustable
process parameters such as the temperature of the
nozzle TD
and the feed rate vD
.
In the first step (Figure 2 left), the applied powder
layer is sintered. In the second step (center), a
roving is integrated into the already sintered layer.
Due to heat transfer between the heated nozzle
(distance dD
) and the surface of the sintered part, a
heat-affected zone (HAZ) is created in the sintered
layers. Simultaneously with the melting process,
the roving is placed in the generated melt by a drive
system synchronously with the feed movement of
the nozzle (vD
). The melt wets the roving and fixes
it in the underlying sinter layers. The roving is cut
to the set length with the help of a cutting blade. In
step 3 (Figure 3 right), fresh powder (hP
) is applied
by the recoater blade and the new powder layer is
sintered, thus completely embedding the roving in
the matrix.
Figure 3, which schematically illustrates the
process zone during fibre integration (left) and
during the application of fresh powder (right),
will be used to clarify the prevailing influencing
variables. The process zone (left) consists of a
heated fibre nozzle and the underlying component.
The nozzle parameters which are responsible for
the heat transport, here the radiation surface AD
,
have an influence
on the HAZ. The special importance of the HAZ is
shown in Figure 3 (right). If the HAZ is too small
(depth and width), the roving will not be placed
deep enough in the part. A collision between the
recoater blade and the roving occurs when fresh
powder is applied. This leads to an entrainment
effect of the part and the manufacturing process
has to be interrupted. For successful fibre
integration, the HAZ must therefore be created
in such a way that the roving can fully penetrate
the part. The width wHAZ
of the HAZ should also
be larger than the cross-section of the roving, so
that it can be completely absorbed in the melted
area. In order to obtain an initial indication of
an optimum operating point, the nozzle-related
influencing parameters such as the geometry and
surface as well as the system parameters to be
set must be investigated in greater detail. Due to
the parallel construction of the developed laser
sintering system, the process zone was simulated
in a simplified test setup (test series 1) in order to
perform an influence analysis for the HAZ. The
influence analysis on this simplified test setup
serves to narrow down the parameter space and
to identify an initial operating point for successful
fibre integration.
Figure 3. Process zone during fibre integration (left) and during powder application (right).
28 | SAMPE JOURNAL | NOVEMBER/DECEMBER 2021
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