SAMPE Journal - March/April 2021 - 43

Experimental Set-up and Process Parameters
for Composite Manufacturing
For composite manufacturing the High Pressure
- Resin Transfer Molding (HP-RTM) and the Wet
Compression Molding (WCM) process were used.
Both process routes are state of the art and can
be reviewed in publications10,11. Figure 2 a) shows
the used HP-RTM and WCM trial configuration at
Fraunhofer ICT.
The experimental set-up consists of an injection
machine, a hydraulic press as well as a compatible
mold. In the HP-RTM process, the mixing head is
installed in the mold. The HP-RTM machine circulates resin and hardener separated from each other
continuously from the storage tank to the mixing
head and back to the tank. During the injection
step, the mixing head opens whereupon resin and
hardener are mixed by the kinetic energy released
in the mixing chamber in the so called counter-flow
process. During injection the third component, the
internal mold release agent, is dosed to the resin at
the mixing head. The IMR allows an easy demolding of the cured component. For HP-RTM, a central line injection gate was used, which allows the
resin to impregnate the fibers with a uniform flow
front from the middle to the outer cavity (one-dimensional resin flow as seen in Figure 2 b)). The
modified experimental set-up for the WCM-trials
is seen in the right top corner of Figure 2 a). Since
the resin application is carried out outside of the
press, a slot die was mounted to the mixing head
to achieve a superficial resin application of the
stacked layers. The wetted stack is then transported into the mold by a gripper mounted on a robot.
The same mold was used for both process routes.
Figure 2 b) shows the top view on the lower mold
side. A-A shows the section from the mixing head to
the molds outer side showing the clamping, sealing
and vacuum concept of the mold (Figure 2 c)). In
addition, the functions of the mixing head in the
open and closed state can be seen. To avoid fiber

displacement due to the high injection pressure,
the fibers are clamped at the cavity edges using an
elastomer seal. The outer O-ring with a diameter of
8 mm seals the mold during injection and curing to
keep a constant pressure in the mold. The vacuum
sealing allows the evacuation of the cavity at mold
gaps of up to 6 mm. To measure the fluid pressure
inside the cavity three piezoelectric pressure sensors from Kistler, type 6167A were used. The sensor
positions are shown in Figure 2 b).
Table 2 shows the process parameters used in
this study. Due to a low amount of non-wovens
of type K1 and K6, the optimization and variation
of process parameters was conducted using the
type K4. Three flow rates and four different press
forces during the injection and curing steps were
investigated. The process parameters using the
WCM-Process were kept constant for all non-woven types. A quick curing epoxy resin system from
DOW with the trade name Voraforce 5300 was used
for all trials.
RESULTS
The results of the process characterization and the
mechanical testing of the manufactured composites are described in this section.
HP-RTM Processing
Figure 3 (a) shows the HP-RTM process steps (process start, vacuum, injection, curing, process end)
of the manufactured laminates with type K4. The
vacuum step was set to 60 s at a mold gap of 4 mm.
Due to the low stack compaction at 4 mm mold gap
during vacuum absolute cavity pressures of ≤ 100
mBar are achieved.
The vacuum gap is then closed and a predefined press force is applied. The injection starts
two seconds after reaching the preset press force.
Resin, hardener and IMR are mixed and injected
into the cavity at a predefined injection rate (Table
2). During the injection, the cavity pressure rises as

Table 2. Process parameters for composite manufacturing.
Process

HP-RTM

Material

Flow rate m

Closing speed
(6 to 0 mm)

Press force

Vacuum time

[g/s]

[mm/s]

[kN]

[s]

40, 60, 80

2000, 3000,
4000, 5000

HP-RTM

K1, K6

5000

WCM

K1,K4,K6

0,5

10 s from 0
to 3000

Constant process parameters: Cure time 120 [s], Resin System: Dow Voraforce 5300,
Mixing ratio: (Resin: Hardener: Internal Release Agent) 100:16.2:2 [weight-%], Temperature (Resin: Hardener: Internal Release Agent) 60:23:23 [°C], Mold Temperature 120°C,
Resin amount 900 [g] (depending on stack weight)

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