SAMPE Journal - November/December 2020 - 28

FEATURE / THERMOPL ASTIC COMPOSITE BL ANKS
in-line, but the stacking as well the consolidation
are supposed to deliver a final stack or blank within
about one minute, resp.
Tape Stacking Cell
Thermoplastic composite tape is produced at specific width, where common standards are 300 mm,
500 mm, and 600 mm. However, also tape width of
1.000 mm and even 1.400 mm is seen. For a large
part it is reasonable to use a wide tape and to preferably use it in one piece. Even at 45°-angle, layers
can be arranged from two or three tape cutouts at
beneficial cut-off conditions. First, slitting the wide
tape roll and then combining a single layer from
several tape strips usually is considerably less efficient.
The tape stacking cell can be operated with
cutoffs, which directly come from a tape roll, or
with cutouts. These are pre-cut from the tape roll,
mostly by means of stamping. The latter are fed to
magazines. A stack consists of several, e.g. 15 to 30
cutoffs and/or cutouts from the tapes, each one as
large as possible and useful. Furthermore, a base
layer, like a conventional organo sheet, can replace
the first set of tapes, which gives increased output
rate (kg/h).
In order to finish a tape stack at around one
minute, a tape cutout needs to be added to the
stack every few seconds. For that purpose, two
high-speed, high-precision articulated robots
where arranged that carry out several operations
in sequence - picking, measurement, placing, and
welding, Figure 1. Whilst they are on the move, correction data from the visual measuring unit is sent
to the robot's control that leads to the desired superior stacking precision.
Precision in tape stacking primarily means control over the resultant gap or overlap between adjacent tapes. Typical requirements are +/- 1.0 mm

or, at advanced prerequisites, even +/- 0.5 mm3.
In aviation industry, another concept is discussed;
no overlap and specified max. gap. Utilization of
mechanical guiding elements is very limited concerning usability and reliability. The result can only
be as precise, as the width of the tape used for is
precise. These limitations are overcome when a
high-resolution optical measurement system is
used in combination with precise articulated robots. The readings from the camera systems not
only deliver information on the actual geometry of
the tape cutouts, but also establish a basis for correction data and quality assurance.
Consolidation Unit
The most common industry standard for the consolidation of thermoplastic composites is the usage
of double belt presses. These systems are highly
efficient when continuous production at constant
thickness of the product is the concern. However,
if desired thickness variations in the semi-finished
parts are to be realized, the usability of double belt
presses is very limited. Consolidation of stacks with
thickness variations in a double belt press is possible only with extra means and at reduced productivity.
Intermittent heating and cooling of the stacks
between thin metal dies is more beneficial for that
purpose, Figure 2. Within the scope of this heating-and-cooling approach, the stack is placed
between metal plates, heated and molten by conduction, and subsequently chilled significantly below the crystallization temperature (in the case of
semi-crystalline thermoplastics, e.g. PP and PA), or
below the glass transition temperature (upon processing of tapes with amorphous thermoplastics,
e.g. PC).
The requirement towards the consolidation
is the same as in the case of the stacking - every

Figure 1. Tape stacking cell with
high-speed articulated robots.

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SAMPE Journal - November/December 2020

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