JEC COMPOSITES MAGAZINE - Issue #119 - March 2018 - 29

3D printing MANUFACTURING

Additive manufacturing of
high-performance composite structures

dAvid HAuber,
Engineering Manager
rAlpH MArcArio,
Sales Manager
Automated Dynamics (Part of
Trelleborg Group)

utomated Dynamics was one of the
original inventors of 3D printing
in the 1980s when they invented
BPM, a material jetting technology [1].
Although rapid prototypes were interesting, the company was more interested
in automating the manufacture of
high-performance composite structures.
As such, it was one of the first to develop
in-situ automated fibre placement (AFP)
of thermoplastic-matrix composites
(TPC). Although all composite layup
is inherently additive, thermoset AFP is
not considered additive manufacturing
due to the requirement of post-curing.
Thermoplastic-matrix composites are
melt-bonded during in-situ AFP of TPC,
eliminating post-processes and making it
true additive manufacturing of high-performance composite structures.

In the previous article about "High-performance creations: additive
manufacturing and composites" (JEC Magazine no. 115), the authors
Prof. David Rosen and Dr. Florian Doetzer pointed out the possibilities
that arise when composite manufacturing and additive manufacturing
(AM) processes complement each other. The discussion continued in
"Fibre Patch Placement: expanding the scope of additive manufacturing" (JEC Magazine no. 117). The authors Felix Michel and Thorsten
Groene elaborated how fibre patch placement combines the advantages
of additive manufacturing with state-of-the-art performance expectations of the composite industry. Now the discussion will be led into 3D
printing, learning from rapid prototyping and merging automated fibre
placement with thermoplastic-matrix composites.
The early development of in-situ AFP in
the late 1980s at Automated Dynamics
led to the patented hot gas torch (HGT)
technology, which uses a supersonic jet
of electrically-heated nitrogen to meltbond thermoplastic composites in-situ.
The company used this basic technology
for more than 30 years and currently
produces over 8 metric tons of in-situ
consolidated TPC structures yearly. As
the cost of high-energy lasers continues
to drop, they are now a viable option to
succeed HGT technology. Automated
Dynamics' laser heating system (LHS)
uses an Nd:YAG fibre laser with real-time
temperature control in the melt zone
using an IR pyrometer. This provides
more accurate temperature control, more
efficient heat transfer, and higher energy
density than HGT, yielding about a 300%
increase in speed. Figure 1 illustrates the
progression of in-situ TCP AFP heads
over the past 30 years.

Theory
Classical polymer bonding theory derives
from de Gennes's [2] work on press
consolidation. The general concept is that
melt bonding of polymer surfaces involves
three stages - intimate contact, molecular
diffusion (reptation or autohesion), and
consolidation. The two surfaces make intimate contact under heat and pressure, polymer chains diffuse between the two layers
via thermal molecular vibrations, and the
bond zone is cooled under pressure to consolidate the layers. Attempts to follow this
classical theory for in-situ TPC AFP have
resulted in slow process rates and large
unwieldy heads. The secret to success for
in-situ TCP AFP is the realization that it is
a dynamic process that is not constrained
by the classical reptation theory. In a
properly designed process, the polymer
exhibits squeeze flow, shear thinning, and
shear mixing in the heat-affected zone
(HAZ) before the compaction roller [3].

Fig.1: 1980s HGT,
modern HGT, and LHS
in-situ TPC AFP Heads

N°119 March 2018

/ jec composites magazine

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #119 - March 2018