SAMPE Journal - November/December 2021 - 82

FEATURE / LARGE SCALE ADDITIVE MANUFACTURING
DEMONSTRATION AND APPLICATION
Dual material deposition and blender capabilities
with BAAM has allowed for the printing of
structures that demonstrate properties which
were unattainable with a single material system.
Traditionally, structures that need rigid exteriors
have been designed as thin-walled
hollow
structures, or alternatively a sparse infill has been
used with the same material. Dual material printing
enables solid or sparsely filled structures to achieve
lower cost and weight requirements by strategically
placing lightweight structural materials (e.g. foam)
in areas where loading conditions are low (Figure
4b). For example, in molds, a high cost and heavy
polymer such as PESU can be used on the exterior
molding surface while a high temperature foam is
used on the interior to reduce the weight and cost.
Applications such as wings or turbine blades can
be custom designed to use stiffer materials where
loads are high and lighter weight materials where
loads are low9
. Dual material printing coupled
with custom core structures allows for stiff and
lightweight structures (Figure 4d).
Reinforcing fibers such as CF, Bamboo Fiber
(BF), and Glass Fiber (GF) are often added to
base resins to provide higher stiffness and reduce
warping of the printed parts. Fillers in polymers
typically increase the cost and weight of the
material and the impact on mechanical property
performance depends on the type and amount
of filler used. Dual Material printing enables
placing materials with various fillers or neat resins
throughout a part to tailor mechanical response
in certain locations. Locations with high stiffness
requirements can be printed with a CF filled
material, and areas with low thermal properties
and lower stiffness can be printed with a GF filled
material. Similarly, Figure 4a shows how a fiber
filled bio-derived material exterior and a low-cost
bio filler interior are printed utilizing the dual
hopper system. Utilizing the printing process
and dual hopper system, structures with local
reinforcement can be achieved as well16
.
Blended material compositions can also be
altered during the build to define site-specific
material
composition
properties. Modifying
during
printing
the
creates
material
some
challenges as well. For example, printing with
a combination of foaming and non-foaming
materials can affect the geometry of the build
(layer height, bead width) depending upon the
local foaming conditions. Changes in bead and
layer height must be accounted for in the toolpath
such that material has enough space to deposit and
does not overbuild and cause collisions. Currently,
82 | SAMPE JOURNAL | NOVEMBER/DECEMBER 2021
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high expansion foams are extruded only on every
other layer because the layer height for the foam
is twice that of normal non-foamed materials.
Blending four different materials can create
structures where elasticity, strength, and weight
are altered rapidly. For instance, building with a
blend of thermoplastic polyurethane (TPU) and
CF/ABS can result in highly stiff elastomers for high
toughness applications. Recycled materials can
also be blended with the virgin material to reduce
waste in the AM and industry process to create a
more eco-friendly printing environment.
As materials transition from one to another, a
transition zone must be either purged (the process
of clearing the printer's barrel for next transitioned
material) or deposited into the structure before a
virgin material can be deposited. If this material
is purged, the layer time increases and allows the
structure to cool. For many structures, an increase
in layer time can lead to defects as well as poor
layer-to-layer adhesion, causing delamination
Figure 4. Applications for multi-Material structures showing variations in
weight, cost, stiffness, and custom core designs; a) Multi material bio-derived
leaf (Green: Bamboo/Polylactic Acid (PLA) and Brown: Wood flower/ PLA),
b) Flat panel showing ABS foam used for lightweight structure by strategic
placing of foam in infill pattern with a ridged CF/ABS exterior, c) Optimized
PLA foam core structure for a turbine blade, and d) Zoom out for the
functionally graded core during printing process.
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SAMPE Journal - November/December 2021

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