MATERIALS | ADDITIVE MANUFACTURING
ACCESSIBLE ADDITIVE Dave Veisz of MakerBot discusses
developments enabling engineers to bridge
the chasm between high-end AM and
desktop 3D printing.
If you’ve ever had the misfortune
to stand on a Lego piece, you’ll
know how incredibly painful
– not to mention indestructible
– those little bricks can be. This
impressive combination of durability
and impressive tensile strength,
not to mention the glossy nish, is
due to its construction from ABS, a
thermoplastic polymer widely favored
for injection molded consumer goods.
In addition to its tensile strength,
ABS’ impressive list of material
properties include high temperature
resistance, recyclability, high
chemical resistance and low electric
conductivity. It’s for this reason that
ABS is used to make so many of the
everyday items around us, from car
dashboards and electrical housing, to
computer keyboards and, of course,
children’s toys.
While traditional production
methods, such as injection molding,
continue to provide the largest
source of ABS parts, industrial-grade
additive manufacturing has become
a popular choice for the rapid
production of ABS prototypes and
low volume end-use parts in a costeffective
manner. While the ability
to produce real engineering-grade
ABS parts has become commonplace
in higher-end 3D printers, desktop
additive manufacturing has long
struggled to produce these parts
with the level of reliability and
repeatability expected by an
industrial designer or engineer.
THE CHALLENGE
The problem stems from ABS’ high
temperature resistance and melting
point. When cooled this creates
delamination, leading to a severe
weakening of the structure of the part,
and ultimately creating warping and
cracks – essentially nullifying the
reason for choosing ABS in the rst
instance. If a part is cooled rapidly by
quenching, it may also be subject to
shrinkage forces due to air exposure.
Therefore, when producing parts in
ABS using a desktop 3D printer, a
controlled cooling process and closed
chamber is highly recommended.
The larger the part, the more likely
the shrinkage forces will come into
play, creating a warped or ‘taco’
shaped result.
Some engineers may abandon
ABS altogether and turn instead to
materials such as PLA, which typically
requires a lower print temperature,
as well as offering a reduced risk of
warping. However, PLA’s low melting
point comes at the price of losing
large amounts of tensile strength
when heated, leading to a brittle part.
As engineers we never stray
from a chemical problem, and for
those determined to persist with
ABS, several ‘hacks’ or alternate
approaches can be suggested to
improve part quality. Most solutions
come down to two fundamental
tactics: modify the material or modify
the 3D printer.
Search the internet and you’ll nd
an array of modi ed ABS materials,
from thermochromic and translucent,
to ame retardant and even luminous
(glow in the dark). These chemical
adaptations allow engineers the
freedom to select the ideal formula for
their speci c use.
However, these altered formulas
tend to come at a price, and ABS
that is labelled as ‘optimised for
3D printing’ is no exception. While
chemically modifying ABS can
reinforce heat resistance – either
through the inclusion of an additive
or by increasing the ratio of
polybutadiene (the B in ABS) – this
has to be balanced against a number
of downsides: lower heat de ection
temperatures, reduced tensile
modulus and lower tensile strength.
This can result in an inferior product
that is totally unsuitable for the many
of the high-performance applications
ABS is used for, such as producing
automotive and aerospace parts.
If modifying the material doesn’t
have the desired effect, then the
natural progression is to look at
manipulating the 3D printer itself.
Many desktop 3D printers on the
market today allow the user to control
the temperature of the build plate.
Offering a temperature-controlled
heated bed allows some of the heat
to be transferred to the bottom of
the 3D printed part, reducing the
risk of layer separation. MakerBot
took this approach with its earlier
3D printers, however we found that
Top: All Axis Robotics
– 3D printed robot
end-e ectors.
Above: A 3D printed
pneumatic pump
produced in real
engineering-grade
ABS.
Far right: A 3D printed
sander produced in
real engineeringgrade
ABS.
30 WWW.EUREKAMAGAZINE.CO.UK | MAY 2020
/WWW.EUREKAMAGAZINE.CO.UK