ates weak points—the wheels require more material
and designs are limited to large, simple elements.
Forged wheels are lighter and stiffer (and more
expensive) than their cast counterparts. The
most common method is machine forging, which
involves tempering a block of billet aluminum to
add strength, then CNC-machining it into a wheel.
HRE’s concept wheels used GE’s electron beam
melting (EBM) technology to print five interlock-
ing individual components that formed the face of
the wheel. The EBM process uses a 3-kilowatt elec-
tron beam to solidify layers of metal powder into
potentially complex 3D shapes at temperatures in
excess of 1,800 degrees Fahrenheit. The remaining
powder can then be vacuumed away and recycled.
The final part requires minimal finishing work
thanks to a beam diameter of 140 microns—there
are 25,400 microns in an inch. Unlike traditional
gravity casting’s porosity, these machines can
achieve nearly 100 percent material density.
While additive manufacturing offers an excel-
lent opportunity to disrupt the performance wheel
industry, it necessitates vastly different design
requirements than forged and cast wheels.
“Step one in learning to design for additive is
forgetting everything you know about everything
else,” says Josh Mook, chief engineer and inno-
vation leader at GE Additive. Mook stresses that
EBM technology pushes the boundaries of what’s
required from a material science standpoint.
Despite HRE using a robust Ti-6Al-4V titanium
alloy, the complicated geometries of the HRE
wheels required additional support structures to
suppress thermal distortion during the printing
process. These scaffolds, which get removed during
the finishing process, prevent the hot 3D-printed
metals from sagging during manufacturing.
But how will lighter wheels make your car
faster? This all has to do with the unsprung mass
of an automobile, the components that aren’t sup-
ported by the suspension system—wheels, hubs,
brake discs, calipers, brake lines, and tires. While
these components only make up around 10 percent
of the overall weight, they have an outsized effect
on how your car drives.
As unsprung mass decreases, so does the
workload on the suspension system. In bumpy sit-
uations, this allows the tire to remain in contact
with the road for longer, leading to more traction.
Lower unsprung mass also means lower rotational
inertia, which allows for better acceleration and
shorter braking distances.
While additive technology has yet to be seen in
most production vehicles, GE Additive is currently
developing a more scalable and affordable additive
manufacturing solution to fill this gap.
HRE has no plans to sell these wheels at the
moment, but doesn’t doubt that these types of
wheels will see production at some point. The tech-
nologies behind casting and forging wheels have
essentially plateaued, but additive manufacturing
is just beginning to unlock a higher level of perfor-
mance in the automotive industry.Advantages of Additive
Under the Hood
GE has been working with manu
facturers like Cummins to showcase
the performance and efficiency
advantages of 3Dprinted drivetrain
parts, such as pistons. The stronger,
lighter pistons can be actuated faster
while using less fuel.
Like wheels, pistons are
traditionally produced through
casting or forging, and suffer
material inefficiencies—in this case,
unnecessary material where therod connects to the piston. Additive
manufacturing allows for much
greater control in these tight areas.
Another advantage of additive
manufacturing is that these
performance gains can be achieved
without the added cost of tooling.
Eliminating this expense could even
allow small tuning shops to print
pistons and other complex engine
components without the need to
outsource manufacturing.The face of the
HRE3D+ wheels
were built using
five interlocking
3D-printed
sections.16 November/December 2021
COURTESY HREC a r s &
(^4) Trucks