By just using rays of light, this new 3D printer
“sculpts” objects all at once, making
it one of the first designs of its kind.
This latest method coming from UC Berkeley and Lawrence Livermore National Lab
is called Computed Axial Lithography, or CAL for short.
It uses a newer technique called volumetric
printing.
HAYDEN TAYLOR: Volumetric printing is a category
of additive manufacturing, where all points
inside the 3D objects are materialized or
created pretty much
Simultaneously, as opposed to building up
the geometry, layer by layer, which is how
virtually every other existing additive manufacturing
process works today.
So CAL is printing smooth complex geometries
like those found in the statue The Thinker;
there are no symmetrical sides and no hard
“staircase” looking edges, which is totally
novel!
Another promising feature of this device is
called “overprinting” which is when they
can take objects and print around them.Like
taking the metal component of a screwdriver
and printing the handle.
This is a technique that our additive manufacturing
printers today, have trouble accomplishing.
You see, even other liquid printers, like
those that use Stereolithography, are not
considered volumetric.
Although Stereolithography printers also use
a bath of resin, they’re still printing
objects layer by layer, slowing pulling the
object out and selectivity curing sections
with a light in a process called photopolymerization.
Researchers for CAL eliminated this long process.
Since CAL can print within minutes and is
special since it can print all at once too,
and it’s still a very new technology.
HAYDEN TAYLOR: Computed axial lithography,
you mean?
The merging of the relative rotation to build
up.a 3D intensity dose with fabrication.
This is the first demonstration of that approach.
The original proof of principle was done in
2017 by a big collaboration between the Lawrence
Livermore National Lab, MIT, UC Berkeley, and University
of Rochester.
They used three intersecting stationary beams,
and at the points they intersected, the intensity
of light was high enough to cause the resin
to solidify.
But this early project was limited by simple
shapes.
So Hayden and the team wanted to create something
with some versatility and curves.
HAYDEN TAYLOR: The principle of the CT scan,
the computed tomography scan, came to mind.
We thought, "Well, let's just reverse that
to create objects instead of measuring them.
By calculating what an image would look like
from many different angles, researchers put
the resulting images into a DLP, or “digital
light processing” projector.
(Sounds fancy, but it’s really just an ordinary
digital projector from a store.)
From there they pointed the projector at a
light-sensitive resin.
HAYDEN TAYLOR: And so, as that volume of material
rotates quite steadily, the pattern that is
being projected into the volume is changing
there are rays of light that are controlled
in the brightness, and as they shined through,
photons are getting absorbed out of that beam
at a particular rate.
When that amount of absorbed light energy
goes above a certain threshold value, the
resin will become solid and then the part
is formed.
So a key part of this whole process is this
resin.
It’s a synthetic material called gelatin
methacrylate hydrogel and it’s made of a
few components; liquid polymers (which have
acrylate at the ends), photoinitiators (which
are molecules that react to photons), and
oxygen.
The researchers keep the gel at room temperature
so the oxygen can evenly distribute.
But when a light is shined into the material,
the molecules within the photoinitiators become
reactive and a few things can happen.
HAYDEN TAYLOR: First, they could interact
with the oxygen and become what is called
quenched.
So, the reactive molecule stops being reactive
and is basically dead.
When I say that there's a threshold for light,
it's really the presence of the oxygen that
creates this sharp threshold.
You've got to consume the oxygen before you
could do the solidification.
This threshold process is extremely important
because technically, those rays of light are
going through the entire resin, even the parts
you don’t have to solidify.
The acrylate in the polymers goes through
what’s called polymerization, which is when
resin molecules link together in chains to
make a solid plastic.
And within a few minutes, the researchers
have a solid small structure like that of
The Thinker.
The resin is a flexible material to work with
because it’s cheap, malleable, and reusable.#
We can possibly customize sports equipment,
tools, lenses, or even prosthetic devices.
But to go beyond the centimeter scale the
researchers are at now, they need to evaluate
the resin formula.
AND what about biocompatibility?
HAYDEN TAYLOR: Wow, that is a really excellent
question, and actually, the subject of our
ongoing research.
We know that other research groups have successfully
used gelatin methacrylate in conjunction with
cells in vitro.
That's a huge positive sign for us.
So while this is the latest and breaking research,
it’s probably only going to get better from
here on out.
So How much do you know about 3D printers?
Does this project excite you?
Let us know down in the comments below and
if you liked this project, check out this video. And don’t
forget to subscribe to Seeker for all your material
science updates and I’ll see you next time.
 
