Lesson 8.10ShapeChapter 8 · Additive manufacturing

Volumetric printing (CAL)

Light from every angle cures a spinning vial of resin all at once (volumetric printing)

Volumetric printing makes a whole object at once inside a vial of liquid resin, with no layers at all. In computed axial lithography (CAL), the vial spins while a projector shines changing light patterns through it, like a CT scan run in reverse. A small object can appear in a minute or two.

computed axial lithography · side and top views, 5 stepsLeft: the setup seen from the side. Right: the vial seen from above, with three of the many light directions. Circled numbers match the steps below.

How it works

Compute the patterns. Software turns the 3D model into hundreds of 2D light images, one for each viewing angle, much as a CT scanner works in reverse.
Spin the vial. A clear vial of thick, light-sensitive resin turns steadily on a rotating stage.
Project. A projector shows the image that matches the vial's current angle, so every angle gets its own pattern.
Let the dose add up. Each point in the resin collects light from every angle. Only points inside the object pass the threshold (the minimum light dose that makes resin gel) and turn solid.
Drain, rinse and cure. After roughly 30 seconds to a few minutes, the liquid resin is poured off. The object is rinsed and given a final UV cure.

Key facts

Materials: Clear, thick photopolymer resins (acrylates), hydrogels that can carry living cells, and resins filled with glass particles that are later fired into glass
Typical parts: Small research parts: lenses and optics, glass microfluidic chips, soft tissue scaffolds, objects printed around an existing insert
Part size: A few millimeters to a few centimeters, limited by the vial
Precision: Features down to about 0.3 mm in the first printers; research systems reach tens of micrometers
Surface finish: Very smooth, with no layer lines
Batch size it suits: One-offs and research samples
Tooling and machine cost: No tooling. Mostly laboratory setups built around a projector and a rotation stage; few commercial machines exist yet
Speed: Seconds to a few minutes for a centimeter-sized object

Strengths and limits

Strengths

No layers: smooth surfaces and no weak layer boundaries
Very fast for small parts
No supports, since the thick resin holds the part in place
Can print around an existing object, such as a metal rod

Limits

Small objects only, a few centimeters at most
Resin must be clear and thick, so few materials work
Light scattering and dose errors blur fine details
Still mostly a research technique

Where it's used

Research labsTesting new resins, optics and printing methods
BiomedicalSoft hydrogel scaffolds with living cells for tissue research
OpticsSmall lenses and light guides
MicrofluidicsGlass chips with tiny internal channels

How to recognize it

Small, perfectly smooth resin objects with no stair steps on curves.
No support marks anywhere, even under overhangs.
Sometimes an object fused around an insert, like a handle printed onto a metal shaft.

Compare with

Stereolithography8.2also hardens resin with light, but one thin layer at a time; CAL cures the whole volume at once.Two-photon polymerization13.8also cures inside a volume, but point by point with a focused laser, at the micrometer scale.

Watch it

Seeker · A beginner's explanation of the Berkeley volumetric printer

The Action Lab · A hands-on demo of an object appearing inside resin

KPIX | CBS NEWS BAY AREA · Real lab footage with the researchers who built it

Berkeley Sensor & Actuator Center · A research talk on how CAL works, including printing in microgravity

See real photos

Wikipedia: Computed axial lithography — the principle and its history; few images
Wikimedia Commons photo search

Remember

Volumetric printing hardens a whole object at once, with no layers.
CAL spins the resin and lights it from every angle; only where enough light adds up does it turn solid.
It is fast and smooth, but still small-scale and mostly in research labs.