How 3D Printers Build Objects Layer by Layer from Liquid
This patent describes the foundational method for 3D printing, where a machine builds a three-dimensional object layer by layer by hardening a liquid material with light or other energy.
Original patent title: “Apparatus for production of three-dimensional objects by stereolithography”
This patent describes the foundational method for 3D printing, where a machine builds a three-dimensional object layer by layer by hardening a liquid material with light or other energy. Granted to UVP Inc in 1986 with 52 claims and 1,094 forward citations, and it is now in the public domain.
Key facts
Coverage
What does this patent actually cover?
The patent describes a system (ClaimclaimA numbered sentence at the end of a patent that legally defines what the inventor owns. The most important section.Read more → 1) that creates 3D objects by forming thin layers, called "laminae," from a special fluid that hardens when exposed to specific energy. The system uses "reaction means" (Claim 2) like a beam of ultraviolet light (Claim 9) to draw each cross-section of the object on the liquid's surface. As each layer solidifies, an "object support means" (Claim 2) moves the partially built object away, allowing the next layer to form and attach. For example, a laser draws the bottom layer of a small plastic toy boat on a liquid resin, then the boat dips slightly, and the laser draws the next layer, building the boat up from the liquid.
The gap
What does this patent NOT cover?
- 3D printing methods that use powdered materials, like selective laser sintering (SLS), instead of a fluid medium.
- 3D printing methods that extrude melted plastic filaments, like Fused Deposition Modeling (FDM).
- Systems that build objects by adding material from the side or top, rather than "extracting" them from a designated surface of a fluid.
- Methods that don't rely on a "synergistic stimulation" (e.g., light, electron beam, chemical jet) to change the material's state.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
What made this novel
The core innovation was the precise, automated, layer-by-layer construction of complex 3D objects from a liquid bath, using a controlled energy source to solidify specific cross-sections. This allowed for the creation of intricate shapes that were otherwise impossible to mold or machine.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Stereolithography (SLA) 3D printers
Digital Light Processing (DLP) 3D printers
Formlabs Form series printers
Carbon 3D printers
Why it matters
The bigger picture
This patent, by Charles Hull, is widely considered the foundational patent for stereolithography (SLA), the first commercially viable 3D printing technology. It laid the groundwork for an entire industry, enabling the rapid prototyping of parts and the creation of complex geometries previously impossible to manufacture.
Filed
August 8, 1984
Granted
March 11, 1986
Market context
Who's building on this
Companies in this space
Companies like 3D Systems (founded by Hull), Formlabs, Carbon, and Stratasys continue to develop and sell advanced stereolithography and resin-based 3D printing systems. These companies are constantly innovating on the materials, speed, and precision of this foundational technology.
Market impact
This patent enabled the birth of the commercial 3D printing industry. It allowed for the creation of rapid prototypes, tooling, and eventually end-use parts, fundamentally changing product development cycles across many industries. It established the layer-by-layer additive manufacturing paradigm that dominates the field.
Claim 1 — Plain English
What this patent covers
The patent describes a system (Claim 1) that creates 3D objects by forming thin layers, called "laminae," from a special fluid that hardens when exposed to specific energy. The system uses "reaction means" (Claim 2) like a beam of ultraviolet light (Claim 9) to draw each cross-section of the object on the liquid's surface. As each layer solidifies, an "object support means" (Claim 2) moves the partially built object away, allowing the next layer to form and attach. For example, a laser draws the bottom layer of a small plastic toy boat on a liquid resin, then the boat dips slightly, and the laser draws the next layer, building the boat up from the liquid.
The clever bit
The core innovation was the precise, automated, layer-by-layer construction of complex 3D objects from a liquid bath, using a controlled energy source to solidify specific cross-sections. This allowed for the creation of intricate shapes that were otherwise impossible to mold or machine.
What it does not cover
- 3D printing methods that use powdered materials, like selective laser sintering (SLS), instead of a fluid medium.
- 3D printing methods that extrude melted plastic filaments, like Fused Deposition Modeling (FDM).
- Systems that build objects by adding material from the side or top, rather than "extracting" them from a designated surface of a fluid.
- Methods that don't rely on a "synergistic stimulation" (e.g., light, electron beam, chemical jet) to change the material's state.
Patent Journey
From filing to expiry
PatentBrief Score
Impact Score
Strong
Citation count
40/40
Highly cited
Claim breadth
20/20
Very broad protection
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$65K – $207K
Midpoint $130K · expired or expiring · industry ×0.9
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
The original legal language
Original claims
52 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Hull, C. W. (1986). How 3D Printers Build Objects Layer by Layer from Liquid (U.S. Patent No. 4,575,330). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/4575330/stereolithography-3d-printing
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does How 3D Printers Build Objects Layer by Layer from Liquid cover?
This patent describes the foundational method for 3D printing, where a machine builds a three-dimensional object layer by layer by hardening a liquid material with light or other energy.
Who owns patent US 4575330?
UVP Inc owns this patent, granted in 1986.
When does this patent expire?
This patent has expired and is now in the public domain — anyone can use the invention freely.
What is patent US 4575330 cited by?
This patent has been cited by 1094 later patents that build on its ideas.
What problem does this patent solve?
This patent, by Charles Hull, is widely considered the foundational patent for stereolithography (SLA), the first commercially viable 3D printing technology. It laid the groundwork for an entire industry, enabling the rapid prototyping of parts and the creation of complex geometries previously impossible to manufacture.
What does this patent NOT cover?
3D printing methods that use powdered materials, like selective laser sintering (SLS), instead of a fluid medium.
Patent monitoring