# 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. - **Patent:** US 4575330 - **Original title:** Apparatus for production of three-dimensional objects by stereolithography - **Owner:** UVP Inc - **Granted:** 1986 - **Status:** Public domain (expired) - **Times cited:** 1,094 - **Field:** manufacturing, mechanical, materials, software, consumer_electronics ## What it does 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. ## 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. ## 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. ## Real-world examples 1. Stereolithography (SLA) 3D printers 2. Digital Light Processing (DLP) 3D printers 3. Formlabs Form series printers 4. Carbon 3D printers ## Why it matters 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. ## 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. **Full plain-English explainer:** https://patentbrief.org/patent/us/4575330/stereolithography-3d-printing **Original patent:** https://patents.google.com/patent/US4575330 --- _Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._ ## Related patents Semantically similar inventions in the PatentBrief corpus: - [How Machines Build 3D Objects Layer by Layer from Melting Plastic](https://patentbrief.org/patent/us/5121329/fdm-3d-printing-stratasys) — This patent describes a method and machine for creating three-dimensional objects by precisely depositing melted material, layer by layer, from a movable nozzle onto a base. - [How Piezoelectric Inkjet Printing Works](https://patentbrief.org/patent/us/3946398/drop-on-demand-inkjet) — A 1970 patent describing how to print images by using electrical pulses to bend a tiny crystal plate, squeezing individual ink drops out of a nozzle on demand. - [How Laser Printers Use Rotating Mirrors to Write Information](https://patentbrief.org/patent/us/3867571/laser-printer-starkweather) — A 1972 Xerox patent describing how to use a spinning mirror to scan a laser beam across a page, adjusting the speed of the data to keep the image sharp. - [How Canon's Bubble Jet Printers Make Ink Droplets](https://patentbrief.org/patent/us/4723129/inkjet-bubble-jet-printing) — Canon's 1988 patent on bubble jet printing uses a tiny heater to instantly vaporize ink, creating a bubble that pushes out a droplet of ink from the printer head. - [How Stores Make Custom Products On-Demand with Remote Approval](https://patentbrief.org/patent/us/4528643/digital-distribution-point-of-sale) — This patent describes a system where a store can make a custom product for a customer, but only after getting permission and the necessary design information from a central, remote office.