3D printing, also called additive manufacturing, builds solid objects by depositing or solidifying feedstock layer by layer from a digital 3D model. It is the opposite of subtractive manufacturing, which cuts away from a solid block, and of formative manufacturing, which shapes material with molds or dies. The core technologies described here are mature. They have been established industrial production methods since the late 1980s and early 1990s.
In September 1984, Charles Hull filed the first patent for stereolithography, a method that uses an ultraviolet laser to solidify liquid photopolymer resin. Hull later co-founded 3D Systems. In 1989, Scott Crump invented Fused Deposition Modeling, which extrudes molten thermoplastic filament through a heated nozzle. Crump co-founded Stratasys. Those two inventions defined the main families of 3D printing still in wide use: photopolymer-based systems and thermoplastic extrusion systems.
A third major category, Selective Laser Sintering, uses a high-power laser to fuse powdered feedstock such as nylon or polyamide. The unsintered powder supports the part during the build, so removable support scaffolds are unnecessary. Together, these three technologies account for the majority of all 3D printers, both industrial and consumer, operating as of 2024.
How the 3D Printing Workflow Works
From CAD Model to Machine Instructions
The workflow begins with a 3D model created in computer-aided design software. The model is exported as an STL file, a format originally developed by 3D Systems that represents the object's surface as a mesh of triangles. The STL file is loaded into slicing software, which divides the model into thin horizontal layers and generates the machine commands the printer will execute.
How Each Technology Builds a Layer
The printer then follows those commands, building the object one layer at a time. In FDM printing, a spool of thermoplastic filament feeds into a heated nozzle that melts the plastic and deposits it on a build platform. The platform lowers by one layer height after each pass. In SLA printing, a build platform lowers into a vat of liquid photopolymer resin, and an ultraviolet laser traces each layer to cure it. In SLS printing, a roller spreads a thin coat of powder, and the laser sinters the cross-section of the part before the next layer is applied.
Post-Processing Requirements by Technology
Post-processing varies by technology. FDM parts may need sanding or acetone smoothing to improve surface finish. SLA parts call for washing in isopropyl alcohol to remove uncured resin, followed by UV curing. SLS parts are dug out of a block of unsintered powder, which can be reused. Support structures, when present, are removed manually or dissolved.
Materials: From Thermoplastics to Metal Powders
Filaments for Consumer FDM
Consumer-level FDM printing uses thermoplastics, most commonly Acrylonitrile Butadiene Styrene and Polylactic Acid. ABS is durable and heat-resistant but emits fumes during printing. PLA is easier to print, biodegradable under industrial composting conditions, and produces less odor. Both come as spools of filament in standard diameters.
Photopolymer Resins for SLA
SLA uses photopolymer resins that cure into rigid, tough, or flexible parts depending on the formulation. These resins offer higher resolution and smoother surfaces than typical FDM prints, but the consumables are costlier and demand careful handling because uncured resin is a skin irritant.
Engineering Powders for SLS and Metal Systems
SLS and other powder-bed methods use engineering thermoplastics such as nylon and polyamide, which produce strong, functional parts. Industrial systems also print in metal powders, including titanium, stainless steel, and aluminum alloys, using techniques derived from SLS. These metal parts go into aerospace assemblies, medical implants, and tooling where the capital cost of the machine and feedstock is justified by the value of the final part.
From Rapid Prototyping to Production Parts
The Prototyping Era
For the first two decades after Hull's patent, 3D printing was used almost exclusively for rapid prototyping. Designers and engineers produced physical models to test form, fit, and function before committing to costly injection molds. The technology was too slow, too expensive, and too narrow in material choice for production runs.
The Shift to End-Use Parts
That changed as machine costs fell, material properties improved, and build volumes grew. By the 2010s, aerospace companies were printing complex ducting, brackets, and engine components that could not be machined from a single billet. Medical device manufacturers used 3D printing to produce patient-specific surgical guides, implants, and prosthetics. Tooling shops printed jigs, fixtures, and injection mold inserts with conformal cooling channels that reduced cycle times.
The Rise of Mass Customization
Mass customization became a practical use case. Hearing aids, dental aligners, and orthotic insoles are now routinely produced from 3D scans of individual patients, with each part being unique. The unit cost in these applications runs lower than custom machining or manual fabrication, and the turnaround time is measured in hours or days rather than weeks.
What 3D Printing Does Well and Where It Falls Short
Geometric Freedom and Parts Consolidation
The principal advantage of additive manufacturing is geometric freedom. Internal channels, lattice structures, undercuts, and organic shapes that are impractical or prohibitively expensive to machine can be printed as a single piece. That freedom often enables parts consolidation: an assembly of 10 welded components can be redesigned as one printed part, cutting weight and eliminating failure points.
Speed, Surface, and Strength Constraints
Build speed is the main constraint. Each layer takes time to deposit or solidify, and total print duration scales with the volume of the part. For high-volume output of simple shapes, injection molding or die casting is orders of magnitude faster and cheaper per unit. Surface finish is another limitation: FDM parts show visible layer lines, and even SLA and SLS parts demand post-processing for a smooth appearance. Anisotropic mechanical properties mean that a printed part is weaker in the direction perpendicular to the layers than along them, which engineering design must account for.
Where the Technology Fits
The technology is best suited to low-volume production, complex geometries, and applications where weight reduction or customization delivers a return. For commodity parts that can be stamped or molded, subtractive and formative methods remain more economical. The three core technologies from the 1980s have not been superseded; they have been refined, and the choice among them depends on the material, resolution, and throughput the application demands.
Key Facts
- First patent: Stereolithography (SLA) filed by Charles Hull in 1984
- FDM invented: Fused Deposition Modeling by Scott Crump in 1989
- Core file format: STL (stereolithography) created by 3D Systems
- Common FDM materials: ABS (Acrylonitrile Butadiene Styrene) and PLA (Polylactic Acid)
- SLS material: Nylon or polyamide powder, no support structures needed
- Status of core technologies: Mature, established industrial processes since late 1980s/early 1990s
Major 3D Printing Technology Categories
| Technology | Inventor/Year | Feedstock | Key Feature |
|---|---|---|---|
| Stereolithography (SLA) | Charles Hull, 1984 | Liquid photopolymer resin | UV laser cures resin layer by layer; high resolution |
| Fused Deposition Modeling (FDM) | Scott Crump, 1989 | Thermoplastic filament (ABS, PLA) | Melted filament extruded through nozzle; most common consumer type |
| Selective Laser Sintering (SLS) | Not specified in brief | Powdered nylon or polyamide | Laser fuses powder; no support structures required |
Frequently Asked Questions
Is 3D printing the same as additive manufacturing?
Yes. Additive manufacturing is the formal industrial term for 3D printing. Both refer to building objects layer by layer from a digital model, as opposed to subtractive or formative processes.
What is the difference between FDM and SLA?
FDM extrudes melted thermoplastic filament through a nozzle. SLA uses a UV laser to solidify liquid resin. FDM parts are typically less expensive and easier to produce at home. SLA parts have smoother surfaces and finer detail but require post-processing and careful handling of uncured resin.
Can 3D printing be used for mass production?
It is used for mass production only in specific cases, such as custom medical devices and dental aligners, where each part is unique. For identical high-volume parts, injection molding or machining is faster and cheaper per unit.
