Additive manufacturing builds physical objects by depositing material one thin layer at a time, guided by a digital 3D model. Instead of cutting, drilling, or milling material away from a solid block (the traditional approach), it adds material only where it’s needed. This near-net-shape process can reduce steel consumption by roughly 60 to 70% compared to conventional machining. The term covers seven distinct process categories, but they all share the same core logic: slice a digital design into hundreds or thousands of cross-sections, then recreate each cross-section as a physical layer fused to the one below it.
From Digital File to Physical Layers
Every additive manufacturing job starts with a 3D model, typically created in CAD (computer-aided design) software. That model gets exported to a file format the printer can interpret. The most common is STL, which represents the object’s surface as a mesh of tiny triangles, but newer formats like 3MF and AMF carry additional data such as color and material information. The quality of this file matters: how the CAD software breaks the surface into triangles (a step called tessellation) directly affects the dimensional accuracy of very small features in the final part.
Once the file is ready, slicing software takes over. The slicer divides the 3D model into horizontal layers, each typically between 0.05 and 0.3 mm thick depending on the process and the desired surface quality. For each layer, the slicer generates a toolpath: instructions telling the printer exactly where to deposit, melt, or cure material. The slicer’s handling of geometry is one of the biggest factors in how accurately the printed part matches the original design. After slicing, the instructions are sent to the printer and fabrication begins.
Seven Categories of Additive Manufacturing
The American Society for Testing and Materials classifies all additive manufacturing processes into seven categories. Each uses a different combination of energy source and raw material, but they all build layer by layer.
Material Extrusion
This is the most widely recognized process, commonly called FDM (fused deposition modeling) or FFF (fused filament fabrication). A spool of solid thermoplastic filament feeds into a heated chamber, where it melts and pushes through a nozzle. The nozzle traces the shape of each layer onto a build platform, then the platform drops by one layer height and the next layer is printed on top. Bonding between layers happens through a three-stage process: the hot surfaces make contact, surface tension drives the formation of a neck between adjacent strands, and polymer chains physically diffuse across the interface and entangle. The strength of a finished part depends heavily on how well those interlayer bonds form during cooling.
Vat Photopolymerization
Instead of melting solid material, this process starts with a vat of liquid resin and uses light to harden it. The resin contains a photoinitiator, a chemical additive that absorbs UV light energy and becomes reactive. Those activated molecules attack the bonds in the liquid resin monomers, triggering a chain reaction: individual molecules link together into longer and longer chains, which then cross-link into a rigid network. On a visible scale, the liquid simply hardens wherever the light hits it. Stereolithography (SLA) uses a UV laser (typically 355 nm) that traces each layer point by point, while digital light processing (DLP) uses a projector (typically 405 nm) to flash an entire layer at once. DLP is faster per layer because it cures the whole cross-section simultaneously.
Powder Bed Fusion
A thin, even layer of powdered material is spread across a build platform by a recoating blade or roller. Then a laser or electron beam selectively scans the powder surface, following a path generated from the model’s slice data. Wherever the beam hits, the powder particles melt and fuse together. The platform drops, a new layer of powder is spread, and the process repeats. The surrounding unfused powder supports the part during the build, which means complex geometries can be printed without extensive scaffolding. This category includes several well-known techniques: selective laser sintering (SLS) for polymers, selective laser melting (SLM) and direct metal laser sintering (DMLS) for metals, and electron beam melting (EBM) for high-performance alloys.
Material Jetting
This process works much like a 2D inkjet printer, but instead of ink, it deposits droplets of photopolymer or wax onto a build platform. A print head moves across the surface, placing tiny droplets precisely where needed, then a UV light immediately cures each layer. Material jetting produces some of the smoothest surfaces and finest details of any additive process, but the build volume tends to be small.
Binder Jetting
Binder jetting uses two materials: a powder spread in thin layers across the build platform, and a liquid binding agent deposited by a print head. The binder glues the powder particles together in the shape of each cross-section. After printing, the part is typically fragile and requires a secondary step (sintering in a furnace or infiltrating with another material) to achieve full strength. Because no high-energy beam is involved during printing, binder jetting can work at high speeds and across large build areas.
Sheet Lamination
Rather than powder or liquid, sheet lamination bonds layers of flat material, often paper, plastic film, or metal foil. Ultrasonic additive manufacturing (UAM) uses high-frequency vibrations to weld thin metal sheets together, then a CNC cutter trims each layer to shape. Laminated object manufacturing (LOM) takes a similar approach with paper or polymer sheets. These processes are less common but useful for producing large parts or embedding sensors and electronics between metal layers.
Directed Energy Deposition
A focused energy source (laser or electron beam) melts material as it’s being deposited, usually through a nozzle that feeds metal wire or powder directly into the melt pool. Unlike powder bed fusion, the material is only delivered where it’s needed rather than spread across an entire bed. This makes directed energy deposition well suited for repairing damaged components or adding new features to existing parts. It’s common in aerospace maintenance and heavy industry.
Materials You Can Print
The range of printable materials has expanded well beyond basic plastics. Polymers remain the most accessible category, from common thermoplastics like PLA and ABS used in desktop extrusion printers to high-performance engineering plastics like PEEK and nylon used in industrial applications. Metals include stainless steel, titanium, aluminum alloys, nickel superalloys, and cobalt-chrome, primarily processed through powder bed fusion and directed energy deposition. Ceramics can be printed using vat photopolymerization (with ceramic particles suspended in the resin) or binder jetting. Advanced materials such as composites, biomaterials for medical implants, and metamaterials with engineered internal structures are also active areas of production.
What Happens After Printing
A part fresh off the printer is rarely finished. Post-processing is a standard part of the additive manufacturing workflow, and the steps required depend on the process and material used.
Cleaning comes first: removing residual powder from internal channels in a powder bed fusion part, or washing uncured resin from a photopolymerized part. Support structures, temporary scaffolding printed to hold overhanging features in place, need to be cut, broken, or dissolved away. For metal parts, heat treatments like annealing or stress relieving are common. Printing creates rapid heating and cooling cycles that leave internal stresses in the material, and thermal treatment redistributes those stresses to improve strength, durability, and fatigue resistance.
Surface finishing addresses the visible layer lines inherent to any layer-by-layer process. Techniques range from simple sanding or abrasive blasting to electropolishing for metal parts. Hot isostatic pressing, which applies heat and high pressure simultaneously, can close internal pores in metal prints and improve density. Many of these steps are labor-intensive and require skilled operators, which adds both time and cost to the final part.
How It Compares to Traditional Manufacturing
The biggest material advantage of additive manufacturing is waste reduction. Conventional machining starts with a block of raw material and cuts away everything that isn’t the final part. For complex aerospace components, the “buy-to-fly” ratio (how much material you purchase versus how much ends up in the finished piece) can be extremely high. Additive processes reduce material consumption by 35 to 65% compared to milling and turning, with some wire-based deposition methods achieving roughly 70% material savings and an 80% reduction in waste.
Design freedom is the other major advantage. Because material is added rather than removed, additive manufacturing can produce internal channels, lattice structures, and organic shapes that would be impossible to machine or mold. Parts can be consolidated: an assembly that previously required dozens of individually machined and fastened components can sometimes be printed as a single piece.
The trade-offs are real, though. Printing speed remains slow for mass production. Build volume is limited by the size of the printer’s chamber, restricting the dimensions of parts that can be produced in one piece. And the layer-by-layer process can create anisotropic mechanical properties, meaning a part may be stronger in one direction than another depending on how the layers are oriented. For these reasons, additive manufacturing is most cost-effective for low-volume production, highly complex geometries, and applications where performance gains justify higher per-unit costs.
Where Additive Manufacturing Is Used Today
Aerospace and medical devices lead adoption of additive manufacturing for safety-critical parts. In aerospace, the market was valued between $1.76 and $2.66 billion in 2021 and is growing at roughly 19 to 20% per year, driven by demand for lightweight components, faster development timelines, and localized production. Powder bed fusion and directed energy deposition are used for direct part manufacturing, tooling, and maintenance and repair. Titanium brackets, fuel nozzles, and structural components that save weight translate directly into fuel savings over an aircraft’s lifetime.
In medicine, patient-specific implants, surgical guides, and dental restorations are printed from biocompatible metals and polymers tailored to individual anatomy. The ability to produce a custom part without dedicated tooling makes additive manufacturing practical even for one-off production runs, which is exactly what personalized medicine requires.