What Is Three-dimensional Printing?

Three-dimensional printing is an additive manufacturing process in which a physical object is constructed by depositing, fusing, or solidifying material layer by layer, following a digital model as a blueprint. Each successive cross-sectional layer is added on top of the previous one until the complete three-dimensional geometry is realized. The technique contrasts with subtractive manufacturing methods such as machining, which remove material from a solid block, and with formative methods such as injection molding, which shape material using dies and pressure. Three-dimensional printing encompasses a broad family of processes that differ in the feedstock material, the energy source used to consolidate layers, and the achievable precision and throughput.

The technology traces its commercial origins to Charles Hull's 1986 patent on stereolithography, which used an ultraviolet laser to cure thin layers of photopolymer resin. Over the following decades, complementary processes emerged for polymers, metals, ceramics, and biological materials, and ISO/ASTM 52900 now provides a standardized taxonomy of seven distinct additive manufacturing process categories.

Additive Manufacturing Process Categories

ISO/ASTM 52900 classifies three-dimensional printing processes into seven categories: vat photopolymerization, powder bed fusion, binder jetting, material jetting, material extrusion, directed energy deposition, and sheet lamination. Vat photopolymerization, which includes stereolithography and digital light processing, uses UV or visible light to selectively cure liquid photopolymer resin. Powder bed fusion processes, such as selective laser sintering and selective laser melting, use a laser or electron beam to fuse a powder bed of polymer or metal particles one layer at a time. Material extrusion, commonly marketed under the trade name fused deposition modeling, pushes a thermoplastic filament through a heated nozzle and deposits it along a computed path. Binder jetting, which is related to inkjet printing, selectively deposits a liquid binder onto a powder bed to bond particles layer by layer, producing parts that are then sintered in a furnace. A review published through PMC covering additive manufacturing evolution and applications documents the comparative capabilities and limitations of these process families.

Materials for Three-dimensional Printing

Feedstock materials for three-dimensional printing span polymers, metals, ceramics, composites, and biological substrates. Polymers including polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), and nylon are the most widely used because they are inexpensive and suitable for material extrusion and powder bed fusion. Metal printing using titanium alloys, stainless steel, aluminum, and cobalt-chrome alloys serves aerospace, medical implant, and tooling applications, typically through selective laser melting or directed energy deposition. Ceramic inks are deposited by inkjet-derived print heads in processes for dental restorations and high-temperature structural components. Hydrogel bioinks, which encapsulate living cells, are the basis for bioprinting of tissue constructs and organ models. The ScienceDirect overview of three-dimensional printing materials organizes the material families by process compatibility and property profiles.

Design and Process Considerations

Effective three-dimensional printing requires adapting part geometry and tolerances to the capabilities and constraints of the chosen process. Support structures, required to hold overhanging features during builds in most extrusion and fusion processes, add material and post-processing time. Layer anisotropy, in which mechanical properties differ between the build direction and the in-plane directions, must be accounted for in structural design. Surface finish is inherently stepped at the layer scale, and post-processing operations including sanding, electropolishing, and chemical smoothing are typically required for functional surfaces. The Wiley overview of 3D printing techniques, materials, and applications covers design-for-additive-manufacturing principles including topology optimization and lattice structures.

Applications

Three-dimensional printing has applications in a range of fields, including:

• Aerospace structural and engine components requiring complex internal geometries
• Medical implants, surgical guides, and patient-specific prostheses
• Rapid prototyping and tooling for consumer product development
• Construction of architectural models and experimental building components
• Electronics manufacturing, including conformal antennas and printed circuit substrates