What Is Layered Manufacturing?

Layered manufacturing is a family of fabrication processes that build three-dimensional objects by depositing, fusing, or curing successive thin cross-sections of material derived from a digital model, as opposed to removing material from a solid billet (subtractive manufacturing) or reshaping it under pressure (formative manufacturing). The approach is codified in ISO/ASTM 52900, the international standard for additive manufacturing terminology, which defines the process as "joining materials to make parts from 3D model data, usually layer upon layer." Layered manufacturing is used interchangeably with additive manufacturing and, in popular contexts, with 3D printing, though the latter term technically refers to a subset of processes involving an inkjet-style printhead.

The method's primary advantage is the ability to produce geometries, such as internal lattice structures, conformal cooling channels, and hollow forms, that are inaccessible or economically impractical by conventional machining. A digital model is the only required intermediate representation: the same file can drive production of one part or a thousand without tooling or fixturing changes. This characteristic makes layered manufacturing particularly valuable for low-volume, high-complexity components in aerospace, medical implants, and tooling.

Process Categories and Material Systems

ISO/ASTM 52900 defines seven process categories, distinguished by how material is consolidated layer by layer. Powder bed fusion processes, including selective laser sintering (SLS) and selective laser melting (SLM), spread a thin layer of powder across a build platform and fuse it selectively with a laser beam; this category covers both polymers and metals and is widely used for structural components. Directed energy deposition (DED) processes, such as laser metal deposition and wire-arc additive manufacturing, feed metal powder or wire into a focused energy beam and deposit material directly onto a substrate or partially built part, enabling repair of existing components as well as net-shape fabrication.

Material extrusion processes, the most accessible category and exemplified by fused deposition modeling (FDM), push a thermoplastic filament through a heated nozzle and trace each layer as a continuous tool path. Vat photopolymerization processes, including stereolithography (SLA) and digital light processing (DLP), cure liquid resin with a controlled light source, achieving the highest dimensional resolution of any layered manufacturing category. Binder jetting, material jetting, and sheet lamination round out the classification. Each category carries its own tradeoffs in resolution, surface finish, material availability, build rate, and post-processing requirements.

Slicing and Computational Geometry

The bridge between a digital model and a physical part is the slicing step, in which software intersects the model with a series of horizontal planes, each at height z_i, to produce the two-dimensional contours that define each layer. The slicer must handle mesh repair, offset path generation for wall thickness, support structure synthesis for overhanging features, and infill pattern selection. These operations are problems in computational geometry: Boolean set operations on polygonal regions, offset polygon computation using Minkowski sums, and topological analysis of the model to identify connected components requiring support.

Path planning within each layer determines the order in which the deposition tool traverses contours and fill regions, affecting residual stress, surface quality, and build time. NIST's work on additive manufacturing standards and benchmarks includes reference artifacts designed to expose the dimensional accuracy limitations of each process category, providing the metrology basis for characterizing how slicer and path planner choices propagate into geometric error.

Quality and Process Control

Dimensional accuracy, surface roughness, and mechanical property uniformity are governed by process parameters including layer thickness, energy input, scan speed, and temperature. In-process monitoring using optical coherence tomography, infrared thermography, and acoustic emission sensors provides real-time feedback on melt pool stability and layer uniformity, enabling defect detection before the build completes. Loughborough University's Additive Manufacturing Research Group documents the technical basis for each process category and the measurement challenges specific to powder bed fusion, DED, and material extrusion.

Applications

Layered manufacturing is applied across industries where geometry complexity, customization, or short production runs justify the process, including:

• Aerospace structural and ducting components in titanium and nickel superalloys
• Patient-specific orthopedic implants and dental prosthetics
• Tooling inserts with conformal cooling channels for injection molding
• Electronics enclosures and antenna structures with integrated geometric features
• Rapid prototyping and functional testing at the early product development stage