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Rapid Prototyping Glossary

3-Dimensional Printing (3DP): A rapid prototyping process developed at the Massachusetts Institute of Technology (MIT). Layers of powder are bonded by inkjet to form a part. The term is also used generically as synonym for rapid prototyping.

3D printer / 3D printing: Refers generally to the low-cost segment of the rapid prototyping machine market. The output of these systems is typically considered adequate for concept and appearance modeling, but may lack the accuracy or other attributes of more costly systems. This terminology is used extensively in the Wohlers Report, but others may not draw as fine a distinction.

Absolute Accuracy: Defined as the difference between an intended final dimension and the actual dimension as determined by a physical measurement of the part. In addition to those for linear dimensions, there are accuracy specifications for such features as hole sizes and flatness.

Adaptive Slicing: The use of variable layer thickness in an additive fabrication process, generally thinner layers being used where part detail is greatest.

Additive Fabrication: Fabrication of a part by adding materials to a substrate or previously formed portions of a part. The most common additive fabrication methods utilize a layered approach, but other geometries are possible. The term is also used generically as a synonym for rapid prototyping.

Advanced Digital Manufacturing (ADM): 3D Systems' trade name for direct manufacturing or direct fabrication. Often used in conjunction with the company's OptoForm technology.

Anisotropic: Refers to the fact that parts may have different physical properties depending on which direction measurements are made, and such differences can also arise if the exact same part is made in a different way. This can happen if the building orientation of the part in the machine is changed, and also from the sequence in which the part's elements are fabricated.

Ballistic Particle Manufacturing (BPM): A rapid prototyping process which deposits materials by means of inkjet technology. At one time the term was used to refer to a specific company's technology, BPM, Inc., now defunct, but prior to that it was an early generic term for inkjet-based RP. The term is not often used at present.

Bridge Tooling: Tooling which is typically capable of producing quantities of several tens to several hundreds of parts. That is to say, it "bridges" the quantity between very low volume prototype tooling and full production tooling. In some cases bridge tooling may offer sufficient volume to meet production requirements.

Brown Part: A part which has been sintered or had other secondary operations performed on it to bring it from the loosely-bonded, as-formed "green" state. Parts in the brown state are generally dimensionally stable, but are often porous and usually must be infiltrated with another material before use.

Computer Numerical Control (CNC): Refers to a machine tool which is operated under automatic control, as opposed to manually by an operator.

Computer-Aided Design (CAD): Also sometimes called computer-aided drafting, is a computer program which implements the functions of geometric design, drafting and documentation.

Computer-Aided Engineering (CAE): A computer program which automates one or more engineering analysis functions to determine the mechanical, thermal, magnetic or other characteristics or state of a system. CAE programs may use a geometry definition from a CAD program as a starting point, and usually utilize some form of finite element analysis (FEA) as the means to perform the analysis.

Computer-Aided Manufacturing (CAM): A computer program that generates tool paths or other manufacturing data to fabricate tooling, usually by subtractive means. CAM programs may use a geometry definition from a CAD program as a starting point.

Concept Model / Conceptual Model: A part intended primarily for form or appearance study, but which typically cannot be used to either check fit to other parts, or provide functionality of the final part in an application.

Conformal Cooling: Cooling lines in an injection molding tool that closely follow the geometry of the part to be produced.

Desktop Manufacturing (DTM): An early synonym for rapid prototyping, but no longer in current usage. DTM Corp., now incorporated into 3D Systems, was named after this terminology. Use of DTM as a company name became more common usage than the prior technical definition itself.

Direct (Fabrication) Processes: Generally refers to tooling which is made directly by a rapid prototyping system, as opposed to using the RP part as a pattern in a secondary process.

Direct AIM tooling: 3D Systems' trade name for a process of producing injection-mold tooling directly by stereolithography. AIM stands for ACES Injection Molding, where ACES stands for Accurate Clear Epoxy Solid, another 3D trade name.

Direct Composite Manufacturing: 3D Systems' trade name for OptoForm technology, a stereolithography process which utilizes paste-like photopolymers to fabricate useable parts.

Direct Manufacturing: A synonym for rapid manufacturing. It refers to parts made directly for end-use by an additive rapid prototyping process.

Direct Metal Deposition (DMD):A rapid laser powder forming process commercialized by POM Group and based on research done at the University of Michigan.

Directed Metal Deposition System (DMDS): Optomec's trade name for the LENS ® (Reg. trademark of Sandia National Labs. and Sandia Corp.) process.

Direct Shell Production Casting (DSPC): Soligen is the exclusive supplier for this specialized version of MIT's three dimensional printing process (3DP). It is used exclusively for investment casting applications.

Directed Light Fabrication (DLF): A laser powder forming rapid prototyping process developed by Los Alamos National Laboratory.

Dots Per Inch (DPI): A measure of the resolution of a printer. The number of discrete and distinct printed marks that an instrument is capable of producing in a linear inch. Also sometimes used in RP to describe the ability of an RP system to produce discrete voxels in the X-Y axial directions.

Electron Beam Melting (EBM): The Electron Beam Melting (EBM) process from Arcam is a powder-based process having a lot in common with selective laser sintering, but replaces the laser with a scanned electron beam to produce fully-dense metal parts.

Electronic Marketplace: A virtual market for buyers and sellers implemented through the Internet or World Wide Web. Also known as a web exchange.

Final Machining: A secondary operation in which parts formed by a rapid prototyping method are brought to acceptable final finishes and tolerances typically by subtractive CNC technology.

Finish (Part Finish): A qualitative term for the appearance of a part. For example, technologies based on powders have a sandy or diffuse finish; some inkjet technologies produce a smooth finish due to use of extremely thin layers; sheet-based methods might be considered poorer in finish because stairstepping is more pronounced.

Freeform Fabrication (FFF): A synonym for rapid prototyping. The term is more precise and wider in scope, and somewhat favored by the academic community. One variant is freeform manufacturing (FFM), but a more common one is solid freeform fabrication (SFF).

Fused Deposition Modeling (FDM): A thermoplastic extrusion-based rapid prototyping technology provided by Stratasys.

Fused Deposition of Ceramics (FDC): Fused deposition modeling using a composite material of thermoplastic or other binder containing ceramic particles or fibers.

Green Part: A part that has been formed by a rapid prototyping process, but is in a loosely-bonded state. For example, metal or ceramic parts formed by some selective laser sintering systems are in a "green" state when removed from the machine. They are then sintered by a secondary operation to a "brown" state.

Indirect (Fabrication) Processes: Generally refers to tooling which is made by using an RP-generated part as a pattern for a secondary process as opposed to directly fabricating a tool using the RP process itself.

Initial Graphic Exchange Specification (IGES): A standard neutral format for the exchange of 2D and 3D CAD data. STEP is a follow-on to IGES and stands for Standard for the Exchange of Product Model Data.

Laminated Object Manufacturing (LOM): Helisys, now defunct and succeeded by Cubic Technologies, was the first producer but also several other manufacturers provide this technology. :Layers of paper or other materials are cut and bonded to form a part.

Laser Additive Manufacturing (LAM): A laser powder forming rapid prototyping process developed by AeroMet Corporation. It's mainly aimed at producing large parts from reactive materials such as titanium for aerospace applications.

Laser Engineered Net-Shaping (TM) (LENS ®): A rapid prototyping process which deposits metal powder into a pool of molten metal or other build material formed by a focused laser beam. There are several variants either commercially available or under development. LENS ® was developed by Sandia National Laboratories and commercialized by Optomec. It can also be used for repairing and modifying existing parts and tools. (LENS ® and Laser Engineered Net-Shaping (TM) are registered trademarks of Sandia National Labs. and Sandia Corp.)

Liquid Metal Jet Printing (LMJP): Similar to inkjet printing where individual molten droplets are controlled and printed to specific locations.

Mass Customization: A process whereby small lots of individualized parts or products are produced. The opposite of mass production whereby large numbers of identical parts or products are produced.

Mesoscopic Integrated Conformal Electronics (MICE): This DARPA program is aimed at simplifying the manufacture of electronic devices and systems, and providing greater flexibility than is possible using existing technologies. In size, mesoscale devices fall between integrated circuits and surface-mount components.

Minimum Feature Size: Refers to the smallest detail of a part that can faithfully be reproduced. Mathematical definitions are usually based on a minimum curvature as a limit, but anecdotal values based on experience are more commonly utilized.

ModelMaker: This is an inkjet RP method produced by Solidscape (formerly Sanders Prototypes), and the related company, Sanders International. It produces the highest accuracy and resolution of all RP methods, but is slow and has limited material choices.

MultiJet Modeling: This is an inkjet RP method produced by 3D Systems, Inc. It uses a wide area head and is most often used for generating quick concept models. The materials available are wax-like plastics and accuracy is lower than that available from stereolithography.

Paper Lamination Technology (PLT): A variant on laminated object manufacturing RP technology from Kira Corp. of Japan.

Pattern: An object or part which possesses the mechanical geometry of a final object or part, but which may not possess the desired mechanical, thermal or other attributes of the final parts. Patterns are used in secondary processes to form tools to make parts for end-uses.

Photopolymer: Material systems which change from a liquid to a solid state upon application of light (actinic) radiation. Light sources can be a laser or lamp, but related radiation-curable materials may be made solid by application of microwave or heat-based radiation sources. Photopolymers are typically complex mixtures of compounds rather than consisting of a single component.

Precision: See absolute accuracy.

ProMetal: An application of MIT's Three Dimensional Printing Process to the fabrication of injection molds. Steel powder layers are bonded by photopolymer selectively applied by a wide area inkjet head.

QuickCast: 3D Systems' trade name for a stereolithography build style used to make investment casting patterns.

Rapid Manufacturing: Refers to the process of fabricating parts directly for end-use from a rapid prototyping machine. A synonym is direct manufacturing.

Rapid Prototyping: Computer-controlled additive fabrication. Commonly used synonyms for RP are: 3-Dimensional Printing, additive fabrication, freeform fabrication, solid freeform fabrication, stereolithography. Note that most of these synonyms are imprecise.

Rapid Tooling: Most often refers to the process of fabricating tools from a rapid prototyping process. Rapid tooling may utilize direct or indirect methods: In direct methods, the part fabricated by the RP machine itself is used as the tool. In indirect methods, the part fabricated by the RP machine is used as a pattern in a secondary process. The resulting part from the secondary process is then used as the tool. In recent years, the term rapid tooling has been borrowed by practitioners of industry-standard methods such as subtractive CNC to refer to the ability to streamline these processes to compete with additive technologies.

Resolution: Refers to the minimum increment in dimensions that a system achieve. It's one of the main determining factors for finish, appearance and accuracy, but certainly not the only one.

Reverse Engineering: The process of measuring an existing part to create a geometric CAD data definition of the part. In common non-technical usage, reverse engineering may also refer to measuring or analyzing a part or a product for the purpose of copying it.

Secondary operations: Manual or machine-based operations which must be carried out on a part fabricated by a rapid prototyping system before use. Secondary operations may include, post curing, support-removal, sanding, machining, etc.

Secondary process: Any one of a large number of processes such as rubber molding. Sprayform, EcoTool, etc., that utilize a rapid prototyping-fabricated part as pattern to create a final tool or part.

Selective laser sintering (SLS): A rapid prototyping technology in which powders are fused laser fused layerwise by a laser. The technology produces accurate parts and models in engineering polymers, metals and polymer-coated sand for casting applications. Speed is similar to stereolithography, but material selection is wider.

Solid freeform fabrication (SFF): A synonym for rapid prototyping. The term is more precise and wider in scope, and somewhat favored by the academic community. A variant is freeform fabrication (FFF).

Solid ground curing (SGC): This photopolymer-based technology was provided by Cubital. The company has been dissolved, but the process may still be available from a very few companies. A xerographically-generated mask is used to cure an entire layer of photopolymer at one time. It offers good accuracy coupled with high throughput, but is considered quite expensive.

Stairstepping: A type of inaccuracy, as well as a visual appearance artifact It refers to the stepped appearance of the edges of a part, a consequence of additive fabricating a part in layers of necesarily finite thickness.

STEP: A follow-on to the IGES neutral file exchange format. The acronym stands for Standard for the Exchange of Product Model Data.

Stereolithography (SL) (SLA): A rapid prototyping process that fabricates a part layerwise by hardening a photopolymer with a guided laser beam. Stereolithography is frequently used as a general term for "rapid prototyping," but this is neither precise nor correct.

STL: A file format used in RP to define the geometry of the part to be made. STL files are created by CAD programs by translating their native or neutral files into the STL format. The STL file defines the coordinates of numerous triangular facets that approximate the shape of an object or part.

Subtractive Machining: The fabrication of a part by removing material from a stock shape of material. The stock shape may be a prismatic solid, cylinder, plate, etc. The removal of material may by cutting, turning, electro-discharge or other means. Common machinery such as millers, lathes and drills are subtractive tools.

Support Structure:Many rapid prototyping machines need a means to hold in place unsupported geometries during fabrication, such as the top of a part in the shape of the letter "T." These supports are usually calculated and added to the part by the system's software and may be formed of the same material as the part, or from a different material entirely. Support structures are either mechanically removed or dissolved away in secondary operations before the part can be used.

Virtual Prototyping: Computer-based prototyping without recourse to a physical part or object.

Voxel: The three dimensional equivalent of a pixel. A pixel is a "picture element," and a voxel is a "volume element." A voxel may also be defined as the minimum volume that a rapid prototyping system can fabricate.

Web Exchange: A virtual market for buyers and sellers implemented through the Internet or World Wide Web. Also known as an electronic marketplace.