Additive manufacturing

Additive manufacturing (AM) is defined by ASTM as the "process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies, such as traditional machining. Synonyms: additive fabrication, additive processes, additive techniques, additive layer manufacturing, layer manufacturing and freeform fabrication".

The term additive manufacturing describes technologies which can be used anywhere throughout the product life cycle from pre-production (i.e. rapid prototyping) to full scale production (also known as rapid manufacturing) and even for tooling applications or post production customisation.

Examples of AM are fused deposition modeling and laser sintering.

Additive manufacturing (AM) can be defined as “the manufacture of end-use products using additive manufacturing techniques” or more broadly, the application of layer manufacturing techniques to fabricate end use products. Just three inputs are necessary for AM to take place; materials, energy and a CAD model.

AM is a new method of manufacturing, with many of its processes still unproven. Some of the most promising processes are adaptations of well established rapid prototyping methods such as laser sintering (LS). However, due to the immaturity of AM itself, these techniques are still very much in their infancy. Advances in RP technology have brought about the ability to use materials that are appropriate for final manufacture. These advances in material use have brought about the prospects of directly manufacturing finished components, however, many obstacles still need to be overcome before AM can be considered as a realistic manufacturing choice.

Laser processing

Laser based additive manufacturing is accomplished by directing a high power laser at a substrate to create a melt pool. Material is then added to the melt pool. The added material enlarges the melt pool and adds to the part. To create the desired geometry, the laser is rastered across the substrate while material is continuously added. See selective laser sintering, direct metal laser sintering and cladding (metalworking) for more information on methods and applications. For even more information, or to learn more about the applications of lasers in additive manufacturing, a non profit resource is available. The Laser Institute of America (LIA) [ the publisher and secretariat of the ANSI Z136 series of laser safety standards] hosts LAM, the Laser Additive Manufacturing workshop. This workshop teaches the applications of lasers in additive manufacturing and showcases the advantages that come with the use of lasers in cladding, rapid manufacturing and sintering.

Electron beam melting

Electron beam melting (EBM) is a type of additive manufacturing for metal parts. It is often classified as a rapid manufacturing method and is also known as layered fabrication. The technology manufactures parts by melting metal powder layer by layer with an electron beam in a high vacuum. Unlike some metal sintering techniques, the parts are fully dense, void-free, and extremely strong.

Electron beam direct manufacturing (DM) is the first commercially available, large-scale, fully programmable means of achieving near net shape parts.

Aerosol jetting

Aerosol jetting consists of directing a focused stream of atomized particles towards a substrate. The high velocity of the stream causes the particles to impact on the substrate. Thermal post processing is usually required to sinter the particles together to adhere them to the substrate and/or make them conductive.

Inkjet

Inkjet works by propelling individual small droplets of ink towards a substrate. The ink is forced through a small orifice by a variety of means including pressure, heat, and vibration. The liquid droplets impact the substrate and wet. To be used for additive manufacturing, the liquid droplets must change phase to solid upon deposition on the substrate when printing a pattern as a layer. Depending on the deposited material, the phase change could be by heat transfer, UV light or chemical reaction. When jetting particle suspension liquids, the deposited pattern is dried for the liquid vehicle to vaporise and the remaining particles could be sintered for layer solidification.

Semi-solid freeform fabrication

In the experimental semi-solid freeform fabrication process, a semi-solid slurry of metallic alloy is created by heating the alloy at a specific temperature to give the material a paste-like consistency (i.e., neither liquid or solid) in preparation for deposition. A key part of the whole process is to also maintain shear-stress on the material while it is being deposited. This creates the desired "grain" structure within the material as well as eliminating any stratification, porosity, and other defects in the part being made. Currently, however, some amount of surface machining is required to remove unwanted material post-deposition.

Historical development and broadening applications

In the history of manufacturing, and most especially of machining, subtractive methods have often come first. In fact, the term "subtractive manufacturing" is a retronym developed in recent years to distinguish traditional methods from the newer additive manufacturing techniques. Although fabrication has included methods that are essentially "additive" for centuries (such as joining plates, sheets, forgings, and rolled work via riveting, screwing, forge welding, or newer kinds of welding), it did not include the information technology component of model-based definition; and the province of machining (generating exact shapes with high precision) was generally a subtractive affair, from filing and turning through milling and grinding. For example, an encyclopedia article on threading today mentions both additive and subtractive methods as well as various integrations of the two, whereas an article on the same topic 20 years ago would not have contained the words "additive" and "subtractive" and would probably not have mentioned any additive techniques at all (let alone naming and differentiating them via use of those labels).

Additive manufacturing's earliest applications have been on the toolroom end of the manufacturing spectrum. For example, rapid prototyping was one of the earliest additive variants, and its mission was to reduce the lead time and cost of developing prototypes of new parts and devices, which was earlier only done with subtractive toolroom methods (typically slowly and expensively). However, as the years go by and technology continually advances and disseminates into the business world, additive methods are moving ever further into the production end of manufacturing—sometimes even in ways that the pioneers of the techniques didn't foresee. Parts that formerly were the sole province of subtractive methods can now in some cases be made more profitably via additive ones. However, the real integration of the newer additive technologies into commercial production is essentially a matter of complementing subtractive methods rather than displacing them entirely. Predictions for the future of commercial manufacturing, starting from today's already-begun infancy period, are that manufacturing firms will need to be flexible, ever-improving users of all available technologies in order to remain competitive.

It is also predicted by some additive manufacturing advocates that this technological development arc will change the nature of commerce, because end users will be able to do much of their own manufacturing rather than engaging in trade to buy products from other people and corporations.^{[citation needed]}

See also

• 3D printing
• Desktop manufacturing
• Digital fabricator
• Direct digital manufacturing
• Instant manufacturing, also known as "direct manufacturing" or "on-demand manufacturing"
• Solid freeform fabrication
• Additive Manufacturing File Format
• Laser cladding

Bibliography

• Vincent; Earls, Alan R. (February 2011), "Origins: A 3D Vision Spawns Stratasys, Inc. Today's Machining World's new feature "Origins" tells us the stories of how successful technologies, companies and people got their start. This month we interview a pioneer of rapid prototyping technology, Scott Crump, the founder and CEO of Stratasys Inc.", Today's Machining World (Oak Forest, Illinois, USA: Screw Machine World Inc) 7 (1): 24–25, http://www.todaysmachiningworld.com/origins-a-3d-vision-spawns-stratasys-inc/. 
• Albert, Mark [Editor in Chief] (2011-01-17), "Subtractive plus additive equals more than ( − + + = > ): subtractive and additive processes can be combined to develop innovative manufacturing methods that are superior to conventional methods ['Mark: My Word' column—Editor's Commentary"], Modern Machine Shop (Cincinnati, Ohio, USA: Gardner Publications Inc) 83 (9): 14, http://www.mmsonline.com/columns/subtractive-plus-additive-equals-more-than.