Additive Manufacturing

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Additive Manufacturing

Additive manufacturing (AM), also referred to as 3D printing or rapid prototyping, is “a process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies.” This definition is broadly applicable to all classes of materials including metals, ceramics, polymers, composites, and natural materials. Current AM technology is widely used to print polymers, metals and ceramics but is limited to other commonly used materials. By far polymer remains one of the most versatile materials. The use of polymers in 3D printing encompasses thermoplastics, thermosets, elastomers, hydrogels, functional polymers, polymer blends, composites, and biological systems.

Additive manufacturing processes take the information from a computer-aided design (CAD) file and convert it to a stereolithography (STL) file. CAD, computer-aided manufacturing (CAM), and computer numerical control (CNC), these three technologies are combined to make the manufacturing possible. In this process, the drawing made in the CAD software is approximated by triangles and sliced containing the information of each layer that is going to be printed. Different additive manufacturing processes have been developed to build and consolidate layers in different ways.* Some processes use thermal energy from laser or electron beams, which is directed via optics to melt or sinter metal or plastic powder together. Other processes use inkjet-type printing heads to accurately spray binder or solvent onto powdered ceramic or polymer. Those processes include stereolithography (SL), Polyjet, fused deposition modeling (FDM), laminated object manufacturing (LOM), 3D printing (3DP), Prometal, selective laser sintering (SLS), laminated engineered net shaping (LENS), and electron beam melting (EBM). The liquid-and powder-based processes seem more promising than solid-based processes of which LOM is most commonly used. It was not until 2004 that EBM, Prometal, LENS, and Polyjet became available.

Additive manufacturing processes. Reprinted from Ref 1.*

Stereolithography (SL), developed by 3D Systems, Inc., was the first and is most widely used process of rapid prototyping, so, in the past the two terms were used synonymously. This is a liquid-based process that consists in the curing or solidification of a photosensitive polymer when an ultraviolet laser makes contact with the resin.

3D printing (3DP) process is a MIT-licensed process in which water-based liquid binder is supplied in a jet onto a starch-based powder to print the data from a CAD drawing. The powder particles lie in a powder bed and they are glued together when the binder is jetted. This process is called 3DP because of the similarity with the inkjet printing process that is similar to two-dimensional printing. This process can handle a high variety of polymers.

Laminated Object Manufacturing (LOM) is a process that combines additive and subtractive techniques to build a part layer by layer. In this process the materials come in sheet form. The layers are bonded together by applying pressure and heat, in addition to using a thermal adhesive coating. A carbon dioxide laser cuts the material to the shape of each layer given the information of the 3D model from the CAD and STL file.

Wong, Kaufui V. "A review of additive manufacturing." ISRN Mechanical Engineering 2012.


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