Additive fabrication can be defined as an assortment of techniques of making solid objects through the chronological delivery of material and/or energy to specific points in the space for production of that solid. Additive fabrication is also known as solid freeform fabrication, layered manufacturing, rapid manufacturing, and rapid prototyping.
Techniques: Additive fabrication is carried out using a number of techniques. Let some of them be studied in detail.
‘Electron Beam Melting’: EBM (Electronic Beam Melting) can be described as the ‘rapid prototyping’ for metals. It is better known as ‘rapid manufacturing’ method. The parts are manufactured by having the metal powder melted layer by layer through a beam of electron in high vacuum. The parts produced acquire strength, solidity, and are void-free as well. The electrons have a very high speed; around 5 to 8 times the light speed. The bombardment of these electrons takes place on the work material’s surface. This generates heat which is enough for melting the part’s surface and causing it to vaporize locally. Vacuum is required for the operation of EBM. This means that the size of work piece is directly proportional to vacuum used. This technique works on composites, ceramics, non-metals, and as stated above, metals.
Fused Deposition Modeling: Fused Deposition Modeling (FDM) can be described as a kind of rapid manufacturing (RP) or rapid prototyping technology which is generally used in engineering design. S.Scott Crump had founded this technology in 1980s. It caught the commercial market in 1990. Like most of the RP processes, the principle of working of FDM is the ‘additive principle’. It states that the material has to be laid down in layers. The metal wire or plastic filament is then unwound and material is supplied through it to the extrusion nozzle that can turn off and on the flow.
The nozzle’ then is heated for melting the material. It could be moved in vertical and horizontal directions with the help of a mechanism which is numerically controlled. This numerical control is obtained through ‘Computer Aided Design’ software package. Like stereo lithography, the building of the model takes place from layers. This happens because the material starts hardening after getting extruded from nozzle.
Numerous materials are offered with diverse trade-offs between temperature and strength. One can use the FDM technology with polycaprolactone, polycarbonates, polyphenylsulfones, and Acrylonitrile butadiene styrene (abs). Temporary supports can be made by using a ‘water-soluble’ material. These supports are needed when manufacturing is still going on. The commercial applications include making prototypes of servo or stepper motors.
‘Selective Laser Sintering’: Selective Laser Sintering can be defined as an additive type of rapid manufacturing wherein a ‘high power laser’ (like carbon dioxide laser) is used for fusing tiny particles of ceramic, metal, or plastic powders into mass representing the desired three-dimensional object. In comparison to other methods of rapid manufacturing, ‘selective laser sintering’ has the capacity of producing parts from several powder materials available. They include polymers (polystyrene and nylon), metals (composites, alloy mixtures, titanium, steel), and not to forget- green sand. This physical process could be liquid-phase sintering, partial melting, or full melting.