The computed CAD design is then formatted into an STL (stereolithographic) file format. The STL file displays the peripherally closed external surface of the CAD geometry and performs the slice calculation using a slicing software, and then it is sent to the AM machine which is verified for its build orientation and position (Brandsmeier 2017). The construction of the material is automatically carried out in a layered fashion by the machine (3D printer) without any human supervision. The 3D printer needs manpower to only monitor the availability of raw materials and to check for any run-time errors. After completing the product, the interaction of the part with the machine is cut down by adjusting the machine temperature and then detached. In post-processing, the part is cleaned before use and treated mechanically for surface finish and the required texture (Scheck 2016).
Figure 1.2. Additive manufacturing procedure. For a color version of this figure, see www.iste.co.uk/kumar/materials.zip
1.3. Classification of AM technology
The diversity of materials has convoluted the 3D structures being fabricated with a distinct class of functional time and assembly. AM technology emerged as a great boon over conventional methodologies for creating complex geometries (Ngo 2018). The prominent process of AM is classified into the following seven types:
– laser beam melting;
– electron beam melting;
– selective laser melting;
– direct metal laser sintering;
– laser metal fusion;
– direct metal deposition.
1.3.1. Laser beam melting
The laser beam melting (LBM) technology uses a laser beam to fuse the succeeding layers of metal powders, which are suitably used in thin-walled, small-scale structures to build a 3D part from the powder bed. In this method, a CAD model is first converted into an STL file and then sliced into a 2D element; at each layer, the powder bed is sintered by distributing the layers of powder throughout the building platform using a laser beam. The above-described process is simultaneous and stops after the completion of the product. This method is suitable for metals, polymers and ceramics (Bayerlein 2018). LBM produces strong parts due to its reduced porosity and controlled crystal structure.
Figure 1.3. Laser beam melting technology (Anderl 2014). For a color version of this figure, see www.iste.co.uk/kumar/materials.zip
1.3.2. Electron beam melting
In electron beam melting (EBM), the raw material is fused together by heating an electron beam under vacuum, which are used to build metallic components, especially in aerospace industries. In this method, a beam of electron acts as a heat transmission source that has a higher melting capacity, as well as productivity, which are controlled by electromagnetic coils, thereby allowing the melting of metals into a solid geometry. The EBM machine obtains input data from a CAD model and builds the part under vacuum (Zhao 2016). It is used to manufacture standard metal parts such as fixtures, prototypes and support structures in a slow and cost-effective process.
Figure 1.4. Electron beam melting (Mandil, 2016). For a color version of this figure, see www.iste.co.uk/kumar/materials.zip
1.3.3. Selective laser melting
Selective laser melting (SLM) uses a high-power density laser to melt the raw material and fuse it together with metallic powders, which is mainly used for low-volume materials. In this technique, various materials such as glass, ceramics and plastics are used. The laser beam will heat the particles at appropriate positions on a bed of metallic powder until it is completely smelted. The AM machine will consecutively increase the melted layers over the metal bed until it reaches the expected design (Jürgen 2017). Its common applications can be found in aerospace industries, automobile industries and medical industry to overcome the demand for human organs.
Figure 1.5. Selective laser melting (Mumtaz 2008). For a color version of this figure, see www.iste.co.uk/kumar/materials.zip
1.3.4. Direct metal laser sintering
Direct metal laser sintering (DMLS) is similar to selective laser melting as the intent is to use a laser with high power density to create the geometry that is best suited for manufacturing metals and metal alloys. DMLS uses a variety of alloys for allowing efficient hardware to design complex geometries. The functional prototypes made using this method have greater strength and ultimate durability. DMLS is most suitable for fabricating complex oil and inert gas components. Metal alloys such as aluminum alloys, stainless steel and niche alloys are widely used (Rizzuti 2019). DMLS materials are completely dense, highly robust and have greater resistance to corrosion, which can be auxiliary treated with heat, sterilization and coating.
Figure 1.6. Direct metal laser sintering process (Marrey 2019). For a color version of this figure, see www.iste.co.uk/kumar/materials.zip
1.3.5. Laser metal fusion
Laser metal fusion (LMF) produces a 3D part from a powder bed by selectively melting the powder and fusing it in a layer-by-layer fashion onto the fundamental substrate used exclusively in medical implants for the construction of ultra-light hollow components. In this technique, the component is constructed on a substrate plate that is coated with a layer of metal under an inert gas atmosphere (Garmendia 2019). The metallic layers are increased in the same continuous process until the part is completely constructed, individually 20–100 microns are identified between each layer. The amount of powder added at each layer can be precisely controlled by the distinguished powder delivery system. The finalized product undergoes laser polishing during its post-processing.
Figure 1.7. Laser metal fusion method (Peyre 2008). For a color version of this figure, see www.iste.co.uk/kumar/materials.zip
1.3.6. Direct metal deposition
Direct metal deposition (DMD) differs from other types of powder beds as it involves a nozzle feeding the raw materials that are extruded as powdered metal into the laser beam and used for producing