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 components such as turbine blades and drive shafts. The laser beams form a melt pool on the metallic surface through which the power is supplied. The laser beam is focused on the spray of powdered metal to scan the substrate in order to deposit the metal A which is formed by the melted powder that is bonded with the substrate. The width of the deposit is found between 0.6 and 2.4 mm, and the layer thickness ranges between 0.2 and 0.8 mm (Eisenbarth 2019). Nickel alloys, titanium, cobalt and copper are the most commonly used materials in this technique.
Figure 1.8. Direct metal deposition process (Mohamed 2017). For a color version of this figure, see www.iste.co.uk/kumar/materials.zip
1.4. Materials used in AM technology
AM is based on a novel resource cumulative philosophy. The materials play a predominant role in AM, which are mainly considered for engineered operational applications. The evolution of AM has a definite class of raw materials that are concomitant with certain AM processes and solicitations. The selection requirements for AM is indispensable for suitable materials to return the feedstock, which is responsible for the unambiguous AM process with appropriate dispensation
