## 2 The Basics of Additive Manufacturing
### Materials Used in the Printing Processes  
3D printing (3 DP) emerges as one of the most creative approaches to produce a broad spectrum of components across various industries, including automotive, aerospace, medical, construction, electronics, and food industries. To fabricate fully functional objects using 3 DP technology, the process involves utilizing high-quality materials from several categories, such as metals, ceramics, composites, polymers, and combinations thereof in hybrid forms. This section classifies the printing materials used in both extrusion-based 3D printing (E3 DP) and selective laser sintering (SLS) into three main categories. The first category encompasses neat polymers, which refer to virgin or recycled polymers printed without additional materials. These often require fine-tuning of processing and printing parameters due to their high melting points and viscoelastic properties, but they offer excellent thermal stability and mechanical strength. The second category, blends, consists of combinations of polymers or polymers with additives. Blends can overcome limitations like anisotropic properties found in neat polymers, offering enhanced dimensional stability, thermal resilience, and unique mechanical characteristics. They also enable the integration of recycled materials, contributing to sustainability. Additives such as thermoplastic elastomers (e.g., TPU) and compatibilizers (e.g., maleic anhydride grafts) further improve miscibility and tailor performance, diversifying the applications for these materials. The final category is composites, which are composed of a distributive phase within a continuous polymer matrix. By incorporating fibers or fillers, composites yield superior mechanical properties, making them ideal for structural and load-bearing applications in various industries [17]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**No** & **Process** & **Definition According to ASTM 52900:2021** \\ \hline
1. & Binder jetting (BJT) & Process in which a liquid bonding agent is selectively deposited to join powder materials. \\
2. & Direct energy deposition (DED) & Process in which focused thermal energy is used to fuse materials by melting as they are being deposited. \\
3. & Material extrusion (MEX) & Process in which material is selectively dispensed through a nozzle or orifice. \\
4. & Material jetting (MJT) & Process in which droplets of feedstock material are selectively deposited. \\
5. & Powder bed fusion (PBF) & Process in which thermal energy selectively fuses regions of a powder bed. \\
6. & Sheet lamination (SHL) & Process in which sheets of material are bonded to form a part. \\
7. & Vat photopolymerization (VPP) & Process in which liquid photopolymer in a vat is selectively cured by light-activated polymerization. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Definitions of 3 DP technologies according to ASTM 52900:2021. Additive manufacturing (AM) encompasses not only core materials, which serve as the primary substances for crafting objects, but also support materials. Core materials, often referred to as build or primary materials, form the essential part of the printed item and shape its fundamental traits such as strength, durability, and function. For example, in fused filament fabrication (FFF), the core material typically involves a thermoplastic filament that is melted and laid down layer by layer to create the object; however, nowadays FFF can print not only thermoplastic filaments but also metal composites and ceramic composites. In powder bed fusion (PBF), the core materials are metal or polymer powders that are selectively bonded using heat or a laser. Support materials, on the other hand, are used temporarily to provide stability and prevent warping during the printing of designs with overhangs or complex details. These assisting materials can differ from the core materials in properties, being water-soluble or easily breakable, to facilitate their removal after printing.