## 5 AM Processes
### Fused Deposition Modeling (FDM)  
Fused Deposition Modeling (FDM), also referred to as Fused Filament Fabrication (FFF), is a solid-based AM technique. Developed in 1989, it is the most commonly used method in AM [36]. The FDM system typically includes a building platform, filament spools, and a heated extrusion nozzle, as shown in Figure 6d. After being passed from the filament spool to the heated extrusion nozzle, the thermoplastic filament melts and becomes semi-liquid. The melted material is then deposited layer by layer onto the building platform or previous layers, where it fuses and solidifies. This procedure is repeated until the part is constructed. Polymeric materials with low melting points, such as Polyethylene Terephthalate Glycol (PETG), Acrylonitrile Butadiene Styrene (ABS), polyamide (PA) which is also known as nylon, Polycarbonate (PC), thermoplastic polyurethane (TPU), Acrylonitrile Styrene Acrylate (ASA), and Polylactic Acid (PLA), are frequently used as filament basis materials in the FDM technique. Fiber-reinforced filaments have been created recently in order to enhance the filaments' mechanical properties [17].  
FDM printing's restriction to thermoplastic polymers with appropriate melt viscosities is one of its disadvantages. The viscosity needs to be sufficiently low to allow for extrusion while still being sufficiently high to support the structure. Additionally, issues such as nozzle clogging can occur, particularly with fiber-reinforced filaments. Furthermore, products manufactured using the FDM technique often display anisotropic properties. Despite these limitations, FDM printing offers significant advantages, like high speed, low cost, and ease of use. An additional advantage of FDM printing is the capability to deposit different materials simultaneously by using several extrusion nozzles loaded with different filaments, which makes it possible to produce parts with a variety of characteristics [38].  
Table 1 summarizes the categories, materials, advantages, and disadvantages of the most prominent AM techniques commonly used in crash box manufacturing.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Methods** & **Category** & **Materials Used** & **Advantages** & \multicolumn{2}{c}{**Disadvantages**} \\ \hline SLA & Liquid-based & Photoresin liquids & High resolution & \(\bullet\) & Limited materials \\  & & & High resolution & \(\bullet\) & High cost \\  & & & & \(\bullet\) & Low printing speed \\  & & & & \(\bullet\) & Toxicity \\ \hline MJT & Liquid-based & Photoresin liquids & \(\bullet\) & Multilateral printing & \(\bullet\) & Toxicity \\  & & & \(\bullet\) & Low cost & \(\bullet\) & Product has poor \\  & & & & \(\bullet\) & Scalability in production & mechanical and thermal \\  & & & & & properties \\ \hline SLM & Powder-based & Metal alloys & \(\bullet\) & High resolution & \(\bullet\) & Low printing speed \\  & & & & \(\bullet\) & Support structure \\ \hline FDM & Solid-based & \(\bullet\) & Polymers & \(\bullet\) & Multilateral printing & \(\bullet\) \\  & & & Fiber-reinforced & \(\bullet\) & High printing speed \\  & & & polymers & \(\bullet\) & Low cost & \\ \hline \hline \end{tabular}
\end{table}
Table 1: AM techniques.  
Figure 6: Illustration of standard AM configurations: (**a**) SLA; (**b**) MJT; (**c**) SLM; (**d**) FDM [39].