## 9 Conclusions  
Crash boxes are critical components for vehicle safety, and the potential of AM to enhance their design and performance has gained significant attention in recent years. AM has unlocked new possibilities for optimizing the crash box design. This review explored key advancements in AM-enabled crash boxes, focusing on innovations in geometric design, material behavior, and manufacturing techniques. AM has demonstrated exceptional capabilities in producing complex structures such as multi-cell tubular, origami-inspired, lattice, and bio-inspired designs that are challenging or impossible to fabricate using traditional methods. A comparative analysis of \(SEA\) values highlighted in recent studies and summarized in Figure 12 shows that bio-inspired structures achieve the highest mean \(SEA\) value of 21.51 J/g, indicating superior crash-worthiness, while lattice structures record the lowest value of 11.61 J/g. Tubular and origami-inspired designs exhibit intermediate performance, with mean \(SEA\) values of 16.29 J/g and 15.29 J/g, respectively. The standard deviation is highest for bio-inspired structures at 23.01 J/g compared to lattice structures at 12.67 J/g and origami-inspired structures at 12.46 J/g, highlighting that the performance of bio-inspired designs can vary \begin{table}
\begin{tabular}{c c c c} \hline
**AM Technique** & **Material** & **Geometry** & **Reference** \\ \hline  & PLA & & \\  & PETG & & \\  & ABS & Lattice & [83] \\  & ASA & & \\  & PA Carbon Fiber & & \\  & PLA & Lattice & [84] \\  & PETG & Origami Tube & [85] \\  & PLA & Multi-Cell Tube & [86] \\  & PA & & \\  & PA Carbon Fiber & Tube & [91] \\  & PA Glass Fiber & & \\  & PA Carbon Fiber & Multi-Cell Tube & [92] \\  & PLA & Auxetic Lattice & \\  & PLA/TPU & Non-Auxetic Lattice & [99] \\  & PLA/PA & & \\  & PLA/Ramie Yarn Fiber & Tube & [42] \\  & PLA & Tube & [117] \\  & PLA & Lattice & [118] \\  & PA Carbon Fiber & Lattice & [119] \\  & PLA & Bio-Inspired Lattice & [120] \\ \hline  & Aluminum/PLA Carbon Fiber & Multi-Cell Tube & [126] \\  & Aluminum/PLA & Multi-Cell Tube & [127] \\  & Aluminum/PA & Multi-Cell Tube & [128] \\  & Aluminum Al1060/ & & \\  & Aluminum AlSi10 Mg & Tube/Gradient Lattice & [130] \\ Hybrid & Aluminum Al6063–T5 & & \\ Manufacturing & /Aluminum AlSi10 Mg & & \\ Technique & Aluminum/Foam & & \\  & Aluminum/PLA & Multi-Cell Tube/Foam & [131] \\  & Aluminum/Foam/PLA & & \\  & PA/Foam & Lattice/Foam & [132] \\  & Stainless Steel 316L/PLA & Spiral Tube/Foam & [133] \\ \hline \end{tabular}
\end{table} 
Table 2: _Cont._widely depending on the specific geometric features employed, while tubular structures demonstrate the most consistent performance at 8.75 J/g. These findings emphasize the significant potential of additively manufactured bio-inspired geometries for enhancing crash energy absorption. Remarkably, the limited number of studies on origami-inspired crash boxes underscores the need for further research to fully explore their energy absorption potential. Future work should focus on combining computational modeling with experimental validation and applying parametric design optimization techniques to refine origami-inspired geometries for enhanced energy absorption efficiency. Material selection plays a pivotal role in the performance of additively manufactured crash boxes, with polymers, fiber-reinforced polymers, and metals each offering distinct advantages and limitations. A comparative analysis of \(SEA\) values, as highlighted in recent studies and summarized in Figure 17, indicates that metals exhibit the highest mean \(SEA\) of 28.65 J/g, followed by fiber-reinforced polymers at 14.23 J/g and polymers at 8.45 J/g, demonstrating superior crashworthiness for metals. The standard deviation of \(SEA\) is highest for metals at 16.50 J/g, reflecting greater variability in the energy absorption performance, while fiber-reinforced polymers show moderate variability at 11.72 J/g, and polymers exhibit the lowest variability at 8.19 J/g.