# Application of Directed Energy Deposition-Based Additive Manufacturing in Repair
## 1 Introduction
Nonetheless, it should be noted that the remanufacturing process is cheaper than the manufacturing process. For example, remanufacturing an engine needs only 55% of energy and 67% of the labor that is required for the production of a new engine [18]. Therefore, repair and remanufacturing processes should be considered as a highly efficient process that can save and reuse sources to eventually boost a country's economy. The first repairs exploited the welding process, so tungsten inert gas (TIG) welding, which is a fusion welding technique, has been dramatically employed [19; 20]. However, this approach results in poor-quality and leads to failing parts, mainly owing to the several issues related to the high residual stresses and, consequently, distortion in the components. Thereafter, to address these problems, alternative welding techniques, such as plasma transferred arc welding (PTAW) and electron beam welding (EBW), have been developed [21; 22]. However, the complexity and cost of these apparatus limit their application [21; 22]. The high-velocity oxyfuel (HVOF) thermal spray has been the next technology developed to repair components in many industries. Indeed, this technique has several merits over the conventional methods, and it is possible to have less distortion in part after repair and to coat the thin and porosity-free layers. Nonetheless, extensive secondary machining, usually necessary after repairing by HVOF, has limited its application and shown the need for developing new techniques of repairing [23; 24]. Table 1 compares the advantage and disadvantages of various processes that have been employed as repair and remanufacturing operations. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Process** & **Post-Processing** & **Advantage** & **Disadvantage** & **Ref.** \\ \hline \hline \multirow{4}{*}{GTAW/TIG} & \(\bullet\) & Stress relieving & \(\bullet\) & Hurricane repairs can be done & \(\bullet\) & Imperfections in the tooling & \multirow{4}{*}{[21, 22]} \\  & \(\bullet\) & Surface finishing & \(\bullet\) & Produces very high-quality results & \(\bullet\) & Limited electrode wear & [21, 22] \\  & & & & & & Limited intolerance to changes \\ \hline \multirow{4}{*}{Electro Spark} & \(\bullet\) & Dimensional & \(\bullet\) & \(\bullet\) & Not automated & \multirow{4}{*}{[25]} \\  & \(\bullet\) & stability evaluations & \(\bullet\) & Prevention of liquid metal erosion & \(\bullet\) & Liquid metal resistant & \multirow{4}{*}{[25]} \\  & \(\bullet\) & Surface finishing & & and Burt forming & & electrodes need to be developed & \\ \hline \multirow{4}{*}{HVOF} & \(\bullet\) & Stress relieving & \(\bullet\) & \(\bullet\) & Extensive & \multirow{4}{*}{[23, 24]} \\  & \(\bullet\) & Surface finishing & \(\bullet\) & Coating porosity-free layers & \(\bullet\) & Extensive & \multirow{4}{*}{[23, 24]} \\  & & & & & & secondary machining & \\  & & & & & & expensive instrumentation & \\  & & & & & & Low dimensional accuracy & \\ \hline \multirow{4}{*}{Laser-based processes, such as DED} & \multirow{4}{*}{Surface finishing} & \(\bullet\) & Lower heat input & \multirow{4}{*}{[25]} \\  & & & \(\bullet\) & Less warpage and distortion & & \\  & & & \(\bullet\) & Lower dilution rate & & \\ \cline{1-1}  & & & \(\bullet\) & Excellent metallurgical bonding & \(\bullet\) & Requires a more complex and & \multirow{4}{*}{[26, 27, 28]} \\ \cline{1-1}  & & & \(\bullet\) & Excellent mechanical performance & & advanced control system to & \\ \cline{1-1}  & & & \(\bullet\) & High precision of & & get the best results & \\ \cline{1-1}  & & & \(\bullet\) & resulting geometry & & \\ \cline{1-1}  & & & \(\bullet\) & Suitability for full automation & & \\ \cline{1-1}  & & & \(\bullet\) & Precise thermal control & & \\ \hline \end{tabular}
\end{table} 
Table 1: Comparison between advantages and disadvantages of various repair and remanufacturing processes.