## 2 Additive Manufacturing Techniques
### Direct Metal Deposition  
DMD is a powder-fed fusion process capable of additively manufacturing large-scale complex metallic parts, unlike SLM, DMLS, and EBM. This process has the advantage of creating a layer thickness of up to 2 mm. The laser scanning speed is the most critical factor in determining whether the final parts manufactured have acceptable dimensions and properties. The compressive stresses were observed to be the common factor in DMD wire-based manufacturing of Ti6 Al4V alloy parts [30]. Therefore, the cutting forces are greatly affected by the nature of the stresses developed during the manufacturing process. A 300 \({}^{\circ}\)C preheating temperature was applied to reduce the effect of temperature build-up during side milling of DMD-manufactured Ti6 Al4V alloy parts; the results showed a significant reduction in the milling forces observed, which was due to the thermal softening effect in the titanium part [31]. Preheating the workpiece before the machining operation could increase the tool's life. This research focuses exclusively on the Ti6 Al4V alloy, omitting the exploration of other alloys. It investigates milling forces and temperature effects only at 300 \({}^{\circ}\)C and above, neglecting lower temperatures and extreme conditions. Additionally, the study does not consider other machining responses, such as tool wear rate, residual stresses, or microstructural changes. There needs to be more reported literature on the DMD powder-based fusion process. Selection of the best laser scanning process parameters results in minimal or zero defects in the specimen. Reports show 850, 1000, 1250, and 1500 mm/s were selected for laser scanning speed; 55% to 100% for laser power, depending on the machine's maximum power output (\(P_{\text{max}}\) = 200 W); spot size: smaller (S), medium (M), and large (L)--based on the settings specific to the machine (from 150 \(\upmu\)m to 250 \(\upmu\)m); the layer always had a 40 \(\upmu\)m thickness [29]. The larger spot size was prepared, and a 1250 mm/s scanning speed resulted in less porosity within the temperature fields [29]. The melt pool region's optimum temperature is an independent singularity higher than the temperature at which Ti-6 Al-4 V vaporizes. The design of a laser scanning technique should incorporate a considerable scan beam length that uniformly rotates the scan vector directions, thereby creating an isotropic stress distribution within the part. In each case, the hatched area is scanned first, followed by a single outer contour. The surface temperature of a single scan vector approximates a melt pool size of 0.14 mm [10]. This paper presents simulation results; however, it lacks comprehensive experimental validation to corroborate its findings. Without such validation, the reliability of the outcomes remains uncertain. Additionally, the study does not fully address the temperature profiles, which is necessary to understand their effects on residual stresses. The molten pool experiences high temperatures and rapid cooling rates due to the concentrated energy source and the relatively short contact time. In the direct metal deposition (DMD) process for Ti6 Al4V alloy, the cooling rate can reach approximately \(7\times 10^{4}\) K/s [12; 29]. AM titanium alloy fabricated by EBM was reported to have low residual stresses, with DMD having low porosity, and SLM high residual stress [12; 32]. Still, they have the advantage of having lower residual stress, and the parts processed utilizing an electron beam can be used without any stress-relieving processes. DMD produces high deposition rates with a higher layer thickness than other AM processes. It was observed that no previous article had reported on investigating the reduction in energy consumption, machined part qualification process, and optimization during the machining of Ti6 Al4V parts produced by the AM process. Hence, this review article will focus on this critical gap.