# An Overview of the Process Mechanisms in the Laser Powder Directed Energy Deposition
###### Abstract
\begin{table}
\begin{tabular}{c c c c} \hline
**Process Category** & **System** & **Process Name** & **Build Volume (mm\({}^{3}\))** \\ \hline \multirow{8}{*}{Powder Bed Fusion (PBF)} & GE Additive Arcam (A2x) & EBM & 200 \(\times\) 200 \(\times\) 380 \\  & GE Additive Arcam (Spectra H) & EBM & \(\Phi\)250 \(\times\) 430 \\  & GE Additive Arcam (Spectra L) & EBM & \(\Phi\)350 \(\times\) 430 \\  & EOS (M400) & DMLS & 400 \(\times\) 400 \(\times\) 400 \\  & Concept laser cusing (M2) & SLM & 300 \(\times\) 350 \(\times\) 300 \\  & MTT (SLM 250) & SLM & 250 \(\times\) 250 \(\times\) 300 \\  & Renishaw (AM 250) & SLM & 245 \(\times\) 245 \(\times\) 360 \\  & Realizer (SLM 250) & SLM & 250 \(\times\) 250 \(\times\) 220 \\  & Matsuura (Lumex Advanced 25) & SLM & 250 \(\times\) \(\Phi\)250 \\ \hline \multirow{8}{*}{Directed Energy Deposition (DED)} & Prima Additive (LaserNext 2141) & DED & 4140 \(\times\) 2100 \(\times\)1020 \\  & POM DMD (66R) & DMD & 3200 \(\times\) 3670 \(\times\) 360\({}^{\circ}\) \\ \cline{1-1}  & Optome (LENS 850-R) & LENS & 900 \(\times\) 1500 \(\times\) 900 \\ \cline{1-1}  & POM DMD (66R) & DMD & 3200 \(\times\) 3670 \(\times\) 360\({}^{\circ}\) \\ \cline{1-1}  & Trumpf & LD & 600 \(\times\) 1000 long \\ \cline{1-1}  & Sciaky (NG1) EBFFF & EBDM & 762 \(\times\) 483 \(\times\) 508 \\ \hline \end{tabular}
\end{table} 
Table 1: Metal AM systems and their building volumes [18]. Figure 1: Metal Additive Manufacturing systems sold from 2003 to 2021 (adapted from [4]). ment of the laser, almost instantaneous solidification of the molten material is obtained. The characteristics of the deposited part depend on a large number of parameters. According to [PERSON], et al. [21], up to 14 parameters can be identified: laser power, laser beam diameter, spatial distribution, shielding gas flow rate, carrier gas flow rate, travel speed, powder flow rate, powder, and building platform material properties, powder characteristics, powder feeding method, layer thickness, overlap percentage deposition strategy. These parameters define the mechanisms of the LP-DED process [22; 23; 24]. The three main mechanisms that can be identified are (i) laser irradiation and material addition, (ii) melt pool generation, and (iii) the solidification process. Moreover, complex parameter interactions are observed during the process. An in-depth description of the LP-DED process, enabling an understanding of the physics of the process, must consider the mechanisms and parameters of the process that are closely related to each other. Figure 2 shows the three mechanisms of the LP-DED process and the relationships among mechanisms, input parameters, and outputs. However, the process is generally analyzed by considering each mechanism independently, and, as a result, the interactions among the various process parameters are neglected. Therefore, a sequential approach is used to study the process, in which the output obtained as a result of each mechanism is used as an input variable for the following mechanism. Several reviews are available in the literature, and most of them focus on the applications of the LP-DED process [12; 25], modeling techniques [23], powder feeder equipment [26; 27], monitoring techniques [28], and the feasibility of different alloys [29; 30; 31; 32; 33; 34]. In contrast, no review in the literature focuses on a comprehensive overview of the mechanisms involved in the LP-DED process. This work aims to describe the main mechanisms involved in the LP-DED process. At first, the laser irradiation and material addition processes are described, highlighting the main results in terms of powder distribution and laser-powder interaction. Then, the description focuses on the melt pool generation and the effect of process parameters on the temperature distribution into the melt pool. In addition, the main forces acting in the melt pool and their influence on the melt pool morphology are analyzed.