# The Current State of Research of Wire Arc Additive Manufacturing (WAAM): A Review
## 2 Materials, Processes and Methods  
The key to understanding wire arc additive manufacturing is deep knowledge of the used welding processes. Basically, all welding processes are suitable for additive manufacturing and are scientifically well understood. The differences between additive \begin{table}
\begin{tabular}{l l l l} \hline \hline \multicolumn{1}{c}{**County**} & \multicolumn{1}{c}{**Research Groups**} & \multicolumn{1}{c}{**Synonyms of Wire Arc Additive Manufacturing (WAAM)**} & \multicolumn{1}{c}{**Reference**} \\ \hline \multirow{3}{*}{United States} & Southern Methodist University & Rapid prototyping (RP) based on gas & \multirow{3}{*}{[32]} \\  & Tufts University & & \\ \cline{3-3}  & \multirow{3}{*}{[33]} & Korea Institute of Science and & \\ \cline{3-3}  & Technology & & \\ \hline \multirow{2}{*}{Japan} & Osaka University & 3D micro welding & [35] \\ \hline \multirow{3}{*}{United Kingdom} & University of Sheffield & Shaped metal deposition & [36] \\  & Cranfield University & Wire and arc additive manufacturing & \\  & & (WAAM) & \\ \cline{3-3}  & University of Manchester & Wire and arc additive manufacturing & \\  & & (WAAM) & \\ \cline{3-3}  & \multirow{3}{*}{Coventry University & Wire and arc additive manufacturing & \\  & & (WAAM) & \\ \cline{3-3}  & \multirow{3}{*}{University of Bath & Wire and arc additive manufacturing & \\  & & (WAAM) & \\ \cline{3-3}  & University of Wales Swansea & Shaped metal deposition & [43] \\ \hline \multirow{3}{*}{China} & Harbin Institute of Technology & GMAW-based rapid manufacturing & [44] \\  & Xi An Jiao Tong University & MPAW-based rapid prototyping & [45] \\ \cline{3-3}  & Shanghai Jiao Tong University & Wire arc additive manufacturing & \\ \cline{3-3}  & \multirow{3}{*}{Foshan University & (WAAM) & \\ \cline{3-3}  & School of Mechanical and & & \\ \cline{3-3}  & Vehicular Engineering, Beijing & Wire and arc additive manufacturing & \\ \cline{3-3}  & Institute of Technology & (WAAM) & \\ \hline \multirow{3}{*}{India} & Indian Institute of Technology & Hybrid layered manufacturing & [48] \\  & Birla Institute & GTAW welding-based additive & [49] \\ \cline{3-3}  & of Technology and Science & manufacturing & \\ \hline \multirow{3}{*}{Australia} & University of Wollongong & Wire arc additive manufacturing & [50; 51] \\  & & (WAAM) & \\ \hline \multirow{3}{*}{Germany} & Claushal University of & Wire arc additive manufacturing & \\ \cline{3-3}  & Technology & (WAAM) & \\ \cline{3-3}  & Ilmenau University of Technology & Wire arc additive manufacturing & \\ \cline{3-3}  & Chemnitz University of & (WAAM) & \\ \cline{3-3}  & Technology and TU Munich & Wire arc additive manufacturing & \\ \cline{3-3}  & University of Technology & (WAAM) & \\ \cline{3-3}  & Braunschweig University of & Wire arc additive manufacturing & \\ \cline{3-3}  & Technology & (WAAM) & \\ \cline{3-3}  & Brandenburg University of & Wire arc additive manufacturing & \\ \cline{3-3}  & Technology Cottbus-Senftenberg & (WAAM) & \\ \cline{3-3}  & RWTH Aachen & Wire arc additive manufacturing & \\ \cline{3-3}  & \multirow{3}{*}{Graz University of Technology} & Wire arc additive manufacturing & \\ \cline{3-3}  & & (WAAM) & \\ \hline \multirow{3}{*}{Italy} & \multirow{3}{*}{University of Bologna} & Wire arc additive manufacturing & \\ \cline{3-3}  & & (WAAM) & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main research groups working on WAAM (modified) [30]. manufacturing and joint welding are based on the differences in the thermal conductivity, which is significantly lower for thin-walled structures. This makes thermal management the key factor to achieve the desired part geometry and material properties and influences the choice of the used welding process. In the following, the used processes for WAAM are described regarding additive manufacturing-related issues. After that process-surveillance and control methods will be summarized, followed by the major process-dependent key factor in wire arc additive manufacturing: the path planning.