# Emerging Trends in Hybrid Additive and Subtractive Manufacturing
## 3 Results and Discussion
### Articles Classification
#### 3.1.1 Research Areas  
A typical feature of emerging technologies can be seen in the multiple areas from which the topic of study is approached. It is expected that some of these will consolidate while others will eventually become residual. The most common areas are actually transversal and can encompass a wide variety of research topics. Thus, Engineering and Materials Science  
\begin{table}
\begin{tabular}{c c} \hline
**Journal/Congress** & **Reference** \\ \hline
30 th international conference on flexible automation and intelligent manufacturing (FAIM) & [50] \\
8 th international conference on through-life engineering services (TESCONF) & [58] \\
_Additive manufacturing_ & [5] \\ _Advanced materials_ & [55] \\ _Computer-aided design_ & [43; 53] \\ _Engineering structures_ & [56] \\ _Fatigue \& fracture of engineering materials \& structures_ \\ _International journal of advanced manufacturing technology_ & [47; 48] \\ _International journal of heat and mass transfer_ & [2] \\ _International journal of machine tools \& manufacture_ & [1] \\ _International journal of mechanical sciences_ & [44] \\ _Journal of manufacturing processes_ & [41] \\ _Journal of materials processing technology_ & [42; 52] \\ _Journal of materials research and technology (JMR\&T)_ & [3] \\ _Materials_ & [4,40; 54; 57; 59] \\ _Mechanical systems and signal processing_ & [21] \\ _Metals_ & [11] \\ _Micromachines_ & [46] \\ _Polymers_ & [49] \\ _Wear_ & [45] \\ \hline \end{tabular}
\end{table}
Table 4: Journals and conferences with selected papers.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Ref.** & **Q** & **Cit.** & **Year** & **Institution** & **Country** & **Hybrid Flow** \\ \hline
[58] & - & 19 & 2020 & \begin{tabular}{c} Tshwane University \\ of Technology, \\ University of Applied \\ Sciences Aschafenburg \\ \end{tabular} & South Africa & \
\begin{tabular}{c} Laser AM + CNC machining \\ (Ti-6 Al-4V) \\ SLM + high-speed micromilling \\ (Margaging steel) \\ \end{tabular} \\ \hline  & & &
\begin{tabular}{c} Where Q- quality criteria; Cit. citations; PP (proceedings paper); LPBF (laser Power Bed Fusion); SLM (selective laser melting); HSM (high-speed machining); PAW (Plasma Arc Welding); WAAAM (wire are additive manufacturing); CNC (Computer Numerical Control); DIW (Direct In Writing); PBF-LB/M (Laser-Based Powder Bed Fusion of Metals); EBM (Electron Beam Melting); PDMS (Polydimethylsiloxane); AM (additive manufacturing). \\ \end{tabular} \\ \end{tabular}
\end{table}
Table 3: _Cont._appear in 70.4% and 48.1% of the reviewed papers. They are followed by generic areas such as Chemistry and Physics, with a similar analysis. Again, a wide dispersion is observed in the remaining areas; these are more specific areas, which are, however, mentioned in greater or lesser depth in many of the articles analyzed: Digital Twin, Feedback Control, Intelligent Manufacturing, and Smart Systems, among others. In fact, they are revealed to be crucial for the future development of hybrid additive and subtractive manufacturing. Polymer Science also appears as a minority area, with only one article (3.7%) among those analyzed. However, it represents an interesting contribution, given that it opens the door to research with new materials, distinguishing the most common ones, which are those related to nickel and titanium superalloys. Figure 6 shows the distribution described.