## 5 Conclusions  
This paper has presented a systematic review of the machinability of AM Ti6 Al4V alloy, covering the wide range of AM techniques used to manufacture titanium parts. The effects of cutting conditions, stresses generated during AM processes on the energy consumption during machining of Ti6 Al4V parts produced from AM techniques, FEA models for machining processes, and the qualification process were examined critically. The following key points were noted, which will aid in the machinability of AM Ti6 Al4V alloy. * It can be concluded that the machinability of a Ti6 Al4V alloy is very challenging due to its low thermal conductivity. The AM titanium alloy was more difficult due to its resulting higher residual stresses, which could lead to high cutting forces in addition to the low thermal conductivity of the Ti6 Al4V alloy. * It was also deduced that energy maps plotted (feed rate against cutting speed) can be used to identify and classify energy consumption into low, medium, and high. * The DMD-based process is the least reported and used among the AM techniques. Hence, this article finds a gap for recommendation as part of the methodology approach. * It was reported that a laser scanning speed of 1200 mm/s at a more prominent spot size yields a low porosity during AM processing of titanium alloy. * It was shown that the Johnson-Cook model was the model most predominantly employed in the numerical analysis of the machining process due to its ability to predict both the lower and higher cutting forces and stresses and its smaller number of constants. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Constant** & **A** & **B** & **C** & **m** & **n** & **T\({}_{\text{O}}\) (\({}^{\circ}\)C)** & **T\({}_{\text{Melting}}\) (\({}^{\circ}\)C)** \\ \hline Ti6 Al4V & 782.7 & 498.4 & 0.028 & 1 & 0.28 & 20 & 1668 \\ WC/Co & 0.003 & 8.0471 & 0.000 & 0.179 & 0.0003 & 20 & 1372 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Material constants of J–C model parameters for the tool and workpiece [56]. \begin{table}
\begin{tabular}{c c} \hline \hline
**Property** & **Value** \\ \hline Density (kg/m\({}^{3}\)) & 4.43 \(\times\) 10\({}^{3}\) \\ Ultimate tensile strength (MPa) & 950 \\ Tensile yield strength (MPa) & 880 \\ Young’s modulus of elasticity (GPa) & 113.8 \\ Thermal conductivity (W/Mk) & 17 \\ Poisson ratio & 0.32 \\ Heat capacity (J/kg K) & 526 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Mechanical properties of Ti6 Al4V alloy for J–C model [56]. * It was observed that the Johnson-Cook model was unable to predict the cutting forces at higher cutting speeds of up to 2000 m/min for Al 6061-T6 alloy. * Multi-objective optimization can achieve the sustainable goal of machining Ti6 Al4V alloys with a high material removal rate, longer tool life, and minimum energy consumption. The Taguchi method was found to be more effective than other optimization methods. * There were limited or no articles to review regarding the qualification of machined parts for assembly manufactured by the AM process. Therefore, this research finds another exciting gap to fill. * The focus will be developing a numerical model that represents the modified J-C model as a way to incorporate the prediction of microstructural changes such as grain size, phase changes, and texture formation. To develop a modified J-C model in a way to incorporates enlarged damage criteria, such as micro-crack nucleation, is important. * Finite element modeling can be further integrated with experimental results to enhance the understanding of machining performance in AM-produced Ti6 Al4V alloy parts. * The energy consumption maps may be further developed to investigate the variations in machine tool dynamics and environmental factors, which could potentially impact their applicability in diverse manufacturing settings. The APC was funded by the Author Voucher discount code (2157477d2 db34e3e). The author appreciates receiving the PhD studentship funding from Robert Gordon University, Aberdeen, Scotland, UK, to support this research.