## 5 Simulation Study of Front- and Back-Microstructure Tools  
Based on simulation studies of T\({}_{2}\) and T\({}_{3}\), appropriate front cutting face and back cutting face microstructure parameters were selected for application on T\({}_{4}\) tools to conduct simulation experiments. The front-cutting face parameters for T\({}_{4}\) tools were defined as follows: D = 50 \(\mu\)m, H = 60 \(\mu\)m, L\({}_{1}\) = 100 \(\mu\)m, and L\({}_{2}\) = 100 \(\mu\)m. The back cutting face microstructure parameters were specified as follows: D = 40 \(\mu\)m, H = 50 \(\mu\)m, L\({}_{1}\) = 140 \(\mu\)m, and L\({}_{2}\) = 90 \(\mu\)m.  
A comparative analysis of temperature and milling force simulation results for four tool configurations is presented in Figure 9. During the initial simulation phase (AB segment), the T\({}_{4}\) tool exhibited a slower temperature rise compared to other tools. In the BC segment, microstructures became active: they initiated chip collection and reduced friction between the cutting face and workpiece, thereby decelerating the temperature increase. Notably, T\({}_{4}\) maintained a more stable thermal profile than other tools, achieving a significantly lower peak temperature at the machining completion stage.  
A comparative analysis of average temperatures for four tool configurations is shown in Figure 10, with the temperature ranking as T\({}_{1}\) > T\({}_{3}\) > T\({}_{2}\) > T\({}_{4}\). The dual microstructures of T\({}_{4}\) demonstrated superior thermal performance by reducing a temperature rise, caused by metal shear slip and extrusion friction near the cutting edge on the back cutting face, further minimizing tool-chip friction, lowering frictional heat generation, and enhancing the heat dissipation area. Compared to T\({}_{1}\), T\({}_{4}\) achieved a 19% reduction in temperature,  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Factor**} & **Average** & **Average Correlation** & **Grey** \\  & **Correlation** & **Coefficient** & **Comprehensive** \\  & **Coefficient (Force)** & **(Temperature)** & **Correlation Degree** \\ \hline D & 0.635 & 0.658 & 0.667 \\ H & 0.612 & 0.765 & 0.683 \\ L1 & 0.722 & 0.782 & 0.768 \\ L2 & 0.745 & 0.743 & 0.785 \\ \hline \hline \end{tabular}
\end{table}
Table 14: Back microstructure results from GRA.  
Figure 9: Temperature comparison chart (A,B,C are milling processes).  
demonstrating its effectiveness in lowering tool temperature and significantly improving overall thermal conductivity.  
As shown in Figure 11, during the AB segment, the tool begins milling the workpiece. The workpiece undergoes elastic deformation under tool indentation, with shear stress continuously increasing until the material reaches its maximum allowable strain. At this point, the cutting layer fractures, causing an instantaneous stress drop on the tool. In the BC segment, the metal is separated from the workpiece and flows along the front cutting face as chips. Here, the front cutting face microstructures reduce friction between chips and the tool. Simultaneously, the back cutting face microstructures store chips, lowering the temperature on T\({}_{4}\)'s back cutting face and indirectly reducing milling forces.  
The average milling forces for the four tool configurations are presented in Figure 12. The findings indicate that the milling forces of T\({}_{4}\) and T\({}_{2}\) are comparable, with T\({}_{4}\) showing a 14% reduction compared to T\({}_{3}\) and a 16% decrease relative to T\({}_{1}\). Compared to T\({}_{1}\) and T\({}_{2}\), T\({}_{4}\) demonstrates superior capability in reducing milling forces generated during machining.  
Figure 11: Comparison chart of milling forces (A,B,C are milling processes).  
Figure 10: Four types of tool temperatures: a comparison chart.