# Analysis of Grinding Flow Field under Minimum Quantity Lubrication Condition
## 4 Experimental Verification
### Discussion  
The effective flow rate of the grinding fluid into the grinding zone directly affects the grinding temperature. Grinding temperature is the main factor affecting the surface quality of the grinding process. Excessive grinding temperature could cause burns, oxidation, cracks, phase transformation of the workpiece material. It also could reduce the surface hardness and smoothness of the workpiece. In this paper, the grinding temperature were obtained under different parameters. The trends of the grinding temperature with the flow rate, the linear velocity of the grinding wheel and the compressed gas pressure are shown in Figures 20-22. As seen in Figure 20, the workpiece grinding temperature decreases with the increase in the flow rate of the grinding fluid. When the flow rate of the grinding fluid is lower than 45 mL/h, the grinding temperature decreases significantly with the increase in the flow rate of the grinding fluid. When the flow rate of the grinding fluid is greater than 45 mL/h, the decreasing tendency of the grinding temperature slows down with the increasing of the grinding fluid flow rate. The reason for this is that the content of the discrete terms in the MQL jet increases as the grinding fluid flow rate increases. The energy exchange between the grinding fluid and compressed air becomes more intense, which reduces the velocity of the MQL jet. Under high air pressure conditions, increasing the flow rate of grinding fluid can reduce the droplet velocity and prevent droplet splashing, which cannot provide cooling and lubrication [23]. In addition, increasing the flow rate of grinding fluid \begin{table}
\begin{tabular}{c c} \hline \hline
**Wheel Rotation Velocity \(v_{s}\) (m/s)** & **20, 25, 30, 35, 40** \\ \hline Feed speed \(v_{w}\) (m/s) & 0.01 \\ Cutting depth \(\alpha_{e}\) (\(\upmu\)m) & 8 \\ MQL flow rate Q (mL/h) & 35.77, 41.53, 54.11, 66.41, 77.17 \\ Compressed P (bar) & 2, 3, 4, 5, 6 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Detailed parameters. Figure 20: Effect of the grinding fluid flow rate on the grinding temperature. can reduce the heat conducting into the workpiece. However, as the grinding fluid flow rate continues to increase, the droplet velocity decreases and the ability to penetrate the gas barrier layer decreases, resulting in a slower trend in the grinding temperature decrease. From Figure 21, it can be seen that the grinding temperature first reduces and then increases as the grinding wheel linear velocity improves. When the linear velocity of the grinding wheel increases, the air barrier layer around the grinding wheel enhances, which hinders the grinding fluid. The velocity of the grinding fluid droplets decreases, reducing the loss of grinding fluid caused splashing. This increases the effective flow rate of the grinding fluid and the heat transfer coefficient, which reduces the amount of heat entering the workpiece and lowers the grinding temperature. When the grinding wheel linear velocity increases to a certain value, such as 30 m/s in Figure 21, further increasing the grinding wheel linear velocity leads to a strong strength of the air barrier layer, resulting in less grinding fluid going into the grinding area and a lower cooling and lubrication effect. Moreover, the increase in the grinding wheel linear velocity of increases heat generation, and eventually leads to the increase in the grinding temperature. According to Figure 22, as the compressed gas pressure increases, the grinding temperature first reduces and then increases, and the temperature curve inflection point is different for different grinding wheel linear velocities. The grinding temperature gets to its minimum value at a grinding wheel velocity of 30 m/s and an air pressure of 4 bar. When the linear velocity of the grinding wheel is 40 m/s and the air pressure is 5 bar, the grinding temperature gets to the lowest value. During the grinding process, the air barrier formed by the grinding wheel rotation has an obstructive effect on the grinding fluid entering the grinding zone.