## 2 Design of Self-Inhaling Internal Cooling Structured Grinding Wheel
### Influence of Grinding Wheel's Cooling Hole Position and Size  
The significance of simulating the internal flow field characteristics of the grinding wheel lies in exploring the influence of cooling hole parameters on the coolant flow rate and outlet velocity. It helps to determine the optimal size and position of the cooling holes. The primary criteria for evaluation are the outlet velocity and flow rate of the coolant. Figure 1: 3D model of internally cooled grinding wheel: (**a**) exploded view; (**b**) coolant flow direction. Figure 2: Simulation process. Models of the grinding wheel base and workpiece were first established in the 3D modeling software SolidWorks 2016, and then imported into the fluid simulation software Ansys Fluent 2020 R2 for analysis. For internally cooled grinding wheels, understanding the properties of the grinding zone requires calculating the relevant parameters of the internal flow field. The parameters used in this simulation are listed in Table 1.  
The mesh division impacts the accuracy and speed of solving the target model, so an appropriate meshing method must be chosen, and the mesh quality should be checked. The mesh quality is considered good when the minimum orthogonal quality value is greater than 0.1 and the maximum skewness value is less than 0.95. The mesh model of the internal flow field is shown in Figure 3, and the number of elements is 71,404. The coolant outlet channel of the grinding wheel base is a vertical flow channel. When the coolant outlet velocity is too high, it can exert a significant impact on the workpiece, affecting the stability of the grinding process and thus reducing grinding efficiency and workpiece surface quality. Conversely, when the outlet velocity is relatively low, the flushing effect in the grinding zone is insufficient, and the generated grinding debris cannot be effectively removed from the grinding zone. The debris can degrade grinding quality and compromise precision. Therefore, a reasonable outlet velocity is more conducive to maintaining grinding efficiency and precision. Similarly, when the outlet velocity is evenly distributed, the grinding wheel's stability improves. It ensures a relatively uniform flushing effect across different parts of the workpiece, leading to a more stable grinding process and contributing to improved machining quality. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Values** \\ \hline Diameter of internal flow field (mm) & 30 \\ Speed of grinding wheel (r/min) & 1000, 2000, 3000, 4000, 5000 \\ Grinding fluid inlet pressure (bar) & 1, 3, 5, 7, 9 \\ Grinding fluid density (kg/m\({}^{3}\)) & 1000 \\ Grinding dynamic viscosity (Pa*s) & 0.001 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Internal flow field simulation parameters. Figure 3: Meshing model of flow field in grinding wheel. Position of the cooling holes  
Based on the previously designed grinding wheel base structure, the center of the cooling holes was determined to be 10.5 mm to 12 mm from the center of the end face. The basic conditions for the simulation were as follows: 12 cooling holes with a diameter of 2.0 mm, a rotational speed of 3000 r/min, and a coolant inlet pressure of 5 bar. Simulation calculations for the internal flow field of the grinding wheel were performed for different cooling hole positions, and the simulation results are shown in Table 2.  
Based on the data in Table 2, with the cooling hole position values as the x-axis, and the outlet average velocity and outlet flow rate values as the y-axis, line graphs are plotted in Figure 4. As the distance increases, the outlet flow velocity of the cooling hole increases monotonically, and reaches its highest value at a distance of 11.25 mm. After that, the outlet flow velocity fluctuates around a relatively stable value. Similarly, as the distance increases, the outlet flow rate of the cooling hole generally shows an increasing trend, with the highest outlet flow rate occurring at a distance of 11.25 mm.