# Surface Quality Evolution Model and Consistency Control Method of Large Shaft Multi-Pass Grinding
## 2 Surface Quality Indexes and Influencing Factors
### Analysis of Surface Quality Influencing Factors  
The full factor experiments are carried out to analyze the influence of grinding parameters on surface roughness and glossiness. The grinding machine is a grinder MKT8445. The workpiece is a shaft with a length of 1480 mm and a diameter of 244 mm. The material of the shaft is 92 CrMo, which is a kind of alloy steel. The grinding wheel is made of silicon carbide with a width of 60 mm. The grinding system and process are shown in Figure 2a,b. The shaft diameter is obtained by measuring arm as shown in Figure 2c, and the measuring resolution is 0.1 \(\upmu\)m. The surface roughness is tested by Surftest-SJ210 roughness meter with a resolution of 0.001 \(\upmu\)m. The direction of measurement of roughness is parallel to the direction of grinding passes as shown in Figure 2d. The glossiness is tested by the YG60 glossiness meter with a resolution of 1 GU and a test angle of 60\({}^{\circ}\). The testing instruments are shown in Figure 2e,f. The full factor experiments consist of four factors, i.e., grinding depth ap, grinding wheel speed Nwheel, shaft speed Nshaft, and pallet speed f. The grinding depth and the grinding wheel speed are set at four levels, while the shaft speed and the pallet speed are set at three levels as shown in Table 1. Thus, the full factor experiments consist of 144 grinding passes. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Level** & \(a_{p}\) (\(\upmu\)m) & \(N_{\text{wheel}}\) (\(\upmu\)/min) & \(N_{\text{shaft}}\) (\(\upmu\)/min) & \(f\) (mm/min) \\ \hline
1 & 0 & 550 & 60 & 800 \\
2 & 2 & 700 & 70 & 1000 \\
3 & 3.5 & 850 & 80 & 1200 \\
4 & 5 & 1000 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Grinding parameters of the full factor experiments. Figure 1: The test method for glossiness. The grinding wheel grinds from the left side of the shaft to the right side in a grinding pass. On the next grinding pass, the grinding wheel grinds from the right side of the shaft to the left side. In order to expand the number of samples, six measuring points are selected along the \(z\)-direction on the shaft after grinding to test the surface roughness and glossiness as shown in Figure 3. The measuring points in this study are distributed uniformly along the length of the shaft, which can reflect the trend of surface quality on the whole shaft. Figure 4 shows the surface roughness and glossiness with different grinding parameters, and the values of surface roughness and glossiness are average values tested on 6 measuring points. The error bar represents the standard deviation. With the increase of grinding depth, shaft speed, and pallet speed, the surface roughness value increases and the glossiness decreases. This is because the increase of these three grinding parameters will increase the grinding force, resulting in more intense plastic deformation of the shaft and a rougher surface. Figure 3: Measuring points of shaft. Figure 2: The grinding system and testing instruments: (**a**) grinding system, (**b**) grinding process, (**c**) diameter measurement, (**d**) roughness measurement, (**e**) roughness meter, (**f**) glossiness meter. For grinding wheel speed, lower surface roughness values and higher glossiness values are obtained in the range from 700 to 850 r/min. The spindle current standard deviations of the grinding passes in Figure 5d are shown in Table 2. It can be seen that the current variances are small when the grinding wheel speeds are 700 r/min and 850 r/min. The spindle runs more stably within this speed range, and the contact between the grinding wheel and the shaft is more stable, resulting in higher surface quality. It should be noted that the grinding depth involved in the above analysis is the nominal grinding depth. In fact, due to grinding wheel wear in the grinding process, the actual grinding depth is less than the nominal grinding depth and unevenly distributed along the \(z\)-direction.