## 5 Results and Discussion
### Statistical Analysis of Oil Pollution Transmission  
The initial source of oil pollution comes from the workpiece processed by the machine tool, so the initial concentration can be represented by the oil pollution concentration of the workpiece. Different production units are involved in the spread of oil pollution. Take production unit 1 (Figure 2) as an example of the effects of different initial concentrations on the oil pollution distribution in the production area and assembly area. The corresponding results are shown in Figure 7. The initial oil pollution concentration of production unit 1, from 100 to 1000 \(\upmu\)g/m\({}^{2}\), is selected. With the increase in the initial oil pollution concentration, the oil pollution in the production area and assembly area per unit time changes faster. The smaller the initial oil concentration, the earlier the oil concentration change curve reaches the equilibrium in both the production area and assembly area. Under different initial oil concentrations, each oil concentration change curve has a proportional relationship with the oil concentration reaching the final time of the simulation. This trend is consistent with the proportion of initial oil concentration. Moreover, in the oil pollution concentration change curve of the assembly table, the greater the initial oil pollution concentration, the shorter the interval time of the curve in the short-equilibrium period, and the greater the slope of the rising section between the different equilibrium periods.  
The different production rates of workpieces in the production area inevitably affect the oil concentration distribution in the production area and the change in oil concentration in the assembly area. Production units 1 and 2 are then subjected to characteristic analysis and production rate comparison. In the case of selecting different production units, the size of the production rate is changed, and the range of variation is 60 to 360 s/piece. For each production rate, the model is randomly calculated 100 times. The results of each simulation calculation are averaged to obtain the oil pollution changes in the production area and assembly area.  
As shown in Figure 8, when the production rate of a production unit slows down, the accumulated oil pollution per unit time in the production area and assembly area decreases. As for the oil pollution change curve of the assembly area, the speed of the production rate affects the oil pollution of the workbench in this area. As for the starting point of the  
Figure 6: Changes in oil concentration on assembly tables in the three assembly areas.  
concentration profile, the faster the production rate, the earlier the contamination. Second, the interval time of the oil pollution concentration to reach the temporary equilibrium has become obvious. The faster the production rate, the shorter the time of temporary equilibrium. Meanwhile, under different production rates, the balance period of each temporary balance has the same oil pollution concentration value because the initial oil pollution concentration and assembly rate have not changed. As shown in Figures 7a and 8c, under the same production rate, the cumulative oil pollution quality per unit time significantly differs. Given the different initial oil pollution concentrations of the two production units, the concentration ratio of each curve is approximately equal to the initial workpiece concentration ratio. This law is similarly reflected in the assembly area.  
Figure 8: Influence of workpiece production rate on oil pollution concentration on the worktable in the production area and assembly table in the assembly area. (**a**) production unit 1 in the production area; (**b**) production unit 1 in the assembly area; (**c**) production unit 2 in the production area; (**d**) production unit 2 in the assembly area.  
Figure 7: Influence of initial oil contamination concentration on the change in oil contamination concentration. (**a**) workbenches in the production area; (**b**) assembly tables in the assembly area.