# Simulation on Cooperative Changeover of Production Team Using Hybrid Modeling Method
## Case Study
### Results and Discussion  
#### 5.3.1 Workload Balance Level  
The mean values of workload balance levels obtained by adopting four strategies in four production scenarios are shown in Figure 5. It can be seen that the non-cooperative strategy has the lowest workload balance level in all production scenarios, while the totally cooperative strategy has the highest one. In addition, the relationship between workload balance level and new parts introduction rate is negative when using the cooperative strategy for mature products and positive when using the cooperative strategy for new products.  
To analyze the reasons for the above results, the average cooperation rates of the changeover tasks under different conditions are calculated, as shown in Table 6. The Pearson correlation analysis is then implemented to obtain the correlation between the average cooperation rate of changeover tasks and the workload balance level in each production scenario, as shown in Table 7. The analysis results show that in the four production scenarios, the cooperation rate of the changeover tasks and the workload balance level are significantly positively correlated, which means the cooperative changeover is an effective way to balance the workload. Therefore, the degree of preference for cooperation by changeover strategies determines the level of workload balance. Because the preference degree for cooperation by the cooperative strategy for mature products or by the cooperative strategy for new products is greatly affected by the new parts introduction rate, the workload balance level presents monotony.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Changeover Strategies** & **0** & **25\%** & **50\%** & **75\%** \\ \hline Non-cooperative strategy & 0 & 0 & 0 & 0 \\ Cooperative strategy for mature products & 50.90\% & 38.30\% & 22.50\% & 9.90\% \\ Cooperative strategy for new products & 0 & 8.00\% & 24.75\% & 38.05\% \\ Totally cooperative strategy & 50.90\% & 49.10\% & 45.65\% & 47.15\% \\ \hline \hline \end{tabular}
\end{table}
Table 6: Average cooperation rates of changeover tasks under different conditions.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**New Parts Introduction Rate** & **Sample Size** & **Correlation Coefficient/Significance** \\ \hline
0 & 40 & 0.830 *** \\
25\% & 80 & 0.748 *** \\
50\% & 80 & 0.685 *** \\
75\% & 80 & 0.682 *** \\ \hline \hline \end{tabular} Note: *** means \(p<0.01\).  
Figure 5: Mean values of workload balance levels under different conditions.  
For the purpose of verifying whether there are significant differences in the mean values of production cycles by adopting different strategies in each production scenario, hypothesis test analysis is conducted using the experimental data in Table 8. The results are shown in Table 9, where \(\overline{T_{r}^{1}}\), \(\overline{T_{r}^{2}}\), \(\overline{T_{r}^{3}}\) and \(\overline{T_{r}^{4}}\) respectively denote the mean values of production cycles when adopting non-cooperative strategy, cooperative strategy for mature products, cooperative strategy for new products and totally cooperative strategy. In addition, the new parts introduction rate is r.  
When Strategy A has a significant advantage over Strategy B, it can be considered that Strategy A is superior to Strategy B in a statistical sense. According to the test results, when only mature products can be produced, the production cycle obtained by adopting the non-cooperative strategy has a significant advantage; when the new products are introduced in small quantities, the production cycle obtained by adopting the cooperative strategy for new products has a significant advantage; when medium or large quantities are introduced, the production cycle, obtained by adopting the cooperative strategy for new products or the totally cooperative strategy, has a significant advantage.