# The Impact of Downtime on the Stability of the Production Schedule
## 2 Materials and Methods
### Production Flow Model 2  
Analysis of the results for the second production flow model 2 showed that the execution time for a set of production orders was dependent on the priority rule used and the variant of the execution times for process operations (Figure 11). The influence of stoppages for rules 2 and 3 was also apparent. The best results for the execution times of the set of orders were obtained using rules 1 and 2, depending on the size of the set of production orders for the variant of operation times 2. For the variant 1 times, the best results were obtained for rule 2. It can be observed that the size of the production orders only had an impact when there were stoppages for critical resources. In the case of the continuity indicator for the execution of production orders, only the introduction of a stoppage for a critical resource affected its deterioration for the variant of process operation times 1 (Figure 12). The best indicator values were obtained for rule 1. On the basis of the results obtained, it can therefore be concluded that in the case of a production flow of a stream character, depending on the evaluation criterion, the best results were achieved in the case of the application of rule 1 of production scheduling. It made it possible to obtain the greatest stability of production scheduling--there was no influence of stoppages. Figure 11: Production flow model 2—lead time for set of production orders. Figure 10: Production flow model 1—average value of production continuity parameter. In addition, the results concerning the influence of the factors studied on individual production orders are presented below. In the case of flow model 1, the influence of priority rules depending on the number of products in production orders was visible (Figure 13). The higher the quantity, the smaller the changes were. The same relationship appeared with the influence of stoppages. It can be concluded that the greater the number of items in the orders, the greater the possibility of changing the production schedule without affecting the total realization time of the production orders. The impact of stoppages depending on the time variant of the process operations can also be seen. For production flow model 2, the results are shown in Figure 14.  
Figure 14: Production flow model 2—number of delayed production orders. Figure 12: Production flow model 2—average value of production continuity parameter. Figure 13: Production flow model 1—number of delayed production orders. The analysis of the results showed that for the stream form of production flow, the priority rules did not show any differences in the number of delayed production orders. Also, the count of products in the production orders did not show any differences in the delayed orders. The results show that the measures for evaluating the schedules developed differently for the production flow models analyzed. The models differed in the structure of the production processes and the structure of the products. The best obtained completion times for entire sets of production orders were directly related to the selection of an appropriate scheduling method for the time variant of the technological processes, the structures of the finished products and their subordinate technological operations. The considered parameter of continuity of flow allowed us to conclude that the scheduling rule, using the sequence of production orders from the shortest time of their duration, allowed us to obtain the smallest average value of this indicator for each model considered, which translates into greater stability of the production schedule. In the case of the application of scheduling rules using the sequence of production orders from the longest duration, it was noted that as the set of production orders increased, the average continuity parameter for the rules also increased. The results indicate that the impact of production downtimes affected individual production orders to a greater extent for smaller sets of orders than for larger sets of orders.