# Selection of Production Reliability Indicators for Project Simulation Model
## 4 Results
### Results of the Quality Function Deployment  
For the determination of the customer requirements, a brainstorming activity, as well as a focus group interview took place with professionals in the field of quality and production. At the end of the activity, the following requirements were established and defined:  
* Time-based (CR1): A crucial part of production scheduling is the time. The time consequences of probable problems should be implemented in the model. * Measurable (CR2): All the included indicators should be described quantitatively. * Correlation among failures (CR3): When a model is created, the dependency among problems should be described to examine domino-effect. * Frequency (CR4): A frequency of a certain problem can be given or calculated. * Critical Path change (CR5): In the case of time increase, total process time and critical path should be evaluated. * Integration to production scheduling method (CR6): A certain component, indicator or parameter only helps the decision-maker when it is logically built in the model. * The speed of calculation (CR7): The execution of a stochastic model should take as little time as it is possible. The calculation speed depends on the complexity of the indicator built in the simulation. During the brainstorming event, a rank and priority was set to each alternative, which was used for an AHP method. The reason for choosing this method is the wide acceptance in numerous disciplines; moreover, it should not be fully consistent to obtain acceptable results, and more importantly, its ability to handle qualitative and quantitative attributes as well as requiring full focus due to dealing with the same questions from two different points of view (compare \(i\) to \(j\), then compare \(j\) to \(i\)) [44; 45]. There was consensus among the participants that the \"Time-based\" and \"Integration to production scheduling method\" are equally favored, but are dominant requirements. The result of the pairwise comparison is considered to be consistent because the Consistency Index falls between the acceptance range (CI = 0.104). The standardized importance table can be seen in the following table (Table 2):  
The most important criteria in this respect are the CR1 (Time-based) and CR6 (Integration to scheduling method), while the least important criteria are CR3 (Correlation among failures), CR7 (Calculation speed), and CR4 (Frequency). Figure 3: Frequency table. The result was built in the QFD method, where criteria are prioritized based on their importance; 0-1-3-9 values were assigned to the relationship matrix where the correlation among customer requirements and technical parameters is identified. In this process, special attention went to understand the objective of the criteria (is the smaller or the higher value more beneficial for the customer? ); 0 values were only added when there was no connection between the criteria and the indicator. Such an example is the rate or probability calculations regarding the criteria titled \"Time-based\". These indicators only show a ratio, and it is hard, or impossible to translate them into time value. As an opposite, all indicators performed well in the criteria called Integration to production scheduling method. Most of the literature collected during the research dealt with the implementation of production scheduling method, or stated that each indicator can be integrated into production arrangement. The following table (Table 3) presents the relationship matrix and the importance values by the QFD. The most important reliability indicators are the mean time between failure and mean downtime values. When a more detailed analysis is carried out on the alternatives, it can be stated that the mean operation time and mean downtime correlate with each other. Additionally, mean repair time is included in the mean downtime indicator, because repair only takes place when there is no operation on the machinery.