## 4 Manufacturing Process Case Study
### Design of the Case Study for a Metallurgical Process  
Firstly, the modeler must define a time horizon and units of time. It is easy to carry out this step by asking to what extent the simulation should be considered. In the case of this study, it was decided to simulate one working year to evaluate influences in the short and medium term. The simulation was performed with 250 time periods, each representing one production day. Secondly, the manufacturing system structure was set to apply the conceptual model and to be able to simulate it under certain conditions. The structure consists of a steel-making manufacturer producing shot-peened round bars. As shown in Figure 3, the process starts at the EAF (electric arc furnace), followed by the secondary metallurgy, rolling process, heat treatment process, as well as finishing and inspection processes. The system consists of warehouses of raw materials and finished products in addition to their production facilities. Finally, end-customers are at the end of the chain receiving the products shown in Figure 3.  
Figure 3: Manufacturing system of the metallurgical case study (own elaboration). Figure 2: Casual-loop diagram (CLD) for the manufacturing process factors. Third, general assumptions were made to answer the research question, thereby allowing a reduction in model complexity. The following assumptions were applied to all scenarios and models of the case study:  
* The product is a finished/sale product after the final inspection process. * The orders have only one product type, shot-peened round bars. * Demand level is based on customer orders, and it is the same for the same scenario in the different simulation models. * The manufacturing system follows a make-to-order production system. * The manufacturing system initiates the simulation with work-in-progress (WIP) units along the production steps and warehouses. * There is no transport limitation or transport means limitation in the different stages. * Replenishment times between stages at the beginning of the case study have the same distribution over the period considered. * Order information along the manufacturing system is available. * Demand is not known, but historical data for all customers are available one day after orders are placed. * Customers do not leave the company or order more if the last orders are not met on time. * At the beginning, all employees have the same experience and have the same capacity to perform warehouse activities. * Production capacity is always between a minimum and a maximum, given a capacity per shift and the number of employees, if no decision has been taken during the simulation. The minimum and maximum production capacities per shift are the same for all models at the beginning of the simulation study. * Storage capacities have a maximum level, and it is the same for all models at the beginning of the simulation. * Products do not suffer any kind of problems/failure in their transportation from the production facility to the customers. * Packaging is performed in the production facility. * Safety stock levels change as required for the target service level. The target service level is calculated based on the reorder point method. * Monetary means to finance the manufacturing process are assumed as given. As a fourth step, the exogenous variables as inputs to the model are described. The following are used in the case study:  
* Market demand is defined by values read from a database outside of the model. Demand defines the evolution of customer orders. * Production capacity has a maximum of 4000 units per day in three shifts at the beginning of the simulation. During the simulation, the capacity levels of the different production processes within the manufacturing system are affected by the information received, the material available, the energy supply, the quantity and qualification of personnel and capital equipment, and the monetary capability. * Storage capacity at the beginning of the simulation is 3000 units.