## 2 Materials and Methods  
### Methodology  
In this study, a simulation case study was applied as the methodological approach. The following is an elaboration of the key components encompassed in the methodology of a simulation case study. We conducted our case study in accordance with the approach recommended by [6]. First, define the specific objectives of the simulation case study, including the questions or challenges the study aims to address within the context of the identified problem in production line. Second, conduct a thorough review of the existing literature to identify relevant theories, models, and methodologies related to the simulation of systems and the literature on productivity improvement research on each workstation through system simulation. By referring to past simulation and productivity-related literature, we understood and became familiar with various practical applications of simulation and workforce planning to solve practical problems.  
Furthermore, the next stage was building a conceptual model--the development of a conceptual model describing the environment, production line data, production line process logical structure, description of each group's scenarios, and description of the production line parameters and data used by each group in the model. The design of simulation models and assessment of their improvements are described in the conceptual model. The subsequent step involves determining scenarios in model simulation. The selection of multiple scenarios is underpinned by thorough discussions with case company personnel. Each chosen scenario represents a unique set of conditions and parameters that are deemed critical to the understanding of the production lines processes. Each scenario was evaluated not only in terms of its representativeness of actual operational conditions but also with respect to the feasibility of inducing or replicating such conditions within the production environment.  
Afterward, the focus shifts to collecting data. The data collected from the production line covers all aspects of the production line of the case factory, including the production hours of each workstation, the types and proportions of production raw materials, the production line process, the number of production personnel at each workstation, the production restrictions of each workstation, and the machines of specific workstations. To make the simulation more accurate, we collected production data from the past three years and integrated and analyzed various data. Among them, the production working hours of each workstation were analyzed using the analysis software MiniTab. Then, data analysis was conducted on the data to confirm what kind of continuous probability distribution they belong to.  
This study conducted a series of observations and discussions with case factory personnel to gain an in-depth understanding of the production line operations and problems faced by the case factory. Through focus group discussions and onsite debate by researchers, the entire production line was divided into three production areas: manufacturing area one, manufacturing area two, and manufacturing area three. This division provided the researcher a clearer understanding of each production area's operation and related conditions. A discussion of results regarding the completed production line model and individual issues in manufacturing areas one, two, and three was carried out. A reflection of the research was performed as a suggestion for potential future research based on the research and results of this paper. Due to data availability, data were collected from the past three years. The simulation assumes that the system reaches a steady state, where its behavior becomes consistent over time. It implies that the results may not accurately represent transient phases or sudden changes in the system. The generalizability of the results may be limited to this specific case company because of industry-specific characteristics of transformer factory and limited variables included in this study.