Certification dependent work scheduling model proposal in the welding process

The rail systems industry is a sector characterized by a wide variety of products, complex production activities, and high customer quality expectations. As a result, profitability is low for manufacturers of sub-components in the industry, and competition conditions are challenging. Therefore, it is crucial for manufacturers producing sub-components for the rail systems industry to effectively leverage the high-cost and limited workforce. In this context, the utilization of scientific approaches in workforce planning is necessary. This would lead to a reduction in defects, late deliveries, and inventory holding costs while increasing capacity. This thesis study aims to minimize the total delay and early completion times within the scope of delivery dates in a company that performs product manufacturing for rail systems using welding processes. To achieve these goals, a Mixed Integer Linear Programming (MILP) model has been used. In the company, the welding operators have welding competency certificates based on the type and thickness of the raw material. Consequently, not every welding operation required for each product can be performed by any welding operator. This situation leads to either prolonged waiting time for the parts that need welding or the operator finishing the job(s) early and having idle time. The proposed mathematical model considers constraints such as worker-competency control, worker availability control, setup time between two welding operations, and the assignment of each welding operation to only one operator. Additionally, the mathematical model utilizes actual data obtained from the company. The study results indicate that the proposed model provides better results than the current situation in the company. The study is considered to be useful for the literature and practitioners in the manufacturing sector in terms of assigning tasks and scheduling based on worker competencies.