Internal logistics investment project selection with Pythagorean fuzzy AHP and fuzzy grey relational analysis method for a porcelain company

Nowadays, companies constantly have to make decisions. Company managers constantly make choices in various situations, such as supplier selection, investment project selection, marketing strategy selection, and new product selection. Choosing investment projects for businesses has become a very complex decision problem due to increasing competition, limited resources, and company strategies; there are various constraints, so choosing the right investment project is very important. The presence of more than one criterion and more than one alternative when selecting investment projects makes the decision-making process more difficult and manageable. Since the decision-making process is complex, it is essential to determine the problem and purpose, determine the criteria, and evaluate the selection method correctly, so the solution must be based on scientific foundations. Multi-criteria decision-making methods solve problems with many criteria and alternatives, such as investment project selection. The criteria are weighted thanks to various MCDM methods found in the literature. Then, each alternative is evaluated and ranked according to these criteria. However, in daily life, definitive judgments cannot be made, so there are questions that Classical MCDM Methods cannot answer. Various fuzzy MCDM methods have been developed using the fuzzy set theory to answer the questions. When the literature is examined, it is seen that a large number of fuzzy MCDM methods have been used. In addition, since the values, judgments, and experiences of decision-making individuals vary from person to person, it is impossible to express these opinions with exact numbers. Instead of using precise mathematical data, building a model with linguistic variables is a better approach. In Fuzzy Multi-Criteria Decision-Making problems, linguistic variables are used to determine the criteria weights and to select alternatives according to the determined criteria. As in every sector, transferring finished products to the porcelain warehouse is essential. Choosing the appropriate internal logistics system is crucial so that products can be readily stocked, workforce efficiency can be increased, and work is organized correctly. In order to efficiently coordinate the process and respond to changes that may be needed in the future, it is necessary to have a flexible system and make appropriate choices. There are many criteria, such as the logistics system's flexibility, cost, and availability of the internal logistics system that enables product transfer. This study aims to select the internal logistics investment project of a company serving in the porcelain industry using fuzzy MCDM methods, Pythagorean Fuzzy AHP, and Fuzzy Gray Relational Analysis method; these methods were developed to solve the decision problem with incomplete or limited information. First, the criteria and alternatives were determined. Decision makers evaluated four alternatives with the help of seventeen criteria, nine main criteria and sub-criteria of the main criteria, and linguistic variables found in the literature. The criteria were weighted using the Pythagorean Fuzzy Analytic Hierarchy Process Method, one of the fuzzy MCDM methods. Then, the alternatives were ranked using the Fuzzy Gray Relational Analysis Method. In the first part of the study, there is an introduction; in the second part, information about decision-making processes, Multi-Criteria Decision Making Methods, and Fuzzy Logic is given, then the solution steps of the Pythagorean Fuzzy AHP and Fuzzy Gray Relational Analysis Method are explained in detail, and the studies in the literature are mentioned. The third part shows the hierarchical structure related to the flow followed in the study. The application was made in the fourth part of the study, and in the fifth part, results and recommendations are presented. Detailed information of the application is explained as follows: Firstly, the main criteria and sub-criteria were determined by taking expert opinions and researching the literature. There are nine main criteria in this study: Flexibility to Adapt to Changes, Automation Level (Dependency on Person), Reliable and Stable Operation of the System, backup management, Loss of Space in the Warehouse, Application Duration, Environmental Friendliness, Ease of Use, Cost. The main criteria of "Flexibility to Adapt to Changes" has four sub-criteria: Adaptability to Product Volume Change, Adaptability to Layout Change, Adaptability to Product Type and Size Change, and Adaptability to Product (Pallet) Weight Change. The main criterion, "Reliable and Stable Operation of the System," has four sub-criteria: low Failure Rate, Ease of Maintenance Intervention, Low Spare Part Stock Amount, and Service Availability. The main cost criterion has three sub-criteria: purchasing, labor, and energy. A pairwise comparison matrix of each criterion was created, and the general and local weights of the criteria were calculated with the Pythagorean Fuzzy AHP method. Secondly, different alternatives were determined by taking expert opinions for project selection. This study has four alternatives: Rail Transit and Flexi AGV, Rail Transit and Shuttle System, Construction In-Tunnel Shuttle System, and Construction In-Tunnel Conveyor. Project selection and importance ranking of alternatives were made with the Fuzzy Gray Relational Analysis method using triangular fuzzy numbers. Criterion weights calculated using the Pythagorean Fuzzy AHP method were also used for this ranking. The alternatives are Rail Transit and Flexi AGV > Rail Transit and Shuttle System > Construction In-Tunnel Shuttle System > Construction In-Tunnel Conveyor. Alternative weights were 0.293, 0.271, 0.229, and 0.208, respectively. Rail Transit and Flexi AGV alternatives have been determined as the most suitable project for selecting internal logistics investment projects. With this study, the company is expected to make more beneficial investment decisions. It is thought that project selection can be made using different decision-making methods and the same alternatives and criteria. When looking at the literature, it has been seen that the Pythagorean Fuzzy AHP Method and the Fuzzy Gray Relational Analysis Method are used less frequently than other MCDM methods. In addition, there are no studies in which these methods are used integrally with each other. It aims to fill the literature gap with this alternative method applied for the first time in the porcelain industry. In addition, this study will contribute to the literature as it can be used not only as a solution to the investment project selection problem but also for any other decision problem.