## 2 Materials and Methods  
In the pursuit of fostering sustainable engineering practices and advancing the circular economy paradigm [33], this article bridges the gap between theory and practical implementation. The introduction sets the stage by highlighting the critical need for resource-efficient approaches to hydraulic drive system maintenance, emphasizing the potential environmental impact reduction and waste minimization. Building upon these foundational principles, the current section of the article provides a comprehensive roadmap for the application of additive manufacturing and reverse engineering techniques [34] in the remanufacture of hydraulic drive system components. The primary novelty of this work lies in the integration of advanced additive manufacturing techniques, particularly 3D scanning and reverse engineering, for the remanufacturing of hydraulic drive system components. This approach allows for the cost-effective and sustainable restoration of these components, thereby contributing to the principles of the circular economy. The fusion of cutting-edge additive manufacturing methods with reverse engineering not only facilitates the accurate reproduction of complex hydraulic components but also provides an environmentally friendly and economically viable alternative to the traditional production of new components. The use of 3D scanning in describing hydraulic drive system components during the remanufacturing process is supported by several key factors. This method excels in accuracy and precision, vital for replicating intricate hydraulic parts to match original specifications. Its reverse engineering capability enables converting physical components into digital models. The technology efficiently captures complex geometries, expedites data capture, and reduces human error in the reverse engineering process. By reusing existing parts and employing 3D scanning for accurate replication, it ensures sustainability and cost-effectiveness. Moreover, its integration into quality control assures remanufactured components meet original quality standards. Overall, 3D scanning proves effective in ensuring accuracy, capturing complex geometries, enabling efficiency, promoting sustainability, and verifying precise adherence to original specifications in the remanufacturing process. In the context of the circular economy, the remanufacturing of hydraulic drive system subassemblies (HDSA) entails the utilization of functional components within the subassemblies, along with the repair or production of a new component (if repair is not feasible) to restore the subassembly to its original operating parameters. Subsequently, the remanufacturing procedure outlines the recommended steps taken to fabricate a remanufactured volumetric flowmeter rotor using additive manufacturing. To begin with, the flowmeter is disassembled to identify the defective part. As shown in Figure 2, one can notice that the rotor of the flowmeter was damaged during a faulty maintenance procedure, leading to the damage of one of its blades. Figure 2: Problem identification—defective flowmeter rotor. The rotor's geometry is intricate, and even the slightest deviations from it can significantly affect the flowmeter's measurement accuracy. In this instance, repairing the rotor is not feasible, and the component is not available on the market as a replacement part; the only viable option is to manufacture a new rotor with identical geometry. To economically produce the new rotor while minimizing material consumption, the Masked Stereolithography Apparatus (MSLA) additive manufacturing technology was chosen. This technology allows for the fabrication of details with dimensions as small as 50 \(\upmu\)m and employs plastic materials resistant to the oils used in hydraulic drive systems (HDS) and their additives. Given the complexity of the flowmeter rotor's geometry, and the limitations of measurement tools to fully describe this geometry, the principle of reverse engineering was adapted to this case.