Development of an Automotive Polymer Expansion Tank : Material selection, design methodology, and manufacturing guidelines for future applications

This master’s thesis presents the development of a lightweight and manufacturable plastic expansion tank foran off-highway vehicle application, aiming to replace the current welded stainless steel design. The existing metal tank design suffers from fatigue-related weld failures and geometric limitations due to manufacturing constraints. To address these issues, the project investigates suitable plastic materials and manufacturing methods and develops a new design tailored to the operational and structural requirements specified by theoff-highway vehicle manufacturer (OHVM).The methodology follows a structured product development process using the double-diamond model. Initial stages involved unstructured interviews, customer requirement gathering, and the creation of a detailed specification of requirements. Concept generation was supported by mind mapping and braindrawing techniques. Material exploration was conducted using the Ashby method in combination with Ansys Granta EduPack, while manufacturing methods were evaluated through a weighted concept selection matrix. Iterative design development was carried out in CAD, followed by structural validation using Finite Element Method simulations. Selective Laser Sintering was ultimately selected as the most suitable manufacturing method, with PA2200 (a PA12-based material) chosen for its mechanical properties and compatibility. The final design reduced the tank volume from 25 to approximately 14 liters, achieving significant weight savings while meeting mechanical and functional performance targets. In addition, the thesis proposes a set of design guidelines to facilitate future development of plastic tanks at the OHVM.The result is a robust, lightweight expansion tank concept with practical design knowledge applicable to future product developments at the OHVM.