Axial Tube Sealing by Plastic Deformation via Rotary Swaging

Many engineering applications require hollow structures that are completely sealed, such as tubes with closed ends. In this study axial plugs or caps are inserted during the forming process to provide a pressure-tight seal. Joining the sealing element and tube by plastic deformation represents one possible process route. Its advantages include the ability to join different materials and the low heat input. Rotary swaging is particularly suitable as it allows for undercuts, resulting in high joint strength. In this study, infeed and forward rotary swaging are used. The material combinations analysed were different grades of steel, aluminium alloys and brass. Additionally, the influence of different undercuts and additional sealing materials is investigated. Comprehensive experimental investigations are carried out in addition to a numerical study. The joint is evaluated by pressure tests, metallographic examinations of the joint zone and an analysis of the material flow. To delineate the process window, failure modes such as cracks of the pipe, insufficient undercuts or excessive deformation of the sealing element are investigated based on the variation of process and material parameters. The process principle is discussed for two applications with different requirements in terms of initial geometries and loads. Firstly for the production of Nd-Fe-B permanent magnets by rotary swaging as an alternative to the conventional sintering process. Secondly for a curved phase change actuator based on paraffin wax. A rectangular tube is to be formed axially symmetrically and sealed with a sealing element against pressures well above 100 bar.