Abstract
In this paper a process sequence, that uses forward rod extrusion with cold forged C15 steel cup billets to produce lightweight shafts, is presented. The steel cup billets feature either a lightweight magnesium alloy core or a granular medium core that is removed after forming to obtain hollow shafts without the need of complex tools and highly loaded mandrels. It is shown that composite shafts featuring magnesium cores can be produced for a wide range of extrusion strains. Due to high hydrostic pressures in forward rod extrusion, the forming limit of magnesium at room temperature can be expanded. The observed bond strength between core and sheath is below the shear yield strength of utilized magnesium AZ31 alloy. Hollow shafts are successfully produced with the presented process route by utilizing zirconium oxide beads or quartz sand as a lost core. As the law of constant volume in metal forming is violated by compressible granular media, a simulation approach using a modified Drucker-Prager yield surface to model these materials is validated to provide a tool for efficient process design. Granular cores and magnesium alloy cores offer new possibilities in production of lightweight shafts by means of composite cold forging. Both process variants allow for higher weight savings than composite shafts based on aluminum cores.
Highlights
Lightweight design in the transportation sector is indispensable nowadays to cut down energy consumption and greenhouse gas emissions
To judge the process success and to reveal the inner surface of the shafts extruded with granular medium core, the components are cut in half after the core is removed
The lightweight potential of composite cold forging can be increased by utilizing magnesium cores or granular medium cores that are removed after forming to obtain hollow shafts
Summary
Lightweight design in the transportation sector is indispensable nowadays to cut down energy consumption and greenhouse gas emissions, . Different lightweight design strategies impose different requirements on forming technologies and production engineering in general. The development and adaption of forming processes to the needs of lightweight design and ecological production is an ongoing field of research. In hybrid lightweight design approaches, materials are applied according to their specific properties and local requirements of a component. The use of multiple materials calls for methodologies to join them. To combine the advantages of hybrid lightweight design with the high precision and high output rate of cold forging, various studies focused on joining materials by means of cold forging processes
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