Mechanical joining technologies like self-piercing riveting are gaining importance with regard to environmental protection, as they enable multi-material design and lightweight construction. A new approach is the use of high nitrogen steel as rivet material, which allows to omit the usually necessary heat treatment and coating and thus leads to a shortening of the process chain. Due to the high strain hardening, however, high tool loads must be expected. Thus, appropriate forming strategies are needed. Within this contribution, the influence of applying different temperatures for each forming stage in a two-stage rivet forming process using the high nitrogen steel 1.3815 is investigated. The findings provide a basic understanding of the influence of the temperature management when forming high nitrogen steel. For this purpose, the rivets are not formed at the same temperature in each stage, but an elevated temperature is applied selectively. Different process routes are investigated. First, cups are manufactured in stage 1 at room temperature, followed by stage 2 at 200°C. Second, cups are formed in stage 1 at 200°C and used for stage 2 at room temperature. By comparing the findings with results when applying the same temperature in both stages, it is shown that the temperature during the first forming operation has an effect on the forming behaviour during the second forming stage. The required forming forces and the resulting rivet hardness can be influenced by process-adapted temperature application. Furthermore, the causes for the temperature impact on the residual cup thickness in stage 1 are evaluated by a cause and effect analysis, which provides a deeper process understanding. The thermal expansion of the tool and the billet as well as the improved forming behaviour at 200°C are identified as the main influencing causes on the achieved residual cup thickness.

In conjunction with mechanical joining processes. Mechanical joining processes play a key role for the realization of multi-material lightweight structures, which are essential with regard to environmental protection. However, joining of dissimilar high-strength materials is challenging due to the varying properties of the joining partners and due to their high flow stresses and often limited ductility. Thus, the evolution of established processes as well as the development of innovative and highly productive joining technologies are necessary. Requirements for a highly volatile production environment are versatility, flexibility, resilience and robustness. Within this contribution, current trends and innovations related to selected mechanical joining processes for enabling the material mix are outlined in order to point out opportunities to address these requirements in the future. In this context, joining using cold formed pin structures is presented as a promising approach for connecting dissimilar materials like metals to fibre-reinforced plastics. Furthermore, it is shown how the shear-clinching technology can be combined with a process-adapted application of locally limited heat treatment in order to promote the joinability and control the material flow during joining. A novel approach for reducing process forces and expanding process windows is the use of ultrasonic assistance for mechanical joining operations, which is demonstrated by the example of a nut staking process with superimposed high frequency oscillation. As concerns the widely used self-piercing riveting technique, current research activities relate not only to the further development of the joining process itself, for example by combining self-piercing riveting and tumbling, but also to the use of new rivet materials like high strain hardening stainless steels. In addition, the evolution towards mechanical joining 4.0 against the background of data-based process control in conjunction with of mechanical joining processes is also subject of the considerations.

High-strength aluminum alloys are more and more used for safety and crash-relevant components due to their advantageous density-to-strength ratio. By using thermal-supported forming strategies, failure-free deep drawing is possible for these materials. In this context, the hot form quench process (HFQ®) has shown to be a promising thermally-assisted forming strategy. By using locally tempered forming tools, the production of tailored components with different mechanical properties is possible. However, material characterization and process design with conventional characterization methods are quite challenging in this context. A new approach is the use of ultrasound-assisted material characterization in combination with a thermo-mechanical simulator. Thereby it is possible to perform an in-situ material characterization. So far, this technology is mainly used for steel materials. In this contribution, the potential of an adapted measurement strategy for high-strength aluminum alloys is presented. For this purpose, the influence of different measurement parameters on modified samples and the resulting measurement signal is investigated. With the help of this study, new standards are set for time-bound material characterization under thermo-mechanical stress. As a result, thermally-assisted forming methods can be designed more efficiently and faster in the future.