Energy Efficiency Based Analysis and Optimization of Friction Riveting

The rapidly growing public concern and awareness on issues related to climate change, has forced a fast shift across several industries toward more sustainable practices and products. Industries which have been some of the most challenged on this regard are those in the transportation sector. Here, designs and engineering solutions have been forced to adapted at a far greater pace than usual. With this push for change, ways to integrate alternative materials and less conventional technologies, which can benefit the overall designs, are becoming a necessity rather than an option. Examples of new designs which embrace the use of dissimilar material combinations are becoming common. In order to effectively increase the use of less conventional materials, e.g. in automotive or aeronautic applications, new technologies are being developed in order to overcome the restrictions imposed by conventional methods, such as mechanical fastening and adhesive bonding. In this work a variant of an alternative dissimilar material joining technology has been investigated. Designated as Friction Riveting, this process allows multi-material overlapping joints to be performed in a fast and relatively simple manner. One variant of this process is designated as force-controlled. The present work studied how this process variant parameters influenced the amount of energy applied to the materials being joined. Design-of-experiments and response surface methodologies were applied in this investigation to maximize the knowledge gained on the fundamentals of the process, the performance of the joints produced and also on their energy efficiency. Statistical analytical models were established, allowing the production of fine-tuned joint formation and resulting mechanical performance. Optimizations on process control, energy efficiency and process parameter flexibility were achieved. Based on mechanical performance, an energy efficiency threshold was established. After this energy level, excessive rivet plastic deformation inside the polymeric plate was observed and did not contribute to an improvement in mechanical performance of the joints. The feasibility of an even more specific process approach, designated as single-phase friction riveting, was successfully and systematically demonstrated. Here, it was possible to achieve sound joints while greatly reducing the forces used during the process. This can lead to a wider range of applications for this technology, requiring less robust equipment and thus, more flexible to be integrated into production designs. The knowledge gathered in this investigation has further demonstrated the potential of the friction riveting for dissimilar material joining.