Study of an innovative joining solution for the wheel system

The objective of this thesis research is to develop an adhesive bonding solution in order to remove the classic welding technology exploited nowadays in the automotive steel wheel system. The examined solution is an hybrid joint, based on adhesive boding combined with the presence of an interference fit. This hybrid joining technology consists in coupling two cylindrical components together by force-fitting one into the other after having placed an adhesive on the mating surfaces. This technique would allow the joining of dissimilar material to enable the design of hybrid lightweight wheels. Moreover, it would provide a better stress distribution in the joint area that could induce fatigue life improvement. The contributions of the adhesive and the interference on the performance of the final hybrid joint is still not completely clear. In particular, the effect of the adhesive nature and of its mechanical and adhesive responses on the performance of the hybrid joint is under concern in this research. A study of the phenomena acting at the interference level is conducted at the laboratory level before industrial case application. An experimental method is set up in order to test the adhesives in a press fit joint. Static and dynamic tests are carried out examining the behavior of different adhesives, including rigid epoxies and flexible polyurethanes, and fractographic analysis are then performed. The second part of the study is focused on the feasibility of the hybrid technology on the wheel system. Exploiting the outcomes of the laboratory analysis, bonded wheel prototypes are assembled and tested statically and dynamically, according to component validation in MW. From the laboratory scale analyses it is found that the adhesive type mainly affects the static resistance of the hybrid joint. In particular the curing technology affects the decoupling behavior and the rheology influences the quantity of adhesive that remains inside the joint despites the interference levels. On the other hand, the interference rules the stiffness of the assembly and strongly affects the fatigue behavior of the cylindrical joint. The study conducted on the wheel component confirms the laboratory scale outcomes. For what concern the feasibility study, the bonded wheel shows similar performances compared to the welded wheel without design modifications of the components. However, the joint geometry has to be redesigned to exploit all the advantages of the adhesive bonding.