During the design of automotive structures assembled using Self-Piercing Rivets (SPRs), a rivet and die combination is selected for each joint stack. To conduct extensive physical tensile testing on every joint combination to determine the range of strength achieved by each rivet–die combination, a great deal of lab technician time and substrate material are required. It is much simpler and less material-consuming to select the rivet and die solution by examining the cross sections of joints. However, the current methods of measuring cross sections by measuring the amount of mechanical interlock in a linear X–Y direction, achieved with the flared rivet tail, do not give an accurate prediction of joint strength, because they do not measure the full amount of material that must be defeated to pull the rivet tail out of the bottom sheet. The X–Y linear interlock measurement approach also makes it difficult to rapidly rank joint solutions, as it creates two values for each cross section rather than a single value. This study investigates an innovative new measurement method developed by the authors called Volumelock. The approach measures the volume of material that must be defeated to pull out the rivet. Creating a single measurement value for each rivet–die combination makes it much easier to compare different rivet and die solutions; to identify solutions that work well across a number of different stacks; to aid the grouping of stacks on one setter for low-volume line; and to select the strongest solutions for a high-volume line where only one or two different stacks are made by each setter. The joint stack results in this paper indicate that there is a good predictive relationship between the new Volumelock method and peel strength, measured by physical cross-tension testing. In this study, the Volumelock approach predicted the peel strength within a 5% error margin.

Self-pierce riveting (SPR) is a complex joining process where multiple layers of material are joined by creating a mechanical interlock via the simultaneous deformation of the inserted rivet and surrounding material. Due to the large number of variables which influence the resulting joint, finding the optimum process parameters has traditionally posed a challenge in the design of the process. Furthermore, there is a gap in knowledge regarding how changes made to the system may affect the produced joint. In this paper, a new system-level model of an inertia-based SPR system is proposed, consisting of a physics-based model of the riveting machine and an empirically-derived model of the joint. Model predictions are validated against extensive experimental data for multiple sets of input conditions, defined by the setting velocity, motor current limit and support frame type. The dynamics of the system and resulting head height of the joint are predicted to a high level of accuracy. Via a model-based case study, changes to the system are identified, which enable either the cycle time or energy consumption to be substantially reduced without compromising the overall quality of the produced joint. The predictive capabilities of the model may be leveraged to reduce the costs involved in the design and validation of SPR systems and processes.

Over the last few years, fuel economy improvement has driven the use of efficient multi-material structures in the car industry. The combination of dissimilar materials, such as metal-metal and metal-polymer, is a complex issue that requires the use of different and emerging joining techniques. In this context, self-pierce riveting (SPR) is an extremely suitable technique for joining two or more metal sheets, particularly when other techniques are not applicable. SPR requires short manufacturing times and provides both high strength and high fatigue resistance. Yet, this technique still faces some hurdles, such as joining Ultra High Strength Steels (UHSS) with high strength low ductility aluminum alloys, which can result in rivet cracking or aluminum button tearing. Suitable process parameters, including the rivet size and the die profile, are usually obtained through a physical testing procedure to satisfy the required joint specification. This is both expensive and time consuming. Finite element simulations of SPR are being increasingly used to reduce the number of physical tests and to estimate the tensile strength of the joint. The capability to accurately simulate aluminum to aluminum riveting has been demonstrated in recent studies. However, very few simulation studies have been conducted on the riveting of UHSS to aluminum, mainly because this type of joint is a relatively new customer demand driven by the rapid adoption of mixed material car body structures. New rivet designs have recently been developed for joining UHSS to aluminum, these rivets have increased column strength and increased stiffness to enable piercing through UHSS materials. In this study the insertion behavior of these higher strength rivets has been simulated and numerical analysis has been conducted to investigate the influence of the key process parameters on the joining result. The simulation results were compared to physical experimental results and good correlation was achieved.