Digital modeling of the self-pierce riveting process

Self-pierce riveting is an increasingly popular process, particularly in the automotive industry, for joining materials of different types and thicknesses. A highly rigid rivet is driven into two or more metal sheets (steel, aluminum, magnesium, plastic) held together by a cap and a clamp. The rivet pierces the first sheet, then expands into the next, depending on the shape of the bolt used. The assembly point created in this way offers a number of advantages, as described in Part 1.

If self-pierce riveting is now well mastered, its improvement is mainly due to trial-and-error techniques, or to the experience of technicians. However, this experimental method is becoming difficult to apply in view of the increasing number of assembly configurations (grades, thicknesses), the multiplicity of process parameters and shorter development times. The use of a numerical simulation tool for the riveting process therefore appears to be a solution for reducing costs and development times, and enabling a more complete exploration of the technique. Finite element numerical modeling is now widely used for material shaping. It has proved very useful for gaining a better understanding of the physical and mechanical phenomena encountered, and thus for modifying and/or improving an existing process. In the context of self-pierce riveting, numerical modeling is particularly challenging, since it involves large plastic deformations, damage and fracture, and multi-material contact. This study is essentially devoted to the simulation of riveting itself. However, the simulation results (geometry, residual stresses, etc.) can be used to optimize the mechanical strength of the joining point.

In the second part, the basics of the mechanical model used are outlined, followed by a discussion of its numerical specificities in the third part. The fourth part is dedicated to the modeling of the process, and in particular to the precautions to be taken to ensure the correct implementation of the simulations, as well as to the validation of the numerical results. Finally, the fifth section shows how numerical simulation can be used to improve the self-pierce riveting process, as well as the final mechanical strength of the resulting assembly point. Finally, we show how the methodology developed for self-pierce riveting can be easily transposed to other contact joining techniques involving large plastic deformations.