Joining by pin shear caulking: an alternative process route using metallic pins as shear cutting tool

Abstract

Pin joining represents a promising approach for the mechanical joining of multi-material structures, as it enables the formation of joints without auxiliary joining elements. To improve process efficiency, a modified pin joining process chain is proposed in which the pin itself acts as the cutting element, eliminating the need for pre-drilled joining partners. However, the interactions between the shear-cutting operation and the subsequent caulking process are not yet fully understood. This work experimentally investigates the influence of sheet thickness, relative pin height and cutting clearance on joint formation and mechanical performance in steel-aluminium joints produced by the pin shear-caulking process. A full-factorial design of experiments is employed. Joint performance is evaluated by tensile-shear and cross-tension testing, while metallographic analyses and microhardness measurements are conducted to characterise cut-edge morphology, undercut geometry and local strain hardening. The results demonstrate the feasibility of the proposed process chain and reveal pronounced interactions between the investigated process parameters. Tensile-shear strength is strongly influenced by the interaction between sheet thickness and cutting clearance. A previously reported non-linear effect of cutting clearance is confirmed for a wide range of process conditions and is linked to differences in burnish-zone formation. In contrast, cross-tension strength increases with increasing cutting clearance and is primarily determined by the geometry of the mechanical interlock formed during caulking. Furthermore, increasing sheet thickness and relative pin height generally enhance joint performance by promoting undercut formation and increasing the available load-transfer area. The findings provide a deeper understanding of the mechanisms governing the pin shear-caulking process and support the identification of suitable parameter combinations for future lightweight multi-material structures.