Abstract
The multi-material design and the adaptability of a modern process chain require joining connections with specifically adjustable mechanical, thermal, chemical, or electrical properties. Previous considerations primarily focused on the mechanical properties. The multitude of possible combinations of requirements, materials, and component- and joining-geometry makes an empirical determination of these joining properties for the clinching process impossible. Based on the established and empirical procedure, there is currently no model that takes into account all questions of joinability—i.e., the materials (suitability for joining), design (security of joining), and production (joining possibility)—that allows a calculation of the properties that can be achieved. It is therefore necessary to describe the physical properties of the joint as a function of the three binding mechanisms—form closure, force closure, and material closure—in relation to the application. This approach illustrates the relationships along the causal chain “joint requirement-binding mechanism-joining parameters” and improves the adaptability of the mechanical joining technology. Geometrical properties of clinch connections of the combination of aluminum and steel are compared in a metallographic cross-section. The mechanical stress state of the rotationally symmetrical clinch points is qualified with a torsion test and by measuring the electrical resistance in the base material, in the clinch joint, and during the production cycle (after clinching, before precipitation hardening and after precipitation hardening).
Highlights
The technical task of joining materials to one another leads to extended or new demands on joining technology against the background of constantly increasing functional integration in production
The change in the inherent resistance of the aluminum material is negligible for the measured increases in the bond resistances. These comparison series were created in order to show the influence of the different mechanical stress states at the clinch point, which in the case of mixed joints leads to different formation of the binding mechanism force-closure as a result of the precipitation hardening process, depending on the joining direction
The strain hardening generated by the clinching process, which is inhomogeneously distributed in the clinching point, affects the residual stress state of the joint
Summary
The technical task of joining materials to one another leads to extended or new demands on joining technology against the background of constantly increasing functional integration in production. The dimensioning of clinched joints is based primarily on the geometric characteristics of neck thickness and undercut (Figure 2b) as well as the main load case in the later life cycle In this design according to the state of the art, the force-closure component has not yet been taken into account in the dimensioning. Due to the large local deformations of the joining parts during the clinching process [3], the recrystallization temperature is reduced [8] This results in a reduction of force in the joint between the parts to be joined, which causes a change in the surface pressure between the parts to be joined and influences the existing binding mechanism of the force –closure component. By knowing these influencing factors, it is possible to produce a functional and function-related clinch connection
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