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Clinching of high strength steels is currently difficult due to their relative low ductility. Hence a new method has been developed to clinch these steel grades. This could be achieved by heating the sheets locally at the joint by a laser during the clinching process. The short-time tempering behaviour of the press hardened steel 22MnB5 has been investigated by dilatometry respectively calorimetry experiments. Different stages of the tempering process have been identified depending on heating rates up to 1000 K s−1. Characteristic tempering reactions were shifted to higher temperatures with increasing heating rate. Based on these results, suitable short-time heat treatment parameters have been selected and transferred to the clinching process. Thereby the press hardened steel 22MnB5 has been successfully clinched with laser assistance for the very first time. The laser assisted clinched joint has been characterised by metallographic analysis and hardness testing. It could be shown, that in the clinching joint only a slight strength loss occurs due to the introduced laser heat.

Wenn schubbeanspruchte Anschlüsse im Stahlbau Belastungen aus Schwingungen und/oder Lastumkehr ausgesetzt sind, kein Schlupf auftreten darf und auf der Baustelle gefügt werden muss, sind gleitfest vorgespannte Schraubverbindungen vorzusehen. Diese so genannten GV‐Verbindungen müssen mit hohem Herstellungsaufwand gefertigt werden, was auf die Reibflächenvorbehandlung zurückzuführen ist. Wird der Korrosionsschutz für die Stahlkonstruktion durch eine Feuerverzinkung gewährleistet, sind für die Reiboberflächen ohne aufwendige Nachbehandlung geringe Haftreibungszahlen festzustellen, die zudem stark in Abhängigkeit von der sich ausbildenden Zinkschicht schwanken. Vor diesem Hintergrund wurden in einem kürzlich abgeschlossenen Forschungsvorhaben Untersuchungen angestellt, die eine Erhöhung der Tragfähigkeit in GV‐Verbindungen durch den Einsatz von Klebstoff aufzeigen. Für die erhebliche Traglaststeigerung gegenüber den elementaren Fügeverfahren – Klebung oder GV‐Verbindung – ist bei der Verfahrenskombination, die im Weiteren als vorgespannte Hybridverbindung verstanden wird, die eingebrachte Vorspannkraft verantwortlich. Bei sorgfältiger Kombination beider Verfahren können die Einzeltragfähigkeiten in etwa addiert werden.

No abstract

The use of clinch joints, e.g. vehicle structures, is determined by the reliability of the joint and its strength properties - in particular the fatigue strength. Clinch connections offer the advantage over form-closure and force-closure processes that they can also be used for hybrid material combinations. In order to be able to evaluate the influence of the geometry parameters such as e.g. undercut, neck thickness or also base thickness on the fatigue behavior, three clinch connections (in optimum and compromise design) with different tool parameters were designed and examined using the example of a joining task with aluminum sheet material. For this purpose, fatigue curves (F-N curves) in the range of high to very high numbers of load cycles (N = 105 to 107) were determined. In this load cycle range, a so-called "neck fracture" is mainly to be expected as the type of failure, whereas for quasi-static tests, a “buckling” is more likely to occur. The tests were carried out on single-cut overlapping shear tensile specimens. Metallographic and scanning electron microscopic examinations of the joints and the fracture surfaces served to identify the crack initiation site and to clarify the respective type of failure. Significant differences in the damage behaviour of the three clinching variants could be shown. This observation enables one step into the direction of fully understanding the relationship along the causal chain "joint requirements - joining process - fatigue strength". Thus the adaptability of the clinching process can be improved.