Connecting elements for connecting hard-pressed steel with aluminium/steel 1. The Tuk-Rivet punched rivet system The rivet comprises a rivet head, a shank area, one or more shank grooves and the cutting edge. The rivet is available in the materials steel, stainless steel and aluminium. Process sequence: Holding-down force FN Holding down device F Setting die L Perforating L force F+ Holding-down force FN F L F N F N F N Punching force FP F P P Bottom die Fix sheet Position rivet Perforation with rivet Form in rivet head Fill shank groove The process sequence shows that the rivet is pressed using a self-punching action through the component. When the rivet head is flush with the upper component, the holding-down device and the punch jointly press down on the component, causing the material of the lower component to be formed into the groove in the shank of the rivet. This process is made possible by a ring-shaped elevation in the bottom die. As the rivet is substantially harder than the component material, no deformation of the rivet takes place. 1
Rivet head Cross-section through the rivet Material in the groove Using Tuk-Rivet, components made of steel, stainless steel or aluminium can be connected. It is also possible to rivet coated or painted materials or more than two sheets together. Because the components are punched as a package, and deformation in the area of the rivet base is only very minimal, there is hardly any visible deformation at the surface of the component. To connect different overall material thicknesses with one rivet, Kerb-Konus has developed the multiple-range rivet. The rivet length is adjusted to the maximum thickness of the component. If the material thickness is reduced, the rivet base projects outwards. This must be taken into account by the designer when positioning the connection point. The material of the lower component is pressed into the nearest groove. If the strength of the rivet connection is not adequate, it is advisable to use a combination of rivets and adhesives. Although the rivet cuts through the component with the adhesive, this does not impact negatively on the rivet system. 2
The material 22MnB5 in combination with steel or aluminium poses a major challenge for the Tuk-Rivet punched rivet. As the following images illustrate, here too we have found a solution. The rivet with a shank diameter of 4.0 mm is able to connect the components using a self-punching technique. 22MnB5 1.6mm Aluminium 1.2mm Aluminium 1.2mm 22MnB5 1.6mm Aluminium 2.0mm 22MnB5 1.4mm HC 340 XD 1.5mm Aluminium 1.2mm These connections are only possible if the workpiece is made of the material 22MnB5 on the punch side or the central layer. In its hardened status, the material 22MnB5 has insufficient forming characteristics to permit its use as a component on the bottom die side. 3
The punched rivet connections are able to absorb not only high static forces but also, as the diagram illustrates, high dynamic forces. 4
2. The Anchor rivet bushing As a fixing element, the Anchor rivet bushing is particularly suitable in conjunction with laser cut retaining holes. When processing the bushing the notched area of the nut presses into the softened zone of the hole wall. Consequently for flush processing, very high torque levels can be transmitted. However, the requirement imposed on the borehole tolerance (max. + 0.1 mm) for the retaining hole must be observed in accordance with the Kerb-Konus works standard. Setting process of an Anchor rivet bushing Cross-section through the anchor Impression in the hole wall An anchor with thread size M 8 is shown here as an example. The admissible tightening torque for an M8 screw of strength class 8.8 is around 25 Nm according to VDI 2230. With the Anchor, we achieve around 38 Nm when testing in accordance with Kerb-Konus works standard 1.5. The withdrawing force is more than 6 KN. This guarantees that if the female thread of the Anchor is damaged, a new thread can be tapped in the event of a repair without the bushing coming adrift in the sheet. 5
Although the bushing in this case is only made of free cutting steel, the requirement imposed on the connecting element is complied with in full. 6