The development of new lightweight construction concepts is posing ever more stringent challenges for connection technology. This applies not just in the field of functional elements such as nuts or bolts, but also in the field of solid punch rivetting. Georg Donhauser reports.

The demands made on functional elements are particularly stringent in the airbag sector. A secure hold inside the airbag housing, which is frequently made of galvanised sheet steel, is reliably guaranteed by the refined steel rivet bushing.

For this application, the serrated throat of the Anchor rivet bushing is inserted in the prepared retaining hole in the component. The overhang is beaded around using a simple tool, leaving the bushing securely anchored in the component.

This process leaves a completely flush rivetted connection as standard. Kerb-Konus is able to guarantee its stringent quality standard by optical measurement of all characteristics of the functional elements with operational relevance. The maximum admissible breakaway torque can be tested for each individual rivet bushing using special machines.

The serrated rivet bushing is used for connecting thin mouldings with a material thickness of between 0.5 and 5.00mm. Installation takes place by means of a hydraulic, articulated lever or eccentric press into punched, drilled or laser cut retaining holes. The Anchor is torsion-proof and can be used on both sides in surface treated, galvanised or non-weldable materials. Depending on the application, either Anchor, Mini-Anchor or Tank-Anchor functional elements can be used, and are available in the materials steel, stainless steel, brass and aluminium. The Anchor rivet bushing is capable of withstanding bilateral loads and also offers an amazing degree of pull-out resistance.

The Anchor rivet bushing is used in wide-ranging sectors of industry. Its high degree of reliability coupled with equally exemplary quality make this technology suitable for successful airbag design.

To allow any possible contact corrosion to be avoided when working with functional elements made of steel or stainless steel in aluminium components in the future, Kerb Konus is investing heavily in research.

Another functional element used in connection technology is the Clifa press-in nut. The nut body comprises an insertion collar, a peripheral groove and knurled area below the head which prevents nut rotation. The hardened thread carrier is available in steel, stainless steel and aluminium. One of the special benefits of this functional element is the minimal installation force required when inserting into mouldings.

This type of press-in element is used primarily in the automotive engineering industry, for example in the construction of transducers. Using highly complex production technology, Kerb-Konus has succeeded in developing a mass product which is capable of withstanding even the most stringent demands: The Clifa press-in nut ensures an absolutely secure hold even when working with widely differing radii.   

A bolt thread complying with the same requirement profile as the Clifa press-in nut was developed in the form of the Clifa press-in stud.

The Clifa press-in stud, known as the Clifa-SP or SA for short, is used depending on the thread size from a sheet metal thickness of 1mm. As in the Clifa nut, the press-in stud also presses the material from the hole wall into the peripheral groove under the head of the stud. The threaded portion of the stud prevents turning, and the material forced into the groove prevents the stud from being pressed out. The press-in stud is available in lengths ranging from 6 to 60mm. For withstanding particularly high loads, Kerb Konus recommends the Clifa-SA, which is capable of absorbing higher

pull-through forces than the Clifa-SP. These functional elements are available in steel or stainless steel.

The punched rivet system Tuk-Rivet guarantees a secure hold for special applications. This joining technique permits not only materials such as steel, stainless steel or aluminium to be connected, but also ensures outstanding strength in components made of coated and lacquered materials too. In addition, the rivet can be used in connections involving more than two layers of sheet material. This innovative new connection system is available in steel, stainless steel and aluminium.

In all of these examples, the rivet length has been dependent upon the sheet metal thickness. But today’s automotive industry is laying down new and stringent challenges to Kerb-Konus technology, with a request for a single rivet capable of use in different material thicknesses. The objective aim was for an aluminium car door to be rivetted as a single component with different sheet metal thicknesses using just one rivet length and one robot. The aim here was to join individual components made of die cast aluminium and aluminium sheet to form total material thicknesses ranging from 2.7mm to 4.3mm.

The multi-grip rivet was developed to address just this type of requirement. This joining technique permits different overall material thicknesses to be joined quickly, simply and without problems. As the self-punching rivet is harder than the component, it retains its original geometry even after punching through the component. To achieve even higher connection strength, the designer favours the additional use of adhesives. Although the rivet cuts through the component with the adhesive in-between, this has no influence whatsoever on the rivetting system.

Another benefit of the Kerb-Konus aluminium punched rivet is that it permits a corrosion-free connection in magnesium components.

To allow greater material thicknesses to be connected even more effectively in aluminium or magnesium, Kerb-Konus is currently working on the development of a technical ceramic material characterised by high stability under pressure. This product will make corrosion a thing of the past. The first usable results have already been attained. 

Georg Donhauser is with Kerb-Konus-Vertriebs-GmbH, Amberg, Germany. www.kerbkonus.de