Fasteners and Sealing
strong, load bearing threads in relatively thin sheets of metal. The generic term for this type of fastener is self-clinching nut. A current day use of the technology illustrates its benefits over other joining methods. In the German automotive sector, there is a
company producing seat rails for three of the leading car manufacturers. In recent times, there has been a need to reduce component weight for environmental considerations while retaining strength for safety reasons. This has meant that the seat rail has become thinner but is now made from a harder material so self-piercing fasteners and even welding are no longer an option.
The result is
that the majority of road cars made in Germany have their seats attached with self-clinching fasteners. Although
primarily intended for the aerospace industry, an interesting new
Fig. 3. Launched at the 2012 Farnborough International Air Show, the RivNut Aero combines the benefits of the rivet nut and the strength of the threaded insert.
development from Böllhoff Armstrong is suitable for joining thin plates or non- metallic panels uses a rivet nut to provide the depth of
thread required and a threaded insert to provide the required strength and load distribution. The new component was launched at this year’s
Farnborough International Air Show and includes a rivet
nut made by Böllhoff in France, with a threaded insert from Böllhoff Armstrong fitted into it. The result is the Rivnut Aero which combines the benefits of both Rivnut and HeliCoil. The user is presented with a high resistance self- locking insert nut which provides a resistant thread on carbon steel and aluminium plates. The design prevents unscrewing and plate sliding and is very flexible in use because of its all- in-one installation kit.
Corrosion resistance
The shank is made of 316L stainless steel, which ensures the necessary corrosion resistance and mechanical characteristics. The HeliCoil Screw-lock helical thread insert prevents unscrewing and plays its part in providing the desired connection performance. The threads can be silver-plated to prevent binding. The design has some real advantages combining the
advantages of blind installation, reliable and reproducible results and possibility of checking the swage quality during the fitting operation with those of the helical thread insert, which include efficient and durable anti-unscrewing to ISO 2320, a high wear resistance of the thread as well as excellent resistance to vibrations and thermal shocks. After the roller coaster ride of 2011, the European motor industry is seeing a marked upturn in fortunes and despite continuing economic uncertainties in the Eurozone, EU motor manufacturing is forecasting car sales of 14 million in 2012. The manufacturers’ adoption of sustainable designs using lighter materials has certainly been a key element of this success. In their own way the fastener industry has made an equally valuable contribution by developing the joining techniques required for fabrication with lighter materials. l
Self-piercing threaded stud A
ston Martin’s designers and engineers teamed up with Henrob to
develop a self-piercing threaded stud that would cope with the extreme demands of auto body applications. Aston Martin’s DB9 has a body
structure fabricated from high- strength aluminium alloys and exotic aerospace composites, and it is every bit as impressive under the skin as it is on the surface. When specifying a trim and
earth attachment studs, the designers at Aston Martin were faced with serious challenges in finding a product that fulfilled all of their stringent design criteria. The studs had to be fixed to anodised
Fig. 4. More than 200 self-piercing studs are inserted in each DB9 body.
aluminium panels, which meant that welding was out, as the difficulty of welding through
the anodic film would prevent the studs from attaching properly to the panel. The head generated during welding would have locally damaged the anodic film, thus
compromising the anti-corrosion performance of the body structure. The studs also required a high
degree of electrical continuity, so they could be used to earth the many electrical components attached to the body structure. This meant that adhesively bonded studs could not be used, as little current would pass through the adhesive layer between the stud and the car body. As heavy items of in-car equipment would be attached to the body using the studs, the studs required a high degree of mechanical strength, torque and vibration resistance. Over 200 Henrob self-piercing
studs are inserted in each DB9 body in a simple one-shot process that does not require pre-drilled holes, is quiet, clean and repeatable. l
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