Fixed ideas

The car industry is constantly seeking faster, more cost-effective fastening solutions to replace traditional welding and riveting.

The car industry is renowned for its relentless quest for better, more cost-effective manufacturing methods. And with perhaps 30,000 individual components in a typical modern car, fastening and joining continues to be a major focus of attention.

So, when car makers design their new models, it is not surprising that they should look for solutions that provide greater benefits than traditional welding and riveting. Various mechanical techniques, such as pierce and clinch fastenings, blind fasteners, bandclamps and adhesives, are growing in popularity.

Land Rover is taking full advantage of the cost and quality benefits associated with pierce fastening, by specifying more than 320 varieties of clinch nuts and studs in the assembly of its latest generation T5 platform Discovery vehicle. The use of fastening technology from Profil has become Land Rover’s preferred method of providing male and female threads in sheet metal components and body panels, superseding welded and other standard threaded fasteners in many areas of its vehicles.

Pierce and clinch fasteners offer high-speed installation, reliable high-strength, foolproof quality control, excellent water sealing and both vibration and corrosion resistance — at minimal installed costs.

According to Profil UK’s Adrian Ellis: ‘Not only can the fasteners be installed during the pressed components’ forming process — using a dedicated station within the multistage progression tooling — but they can also accommodate panel thicknesses from 0.6–6.0mm. They are also suitable for use with coated or uncoated materials, high-grade,

stainless and sandwich steels, and can even be installed in aluminium and magnesium castings.’

These are major benefits over welded fastening methods, which are slow and open to many more process variables than pierce/clinch installation methods.

‘As pierce/clinch fasteners are installed as part of the presswork process, they offer significantly better positional accuracy and repeatability over other fixing methods,’ said Ellis. ‘In most applications, tolerances of +0.2mm can readily be maintained, while a figure five times this value might be expected for corresponding welded parts.’

As they can be secured in sheet metal components as part of their multi-stage forming process, nuts or studs can be installed at more than 100 fasteners/min.

Ellis said that even in manually-fed applications, up to 30 per cent installed cost savings can be achieved. ‘A key factor is that automatic sensing can easily be incorporated into the press, to ensure no components can be made without the required fasteners being correctly installed,’ he said.

Blind fasteners supplied by Rivetnut Technology Systems are used by Aero Tec Laboratories in the production of their fuel bladder tanks for the motorsport industry. The fasteners are used on bolt rings as part of the filler cap entry in a fuel cell construction, and form an integral part of the safety element. The deep female threaded anchor can be securely fitted to thin sheet materials.

Installation is both quick and accurate, using hand-held power tools only.

The M5 and M6 thread steel version used by Aero Tec features a knurled body, which provides increased torque resistance at the fixing point, together with a sealed-end thread to prevent fuel leakage. These features help maintain the high fuel-seal integrity required.

Protex quick-action Bandclamp fasteners are speeding the inspection and testing of water and air-cooled radiators and intercooler systems manufactured by aluminium and titanium welding specialist AH Fabrications.

The Hereford-based firm supplies a wide variety of fuel, oil, air and water systems to customers, ranging from World Rally Championship teams to club racers.

According to the company’s owner, Alex Hanczarski: ‘Band clamps are perfect for securely attaching air adapters used to pressure test radiators, oil coolers and intercoolers. They combine the benefits of a worm drive hose clip with the speed and convenience of an over-centre fastener. Bandclamps can also be adjusted quickly to accommodate a variety of adapter diameters.’

AH primarily employs models from the stainless steel Protex 58 PBC-HT range, which incorporate a triangular platform for the latch to be closed against.

This feature optimises the bandclamp’s geometry during its locking action, avoiding the need for excessive operating pressure and/or the subsequent relaxation of grip as the fastener’s mechanism goes ‘over-centre’ on small diameter parts.

It is not just mechanical fastenings that are gaining greater acceptance, but chemical bonding. On average 15kg of adhesive is used per car, and this is set to rise as more efficient hi-tech products are developed. The importance of the sector to adhesives manufacturers is reflected in the fact that Delo Adhesives of Germany claims that 25 per cent of its R&D activities are focused on the car industry.

Solved applications so far include: airbag, light and rain, fingertip and driver-interface sensors LED encapsulation; micro-switches; navigation systems and anti-theft systems.

The ever-growing requirements concerning stability, reliability and processing drive adhesive manufacturers to continuously develop more efficient hi tech products. Approximately 0.02g of adhesive is necessary to seal a microswitch and 0.1g for airbag sensors. These may be minute amounts, but with permanent temperatures of up to 150º C in the engine compartment, plus contact with oils, fuel, coolants and brake fluid as well as high vibrations and extreme changes in condition, they must provide maximum performance to ensure the safety of the electronic vehicle control.

Another adhesive manufacturer well versed in the demands of the car industry is Huntsman, with its Araldite SMC bonding range. In an application for Scania Trucks, Polynorm Plastics bonded a front radiator grill and engine hood assembly on a range of trucks. The bonded joint had to be able to withstand 80º C during the paint cycle and varied weather conditions (-20º C to +80º C, up to 100 per cent humidity) during the vehicle’s working life.

It also had to be able to resist road vibration for the truck’s life — typically 500,000 miles. Araldite 4910 was used to bond Menzolit 5320 Class A SMC substrates in a secondary process, rather than riveting or welding.

Bonding was found to provide better vibration resistance than mechanical fasteners and also reduced stress concentrations. Each assembly involved four simple lap joints. Two joints bonded stiffeners running the full length of the assembly on each side. Two smaller inserts were then bonded. The process was completed in ambient curing conditions.

‘We chose to use the adhesive because it gave us a number of processing, performance and health and safety advantages, by eliminating the need for a highly volatile primer’, said Polynorm Plastics’ Gordon McDonough. ‘It was suitable for this application as the adhesive was available in cartridges and required only simple pre-treatment of the SMC.

There was also no heating of the jigs, which allowed us to produce parts more cost effectively and still have a short time-to-handling strength.’