A bumper solution to the Millennium challenge...
Creating a fastener for use with a new generation of recyclable components for the new millennium can call for a deep reservoir of expertise and willingness to invest time and money to find the right solution.
Such a case occurred when Norwegian bumper specialist Hydro Raufoss asked TR Fastenings to develop a fastener to hold in place a new product - a totally recyclable aluminium bumper for BMW cars. No suitable solution then existed, as the usual steel inserts would not permit the aluminium to be recycled at the end of the bumper’s working life.
TR was therefore tasked with developing a recyclable aluminium insert. As important as the environmental aspect was the stipulation that there must be no compromise in mechanical efficiency.
Two of the TR team assigned to the project were Colin Mileham, Manufacturing Manager of TR’s Hank Division, and Calum McMinn, a TR Technical Support Engineer. Calum McMinn explains: “We had to develop an aluminium insert, but the aluminium in the new bumper was very hard - approximately 150Hv.”
Colin Mileham recalls: “To get a hard enough aluminium, we had to go one better than automotive standard metal and opt instead for an aerospace quality, with full mechanical stress relief.”
The team then set about tackling the considerable difficulties of adapting aluminium to this specific application and developed a special self-clinching insert strong enough to withstand the eight tonnes of pressure needed to install it into the bumper. TR - part of the Trifast plc worldwide network - invested in a £30,000 tensile testing machine capable of measuring up to 10 tonnes, which was added to the already impressive array of equipment at TR’s dedicated Technical Engineering and Support Service.
Says Calum McMinn: “A lot of development work went into the new insert’s profile to get its dimensions just right. The customer’s pull-out requirement was 500 kg, and we never had any doubt we would achieve that. Getting the rotational resistance right was the difficult bit. There was also a lot of development work on the threads, because we found they tended to strip. So a unique tapping method had to be developed.”
The new fasteners, supplied to Hydro Raufoss through TR Norwegian subsidiary TR Magne Bjørlo, were actually stronger than the steel inserts they replaced.
All that remained was to ensure quality. “One of the customer’s requirements was that they must not have a single defective part,” says Colin Mileham. “So we had a special camera inspection system developed. Each individual insert is checked by three cameras immediately before packing. They check thread form and core diameter and nine exterior dimensions. The result is zero defects.”
HIGH STRENGTH ALUMINIUM BUMPER NUT INSERT