Profil pierce nuts used for foolproof fastening of safety critical vehicle components

Citation

(2002), "Profil pierce nuts used for foolproof fastening of safety critical vehicle components", Assembly Automation, Vol. 22 No. 1. https://doi.org/10.1108/aa.2002.03322aaf.006

Profil pierce nuts used for foolproof fastening of safety critical vehicle components

Profil pierce nuts used for foolproof fastening of safety critical vehicle components

Keywords: Fasteners, Automatic

Clinch nut technology from Profil UK has been specified at the heart of "foolproof" fastening methods used by Land Rover in safety critical assembly areas on the latest generation of Defender vehicles.

Profil M8, M10 and M12 pierce nuts are used to secure specific engine mountings to the chassis via heavy duty adapter plates, as well as to mount all derivatives of tow hook assembly on this rugged range of off-road vehicles (Plate 6).

Plate 6 4 off M12 Profil clinch nuts are used as a cost-effective, high strength and vibration resistant assembly method for mounting all derivatives of tow hook assembly on Land-Rover Defender models

Profil's selection have come as part of a chassis review project and been backed by extensive product trials that not only ensure Land Rover's exacting durability standards are met, but underline the company's long term commitment to product and process improvement.

Anything that can be regarded as a customer reportable fault is totally unacceptable," explains Project Manager, John Rolls. "That's why we go to extreme lengths to 'poke yoke' all our assembly methods. This Japanese term is widely used in the automotive sector – and means designing processes in such a way that errors are prevented during assembly."

With high value end products such as ours, the potential disruption – and costs – associated with even a small number of faulty components installed during final assembly could be enormous."

Key Objective

One of the key objectives of the chassis review project has been the reduction of chassis variants from a potential 38 to 12. To help achieve this goal, chassis assemblies are now 'late configured' to accommodate different engine options. This requires the use of a pair of handed adapter mounting plates, which are secured in place on the common chassis using 10 off M8 Profil nuts.

In the search for a better solution, Rolls and his colleagues investigated a number of alternative fastening methods, including various captive nuts and riveted fixings. These were all rejected in favour of Profil pierce nuts for a variety of reasons – ranging from an inability to meet the restricted space envelope requirements, through to panel distortion in an area adjacent to a visible edge."

By contrast, the Profil pierce nuts offer a highly cost-effective, high strength and vibration resistant assembly method without any of these drawbacks," notes Rolls.

Scrutiny

Another area to come under scrutiny during the chassis review project has been the mounting of the vehicle's tow hook and pintle. Not only do these assemblies have to withstand the rigours of normal domestic use, but Land Rover also supplies UK and overseas military forces with vehicles that are subject to tough NATO specifications.

"Essentially, the towing gear is tested by applying a reciprocating load to it at 3Hz for 1,000,000 cycles," Rolls explains.

Once again, several alternative solutions were evaluated for this application. However, through extensive process FMCA studies, it quickly became clear that Profil fasteners would be the most appropriate product for the job. Even so, a number of issues emerged, which have subsequently been addressed by a team of engineers from Profil, Land Rover and their component suppliers, GKN and Sertec.

"Through our discussions, the key process parameters were identified," continues Rolls. These paved the way for the establishment of a dedicated assembly section at Sertec's Coleshill plant, where the 4 off M12 Profilnuts are inserted into the vehicle's tow bar plate and a further 3 off M10 nuts are installed into the associated tow gear reinforcer bracket.

At the heart of the assembly cell is a purpose-designed hydraulic installation rig developed by Sertec in conjunction with Profil.

"We felt that manual feeding of components would be unreliable, so we devised an automated feed system incorporating several novel features. These include sensors to ensure the correct size of fastener, its orientation and even that the threads are formed in it," Rolls adds.

In operation, the nuts are located, then secured in the sheet metal components by closing the purpose-designed tooling to a pre-determined shut height, rather than to a specified insertion load. The press tools also incorporate a date code stamp to improve traceability, and SPC methods are employed to cover performance parameters, such as torque testing of the installed fasteners.

"We simply can't afford any failures in service," says Rolls, "which is why we try to ensure that nothing is left to chance with our manufacturing methods."

"The adoption of Profil nuts for both of these applications has proved entirely successful," he continues. "Not only have we rationalised our product and processes, but we have gained increased flexibility and reliability as well.

"So far, we have never had a quality problem requiring the rectification of an installed Profil nut – quite an achievement considering each of the 50,000 Defenders we produce annually can have as many as 17 Profil fasteners on board.

"For further information please contact: Adrian Ellis at Profil UK on: 01530 276515.