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Innovative use of materials

Making the clinch nuts from aluminium

The central problem for TR was that normal aluminium would be too soft for clinch fasteners so they had to research and then source a much harder alloy (G)suitable to high volume production at an appropriate cost. To get advice from experts in aluminium fastenings TR approached aerospace companies, which use them widely as aluminium is much lighter than steel. They also had a university student working with them for a year to gain experience, who brought some up-to-date knowledge, which was useful.

"We had to develop an aluminium insert but the aluminium in the new bumper was very hard."

The material had to withstand 8 tonnes pressure when it was pressed into the bumper. To check that the material was strong enough, TR invested £30,000 in a machine to test its tensile (G)strength. This could stretch materials with a force up to 10 tonnes.

They tested a prototype of every design by trying to pull it out of the bumper and by trying to twist it free. BMW required that it resisted a force of 500 Kg pulling it out which was not a problem for TR. However, stopping it breaking loose under torque (twist) was harder.

TR also had to do a lot of development work on the screw threads inside the nut because, in the softer material, they tended to strip out. To stop this they had to develop a new thread-tapping (G) method.

At the end of all this, TR were delighted to find that the new fastenings were actually stronger than the steel inserts they had replaced.

  Task 3 - Tapping threads by hand

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