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Design for manufacturing

Clinch nuts - for mass production

Every nut has a hole through or into it with a thread to match. Then, traditional nut designs have a way of holding them to turn them and tighten them onto the matching screw or bolt. This might be through 'wings' to be held in the fingers, or flats (usually three sets of parallel faces making a hexagon) to be held by a spanner.

  A wing nut being tightened with the fingers

   A hexagonal nut, being tightened with a spanner

Clinch nuts work differently. They are fixed to one of the surfaces being held together by squashing them into place around a hole. The difficulty is that they must resist the turning forces (torque (G)) needed to secure them. The TR patented Hank rivet bush does this by being stamped in a powerful press, causing the inside face of the nut to flare out like a rivet (G). The bush (G) also has a serrated (G) surface which is roughened with knurling (G) or splines (G) to bite into the edges of the hole. In thin materials this is not strong enough - hence the need for riveting down tightly. It is possible to fix these by hand using a hammer on a ball bearing to spread the rim over the material of the component being fixed, but a machine press is more powerful and much quicker.

   A 'Hank' rivet bush.

Believe it or not the precise way in which the bottom of the nut sits against the bumper, was a critically important design feature of the 'Hank Clinch' nut. The final design can be seen on the company's Web site and it shows you what the undercut does to help the nut grip the bumper securely. The key is what happens to the bumper material.

Look at the right hand animation and study carefully what happens to the profile of the nut when the press clamps it on the sheet, and how the sheet changes shape.

  Hank Clinch nut front & end views with part section

These fasteners are less suitable for hand assembly methods than the traditional nuts and bolts due to the pressure needed to fix them reliably. However, in a factory, specialised presses are used which control the force applied to the bushes very reliably and which can be operated very rapidly. They do not even need a human being to sense when the bush and component are in place and the press is ready to be applied (automation (G)).

  Task 2 - Find a Clinch nut

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