Visual assessment of clinched joints is worthwhile because appearance can give a good indication of joint quality.
On the punch side, the top sheet should show an even indentation of the appropriate shape and size, dictated by the tooling. There should be no cracks or tearing in the indentation or in the surrounding material. The joint should not be loose, and there should be little or no distortion of the component.
On the die side, when non-piercing circular tooling has been used, a satisfactory clinch joint should show an even, symmetrical button of correct shape and size in the bottom sheet with no tearing caused by excessive thinning. If semi-piercing rectangular tooling has been used, an even, symmetrical indentation of correct shape and size should be seen. In both cases, there should be no cracks or other imperfections in or around the joint.
The thickness of the base of the button (or thickness of base of indentation) can indicate the amount of sheet compression (and hence the degree of interlocking between sheets) and is a useful dimensional check. Similarly, button diameter indicates the extent of radial expansion of the sheets. These measurements can be used to check joint quality periodically during production.