Explaining The Pinch Trim

When trimming the edge of a part, especially drawn cans & cups; there are 3 Options for the finish on the end. Just a raw formed edge can be uneven both in its height and in it’s cross section. One of the older, and still the most precise ways of controlling that edge, is to machine it (often times turning in a lathe). The image Below shows a rough drawn part on the left and the machined edge on right.

The other edge option is a pinch trim. The die itself will cut the lip to a particular height. However this has 2 potential consequences. First, the material will chamfer from the inside out reducing thickens; and second the lip will bow out some (usually about .25 time material thickness). These can be mitigated; but never eliminated. The cost savings from eliminated secondary handling often justifies the addition of the pinch trim in draw tooling.

