Sheet Metal Fabrication - Punching - Slug Management

It takes more than a salt shaker to manage sheet metal slugs...

Discs, Slugs, circles, diaphragms, blanks, whatever you want to call them - just like the garden variety slugs - you just want to get rid of them when punching sheet metal.  

The suction created during the deformation of the slug during piercing causes the slug to stick to the face of the punch. Lubrication can also make the slug stick to the face. To prevent the slug from sticking, you need to break that suction.

One way is to cut slots into the face of the punch, which mitigates that suctioning effect. Another way is to use a punch with a hole drilled in the center and a spring-loaded steel or urethane pin inserted into it. When ejector pins fail, you can try pulling them out to create a kind of “ported” punch; the empty hole by itself can help break some suction.

You can also use punches with a “rooftop,” or high point on the punch face, known as having a “shear” on the punch tool. When the slug contacts this kind of tool, it tends to naturally spring back and away from the punch face.

In the die, you can use slug retention systems, including a die with a “negative-positive” geometry. By having a narrower diameter at the top of the die, these systems retain the slug once the punch ascends on the return stroke. The punch needs to descend far enough into the die for this to work consistently, but for the most part these systems are very effective.

If you don’t have a die like this on hand,  try a similar welding tool to lay a bead around the perimeter of the die opening. This has a similar effect as the dies described previously: It makes the die opening smaller and so helps retain the slug. Alternatively, you can use a small diamond file to put small notches in the die opening.