Selecting Vacuum Cups for Sheet Metal Handling

Cup type follows the surface

A flat cup gives the highest holding force per area on a smooth, rigid sheet and is the default for flat blanks.

A bellows cup compensates for surface variation and a slight angle, and it absorbs some of the shock when the cup lands. It gives up some holding force in exchange.

Oily, textured or perforated surfaces change the answer completely. Oil reduces the seal, perforation defeats it locally, and both need to be raised at the application review rather than discovered during commissioning.

Layout carries the load, not the cup count

Cups should be spread so the sheet does not sag between them. A sagging sheet peels the cups from the edges inward, which is why a drop usually starts at one corner.

Cups near the edges carry more of the peeling load than cups in the middle. Placing them for even support beats adding cups in the centre where they do less work.

Size for acceleration, not for weight

Holding a static sheet needs far less force than accelerating one. The design case is the fastest move, not the mass at rest.

A safety factor on the theoretical holding force is standard practice, and how large it should be depends on the surface, the acceleration and how much a dropped sheet costs you.

Hold time is the real test

A vacuum circuit that reaches the right level quickly but leaks slowly will pass a static test and fail in production. Measure how long a sheet is held with the generator isolated.

Leak testing the circuit and measuring hold time with the heaviest specified blank should be part of the acceptance test, because that is the number that predicts reliability.

Maintenance is where it degrades

Cup faces pick up oil and swarf, and worn cups lose the seal gradually rather than suddenly. A wipe at shift start and a cup inspection on a cycle based schedule prevent most in service problems.