GlossaryKind of term: Manufacturing termVacuum clamping
What is vacuum clamping?
Vacuum clamping is workholding by suction: air pressure pushes the workpiece onto a table with sealed channels or a porous plate.
Vacuum clamping is workholding by negative pressure. A table with channels and sealing cord, or a porous plate with a sacrificial board on top, is connected to a vacuum pump; the outside air presses the workpiece against the table. No jaws press on the edge, so a thin plate is not squeezed from the side. It works on non-porous material with a sufficiently large, flat underside, such as aluminium, steel and plastic.
What does vacuum clamping depend on?
The holding force perpendicular to the table is the pressure difference times the sealed area. That pressure difference cannot exceed atmospheric pressure, about 1 bar or 10 N per cm², and in practice it is lower because of leakage and pump capacity. Sideways, only friction holds the workpiece against the cutting forces, unless stops or pins help. Cutting through a lot of the plate or cutting out small parts loses sealed area and so holding force. A porous table needs a high-flow pump, because the sacrificial board leaks. A plate that arrives bowed is pulled flat during machining and can spring back after release. Over wide channels a thin plate can sag slightly, which affects its thickness after machining.
How does vacuum clamping work in practice?
Vacuum can save setup time and make thin, flat parts feasible without a special fixture. Its limits shape the strategy: with small parts or many through contours, tabs are left in, a sacrificial board goes underneath or the sequence is chosen so the sealed area stays intact as long as possible. Because holding force is limited, depth of cut and feed are often lower than in a vice, which can lengthen machining time. For heavy roughing, another setup is sometimes faster.
What is vacuum clamping often confused with?
Vacuum clamping is not magnetic clamping: a magnetic chuck works only on ferromagnetic material, vacuum also on aluminium, plastic and austenitic stainless steel. On thick material with good contact a magnetic chuck holds with a much higher force per unit area; on a thin plate or across an air gap that force drops sharply. A magnetic chuck can also leave residual magnetism.
Frequently asked questions
Why does a part come loose on the vacuum table?
Because the sealed area becomes too small or leaks, for instance when you mill small parts out of the plate or cut through a contour. Cutting forces beyond the friction can also shift it sideways. Tabs, a sacrificial board, stops or another sequence help.
Can you mill heavily on a vacuum table?
Only to a degree. Holding force is limited by atmospheric pressure and the sealed area, and sideways only friction holds the part. With heavy stock removal, roughing in another setup is often faster.
Does a plate stay flat after vacuum clamping?
Not necessarily. During machining the vacuum pulls the plate against the table. If the plate carries residual stress or was bowed, it can spring back after release. So measure flatness after release.