A tool clamping system patented by Schunk GmbH & Co. KG for CNC-machining centres, which offers a very high degree of concentricity.

Function - clamping principle

The workpiece holder is not equipped with a round but instead a polygonal locating bore. As soon as this workpiece holder is externally charged with a defined pressure, this changes the shape of the locating bore to a cylinder. Joint changes in the steel are excluded because deformation takes place in the permanently elastic range and below the 0.2% yield point. In this state it is possible to introduce a tool without the application of excessive force. If the external pressure is now reduced again, the internal diameter returns to its original polygonal shape due to the material elasticity, and the tool is clamped through friction-locking.

Advantages:

• fatigue-free clamping of tools (no thermal effects as with shrink fit toolholders)
• high process assurance due to simple and precise length adjustment
• closed system, which is insensitive to dirt, cooling lubricants and shavings - highly balanced
• very high degree of concentricity (< 0.003mm) and very high rotational speeds (up to 85000 1/min) possible

Disadvantages:

• only one shaft diameter per tool holder possible
• when clamping or changing the tools a special tool (manual or automatic clamping device) is required.