Flexible clamping jaws for circular sections

Today the three-jaw chuck is the most commonly used clamping system in turning machines. In order to avoid damage of the work piece by clamping, the surface pressure between the clamping jaw and the work piece should be very homogeneous in the clamping surface. This target is achieved with a jaw cutting attachment for turning unhardened jaws and grinding hardened jaws of the required clamping diameter. The process has to be conducted under gripping force. Since for different clamping diameters and gripping forces many clamping jaw sets were needed, this clamping method is very expensive and consuming. Power chucks in combination with automatic chuck and jaw set changing systems are necessary for an automatic and flexible clamping. The Institute for Machine Tools and Manufacturing Technology of the Technical University Berlin has been conducting research in clamping technology for many years. One aim of this project is to develop flexible clamping jaws for circular sections that are able to self-adapt the clamping surface over a wide range of work piece diameters. The clamping process with conventional and flexible jaws for different work pieces is fundamentally studied with FEM-calculations. The theoretical behaviour of a jaw as well as the interactions between the jaw and the work piece in the contact zone are examined. The results and conclusions of the FEM-calculations are used for the optimization of the flexible jaw structure. A characteristic feature of modern power chucks is the small jaw travel. One assumption for the effective operation of flexible jaws is a large jaw travel of the chuck. So the effective use of flexible jaws in automated manufacturing systems is dependent on new power chuck systems with a large jaw travel. The interrelationship between flexible jaws and chuck with regard to clamping accuracy and clamping safety is studied experimentally.