Chucks are used to securely clamp workpieces during turning. The most commonly used chuck types are chucks with three or four clamping jaws. The use of jaw chucks allows to clamp workpieces with a wide range of diameters. As the chuck is located between the workpiece and the turning spindle, the chuck has a significant influence on the achievable dimensional and shape accuracy. The main cause of dimensional and shape deviations is the clamping force applied to hold the workpiece in place. The clamping force leads to elastic tensioning on the workpiece. In this clamped state, the workpiece is subjected to machining.
After the clamping is released, the elastic spring-back effect of the workpiece reduces the tension. This results in a deformation of the workpiece, which reduces the achievable dimensional and shape deviation of the workpiece. Clamping forces that are set too high pose a major challenge, particularly when machining thin-walled, ring-shaped workpieces such as bearing seats, sleeves or valve rings. Due to the low rigidity of thin-walled workpieces, unacceptably high workpiece deformations can occur even at low clamping forces. If the clamping forces are set too high, the deformations lead to unacceptably high deviations in the shape and dimensions of the workpiece, meaning that the required tolerances cannot be met or can only be met with additional set-up effort.
In the "DefCon" research project, the Institute of Production Engineering and Machine Tools (IFW) at Leibniz Universität Hannover is therefore currently researching a new type of chuck. One new feature of the chuck is an integrated, highly compact electric actuator. The actuator means that the usual external actuation of chucks with an energy-intensive hydraulic clamping actuator is no longer necessary. The new chuck therefore also contributes to a potentially reduced power requirement of the machine tool.
The more direct force application of the actuator also means that the clamping force can be set more precisely compared to conventional chucks. A precisely adjustable clamping force is one of the two basic requirements for minimising workpiece deformation. The second basic requirement is a measuring system to determine the actual workpiece deformation. To determine the workpiece deformation, the chuck is equipped with a sensory clamping jaw. For the first time, the new chuck is able to determine the relationship between the set clamping force and the resulting workpiece deformation. This enables the chuck to automatically set the optimum clamping force based on a e.g. concentricity tolerance specified by the operator. This reduces time-consuming set-up work, especially for thin-walled workpieces.
Contact:
For further information, please contact Eike Wnendt, Institute of Production Engineering and Machine Tools at Leibniz Universität Hannover, on +49 511 762 18257 or by e-mail (wnendt@ifw.uni-hannover.de).
