Measurement of workpiece deformation based on a sensory chuck

Achieving tight tolerances is a challenging problem encountered during turning of thin-walled workpieces. Due to the low stiffness of thin-walled workpieces, inadequate workpiece deformation can occur even when clamping forces are low. Therefore, the workpiece deformation needs to be precisely controlled. Conventional approaches use additional measuring devices (e.g. a touch probe) to measure the workpiece deformation. Afterwards, the clamping force is adjusted accordingly in an iterative, manual process step resulting in non-productive time. To ensure low workpiece deformation and reduce non-productive time, a chuck is required which combines workpiece deformation measurement and automatic clamping force adjustment. Thus, this paper presents a novel method to measure workpiece deformation using a chuck with four integrated electric drives. The electric drives are used to precisely adjust the clamping force. Based on the measured clamping force, the workpiece deformation is calculated considering previously identified correlations between the clamping force and the workpiece deformation. To identify these correlations, workpieces with different ratios between inner to outer diameter are clamped and the resulting workpiece deformation is measured using a coordinate measuring machine. The new method allows to measure workpiece deformations within a tight tolerance grad of up to ISO 286 IT5.