Chuck with integrated clamping force measurement for thin-walled workpieces

During turning processes of thin-walled workpieces, e.g. bearing rings and sleeves, dimensional and shape deviations are a challenging issue. The main cause of these deviations is the clamping force applied by the chuck to hold the workpiece in place. Due to the low stiffness of thin-walled workpieces, high workpiece deformations can occur even when clamping forces are low. For this reason, the clamping force needs to be controlled precisely. Conventional approaches use additional measuring devices in order to measure the clamping force. Afterwards, the clamping force is adjusted 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 clamping force measurement and precise clamping force adjustment. Thus, this paper presents a novel chuck with integrated clamping force measurement. Strain gauges are integrated next to the jaw to ensure high sensor signals. Based on the sensor signals, the clamping force is calculated considering a previously identified calibration coefficients. These calibration coefficients depend on the workpiece geometry. In order to consider this correlation, workpieces with different ratios between inner to outer diameter are clamped and the resulting sensor signals are measured using a reference sensor. The clamping force varies by up to 5 kN resulting to a sufficent low workpiece deformation of Δd ≈ ±7µm and thus meeting IT5 tolerance grade of ISO 286.