Accelerated component testing in production

Ever faster manufacturing processes and increasing quality demands in the production of turbine blades required the renowned turbomachinery manufacturer Leistritz to introduce a new time-saving metrological process. The demand for 100% inspections could no longer be met economically with tactile measuring systems. The integration of the optical scanning system CORE-DS from WENZEL ScanTec into the direct production environment now enables fast non-contact component inspection. Leistritz was able to reduce the measuring times by over 70% with CORE-DS.

Leistritz Turbomaschinen GmbH, based in Nuremberg, specialises in the manufacture of turbine blades. About 70% of these are supplied to the aviation industry. Leistritz's high quality standards ensure that every turbine blade is inspected before it leaves the factory. In addition to some tactile coordinate measuring machines, more than 200 gauging fixtures are in use. Despite this considerable use of measuring and testing equipment, quality assurance was a bottleneck in the production process. In order to transfer the efficiency of production to QA as well, the need to integrate a new faster technology for inspecting the blades became inevitable.

The measured object is a turbine blade for aircraft engines. The blade has a height of 50 mm with leading and trailing edges that are only 120 µm wide. Previously, the measurements were carried out with a tactile coordinate measuring machine in a separate measuring room. This was located in another building complex. Transporting the manufactured blades was very time-consuming and costly. In addition, the measuring time with the tactile CMM was about 20 minutes. The required 100% inspection of the blades thus became a bottleneck in production. The introduction of a new method required that the blade root and blade be completely inspected in a single measuring process. In addition, the throughput time was to be significantly reduced.

‍

‍

To minimize the time required, the CORE-DS was integrated directly into the production environment. During the measurement process, two complete profiles of the blade and one foot profile are scanned. Based on the scan data, about 90 features are evaluated and analyzed. In this measurement task, the properties of the white light point sensor of the CORE-DS can be used optimally. The scan of the foot profile includes the detection of inner radii with a size of 0.3 mm. With a tactile measuring system, radii of this size can hardly be detected in a stable manner.By optical measurement using a light spot with a diameter of 35 µm, even the smallest radii can be detected precisely with a high point density. This effect is also evident in profile measurement. Since the entrance and exit edges have a width of only 120 µm, even the smallest defects must be detected. Where the probe ball of a tactile measuring system smoothes out the smallest defects like a mechanical filter, the optical sensor also reliably detects these shape deviations. In addition, the probe radius correction that would otherwise be necessary is no longer necessary, since the light spot detects the measuring point directly on the blade.

The measuring process is fully automated. The measuring system is loaded by a robot with the finish-ground turbine blades from two grinding machines. One grinding process takes about 11 minutes. Therefore, the required measuring time could not exceed 5 minutes. With CORE-DS, the measuring cycle at Leistritz could be significantly reduced so that it was precisely adapted to the cycle time of the corresponding machining centers.

Another challenge of measuring these blades was the surface condition of the measured object. The measurement process takes place immediately after a grinding process. For this reason, the surfaces of the blades are very shiny. Since the measurement process is time-optimized and fully automated, there is no possibility of matting the highly reflective surfaces, e.g. with chalk spray. Under the given conditions, the optical sensor of the CORE-DS allows the ground blades to be completely detected without pretreatment. By using white light and innovative point detection methods, it is possible to reduce the influence of reflections to a minimum.

The advantages of the CORE-DS are also evident in the clamping device used. For measurements with tactile measuring systems, relatively complex fixtures are often required due to the resulting probing forces. This can be a considerable expense, especially for small components. The optical non-contact measurement of the blade with the CORE-DS allows the use of a simple functional fixture. The blade is merely fixed at the base. Accessibility to the component is not restricted and even the foot profile can still be completely recorded.

‍