Accelerated component testing in production

Ever faster manufacturing processes and increasing quality standards in the production of turbine blades required renowned turbomachinery manufacturer Leistritz to introduce a new time-saving metrological process. The requirement for 100% testing could no longer be met economically with tactile measurement systems. The integration of WENZEL ScanTec's CORE-DS optical scanning system into the direct production environment now enables rapid contactless component testing. Leistritz was able to reduce measurement times by over 70% with CORE-DS.

Leistritz Turbomaschinen GmbH, based in Nuremberg, specializes in the production of turbine blades. Around 70% of this is delivered to the aviation industry. Leistritz's high quality standards ensure that every turbine blade is tested before it leaves the factory. In addition to several tactile coordinate measuring machines, more than 200 teaching devices are in use. Despite this considerable use of measurement and testing equipment, quality assurance represented a bottleneck in the production process. In order to transfer the economic efficiency of production to QA as well, the need to integrate a new, faster technology for testing the blades became inevitable.

The measurement object is a turbine blade for aircraft engines. The blade has a height of 50 mm with entry and exit edges that are only 120 µm wide. The measurements were previously carried out with a tactile coordinate measuring machine in a separate measurement room. This was located in another building complex. Transporting the manufactured shovels was very time-consuming and expensive. In addition, the measurement time with the tactile CMM was around 20 minutes. The required 100% inspection of the blades thus became a bottleneck in production. The introduction of a new process required the blade base and blade to be fully tested in a single measurement process. In addition, the processing time should be significantly reduced.

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To minimize time consumption, CORE-DS was integrated directly into the production environment. During the measurement process, two complete blade profiles and one foot profile are scanned. Based on the scan data, around 90 features are evaluated and analyzed. In this measurement task, the properties of the CORE-DS white light point sensor can be optimally used. The scan of the foot profile includes the recording of inner radii with a size of 0.3 mm. With a tactile measurement system, radii of this size can barely be measured stably. By optical measurement using a light spot with a diameter of 35 µm, even the smallest radii with a high point density can be measured precisely. This effect is also evident when measuring profiles. Since entry and exit detectors are only 120 µm wide, even the smallest defects must be detected. Where the stylus of a tactile measurement system smoothes out the smallest defects like a mechanical filter, the optical sensor also reliably detects these deviations in shape. In addition, the otherwise necessary probe radius correction is omitted, since the light spot detects the measurement point directly on the blade.

The measurement process is completely automated. The measurement system is equipped by a robot with the fully ground turbine blades from two grinding machines. A grinding process takes approximately 11 minutes. The required measurement time should therefore not exceed 5 minutes. With CORE-DS, the measurement cycle at Leistritz was significantly reduced so that it was precisely adapted to the timing of the corresponding processing centers.

Another challenge in measuring these blades was the surface quality of the measurement object. The measurement process is carried out immediately after a grinding process. For this reason, the surfaces of the blades are very shiny. Since the measurement process is time-optimized and completely automated, it is not possible to matt the highly reflective surfaces with chalk spray, for example. Under the given conditions, the CORE-DS optical sensor makes it possible to completely detect the sharpened blades without pretreatment. By using white light and innovative point detection methods, it is possible to reduce the impact of reflections to a minimum.

The advantages of the CORE-DS are also reflected in the clamping device used. Measurement with tactile measurement systems often requires relatively complex fixations due to the resulting probing forces. This can be a considerable effort, especially for small components. The optical contactless measurement of the blade with the CORE-DS enables the use of a simple functional clamping device. In this case, the shovel is only fixed to the foot. Accessibility to the component is not restricted and even the foot profile can still be completely covered.

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