Quality control of turbine blades in an automated production cell

Optical measuring machines offer advantages when it comes to quality testing turbine blades. Therefore, they will CORE high-speed scanning systems from the Swiss Starrag used in an automated production cell for the final quality control of turbine blades. The core requirements for measuring machines are: high accuracy, minimum measurement time and high temperature stability.

For over 50 years, the Starrag Group has been the leading technology partner when it comes to the productive production of gas and steam turbine blades. Turbine, compressor blades, impellers, blisks and complex structural parts are manufactured with the highest precision by Starrag machines. Starragkomplette also develops flexible manufacturing systems, so-called FMS (Flexible Manufacturing Systems), which allow the production of a wide variety of parts in automated mode.

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Two CORE systems were successfully integrated into an FMS for final quality control. The production cell manufactures a wide variety of complex blade types from high-precision forged blanks and consists of four milling machines, which manufacture the turbine blades using a special clamping concept, as well as two cleaning systems and two measuring machines. The individual stations are operated by a robot. Communication with CORE measuring machines is controlled via the cell control system.

The CORE is a coordinate measuring machine with an optical white light point sensor. The optical white light spot measurement is carried out with a double eye sensor. This is similar to the measurement principle with a tactile probe, but with a tiny white light point whose diameter is approximately 40 µm. This makes it possible to precisely capture freeform surfaces or measure the smallest features, such as the small radii of the entry and exit edges on turbine blades. With the double eye sensor and a stable point triangulation measurement routine, even highly reflective surfaces can be measured without spraying the surface.

Saving time for shorter measurement cycles

The CORE is a 5-axis measuring machine with three linear axes and two rotational axes. The rotational axes are formed by the turntable and the swivel joint on the sensor head. This combination and simultaneous control of the linear and rotary axes enables optimum accessibility, optimized travel paths and thus time savings for shorter measurement cycles. Optical measurement technology eliminates the need for probe radius compensation, especially when measuring small entry and exit edges of turbine blades.

“The decision for CORE was made after a strict selection process,” explains Stefan Mahr, Sales Director for Optical High-Speed Scanning Systems at WENZEL. Roland Ziltener, Head of Quality Management at Starrag AG, confirms: “We opted for an optical solution because no tactile system could measure the number of features required by the end customer in the required time. The CORE system enables us to measure the smallest features where we would reach the limit with a tactile system. ”

“One important reason for our measurement solution was that we were able to meet the demanding cycle times,” adds Mahr “In addition, the CORE design is extremely stable. Large linear guides with wide bearing distances guarantee a long service life and stable operation, even under harsh production conditions. Furthermore, the CORE offers a compact floor space and requires no compressed air. The measurement system is therefore extremely portable. ”

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At Starrag, the CORE measuring machine is fully automated and is ideal for direct integration into the production process. On the one hand because of the wide temperature range, and on the other hand, the open design of the CORE with the wide range of accessibility from three sides allows easy automatic loading and unloading with an industrial robot. This communicates with the coordinate measuring machine via an I/O interface or Ethernet connection.

The CORE turntable was modified according to customer requirements so that the pneumatic chuck used was integrated directly into the rotary table of the measuring machine. The system also interacts with complex cell control. This is carried out by CORE's automated remote control. The measuring device automatically provides feedback on cell control, starts and stops measurements on command, transmits measurement reports and reports changes in the state of the machine.

“We have an extremely positive experience working with Wenzel on this project,” says Ivo Ritter, project manager at Starrag. He is the overall manager of the FMS project. “In our experience, Wenzel's communication channels are short and the hierarchical structure is very flat. This allows us to react very quickly to changing requirements, even during project work, which is immensely beneficial to the progress of the project. We love working with Wenzel and are already looking forward to future challenges,” praises Ritter.

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