A burr could become a danger point in the turbine engine. Classical manufacturing processes like turning, milling and grinding can lead to burr formation and unwanted sharp edges. These represent structural weak points where material breakage or cracks can occur. This can lead to a potential danger to the safe operation of an engine.
The more functional properties turbine engines have, the more complex their geometry becomes. This means not only a more complex production but also new demands on the measuring technology for quality control. Dimensional characteristics, such as radii, chamfers and break edge, are to be measured in high accuracy, traceably and repeatably. In addition, modern manufacturing facilities require automation, high measurement speed and a connection to an existing IT landscape (smart manufacturing).
Particularly highly specialized components, such as turbine blades, turbine discs or blisks (Blade Integrated Disk), involve a number of metrological challenges. These include complex geometry with steep flanks, as well as varying reflection properties of surfaces that are either coated or ground. The latter surfaces are highly reflective.
One way to meet these new metrological requirements is the use of high-resolution, optical 3D metrology.
Optical metrology taking the lead
The greatest advantages of optical and thus non-contact methods include the area-based instead of profile-based measurement of surfaces and the increased accessibility of geometries difficult to access tactilely. Several optical technologies for surface-roughness measurement and dimensional measurement are available. One of the most established technologies in industrial metrology is the principle of focus-variation. The small depth of focus of an optical system is used to extract depth information of a surface.
This tech combines functionalities of a roughness measuring system and a coordinate measuring machine. This means users can measure dimension, position, shape and roughness with high accuracy using just one optical sensor.
MTU Aero Engines has been applying focus-variation by Bruker Alicona for years. In total, 15 systems are used in MTU locations worldwide. Since 2017, cobots are in place, a product line that combines a high-resolution optical 3D sensor with a collaborative robot arm. The 3D measurement and evaluation of smallest form deviations is performed automatically and according to common industry standards, including ASME. Cobots are designed for the use of several operators. The handling, measurement and evaluation by means of programmed test routines are easy to handle. Optionally, measuring routines can also be defined in the CAD file of the component using a CADCAM connection.
Defect measurement is another area of application where the aerospace sector benefits from cost and operation advantages when applying optical metrology. The maximum depth of a defect determines whether a component is reused, repaired or disposed of as a reject part. Conventional, manual methods for defect measurement using replica techniques, profile projectors and tactile methods are labor intensive and cannot be automated.
By using focus-variation, MTU Aero Engines is faster, more accurate and above all process capable. This also results from the CADCAM connection. Several hundred measuring positions on a wide variety of parts are automatically measured and evaluated. According to MTU, this brings a reduction in inspection costs by 25 to 50 percent.