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Multi-sensor CMM measures turbine blades with complex geometry in a unique configuration – Metrology and Quality News

To maximize efficiency and reduce fuel consumption, current combustor exit temperatures exceed the melting point temperatures of the turbine blade materials. The external surfaces of the blades are protected by a cooling film, a process in which cool air from the compressor is exhausted through small holes in the turbine blade. Precisely produced cooling holes are critical to preventing turbine failures and ensuring safe aircraft operation.

The small dimensions, narrow distribution and various angles of inclination of the blade cooling holes can make inspection difficult. Additionally, cooling holes made with laser or electric discharge machining processes may have an irregular shape. For functional reasons, they are often created at an angle to the surface or are in a steeply curved section of the turbine blade, making access to the probe difficult.

In addition to overcoming these challenges, manufacturers can reduce measurement scheduling and cycle times by using metrology solutions that combine contact and non-contact sensors while optimizing part and probe positioning. Hexagon Manufacturing Intelligence offers multi-sensor coordinate measuring machine (CMM) solutions that enable precise 3D turbine blade alignment and inspection of coolant hole location and size in a single cycle.

Additional technologies such as rotary tables speed up the measurement process by automatically aligning the axis of each cooling hole parallel to the vertical axis of the CMM. Specialized blade software enables automated measurement paths to scan and assess blade profile characteristics like tangent line, leading and trailing edges and profile thickness in a single procedure.

With its multi-sensor concept, the Optiv Performance 663/664 Dual Z coordinate measuring machine integrates several measurement processes in a single machine and, thanks to the optional Optiv Dual Z and Optiv Dual Rotary options, has innovative technologies that guarantee accessibility to a variety of characteristics in the overall measurement volume and their measurement in one clamping.

Alignment with HP-S-X1 touch sensor

The coordinate alignment of the turbine blade occurs at its base, where the corresponding control geometry elements are located. The required measurement points are registered with the HP-S-X1 touch sensor.

Multi-sensor measurement of cooling holes

First, the position and size of the hole is measured with the vision sensor. Its high-resolution camera and low-distortion precision optics ensure maximum optical precision. A particular challenge is that the cooling holes created with a laser or erosion process have an irregular shape. For functional reasons, they are often created at an angle to the surface or are in a steeply curved section of the turbine blade. This causes the oval-shaped cooling holes to appear during the optical measurement. The solution provided by the PC-DMIS CAD++ measurement software is a specialized image processing algorithm that calculates the center point of the hole based on a calculation of the center of the area.

Using Optiv Dual Rotary Stacked Rotary Tables, the axis of the hole under test is aligned parallel to the sensor axis of the coordinate measuring machine. The shape and position of the hole are then determined by probing with the HP-S-X1 touch sensor (diameter of the spherical tip in the example: 130 μm) at defined depths.

Surface scanning with the chromatic white light sensor

Functionally relevant freeform surfaces of the turbine blade are scanned using profile scans with the chromatic white light sensor (CWS) in the same tightening. This non-contact point sensor enables fast, surface-independent 3D scans with high point density. The surface data obtained is evaluated against the CAD dataset imported into the PC-DMIS CAD++ measurement software.

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