To maximise efficiency and reduce fuel consumption, current combustor exit temperatures exceed the melting point temperatures of turbine blade materials. The external surfaces of the blades are protected by film cooling, a process in which cool air from the compressor is discharged via small holes in the turbine blade. Accurately produced cooling holes are essential to avoid turbine failure and ensure the aeroplane’s safe operation.
The small dimensions, narrow distribution, and diverse inclination angles of the blade cooling holes can make inspection challenging. Furthermore, cooling holes made with laser or electrical discharging machining methods can be an irregular shape. For functional reasons, they are often created at an angle to the surface or lie in a heavily-curved section of the turbine blade, making probe access difficult.
As well as overcoming these challenges, manufacturers can reduce measurement programming and cycle times by using metrology solutions that combine contact and non-contact sensors while optimising workpiece and probe positioning. Hexagon offers multisensor coordinate measuring machine (CMM) solutions that enable the precise 3D alignment of the turbine blade and the inspection of the location and size of the cooling holes in a single cycle.
Additional technology like rotary tables speed up the measurement process by automatically aligning the axis of each cooling hole parallel to the vertical axis of the CMM. Specialised blade software enables automated measurement paths to scan and evaluate blade profile characteristics like tangent line, leading and trailing edge, and profile thickness in a single procedure.