New approach to the inspection of cooling holes in aero-engines

This paper explores a new design for inspecting turbine blade cooling holes. Cooling holes have been incorporated in the design of turbine blades to combat and avert blade failure caused by excessive operating temperatures. In the paper, we examine the inspection techniques currently in use and present a novel optical technique as an alternative. Our design consists of two stages of inspection, each optically based. In the first stage, a sample is mounted on an XY micro-positioning stage, a vision system captures an image of the sample and displays the size and shape of each entrance hole. To measure the presence of a bottom, a second XYZ inspection stage is used. Using a small collimating tube, a micro-beam illuminates a drilled hole in a pre-programmed fashion. Depending on the level of reflected intensity and where it occurs, the presence of a hole's bottom is determined. The optical inspection system consists of a laser, motorized micro-positioning stages, collimating tubes, vision system, data acquisition software and a customized fixture for manipulating the samples.