Product Code: ICA13_701

Determination of the Bore Hole Diameter by Analyzing Process Emissions
Authors:
Stefan Janssen, Chair for Laser Technology, RWTH Aachen University; Aachen Germany
Hermann Uchtmann, Chair for Laser Technology, Rwth Aachen University; Aachen Germany
Ingomar Kelbassa, Chair for Laser Technology, Rwth Aachen University; Aachen Germany
Presented at ICALEO 2013

In order to guide cooling air through turbine blades, bore holes with 500-800 microns diameter need to be drilled into the blades. The tolerance of the bore hole diameter must not exceed a range of about 10-30 microns so that a constant air flow capacity can be guaranteed. For the determination of the bore hole diameter online without destroying the work piece, there are mainly two methods for measuring the diameter. Either the diameter can be measured by evaluating external signals sent into the work piece such as ultrasonic sound, or by evaluating the information coming from the interaction zone such as process emissions. Since the evaluation of external signals is relatively sensitive to environmental influences, e.g. noise and thus not suitable for industrial applications, the focus of this work concentrates on the evaluation of process emissions.
With aid of a high speed camera which records the light emitted by the laser induced plasma in the work piece, and utilizing software tools for analyzing the recorded pictures, the diameter of a bore hole can be determined within a small range of error. Based on results for a flash-pumped laser, the method of this work is used in a fiber laser drilling process.