This thesis experimentally investigates the defect generated at the start and stop zone when trepanning, using CO 2 laser and the nickel-base superalloy Hastelloy X. The project has been performed at Siemens Industrial Turbomachinery AB (SIT) in Trollhättan. Experiments which investigates the effect of altering entrance radius, exit radius (withdrawal) and nozzle distance have been performed. Samples were created by using a Trumpf 2D-laser machine and they were prepared for evaluation by grinding, polishing and etching. The Sample were then evaluated and measured by using an optic microscope. Experiments have been planned according to the method, design of experiments (DOE).

By using the programme Minitab, regression analysis and empirical models were created which describes the effect of the tested parameters. The results show that it is possible to decrease the start and stop defects by altering of the process parameters.