An experimental investigation of the airflow characteristics of laser drilled holes

When using a laser process for the creation of holes to be used in gas turbine film cooling applications, the mass flow rate is a critical factor in judging hole quality. In the present study, an experimental investigation was undertaken to identify the importance of laser drilling process parameters on the hole airflow. It must be remembered that the total mass flow rate through a hole is a function of the aerodynamic losses resulting from both frictional effects and geometric features of the hole inlet and exit. Optimum aerodynamic performance depends upon the proper selection of laser drilling process parameters. A total of four separate parameters were examined, including laser power, relative laser beam focal position, use of a circular laser beam aperture, and workpiece thickness. Relative laser beam focus was determined to be the most effective individual parameter, followed by workpiece thickness. Laser beam aperture was the least effective parameter. Interactions between the relative laser beam focal position, workpiece thickness, and laser power were found to produce the largest change in the hole flow rate. (C) 1998 Laser Institute of America. [S1042-346X(98)00302-7].