Rolls-royce Corporation

David Stroud

Arthur G Corfe

Jonathan P Towill

Brian G Cooper

Anthony J Griffith

Owen Gregory

Small cooling holes, e.g. 0.25-0.9 mm diameter, in cast hollow turbine blades are provided by delivering successive pulses of laser energy to the surface of the blade until penetration of the blade is complete. By leaving the ceramic casting core in situ within the blade during drilling, the laser beam is prevented from striking through to the far wall of the cavity defined by the ceramic core within the blade. The ceramic core is subsequently removed by leaching techniques common to the art.

Drilling turbine blades

In the laser drilling of a hole through a wall of a gas turbine blade into a cavity within the blade there is provided an injectable PTFE substitute for injection into the cavity before laser drilling. The PTFE substitute prevents strike-through of laser light to the opposite wall of the cavity. The PTFE substitute used is fluorinated ethylene propylene or a copolymer having a PTFE backbone and fully fluorinated alkoxy side groups.

Laser barrier material

A variety of configurations for convergent-divergent film cooling holes are disclosed, together with the hole drilling methods necessary to achieve the configurations.

Film cooled components

In the laser drilling of gas turbine engine blades there is provided a method of maintaining constant the distance between a laser nozzle and the surface to be drilled by measuring the topography of the surface and using that data to control the focusing of the laser beam onto the surface. The topography is measured by determining the back pressure of a stream of oxygen blown through the nozzle onto the surface, and relating the back pressure to the distance between the nozzle and the surface. The distance measured is used to control a servo operated table so as to move the surface to the optimum distance from the nozzle.

Laser drilling of components

PTFE-loaded wax is used in the laser drilling of holes in hollow turbine blades to prevent strike-through of the beam to an opposite wall of a cavity in the blade. The PTFE-loaded wax is poured or injected in molten form into the cavity prior to laser-drilling, and is subsequently removed by steaming.

Laser barrier material and method of laser drilling

An apparatus for drilling a shaped hole in a workpiece by means of a laser beam emanating from a laser source, includes (a) means for directing the beam onto the workpiece, (b) means for controlling the angle of the beam striking the workpiece relative to the axis of the hole, and, (c) means for controlling the distance between the intersection of the beam with the surface of the workpiece and the axis of the hole, so that the combination of the means for controlling the angle and the means for controlling the distance enables a shaped hole to be drilled in the workpiece by the laser beam. The apparatus also includes means for rotating the direction of the beam about the axis of the hole so as to describe at least part of the curved surface of a one that has its vertex on or within the body of the workpiece.

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Bristol, United Kingdom

David Stroud