Dual mode high brightness fiber laser for ablation and drilling of aerospace superalloys

Abstract

Aerospace gas turbines require a large number of small diameter holes (<1mm) to provide cooling in the turbine blades, nozzle guide vanes, combustion chambers and afterburner. Many thousands of holes are introduced in the surface of these components to allow a film of cooling air to flow over the component. Film cooling both extends the life of the component and enables extra performance to be achieved from the engine.A typical modern engine will have ∼ 100,000 such holes. Currently these cooling holes are drilled by lamp pumped high peak power pulsed Nd-YAG laser. Such holes can be successfully produced by laser trepanning or percussion drilling. Probably the most popular is trepanning which is really a cutting technique. The laser beam pierces the workpiece just inside the perimeter of the hole and then tracks outwards to the circumference. Then either by rotating the workpiece or the laser beam a hole is cut out to the correct diameter. This technique can produce high quality holes. The roundness and hole variation are as good as CNC machining. The taper of the hole can also be of a reasonable quality. The second drilling method is percussion drilling, this technique requires the laser to fire laser pulses at the workpiece and material is removed from the hole by vaporising material as a liquid melt.High brightness fiber laser with its very good beam quality are very good for welding and cutting, however are not suitable for laser percussion drilling aerospace alloys due to the peak power limitations of the diode pump sources used. This work describes laser trepanning of aerospace alloys and ablation of thermal barrier coatings with a single mode fiber laser. The focus of the work is therefore laser drilling and ablation of a range of aerospace alloys a with a SM fiber laser up to 400W average power.Aerospace gas turbines require a large number of small diameter holes (<1mm) to provide cooling in the turbine blades, nozzle guide vanes, combustion chambers and afterburner. Many thousands of holes are introduced in the surface of these components to allow a film of cooling air to flow over the component. Film cooling both extends the life of the component and enables extra performance to be achieved from the engine.A typical modern engine will have ∼ 100,000 such holes. Currently these cooling holes are drilled by lamp pumped high peak power pulsed Nd-YAG laser. Such holes can be successfully produced by laser trepanning or percussion drilling. Probably the most popular is trepanning which is really a cutting technique. The laser beam pierces the workpiece just inside the perimeter of the hole and then tracks outwards to the circumference. Then either by rotating the workpiece or the laser beam a hole is cut out to the correct diameter. This technique can produce high quality holes. The roundness and h...