Trepanning

Abstract: An improved method and apparatus for laser trepanning a passage through a workpiece, gas turbine engine component or the like includes the method steps of: providing a linearly polarized beam of laser energy; focusing the laser beam on a selected location on the component; moving one of the laser beam or the workpiece relative to one another along a first selected trepanning path and along a second selected trepanning path, which is substantially opposite in direction to the first selected path, to compensate for the linear polarization of the laser beam and to reduce the processing time. The steps of moving one of the laser beam or the workpiece along the first and second trepanning paths are repeated until a passage is cut to a desired depth into the surface of the component or the passage is cut entirely through the component. An apparatus for accomplishing the method of the present invention includes a laser system for generating a linearly polarized beam of laser energy and a manipulator arrangement for moving one of the laser system or the component relative to one another. The apparatus further includes a computer controller which is programmed to move either the laser system or the component along the first and second selected trepanning paths.

Abstract: Laser drilling of metals and alloys is extensively used in modern manufacturing industries to produce holes of various size and shape. Currently, most laser drilling of aerospace nickel superalloys is performed using Nd:YAG laser. Over the years, many attempts were made to increase the productivity of Nd:YAG lasers drilling process, but with little success. This paper investigates the fundamental aspects of millisecond-pulsed-Quasi-CW-fibre laser drilling of aerospace nickel superalloy. The main investigation concentrates on understanding the Quasi-CW-fibre laser parameters on trepanning laser drilled hole quality and speed. The principal findings are based on controlling the recast layer, oxide layer, hole surface characteristic and fatigue performance of the laser drilled samples. The results showed that the high average power of the quasi-CW-fibre lasers can be effectively used to achieve increased trepanning drilling speed without undermining the drilling quality, which is not feasible with a free-space Nd:YAG laser. Also, low peak power and high frequency (of quasi-CW-fibre laser) can be effectively used to produce better laser drilled holes than the high peak power and low frequency, which is common with the traditional millisecond Nd:YAG drilling processes. Recast layer thickness of around 30 μm can be achieved with a trepanning speed of up to 500 mm/min with single orbit Quasi-CW fibre laser drilling of 0.75 mm hole over 5 mm thick material.

Abstract: A new material processing apparatus using a short-pulsed, high-repetition-rate visible laser for precision micromachining utilizes a near diffraction limited laser, a high-speed precision two-axis tilt-mirror for steering the laser beam, an optical system for either focusing or imaging the laser beam on the part, and a part holder that may consist of a cover plate and a back plate. The system is generally useful for precision drilling, cutting, milling and polishing of metals and ceramics, and has broad application in manufacturing precision components. Precision machining has been demonstrated through percussion drilling and trepanning using this system. With a 30 W copper vapor laser running at multi-kHz pulse repetition frequency, straight parallel holes with size varying from 500 microns to less than 25 microns and with aspect ratios up to 1:40 have been consistently drilled with good surface finish on a variety of metals. Micromilling and microdrilling on ceramics using a 250 W copper vapor laser have also been demonstrated with good results. Materialogroaphic sections of machined parts show little (submicron scale) recast layer and heat affected zone.

Abstract: Microhole drilling and microstructure machining with a picosecond (ps) Nd:YVO4 laser (pulse duration of 10 ps) in metals, alloys and ceramics are reported. Blind and through microholes were drilled by percussion drilling as well as trepanning drilling. The diameters of the holes were in the range from 20 μm to 1000 μm. Microfeatures were machined and the flexibility of ps laser machining was demonstrated. The quality of drilled holes, e.g., recast layer, microcrack and conicity, and that of the microstructures, were investigated by optical microscope, surface profilometer, or scanning electron microscope (SEM). Ps laser ablation rate was investigated by experiments as well as a simplified laser ablation model.Copyright © 2008 by ASME