High power fiber laser effusion hole drilling apparatus and method of using same

Abstract

A fiber laser-treated workpiece is configured with a body having a discontinuous surface which defines a plurality of spaced through-going passages so that each passage is delimited by a peripheral layer having a surface characteristic which includes a recast layer or one or more microcracks or a combination thereof. The passages are provided by a high power Yb fiber laser operating in a pulsed regime and configured to output either a single pulse per an entire passage or a train of pulses per the passage. The Yb fiber laser is so configured that, if formed, the recast layer and micro-crack each are smaller than respective standards in an airspace industry.

Claims

1. A method of effusion hole drilling in aerospace engine materials selected from the group consisting of aluminum, ceramics, metallo ceramics, nickel alloys, stainless steels, titanium, and a combination thereof by a single mode (SM) high power ytterbium (Yb) pulsed fiber laser which is operative to emit a plurality of discreet pulses incident on selected locations on the aerospace material and configured to provide a plurality of through-going and substantially uniform spaced effusion holes at respective locations, the method comprising: controllably displacing the aerospace engine material and SM high power Yb pulsed fiber laser relative to one another among a plurality of predetermined locations along a path; and periodically firing the SM high power Yb pulsed fiber laser at each of the locations, thereby outputting at least one pulse incident on the location so as to drill the plurality of effusion holes in the aerospace engine material, operating the SM high power Yb pulsed fiber laser so that the at least one pulse has optical characteristics selected so that a recast layer formed on a periphery defining an effusion hole has a thickness less than 0.0015 inches and one or more microcracks having a width less than 0.005 inches.

2. The method of claim 1, wherein the periodic firing of the SM high power Yb pulsed fiber laser includes outputting a single pulse per each location, the single pulse being shaped and configured to drill an entire passage.

3. The method of claim 2, wherein the single pulse at each location has a pulse width of about 10 milliseconds, a square shape, a peak power varying between 6 kW and 20 kW.

4. The method of claim 1, wherein the periodic firing of the SM high power Yb pulsed fiber laser includes outputting a plurality of pulses per each location at a repetition rate varying between 25 Hz and 50 Hz.

5. The method of claim 4, wherein the outputting of the pulses includes configuring uniform square pulses each having a pulse width between 0.5 to 3 milliseconds.

6. The method of claim 5, wherein the outputting of the uniform pulses occurs in substantially a fundamental mode having substantially uniform parameters which include an M.sup.2 value, focal point, spot size, and peak power ranging between 6 kW and 20 kW.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other features and advantages of the disclosed apparatus, method and product will become more readily apparent from the specific description accompanied by the following drawings, in which:

(2) FIG. 1 is a diagrammatic view of the disclosed fiber laser system.

(3) FIG. 2 is a workpiece having a plurality of passages which are provided in accordance with the disclosed method and apparatus practicing the disclosed method.

(4) FIGS. 3-7 are computer generated shots illustrating respective micro-cracks obtained with differently configured pulses which are emitted by the disclosed apparatus and method.

(5) FIG. 8 is a chart summarizing the results illustrated in FIGS. 3-7 and comparing these results with industry standard.

(6) FIGS. 9-13 are respective computer generated shots illustrating recast layers produced under different operating conditions of fiber laser system of FIG. 1.

(7) FIG. 14 is a chart illustrating the results shown in FIGS. 9-13, respectively, and compared to the industry standard.

SPECIFIC DESCRIPTION

(8) Reference will now be made in detail to several embodiments of the invention that are illustrated in the accompanying drawings. Wherever possible, same or similar reference numerals are used in the drawings and the description to refer to the same or like parts or steps. Certain drawings are in simplified form and are not to precise scale. The word couple and similar terms do not necessarily denote direct and immediate connections, but also include connections through intermediate elements or devices.

(9) FIG. 1 illustrates a fiber laser drilling system 10 including a high power fiber laser 12, a beam delivery system 14 typically having beam guiding optics which guides the laser output beam to a laser head 16. The latter is operative to focus the beam on the desired location of a workpiece 18 and typically has up to twelve (12) degrees of freedom so as to allow for convenient displacement of the head and workpiece relative to one another along a predetermined path over a plurality of locations corresponding to respective passages to be drilled.

(10) The fiber laser 12 includes a plurality of separate laser modules each provided with an Ytterbium (Yb) oscillator operative to output at about 500 W or higher. The configuration may be altered by utilizing known to one of ordinary skill in the laser art master oscillator and power amplifier (MOPA) schematics. Preferably, the laser is a model YLRxxxx available from IPG Photonics Corporation, Oxford, Mass.

(11) The cumulative output of the modulessystem lightcan easily reach a multi-kW level ranging between about 10 kW and about 20 kW and higher. The Yb fiber laser 12 is configured to emit square-shaped pulses at a repetition rate between about 25 Hz and about 50 Hz in low multimode (MM) radiation at wavelengths around 1070 nm. The system light has a stable, low beam product parameter (BPP) which ranges from about 3 to about 5 and an M.sup.2 value roughly around 10.

(12) Referring to FIG. 2, specific parameters of Yb fiber laser 12 within the above-disclosed ranges are so selected that all of the drilled passages 20 are clean, free of surface splatter and have substantially uniform diameter, taper, passage entrance and clean passage exit. In other words, the pulses have a stable uniform pulse-to-pulse rate, uniform amplitude or peak power and uniform square pulse shape all leading to the formation of substantially uniform passages.

(13) FIG. 2. Provides a workpiece 18 with oval passages having a major axis of x and a minor axis of diameter at the top surface with a standard deviation of z. The area of the surface removed by the oval equaling Aoval.

(14) The foregoing results required by many industries including the aerospace industry have been achieved with the above-disclosed laser system treating workpiece 18 which is made from aluminum, ceramic, metallo ceramics, nickel and nickel alloys including but not limited to Hastelloy variants, Inconel variants including Inconel 625, Inconel 718, Mar-M variants, Single Crystal, carbon steels, stainless steels, Titanium and/or Waspalloy variants and various oxides, alloys and combinations of these.

(15) Referring to FIGS. 3-7, the importance of disclosed system 10 of FIG. 1 becomes readily apparent from experimental results including the formations and dimensions of recast layers and micro cracks in workpiece 18 which may be configured, without any limitation, as turbine blades, nozzle, guide vanes, combustion chambers and afterburner and others. The following parameters are common to all of the experiments shown in respective FIGS. 3-6 and include laser system 10 outputting fifteen (15) square pulses at a repetition rate 25 Hz and with at 15 kW peak power per each pulse. Despite different pulse widths, as disclosed below, an average time necessary for drilling the passage is about 6 seconds.

(16) Despite different pulse with, as disclosed below, an average time necessary for drilling the passage is about 6 seconds. What were the materials?

(17) Referring specifically to FIGS. 3 and 8, system 10, which is configured with the above-listed parameters, produces a microcrack 24 on a wall of passage 20 in workpiece 18. The pulse width in this experiment is about 0.5 milliseconds. This experiment shown in FIG. 8 as 1 results microcrack 24 having a width of about 0.0004.

(18) Referring specifically to FIGS. 4 and 8, system 10 is operative to output pulses each having a pulse width of 1 millisecond. Denoted by numeral reference 2 in FIG. 8, microcrack 24 is produced with about 0.0006 width.

(19) FIG. 5 illustrates the results of a pulse width of about 2 milliseconds. The result of this experiment is referenced by numeral 3 in FIG. 8 and includes the width of microcrack 24 of about 0.001.

(20) FIG. 6 illustrates the results produced by drilling workpiece 18 with laser system 10 operative to emit square pulses each with pulse width of about 3 milliseconds. This experiment corresponds to reference numeral 4 in FIG. 8 and results in about a 0.0008 width.

(21) FIG. 7 illustrates microcrack 24 formed with parameters which are somewhat different from the previous four experiments. In particular, instead of a pulse train, system 10 fires a single 10 millisecond pulse, which is not available from Nd-YAG lasers. As can be seen in FIG. 8, under reference numeral 5, the result, 0.0002 width, is substantially the same as in the case of the shortest pulse width of 0.5 milliseconds in experiment 1. However, in contrast to all previous settings, the drill time per passage in this experiment is about 0.05 milliseconds which is substantially shorter than 0.6 milliseconds needed in previous experiments.

(22) FIG. 8 dearly illustrates the advantages of using system of the present disclosure. Compared to aerospace standard of about 0.014 denoted by reference numeral 6, even the worst result obtained in experiment 3 by disclosed fiber laser system 10 is considerably better than the standard.

(23) Referring now to FIGS. 9-14, laser system 10 configured with the same parameters as disclosed in reference to FIGS. 3-8 also shows a substantially improved recast layer's thickness compared to the aerospace industry's standard.

(24) In particular, the same five experiments corresponding to respective pulse widths 0.5, 1.0, 2.0, 3.0 and single pulse of 10 milliseconds have been conducted and resulted in a recast layer 26 clearly seen in respective FIGS. 9-13. FIG. 14 illustrates the results of five experiments referenced by respective numerals 1, 2, 3, 4 and 5 and reference numeral 6 being the industry standard.

(25) As can be seen from FIG. 14, the first three experiments with respective pulse widths of 0.5, 1.0 and 2.0 milliseconds produced about 0.0018, 0.0022 and 0.0025 thick recast layers, respectively. The fourth setting with a 3.0 millisecond pulse width resulted in a recast layer having a thickness of about 0.0022. All of the above experiments produced the respective results, recast layer thickness lower than the standard thickness of about 0.005 corresponding to the right old column 6.

(26) The last experiment, number 5 with a single 10 millisecond pulse width again showed to be advantageous in many respects and had substantially the same result, 0.0018, as experiment 1 with the shortest pulse width.

(27) All the results were obtained in a certified Metallurgical laboratory and are correlated to the configuration and use of a high power MM Yb fiber laser of the present disclosure. Having described at least one of the preferred embodiments of the present disclosure with reference to the accompanying drawings, it will be apparent to those skills that the invention is not limited to those precise embodiments, and that various modifications and variations can be made in the presently disclosed workpiece, method and system for laser drilling of aerospace material. It is believed that with higher powers soon to be available, various pulse widths, shot counts and maybe even modified pulse shapes, the results may be even more encouraging Thus, it is intended that the present disclosure cover the modifications and variations of this disclosure provided they come within the scope of the appended claims.