Patent Application
20080067159
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
As discussed in detail below, embodiments of the present invention provide a laser processing system in which a hollow focusing device is configured to focus a laser beam onto a work piece. A pressure source feeds a pressurized liquid through the hollow focusing device. A liquid container is configured to receive a portion of the pressurized liquid from the hollow focusing device. The laser beam is transmitted through the pressurized liquid in the hollow focusing device to the work piece disposed in the portion of the pressurized liquid in the liquid container. The laser processing system in accordance with the embodiments of the present invention transmits “sufficiently high laser energy” to the work piece through the pressurized liquid. It should be noted that “sufficiently high laser energy” is the energy required to cause ablation of material from the surface of the work piece. In certain exemplary embodiments, the laser energy required to cause ablation of material from the surface of the work piece may be in the range of 0.01 to several Giga watts per centimeter squared (GW/cm2). The pressurized liquid flow facilitates to reduce heat-affected zone of the work piece, thereby preventing initiation of micro cracks. The pressurized liquid flow also facilitates flushing away the machined material from the work piece. Specific embodiments of the present invention are discussed below referring generally to
Referring to
The illustrated focusing device 12 includes a transparent portion 24 configured to transmit a laser beam 26 from a laser source 28 to a work piece 30 disposed in the portion of the pressurized liquid filling the liquid container 22. In the illustrated embodiment, the transparent portion 24 includes a focusing lens 32 provided to focus the laser beam 26 via the nozzle 20 to the work piece 30. The lens 32 and the work piece 30 are disposed in such a way so as to maintain a predetermined distance “L” between one side (rear side) 34 of the lens 32 and a first side 36 of the work piece 30. Decay of laser energy increases with increase in the distance “L”. The distance “L” is chosen in such as way so as to transmit sufficiently high laser energy to the work piece 30. As mentioned earlier, “sufficiently high laser energy” is the energy required to cause ablation of material from the surface of the work piece 30. The propagation of laser energy to the work piece occurs entirely through the liquid medium. Liquid flow velocity inside machined features of the work piece 30 increases with decrease in the distance “L”. The liquid flow is generated due to the flow of pressurized liquid from the inlet 16 to the outlet 18 and also due to shock wave generated in the portion of pressurized liquid in the liquid container 22 when the laser beam 26 strikes the surface of the work piece 30. The liquid flow within the hollow focusing device 12 and the liquid container 22 facilitates flushing away machined material from the work piece 30 and also reduces heat-affected zones in the work piece 30.
Distance “L” is determined based on the amount of laser absorption in the liquid medium. In certain embodiments, L is less than 20 mm and laser beams having a wavelength of 450 nanometers, 532 nanometers, and 355 nanometers retain more than 95% of their initial laser energy when the beam strikes the work piece via the liquid medium. In certain other embodiments, L is equal to 10 mm and laser beams having a wavelength of 1060 nanometers retain more than 87% of their initial laser energy when the beam strikes the work piece via the liquid medium. In certain embodiments, the liquid medium may include water, or chemical solutions such as acid.
A laser processing system 10 in accordance with certain exemplary embodiments of the invention may be used for various applications such as, but not limited to, laser drilling, laser cutting, microscale laser machining, laser cleaning, laser marking, laser direct writing, laser material treatment, laser shock peening, or the like. In certain embodiments, the exemplary laser processing system 10 may be used to drill cooling holes for aircraft engines. In certain other exemplary embodiments, the laser processing system 10 may use a micro-lens as the transparent portion and may be used for high spatial resolution laser machining, such as micro and nano laser machining. In certain other exemplary embodiments, the laser processing system 10 may use chemical solutions such as acid for chemical etching and laser machining the work piece disposed in the liquid container.
Referring to
In accordance with certain exemplary embodiments of the present invention, lower power laser beams having a wavelength in the visible and ultraviolet range, or higher power lasers may be used. In one example, industrial high power lasers having a wavelength of 1070 nanometers, or 1060 nanometers, or 810 nanometers, or 532 nanometers, or 355 nanometers, or combination thereof may be used. The industrial high power lasers may include direct diode lasers, fiber lasers, Nd:YAG lasers, and carbon dioxide lasers, 532 nanometer green lasers, 355 nanometer ultraviolet lasers, or the like.
Referring now to
In the illustrated embodiment, the device 12 includes the focusing lens 32 provided to focus the laser beam 26 via the nozzle 20 to the work piece 30. In alternate exemplary embodiments, the device 12 may include a delivery fiber or a combination of focusing lens and the delivery fiber to focus the laser beam to the work piece. It should be noted that the delivery fiber may include a solid core fiber and may be located protruding closer towards the work piece to focus the laser beam to the work piece. In certain other exemplary embodiments, the device 12 includes a micro lens to focus the laser beam to the work piece. The lens 32 and the work piece 30 are disposed in such a way so as to maintain a predetermined distance “L” between one side (rear side) 34 of the lens 32 and the first side 36 of the work piece 30. The distance “L” is chosen in such as way so as to transmit sufficiently high laser energy to the work piece 30. The distance “L” is minimized to limit the amount of laser power decay due to transmission of laser beam through the liquid medium. The provision of hole 50 further facilitates reducing the distance “L”. The liquid flow within the hollow focusing device 12 and the liquid container 22 facilitates flushing away machined material from the work piece 30 and also reduces heat-affected zones in the work piece 30.
When a hole is drilled using conventional laser processing techniques (for example, transmitting laser beams through air to the work piece), removed material tends to build up at the edge of the machined region and may fuse to the non-machined region, forming a ring on the work piece. In accordance with exemplary embodiments of the present invention, the pressurized liquid flow facilitates flushing away the machined material from the work piece and preventing it from fusing to the edge of the machined region. Thereby the liquid medium facilitates to reduce the extrusion of removed material from the work piece. The extrusion of removed material is mitigated due to enhanced strength of the liquid medium.
In another exemplary embodiment, the laser processing system 10 may be used to drill holes at an angle to a surface of a work piece 30. A short decay nozzle system (not shown) may be used to focus the laser beam 26 to the surface of the work piece 30. The short decay nozzle system is configured to feed a pressurized liquid against the work piece 30. The laser beam is transmitted through the pressurized liquid to the work piece disposed in the portion of the pressurized liquid in the liquid container. When the short decay nozzle system is tilted relative to the work piece 30, tilted holes may be drilled in the work piece. In certain exemplary embodiments, the nozzle system may be tilted and the laser beam may be focused to the surface of the work piece. In certain other exemplary embodiments the nozzle system may be tilted and the laser beam may be focused to a portion below the surface of the work piece. It should be noted here that focusing the laser beam to a portion below the surface of the work piece is an exemplary technique and that other techniques may be adopted depending on the requirement. The laser processing system in accordance with the embodiments of the present invention transmits sufficiently high laser energy to the work piece through the pressurized liquid. As discussed in previous embodiments, “sufficiently high laser energy” is the energy required to cause ablation of material from the surface of the work piece 30. The laser beam may be transmitted to the work piece without significant energy losses through the liquid medium. The pressurized liquid flow facilitates reducing the heat-affected zone of the work piece, thereby preventing initiation of micro cracks. The pressurized liquid flow also facilitates flushing away the machined material from the work piece.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
