Electric heating – Metal heating – By arc
Reexamination Certificate
1998-12-15
2001-09-11
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121850
Reexamination Certificate
active
06288358
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention.
The present invention relates to the use of coherent energy pulses to improve the properties of a solid material by providing shock waves therein and in particular methods and apparatus for remotely directing the pulse of coherent energy.
2. Description of the related art.
Laser shock processing involves directing a pulse of coherent radiation to a piece of solid material to produce shock waves therein. The produced shock wave causes compressive residual stresses to form within the solid material. These compressive residual stresses improve the fatigue properties of the solid material.
Currently, laser shock processing utilizes two overlays: a transparent overlay (usually water) and an opaque overlay (usually an oil based paint or black plastic tape). During processing, a laser beam is directed to pass through the water overlay and is absorbed by the black paint, causing a rapid vaporization of the paint surface (plasma creation) and a generation of a high-amplitude shock wave. The shock wave cold works the surface of the part and creates compressive residual stresses, which provide an increase in fatigue properties of the workpiece. A workpiece is typically processed by processing a matrix of overlapping spots that cover the fatigue critical zone of the part.
Currently, laser shock processing apparatus are mounted in a fixed or stationary location. The laser and the laser beam pathway are held in a fixed position directed toward a workpiece located in an immobile or stationary processing station. In order to laser shock process a workpiece, the workpiece must be placed within the stationary processing station and aligned within the laser beam pathway. As a result of the workpiece having to be located within the processing station, the size or dimension of the workpiece to be processed is thereby limited; the workpiece must fit within the finite space of the stationary processing station.
SUMMARY OF THE INVENTION
The present invention provides an apparatus for laser shock peening large or difficult to move workpieces, such as aircraft structures, stationary machines, building structures, and other large, similar workpieces. The apparatus includes a laser system and a laser beam delivery means for delivering a laser beam to a moveable, remote, and relocatable remote output end. The remote output end is first aligned to the workpiece to be laser peened. Then, a pulse of laser energy is transmitted from the laser system, through the laser beam delivery means, through the remote output end, and onto the large workpiece. With the present invention, the part-size constraint imposed by typical laser peening cells is eliminated. The laser beam is brought to the area of the workpiece, rather than manipulating the workpiece in the laser beam.
The invention in one form thereof, is an apparatus for improving the properties of a workpiece by providing shock waves by remote processing therein. The apparatus includes a remote output end and a laser operatively associated with the remote output end. There is means for aligning the remote output end. The laser beam delivery means delivers a beam of coherent energy from the laser to the remote output end.
In a further embodiment, the apparatus includes a power unit and the apparatus is mobile. In various alternate embodiments, the laser beam delivery means includes fiber optics, a light pipe, an articulated arm with pivotable mirrors, or a laser beam delivery service integrated within a building, factory, or structure. Alternate embodiments include a combination of the aforementioned laser delivery systems. The apparatus may also include an overlay system for applying an opaque and transparent overlay to the workpiece to be laser shock processed.
The invention in yet another form thereof is a method of improving the properties of a workpiece by providing shock waves therein. The method includes applying an overlay to the workpiece. A remote output end is aligned to the overlay portion of the workpiece. A pulse of coherent energy is directed to the overlay portion of the workpiece. In a further embodiment, the step of directing a pulse of coherent energy to the overlay portion of the workpiece occurs through various means such as a fiber optic bundle, a light pipe, an articulated arm comprising a plurality of pivotable mirrors, a laser beam delivery service integrated within a structure, and/or a combination thereof.
An advantage of the present invention is that large workpieces, which can not fit into a conventional laser shock processing station, can now be laser shock peened. For example, air craft structures, such as large wing sections and the fuselage, ships, and large earth moving equipment may now be laser shock processed. Moreover, these large structures may be laser shock processed in their assembled position or condition. The present invention's remote output end can be aligned to a desired location on the workpiece. In one embodiment of the invention, the laser system is mobile, allowing the laser system to be moved near the workpiece; thereby reducing the size and complexity of the laser beam delivery means. The workpiece no longer has to be moved to and manipulated within a stationary processing station.
A laser beam delivery means delivers a pulse of coherent energy from a laser to the remote output end which allows the remote output end to be mobile and relocatable along the workpiece. In other words, the workpiece stays stationary while the remote output end moves as required for laser shock processing. In addition, a laser beam delivery system may be incorporated within a building layout to deliver a pulse of coherent energy to the remote output end. As a result, processing of large material workpieces is achieved.
An additional advantage of the present invention is the ability to move the laser processing apparatus from place to place. One embodiment of the present invention is a self-contained or mobile laser shock processing apparatus. The entire apparatus may be moved from one location to another in order to process a workpiece, as opposed to the current practice of sending the material to be laser peened to an offsite processor. For example, the mobile laser peening apparatus may be transported to a manufacturer's assembly factory where the apparatus could be used to laser shock process a workpiece. Therefore, a workpiece can be assembled and processed within the manufacturer's own factory. As a result, there may be a decrease in manufacturing costs associated with the increase in convenience of being able to laser process a workpiece within a manufacturer's own factory.
Another advantage of the present invention is an alignment device, such as a bore-sighting device, with a cross hair or other guidelines for properly aiming the pulse of coherent energy to a specific location on the workpiece. In one embodiment, the remote output end contains a window or opening whereby an operator may view the location of where the beam of coherent energy will be placed. As a result, the operator is able to precisely direct the beam of coherent energy to a specific location along the workpiece.
In an additional embodiment, a camera is used to remotely align or guide the remote output end to a specific location along the workpiece. An operator may remotely control the remote output end by viewing the processing location on the workpiece via the camera. If the remote output end is located on the end of a robot arm, an operator will be able to process very large or cumbersome workpieces, for example, an airplane fuselage or large wing section, with ease. Consequently, once unprocessable workpieces may be simply and easily laser shock processed.
Another advantage of the present invention is that the remote output end may include a light safe seal or shield. This seal or shield may be adaptable to fit the varying geometries of the peened surface. As a result, the seal will prevent potentially dangerous pulses of coherent energy from being emitted from the remote output
Clauer Allan H.
Dulaney Jeffrey L.
Toller Steven M.
Evans Geoffrey S.
Knuth Randall J.
LSP Technologies Inc.
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