Electric heating – Metal heating – By arc
Reexamination Certificate
2003-02-21
2004-06-08
Heinrich, Samuel M. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121680, C219S121820
Reexamination Certificate
active
06747240
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the use of coherent energy pulses, as from high powered pulsed lasers, as well as an ultraviolet curable resin and an ultraviolet light in the shock processing of materials, and, more particularly, to methods and apparatus for improving properties of solid materials by providing shock waves therein. The invention is especially useful for enhancing or creating desired physical properties such as hardness, strength, and fatigue strength.
2. Description of the Related Art
Laser peening (hereinafter referred to as laser shock processing) utilizes two overlays, a transparent overlay (usually water), and an opaque overlay (previously a black paint). During processing, a laser is directed to pass through the water overlay and is absorbed by the black paint, causing a rapid vaporization of the paint surface and the generation of a high-amplitude shock wave. The shock wave cold works the surface of the part creating compressive residual stresses, which provide an increase in fatigue properties of the part. A workpiece is typically processed by processing a matrix of overlapping spots that cover fatigue critical zones of the part.
The current art utilizing laser shock processing has a problem with the amount of time necessary to dry the black paint. The problem with drying the black paint usually occurs with solvent-based paint but other types of paint may have this problem. Another problem is that the black paint begins eroding as soon as the water layer is applied to the paint. This problem with erosion usually occurs with water-based paint but other types of paint may have this problem. During the laser processing of a workpiece, the black paint must be applied to the workpiece multiple times. Each coat of paint takes approximately ten minutes to dry, which makes the processing time lengthy. Also, once the transparent overlay is applied to the paint, the paint may start to erode immediately. This opaque layer erosion causes a turbulence in the surface of the workpiece and reduces the shock pressure during the laser shock processing cycle. Therefore, the paint must be applied again to the workpiece further increasing the processing time. This problem with erosion of the paint decreases the efficiency and effectiveness during the laser shock processing of the workpiece. The reasons for the efficiency and effectiveness being decreased is because of the amount of time the paint takes to dry and because the paint begins eroding immediately once the transparent overlay is applied which causes the shock pressure to the workpiece to be reduced once the laser is applied to the eroding paint.
SUMMARY OF THE INVENTION
The present invention provides a method of laser shock processing that can be used in a production environment that significantly reduces laser shock processing time and increases the effectiveness of the laser shock processing of the workpiece. The method begins with a step of applying an energy absorbing coating to the surface of the workpiece that is to be laser shock processed. In one form of the invention, an ultraviolet-curable resin, such as an ultraviolet-curing acrylic or urethane resin, is applied to the energy absorbing coating of the workpiece. The present invention is not necessarily limited to ultraviolet-curable resins, any type of curable resin can be used. A resin is cured when the resin becomes chemically inert or upon the polymerization of the resin. In one form, the ultraviolet-curable resin is exposed to an ultraviolet light which causes the curable resin to form a pellicle over the energy absorbing coating of the workpiece. The present invention is not limited to an ultraviolet light to form a pellicle or skin over the resin. The curing effect is determined by the type of resin used and the means of curing that resin. A transparent overlay, such as water, is applied in a thin flowing layer over the pellicular energy absorbing layer. When the transparent overlay has covered the energy absorbing layer of the workpiece, the laser is fired through the transparent overlay and onto the energy absorbing coating. After the laser has been fired, the remaining portion of the coating can be washed off of the surface of the workpiece using a high-speed jet of fluid. The entire sequence and event timing is controlled by an electronic processor. The sequence is repeated for each spot to be processed along the workpiece surface.
The invention, in one form thereof, comprises a method of laser shock peening the surface of a solid material. An energy absorbing coating is applied to a portion of the surface of the solid material. An ultraviolet-curable resin is applied to the coated portion of the solid material and the curable resin is exposed to an ultraviolet light and forms a pellicle over the energy absorbing coating. A transparent overlay material is applied to the pellicular portion of the energy absorbing coating. A pulse of coherent energy is directed to the energy absorbing coating of the solid material to create a shockwave.
The invention, in another form thereof, comprises a method of laser shock peening the surface of a solid material with or without the use of a transparent overlay material. An energy absorbing coating is applied to a portion of the surface of a solid material. An ultraviolet-curable resin coating is applied to the energy absorbing coating and the curable resin is exposed to an ultraviolet light and forms a pellicle over the energy absorbing coating. A pulse of coherent energy is directed to the energy absorbing coating of the solid material to create a shock wave.
The invention, in yet another form thereof, comprises a method of laser shock peening the surface of a solid material. An energy absorbing material is mixed with an ultraviolet-curable resin to form an energy absorbing mixture coating that is applied to the surface of the solid material. The mixture coating is exposed to an ultraviolet light and forms a pellicle over the mixture coating. A transparent overlay material is applied to the pellicular portion of the energy absorbing coating and a pulse of coherent energy is directed to the energy absorbing coated portion of the solid material to create a shockwave.
The invention, in still another form thereof, comprises a method of laser shock peening the surface of a solid material without the use of a transparent overlay material and using a mixture of the resin and the energy absorbing material. An energy absorbing material is mixed with an ultraviolet-curable resin to form an energy absorbing mixture coating that is applied to the surface of the solid material. The mixture coating is exposed to an ultraviolet light and forms a pellicle over the mixture coating and a pulse of coherent energy is directed to the energy absorbing coated portion of the solid material to create a shock wave.
The invention, in yet another form thereof, comprises a method of laser shock peening the surface of a solid material using a mixture consisting of a wet energy absorbing material and a resin. A wet energy absorbing material is mixed with an ultraviolet-curable resin to form an energy absorbing coating that is applied to the surface of the workpiece. The curable resin causes the wet energy absorbing coating to form a pellicle over once exposed to an ultraviolet light. A pulse of coherent energy is directed to the energy absorbing coated portion of the solid material to create a shock wave.
The invention, in still another form thereof, comprises an apparatus for laser shock peening the surface of a solid material. The apparatus includes a material applicator for applying an energy absorbing material onto the workpiece to create a coating on the workpiece. A curable resin applicator applies an ultraviolet curable resin onto the energy absorbing coating of the workpiece and a light applicator applies an ultraviolet light to the curable resin. A transparent overlay applicator applies a transparent overlay to the energy absorbing coating of the workpiece. A laser provides a
Clauer Allan H.
Dulaney Jeff L.
Tenaglia Richard D.
Heinrich Samuel M.
Knuth Randall J.
LSP Technologies Inc.
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