Method for marking the surface of a mechanical part with a predefined graphical representation having a holographic effect

Abstract

A method of marking the surface of a mechanical part with a predefined graphic having a holographic type effect, the method including using a laser source to apply a succession of laser pulses to the outside surface of a part for marking, with different masks being interposed between the laser source and the outside surface of the part, each mask having a particular pattern, each laser pulse having a power density of at least 20 MW/cm.sup.2 and a duration that is less than or equal to 100 ns.

Claims

1. A method of marking an outside surface of a mechanical part with a predefined graphic, the method comprising: using a laser source to apply a first laser pulse to the outside surface of the mechanical part with a first mask being interposed between the laser source and the outside surface of the mechanical part; and using the laser source to apply a second laser pulse to the outside surface of the mechanical part with a second mask being interposed between the laser source and the outside surface of the mechanical part, wherein each of the first and second masks has a particular pattern, and each laser pulse has a power density of at least 20 MW/cm.sup.2 and a duration that is less than or equal to 100 ns, wherein the predefined graphic has a holographic type effect in which light reflection changes as a function of an angle at which the graphic is observed, and wherein the mechanical part is a blade of a turbine engine.

2. The method according to claim 1, wherein at least one of the power density of the first laser pulse and the second laser pulse, a diameter of the first mask and the second mask, or the particular pattern of the first mask and second mask are different from each other.

3. The method according to claim 1, wherein a focusing lens is interposed between the laser source and the outside surface of the mechanical part.

4. The method according to claim 1, wherein the laser source is an Nd-YAG laser.

5. The method according to claim 1, wherein the first laser pulse and the second laser pulse each has an impact diameter of at least 0.5 mm.

6. The method according to claim 1, wherein when the mechanical part is made of metal, each of the first laser pulse and the second laser pulse has power density lying in a range of 0.04 GW/cm.sup.2 to 0.55 GW/cm.sup.2.

7. The method according to claim 1, wherein when the mechanical part is made of composite material comprising carbon fibers and an epoxy matrix, each of the first laser pulse and the second laser pulse has a power density lying in a range of 0.15 GW/cm.sup.2 to 2 GW/cm.sup.2.

8. The method according to claim 1, wherein when the mechanical part is made of ceramic, each of the first laser pulse and the second laser pulse has a power density lying in a range of 0.10 GW/cm.sup.2 to 0.34 GW/cm.sup.2.

9. The method according to claim 1, wherein the blade is a blade of a fan, a blade of a turbine, or a blade of a compressor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages of the present invention appear from the following description made with reference to the accompanying drawings, which show an implementation having no limiting character. In the figures:

(2) FIG. 1 is a diagrammatic view of an example setup for performing the method; and

(3) FIGS. 2 to 5 show an implementation of the method of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(4) The invention applies to marking the surface of any part of a gas turbine engine with a predefined graphic having a holographic type effect.

(5) The term predefined graphic is used to mean any predetermined geometrical shape or design, such as for example a logo, a serial number, a Datamatrix code, etc.

(6) The term holographic type effect is used to mean a graphic for which light reflection changes as a function of the angle at which said graphic is observed.

(7) A nonlimiting application example of the invention is that of surface marking blades for a fan, a turbine, or a compressor in an aviation turbine engine.

(8) The method of the invention comprises applying a succession of laser pulses to the outside surface of a part for marking, with various masks being interposed between the laser source and the outside surface of the part, each mask having a particular pattern such that when the patterns are added to one another they define the graphic that it is desired to mark on the part.

(9) According to the invention, each laser pulse that is applied to the outside surface of the part possesses a power density of at least 20 MW/cm.sup.2 and a duration that is less than or equal to 100 ns.

(10) FIG. 1 shows diagrammatically an example of a setup that can be used for performing the marking method of the invention.

(11) A part for marking 10 (e.g. a turbine blade) having an outside surface 10a on which the marking is to be performed is supported by a holder jig 12. The outside surface 10a of the part faces upwards.

(12) A laser source 14, e.g. a laser of the frequency-doubled Nd-YAG type producing radiation at a wavelength of 1.064 micrometers (?m), is positioned above the holder jig 12 and is configured to deliver pulses having a power density of at least 20 MW/cm.sup.2 and a duration that is less than or equal to 100 ns.

(13) Furthermore, a mask 16 having a particular graphic pattern is interposed between the laser source and the outside surface 10a of the part 10 for marking. Likewise, a focusing lens 18 (which may be converging or diverging) is positioned between the laser 14 and the mask 16 in order to match the size of the laser beam emitted by the laser to the dimensions of the mask.

(14) As a result, the laser 14 produces radiation that is focused by means of the focusing lens 18 into a beam that passes through the mask 16 prior to illuminating a selected zone of the outside surface of the part. The laser pulse produced by the laser 14 generates a plasma in this zone, with expansion of the plasma being accompanied by the release of a large amount of energy (thermomechanical and acoustic energy), leading to local modification at the surface of the part for marking. When the laser pulse produced by the laser has the above-specified settings (i.e. a power density of at least 20 MW/cm.sup.2 and a duration that is less than or equal to 100 ns), this local modification at the surface of the part gives rise to an imprint left in the surface of the part.

(15) By applying a succession of laser pulses under such conditions, while changing the mask and changing the power density of the pulse between each successive pulse, the marking obtained by the method of the invention consists in a superposition of different mask patterns forming a design with a holographic type effect.

(16) The marking method of the invention may be applied to any type of material. In particular, it is well adapted to marking parts made of metal, of ceramic, or of composite material. The method also applies to any material for coating the surface of a part.

(17) When the part for marking is made of metal, the laser pulse that is applied has a power density that preferably lies in the range 0.04 GW/cm.sup.2 to 0.55 GW/cm.sup.2 so as to obtain an imprint that is entirely intelligible.

(18) More precisely, for a part made of nickel, the power density that is applied advantageously lies in the range 0.10 GW/cm.sup.2 to 0.52 GW/cm.sup.2. For a part made of aluminum, the applied power density lies in the range 0.20 GW/cm.sup.2 to 0.55 GW/cm.sup.2, and for a part made of steel, the applied power density preferably lies in the range 0.10 GW/cm.sup.2 to 0.50 GW/cm.sup.2.

(19) Furthermore, when the part for marking is made of a composite material having carbon fibers and an epoxy matrix, each laser pulse preferably has a power density lying in the range 0.15 GW/cm.sup.2 to 2 GW/cm.sup.2 so as to obtain an imprint that is entirely intelligible.

(20) Finally, when the part for marking is made of a ceramic, each laser pulse preferably has a power density lying in the range 0.10 GW/cm.sup.2 to 0.34 GW/cm.sup.2 so as to obtain an imprint that is entirely intelligible.

(21) With reference to FIGS. 2 to 5, there follows a description of an implementation of the marking method of the invention.

(22) In this example, the part for marking is made out of a nickel-based superalloy. The outside surface of the part is subjected to a succession of three laser pulses, with three different masks being interposed between the laser source and the outside surface of the part.

(23) FIG. 2 shows a first mask 16-1 that is interposed between the laser source and the outside surface of the part for marking. This first mask presents a diameter of about 15 mm and a particular graphic pattern (circle split up by radii with the presence of a higher-contrast square in the center).

(24) A first laser pulse with a power density P1 of 0.09 GW/cm.sup.2 is applied to the outside surface of the part through the first mask 16-1.

(25) FIG. 3 shows a second mask 16-2 that is used during the second laser pulse that is applied to the outside surface of the part. This second mask 16-2 presents a diameter of about 10 mm and a particular graphic pattern (an opaque circle with lower opacity in a peripheral portion 20).

(26) A second laser pulse with a power density P2 of 0.130 GW/cm.sup.2 is applied to the outside surface of the part through the second mask 16-2.

(27) FIG. 4 shows a third mask 16-3 that is used during the third laser pulse that is applied to the outside surface of the part. This third mask 16-3 presents a diameter of about 6 mm and a particular graphic pattern (circle with an S-shaped pattern at the center).

(28) A third laser pulse with a power density P3 of 0.300 GW/cm.sup.2 is applied to the outside surface of the part through the third mask 16-3.

(29) FIG. 5 shows the results obtained by applying these three laser pulses to the outside surface of the part. In this figure there can be seen an imprint formed on the outside surface of the part, this imprint having a graphic that is constituted by adding the graphic patterns of the three masks that were used.

(30) Furthermore, the three images shown in this figure are views of the imprint seen looking along three different angles of observation. It can thus be seen that the graphic marked on the surface of the part can appear or disappear depending on its angle of inclination relative to the eye of the observer, thereby creating an illusion of depth or relief.