TWI549836B - Method and apparatus for reliably laser marking articles - Google Patents

Description

Method and apparatus for reliably laser marking articles

The present invention relates to laser marking of an anodized article. In particular, the use of a laser processing system to mark an anodized article in a manner that is durable and commercially desirable. Specifically, it has a unique feature of making the interaction between ultraviolet, visible, and infrared wavelength lasers and anodized articles to reliably and reproducibly build on anodized articles. A white mark that is persistent and meets commercial needs.

Products on the market are based on commercial, regulatory, decorative or functional purposes and often require some form of marking on them. The required marking characteristics include consistent appearance, durability, and ease of application. Appearance refers to the ability to reliably and reproducibly present indicia in selected shapes, colors, and optical densities. Persistence maintains consistent quality despite the wear of the marked surface. Ease of application refers to the cost of materials, time, and resources to make a mark with programmability. Programmability refers to programming a marking device with a new pattern to be marked by changing the software, rather than changing a hardware such as a screen or mask.

The anodized metal object is light, strong, easy to shape, and has a durable surface finish, so it has many applications in industrial and commercial goods. Anodizing means any of a variety of electrolytic passivation treatments in which a natural oxide layer is proliferated on a metal such as aluminum, titanium, zinc, magnesium, niobium or tantalum to enhance Corrosion or wear resistance and the purpose of decoration. These surface laminates can in fact be colored or dyed to create a permanent, non-fading, durable surface on the metal. Many of these metals can be effectively labeled using the features of the present invention. In addition, metals such as corrosion-resistant stainless steel can be marked in this manner. Many metal products such as these require permanent, clearly visible, commercially desirable markings. Anodized aluminum has a typical material of this need.

It has been a long time for color changes on the surface of an anodized aluminum article with a laser pulse. In a paper titled "Dry laser cleaning of anodized aluminum" by P. Maja, M. Autric, P. Delaporte, P. Alloncle et al. (COLA'99) -5th International Conference on Laser Ablation, July 19-23, 1999, G Ttingen, Germany, published in Appl. Phys. A 69 [Suppl.], S343-S346 (1999), pp S43-S346), which describes the removal of anodization from the surface of aluminum, but it should be noted that its color change This occurs where the laser energy is lower than the laser energy required to remove the anodization from the surface.

One of the mechanisms proposed to explain the optical density or color change of the metal surface is the generation of laser-induced periodic surface structures (LIPSS). AY Vorobyev and Chunlei Guo, "Colorizing metals with femtosecond laser pulses" (Applied Physics Letters 92, (041914) 2008, pp. 49141-1 to 141914 -3 pages) Describes the various colors that can be made on aluminum or aluminum-like metals using femtosecond laser pulses. This paper describes the creation of black or gray markings on metal and the creation of a golden color on the metal. It also mentions some other colors, but it is not mentioned. LIPSS is the only description provided for marking on metal surfaces. In addition, it only teaches or proposes a laser pulse having a 65 femtosecond timing pulse width to establish such a structure. Also, it does not mention whether the aluminum sample is anodized or whether the surface has been cleaned before the laser treatment. The paper also does not discuss possible damage to the oxide layer.

When dealing with the duration of a laser pulse, the method of measuring the duration of the pulse should be defined. Timing pulse shapes can range from simple Gaussian pulses to more complex shapes associated with individual jobs. An exemplary exemplary non-Gaussian laser pulse for a particular type of processing is described in US Patent No. 7,126,746, US Patent GENERATING SETS OF TAILORED LASER PULSES, inventor Sun et al. The assignee of the present invention is hereby incorporated by reference. This patent discloses a method and apparatus for generating a laser pulse having a typical Gaussian time waveform produced by a temporal profile different from a diode pumped solid state (DPSS) laser. These non-Gaussian pulses are referred to as "trimmed" pulses because their time waveform is changed from a typical Gaussian waveform by combining more than one pulse to produce a single pulse and/or a photoelectrically modulated pulse. . This produces a pulse whose pulse energy changes over time and typically contains one or more power peaks, wherein the instantaneous power is increased over a fraction of the pulse duration to a value greater than the pulse average power. Such tailored pulses can be useful in high rate processing materials that do not cause debris or overheating problems around the material. The problem is that measuring the duration of such complex pulses with standard methods that are basically applied to Gaussian pulses may produce anomalous results. Gaussian pulse duration measurements are typically measured using a full width at half maximum (FWHM) of duration. In contrast, using the integral flat method, as described in US Patent No. 6,058,739, LONG LIFE FUSED SILICA ULTRAVIOLET OPTICAL ELEMENTS, inventor Morton et al., allows complex time series shapes to be measured And compare it in a more meaningful way. In this patent, it uses the following formula to measure the pulse duration

Where T(t) is a function of the shape of the laser pulse timing.

Another problem with reliable and repeatable marking of a predetermined color and optical density on anodized aluminum is that it is required to produce very dark markings with a very readily available nanosecond pulse width solid state laser. The energy is enough to cause damage to the anodized zone, which is an unacceptable result. "Darkness" or "brightness" or color names are relative terms. A standard method of expressing color by number is the CIE system of reference colorimetry. This system is described in "CIE Fundamentals for Color Measurements" by Ohno, Y. (IS&T NIP16 Conf, Vancouver, CN, October 16-20, 2000, pp. 540-545 ). Among the measurement systems, a black mark that meets commercial requirements needs to be less than or equal to L*=40, a*=5, and b*=10. This produces a neutral black with no visible grayscale or chroma. In the US patent MARKING OF AN ANODIZED LAYER OF AN ALUMINIUM OBJECT, the inventor Keng Kit Yeo describes a method of marking an anodized aluminum article with a black mark, among the US patents MARKING OF AN ANODIZED LAYER OF AN ALUMINIUM OBJECT (No. 6,777,098). The black mark is located in the stack between the anodization zone and the aluminum and is thus as durable as the anodized surface. The indicia described therein are described as having a dark gray or black chroma and appear slightly less glossy than portions that have not been marked with nanosecond infrared laser pulses. In addition, it must remove all surface particles of aluminum, for example, particles that remain after anodization after polishing. There are two reasons for the disadvantages of marking according to the method claimed in the patent: First, the creation of a black mark that meets commercial requirements with a nanosecond pulse tends to cause damage to the oxide layer; second, after polishing or other processing The cleaning of the following aluminum adds extra steps to the process, adding to the associated costs and possibly interfering with the surface finishes required for other processing.

What is required, but not disclosed in the foregoing, is a reliable and repeatable method of producing black, white or gray or colored markings between the anodized aluminum, which does not require expensive femtosecond lasers. Or it may interfere with the oxide layer during the process or after the surface is ready. Moreover, it does not provide information on how to reproducibly create a variety of different colors on the surface of anodized aluminum, nor does it thoroughly trace the effects of discoloration or damage to the anodized layer. Therefore, it is necessary to propose a method for reliably and reproducibly establishing a mark having a predetermined optical density or gray scale and color on anodized aluminum using a lower cost laser, which does not cause oxides thereon. Poor damage and no cleaning required before anodizing.

One feature of the present invention is the addition of visible white markings of various optical densities to the anodized aluminum article. These markings are durable and have an appearance that meets commercial needs. This is achieved by establishing the markers using a laser marking system. These marks are built into or under the oxide layer and are therefore protected by oxides. The laser pulses establish a mark that meets commercial requirements and do not cause substantial damage to the oxide layer, thereby rendering the marks durable. It establishes a durable and commercially desirable mark on anodized aluminum by controlling the laser parameters that generate and direct the laser pulse. In one feature of the invention, the laser processing system is configured to produce a laser pulse with appropriate parameters in a programmable manner.

Exemplary laser pulse parameters that may be selected to enhance the reliability and repeatability of laser marked anodized aluminum include laser type, wavelength, pulse duration, repetition rate, number of pulses, pulse energy , pulse timing shape, pulse space shape, and focal spot size and shape. Further laser pulse parameters include specifying the position of the focal spot relative to the surface of the article and the speed at which the relative motion of the guided laser pulse relative to the article is controlled.

A feature of the present invention establishes durable and commercially desirable markings by whitening the oxide layer of the upper layer of the metal article from an optical density that is barely perceptible to the naked eye depending on the particular laser pulse parameter used. Other features of the present invention provide for durable and commercially desirable markings on anodized aluminum by decolorizing or partially discoloring the dyed or colored anodized regions while or without marking the underlying aluminum. . Another feature of the present invention is to establish a change in the microscopic size of the anodized layer of the scattered light and to establish an appearance from a slight "creamy" or diffuse appearance to an opaque, bright, without completely removing the anodized region. Different markings for white appearance.

In order to achieve the foregoing and other features in accordance with the purpose of the present invention, a method for establishing a visible mark of color and optical density on an anodized aluminum sample, and a method of modulating it, is disclosed and broadly stated herein. Constructed to perform the method. A feature of the present invention is the creation of visible indicia of selectable color and optical density on an anodized aluminum article. The method includes providing a laser marking system having a laser, a laser optics, a controller operatively coupled to the laser to control laser pulse parameters, and a controller having stored laser pulse parameters Selecting a stored laser pulse parameter associated with a predetermined color and optical density, directing the laser marking system to generate a laser pulse having a laser pulse parameter associated with a predetermined color and optical density, comprising greater than about 1 picosecond and less than A timing pulse width of approximately 1000 nanoseconds, or a continuous wave (CW), is applied to the anodized aluminum.

Embodiments of the present invention label an anodized aluminum article durable, selectively, predictably, and reproducibly with visible marks of various optical densities and colors. In an advantageous manner, it is such that the marks appear on or near the surface of the aluminum or within the anodization zone and maintain the anodized layer substantially intact to protect the surface and the indicia. The mark made in this way is called an interlayer mark because it is formed at or on the surface of the aluminum under the oxide layer forming the anodization region, or within the oxide layer itself. Embodiments of the present invention maintain the surface of the oxide substantially intact after marking to protect the indicia and provide a surface that is mechanically contiguous between adjacent indicia and non-marking regions. The tactile sensation of the human body is substantially indistinguishable from the surrounding unlabeled anodized area for the texture of such marks. In addition, the markings should be able to be produced reliably and reproducibly, meaning that if a marking of a particular color and optical density is desired, it is known that when the anodized aluminum is processed by a laser processing system, a predetermined result will result. A set of laser parameters. It should also be understood that in some cases, the white mark created by modifying the anodized layer by laser treatment may be further processed by adding a fluorescent or phosphorescent dye to the anodized region, possibly before laser processing. Or afterwards.

One embodiment of the present invention uses a structured laser processing system to mark an anodized aluminum article. An exemplary laser processing system that can be tuned to mark an anodized aluminum article is the ESI MM5330 micromachining system manufactured by Electro Scientific Industries, Inc., 97229, OR, Portland. This system is written in the "Model 5330ns Service Guide" issued by ESI, ESI P/N 178987a, October 2009, which is incorporated herein by reference in its entirety. This system uses a diode-excited Q-switched solid state laser micromachining system with an average power of 5.7 W at 30 KHz pulse repetition rate and second resonance multiplication to 532 nm wavelength. Another exemplary laser processing system that can be tuned to mark anodized aluminum articles is also the ESI ML5900 micromachining system manufactured by Electro Scientific Industries, Inc., 97229, OR, Portland. This system is written in the "Model 5900 Service Guide" issued by ESI, ESI P/N 178472A, October 2009, which is incorporated herein by reference in its entirety. The solid-state diode-excited laser used in this system can be grouped to emit wavelengths from about 355 nanometers (UV) to about 1064 nanometers (IR) at pulse repetition rates up to 5 MHz. Any of the above systems can be configured to incorporate an appropriate laser, laser optical module, component handling device, and control software for use on the surface of anodized aluminum in accordance with the method disclosed in this specification. The marking is produced reliably and reproducibly. These modifications enable the laser processing system to direct laser pulses with appropriate laser parameters to a properly positioned and placed anodized aluminum article at a predetermined rate and spacing to establish a predetermined Marking of color and optical density.

1 shows a schematic diagram of an ESI MM5330 micromachining system configured to mark an article in accordance with an embodiment of the present invention. The configuration includes laser 10, which in one embodiment of the invention operates a diode-operated Nd:YVO4 solid state laser at a wavelength of 1064 nm, a Rapid model unit manufactured by Lumera laser GmbH of Kaiserslautern, Germany. The laser selectively utilizes a solid-state resonant frequency generator to multiply the frequency to reduce the wavelength to 532 nm or to triple the frequency and to reduce the wavelength to 355 nm, thereby producing visible light (green) or ultraviolet light, respectively ( UV) laser pulse. This laser 10 is rated to produce 6 watts of continuous power and has a maximum pulse repetition rate of 1000 KHz. This laser 10 cooperates with the controller 20 to produce a laser pulse 12 having a duration of 1 picosecond to 1,000 nanoseconds. These laser pulses 12 may be Gaussian or specially shaped or tailored via the laser optics module 14 to allow for the application of predetermined indicia. The laser optics module 14, in cooperation with the controller 20, directs the laser pulses 12 to form a laser spot 16 on or near the article 18. The article 18 is secured to the platform 22 and includes a movement control member that cooperates with the controller 20 and the laser optics module 14 to provide composite beam positioning capabilities. The composite beam positioning compensates for the platform 22, the laser spot 16, or both by causing the controller 20 to direct the steering member in the laser optical module 14 as the article 18 moves relative to the laser spot 16. Relative motion, a function of marking a shape on an item 18.

When the laser pulse 12 is directed to form the laser spot 16 on or near the article 18, it is also shaped by the laser optics module 14 in conjunction with the controller 20. The laser optics module 14 controls the spatial shape of the laser pulse 12, which may be Gaussian or specially shaped. For example, it may use a "top hat" spatial topography that delivers a laser pulse 12 having a uniform radiation dose throughout the spot that is illuminated to the marked item. The spatial shape of a special shaped shape such as this can be created using a diffractive optical member. The laser pulse 12 can also be gated or guided by a photovoltaic component, an steerable mirror component, or a galvanometer component in the laser optics module 14.

The laser spot 16 is the focal spot of the laser beam formed by the laser pulse 12. As previously mentioned, the laser energy distribution at the laser spot 16 is dependent on the laser optics module 14. In addition, the laser optics module 14 controls the depth of focus of the laser spot 16, or the speed at which the spot is out of focus when the plane is away from the focal plane. By controlling the depth of focus, the controller 20 can direct the laser optics module 14 and the platform 22 to repeatedly position the laser spot 16 at or near the surface of the article 18 with high precision. Marking the focal spot above or below the surface of the article to create a mark allows the laser beam to be out of focus to a certain extent, thereby increasing the area illuminated by the laser pulse and reducing the radiance of the laser energy at the surface. Since the geometry of the beam waist diameter is known, determining the focal spot above or below the actual surface of the article provides further precise control of spot size and energy density.

Figure 2 is a photomicrograph showing the creation of a mark on anodized aluminum 30 using a prior art laser having a pulse of greater than one nanosecond. The anodization zone shows a clear crack mark 32 in the marking area 34, a poor result. Figure 3 shows the same color and optical density mark 38 made on the same form of anodized aluminum 36 using a picosecond laser showing no cracks. The picosecond laser applies a black marking that meets commercial requirements to the anodized aluminum article without causing damage to the oxide layer. A commercially acceptable black color is defined as a mark having a CIE chromaticity L*=40, a*=5, and b*=10 or less. Another advantage of using picosecond lasers is that they are cheaper, require less maintenance, and generally have a much longer operational life than prior art femtosecond lasers. Moreover, the features of the present invention do not require cleaning the surface of the aluminum prior to anodization to create a marking that meets commercial requirements.

One embodiment of the invention performs the application of the mark on the anodized aluminum under the anodization zone. For creating a sandwich mark without harming the anodization zone, the laser energy density is defined as:

F=E/s

Where E is the laser pulse energy and s is the laser spot area, it must satisfy Fu<F<Fs, where the laser of the Fu-based substrate is modified by the threshold value. In this example, the substrate is aluminum, and the Fs is surface layer or anodized. The damage threshold of the district. Fu and Fs have been experimentally obtained and represent the energy density at which the selected lasers begin to damage the substrate and surface layer. For a 10 picosecond (ps) pulse, experiments have shown that Al (aluminum) Fu is ~0.13 joules per square centimeter (J/cm ² ) for picosecond green light and ~0.2 joules per square centimeter for picosecond IR, Fs is ~0.18 joules per square centimeter for picosecond green light and ~1 joules per square centimeter for picosecond IR. Changing the laser energy density between these values produces markers of different colors and optical densities. Different pulse durations and laser wavelengths will each have a corresponding Fu and Fs value. The actual threshold for a particular set of laser parameters is determined experimentally.

An embodiment of the present invention precisely controls the position of the laser spot by adjusting the position of the laser spot from a surface located at the surface of the aluminum article to a clear distance above or below the surface of the aluminum. Laser energy density. Figure 4 shows a schematic representation of the beam waist diameter of the laser pulse focal spot 40 and its vicinity. The beam waist diameter is represented by a surface 42 which is the diameter of the spatial energy distribution measured by the FWHM method on the optical axis 44 along which the laser pulse travels. Diameter 48 represents the size of the laser pulse spot on the surface of the aluminum when the laser processing system focuses the laser pulse at a distance (A-O) above the surface. Diameter 46 represents the size of the laser pulse spot on the surface of the aluminum when the laser processing system focuses the laser pulse at a distance (B-O) below the surface.

In addition to the black color that meets commercial needs, it is also effective to apply a mark having a grayscale value to the article. Figures 5 and 6 show a series of gray scale marks applied to anodized aluminum by an embodiment of the present invention. The optical density of the mark ranges from almost indistinguishable to the background to all black. According to one feature of the invention, each gray scale mark can be represented as a unique ternary array of CIE color metric values, L*, a* and b*. One feature of the present invention combines each predetermined gray scale value with a set of laser parameters that reliably and reproducibly produce predetermined gray scale value indicia on the anodized aluminum in accordance with the command. It should also be noted that indicia that may appear undetectable to the naked eye, when illuminated at frequencies other than wide-area visible light, such as ultraviolet light, may become visible.

Figure 5 shows black indicia 60, 62, 64 and 66 fabricated on anodized aluminum 70 in accordance with one embodiment of the present invention. These indicia 60, 62, 64, and 66 have CIE chromaticities ranging from less than L*=40, a*=5, and b*=10 to fully transparent, making them a mark of commercial need. Another feature of the markers is that they have a consistent appearance over a wide viewing angle range since they are located below the non-damaging anodization zone. The mark made by the prior art method tends to have a large difference in appearance with a change in the viewing angle due to damage to the anodized layer. In particular, when marking with prior art nanosecond pulses, applying sufficient laser pulse energy to the surface to make dark marks causes damage to the anodization region, which causes the appearance of the mark to vary with viewing angle. According to a feature of the present invention, no matter how deep the mark is, it does not damage the anodization zone, and does not change in appearance depending on the viewing angle. These improved markings are caused by the following laser parameters:

The optical densities of the indicia 60, 62, 64, 66 range from 60 to almost black 66, which is barely noticeable relative to unlabeled aluminum. The grayscale optical density 64, 66 between the two extremes is created by moving the focal spot closer to the article, increasing the energy density to create a darker mark. The change in height of the focal spot above the surface of the aluminum begins at zero, i.e., the darkest optical density mark 62, which is incremented by 500 microns in each of the marks 64, 66 from right to left in Figure 5, ending at the surface. The lightest mark 60 at 5 mm above. Note that the indicia 64 produced by a focal spot located 4.5 to 1.5 mm above the surface of the aluminum exhibits a brown or golden yellow color, while the indicia 62 and 66 produced with a focal spot of one millimeter or less appear gray or black. Maintaining this precise control of the distance from the laser focal spot to the working surface and maintaining other laser parameters within the tolerances of normal laser processing, allowing it to be made of a predetermined color and optical density on the anodized aluminum. Laser marker. In addition, the darkest mark shows a CIE chromaticity less than L*=40, a*=5 and b*=10, making it a black mark that meets commercial needs.

Another feature of the invention determines the relationship between the indicia of the color outside the grayscale and the picosecond laser pulse parameters. Colors other than the gray scale can be produced on the anodized aluminum in two different ways. First, it can produce a golden hue in the range of optical density. This color is produced by making changes at the interface between the aluminum and oxide coatings. Careful selection of the laser pulse parameters will produce a predetermined golden color without damaging the oxide coating. Figure 5 also shows various colors of golden or brown produced by one of the features of the present invention.

The laser marking of the anodized aluminum can also be achieved by the use of an IR wavelength laser pulse to characterize the aluminum. This feature produces markers of different gray scale densities by varying the laser energy density at the surface of the aluminum in two different ways. As described above, it is possible to create a gray scale by positioning the focal spot above or below the surface of the aluminum to change the energy density at the surface. The second way to control the gray scale is to change the total dose at the surface of the aluminum by changing the bite size or line spacing when marking the predetermined pattern. Changing the illumination point distance means adjusting the rate at which the laser pulse beam moves relative to the surface of the aluminum or changing the pulse repetition rate or both, which results in a change in the distance between successive laser pulse impact locations on the aluminum. Changing the line spacing means adjusting the distance between the marked lines to achieve a different degree of overlap. FIG. 6 shows an aluminum article 74 having an array of indicia 72. These indicia 72 are arranged in an array comprising six rows and four columns. These six rows represent the six focal spot Z-direction heights above the surface of the aluminum ranging from 0 (top column) to 5 mm (bottom column). The four columns represent the distance between 5, 10, 20 and 50 microns from left to right. It should be seen from Figure 6 that changing the Z-direction height of the focal spot and changing the laser pulse spacing can be produced in a predictable manner from less than CIE L*=40, a*=5 and b*=10 to near The gray scale of any predetermined optical density between the transparents creates a mark on the anodized aluminum that meets commercial requirements.

A second type of mark that can be applied to the anodized aluminum by a picosecond or nanosecond laser pulse is a change in color contrast caused by decolorization of the dyed anodization zone. In general, the anodization zone is porous and will readily accept many dyes. Referring again to Figure 3, this photomicrograph of anodized aluminum shows the porous nature of the surface. The laser pulse for marking the anodized aluminum after dyeing can, depending on the wavelength and the pulse energy, remove the dye when the aluminum is marked, so that the anodization zone becomes transparent, thereby revealing the mark on the underlying aluminum. come out. With a higher energy density, it is possible to simultaneously perform dye removal as well as aluminum under the anodized layer in black, grayscale, or color as described in the previous paragraph. The lower energy pulse can partially remove the dyeing of the anodization zone to make it translucent, thereby locally coloring the underlying aluminum mark. Finally, longer wavelength pulses can be applied to the aluminum with a black or grayscale color that meets commercial requirements without causing discoloration of the anodization zone. Figure 7 shows the dyed anodized aluminum article with a mark made from visible (532 nm) laser pulses. Note that the staining in the anodization zone is removed in the area where the laser pulse is received. Figure 8 shows the same dyed anodized aluminum article with a mark made from IR (1064 nm) laser pulses. Note that the anodization region was not discolored by the IR laser pulse, so the underlying aluminum color did not appear to pass through the translucent state of the original oxide.

Another feature of the invention relates to the application of a laser marking to anodized aluminum using a picosecond or nanosecond laser to pass a colored anodization zone. Since anodization generally forms a porous surface, it is possible to introduce a dye which changes the appearance of aluminum. These dyes may be opaque or translucent, allowing a different amount of incident light to reach the aluminum and be reflected back through the anodization zone. Figure 7 shows an anodized aluminum article 80 having a pink coloration in the anodization zone and an array of indicia 82 in accordance with one feature of the present invention. The color is produced by removing the dye from the oxide layer, while the underlying aluminum exhibits a color from the original (silver) color to a series of laser-marked colors from brown to gray to black. These colors are produced by varying the energy density of the laser pulses at the surface of the aluminum. The four columns in the figure represent the change in the distance between the laser pulses from 10 microns to 50 microns, while the row represents the change in the focal spot distance from the surface from 0.0 mm to 5.0 mm. These laser parameters in all cases result in the removal of dye in the oxide covering the aluminum, allowing the marking on the aluminum to be revealed. The laser marker optical density ranges from transparent to CIE chromaticity less than L*=40, a*=5, b*=10. The laser parameters used to generate these markers are shown in Table 3.

The removal of dyeing in the anodization zone is frequency dependent. As shown in Figure 7, the 532 nm laser pulse removes the dyeing of the anodization zone even when the lowest energy density is applied. On the other hand, the IR laser wavelength establishes a mark on the anodized aluminum after dyeing and does not remove the dye for most translucent dye colors. Figure 8 shows an anodized aluminum article 100 having a pink coloration and indicia 102 made from IR laser pulses. The marks are from translucent to black and are made by modifying the distance of the focal spot to the surface and by varying the spacing to modify the laser energy density. The six rows in the figure represent the change in the distance between the laser pulse focal spot and the surface of the aluminum from 5.5 mm (right side) to zero (left side). The four columns in the figure represent a change in the laser pulse pitch from 10 microns to 50 microns. The laser parameters used to generate these markers are shown in Table 4.

The relationship between dye removal for the anodic oxidation zone of the 532 nm (green) laser wavelength, marking of aluminum, and surface ablation is shown in FIG. For the 532 nm (green) laser pulse with the parameters given in Tables 1, 2 and 3, Figure 9 shows the anodization zone decolorization (Fb) in Joules per square centimeter (Joules/cm ² ), Mark the energy density threshold for aluminum (Fu) and surface ablation (Fs) under the anodization zone. In one aspect of the invention, the 532 nm laser pulse produces a value of Fb = 0.1 joules per square centimeter, Fu = 0.13 joules per square centimeter, and Fs = 0.18 joules per square centimeter. Figure 10 shows the energy density threshold in joules per square centimeter for 1064 nanometer (IR) laser pulses given the parameters given in Tables 1, 2 and 3. In one feature of the invention, the energy density threshold of Joules per square centimeter for 1064 nanometer (IR) laser pulses is Fu = 0.2 joules per square centimeter and Fs = 1.0 joules per square centimeter. Note that there is no threshold for the decolorization of the anodization zone because the IR wavelength laser pulse cannot begin to decolorize the anodization zone until the laser energy density is large enough to damage the covered anodization zone. It should also be noted that the exact values of Fb, Fu and Fs will depend on the particular laser and optical module used. For a particular processing configuration and the item to be marked, it should be experimentally determined and stored in the controller for subsequent use.

In another embodiment of the invention, the programmable nature of the modulated laser processing system allows the anodized aluminum article to be marked to conform to commercially demanded marking patterns. As shown in FIG. 11, in this feature, a pattern 110 is converted into a digital representation 112 that is broken down into a list 114, wherein each item 116 in the list 114 includes a representation of a position or a plurality of positions. The way, with a color and optical density associated to each location. The list 114 is stored in the controller 20. The controller 20 will cause each item 116 in the laser parameter linkage list 114 to cause the laser when the laser parameters are transmitted to the laser 10, the optical module 14 and the mobile control platform 22 in the form of commands. 10 emits one or more laser pulses 12 that illuminate the surface 16 of the aluminum article 18 or its vicinity. These pulses will create a mark with a predetermined color and optical density. When the mark is being created, the laser beam 12 is moved relative to the aluminum article 18 in accordance with the position stored in the list such that the predetermined range of color and optical density marks are made in the predetermined pattern on the anodized aluminum. Above the surface.

In another embodiment of the invention, the colored anodized regions are patterned over the previously patterned indicia to exhibit additional color and optical density. Among these features, the grayscale pattern is built on an anodized aluminum article. The article is then coated with a photoresist coating that can be developed by exposure to a laser pulse. The gray-scale patterned and photoresist-coated articles are placed into the laser processing system and aligned for alignment so that the system can accurately apply laser pulses to the pattern that has been applied to the article. The photoresist used is a type of "negative" photoresist where the area exposed to the laser radiation will be removed and the unexposed areas will remain on the item for subsequent processing. The residual photoresist protects the surface of the article from being stained, while the anodized regions that have been exposed and subsequently removed will be dyed to a predetermined color. The anodized layer is designed to be translucent to allow light to pass through the anodization region to the underlying pattern and be reflected back through the anodization region to produce a colored pattern having a selected color and optical density. The colored anodization zone can also be decolorized, if desired, using techniques disclosed by other features of the present invention to produce a predetermined color having a predetermined transparency. This color can be applied to the entire area of the underlying pattern, or in a point-by-point manner, limited only by the resolution of the laser system, typically in the range of 10 to 400 microns. This action can be repeated to create a multi-color overlay. In one feature of the invention, an anodic oxidation zone color overlay, such as a Bayer pattern, is applied in the form of a multi-color overlay grid. By designing the grayscale pattern to match the color overlay grid, a durable, commercially available full color image can be created on an anodized aluminum article.

Figures 12a through 12i show a series of steps for establishing such a color overlay using two colors. In Figure 12a, the aluminum article 118 has a transparent anodized layer 120 and indicia 122 previously applied in accordance with other features of the present invention. A negative photoresist 124 is applied to the surface of the transparent anodized layer 120. In Figure 12b, laser pulse 126 exposes regions 128, 130 of photoresist 124. In Figure 12c, the unexposed photoresist 134 remains after the photoresist treatment, but the exposed photoresist is removed leaving the vacancies 132 in the processed photoresist layer 134. Figure 12d shows that the anodization zone in section 136 below the vacancies 132 in the treated photoresist layer 134 in the base anodized layer 120 is colored. The intact photoresist layer 134 prevents the anodized regions from being colored, except for the regions 132 of the photoresist layer 134 that have been removed. Figure 12e shows the relative position of the article 118 comprising the base anodization region 120 having an anodized region 136 having a color portion and the previously applied indicia 122 after removal of the treated photoresist layer.

Figure 12f shows article 118 having a base anodization region 120 comprising a color portion 136 and a second photoresist layer 138. Figure 12g shows that the second stack 138 of photoresist is illuminated by a laser pulse 142 such that region 140 is exposed. Figure 12h shows the condition after the article 118 having the base anodization region 120 is subjected to the dyeing of the anodization region below the removed photoresist 140 and the residual photoresist 138 is removed. This causes the intact underlying anodized layer to contain colored regions 136, 144 overlying the previously marked regions 122. Figure 12i shows that subsequent laser pulses 146 are used to selectively decolorize the previously anodized and dyed portions of the aluminum article to produce an additional predetermined color or optical density. The process described in this feature of the present invention causes the color pattern to be overlaid on the grayscale pattern to produce a wide range of markers of durable and commercially desirable color and optical density in a programmable pattern.

In another embodiment of the invention, a colored pattern of anodized regions can be created on the anodized aluminum article using a particular pattern to produce a full color image for viewing. Within this feature, a pattern representation of an image is applied to the surface using the techniques described herein. The colorants are introduced in the manner illustrated in Figures 12a through 12i, but the pattern in which the dyes are introduced into the anodized base layer is designed to convert the gray scale representation into a full color. An example of such a pattern is a Bayer filter (not shown) that juxtaposes red, green, and blue filter elements in a pattern that causes the eyes to be red, green, and blue. The perception is fused to a single color associated with the grayscale markings beneath the filter of the colored anodization zone to produce a full color image or pattern appearance. The photoresist may be a negative or positive photoresist, and the pattern exposing the photoresist may be produced by a mask, such as for use in a circuit or semiconductor application, or written directly by an electronic device, or by such as The technique of inkjet is deposited directly or directly by laser ablation.

In another embodiment of the invention, a bright white marking can be applied to the anodized aluminum article using a laser marking system as configured herein. In this embodiment, it selects the laser parameters to slightly exceed the damage threshold of the anodized layer without causing ablation. As shown in Figure 13, this embodiment marks an anodized aluminum article by creating a low degree of damage in the anodized layer without ablating or otherwise removing the anodized layer from the surface. . Figure 13 shows an anodized article 150 having a white marking 152 created in such a manner in accordance with an embodiment of the present invention. This low level of damage involves a large number of small "micro" cracks in the anodization zone that circulate light of all wavelengths, resulting in a "creamy" or clustered white appearance on the surface. Since the anodized region is not structurally damaged or broken in the macroscopic size, the surface maintains its durability and does not change significantly on the grain. The laser parameters used to create a bright white mark on the anodized aluminum provide a laser energy density that is slightly greater than the damage threshold of the anodization zone. It is chosen such that the laser energy density is large enough to create microcracks in the anodization zone, but not large enough to cause sufficient damage to alter the durability or perceptible texture of the article. Table 5 contains the laser parameters used to create a bright white marking on an anodized aluminum article as shown in FIG.

By varying the laser energy density used within a specified range close to the specific anodization zone and the damage threshold of the article, the appearance of the marker can vary from light frosted to completely opaque bright white. Moreover, this embodiment can combine this effect with a colored anodization zone to produce a mark having a different degree of saturation. As the laser energy density increases, a dyed anodized layer will first appear to be unsaturated, meaning that the color appears to be mixed into white. As the laser energy density increases, the colored anodized zone produces discoloration, while the indicia exhibits a bright white appearance with no color.

The laser parameters used to generate the bright white markings include the use of a 355 nm wavelength third resonant diode excited solid state Nd:YVO ₄ laser with a range of emission energy ranging from 266 to 532 nm. High power pulsed laser. The laser operates at 4 KW and is basically in the range of 1 KW to 100 KW. The preferred embodiment is between 1 KW and 12 KW. The laser energy density ranges from about 0.1 x 10 ^-6 joules per square centimeter to 100.0 joules per square centimeter, or especially from 1.0 x 10 ^-6 joules per square centimeter to 10.0 joules per square centimeter. The pulse duration ranges from 1 picosecond to 1000 nanoseconds (ns), or a preferred embodiment is from 1 nanosecond to 200 nanoseconds. The laser repetition rate is in the range from 1 KHz to 100 MHz, or the preferred embodiment is from 10 KHz to 1 MHz. The speed at which the laser beam moves relative to the marked item ranges from 1 mm/sec to 10 m/sec, or preferably from 100 mm/sec to 1 m/sec. The spacing or spacing between adjacent columns of laser pulses on the surface of the article ranges from 1 micron to 1000 microns, or a preferred embodiment is from 10 microns to 100 microns. The laser pulse spot size measured at the surface of the article ranges from 10 microns to 1000 microns, or preferably from 50 microns to 500 microns. The location of the laser pulse focal spot relative to the surface of the article ranges from -10 mm to +10 mm, or especially from 0 to +5 mm.

Figure 14 shows a clear anodized aluminum article 160 having six columns of 162 per column containing six, each applied to the surface using the laser parameters listed in Table 5, with the spot size from the leftmost row. At 200 microns, each row is incremented by 60 microns to 500 microns on the far right row. The spacing or distance between adjacent lines of the laser pulse ranges from 10 microns in the top row to 20 microns in the middle column to 50 microns in the bottom row. It can be seen that as the power increases, the brightness of the white mark increases and the transparency decreases.

Embodiments of the invention mark an article with an infrared laser pulse comprising a CO ₂ laser. The laser parameters used to successfully mark the anodized articles are shown in Table 6 with white markings made by changes in the anodized layer.

The laser parameters used to create such white marks include the use of a 10.6 micron wavelength CO ₂ laser. The laser operates at 75 kW and is basically in the range of 1 KW to 500 KW. The preferred embodiment is between 50 KW and 150 KW. The laser energy density ranges from about 1.0 x 10 ^-6 joules per square centimeter to 100.0 joules per square centimeter, or especially from 1.0 x 10 ^-6 joules per square centimeter to 10.0 joules per square centimeter. The pulse duration ranges from 1 nanosecond to continuous wave application, or a preferred embodiment is from 100 nanoseconds to 100 milliseconds (ms). The laser repetition rate is in the range from 1 KHz to 1 MHz, or the preferred embodiment is from 10 KHz to 250 KHz. The speed at which the laser beam moves relative to the marked item ranges from 1 mm/sec to 10 m/sec, or preferably from 100 mm/sec to 1 m/sec. The spacing or spacing between adjacent columns of laser pulses on the surface of the article ranges from 1 micron to 1000 microns, or a preferred embodiment is from 10 microns to 100 microns. The laser pulse spot size measured at the surface of the article ranges from 10 microns to 1000 microns, or preferably from 50 microns to 500 microns.

The details of the foregoing embodiments may be modified in many ways without departing from the basic principles of the invention, which should be apparent to those skilled in the art. The scope of the invention is therefore intended to be defined by the scope of the following claims.

10. . . Laser

12. . . Laser pulse

14. . . Laser optical module

16. . . Laser spot

18. . . article

20. . . Controller

twenty two. . . platform

30. . . Anodized aluminum

32. . . crack

34. . . Marked area

36. . . Anodized aluminum

38. . . mark

40. . . Focal spot

42. . . Beam waist surface

44. . . Optical axis

46. . . diameter

48. . . diameter

60-66. . . mark

70. . . Anodized aluminum

72. . . mark

74. . . Aluminum goods

80. . . Aluminum goods

82. . . mark

100. . . Anodized aluminum article

102. . . mark

110. . . pattern

112. . . Digital representation

114. . . List

116. . . Items in the list

118. . . Aluminum goods

120. . . Transparent anodized layer

122. . . mark

124. . . Photoresist layer

126. . . Laser pulse

128. . . Photoresist area

130. . . Photoresist area

132. . . Vacancy in the photoresist layer

134. . . Photoresist layer

136. . . Section below the vacancy

138. . . Second photoresist layer

140. . . Area in the second photoresist layer

142. . . Laser pulse

144. . . Colored area

146. . . Colored area

150. . . Anodized article

152. . . White mark

160. . . Anodized aluminum article

162. . . mark

Fb. . . Energy density threshold for decolorization in anodized zone

Fu. . . Marking the energy density threshold of aluminum under the anodized zone

Fs. . . Surface ablation energy density threshold

Figure 1. Laser processing system.

Figure 2 is a representation of the prior art nanosecond pulse system.

Figure 3. Marks made in picosecond pulses.

Figure 4, beam waist diameter.

Figure 5 is a gray scale mark on anodized aluminum.

Figure 6. Mark on the anodized aluminum.

Figure 7. Aluminized anodized aluminum with a visible mark after dyeing.

Figure 8. Aluminized anodized aluminum with an IR mark after dyeing.

Figure 9 is a graph showing the relationship between thresholds of visible laser light pulses.

Figure 10 is a graph showing the relationship between IR laser pulse threshold values.

Figure 11. Image data converted to laser parameters.

Figures 12a-i are applied to the colored anodization zone of an aluminum article.

Figure 13, white mark.

Figure 14. Gray scale mark on anodized aluminum.

150. . . Anodized article

152. . . White mark

Claims (44)

A method for establishing a mark having a predetermined property on an anodized article, the predetermined property comprising optical density, color, texture, and durability, the method comprising: providing a laser marking system comprising a controllable mine a laser that emits an energy density; determining the laser energy density associated with establishing the mark having the predetermined property; and directing the laser mark system to mark the anodized process with the determined laser energy density The article, thereby establishing the indicia, has an optical density in the range from transparent to opaque, a white color, a texture that is substantially indistinguishable from surrounding unmarked lines, and an anodized region that is durable and substantially intact. A method for establishing a mark having a predetermined property on an anodized article as described in claim 1 wherein the article comprises a metal. A method for establishing a mark having a predetermined property on an anodized article as described in claim 2, wherein the metal comprises aluminum. The method for establishing a mark having a predetermined property on an anodized article as recited in claim 1, further comprising adding a dye to the anodization zone of the anodized article. A method for establishing a mark having a predetermined property on an anodized article as described in claim 4, wherein the dyed film is dyed The anodized region is also additionally decolored by the laser. A method for establishing a mark having a predetermined property on an anodized article as described in claim 4, wherein the dye in the anodized region contributes to laser processing to establish an additional The mark of color. A method for establishing a mark having a predetermined property on an anodized article as described in claim 1, wherein the mark has a uniform appearance over a wide viewing angle range. A method for establishing a mark having a predetermined property on an anodized article, as described in claim 1, wherein the mark is invisible under ambient viewing conditions, and wherein the mark is at least one Visible under non-circular viewing conditions. A method for establishing a mark having a predetermined property on an anodized article, as described in claim 1, wherein the at least one non-circumferential viewing condition comprises UV light. A method for establishing a mark having a predetermined property on an anodized article as recited in claim 1, wherein the mark is visible to the naked eye when the mark is illuminated by broad-spectrum visible light The marked area is difficult to discern, and wherein the mark is visible to the naked eye when illuminated by the broad spectrum of visible light. A method for establishing a mark having a predetermined property on an anodized article, as described in claim 1, wherein the mark includes a mark region adjacent to the anodized article Unmarked area, and the anodized article therein The oxide layer surface is mechanically adjacent to the adjacent one of the marking regions and the non-marking regions. A method for establishing a mark having a predetermined property on an anodized article as recited in claim 1, wherein the article comprises a substrate and an oxide layer deposited on the substrate, wherein the oxide layer has oxidation a layer surface, wherein the mark is established below the surface of the oxide layer. A method for establishing a mark having a predetermined property on an anodized article as described in claim 12, wherein the mark is made at a clear distance below the surface of the oxide layer of the article. A method for establishing a mark having a predetermined property on an anodized article as recited in claim 1, wherein the article comprises a substrate and an oxide layer formed on the substrate, wherein the oxide layer comprises oxidation a layer surface, wherein the laser pulse has a focal spot, and wherein the focal spot is positioned at a distinct distance below the surface of the oxide layer of the article. A method for establishing a mark having a predetermined property on an anodized article, according to any one of claims 1 to 14, wherein the article comprises a substrate and oxidation formed on a surface of the substrate a layer, wherein the laser pulse has a focal spot, and wherein the focal spot is positioned at a clear distance above the surface of the substrate. A method for marking an anodized article, the method comprising: providing a laser marking system comprising controlled laser energy density a laser; determining the laser energy density associated with establishing a mark having a white color; and directing the laser marking system to mark the anodized article with the determined laser energy density to establish The indicia having a white color, wherein directing the laser marking system includes directing the laser marking system to mark the anodized article such that the surface of the anodized article in the vicinity of the marking The texture is substantially indistinguishable from the texture of the surface of the anodized article outside the vicinity of the mark. A mark made by laser on an anodized sample having an optical density ranging from transparent to opaque, a white color, a texture that is substantially indistinguishable from surrounding unmarked lines, and an anodizing that is durable and substantially intact. a region wherein the appearance of the mark is the result of a laser induced damage that scatters light in a layer of the anodization zone. A mark made by laser on an anodized sample as described in claim 17 of the patent application, wherein the sample contains a metal. A mark made by laser on an anodized sample as described in claim 18, wherein the metal comprises aluminum. A mark made by laser on an anodized sample as described in claim 17 wherein the anodization is dyed plus laser treatment to create the mark with an additional color. As described in claim 20, the laser is passed through the anode. A mark is made on the oxidized sample, wherein the anodized region that is dyed is additionally decolored by the laser. An anodized aluminum article comprising: an aluminum substrate; an oxide layer disposed over the aluminum substrate; and a laser mark having an optical density ranging from transparent to opaque, white color, and surrounding unmarked lines An indistinguishable texture and a durable and substantially intact anodization zone wherein the appearance of the mark is the result of laser induced damage that causes light to scatter in the oxide layer. The aluminum article of claim 22, wherein the layer of the anodization zone is dyed with a dye. The aluminum article of claim 23, wherein the dye of the layer of the anodized region that is dyed is decolored by a laser. The aluminum article of claim 22, wherein the indicia has a uniform appearance over a wide viewing angle range. The aluminum article of claim 22, wherein the indicia is invisible under ambient viewing conditions, and wherein the indicia is visible under at least one non-circumferential viewing condition. The aluminum article of claim 22, wherein the at least one non-circumferential viewing condition comprises UV light. The aluminum article of claim 22, wherein when the mark is illuminated by broad-spectrum visible light, the mark is indistinguishable to the naked eye from the unmarked area, and wherein the mark is by a broad spectrum This mark is visible to the naked eye when illuminated by visible light. The aluminum article of claim 22, wherein the mark comprises a marking region adjacent to a non-marking region in the anodized aluminum article, and wherein the anodized aluminum The oxide layer surface of the article is mechanically contiguous between adjacent ones of the marking regions and the non-marking regions. The aluminum article of claim 22, wherein the oxide layer has an oxide layer surface, and wherein the mark is established below the surface of the oxide layer. The aluminum article of claim 30, wherein the indicia is made at a clear distance below the surface of the oxide layer of the article. The aluminum article of claim 22, wherein the oxide layer comprises an oxide layer surface, wherein the laser pulse has a focal spot, and wherein the focal spot is positioned below the surface of the oxide layer of the article Clear distance. The aluminum article of any one of claims 22 to 32, wherein the laser pulse has a focal spot, and wherein the focal spot is positioned at a clear distance above the surface of the substrate. A method for marking an anodized article having a substrate and an anodized layer formed on the substrate, the method comprising: adjusting a region of the anodized layer to form an adjusted having a plurality of cracks An oxidized region configured to scatter light within the adjusted oxidized region, wherein the adjusted oxidized region comprises a white color Marked. The method of claim 34, wherein adjusting the region of the anodized layer comprises directing a laser pulse to the anodized article. The method of claim 34, further comprising adding a dye to the region of the anodized layer. The method of claim 34, wherein the plurality of cracks are configured to scatter light in the adjusted region such that a visible appearance of a portion of the anodized article within the mark is The visible appearance of the other portion of the anodized article outside the marking is also bright. The method of claim 34, wherein the indicia has a uniform appearance over a wide range of viewing angles. The method of claim 34, wherein the indicia comprises a marking region adjacent to the non-marking region in the anodized article, and wherein the oxide layer is mechanically adjacent to the adjacent An upper surface between the marking area and the non-marking area. The method of any one of claims 34 to 39, wherein the oxide layer has an oxide layer surface, wherein the laser pulse has a focal spot, and wherein the focal spot is positioned on the oxide surface of the article A clear distance below it. The method of claim 34, wherein the laser pulse has a focal spot, and wherein the focal spot is positioned at a clear distance above the substrate. The method of claim 34, wherein the indicia is invisible under ambient viewing conditions, and wherein the indicia is visible under at least one non-circumferential viewing condition. The method of claim 34, wherein the at least one non-circumferential viewing condition comprises UV light. The method of claim 34, wherein when the mark is illuminated by broad-spectrum visible light, the mark is indistinguishable to the naked eye from the unmarked area, and wherein the mark is by a broad spectrum of visible light This mark is visible to the naked eye when illuminated.