Metal surface processing method

Abstract

To provide a metal surface working method capable of easily working a pattern with gradation.SOLUTION: Irradiating a metal surface with a laser and scanning the laser along the metal surface such that a plurality of spots, which are irradiation points of the laser on the metal surface, partially overlap each other; A method for processing a metal surface to draw a predetermined pattern on the metal surface includes a first irradiation step of scanning a laser such that spots are arranged in a matrix to form a predetermined pattern A including the spots arranged in the matrix on the metal surface, and a second irradiation step of scanning the laser in a direction intersecting a scanning direction of the laser in the first irradiation step by a predetermined angle θ to irradiate the laser such that a pattern B same as the predetermined pattern A in which the spots are arranged in the matrix is superimposed on the pattern A in the first irradiation step.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for processing the surface of a metal part such as aluminum or its alloy by using a laser, and in particular to a method for forming a gradation pattern on the surface of a metal part. [Background technology]

[0002] When a laser beam is applied to a metal surface with a small spot, the spot melts instantly, creating a minute depression or an oxide film. When such spots are densely arranged within a given area, the way the light is reflected creates a colored pattern. The color tone or shading varies depending on the thickness of the oxide film and the overlap of the spots. Therefore, by gradually changing the arrangement or overlap of the laser-irradiated spots through the scanning method of the moving laser spot, it is possible to create a gradation in color tone or shading. Such methods for processing metal surfaces using a laser are proposed in Patent Documents 1 and 2.

[0003] The method described in Patent Document 1 is a decoration method that applies a pattern to the surface of a metal plate, such as aluminum, by irradiating the surface with laser light to form an oxide film and varying the color tone or shade depending on the overlap of the oxide film. The method described in Patent Document 1 applies a gradation to the surface of the metal plate, in which the color tone or shade gradually changes from a predetermined center toward the outer periphery. To achieve this, a laser light is irradiated from an irradiation unit toward the metal plate, and the irradiation unit and the metal plate are moved relative to each other so that the areas or locations (spots) hit by the laser light change linearly on the surface of the metal plate. In this case, the spots are partially overlapped. Furthermore, scanning lines that move the spots linearly are set radially from a predetermined center, and spots on adjacent scanning lines are partially overlapped. Because the scanning lines are set radially, the overlap amount (overlap ratio) of the spots at the predetermined center decreases toward the outer periphery, which is farther from the center. As a result, the thickness and density (or coarseness and fineness) of the oxide film formed on the surface of the metal plate gradually change from the center to the periphery, resulting in a decoration with a gradation of color tone or shades on the surface of the metal plate.

[0004] Patent Document 2 also describes a method for forming a colorful pattern on the surface of a metal plate by forming an oxide film on the surface of the metal plate using laser light, and a method for creating a gradation in color tone. In this method, a first processing surface is processed using a femtosecond laser, and then a part of the processed surface is irradiated with a nanosecond laser to form a second processing surface. When irradiating the second processing surface with the nanosecond laser, the pitch during the scanning process is gradually changed. As a result, the thickness of the oxide film changes gradually, creating a gradation in gloss and color tone. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-106384 [Patent Document 2] Japanese Patent Publication No. 2023-011165 Summary of the Invention [Problem to be solved by the invention]

[0006] The method described in Patent Document 1 can form a pattern in which the color tone or shade changes toward the periphery in an area that gradually expands from the center toward the periphery. However, the method described in Patent Document 1 gradually widens the distance between the centers of the spots toward the periphery, reducing the overlap of the spots toward the periphery. Because the change in color tone or shade is uniform, it is not possible to form a pattern or pattern with a repeating gradation within the decorative surface. If such a repeating pattern or pattern were to be formed, the laser spot would need to be scanned in a complex manner and multiple times, which could result in poor processing efficiency or workability.

[0007] Furthermore, in the invention of Patent Document 2, in order to create a gradation, the second processing is performed using a laser with higher energy than the first processing, and the pitch is gradually changed. In other words, the thickness of the oxide film that creates the gradation is varied by changing the pitch, so if gradation is to be created in a pattern that repeats in a certain direction, the scanning line and pitch must be changed in a complex manner, which may result in a decrease in processing efficiency or workability.

[0008] An object of the present invention is to provide a metal surface processing method that can easily process a gradation pattern. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, the present invention provides a method for processing a metal surface, which involves irradiating a metal surface with a laser and scanning the laser along the metal surface so that a plurality of spots, which are irradiation points of the laser on the metal surface, partially overlap one another, thereby forming a predetermined pattern on the metal surface. The method is characterized by comprising: a first irradiation step in which the laser is scanned so that the spots are arranged in a matrix, thereby forming a predetermined pattern on the metal surface consisting of the spots arranged in a matrix; and a second irradiation step in which the laser is scanned in a direction intersecting the scanning direction of the laser in the first irradiation step at a predetermined angle, thereby irradiating the laser so that a pattern identical to the predetermined pattern in which the spots are arranged in a matrix is ​​superimposed on the pattern in the first irradiation step.

[0010] In the present invention, the spots may have a circular shape on the metal surface, and the amount of partial overlap between the spots in each of the two orthogonal directions in which the spots are aligned may be less than the radius of the spots.

[0011] In the present invention, the predetermined angle may be equal to or greater than 1 degree and equal to or less than 20 degrees. [Effects of the Invention]

[0012] According to the method of the present invention, the metal surface is melted at the spots arranged in a matrix in the first irradiation step, forming depressions and oxide films, resulting in color due to interference of reflected light. Because adjacent spots partially overlap, upon close observation, the overlapping and non-overlapping areas appear to have different color tones or shades. However, because the diameter of the spots or depressions is approximately several millimeters per hundred, visually, the entire area irradiated with the laser appears as a single color with no particular shade. In the second irradiation step, the scanning direction of the spots on the laser-irradiated metal surface is set to a direction that intersects the scanning direction in the first irradiation step at a predetermined angle, resulting in variations in the overlapping state and amount of overlap between the spots or depressions in the first irradiation step and those in the second irradiation step. As a result, areas with different color tones and shades are created, and the changes in color and shade are repeated along the metal surface, forming a gradation or pattern with gradually changing color or shade. That is, according to the method of the present invention, a pattern or gradation can be applied to a metal surface by performing two laser irradiations with different spot scanning directions, so that processing to form a pattern or gradation on a metal surface can be performed easily and efficiently. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing an example of a laser processing device. [Figure 2] FIG. 1 is a schematic diagram showing some of the spots arranged in a matrix. [Figure 3] FIG. 2 is a schematic diagram showing an example of an arrangement pattern of spots. [Figure 4] FIG. 1 is a schematic diagram showing a state in which pattern B is superimposed on pattern A. [Figure 5] 10 is a flowchart illustrating a processing step. [Figure 6] 1 is a graph showing the measurement results of the brightness of a pattern or gradation obtained by the method of the present invention. [Figure 7]10 is a graph showing the relationship between laser output, feed speed, and pulse period in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Next, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the embodiment described below is merely an example of how the present invention can be implemented, and is not intended to limit the present invention.

[0015] The metal surface processing method according to the present invention is a method of forming a pattern on a metal surface by irradiating the metal surface with laser light (laser beam, hereinafter sometimes simply referred to as laser). The laser processing device used may be a conventionally known device, an example of which is shown schematically in FIG. 1. An irradiation unit 2 is connected to a laser oscillator 1 via a transmission optical system 3. A laser 4 is focused by a condenser lens (not shown) of the irradiation unit 2 and is irradiated onto the surface S of a predetermined metal part 5.

[0016] The laser 4 may be any conventionally known laser, such as a YAG laser, a CO2 laser, a fiber laser, or a high-power semiconductor laser. The laser 4 may also be any of a nanosecond laser, a picosecond laser, or a femtosecond laser. The metal part 5 to be processed may be any product made of metal, such as a light alloy part made of aluminum or an iron-based metal part made of mild steel.

[0017] The laser 4 irradiates the surface of the metal part 5 as an irradiation point (spot) 6, and by moving the spot 6, linear processing can be performed or a surface with a predetermined spread can be processed. The spot 6 can be moved on the metal surface S by moving the irradiation unit 2 or by moving the metal part 5.

[0018] In an embodiment of the present invention, in order to form a pattern or gradation on the metal surface S, the spots 6 are moved so as to be arranged in a two-dimensional direction along the metal surface S. An example of the arrangement of the spots 6 is schematically shown in FIG. 2. The spots 6 are circular, and the diameter D thereof is about several mm / 100. The direction in which the spots 6 are continuously moved (i.e., the scanning direction) is shown by a straight line L in FIG. 2. Since the spots 6 only need to be continuous in this scanning direction, each spot 6 may be slightly separated or in contact in the scanning direction, or may slightly overlap as shown in FIG. 2. The overlapping amount M is preferably less than the radius D / 2 of the spot. That is, when the center-to-center distance (scanning direction pitch) of the spots 6 in the scanning direction is “P”, it is preferable that “D / 2<P”.

[0019] By scanning the spots 6 adjacent to the spots 6 arranged in the scanning direction indicated by the straight line L, the processed portion spreads in the plane direction due to the width of the processed portion. FIG. 2 shows an example in which after scanning the spots 6 in the right direction of FIG. 2, the scanning location is changed to the lower side of FIG. 2 and then scanned in the left direction of FIG. 2. Thereafter, similarly, multiple rows of scanning are performed. That is, the portions or spots 6 that are instantaneously melted by the laser 4 to form depressions are arranged in a matrix.

[0020] The spots 6 arranged linearly along the straight line L and the spots 6 arranged linearly adjacent to each other by scanning in the opposite direction thereto may be slightly separated or in contact in a direction orthogonal to the scanning direction, or may slightly overlap as shown in FIG. 2. The overlapping amount M may be the same as the overlapping amount in the scanning direction. Therefore, the center-to-center distance R between the spots 6 in the direction orthogonal to the scanning direction is preferably less than the radius D / 2 of the spot (D / 2<R), similar to the above scanning direction pitch P.

[0021] In an embodiment of the present invention, in the first irradiation step, a series of zigzag laser irradiations are performed on an unprocessed metal surface S, with lines (scan lines) indicating the scanning direction offset by the center-to-center distance R. An example of a pattern A formed on the metal surface S is schematically shown in FIG. 3. In the example shown in FIG. 3, spots 6 or depressions melted or oxidized by the laser 4 (hereinafter, the depressions will be referred to as spots 6 inclusive) are indicated by "○." As shown in FIG. 3, adjacent spots 6 partially overlap. Because the overlap amount M is set to be less than the radius of the spot 6, a gap H is generated between adjacent spots 6 in the example shown in FIG. 3. This gap H is an area not irradiated with laser light, where no oxide film is formed or where slight oxidation is unavoidably caused by the influence of heat from the surroundings.

[0022] In this pattern A, three elements are arranged in a regular (matrix) pattern: the central part of the spot 6 that has been irradiated once with the laser; the overlapping parts of the spots 6 that have been irradiated twice with the laser, or the raised parts around the depressions; and the gaps H that have not been irradiated with the laser. These parts may or may not have changed compositions, such as the presence or absence of an oxide film and the thickness of the oxide film, and the color tone or shade of color produced by exposure to visible light is different. However, because each spot 6 is minute and the above-mentioned parts are regularly arranged, the entire pattern A has a predetermined single color tone, and although the metal surface S has color or light and dark, it does not form a pattern or gradation with a specific shape.

[0023] In an embodiment of the present invention, the second irradiation step is performed in the same manner as the first irradiation step, except that the scanning direction of the spot 6 is different from that of the first irradiation step. The scanning direction is the direction indicated by the straight line L in FIG. 2, and in the second irradiation step, the spot 6 is scanned in a direction intersecting the direction in the first irradiation step at a predetermined angle θ. An example of a pattern formed on the metal surface S in this manner is schematically shown in FIG. 4. As can be seen from FIG. 4, the pattern shown here is pattern C, which is pattern A formed by the first irradiation step described above, superimposed on pattern B, which is pattern A rotated by a predetermined angle θ on the metal surface S.

[0024] The pattern C formed on the metal surface S by the second irradiation step is a pattern consisting of: areas where the gaps H overlap and are not irradiated with the laser; areas where the gaps H overlap and the centers of the spots 6 and are irradiated once; areas where the centers of the spots 6 overlap and are irradiated twice; areas where overlapping spots 6 in one irradiation step and the centers of the spots 6 in another irradiation step overlap and are irradiated three times; and areas where overlapping spots 6 in one irradiation step and overlapping spots 6 in another irradiation step overlap and are irradiated four times. Each of these areas has a different or unchanged composition, such as the presence or absence of an oxide film or the thickness of the oxide film, and exhibits different color tones and shades of color when exposed to visible light. The density, which is the degree of aggregation of each area or the proportion of each area per unit area, varies regularly according to the predetermined angle θ. As a result, areas of a specific color tone, or dark or light colored areas, are arranged in specific shapes, such as circles, straight lines, or wavy lines, and this appears as a visually perceptible pattern. In addition, parts that have been irradiated with laser light a different number of times are aligned in a specific direction, creating a gradation in which the color tone or shade of color changes gradually.

[0025] The pattern, color tone, and gradation obtained by performing the first and second irradiation steps described above vary depending on the depth or diameter of the oxide film or depressions formed by the laser irradiation. Therefore, it is preferable to modify and determine the irradiation conditions of the laser 4 based on the evaluation results of the obtained pattern or gradation (in other words, the laser processing results). Figure 5 shows a flowchart illustrating an example of the process according to an embodiment of the present invention.

[0026] In the example shown in Fig. 5, first, processing conditions are determined in step S1. The processing conditions include the laser output, the feed rate at which the spot 6 is scanned, the laser pulse period, the pitch width which is the center-to-center distances P and R between the spots 6, the laser pulse width, and the angle of the scanning line shown by the straight line L in Fig. 2 between the first irradiation step and the second irradiation step (in other words, the relative rotation angle between pattern A and pattern B). The laser output may be about the same as that of a conventional laser processing machine used to engrave letters on aluminum plates. However, the amount of energy applied to the metal surface varies depending on the feed rate and pulse period, so it may be set to 20 to 80 W (watts), for example.

[0027] The diameter D of the spots 6 and the amount of overlap M between the spots 6 can be set as appropriate in the design, and the scanning direction pitch P between the spots 6 in the scanning direction is determined based on these values. The pulse period can also be set as appropriate depending on the laser processing machine being used, and the laser frequency (kHz) is determined based on that pulse period. The scanning speed (feed rate, mm / s) is calculated using the scanning direction pitch P (mm) and frequency (kHz) using the following formula: Scanning speed (mm / s) = Scanning direction pitch P (mm) x Frequency (kHz) x 1000

[0028] Furthermore, the laser pulse width is determined by the laser used. The scanning line angle is determined by the desired pattern or gradation. For example, a test piece is used to perform the first and second irradiation steps described above, and the pattern or gradation obtained under predetermined processing conditions is evaluated. Based on the evaluation results, the scanning line angle can be appropriately determined in advance. An example of the angle is approximately 1 to 20 degrees. Note that this angle is the angle when the relative angle between the spot 6 in pattern A and the spot 6 in pattern B, where they completely overlap, is set to 0 degrees. Therefore, when the horizontal direction shown in FIG. 4 is set to 0 degrees, the predetermined angle may be approximately 1 to 20 degrees or approximately 70 degrees (= 90 degrees - 20 degrees) to 89 degrees (= 90 degrees - 1 degree).

[0029] With the provisional processing conditions set in step S1, the metal part 5, which is the part to be processed (workpiece), is set in a predetermined location on the laser processing machine. This is shown as step S2 in Figure 5. Then, a first irradiation step (step S3) and a second irradiation step (step S4) are performed under the processing conditions set in step S1. In the first irradiation step, for example, pattern A shown in Figure 3 above is formed on the metal surface. In the second irradiation step, the angle of the scanning line is changed and laser irradiation is performed in the same manner as in the first irradiation step, so pattern B, which has the same arrangement of spots 6 as pattern A but is shifted in the direction of the arrangement by a predetermined angle θ from pattern A, is superimposed on pattern A. Therefore, pattern C (see Figure 4) is obtained by superimposing patterns A and B.

[0030] In step S5, the workpiece that has undergone the second irradiation process is removed. Next, in step S6, the pattern or gradation on the metal surface is inspected. This inspection is a visual check to see if the pattern or gradation that appears on the metal surface is the expected pattern or gradation. If the inspection result is "OK" because the expected pattern or gradation appears on the metal surface, proceed to step S7 and ship the metal part 5. Conversely, if the inspection result is "NG," return to step S1 and change the processing conditions.

[0031] Here, to explain an example of the general relationship between the resulting pattern or gradation and the processing conditions, the color tone depends on the thickness of the oxide film formed by laser irradiation, and as described in the aforementioned Patent Document 2, for example, the color changes from yellow to blue as the oxide film increases, and then the yellow or red gradually becomes stronger. Therefore, the color tone can be controlled by adjusting the laser output or pulse width.

[0032] As can be seen from FIG. 4, the pattern or gradation is generated by the degree of overlap of the spots 6, and the greater the difference in the degree of overlap, the clearer the pattern or gradation tends to be. Therefore, the clarity of the pattern or gradation can be adjusted by changing the pitch width or the scanning line angle. It is preferable to set the scanning direction pitch P and the center-to-center distance R between the spots 6 in the direction perpendicular to the scanning direction pitch P to approximately equal values ​​in order to arrange the spots 6 in a matrix. Furthermore, the pitch width is adjusted to ensure a certain degree of the aforementioned gap H between the spots 6 and the proportion of areas where the laser is irradiated only once.

[0033] Furthermore, regarding the scanning line angle, if pattern A in the first irradiation step and pattern B in the second irradiation step are offset from each other in the rotational direction within the horizontal plane, the spots 6 in each pattern A and B will be offset and overlap with each other, resulting in a variety of dispersed areas of different color tones or shades, resulting in a pattern or gradation. However, depending on the scanning line angle, the area ratio of areas that have been irradiated with the laser the same number of times may increase, making it difficult to see the pattern or gradation. Furthermore, the color tone may also make it difficult to see the pattern or gradation. Furthermore, the brightness of the processed surface may be reduced, making the pattern or gradation difficult to see. Therefore, the scanning line angle is adjusted based on visual inspection. The inventors measured the brightness and obtained the results shown in Figure 6.

[0034] FIG. 6 shows the results of measuring the brightness of patterns or gradations processed by varying the scan line angle. The horizontal axis represents the scan line angle, and the vertical axis represents the brightness measured with a luminance meter. A pattern or gradation was visible when the brightness was 0.9 or higher, and the scan line angle within this range was 1 to 20 degrees. Therefore, to form a visible pattern or gradation, including brightness, on a metal surface, it is preferable to set the scan line angle to approximately 1 to 20 degrees. Note that, as mentioned above, this angle is measured when the relative angle between patterns A and B, where the spots 6 in pattern A and the spots 6 in pattern B completely overlap, is set to 0 degrees. Therefore, in a pattern in which the spots 6 are arranged in a complete matrix, the overlapping of the spots 6 in patterns A and B will be the same even when the scan line angle is 70 to 89 degrees. Therefore, the above-mentioned "approximately 1 to 20 degrees" includes "approximately 70 to 89 degrees."

[0035] Here, we will explain examples and comparative examples in which laser processing was performed with different scan line angles. The processing conditions in both the examples and comparative examples were a laser output of 80 W, a feed rate (scanning rate) of 7500 mm / s, a pulse period of 10 μs, a pitch width of 0.075 mm, and a pulse width of 50 ns. The angular deviation of pattern B from pattern A from the first irradiation step, i.e., the scan line angle, was set to "0°" in comparative example 1, "5°" in example 1, "10°" in example 2, "15°" in example 3, "20°" in example 4, and "25°" in comparative example 2. The laser-processed portions of the metal surfaces obtained in these comparative examples and examples were visually observed to determine whether a pattern or gradation was clearly visible.

[0036] In Comparative Examples 1 and 2, the entire area subjected to laser processing was a so-called "solid state," and no continuous change in shape, color tone, or shade was observed, resulting in a rating of "fail." In contrast, in Examples 1 to 4, a vaguely outlined pattern and its repetition, or a gradation that is a continuous change in color tone or shade in a predetermined direction, could be observed, resulting in a rating of "good."

[0037] In the above-described examples and comparative examples, the laser output was set to "80 W," but the present invention can be implemented with different laser output. The amount of energy applied to the metal surface at each laser spot increases with increasing laser output, slowing the feed rate, and increasing the pulse period. Therefore, when the laser output is reduced compared to the above-described examples and comparative examples, the feed rate is reduced and the pulse period is increased.

[0038] 7 is a graph showing the relationship between the laser output, feed rate, and pulse width in Example 5, in which processing was performed under the same conditions as Examples 1 to 4, except that the laser output was changed to "25 W," the feed rate was changed to "1875 mm / s," and the pulse period was changed to "40 μs" among the processing conditions in Examples 1 to 4, and in Examples 1 to 4. Note that Example 5 also enabled the application of a pattern or gradation to the metal surface.

[0039] In the embodiment of the present invention, the relationship between the laser output, feed rate, and pulse period is considered to be the relationship shown by the dashed line in Figure 7. Therefore, when any one of these three conditions is appropriately set, a pattern or gradation can be formed on the metal surface by setting the other conditions to the conditions on the dashed line in Figure 7.

[0040] As described above, according to the embodiment of the present invention, a surface with a pattern or gradation can be formed on a metal surface by the first irradiation step and the second irradiation step under the same processing conditions, with only the scanning direction (or scanning angle) of the spot 6 being different. Therefore, according to the embodiment of the present invention, decoration of a metal surface with a pattern or gradation can be easily or efficiently performed.

[0041] The present invention is not limited to the above-described embodiments, and can be appropriately modified and implemented within the scope of the object of the present invention. In particular, since the shape of the metal surface to be obtained by laser processing can be grasped visually, the boundary or judgment of the presence or absence of a pattern or gradation may vary slightly depending on the observer. Therefore, the processing conditions for the method of the present invention may be determined by trial and error of the method of the present invention. [Explanation of symbols]

[0042] 1 Laser oscillator 2 Irradiation Unit 3 Transmission optics 4 Laser 5. Metal parts 6 Spot θ Predetermined angle A, B, C patterns D diameter H gap L straight line M overlap amount P: Scanning direction pitch R Center distance S Metal surface

Claims

1. A method for processing a metal surface, comprising: irradiating a metal surface with a laser; and scanning the laser along the metal surface so that a plurality of spots, which are irradiation points of the laser on the metal surface, partially overlap each other, thereby forming a predetermined pattern on the metal surface, the method comprising: a first irradiation step of scanning the laser so that the spots are arranged in a matrix to form a predetermined pattern on the metal surface, the predetermined pattern being made up of the spots arranged in a matrix; a second irradiation step of scanning the laser in a direction intersecting the scanning direction of the laser in the first irradiation step at a predetermined angle, and irradiating the laser so that a pattern identical to the predetermined pattern in which the spots are arranged in a matrix is ​​superimposed on the pattern in the first irradiation step. A metal surface processing method characterized by:

2. The metal surface processing method according to claim 1, the spot is circular in shape on the metal surface; The amount of partial overlap between the spots in each of the two orthogonal directions in which the spots are aligned is less than the radius of the spots. A metal surface processing method characterized by:

3. 3. The metal surface processing method according to claim 1 or 2, A metal surface processing method, characterized in that the predetermined angle is equal to or greater than 1 degree and equal to or less than 20 degrees.

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