JP2013066925A - Laser marking method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser marking method that can obtain clear printing irrespective of the condition of a surface of steel that is a surface to be printed.SOLUTION: When printing a symbol formed of a plurality of characters by scanning a laser to bake and carbonize a heat resistance paint applied on an edge surface of a steel material that is a surface 1 to be printed, a scan path of a laser provides a plurality of paths for one symbol, a first path among all the plurality of paths or the paths from the first path provides non-focused paths that are to be scanned in short focus or over focus, and the remaining paths provides focused paths that is to be scanned in just focus.

Description

  The present invention relates to a laser marking method, and in particular, when a symbol for identifying a steel material is printed on an end surface of a steel material such as a thick steel plate by laser scanning, clear printing is performed regardless of the state of the steel material end surface to be printed. The present invention relates to a laser marking method.

Conventional laser marking methods include irradiating and running a base coating applied to a print surface with a laser, that is, scanning the base coating with a laser to burn and carbonize the coating (see Patent Document 1), and There is a method of scanning with a laser after applying the paint and removing the paint (see Patent Document 2).
The conventional laser marking method is performed on a flat surface of a steel material, and printing is completed only once. Further, in order to improve the efficiency, the printing surface is descaled so that printing can be performed once, or the warping of the printing surface is measured and printed so as to follow the warping.

JP 2009-62086 A Japanese Patent No. 4519105

  However, in the laser marking method in which the coating material is applied to the end surface of the steel material and then baked and carbonized by a laser, it has been found that the state of the end surface of the steel material affects the sharpness of printing. In other words, it was found that relatively clear prints were obtained on a relatively flat cut surface by gas fusing or laser fusing, but on a cut surface having uneven marks due to shear shearing, it was found that the print was remarkably blurred. There was an unresolved issue in this regard.

  Therefore, an object of the present invention is to provide a laser marking method capable of obtaining clear printing regardless of the state of the steel material end face to be printed.

The present invention made to solve the above problems
(1) After applying a heat-resistant paint to the end surface of the steel material to be printed, the laser scan path is used to print a symbol consisting of a series of multiple characters by scanning with a laser to burn and carbonize the paint. A plurality of passes per symbol, and the first pass or the first pass to the middle of the multiple passes is a non-focus pass that scans with short focus or over focus, and the remaining passes are just focus. It is a laser marking method characterized by using a focal path for scanning.

  In the present invention, it is preferable that (2) the surface to be printed is ground with a wire brush in advance before application of the heat resistant paint, and (3) the color of the heat resistant paint is any one of white, light brown, blue, and yellow. Preferably, (4) the steel material is a steel material at 350 ° C. to room temperature.

  According to the present invention, a clear symbol can be laser-marked regardless of the state of the end face of the steel material that is the printing surface.

It is a definition explanatory view of just focus, short focus, and overfocus according to the present invention.

A commercially available heat-resistant paint can be used. The method for applying the heat-resistant paint to the steel material end face may be any of spray coating, brush coating, roll coating, and the like.
In the laser marking according to the present invention, each time a laser is irradiated, a symbol type (a region where the symbol is shaped) is scanned once with a laser beam, and this is regarded as one pass, and this is repeated a plurality of passes per symbol. The CO ₂ laser, known for its large continuous oscillation output (up to 10 kW or more), is used to draw characters by baking and carbonizing the coating in the symbol type during scanning with a laser beam. Is preferred. The laser irradiation distance (distance from the laser injection port of the laser irradiation device to the steel material end surface) to the printing surface (steel material end surface) is preferably in the range of 230 to 280 mm. Within this range, when targeting thick steel plates on the transport line, the laser marking device may interfere with the thick steel plate transport equipment, or the laser beam may be blocked by other equipment existing around the thick steel plate transport equipment. Easy to avoid problems.

In order to draw a symbol by baking the surface of a coating film formed by applying a heat-resistant paint with a CO ₂ laser and carbonizing it, the laser beam diameter is preferably 0.05 to 0.2 mm. If the beam diameter is reduced to less than 0.05 mm, if the laser output is comparable, the heat input to the coating will be too great and the paint will burn over a wide range beyond the desired degree of baking and carbonization. As a result, the characters are blurred, but if the laser output is reduced while the beam diameter is reduced, carbonization will not occur and printing cannot be performed. In addition, if the beam diameter is increased to more than 0.2 mm, a large laser output is required to burn and carbonize, and it becomes difficult to control with high accuracy for printing, blurring of characters, and expensive equipment. Economically disadvantageous.

Therefore, the beam diameter is preferably 0.2 mm or less. However, in the case of scanning only one pass, the character line width may be 0.2 mm or less, which may make it difficult to read. Although the character line width can be increased by slightly shifting the irradiation position of the laser beam between the passes as a plurality of passes, the control is complicated and it is economically disadvantageous.
Therefore, in the present invention, the first path or the path from the first path to the middle path (= previous path) among all the multiple paths is a non-focus path that scans with short focus or over focus, and the remaining paths. The pass (= latter pass) is a focus pass that scans with just focus.

  FIG. 1 is an explanatory view of the definition of just focus, short focus, and overfocus according to the present invention. As shown in FIG. 1, the distance x from the printing surface 1 to the front side is negative (−) and the back side is shown. When the distance x is positive (+), the just focus means that the laser condensing point (focal point) is located in the range F0 shown in FIG. Focusing means that a laser condensing point (focal point) is located within a range F1 of x = −5 mm or less (preferably −30 mm or more) shown in FIG. 1B. The laser condensing point (focal point) is located within a range F2 of x = + 5 mm or more (preferably +30 mm or less) shown in 1 (c).

  Here, the focus position of the just focus is within the range of x = more than −5 mm and less than 5 mm because the focus position control tolerance of a normal laser marker is within ± 5 mm (but not including the boundary). is there. The focal position of the short focus and the over focus is in the range of | x | ≧ 5 mm because it is in contact with the just focus, but is preferably in the range of 5 mm ≦ | x | ≦ 30 mm. This is because if | x | is greater than 30 mm, the character line width may be too wide and the entire symbol may be difficult to see.

According to the present invention, it is possible to widen the character line width by making the preceding path a non-focal path and making the character easy to see, and by making the latter path a focus path, the inside of the character line width is made clear. I can do things. Therefore, it is possible to obtain a printed symbol that is clearer and easier to see than before.
The control is easy because it is only necessary to change the focal position of the laser once in all the multiple passes.

On the other hand, when all the paths are scanned with the just focus, the print may overlap on one line, the character line width becomes narrow, and the print may be difficult to see. On the other hand, scanning all paths with short focus or over focus makes the entire symbol blurred and difficult to see although the character line width is wide.
In order to make printing clearer, the surface to be printed is ground with a wire brush in advance before applying the heat-resistant paint, and a heat-resistant paint of white, light brown, blue, or yellow is used. It is preferable to implement either one or both.

  Moreover, if the temperature of the steel material to be printed exceeds 350 ° C., the heat-resistant paint may be discolored and the printing may be difficult to visually recognize. Therefore, the steel material to be printed is preferably a steel material at 350 ° C. to room temperature. .

A thick steel plate is used as the printing target steel, and the end surface of the steel plate formed by cutting in the thickness direction by laser fusing or shear shear is used as the printing surface, with or without grinding with a wire brush on the printing surface. After coating, an experiment was performed in which the symbol “ABCDEFGHIJ” was printed so that the final character size would be 2 mm square by scanning multiple passes with a CO ₂ laser. As the laser marking device, a cross-sectional marking device manufactured by Nireco Corporation was used. The laser irradiation distance to the printing surface (distance from the laser injection port of the laser irradiation apparatus to the steel end surface) was 240 mm. The heat-resistant paint used was made by Nireco.

Laser marking was performed with various laser scanning conditions as shown in Table 1, and the quality of the printed state after laser marking was investigated. When determining the quality of the printed state, it was evaluated by visual observation with three grades (good, slightly poor, and defective).
The results of the investigation are shown in Table 1. In the invention example, a good printing state was obtained even on the printing surface formed by shear shearing.

  1 Steel surface (printed surface)

Claims (4)

  After applying a heat-resistant paint to the end surface of the steel material to be printed, the laser is scanned with a laser, and the paint is baked and carbonized to print a symbol consisting of a series of multiple characters. A plurality of passes, and the first pass or the first pass to the middle pass of all the passes is a non-focus pass that scans with a short focus or over focus, and the remaining passes are a focus that scans with a just focus. A laser marking method characterized by using a pass.   2. The laser marking method according to claim 1, wherein the surface to be printed is ground with a wire brush in advance before application of the heat resistant paint.   The laser marking method according to claim 1 or 2, wherein the color of the heat-resistant paint is any one of white, light brown, blue, and yellow.   The laser marking method according to claim 1, wherein the steel material is a steel material at 350 ° C. to room temperature.

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