JP2012139698A - Laser marking method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser marking method capable of providing clear printing regardless of a condition of a steel material end face used as a printing object surface.SOLUTION: When printing a code consisting of one character or a series of a plurality of characters by applying a heat-resistant coating to a steel material end face 1 used as a printing object surface and thereafter burning and carbonizing the coating by irradiating a laser beam, the irradiation number of the laser beam is set to multiple times per character. The focal position of the laser beam may be separated from the printing object surface by 5-30 mm to the outside or inside of the steel material along a laser optical axis. The printing object surface is preferably previously ground with a wire brush before the application of the heat-resistant coating, the color of the heat-resistant coating is preferably selected from white, pale brown, blue and yellow, and the steel material is preferably set at 350°C to room temperature.

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 irradiation, clear printing is performed regardless of the state of the steel material end surface to be printed. Relates to a laser marking method.

Conventional laser marking methods include a method of irradiating a base coating applied to a surface to be printed with a laser and baking the coating to carbonize the coating (see Patent Document 1), and a method of irradiating a laser after coating and removing the coating. (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, it has been found that 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, the state of the end surface of the steel material affects the sharpness of printing. In other words, it was found that a relatively clear print could be obtained with a flat cut surface by gas fusing or laser fusing, but the print would be remarkably smeared with a cut surface having uneven marks due to shear shear. Had unresolved issues.

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

The present invention made to solve the above problems is as follows.
According to the present invention, (1) after applying a heat-resistant paint to the end surface of a steel material to be printed, a laser is irradiated to burn and carbonize the paint, thereby printing a symbol consisting of one or more characters. In doing so, the laser marking method is characterized in that the number of times of laser irradiation is set to a plurality of times for each character.

  In the present invention, (2) the focal position of the laser may be separated from the surface to be printed by 5 mm to 30 mm along the laser optical axis outside or inside the steel material. Further, (3) it is preferable to grind the printed surface with a wire brush in advance before applying the heat resistant paint, and (4) the color of the heat resistant paint is any one of white, light brown, blue and yellow. Preferably, (5) 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 steel material end face that is the printing surface.

Explanatory drawing which shows the evaluation method of the printing state by laser marking on the steel material end face

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, the character shape (the region where the character is shaped) is scanned once with the laser beam for each laser irradiation. A CO ₂ laser known for its large continuous oscillation output (possible up to 10 kW or more) is suitable for printing a charcoal by burning and carbonizing the coating film in the shape during scanning with a laser beam. It is. The laser irradiation distance (distance from the laser emission port of the laser irradiation apparatus to the steel material end surface) to the printing surface (steel material end surface) is preferably in the range of 250 to 280 mm. Within this range, when targeting thick steel plates on the transport line, the laser marking device interferes with the thick steel plate transport equipment, or the laser beam is blocked by other equipment existing around the thick steel plate transport equipment. Easy to avoid problems.

In order to draw a character 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 0.1 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. However, if the laser output is reduced, it will not carbonize. In addition, if the beam diameter is increased to more than 0.1 mm, a large laser output is required for baking and carbonization, which makes it difficult to control with high accuracy for printing, blurring of characters, and expensive equipment. Economically disadvantageous.

The thickness of the steel plate is about 4 mm at the minimum. To print on the cut surface in the thickness direction, 2 x 2 mm is required as the minimum character size, and to make the printed characters visible visually. The character line width needs to be 0.15 mm or more.
Therefore, the present inventors have taken the following method in order to bake and carbonize while suppressing the combustion spreading over a wide range of the coating film and to secure a line width of 0.15 mm or more.

  That is, this is a method in which the number of times of laser irradiation is set to a plurality of times for each character. More specifically, for each character in the symbol to be printed, a laser beam with a beam diameter of 0.05 to 0.1 mm is preferably irradiated with a small beam position for each irradiation within the same character shape, preferably slightly ( For example, printing is performed by repeatedly irradiating a plurality of times with a shift of 1/10 to 9/10 of the in-plane scanning interval. In this way, the character shape is irradiated multiple times (scanned multiple times with a laser beam whose beam position is slightly shifted each time), and finally a character line width of 0.15 mm or more can be secured, and unevenness caused by shear shearing A clear printed state can be obtained even on a cut surface with a mark. In addition, the focal position of the laser at this time is a position in the vicinity of the printing surface, for example, a position where the separation distance along the laser optical axis from the printing surface to the outside or inside of the steel material is 0 mm or more and less than 5 mm, as in the past. Just keep it as. When this separation distance is 0 mm, the focal position of the laser coincides with the position of the printing surface.

  In addition, the separation distance is set to 5 mm or more, which is outside the conventional range, and the received light energy density of the printing surface is lowered and the coating film is baked and carbonized by moving the focal position of the laser away from the vicinity of the printing surface. In order to compensate for less than the required level, laser irradiation may be repeated a plurality of times for each character. However, at this time, if the separation distance is increased to more than 30 mm, it is difficult to achieve a light receiving energy density level required for baking and carbonizing the coating film on the surface to be printed even by multiple laser irradiations. The separation distance is preferably 30 mm or less. According to this, the allowable range of the alignment accuracy of the laser marking device with respect to the printing surface is expanded from the normal range of more than −5 mm and less than 5 mm to the range of 0 ± 30 mm, and the alignment operation is facilitated accordingly.

In order to make the 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 steel plate is used as the steel material to be printed, and the end surface of the steel plate formed by cutting in the plate thickness direction by laser fusing or shear shear is used as the printing surface, and with or without grinding with a wire brush on the printing surface. After coating, an experiment was performed to print the symbol “12345567890” so that the final character line width is about 0.2 mm by irradiating and carbonizing the coating film by irradiating a CO ₂ laser several times for each character. Went. As the laser marking device, a cross-sectional marking device manufactured by Nireco Co., Ltd. was used. The laser irradiation distance to the printing surface (distance from the laser emission port of the laser irradiation apparatus to the end surface of the steel material) was 240 mm. The printing speed was about 50 characters / second per irradiation. The heat-resistant paint used was made by Nireco. For comparison, an experiment was conducted in which the number of times of laser irradiation was one as before.

  Thick steel plate thickness and plate temperature, cutting method, presence / absence of wire brush grinding, color of heat resistant paint, separation distance of focal point of laser from printing surface (focal separation distance L for short), laser output and nominal beam diameter (Incoming beam diameter to the lens at the laser exit), laser irradiation repetition number per character (abbreviated number of irradiations N), relative beam position shift amount per irradiation (represented by a ratio with respect to the in-print surface scanning interval) ) Were variously changed as shown in Table 1, and the quality of the printed state after laser marking was investigated. In determining the quality of the printed state, the evaluation was made by visual observation with three grades (◎: excellent, ○: good, ×: defective) as shown in FIG. In FIG. 1, reference numeral 1 denotes a surface to be printed.

  The results of the investigation are shown in Table 1. In the invention example, it can be seen that a clear printing state was obtained even on the printing surface formed by shear shearing.

  1 Steel surface (printed surface)

Claims (5)

  The number of times of laser irradiation when printing a symbol consisting of a series of one or more characters by applying a heat-resistant paint to the end surface of the steel material to be printed and then irradiating a laser to burn and carbonize the paint. A laser marking method characterized in that a plurality of times per character.   2. The laser marking method according to claim 1, wherein the focal position of the laser is separated from the surface to be printed by 5 mm to 30 mm along the laser optical axis to the outside or inside of the steel material.   3. The laser marking method according to claim 1, wherein the printing surface is ground with a wire brush in advance before application of the heat-resistant paint.   The laser marking method according to any one of claims 1 to 3, 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.