JPH0428487A - Laser beam heating method - Google Patents

Abstract

PURPOSE:To carry out hardening at the low cost by making a plane of polarization of a laser beam of linear polarization vertical to the laser beam irradiation surface of material to be heated and making a laser beam incident angle lower than a Brewster angle of the material to be heated. CONSTITUTION:A heating part 3 of the material 1 to be heated is irradiated with the laser beam 2 and heated. At that time, the laser beam 2 of the linear polarization is used. Therewith, the plane of polarization of the laser beam 2 is made vertical to the laser beam irradiation surface of the material 1 to be heated and the laser beam incident angle theta is made lower than the Brewster angle of the material 1 to be heated. Consequently, the effective heating method can be also offered for remelting, alloying, etc., of Al material, etc.

Description

[Detailed description of the invention] [Purpose of the invention]

(Industrial Application Field) This invention is applicable to laser processing, for example, surface hardening such as surface hardening, surface alloying, etc., by irradiating the surface of a workpiece such as a metal member with a laser beam and heating it. Micro processing such as modification, welding, drilling, cutting, trimming and engraving,
This invention relates to a laser heating method used for chemical processing and the like. (Prior Art) Conventional laser heating methods include, for example, the method shown in FIG. 11 and the method described in Japanese Patent Publication No. 63-9004. The laser heating method shown in FIG.
The laser beam 52 is irradiated perpendicularly to the laser irradiation surface of the object 5. In this laser heating method, the object to be heated 5
Since the surface of the object 51 reflects the laser beam 52 and the heated portion 53 of the object 51 is not heated sufficiently, a laser absorbing material 54 is formed on the surface of the object 51 to be heated and the laser beam 52 is reflected. A method of irradiation heat treatment is used (
In this case, the laser absorbing substance may be, for example, "Laser Processing Technology," published by Nikkan Kogyo Shimbun, July 1, 1988, p. 77, Table 4 - IRCO2 absorption coating composition table
There is something written in. ). (Problems to be Solved by the Invention) However, in such a conventional laser heating method, a layer 54 of laser absorbing material is formed by applying a laser absorbing material to the surface of the object to be heated 51 by spraying, brushing, etc. Since the surface was coated by forming a layer and removed after laser heating, there was a problem that the process was complicated and costly, and it was a challenge to solve these problems. (Object of the Invention) The present invention has been made in view of the above-mentioned conventional problems, and it is possible to sufficiently heat the heated part without providing a layer of laser absorbing material on the object to be heated during laser heating. It is an object of the present invention to provide a laser heating method capable of performing uniform heating and, for example, obtaining a uniform hardened layer.

[Structure of the invention]

(Means for Solving the Problems) The laser heating method according to the present invention uses linearly polarized laser light and changes the polarization plane of the laser light when irradiating the heated part of the object with laser light to heat it. It is characterized by a configuration in which the laser beam is perpendicular to the laser irradiation surface of the object to be heated and the laser incident angle is lower than the Brewster angle of the object to be heated, and in an embodiment, the laser beam is parallel light. In the same embodiment, the laser beam is a parallel beam, and its shape has a ratio of a dimension a perpendicular to the polarization direction to a dimension in the polarization direction of 2≦a/b≦
This laser heating method is characterized by having a structure as shown in FIG. (Function of the Invention) Hereinafter, the basic structure of the laser heating method according to the present invention and its function will be explained based on the drawings. 1 to s4 show the basic structure of the laser heating method according to the present invention, in which 1 is an object to be heated, 2 is a laser beam, and 3 is a heated portion heated by the laser beam 2. In addition, in FIG. 1(b), arrow A indicates the polarization direction of the linearly polarized laser beam, and angle θ indicates the incident angle of the laser beam 2 with respect to the object to be heated 1. 2 is parallel light, and its shape is such that the ratio of the dimension a in the direction perpendicular to the polarization direction and the dimension in the polarization direction is 2≦a/b
≦18. Moreover, FIG. 2 shows a case where the incident angle of the laser beam 2 is shifted to a lower angle 02 than the initial setting value θ1 (θ1>θ2),
FIG. 3 shows a case where the incident angle of the laser beam 2 is shifted to a higher angle 03 than the initial setting value θ1 (θ1 minus θ3). By the way, a laser beam has a component in which the electric field oscillates parallel to the incident plane (P component) and a component in which the electric field oscillates perpendicularly to the incident plane (S component). The change in absorption rate with respect to the incident angle is approximately as shown in FIG. Among these, the angle θ shows the maximum absorption rate. is called the Brewster's angle, and this value is related to the electrical conductivity of the material and has a specific value depending on the material. In FIG. 1, the polarization plane of the linearly polarized laser beam 2 is perpendicular to the laser irradiation surface of the object to be heated 1, that is, it is P-polarized, and the incident angle θ of the laser beam 2 is Star angle θ. 60°≦θ! Kuθ. The initial value θ1 is set so that In this case, as shown in FIG. 4, the laser absorption rate on the heated object 1 is:
Even slight changes in the angle of incidence can cause large changes, but as shown in Figure 2, when the angle of incidence changes from θl to 02 (θ2 × θ1) and the absorption rate decreases, the beam width By changing from Wl to Wl (Wl < Ws), the power density improves, and the
The power density is adjusted to maintain a constant power density. Also. Conversely, as shown in Figure 3, if the incident angle changes from 01 to 03 (θ3>θ1) and the absorption rate increases, the beam width changes from Wl to W3 (Wa > Wl). )
As the power density changes, the power density decreases, and the direction adjustment is made to maintain a nearly constant power density. By uniformly heating the heated part 3, for example, it is possible to prevent surface melting or unhardened parts during laser hardening. A sound quenched layer with no cracks can be obtained. On the other hand, as shown in FIG. 5, in this type of laser heating method, when trying to form a heated portion (hardened layer) 3 using the laser light 2 of the defocus beam, When the beam length is matched to the hardened layer, the beam width is intentionally determined to be extremely narrow in the direction of beam movement, and as a result, the power density becomes high, and a molten part 3b is formed in addition to the hardened layer 3a. As a result, the range of conditions for quenching without causing surface melting becomes narrower. In addition, since the power density distribution becomes non-uniform, a molten part 3b is likely to be formed in the upper part of the hardened part, making it impossible to perform uniform hardening. Therefore, it is preferable that the laser beam used in the laser heating method of the present invention be a parallel beam whose power distribution is uniform in principle, as shown in FIG. Further, as shown in FIG. 6, the ratio a/b of the dimension a in the direction perpendicular to the polarization direction of the laser beam 2 and the dimension in the polarization direction is 2.
If the laser output is smaller than that, if you select a laser output that achieves the energy density required for hardening, the power density will become too high and the heated part 3 will easily become the melted part 3b. There is a high possibility that the range of conditions to be set for carrying out this process will become narrower. On the other hand, as shown in FIG. 7, the ratio a/b of the dimension a in the direction perpendicular to the polarization direction of the laser beam 2 and the dimension in the polarization direction
If is larger than 18, there is a high possibility that the beam length in the beam traveling direction will become long on the object to be heated 1, making it impossible to obtain the cooling rate necessary for hardening. Therefore, the beam shape in the laser heating method according to the present invention should be 2≦a/b as the above value of a/b.
It can be said that it is particularly desirable that b≦18. (Example) In this example, J
IS 545C steel material, laser output 1.85kw,
Incident angle = 75°, beam shape near mm x 1.5 mm (
a/b=4.7), beam feed speed: 1. Om/min
Heating was performed by irradiating with a linearly polarized C02 laser under the following conditions. As a result, as shown in the metallurgical micrograph (magnification: 3x) in Figure 8, a sufficiently satisfactory process was achieved without using a laser absorber. A hardened layer was obtained. Also. As shown in the metallurgical micrograph in FIG. 9 (magnification = 0.8x), the surface condition of the hardened portion was constant and stable. In addition, a day focus beam is used as the laser beam 2,
Heating was performed with the beam shape set to a/b=1 and the other conditions being the same as above. As a result, the metal JIi micrograph shown in Fig. 10 (magnification: 1.
8 times), the area above the hardened part where the power density distribution was high melted, and uniform hardening could not be performed.

【Effect of the invention】

In the laser heating method according to the present invention, when irradiating the heating part of the object to be heated with laser light to heat it, a beam-shaped linearly polarized laser beam is used, and the polarization plane of the laser beam is adjusted to the laser irradiation of the object to be heated. Since the laser is perpendicular to the surface and the laser incidence angle is lower than the Brewster's angle of the object to be heated, it is not necessary to provide a layer of laser absorbing material on the heated part of the object when performing laser heating. Laser heating of the heated part has become sufficient, for example, it is possible to obtain a uniform hardened layer during hardening, and the process is simple and low cost hardening is possible. In addition, remelting of AM materials, etc.
This heating method is also effective for alloying, which brings about an extremely excellent effect.

[Brief explanation of drawings]

Figures 1 (a) and (b) are front and side views showing the basic configuration of the laser heating method according to the present invention, respectively, and Figure 2 shows that the incident angle of the laser beam is lower than the initial setting value. Figure 3 is a side view showing what happens when the incident angle of the laser beam deviates to a higher angle than the initial setting value. Explanatory diagram showing the relationship between absorption rate and incident angle, FIG. 5(a)
(b) is a front explanatory view and a side explanatory view when a day focus beam is used, and Figure 6 (&) (b) is the dimension a in the direction perpendicular to the polarization direction of the laser beam and the dimension in the polarization direction. A front explanatory view and a side explanatory view respectively showing the situation when the ratio a/b is smaller than 2, and FIGS. Figures and side explanatory views, Figures 8 and 9 are metal Jl microphotographs of the cross section and appearance of a hardened layer obtained by hardening using a parallel beam under the conditions of a/bζ4.7, No. 10 The figure is a metallurgical micrograph of the appearance of a hardened layer obtained by hardening using a defocus beam under the condition of a/b = 1, and FIG. 11 is an explanatory diagram of a slope showing a conventional laser heating method. DESCRIPTION OF SYMBOLS 1... Heated object, 2... Laser light, 3... Heated part, θ... Laser incident angle, θ. ...Brewster's angle. Figure 1 (b> Figure 4 Figure 6 (b) Figure 7 (b) Procedural amendment (Manni) 1. Indication of the case Hei I & 2002 Patent Application No. 132291 2. Name of the invention Laser heating method 3 , Relationship to the case of the person making the amendment Patent applicant address (residence) 2 Takaracho, Kanayō-ku, Yokohama-shi, Kanagawa Prefecture Name (
Name) (399) Nissan Motor Co., Ltd. Representative Hisashi
Yutaka Yone 4, Agent address (residence) Kobikikan Ginza Building, 2-8-9 Ginza, Chuo-ku, Tokyo 104 Phone: 03 (567) 2761 (
Representative) Electrophotography No. 03 (567) 71333 (G iris) 6, number of inventions increased by amendment 7, subject of amendment 1, “11th "Fig. 8" is corrected to "Fig. 8". 2. On page 9, lines 4 and 5 are corrected as follows. ``As a result, using parallel beams and a / b = 4
．． When hardening is performed under the conditions of 7, do not use a laser absorbent.'' 3. In the same page 9, lines 6 to 8, [Also, Fig. 9...quenched part] is as follows. to correct. Correct to "Also, quenched part". 4. Correct page 9, line M49 to line 1O as follows. It had become a r thing. Furthermore, as the laser beam 2, "Day Focus Beam" 5, page 9, lines 13 to 14 are corrected as follows. ``As a result, using the day focus beam a/
When hardening is performed under the condition of b = 1, the power on the upper side of the hardened part" 6, page 11, lines 9 to 15 are corrected as follows. "Diagrams and side explanatory drawings, Figure 8" 7. Figures 8, 9, and 10 of the drawings have been deleted, and Figure 11 has been changed.
The figure is corrected to Figure 8 as shown in the attached sheet. that's all

Claims (1)

[Claims] (1) When heating the heated part of the object to be heated by irradiating it with laser light, use a linearly polarized laser beam, make the polarization plane of the laser beam perpendicular to the laser irradiation surface of the object, and enter the laser beam. A laser heating method characterized by making the angle lower than the Brewster angle of the object to be heated.