JPH0377252B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a heat treatment method and apparatus for heat treating a workpiece by irradiating a laser beam to the workpiece through a conical mirror whose inner or outer surface is a mirror surface. be.

[Prior Art] Heat treatment using a laser beam has excellent features such as being able to process only the surface layer of a workpiece and shortening the processing time. When using a laser beam as a processing energy source,
Since laser beams have strong directivity and concentration, in surface treatment processes such as heat treatment, it is necessary to design a laser beam focusing optical system so that a uniform energy distribution can be formed over a relatively wide area. For example, for compounds in which the workpiece has a two-dimensional spread such as a flat plate, various condensing optical systems as shown in FIGS. 10a to 10f have been considered.
Figure 10a shows the defocus beam method, and Figure 10b shows the
Figure c shows the split mirror linear beam method, figure c shows the beam scanner method, figure d shows the integrated mirror method, figure e shows the kaleidoscope method,
FIG. 3f is a diagram showing the polygon mirror method. In any case, the method using a condensing optical system as shown in Fig. 10 has a lower energy density than welding or cutting, and as shown in Fig. 11, it depends on the material of the steel material. The surface has a high reflectance and requires the application of an absorbing material.

FIG. 11 is a diagram showing the reflectance of a laser beam on the surface of a steel material, with the horizontal axis representing the angle of incidence on the steel material and the vertical axis representing the reflectance. As is clear from FIG. 11, the smaller the angle of incidence, the higher the reflectance.

Figure 9 shows an example of conventional heat treatment using a laser beam on a cylindrical workpiece such as a steel wire or a round bar. , Figure b (disclosed in Japanese Unexamined Patent Publication No. 61-170521) shows a workpiece irradiated with a laser beam from the longitudinal direction. As is clear from Figure 9a, when the laser beam is irradiated from above,
The absorption state of the laser beam is non-uniform in the circumferential direction of the workpiece, resulting in low energy efficiency. Therefore, in order to improve energy efficiency, it is necessary to apply a laser beam absorbing material to the surface of the workpiece, but it is very difficult to apply this absorbing material. In addition, in the case of b in the same figure, the incident angle of the laser beam on the surface of the workpiece is decreasing, so in this case, the 11th
As is clear from the figure, the reflectance of the laser beam increases and the energy utilization efficiency also decreases significantly.

[Problems to be Solved by the Invention] As mentioned above, in the conventional method of heat treatment of a workpiece by laser beam irradiation, the absorption state of the workpiece is nonuniform with respect to the laser beam, and the reflectance is high. Therefore, there was a problem that the utilization efficiency of the laser beam was extremely low.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method and apparatus for heat treating a workpiece with high laser energy utilization efficiency.

[Means for Solving the Problems] In order to achieve the above object, the present invention places a workpiece for heat treatment on the central axis of a cone mirror whose inner or outer surface is a mirror surface. A laser beam that is parallel or substantially parallel to the workpiece is irradiated onto the surface or inner surface of the workpiece through the cone mirror, and the laser beam is directed toward the workpiece. and an inner or outer surface of the cone-shaped mirror, and simultaneously move the workpiece or the cone-shaped mirror to continuously heat-treat the surface layer or inner layer of the workpiece. It is to obtain.

[Function] With the above method and apparatus, the efficiency of laser use can be increased, and the surface layer of the workpiece can be heat-treated to a thickness of several tens of micrometers.

FIG. 2 is a diagram schematically showing a condensing optical system for laser heat treatment using a conical mirror (hereinafter referred to as a cone mirror) 1. As shown in FIG. In Figure 2, 2 is the workpiece, 3
is the laser beam and the arrow indicates the direction of its output.
The cone mirror 1 is a hollow cone or square pyramid structure made of copper or the like, and its inner surface is mirror-finished. Note that the workpiece 2, which is the irradiated part,
If the reflectance of the cone mirror 1 is high, the mirror surface of the cone mirror 1 is further coated with a reflective material such as gold. The apex angle θ of the cone of this cone-shaped mirror 1 is in the range of 2° to 15°. Further, the diameter D ₂ of the outlet on the apex side of the cone is made slightly larger than the outer diameter D ₁ of the workpiece 2 . Also,
A workpiece 2 is inserted into the center of the axis of the cone mirror 1 and moved at a speed V along the axial direction. Note that the speed V is a value determined by the outer diameter D ₁ of the workpiece 2 such as steel, the output of the laser beam 3, the apex angle θ of the cone of the cone mirror 1, and the like. Then, the laser beam 3 is made incident at an incident angle α with respect to the center of the axis of the cone mirror 1 through the opening of the cone mirror 1, which is the bottom surface of the cone. Normally, the incident angle α of the laser beam is several mrad, and the laser beam 3 can be considered to be a parallel beam (α≈0), so it will be described below as a parallel beam. Each light beam 4 forming the laser beam 3 is automatically converged while repeating multiple reflections between the inner surface of the cone mirror 1 and the surface of the workpiece 2. Figure 4 shows this multiple reflection.
FIG. As mentioned above, since the incident angle α of a laser beam is generally several mrad, multiple reflections of a parallel beam on a cone mirror with α=0 will be explained using FIGS. 4 and 5.

When the apex angle of the cone is θ, the outer diameter of the laser beam d
The angle α _o that enters the wall of the cone-shaped mirror and the distance l _o from the apex of the cone are expressed by equations (1) and (2), respectively.

α _o = θ/2(2n+1) ……(1) l _o = α/2tanθ/2 _o 〓 ⁱ⁼¹ taniθ−tanθ/2/taniθ+tanθ/2……(2) Figure 5 shows that the diameter of the laser beam is It is a figure showing the position of the reflection point when the apex angle of the cone is 3° and 5°, respectively, at 8 mm.

From Figure 5, if the apex angle θ of the cone is small,
Compared to the larger case, the reflecting point is much further forward, and the final convergence point is also closer to you. On the surface of the workpiece, the energy density of each beam of the laser beam depends on the incident angle of the laser beam, and the laser energy is absorbed or reflected. Here, if the energy distribution of the laser beam is rotationally symmetrical with respect to the output direction of the laser beam, a rotationally symmetrical axial energy distribution as shown in FIG. 6 is finally obtained on the surface of the workpiece. Figure 6 shows laser output
1000W, beam diameter 10mmφ, the apex angle of the cone is θ
1000W, beam diameter 10mmφ, cone apex angle θ is 5°,
This figure shows the case of 15°. When θ = 15°, the distance Z from the cone tip is 0.08 mm, and the energy density shows a peak value of 8.77 W/mm ² , and θ = 5°. When , Z = 0.63 mm and the energy density is 2.86 W/mm ² . In this way, when θ exceeds 15°, the distance Z from the tip of the cone, which indicates the peak value of energy density, becomes almost 0, and the width over which the steel workpiece is heated becomes narrower, making it difficult for sufficient heat treatment to occur. become unable. Furthermore, when θ is less than 2°, the peak value of energy density becomes small, which also makes it impossible to perform sufficient heat treatment.

A cone mirror in which a reflective coating is applied to the inner surface of a hollow cone has been described above. Next, a case in which a reflective coating is applied to the outer surface of a cone or a square pyramid will be described using FIG. 3.

Figure 3 is a diagram showing an outline of heat treatment using an external reflection type cone mirror, where 1' is an external reflection type cone mirror, 2' is a pipe-shaped workpiece, and Figure 2 The same reference numerals indicate the same or equivalent parts. In FIG. 3, a cone mirror 1' is inserted into a pipe-shaped workpiece 2', and either the workpiece 2' or the cone mirror 1' is moved at a speed V
to move it. The apex angle θ of the cone of the cone mirror 1' is in the range of 2° to 15° as in the example of FIG.
When the laser beam 3 is incident, the laser beam 3 undergoes multiple reflections based on the same principle as explained in the example of FIG. A rotationally symmetrical axial energy distribution is obtained.

As a result of the above, the shape of the cone mirror 1 or 1' (θ, D ₀
etc.) and by changing the output, energy distribution, shape, etc. of the laser beam 3, the energy distribution shown in FIG. 6 can be controlled.

Similar effects and actions can be obtained by using either of the cone mirrors shown in FIGS. 2 and 3, so only the case shown in FIG. 2 will be described below.

After multiple reflections between the cone-shaped mirror and the steel wire, the laser beam travels toward the apex of the cone-shaped mirror,
In this process, the reflectance of the mirror is always high, but the reflectance of the steel wire decreases as the incident angle of the laser beam increases, as shown in Figure 11. absorbed into.

When the workpiece is scanned with the energy distribution shown in FIG. 6, the absorbed energy distribution is converted into thermal energy, resulting in an increase in the temperature of the workpiece.

FIG. 7 is a diagram showing the temperature change over time on the surface of the workpiece when the workpiece is moved within the cone mirror. In the energy distribution state shown in Fig. 6, the temperature history curve shown in Fig. 7 can be changed by changing the relative moving speed V and surface absorption rate of the workpiece, and the maximum temperature
By various combinations of T _nax , temperature change rate dT/dt, etc., various heat treatments such as quenching and tempering or in combination with other equipment can be used to make the surface layer amorphous.
It can also be applied to treatments such as alloying. For example, in the case of wire tempering, T _nax is 400 to 600°C, dT/dt is 50°
~100℃/sec.

FIG. 1 is a diagram schematically showing an apparatus for heat-treating a steel wire with a laser beam using a cone mirror according to an embodiment of the present invention. Laser oscillator 5
After adjusting the divergence angle and beam diameter of the laser beam 3 irradiated from the converter 6, the laser beam 3 is controlled by bending mirrors 7 and 12, which are mirrors that control the angle of incidence with respect to the cone mirror 1. Then, it is guided inside the cone mirror 1 at θ=7°. The workpiece 2 is moved on the axis of rotational symmetry of the cone mirror 1 by a drive device 9. An auxiliary device 8 is installed before and after the cone mirror 1, and can perform pre- and post-processing such as preheating, post-heating, and rapid cooling as necessary.

In order to cool and clean the inside of the cone mirror 1 and to prevent the additive 2 from oxidizing, a gas inlet 13 is provided.
Inert gas is introduced from

A specific example of this heat treatment is as follows.
Laser beam with output of 1000W (beam diameter, approx. 10mm)
φ) is incident coaxially with a high carbon steel wire (0.3mmφ) and the steel wire is moved at a speed of 200mpm,
The surface temperature of the steel material rose to 600°C, and as a result, a uniform annealed layer was formed in the circumferential direction on the extreme surface layer of the cross section of the steel wire, approximately 10 μm thick. FIG. 8 is a diagram showing the results of a bending fatigue test and a twisting test of a steel wire heat-treated according to this specific example and a steel wire manufactured by a conventional method.

As is clear from FIG. 8, there was no difference in the torsion value in the torsion test when comparing the embodiment of the present invention and the conventional example, but the laser treatment according to this embodiment showed no difference in the bending fatigue life. It can be seen that the results have improved significantly.

[Effects of the Invention] As explained in detail above, the present invention provides a method for arranging a workpiece for heat treatment so that the center axis of the workpiece coincides with the center axis of a cone-shaped mirror whose inner or outer surface is a mirror surface. A laser beam parallel or substantially parallel to the compound is irradiated onto the surface or inner surface of the workpiece through the cone mirror, and the laser beam is directed onto the workpiece and the inner surface of the cone mirror. Alternatively, all kinds of processing can be performed using a laser beam by multiple reflections between the outer surface and the surface layer or inner layer of the workpiece by moving the workpiece or a cone-shaped mirror and continuously heat-treating the surface layer or inner layer of the workpiece. The surface layer of an object can be heat treated to a thickness of several tens of micrometers, and this can also be useful in improving the bending fatigue life of steel materials.

[Brief explanation of drawings]

Fig. 1 is a diagram schematically showing an apparatus for laser beam heat treatment of steel wire using a cone-shaped mirror, which is an embodiment of the present invention, and Fig. 2 is a condensing optical system for laser heat treatment using a cone-shaped mirror. FIG. 3 is a schematic diagram of a heat-treated product using an external reflection type cone mirror, and FIG. 4 is an explanatory diagram of multiple reflections of a laser beam on the inner surface of a cone mirror. Figure 5 shows the position of the reflection point when the diameter of the laser beam is 8 mm and the apex angle of the cone is 3° and 5°, respectively. Figure 6 shows the position of the reflection point when the laser beam diameter is 1000 W and the beam diameter is 10.
mmφ and the apex angle of the cone is θ5° and 15°. Figure 7 is a diagram showing temperature time changes on the surface of the workpiece when the workpiece is moved within the cone mirror. Figure 8 is a diagram showing the results of bending fatigue tests and twisting tests for steel wires heat-treated by this specific example and steel wires manufactured by conventional methods, and Figure 9 shows cylindrical shapes of steel wires, round bars, etc. Figure 10 shows an example of conventional heat treatment processing using a laser beam for a workpiece. Figure 10a shows the defocus beam method, Figure 10b shows the split mirror linear beam method, and Figure 10c shows the beam scanner method. , Figure d shows the integration mirror method, Figure e shows the kaleidoscope method, Figure f shows the polygon mirror method, and Figure 11 shows the reflectance of the laser beam on the steel surface. It is a diagram. In the figure, 1: cone mirror, 2: workpiece, 3:
Laser beam, 5: laser oscillator, 7, 12: bending mirror, 9: driving device.

Claims (1)

[Claims] 1. A workpiece for heat treatment is placed on the central axis of a conical mirror whose inner or outer surface is a mirror surface, so that the central axis of the workpiece coincides with the center axis of the conical mirror, and the surface or outer surface of the workpiece is A laser beam parallel or substantially parallel to the workpiece is irradiated onto the inner surface through the conical mirror, and the laser beam is multiplexed between the workpiece and the inner or outer surface of the conical mirror. A method for heat-treating a workpiece, characterized in that the surface layer or inner surface layer of the workpiece is continuously heat-treated by moving the workpiece or a conical mirror at the same time as the reflection. 2. The method for heat treating a workpiece according to claim 1, wherein the workpiece is a steel bar, a wire rod, or a steel pipe. 3. A laser beam irradiation system consisting of a laser oscillator, a conical mirror whose inner or outer surface is a mirror surface, and a mirror that transmits the laser beam from the laser oscillator and controls the incidence angle of the laser beam with respect to the conical mirror. and a drive device for moving the workpiece or a conical mirror. 4. A conical mirror is characterized in that the apex angle of the cone is either one in which the inner surface is a mirror surface within the range of 2 degrees to 15 degrees, or one in which the outer surface is mirror surface within the range of 2 degrees to 15 degrees. A heat treatment apparatus for a workpiece according to claim 3.