JPH06330156A - Laser quenching method - Google Patents

Abstract

PURPOSE:To perform a deep hard-facing on a small component by a laser quenching. CONSTITUTION:A material 15 to be worked is dipped in a liquid coolant 17, the surface in a cooled state is irradiated with a laser beam and locally heated to raise the temperature. The heat is conducted peripherally at the heated temp. rising part and the material itself is cooled, since the material 15 is cooled in the coolant in this case, the elevation of temp. is not so much except the heated temp. rising part, consequently, the cooling of the heated and temp. rising part by the laser beam is sure, and a deep hard-facing is made possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser hardening method for hardening a surface of a metal material by irradiating a laser beam, and more particularly to a hardening method for improving wear resistance of sliding parts of small rail guides and precision small parts. The present invention relates to a laser hardening method suitable for performing surface hardening on small parts such as hardening processing.

[0002]

2. Description of the Related Art Conventionally, induction hardening, carburizing and nitriding have been known as methods for hardening the surface of materials such as machine parts. However, none of them may be suitable depending on the surface hardening specifications of the work piece, and in particular, there is no suitable method for surface hardening of small objects such as small rail guides. For example, like a work material 1 shown in FIG. 2, it has a shape in which a groove 2 is formed on one surface of a square bar, and its dimensions are width W = 8 mm, height H = 7 mm, and groove radius R = The inner surface of the groove 2 of a small part having a size of about 3 mm is subjected to a surface hardening treatment, and a deep hardened layer (for example, a depth t
= 0.6 mm or more), the heating method is difficult for induction hardening, and the hardened layer is too shallow for nitriding.
The cost of carburizing and quenching is high, the amount of work is large, and the strain is large. In this way, induction hardening, carburizing and quenching, and nitriding all have problems for small parts.

[0003]

Therefore, it is conceivable to adopt laser quenching, which is a new quenching method utilizing high-density energy, as a surface hardening method which is an alternative to these methods. That is, laser quenching facilitates local heating of the surface of the workpiece, and therefore it is considered that quenching can be performed by easily raising the inner temperature of the groove to the quenching temperature. However, when the groove 2 of the material 1 to be processed was actually irradiated with a laser beam having a spot approximately equal to the groove width and sufficient hardening was performed to form a deep hardened layer, the surface of the groove 2 was thin. It was found that there was a problem that although the portion was quench-hardened, the hardness of the lower portion was not sufficiently increased even though it was heated, and good curing could not be performed.

The present invention has been made in view of the above problems, and an object thereof is to provide a laser hardening method capable of deeply hardening a surface of a small component by using a laser beam. .

[0005]

Means for Solving the Problems As a result of studying the reason why sufficient hardening is not performed when laser hardening is performed on small parts, the present inventors have found the following matters. That is,
In general, laser hardening is performed on a work material that is much larger than the spot of the laser beam, and the portion heated by the laser beam is rapidly cooled by the large mass around it. That is, when laser beam irradiation is performed on a small part that has been cured by self-cooling but has a width that is approximately the same as the spot diameter of the laser beam, the portion heated by laser beam irradiation Heat is transferred to the surrounding area, and the mass of the surrounding area is small, which causes the surrounding area to rise in temperature, resulting in a large amount of residual heat, resulting in insufficient cooling of the area irradiated by the laser beam. Hard quenching was impossible.

The present invention has been made on the basis of such knowledge, and in a laser hardening method of irradiating a surface of a material to be processed with a laser beam to harden the surface, irradiating the laser beam while forcibly cooling the material to be processed. The subject is a laser hardening method characterized by the following.

Here, the irradiation of the laser beam may be performed by irradiating the work material at a fixed position for a certain time, or by irradiating the work material while moving the laser beam relative to the work material. It may be a method. In either case, if the size of the region cured by one laser beam irradiation is 10% or more of the cross section of the workpiece, a sufficient cured layer cannot be obtained without using this method.

Examples of the method for forcibly cooling the material to be processed include a method in which the material to be processed is immersed in a cooling liquid for cooling, a method using water spray or mist cooling, and the like.

[0009]

As described above, the laser hardening method of the present invention is
Since the laser beam irradiation is performed while forcibly cooling the workpiece, even if the workpiece is a small part, the temperature rise of the portion other than the portion heated by the laser beam is prevented. The beam-irradiated portion is rapidly cooled in the surrounding portion, and the desired surface hardening can be performed. Further, as a result of preventing the temperature rise of the work material as a whole, thermal deformation is unlikely to occur, and bending is unlikely to occur even when quenching a long work material.

Here, the self-cooling at the time of laser beam hardening becomes smaller as the hardening region becomes larger, and therefore the effect of the forced cooling according to the present invention becomes larger. As a result of experiments conducted by the present inventors, it was found that the degree of quench-hardening is remarkably improved when the hardening region by one laser beam irradiation is 10% or more of the cross section of the work material.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an apparatus 1 used for carrying out the method of the present invention.
For example, 10 is a laser oscillator, 11 is a laser beam emitted from the laser oscillator 10, 12 is a mirror, 13 is a torch, 14 is a lens, 15 is a work material to be surface-processed, and 16 is the A container capable of containing the material to be processed 15 is a cooling liquid (water in this embodiment) 17 contained in the container 16. The container 16 is placed on a moving device (not shown) and is movable in the arrow A direction.

Next, the laser hardening operation using the above apparatus will be described. The work material 15 is placed in the container 16 and the cooling liquid 1
7 is placed so that the liquid level is slightly higher than the upper surface of the workpiece 15. Next, the laser oscillator 10 is operated to irradiate a laser beam, the lens 14 narrows the spot to a desired size, and irradiates the surface of the workpiece 15. In this state, the container 16 is moved in the direction of arrow A at a predetermined speed. Thus, the laser beam spot is the work piece 1
The surface of No. 5 is scanned at a predetermined speed to heat the surface of the workpiece,
Raise the temperature. In the part where the laser beam spot has passed, the heat of the heated part immediately escapes to the part adjacent to it,
Therefore, the temperature rising portion itself is rapidly cooled and hardened. Here, when the work material 15 is small, there is a tendency that the entire temperature rises due to heat transfer from the portion irradiated with the laser beam, but in the present embodiment, the work material 15 enters the cooling liquid. For this reason, it is forcibly cooled with a cooling liquid, and for this reason, the temperature does not rise so much except for the laser beam irradiation portion,
Cooling of the temperature rise part by laser beam irradiation is reliable,
The surface can be satisfactorily hardened. At this time, the output of the laser oscillator 10 is increased or the workpiece 15
By slowing down the moving speed of, the heating portion can be surely cooled even when the energy given per unit area of the work material 15 by the laser beam is increased. Therefore, the baking from the surface to the deep position is performed. Curing and hardening can be performed. Further, as a result of suppressing the temperature rise of the work material as a whole, the occurrence of bending can be reduced.

The cooling liquid 17 used in the above embodiment is preferably one that is easily available, easy to handle, and has a small laser beam absorption. Usually, water is used. In the above-described embodiment, the entire work material 15 is immersed in the cooling liquid 17, but the upper surface of the work material 15 (the surface to be surface hardened) may be exposed on the liquid surface. Even in that case, since most of the material to be processed 15 is cooled by the cooling liquid, the portion heated and heated by the laser beam irradiation is surely cooled in the peripheral portion, and the surface can be hardened. . Further, the cooling liquid is not limited to the case of being simply stored in the container 16, and may be in a state of appropriately flowing in the container.

Next, an example in which quenching is actually performed using the above apparatus will be described.

Example 1 Two types of test pieces A and B having the shape shown in FIG. 2 and having different sizes were prepared. The specifications of the test pieces A and B are as follows. Test piece A: Material SUJ2 W = 8 mm, H = 7 mm, L = 100 mm, R = 3.2
mm Test piece B: Material SUJ2 W = 6 mm, H = 4 mm, L = 100 mm, R = 2.0
mm

The test pieces A and B are shown in FIG.
Inside, the groove forming surface was set upward, water was put in the state shown as a cooling liquid, and laser hardening was performed on the groove on the upper surface under the conditions shown in Table 1. Also, for comparison,
Laser quenching was also performed when water was not added.

The cross-section of each test piece after quenching under the conditions shown in Table 1 was macro-etched with nitric acid alcohol and the hardening pattern was observed. The results are shown in FIGS. 3 and 4. Further, the hardness distribution of the cross section of each of the obtained test pieces was measured.
The results are shown in FIGS. Table 2 shows the relationship between the used test piece, FIGS. 3 and 4, and the relationships in FIGS. 5 to 8. In addition, the curves a and b shown in FIGS.
The hardness distributions of cross-sections A and B in FIGS. 3 and 4 are shown. Further, the bending (warpage) of the test piece after quenching was measured. The results are also shown in Table 2.

[0018]

[Table 1]

[0019]

[Table 2]

As can be seen from the cross-sectional view of FIG. 3, in the test piece which has been quenched in water, a thick hardened portion 3 is formed on the surface, and the heating portion (insufficiently hardened portion) 4 behind it is extremely hard. Although it is thin, in the test piece subjected to in-air quenching, as can be seen from the sectional view of FIG. 4, the surface hardened portion 3'is extremely thin and the heating portion (insufficiently hardened portion) 4'behind it is extremely thick. Was becoming. Further, as is clear from the hardness distribution curves shown in FIGS. 5 to 8, the hardness increased to a deeper position when the underwater quenching was performed.

[Embodiment 2] As shown in FIG.
A bar material 20 (material SUJ2) having a size of mm × 6 mm was prepared, and the bar material was used as a test piece to perform underwater quenching in the same manner as in Example 1, and the quenching depth was changed by changing the feed rate at that time. . As shown in FIG. 9, the obtained test piece 20 has a hardened portion 21 formed on the surface thereof. Therefore, the hardness distribution in the direction from the surface to the center was measured at the central portion. The results are shown in FIGS. Further, the area of the hardened region was obtained from the hardness distribution, and the ratio to the cross section of the bar was calculated. As a result, 8% in FIG.
It was 10% in FIG. 1, 12% in FIG. 12, and 16% in FIG. Further, quenching was performed under the same conditions as the quenching conditions, but in air, and the hardness distribution of the obtained test piece was measured. The results are also shown in FIGS. 10 to 13.

As is clear from the results of FIGS. 10 to 13, when the ratio of the hardened region is small (8% in FIG. 10), the difference between the underwater quenching and the air quenching is small, but FIG.
As shown in FIGS. 1 to 13, as the ratio of the hardened region is increased, the difference between the underwater quenching and the air quenching becomes large, and in particular, as shown in FIG.
In the case of 16% shown in No. 3, even if quenching is performed in the air under the same conditions, quenching hardly occurs, and the surface hardening is extremely small. This is considered to be because if the amount of heat to be heated is increased in order to deeply quench by air quenching, the temperature of the entire bar becomes high, the cooling of the laser beam irradiation part is insufficient, and quenching becomes impossible. . On the other hand, in underwater quenching, the laser quenching is performed while the bar is put in water and forcibly cooled, so even if the heating heat amount is increased, it is possible to suppress the temperature rise of the part other than the part to be hardened, The portion heated by the beam can be reliably cooled, and deep quenching can be performed. As can be seen from these results, the method of the present invention is particularly effective in the case of hardening 10% or more of the cross section of the workpiece by one laser beam irradiation.

[0023]

As described above, according to the present invention, surface hardening can be efficiently and deeply performed on small parts such as small rail guides and precision small parts, and distortion is generated. Therefore, it is possible to obtain the effect that the manufacturing cost can be reduced and the quality can be stabilized.

[Brief description of drawings]

FIG. 1 is a schematic side view showing an example of an apparatus used for carrying out the method of the present invention.

FIG. 2 is a schematic perspective view showing an example of a material to be surface-hardened.

FIG. 3 is an end view showing a hardening macro pattern of a work-hardened material according to an embodiment of the present invention.

FIG. 4 is an end view showing a hardening macro pattern of a work piece that has been subjected to quenching by air quenching (comparative example).

FIG. 5 is a graph showing the cross-sectional hardness distribution of a test piece that has been subjected to quenching under condition 1 (example of the present invention).

FIG. 6 is a graph showing the cross-sectional hardness distribution of a test piece that has been subjected to quenching under condition 2 (comparative example).

FIG. 7 is a graph showing the cross-sectional hardness distribution of a test piece that has been subjected to quenching under condition 3 (example of the present invention).

FIG. 8 is a graph showing a cross-sectional hardness distribution of a test piece that has been subjected to quenching under condition 4 (comparative example).

FIG. 9 is an end view showing a hardening macro pattern of a bar material that has been quenched in Example 2;

FIG. 10 is a graph showing the cross-sectional hardness distribution of a bar material that has been quenched under certain conditions in Example 2.

11 is a graph showing a cross-sectional hardness distribution of a bar material that has been quenched under conditions different from those of FIG. 10 in Example 2;

FIG. 12 is a graph showing a cross-sectional hardness distribution of a bar material that has been quenched under the conditions different from those of FIGS. 10 and 11 in Example 2;

FIG. 13 is a diagram illustrating a second embodiment of FIGS.
Graph showing the cross-sectional hardness distribution of a bar material quenched under conditions different from those of

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Worked material 2 Groove 3, 3'hardened part 4, 4'heating part (insufficiently hardened part) 10 Laser oscillator 11 Laser beam 15 Worked material 16 Container 17 Coolant

Claims (4)

[Claims] 1. A laser hardening method for irradiating a surface of a material to be processed with a laser beam for surface hardening, wherein the laser beam irradiation is performed while forcibly cooling the material to be processed. 2. The laser hardening method according to claim 1, wherein a region of 10% or more of the cross section of the workpiece is hardened by one laser beam irradiation. 3. The laser hardening method according to claim 1, wherein the laser beam irradiation is performed in a state where the material to be processed is placed in the cooling liquid. 4. The laser hardening method according to claim 1, wherein the laser beam irradiation is performed while water spraying or mist cooling the material to be processed.