JPH04280914A - Laser beam quenching method - Google Patents

Abstract

PURPOSE:To provide a laser beam quenching method, which can easily achieve the uniform quenching. CONSTITUTION:In the laser beam quenching method, in which the laser beam L irradiates surface of a spline shaft 21 forming tooth part 21a while rotating this shaft, because the axis Z of the above laser beam L is inclined by the prescribed angle alpha to the direction, in which the laser beam L irradiates toward the front face side of the rotating direction of the above tooth part 21a with respect to the radius line Y passing through the rotating center of spline shaft 21, the irradiated surface area is varied according to angle of the surface of the spline shaft 21, energy density is adjusted and the excess heat is prevented and the uniform quenching is achieved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of hardening products, such as gears and spline shafts, which have tooth profiles formed on their surfaces, while rotating them, using a laser beam as a heating means.

0002

[Prior Art] The laser hardening method irradiates a workpiece made of a hardenable material with a high-energy-density laser beam to rapidly heat the vicinity of the surface, and the heat is transferred into the workpiece through thermal conduction. This is a method of quenching by so-called self-cooling, in which the steel is rapidly cooled.

[0003] When applying this laser hardening to a product with a tooth profile formed on its surface, such as a gear or a spline shaft, it is necessary to irradiate the product with the optical axis perpendicular to the rotation axis of the product. is common.

For example, as shown in FIGS. 5 and 6,
In the conventional laser hardening method, when the gear 2 is hardened while rotating clockwise in the figure, the laser beam L focused on the convex lens 1 is directed to the tooth tip 2a, which is the side where the hardening starts.
When irradiating the right side of the tooth, since the surroundings are at room temperature, heat is transferred relatively efficiently and self-cooling occurs. However, when irradiating the left side of the tooth at the end of firing, the tooth tip 2a is irradiated due to heat transfer during right side irradiation.
Since the entire body is at a high temperature and its self-cooling ability is reduced, it is heated to a higher temperature than the firing start side, resulting in a problem that the left side surface 3 is hardened deeper than the right side surface.

[0005] Therefore, as a laser hardening method for uniformly hardening, for example, Japanese Patent Laid-Open No. 61-28451
There is one shown in Publication No. 9.

As shown in FIG. 7, this method involves hardening the surfaces of the tooth tips 4a and tooth bottoms 4b of the internal gear 4 by irradiating them with a laser beam L focused by a convex lens 5. A laser beam absorbent 6 is applied in advance to the side surface of the tooth top portion 4a and the tooth bottom portion 4b of the gear 4.

In this laser hardening method, the portion coated with the laser beam absorbent 6 absorbs more energy than the tooth tip 4a, which is easily overheated, so that the tooth tip 4a and the tooth bottom 4
(b) are heated almost evenly, making it possible to harden to a uniform depth.

Another method is shown in FIG.

[0009] In this method, the laser beam L is passed through the half mirror 7 and is divided into reflected light L1 and transmitted light L2.
At the same time, each laser beam L1, L
2 is reflected by the total reflection mirror 8, and only the tooth side surface 9a and the tooth bottom surface 9b of the gear 9 are irradiated to harden each tooth one by one.

Another method similar to this is shown in FIG.

This is a laser hardening method described in Japanese Patent Application Laid-Open No. 60-215715, in which the laser beam L is divided into two using a wedge-shaped mirror 10, and each of the divided laser beams L3 and L4 is totally reflected. mirror 11,1
1 and convex lenses 12, 12, respectively.
After condensing the light, the light is irradiated only onto the mutually opposing tooth side surfaces 13a, 13a of the rack 13 to harden each tooth one by one.

Furthermore, Japanese Patent Application Laid-Open No. 62-67110 describes a method using a chilled metal.

As shown in FIG. 10, the laser beam L is irradiated while the gear 14 is rotated intermittently to heat the side surfaces 14a and 14b of each tooth one side at a time, and the cooling metal 15 is intermittently rotated. The cylinder 16 is driven forward and backward in synchronization with the rotation, and the heated part of the gear 14 is brought into close contact with the chiller 15 to cool it, and both sides are continuously heated by heating one side at a time. In addition to preventing overheating that would otherwise occur, the chiller 15 is brought into close contact with the cooler 15 to absorb heat, and the absorbed heat is released to the outside by the cooling water circulated within the chiller 15, so that the entire body is uniformly heat-treated. Can be done.

[0014]

However, the method of applying the laser beam absorbent 6 described above is not suitable for mass production because it takes time and effort to apply the absorbent.

Furthermore, in the method using the half mirror 7 or the wedge-shaped mirror 10, since a plurality of mirrors are used in multiple stages, if there is a deviation in the mirror angle, the deviation is amplified. , 10, and 11 are required, which poses a problem in that adjustment is difficult and time-consuming. Further, after dividing the laser beam L into two, the divided laser beams L1, L2 or laser beams L3, L4 are reflected by total reflection mirrors 8, 11, and if necessary, condensed by a convex lens 12, and then Tooth side surfaces 9a, 13a and tooth bottom surface 9 of rack 13
Since the beam is irradiated and hardened one tooth at a time, the amount of energy per beam is halved and processing capacity is reduced, making it unsuitable for mass production.

Furthermore, in the laser hardening method using the chilled metal 15 described above, it is possible to perform heat treatment to a uniform hardening depth. It is necessary to drive the machine forward and backward, and since the cooling water is circulated through the chiller 15, the device becomes large and the control becomes complicated, and the processing time per piece becomes long, so the problem is that it is not suitable for mass production. There is.

The present invention was made in view of the above circumstances, and uniform hardening can be easily achieved by changing the energy density irradiated to both side surfaces of one tooth profile.
The aim is to provide a laser hardening method suitable for mass production.

[0018]

[Means for Solving the Problems] As a means for solving the above-mentioned problems, the present invention provides a laser hardening method in which a laser beam is irradiated onto the surface of a workpiece in which a tooth profile is formed while rotating the workpiece, in which the laser beam is irradiated. It is characterized in that the optical axis is inclined at a predetermined angle with respect to a radial line passing through the rotation center of the workpiece so that the laser beam is irradiated toward the front side of the tooth profile in the rotation direction.

[0019]

[Operation] According to the above method, when a laser beam is irradiated to a workpiece having a tooth profile formed on its surface, the optical axis of the laser beam is relative to a radius line passing through the rotation center of the workpiece.
The tooth profile is arranged so as to be inclined at a predetermined angle in the direction in which the laser beam is irradiated toward the front side in the rotational direction, and when the laser beam is irradiated while rotating the workpiece, the first part of the tooth surface of one tooth profile is heated. The side surfaces of the teeth on the side are irradiated at a large angle, and the side surfaces of the teeth on the finished firing side are irradiated at a small angle.

As a result, the irradiation area of the laser beam that is irradiated on the tooth side surface on the start-of-firing side, which has a high self-cooling ability, is small and the amount of energy per unit area is large. The irradiation area of the laser beam is large and the amount of energy per unit area is small because the laser beam irradiates the tooth side surface on the finished firing side, which has already reached a high temperature and its self-cooling ability has decreased, resulting in the difference in self-cooling ability and the energy density. The difference is balanced, and excessive hardening due to overheating of the tooth side surface on the end-of-firing side is prevented, and the hardening depth of both tooth side surfaces becomes uniform.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the laser hardening method of the present invention is applied to laser hardening the surface of a spline shaft will be described below with reference to FIGS. 1 to 4.

The spline shaft 21 to be laser hardened has a large number of tooth portions 21a and tooth bottom portions 21b alternately formed on the surface of the cylinder, and the tooth portion 21a has tooth side surfaces 21c, 2 on both sides.
1d, and is provided so as to be driven to rotate counterclockwise around O in FIG.

On the other hand, the irradiated laser beam L has a radius whose optical axis Z passes through a straight line perpendicular to the root circle R where the teeth 21a of the spline shaft 21 are formed, that is, the rotation center O of the spline shaft 21. α toward the front in the rotational direction with respect to line Y
It is arranged so that it is tilted by a degree and is on a straight line that does not pass through the rotation center O, and this laser beam L is directed to the convex lens 22.
The surface of the spline shaft 21 is irradiated with a portion beyond the focal point F where the light is focused.

When hardening is performed, the spline shaft 21 is continuously rotated counterclockwise in FIG. 1 at a constant speed while the laser beam L is irradiated at a predetermined irradiation angle. Therefore, the irradiation area of the laser beam L onto the surface of the spline shaft 21 increases or decreases with rotation.

That is, the firing start side of one tooth portion 21a,
That is, in the tooth side surface 21c on the left side in FIG.
Since the laser beam L is irradiated at a large angle, its irradiation surface S1 is narrow, and since the irradiation surface S1 of the same tooth portion 21a on the finished firing side, that is, the tooth side surface 21d on the right side in FIG. 2, is irradiated at a small angle, The irradiation surface S2 becomes wider.

Therefore, each tooth portion 2 of the spline shaft 21
1a, since the irradiation surface S1 is narrow on the tooth side surface 21c, which is the firing start side, the laser beam L with high energy density is irradiated, and the vicinity of the surface is rapidly heated, and then the heat is diffused to the surroundings. Hardened by self-cooling. Then, the tooth side surface 2 which becomes the firing end side of the same tooth portion 21a
1d, since the irradiation surface S2 becomes wider, the energy density of the irradiated laser beam L becomes lower than that at the irradiation surface S1.

However, the tooth side surface 21d, which is the end of firing,
Before being irradiated with the laser beam L, the heat transferred from the tooth side surface 21c increases the temperature, and the self-cooling ability decreases, so overheating is prevented rather than insufficient heating due to low energy density. be able to.

As a result, the tooth side surface 2 is irradiated with the laser beam L with high energy density and has a high self-cooling ability.
1c and the tooth side surface 21d, which is irradiated with the laser beam L with low energy density and has a low self-cooling ability, are almost uniformly hardened, so that the thickness of the hardened layer T becomes uniform.

Furthermore, when hardening the tooth side surface 21d on the end-of-firing side, even if there is a part that is in the shadow of the tooth part 21a and is not irradiated with the laser beam L, this shadow part is affected by the heat transferred from the surroundings. It is heated and quenched almost evenly with the surrounding area.

Therefore, according to the laser hardening method of this embodiment, uniform hardening is achieved on the tooth surface without using a mirror group that requires angle adjustment, an intermittent drive device, a forced cooling device, etc. as in the conventional hardening method. Hardening can be done at a deep depth, improving gear accuracy.

[0031] In order to confirm the effect, we actually used a spline with a diameter of 32 mm, a tooth height of 1 mm, and a tooth width of 3 m.
The laser hardening of the present invention is performed with the optical axis of the laser beam tilted at an eccentric angle α = 11.5 degrees about the intersection of the radius line of the spline axis and the tooth root circle with respect to the spline axis of m. The method was implemented. FIG. 11 is a photograph showing the metal structure of a spline shaft laser hardened by the method of the present invention.
It is also a photograph showing the metal structure of the spline shaft laser-hardened by the conventional method shown in FIG. 12, and as can be seen from the comparison of the two, the hardened layer of the spline shaft hardened by the method of the present invention is formed to have a uniform thickness. There is.

Further, the inclination of the optical axis Z of the laser beam L, that is, the eccentric angle α, is determined by the tooth height a, the tooth width b,
It is determined experimentally depending on the tooth profile shape, energy irradiation intensity, etc., and as shown in Figure 4, the larger the tooth height a, the smaller the eccentric angle α, and the smaller the tooth height a, the smaller the eccentric angle α. The angle α is large. Also, the larger the tooth width b, the eccentric angle α
is smaller, and the smaller the face width b, the larger the eccentric angle α.

[0033]

As explained above, the laser hardening method of the present invention is a laser hardening method in which a laser beam is irradiated onto the surface of a workpiece on which a tooth profile is formed while rotating the workpiece. Since the workpiece is tilted at a predetermined angle so that the laser beam is irradiated toward the front side in the direction of rotation of the tooth profile with respect to the radius line passing through the rotation center of the workpiece, the workpiece can be hardened to a uniform hardening depth.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the state of the teeth at the beginning of burning in an embodiment of the method of the present invention.

FIG. 2 is an explanatory diagram showing the state of the same tooth portion at the end of firing.

FIG. 3 is an explanatory diagram showing eccentric angle α, tooth height a, and tooth width b.

FIG. 4 is an explanatory diagram showing the relationship between eccentric angle α, tooth height a, and tooth width b.

FIG. 5 is an explanatory diagram showing a state at the beginning of hardening of a tooth portion in a conventional laser hardening method.

FIG. 6 is an explanatory diagram showing the state of the same tooth portion at the end of firing.

FIG. 7 is an explanatory diagram showing another example of a conventional laser hardening method.

FIG. 8 is an explanatory diagram showing another example of the conventional laser hardening method.

FIG. 9 is an explanatory diagram showing yet another example of the conventional laser hardening method.

FIG. 10 is an explanatory diagram showing another example of the conventional laser hardening method.

FIG. 11 is a photograph showing the metal structure of a member hardened by the laser hardening method of the present invention.

FIG. 12 is a photograph showing the metal structure of a member hardened by a conventional laser hardening method.

[Explanation of symbols]

21 Spline shaft 21a Teeth 21b Bottom of tooth 21c Tooth side part 21d　Tooth side part 22 Convex lens L Laser beam T Hardened layer R Root circle Y Radius line passing through the center of rotation O Z Laser beam optical axis

Claims (1)

[Claims] 1. A laser hardening method in which a workpiece on which a tooth profile is formed is rotated and the surface thereof is irradiated with a laser beam. A laser hardening method characterized in that the laser beam is tilted at a predetermined angle so that the laser beam is irradiated toward the front side in the rotation direction.