JPH08291322A - Laser hardening method - Google Patents

Abstract

PURPOSE: To easily harden a metallic material by specifying the quality and surface roughness of the material to be treated, the wave length of laser beam, etc., respectively, at the time of applying laser hardening to the metallic material having ruggedness in its surface. CONSTITUTION: A member 6 made of cast iron, having ruggedness of >=1.2μm surface roughness Ra, is placed on a turntable 2. While turning the turntable 2, the part P, to be hardened, of a spline 6a of the member 6 to be treated is irradiated with a laser beam B, emitted from a laser hardening machine A consisting of a laser generator 4, an optical fiber 5 for laser beam transmission, and a condenser lens unit 3 and reflected by a reflecting means 7, to undergo hardening. At this time, the carbon content and surface roughness Ra of the work to be treated are regulated, respectively, to >=2.1% and >=1.2μm and also the wavelength of the laser beam B is regulated to <=1.06μm, by which a hardened layer of uniform thickness, having excellent laser beam absorptivity, can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser quenching method for a molded part such as a gear or spline hole having irregularities on its surface.

[0002]

2. Description of the Related Art In a surface hardening method using a laser,
Only local surface is A1 with high energy density laser beam
The layer is heated above the transformation point and quenched by self-cooling due to thermal diffusion to the member to form a hardened layer. Therefore, since only the surface layer needs to be heated, the amount of heat input is small, and thermal distortion is small.

By the way, there is a special problem in the laser hardening of a molded part because the form of heat diffusion is different from that of a flat plate. That is, if the internal gear is subjected to laser hardening, even if the same beam is used, the heat easily collects depending on the part (eg, the tip of the tooth) and is easily heated up to the A1 transformation point or higher. hard. Further, since the incidence angle of the laser beam on the tooth side wall is different from that on the tooth tip or the tooth bottom, the irradiation energy density of the laser beam becomes small and it is difficult to heat.

As a result, when quenching is performed so that a hardened layer is formed on the tooth side wall and the tooth bottom, the tooth tips are melted and cracks are likely to occur. On the other hand, when quenching is performed so that a hardened layer that does not melt at the tooth tip is formed, there is a problem that a hardened layer cannot be obtained on the tooth sidewall and the tooth bottom.

As a solution to this problem, there is a technique disclosed in Japanese Patent Application Laid-Open No. 61-284519.
The disclosed technique removes C on the surface of the region to be hardened of the molded part, excluding a portion having a small heat capacity and easily hardened.
This is a laser hardening method in which a laser beam absorption coating for increasing the absorption rate of O ₂ laser is applied and a laser beam is applied to a molded part provided with the laser beam absorption coating.

[0006]

However, in the above-mentioned conventional laser hardening method, since the laser beam absorption coating for increasing the absorption rate of the CO ₂ laser is applied to the surface of the region of the molded part to be hardened, the laser beam absorption is performed. There is a problem in that mass production is lacking because coating work and removal work in a later step are required. In addition, high output C
There is a problem that the price is high because an oscillator such as an O ₂ laser is required.

The present invention has been made in view of the above problems, and an object thereof is to apply a laser beam absorption coating to the surface of a region to be hardened in a conventional molded part. There is no need, and the work of applying this laser beam absorbing film and the work of removing it in the subsequent process become unnecessary, and it is possible to use an inexpensive laser oscillator such as a low-output YAG laser oscillator, which has mass productivity. It is to provide a laser hardening method.

[0008]

In order to achieve the above object, a laser hardening method according to the invention of claim 1 is a hardening method in which a laser beam is applied to a hardening portion of a workpiece. It is characterized in that a material having a high carbon content of C2.1% or more is selected as a work to be processed and the laser output is processed in combination with a laser beam having a short wavelength of 1.06 μm or less.

In order to achieve the above object, the laser hardening method according to the invention of claim 2 is the laser hardening method according to the invention of claim 1, in which the workpiece is rotated at a predetermined peripheral speed, In the laser hardening method of irradiating a laser beam to the quenching point of the work to be processed, a laser beam moving means for moving the laser beam at a right angle to the quenching point of the work to be processed is provided.

A laser hardening method according to a third aspect of the present invention is the laser hardening method according to the first or second aspect of the present invention, wherein Ra = 1.2 μm or more having a large surface roughness as a workpiece to be processed. It is characterized in that the material is selected.

A laser hardening method according to a fourth aspect of the present invention is the laser hardening method according to the first, second or third aspect of the present invention, in which the workpiece is an internal gear or an inner diameter spline. .

[0012]

The absorption rate of laser light is determined by the characteristics of the material itself. The carbon content of the material is C2.1%
When the above-mentioned high materials are selected, most of the metals have a poor absorption of light having a wavelength with respect to the absorptance and the wavelength of light.

Therefore, according to the laser quenching method of the present invention, the energy density per unit area can be increased, the depth of the hardened layer can be increased, and the conventional molded parts can be manufactured. Since it is not necessary to apply a laser beam absorption coating on the surface of the hardened region, mass production efficiency is improved.

The absorptance of the laser beam is changed by irradiating the laser beam at a right angle to the quenching point of the work to be processed.

Therefore, according to the laser hardening method of the present invention, the laser beam is moved at a right angle to the hardening portion of the workpiece by the laser hardening device moving means, and the workpiece is rotated and irradiated at the same speed. The energy density per unit area can be increased, the depth of the hardened layer can be deepened, and there is no need to apply a laser beam absorption coating on the surface of the hardened region of molded parts as in the past, resulting in high mass production efficiency. Will be things.

The absorption rate of laser light is determined by the characteristics of the material itself, the surface roughness of the work, and the device having a short laser beam wavelength.

Therefore, according to the laser hardening method of the present invention, a material having a high carbon content of C2.1% or more is selected, and a work having a large surface roughness Ra is selected.
= 1.2 μm or more, select a laser beam with a short wavelength of 1.06 μm or less as the laser output, rotate the work piece at the same speed, and irradiate the laser beam on the quenching point By doing so, the energy density per unit area can be increased, the depth of the hardened layer can be deepened, quenching of the molded part as in the conventional case, and the laser beam absorption coating on the area surface are applied. There is no need, and mass production efficiency is good.

The absorption rate of laser light is determined by the characteristics of the material itself, the surface roughness of the work, and the device having a short laser beam wavelength. According to the laser hardening method of the present invention, it is determined by setting the work to be processed as the internal gear, the inner diameter, and the splice.

[0019]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration explanatory view of a laser hardening apparatus used in a laser hardening method according to the present invention, and FIG. 2 is a sectional view showing a state in which a workpiece is set on a turntable in the laser hardening apparatus.

The laser hardening apparatus A includes a turntable 2 provided on a base 1 and a condenser lens unit 3 provided on the base 1 via a supporting member (not shown).
Laser beam reflecting means 7 for reflecting the laser beam B focused by the condenser lens unit 3 and irradiating it to the quenching point P of the spline 6a of the workpiece 6, the laser oscillator 4, and the output side of the laser oscillator 4. Connected to the laser beam B on the input side of the condenser lens unit 3.
And an optical fiber 5 for transmitting.

Then, the carrier of the planetary gear device as the workpiece 6 is mounted on the turntable 2, the turntable 2 is rotated at a predetermined peripheral speed, and the laser beam B oscillated from the laser oscillator 4 is generated. The laser beam B, which is transmitted through the optical fiber 5 to the condenser lens unit 3 and focused by the condenser lens unit 3, is reflected by the laser beam reflecting means 7 to be processed workpiece 6
The workpiece 6 is quenched by irradiating the quenching point P of the spline 6a.

A YAG laser oscillator is used as the laser oscillator 4. The laser beam B oscillated from this YAG laser oscillator has an extremely short wavelength of 1.06 μm.

As the condenser lens unit 3, an f20 lens and a cylindrical lens are used. This cylindrical lens has a property of condensing light in only one direction and has a characteristic of focusing in an elliptical shape of 10 × 3 mm. Further, as the laser beam reflecting means 7, 90
A reflection mirror is used, and the power density can be maximized by irradiating the quenching point P with the laser beam B vertically.

If the distance from the center of the 90 ° reflection mirror to the processing point is different, the focus is also changed. From the principle that "just focus has maximum power density", if the inner diameter of the workpiece 6 changes, the focal length is adjusted by moving the cylindrical lens.

(Laser output) The laser output is 407W-4.
Fig. 3 shows the shape of quenching when changing in 3 steps up to 50W.
Shown in In conclusion, in order to increase the depth of the hardened layer,
The laser beam B needs to "increase the energy density per unit area". Therefore, it is better to increase the laser output.

(Laser Beam Offset and Hardenability)
In the workpiece 6 whose spline specifications are nominal diameter 32 modile 1.00 number of teeth 30 pressure angle 30 ° large diameter 32H14 small diameter 30h11 standard pitch circle diameter 30.00, the tooth surface irradiation angle due to the change of laser beam offset is As shown in FIG. 4, when the offset amount is 0, 33 ° 12 ′, the offset amount is 10
In the case of mm, it becomes 73 ° 23 '.

The offset amount is 5 mm to 10 mm
When the processing conditions are an oscillator output of 600 W, a processing point output of 530 W, and a work peripheral speed of 1.0 m / min, the quenching shape in the case of changing the above in six stages is as shown in FIG.

Therefore, in order to deeply harden the tooth surface, the laser beam B must be "close to the tooth surface at a right angle" as much as possible. Therefore, it is better to set a large offset amount.

(Material of Workpiece) As for the workpiece 6, the carbon content (C
A material that has an extremely high wt% ≧ 2.5 and has a possibility of quenching with a slight laser output (easy to quench) is preferable.

[Table 1]

The structure of FCD600 (spheroidal graphite cast iron) is roughly classified into three phases of pearlite phase, ferrite phase and graphite. The laser beam B rapidly heats the surface layer,
It is known that when cooled, only the pearlite phase undergoes martensitic transformation and hardening, and the ferrite phase and graphite do not undergo transformation hardening.

The structure of FC250 (gray cast iron) is roughly classified into three phases of pearlite phase, ferrite phase and graphite. It is known that when the surface layer is rapidly heated and cooled by the laser beam B, only the pearlite phase undergoes martensite transformation and is hardened, and the ferrite phase and graphite are not transformation hardened.

{Surface state of material (roughness and absorptivity)} The absorptance of the laser beam B is determined by the characteristics and surface state of the material itself. Also, regarding the relationship between the absorptance and the wavelength of light, most metals tend to have poor absorption for light having a long wavelength.

The main component of the above-mentioned FCD and FC materials is Fe, and there is data that the absorptance of the laser beam B is about 34% (in the case of YAG oscillator).

The influence of the surface state (surface roughness) on the absorptivity was investigated by using the above FCD550 and FC250 materials and the depth of the quench hardened layer as a substitute characteristic. The results are shown in (1) and (2) of FIG. 7 and (1) and (2) of FIG.

Therefore, the result is that if the surface roughness is good, the laser beam B is reflected and the quench hardened layer becomes shallow. It was also found that the influence of surface roughness can be reduced by setting the laser output higher.

(Work Peripheral Speed and Hardenability) When the work peripheral speed is changed in four steps from 1.2 m / min to 0.75 m / min, the quenching shape has a machining condition of an oscillator output of 600 W,
When the processing point output is 530 W and the offset amount is 10 mm, the result is as shown in FIG.

As a result, the laser beam B must "give a large amount of energy density per unit area" in order to increase the depth of the hardened layer. Therefore, it is better to lower the work peripheral speed.

[0038]

As described above, the laser quenching method according to the invention of claim 1 is a quenching method in which the laser beam is applied to the quenching point of the workpiece, and the carbon content of the workpiece is , C2.1% or higher material is selected, and the laser output has a short wavelength of 1.
It is characterized in that it is processed in combination with a laser beam of not more than 06 μm.

The absorption rate of laser light is determined by the characteristics of the material itself. Further, the carbon content of the material is C2.
When a material having a high content of 1% or more is selected, most of the metals have a poor absorption of light having a wavelength in relation to the absorptance and the wavelength of light. However, according to the laser hardening method of the first aspect of the present invention, the energy density per unit area can be increased, the depth of the hardened layer can be increased, and the conventional molded part can be obtained. Since it is not necessary to apply a laser beam absorption coating on the surface of the quenched region, the mass production efficiency is improved.

A laser hardening method according to a second aspect of the present invention is the laser hardening method according to the first aspect of the invention, in which the workpiece is rotated at a predetermined peripheral speed, and the workpiece is hardened at a quenching point. A laser hardening method for irradiating a laser beam is characterized in that a laser beam moving means for bringing the laser beam close to a hardening portion of a workpiece to be processed at a right angle is provided.

The absorptance of the laser light is changed by irradiating the laser beam at a right angle to the quenching point of the work to be processed. Therefore, according to the laser hardening method of the second aspect of the present invention, the laser beam is moved by the laser hardening device moving means at a right angle to the quenching point of the workpiece, and the workpiece is rotated and irradiated at the same speed. The energy density per unit area can be increased, the depth of the hardened layer can be increased, and it is not necessary to apply a laser beam absorption coating on the surface of the hardened region of the molded part as in the conventional method, which improves mass production efficiency. It will be good.

A laser hardening method according to a third aspect of the present invention is the laser hardening method according to the first or second aspect of the present invention, in which Ra = 1.2 μm having a large surface roughness as a workpiece. It is characterized in that the above materials are selected. The absorptance of laser light is determined by the characteristics of the material itself, the surface roughness of the work, and the device with a short laser beam wavelength. Therefore, according to the laser hardening method of the third aspect of the present invention, the absorptance of the laser light becomes good.

The absorptance of laser light is determined by the characteristics of the material itself, the surface roughness of the work, and the device with a short laser beam wavelength. According to the laser hardening method of the invention of claim 4, it is determined by setting the work to be processed as the internal gear, the inner diameter and the splice.

[Brief description of drawings]

FIG. 1 is a structural explanatory view of a laser hardening apparatus used in a laser hardening method according to the present invention.

FIG. 2 is a cross-sectional view showing a state in which a workpiece is set on a turntable in the laser hardening device.

[Fig. 3] Laser power of 407 W in a workpiece.
It is explanatory drawing of the hardening shape at the time of changing it to 3 steps from -450W.

FIG. 4 is an explanatory diagram of a tooth surface irradiation angle with a change in laser beam offset in a workpiece.

[Fig. 5] Offset amount of 5 mm in a workpiece.
It is explanatory drawing of the quenching shape at the time of changing to 10 mm in 6 steps.

FIG. 6 shows a workpiece peripheral speed of 1.2 m in the workpiece.
It is explanatory drawing of the quenching shape at the time of changing in 4 steps from / min to 0.75 m / min.

7 (1) and (2) are diagrams showing the relationship between the surface roughness and the depth and width of the hardened layer in the FCD550.

8 (1) and (2) are diagrams showing the relationship between the surface roughness and the depth and width of the hardened layer in FC250.

[Explanation of symbols]

 1 Base 2 Turntable 3 Condensing Lens Unit 4 Laser Oscillator 5 Optical Fiber 6 Workpiece 6a Spline 7 Laser Beam Reflecting Means A Laser Hardening Device B Laser Beam P Hardened Location

Claims (4)

[Claims] 1. A quenching method in which a quenching point of a workpiece to be treated is irradiated with a laser beam, a material having a high carbon content of C2.1% or more is selected as the workpiece, and the laser output has a wavelength of The laser hardening method is characterized in that it is processed by a combination with a laser beam having a short length of 1.06 μm or less. 2. A laser quenching method in which a workpiece is rotated at a predetermined peripheral speed and a quenching point of the workpiece is irradiated with a laser beam, and the laser beam is perpendicular to the quenching point of the workpiece. 2. A laser beam moving means for bringing the laser beam closer to
The laser hardening method described. 3. A workpiece having a large surface roughness Ra.
3. A laser hardening method according to claim 1, wherein a material having a thickness of 1.2 μm or more is selected. 4. The laser hardening method according to claim 1, 2 or 3, wherein the workpiece is an internal gear or an inner diameter spline.