JPS6154085B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for laser hardening parts that require surface hardening, such as various mechanical parts or automobile parts.

Conventionally, when only the surface of mechanical parts, automobile parts, etc. is hardened, induction hardening or carbonitriding is performed, but in both of these methods, the entire part is heated to a high temperature, resulting in thermal deformation. For this reason, in the conventional method, machining is performed after hardening treatment to correct and cut the thermally deformed portions.

However, it is extremely difficult to perform machining on parts that have already hardened, and a huge amount of man-hours are spent on repairing and cutting the thermally deformed parts. Furthermore, in the conventional method, it is difficult to control the quenching depth, quenching width, quenching hardness, etc., and there are many variations in the quality of the quenching part. Furthermore, since the conventional method requires heating the entire part, it is difficult to locally harden only a small portion of the surface.

In order to eliminate these drawbacks, laser hardening methods have recently been developed and are being put into practical use. This laser hardening method has an energy density of 10 ³ to ^{10 5} W/cm ²
This is a method of irradiating the hardened part with a laser beam to heat it to a temperature above the transformation point, and then self-cooling it. For example, when laser hardening the peripheral surface of shafts, as shown in Figures 1 and 2, the member to be hardened (shafts) 1
While rotating, the peripheral surface, that is, the hardened portion 2, is irradiated with a laser beam 4 focused by a convex lens, sequentially heated to a transformation point or higher, and then self-cooled to harden the entire peripheral surface. In this case, the rotational speed of the member to be hardened 1 is set to be slow enough to sufficiently heat the irradiated area of the laser beam 4.

However, in this method, a softened region 6 occurs near the laser beam irradiation end portion 5, as shown in FIG. In other words, the softened region 6 corresponds to the starting end of laser beam irradiation and has already been hardened, but since the workpiece 1 to be hardened is rotated once, the temperature at the end end 5 is lower than the transformation point due to the heat generated during hardening. It is reheated and tempered to soften it. This softening region 6 is
This occurs no matter where the end portion 5 is located, and this poses a major problem in terms of the performance of the member 1 to be hardened.

The present invention was made in view of the above circumstances, and
The purpose is to provide a laser hardening method that can prevent a softened region by uniformly heating the entire hardened part and then cooling the whole part.

That is, instead of the method of sequentially hardening the hardened part, the present invention heats the entire hardened part to a predetermined temperature by irradiating a laser beam while rotating the workpiece, and then stops the laser beam irradiation and hardens the hardened part. This method cools the entire section.

The present invention will be explained below with reference to the drawings.

First, in the present invention, as shown in FIG. 3, after degreasing, removing rust, and cleaning the surface of the hardened part 12 of the member to be hardened 11, an oxide film 13 is formed on the hardened part 12.
The generation of the oxide film 13 is performed to increase the absorption rate of the laser beam. Oxygen gas, air, carbon dioxide gas, etc. are flowed into the nozzle 14, and in this state, the laser beam 15 is focused through the convex lens 16.
An oxide film 13 is generated by out-of-focus irradiation. In this case, as shown in FIG. 4, the rotational speed of the hardened member 11 is lower than the rotational speed during the hardening process, and the energy density of the laser beam irradiation part is set to about 10 ³ W/cm ³ , for example, and heated to a low temperature. do.

In this way, the oxide film 1 is formed on the entire hardened part 12.
After forming the hardened portion 12, a laser beam 15 is irradiated while rotating the hardened portion 12. In this case, the hardened part 1
The rotation speed of 2 is made faster than the oxide film formation process,
Avoid heating to the transformation point temperature instantaneously,
Further, the member to be hardened 11 is rotated multiple times so that the hardened portion 12 is irradiated with the laser beam multiple times. Further, the energy density of the laser beam irradiation part is set to, for example, about 10 ⁴ W/cm ² , which is the energy density necessary for heating above the transformation point, and no gas is allowed to flow into the nozzle 14 . Hardened part 12 by laser beam irradiation
is gradually heated, and after a predetermined period of time, the hardened part 1
2. The entire temperature uniformly reaches or exceeds the transformation point temperature. The settings for the rotation speed and laser beam energy density are as follows:
It can be determined in advance by heat conduction calculation from the diameter of the member 11 to be hardened, the hardening depth, etc.

At this point, the laser beam irradiation is stopped and the member to be hardened 11 is self-cooled. In this case nozzle 4
If self-cooling is assisted by flowing high-speed nitrogen gas, air, water, etc. from 4, the cooling of the hardened part 12 will be faster, and the hardened depth and hardness can be further increased.

However, according to the present invention, the workpiece to be hardened is rotated multiple times at a relatively high speed to uniformly heat the entire hardened part and then cooled, so that the hardened part is hardened at once, and the softened area is not Does not occur. Furthermore, since the entire hardened part is heated uniformly, thermal deformation is extremely small.

In addition, the laser beam irradiation forms an oxide film with a high laser beam absorption rate, so this can be produced on the same line as the laser hardening process.
High productivity. Furthermore, since no special chemicals are required to generate the oxide film, it is economical and excellent in terms of safety and health. In addition, this oxide film has a high laser absorption rate, so it can be hardened even with a relatively low-output laser device, and this film can be made uniform under constant conditions, resulting in high-quality hardened parts. can be obtained.

Next, examples of the present invention will be described.

Carbon steel S45C for machine structures is used as a hardened part.
was machined to an outer diameter of 9.2 mmφ, and this was installed in a rotating drive jig.

This workpiece to be hardened is rotated at a rotation speed of 0.33 times/second, oxygen gas is flowed at 20/min from the nozzle, and a laser beam is irradiated for 4 seconds with an energy density of 10 ³ W/cm ² at the irradiated part to form an oxide film. were produced uniformly.

Next, the rotation speed of the workpiece to be hardened was increased to 0.67 times/second, the gas flow from the nozzle was stopped, and a laser beam was irradiated for 7 seconds with an energy density of 10 ⁴ W/cm ² in the irradiated part, and the entire hardened part was irradiated with a laser beam for 7 seconds. was heated to a temperature above its transformation point. In this case, the energy density of the irradiated part is increased by bringing the convex lens closer to the hardened part.

Immediately after this irradiation, the laser beam irradiation was stopped and nitrogen gas was flowed through the nozzle at 50/min to self-cool, completing the laser hardening.

As a result of examining the hardened part of the part to be hardened which was laser hardened in this way, the hardening depth was 1 mm and the hardening hardness was uniformly Hv800, and this result was the hardening quality as originally targeted. Moreover, no hardened area was observed in any of the quenched parts.

As described above, according to the present invention, since the entire hardened part is heated and then cooled, it is possible to prevent the occurrence of a softened region and to obtain a product with excellent hardenability.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a conventional laser hardening method, FIG. 2 is a sectional view taken along the - line in FIG. 1, FIG. 3 is an explanatory diagram showing an example of the laser hardening method of the present invention, and FIG. It is a figure showing the quenching conditions in the same method. 11... Member to be quenched, 12... Quenched portion, 1
3... Oxide film, 14... Nozzle, 15... Laser beam, 16... Convex lens.

Claims (1)

[Claims] 1 Rotate the member to be hardened multiple times, and at the same time as the rotation, irradiate the hardened part of the member with a laser beam to heat the entire hardened part to a predetermined temperature, then stop irradiating the laser beam and cool the hardened part. A laser hardening method characterized by: