JPS6223054B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for heat treating the surface of steel products, particularly gears,
The present invention relates to an apparatus for heat-treating the surface of the valley-shaped portion of a steel product having a rough valley-shaped portion using a laser beam.

In order to increase the strength of the valley-shaped portions of gears, racks, etc., that is, the tooth groove surfaces, it is essential to heat treat the surface of the tooth grooves.Industrially, electromagnetic induction heating,
Currently, this heat treatment is performed by methods such as carburizing and nitriding. However, when this method is used, the flat top of the tooth tip, which does not require heat treatment, is excessively heat treated, which is not desirable in terms of strength, but also causes a large energy loss, and as a result, heat treatment distortion increases, making it necessary to develop a new heat treatment method. is awaited.

Recently, various attempts have been made to use laser beams as heating means. However, although heat treatment of the surface of steel products is being applied to steel products with flat surfaces, there are various practical problems with steel products with uneven surfaces such as gears and racks, and it is still being applied. The reality is that it has not been put into practical use industrially.

For example, when a laser beam is irradiated directly above the tooth groove as shown in Figure 2 in order to heat-treat the surface of a tooth groove, the distribution of the hardened layer (indicated by diagonal lines) will be thin on the side wall surface layer and thick on the bottom surface layer. , only extremely non-uniform heat treatment can be performed. In other words, if you want to form a hardened layer with an appropriate thickness on the surface layer of the side wall, the bottom surface layer will melt, and conversely, if you want to form a hardened layer with an appropriate thickness on the bottom surface layer, the hardened layer will have a sufficient thickness on the side wall surface. No layer will be formed. One of the reasons for this phenomenon is that the energy distribution of a laser beam has a so-called Gaussian distribution, with high energy at the center of the beam and decreasing energy toward the periphery of the beam. The bottom surface of the tooth groove, where the center of the beam is projected, is strongly heated, and conversely, the side wall surface of the tooth groove, where the peripheral edge of the low-energy beam is projected, is weakly heated. In order to eliminate this cause, a device has been developed that generates a laser beam with a so-called tophat-shaped distribution, in which the energy distribution is uniform over almost the entire region of the laser beam. Uniform heat treatment cannot be achieved due to the following reasons caused by the groove shape. That is, if the opening angle of the tooth groove or the angle formed by the left and right side wall surfaces shown in Fig. 2 is 40 degrees, the incident angle of the laser beam with respect to the bottom surface is 0 degrees, but the incident angle of the laser beam with respect to the side wall surfaces is 70 degrees. °, and the energy absorption capacity of both parts will be significantly different. In addition, a part of the laser beam incident on the side wall surface is repeatedly reflected between both side wall surfaces and reaches the bottom surface, contributing to the heating of this area. On the contrary, there is a disadvantage that the hardened layer on the bottom surface becomes thick, even though the hardened layer may be thin. For these reasons,
Surface heat treatment of tooth grooves of racks, gears, etc. using a laser beam has not yet been put to practical use.

The present invention has been made against the above-mentioned technical background, and its purpose is to provide a trough-shaped portion having two wall surfaces facing each other at a predetermined angle, like the tooth grooves of a gear. The surface of the valley-shaped portion of the steel product is heat-treated using a laser beam, thereby making it possible to obtain a steel product with a desirable hardened layer distribution and excellent mechanical strength, and at the same time making it possible to obtain a steel product with excellent mechanical strength. To provide a heat treatment apparatus which uses a single generation source for laser beams projected onto each of two wall surfaces, facilitates alignment of the laser beams projected onto each wall surface, and has a simple configuration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on drawings showing embodiments thereof.

In FIG. 1, reference numeral 21 denotes a laser beam generator, which is arranged so that a laser beam 21b is emitted toward the tooth groove 201 of the rack 20. As shown in FIG.
22 is a triangular prism-shaped two-sided mirror whose cross section is an isosceles triangle, and there are reflecting mirrors 2 on each of the two equilateral sides.
21, 222, both reflecting mirrors 221, 2
22 coincides with the diameter of the laser beam 21b facing the center line extending in the longitudinal direction of the gear 201, and each of the reflecting mirrors 2 of the laser beam 21b
In other words, the laser beam 21b is directed to the tooth space 201 so that the incident angles to the tooth spaces 201 and 222 are equal.
It is arranged so that it can be divided into two parts, the second wall surface 2012 side and the first wall surface 2011 side. The laser beam 21 is
b is divided into two parts, the first and second parts moving in different directions.
The first divided laser beam 221 distributed to the second wall surface 2012 side by the reflecting mirror 221 becomes the divided laser beams 221b and 222b.
In the optical path of b, the first divided laser beam 221
A plane mirror 231 is disposed to reflect the laser beam b toward the first wall surface 2011 of the tooth groove 201, and a convex lens 241 is provided between the plane mirror 231 and the first wall surface 2011 to focus the divided laser beam 221b. is installed. On the other hand, in the optical path of the second divided laser beam 222b distributed to the first wall surface 2011 side by the reflecting mirror 222, the second divided laser beam 222b is directed toward the second wall surface 2012 of the tooth space 201. A plane mirror 232 is disposed to reflect the reflection, and the plane mirror 232 and the second
A convex lens 242 for focusing the divided laser beam 222b is disposed between the laser beam 2012 and the wall surface 2012.

In this case as well, the first divided laser beam 2
21b is projected onto the first wall surface 2011 like the first laser beam, and the angle of incidence thereof is as small as possible.
22b is the first divided laser beam 22 on the second wall surface 2012 similar to the second laser beam.
It is necessary to ensure that the laser beam is projected onto the area opposite to the projection area of the first wall surface 2011 by laser beam 21b, and the angle of incidence thereof is as small as possible, but these conditions are determined by the beam diameter of laser beam 21b, The angle formed by the reflecting mirrors 221 and 222 of the plane mirror 22, and the plane mirrors 231 and 241 of the divided laser beams 221b and 222b
This can be achieved by appropriately selecting the incident angle and the like according to the wall depth of the tooth groove 201, the tooth groove angle, etc. Note that the divided laser beams 221b, 222
b respectively the first wall surface 2011 and the second wall surface 201
The optical means for condensing and projecting light onto each of the above-mentioned plane mirrors 231 and 232 and convex lenses 241 and 242
Instead of the combination with the above, one concave mirror may be used and these may be disposed at approximately the same position as the plane mirrors 231 and 232.

When the width of the rack 20 is large, it is of course necessary to project and scan both the laser beams 221b and 222b along the longitudinal direction of the tooth space 201, that is, along the width direction of the rack 20. To perform heat treatment on a large number of tooth spaces, it is sufficient to slide the rack 20 by one pitch.

If heat treatment is performed using such a device, both wall surfaces 2011 and 2012 will be heat treated simultaneously and under approximately equal conditions, and both wall surfaces will be thicker on the edge side of the flat top of the tooth and thinner on the bottom side. A cured layer with ideal distribution will be formed. In the case of this heat treatment, the laser beam 21b and divided laser beams 221b, 22 shown in FIG.
As can be understood from the optical path 2b, when a Gaussian distribution type laser beam 21b is used, the center of the laser beam 21b with high energy density is projected near the tips of the walls 2012 and 2011, and the center part with low energy density The peripheral edge of the laser beam 21b is projected toward the bottom of the tooth space 201, and a secondary projection effect due to reflection appears slightly on the bottom side, resulting in a more desirable heat treatment pattern. In addition, by moving the plane mirrors 231 and 231 closer to each other within an appropriate range, the areas with high energy density can be transferred to the tooth space 20.
Since the split laser beams can be spaced apart from or approached the center of the bottom surface of the split laser beam, the projection energy distribution of the area onto which the divided laser beams are projected can be made into a desired shape. Furthermore, both reflecting surfaces 22 are used as a dihedral mirror 22.
It is also possible to use a structure in which the angle θ formed by 1,222 can be adjusted, and in this case as well, the projection energy distribution can be made into a desired form by appropriately adjusting the angle θ. In other words, with only a few operations, it is possible to project the beam with the optimum energy distribution even on objects to be processed with different wall surface depths and tooth groove angles.

Note that it is appropriate that the energy density in the laser beam projection area is about 10 ² to ^{10 5} watt/mm ² , and the output of the laser beam generator 21 or the beam should be adjusted so that the energy density is within this range. The projection time or scanning speed is selected. By setting the energy density to a value within this range, the temperature of the surface layer of the beam projection area will be higher than the transformation point, and appropriate surface hardening will be performed without exceeding the melting point.

In the case of heat treatment using the apparatus of the present invention as described above, the distribution of the projected energy at each part of the wall surface is made uniform compared to the conventional method in which a laser beam is projected from directly above the tooth groove, and as a result, the tooth groove 20
The surface layer of No. 1 is an ideally distributed hardened layer that is slightly thicker on the edge side of the flat top of the tooth and slightly thinner on the bottom side (indicated by diagonal lines)
As a result, steel products with excellent mechanical strength are obtained.

Now, the effect as described above is not obtained only by projecting a laser beam on one wall surface 2011 or 2012 from the side, that is, in such a manner that the angle of incidence on the wall surface 2011 or 2012 is small; , 2012 by simultaneously projecting from the side. That is, in the process of completing the present invention, the present inventor tried the following heat treatment method. That is, in the first step, the first wall surface 20
A laser beam is projected only onto the second wall surface 20 in the next step.
We tried a method of projecting a laser beam only to No. 12 from the opposite direction, but in this case, the first wall surface would be overtreated due to the laser beam reflection in the subsequent process, resulting in the appearance of a softened zone.
In addition to the asymmetry appearing in the heat treatment state of both wall surfaces, an overlap region appears between the hardened layer formed in the previous process and the hardened layer formed in the subsequent process on the surface layer of the bottom surface, which is an unfavorable result in terms of product strength. will be invited. Figure 3 is a metallurgical micrograph of the rack treated as described above, magnified 10 times.The black part appearing on the right wall is the softening zone, indicating that the heat treatment is asymmetrical. It is shown that an overlap area appears on the bottom surface. On the other hand, in the case of the apparatus of the present invention, the opposing regions of both wall surfaces 2011 and 2012 are heat-treated simultaneously, so that the disadvantages of the above-mentioned method do not appear at all.

〔Example〕

When heat treatment was carried out using the apparatus of the present invention under the following conditions, the surface layer of the wall surface became a hardened layer, and this hardened layer was thicker near the edge of the flat top of the tooth tip and thinner in the center of the wall surface, resulting in excellent tooth tip strength. I got a lot of luck.

Processing symmetrical rack specifications: m = 2.5 Pressure angle = 20° Laser beam generator used: Carbon dioxide laser beam generator 1 unit output 1.5KW Beam diameter 17mmφ Dimension from laser beam head to wall: 281.5mm Beam scanning speed: 130mm/min Irradiation surface pre-treatment: black body treatment In the case of the present invention, a hardness of 200 Hv or more in Vickers hardness can be obtained even on the bottom part where the hardened layer is relatively thin, and on the wall surface near the edge of the flat top of the tooth where the hardened layer is thick. A hardness of over 600Hv was obtained.

As detailed above, in the case of the present invention, not only the self-quenching effect obtained in general surface heat treatment technology for steel products using high-energy beams is achieved, but also the hardened layer has a desired thickness distribution. The present invention greatly contributes to the improvement of this type of heat treatment technology, as it has the advantage of preventing the formation of softened zones due to melting.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the heat treatment apparatus according to the present invention, Fig. 2 is an explanatory diagram of the problems of the conventional method, and Fig. 3 is a metallurgical micrograph of a rack in which the tooth groove wall surface was sequentially heat-treated one side at a time. be. 21... Laser beam generator, 22... Biface mirror,
231, 232...Plane mirror, 241, 242...Convex lens.

Claims (1)

[Scope of Claims] 1. An apparatus for heat-treating the surface of a valley-shaped portion of a steel product comprising a valley-shaped portion having two wall surfaces facing each other at a predetermined angle, comprising: a laser beam generator; , a biface mirror having at least two reflecting surfaces and disposed in the optical path of the laser beam to divide and reflect approximately half of the laser beam generated by the laser beam generator in different directions; two optical means for condensing and projecting each of the divided laser beams reflected by the two reflecting surfaces of the biplane mirror onto each of the first and second wall surfaces forming the valley-shaped portion; A heat treatment device for the surface of steel products, characterized by comprising: 2. The heat treatment apparatus for the surface of a steel product according to claim 1, wherein the angle formed by the two reflecting surfaces of the double mirror is adjustable. 3. The heat treatment apparatus for the surface of steel products according to claim 1, wherein the optical means is a combination of a plane mirror and a convex lens. 4. The heat treatment apparatus for the surface of steel products according to claim 1, wherein the optical means is a concave mirror.