JP3137345B2 - Gear manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a gear.

[0002]

2. Description of the Related Art Conventionally, in producing a gear, a steel material is processed into a gear shape, and then a surface carbon concentration of 0.7 to 0.7%.
Gas carburizing, quenching and tempering with a target of 0.8%, followed by shot peening have been adopted. The gear manufactured by adopting this shot peening process is compared with the case of simply carburizing the gas,
The bending fatigue strength of the tooth root was improved, and in that respect, it was excellent. However, the fatigue strength of the tooth surface becomes relatively deteriorated in response to the improvement of the bending fatigue strength of the tooth root, and the pitching fracture on the tooth surface has become a factor that determines the life of the gear.

[0003] Therefore, attention has been paid to a method of carburizing, in which a so-called high-concentration carburization at a surface carbon concentration of 1% or more is performed and then a shot peening treatment is performed, and the bending fatigue strength of the tooth root and the pitting resistance of the tooth surface are both increased. It was found to improve.

[0004]

However, in such a method of performing shot peening after carburizing, the bending fatigue strength of the tooth root and the pitting resistance of the tooth surface are improved, but the toughness of the tooth root and the tooth root is remarkably increased. There was a problem that it deteriorated. In particular, in the case of high-concentration carburization, the impact value may be reduced to about 1/3 as compared with the case of only gas carburization.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is intended to manufacture a gear having good fatigue strength at the root, good pitting resistance at the tooth surface, and good impact resistance at the root and at the root. The purpose of the present invention is to provide a method for manufacturing a gear.

[0006]

SUMMARY OF THE INVENTION To achieve this object, a method of manufacturing a gear according to the present invention is described in which a gear made of steel for machine structural use is provided with an area ratio at a depth of 50 μm from the surface. After performing a high concentration carburizing treatment for precipitating 5 to 30% of carbide, the tooth bottom and the root portion are cut or ground.

As will be described later, with this configuration, the desired operation and effect can be sufficiently exhibited. However, in this method of manufacturing a gear, the amount of cutting or grinding of the tooth bottom and the root portion is set to 100 μm or more. By doing so, more favorable actions and effects can be obtained.

[0008] Further, after the cutting or grinding is performed on the root and the root portion with the amount of cutting or grinding being 100 μm,
When shot peening of 0.5 mm or more is performed at the arc height, the fatigue limit of the tooth root further increases.

[0009] In addition, if shot peening is performed after the cutting or grinding, and then the tooth bottom and the root are further cut or ground, more excellent operation and effect can be obtained. On the other hand, gears made of steel for machine structural use are subjected to high-concentration carburizing treatment for precipitating carbide at an area ratio of 5 to 30% at a depth of 50 μm from the surface, and then shot with an arc height of 0.5 mm or more. peened, by construction, characterized in that the cutting or grinding teeth <br/> bottom and the tooth root portion after the can achieve the remarkable action and effect.

In the method of cutting or grinding after shot peening, as described above, the root and root portion may be cut or ground after carburization, and may be further cut or ground after shot peening .
If the total amount of the cutting or grinding is 100 μm or more
Good.

According to the respective methods of the present invention having the above-described structure, by performing high-concentration carburization, carbides are precipitated and the pitting resistance of the tooth surface is improved. In the case of performing shot peening, a compressive residual stress is applied by the treatment to further improve the pitting resistance of the tooth surface. Then, by cutting or grinding the root and the root, the hardened layer of the root and the root are made shallow, and the action of the compressive residual stress given by the cutting or grinding is also applied. And improve the fatigue strength and impact strength of the tooth root.

Since the precipitation of carbides due to carburization changes in the depth direction, if the amount of cutting or grinding is set to 100 μm or more as in the method of the present invention as described in claim 2, the roots and roots are reduced. With regard to (1), the effect of removing the adverse effect of the hardened layer appears remarkably, and both the fatigue strength and the impact strength are greatly improved.

When shot peening is performed, a compressive residual stress is applied to the gear by this, and the maximum value of the compressive residual stress is formed slightly inside the surface. Therefore, when cutting or grinding is performed after the shot peening as in the method of the present invention, the effect of the compressive residual stress is largely brought out in addition to the removal of the hardened layer by carburization.

According to the method of the present invention, the hardened layer can be sufficiently removed and shot peening can be achieved by setting the amount of cutting or grinding to 100 μm or more. To maximize the effect of residual compressive stress due to fatigue strength,
Both pitching resistance and impact strength can be maximized.

As described above, the methods of the present invention all aim at removing the hardened layer due to carburization at the root and root portion by cutting or grinding. Further, the reason why the cutting or grinding is performed after the shot peening is to largely exert the effect of the compressive residual stress due to the shot peening. From the viewpoint of removing the hardened layer, the amount of cutting or grinding is preferably set to 100 μm or more. Therefore, in the method of performing cutting or grinding after shot peening, if the total amount of cutting or grinding is set to 100 μm or more, including the method of performing cutting or grinding before shot peening, the method of the present invention according to claim 4 It is clear that the same action as described above is achieved. This means that when cutting or grinding is performed after shot peening as in the method of the present invention, the amount may be 100 μm or more.

[0016]

Next, in order to further clarify the present invention, a preferred embodiment to which the present invention is applied will be described.

First, steel materials A to A having the component compositions shown in Table 1 were prepared.
Using G, the pitch circle diameter is 70 in module 2.5.
A gear having a diameter of 8 mm, a thickness of 8 mm, and 28 teeth was manufactured.

[0018]

[Table 1]

The gear was carburized in various patterns as shown in FIGS. Table 2 shows which pattern of carburizing treatment was performed on which steel material. The symbols P-1 to P-5 indicate the treatment by plasma carburization, and the symbols G-1 and G-2 indicate the treatment by gas carburization.

The gas carburization of symbol G-1 was carried out with the carbon potential at the time of carburization being 0.7 to 0.8%. The gas carburization of symbol G-2 was performed with the carbon potential at the time of carburization being 1.4 to 1.6%.

Further, the area ratio of carbide at a depth of 50 μm from the surface of the gear subjected to various carburizing treatments was measured. Table 2 also shows the results. Test No. corresponding to the example. 1 to 15 all have a surface carbide area ratio of 5% or more (high-concentration carburizing condition of the present invention). On the other hand, some of the comparative examples have a lower surface carbon concentration (Test Nos. 16, 17, 20) and those satisfying the condition of high-concentration carburization referred to in the present invention (Test N).
o. 18, 19). In addition, the test No. Reference numeral 20 denotes eutectoid carburization.

[0022]

[Table 2]

After the carburizing treatment was performed in this manner, in the examples, the tooth bottom and the root portion were removed by a predetermined amount by cutting or grinding. This cutting was performed using a CBN tool having a nose radius of 0.8 to 1.0 mm (or a ceramic tool) at a feed condition of 0.05 mm / rev.
Grinding was performed using a grinding tool having an abrasive particle size of 10 μm under feed conditions of 50 mm / min.

The test No. For Test Nos. 1 to 6, the removal thickness of the root and the root was 50 μm. 4
Regarding the samples No. to No. 6, the arc height was set to 0.
Shot peening was carried out at 5 mm or more.

Further, in Test No. In Test Nos. 7 to 15, the removal thickness of the root and the root was set to 100 μm.
o. In Nos. 10 to 15, shot peening was performed at an arc height of 0.5 mm or more before cutting or grinding. In addition, Test No. In Nos. 13 to 15, after this shot peening, cutting or grinding of the tooth bottom and the root portion was further performed.

The test No. Carburization in 11 and 15 →
After diffusion → slow cooling, cutting or grinding is performed, and then heating is performed again to perform quenching. In other cases, cutting or grinding is performed after quenching.

For shot peening, φ0.8
A shot ball of mm and hardness of HRC50 was used. In contrast to these examples, the comparative example is the test No. In 16 to 19, only shot peening was performed, but cutting or grinding was not performed.

[0028] Thus, the gear of the examples and comparative examples were prepared, subjected to gear fatigue test using the power circulating fatigue tester in combination with the number of teeth 28 × 32, was determined 10 ⁷ times fatigue limit. In addition, when the vibrometer generated unsteady vibration (when pitching occurred, meshing became poor), the test was interrupted, and the tooth surface was visually observed to evaluate the presence or absence of pitching.

Further, as shown in FIG. 3, a set of two gears 1 and 2 was set on an impact tester 3 to perform an impact test.
The impact tester 3 will be briefly described.

This impact tester 3 is manufactured for gears. One of the gears (fixed gear) 1 is attached to the main body 4 side, and the other gear is engaged with the fixed gear 1 on the moment arm 5 side. The gear (rotating gear) 2 is attached, the instrumented hammer 6 is swung down, the moment arm 5 is hit, and the load when the rotating gear 2 breaks is obtained from the value measured by the strain gauge. The swing angle of the instrumented hammer 6 at this time was 60 °.

[0031] shows these 10 ⁷ times endurance limit, presence or absence of pitting, the impact value shown in Table 3. Table 3 also shows the conditions for the above-described cutting or grinding and the conditions for shot peening (SP).

[0032]

[Table 3]

Table 3 will be described. First, a comparative example will be described. Test No. corresponding to the conventional product As can be seen from FIG. 20, there is no problem in pitting resistance and impact resistance, but it is understood that fatigue resistance is inferior. Therefore, what is said to be an improvement in fatigue resistance by shot peening, Test No. As can be seen from FIGS. 16 and 17, it can be understood that the pitting resistance deteriorates with the improvement of the fatigue resistance. Test No. In the case of No. 16, the impact resistance was also significantly deteriorated. Therefore, the effectiveness of high-concentration carburization is said to be higher. 18,
As is clear from FIG. 19, a significant deterioration in impact resistance is observed.

As described above, the conventional method and the method improved as a result of the conventional method have failed to provide satisfactory fatigue resistance, pitting resistance and impact resistance.

On the other hand, in the example (Test No. 1)
To 15) were all satisfactory in fatigue resistance, pitting resistance and impact resistance. When the examples were compared with each other, the test No. 13 to 15 were the best for each property. It is known that the compressive residual stress formed in the gear by shot peening is the largest inside a predetermined amount from the surface, and by performing cutting or grinding once more at the end, compression by this shot peening This is because the vicinity of the peak of the residual stress can be brought to the surface, and the effect can be maximized.

Further, in Test No. 1-3 and Test No. 7
As can be seen from a comparison with Nos. 1 to 9, the impact resistance is further improved when the thickness of the tooth bottom and the root portion is 100 μm or more.

In the test no. Nos. 4 to 6 and Test Nos.
10 to 12 show that it does not matter whether shot peening is performed before or after cutting or grinding.

As described above, according to this embodiment, a gear having good fatigue resistance, pitting resistance and impact resistance can be manufactured. In addition, as a result of the comparative study of the example and the comparative example, (1) "high concentration carburization"
(2) It is considered that "removing a predetermined amount of the tooth bottom and the root by carburizing or grinding after carburizing" acts synergistically, resulting in such a remarkable effect. In addition, when the “removal amount is 100 μm or more” at that time, it can be further improved, and “implementing shot peening” is particularly effective in improving fatigue resistance characteristics, and “after shot peening”. By performing cutting or grinding again, remarkable improvement in fatigue resistance and impact resistance can be realized.

Here, Test No. 4-6 and test N
o. From 13 to 15, it was found that cutting or grinding after shot peening was effective. Test No.
From 7 to 15, it is necessary to reduce the amount of cutting or grinding by 10 to remove the hardened layer formed on the root and the root by carburization.
It was also found that the thickness should be 0 μm or more. Therefore,
After the shot peening, a method of cutting or grinding 100 μm or more may be adopted. It is considered that a result equivalent to 13 to 15 is obtained.

Although the embodiments of the present invention have been described above, the present invention is not limited to these, and it goes without saying that the present invention can be implemented in various modes without departing from the scope of the invention.

For example, as the steel material, various machine structural steels such as manganese steel, manganese chrome steel, chromium steel, chromium molybdenum steel, nickel chromium steel and nickel chromium molybdenum steel can be applied.

The carburizing method is not limited, and the conditions of the present invention must be set so that carbides can be precipitated so that the area ratio is 5% or more at a position at a depth of 50 μm from the surface. It suffices if satisfactory high-concentration carburization can be performed. In the case of a steel material having a large content of Cr, Si, and Mn, plasma carburization is desirable.

Further, with regard to vacuum carburization, there is a concern that crystal grains may be coarsened by high-temperature treatment, but there is no problem if refining is performed by re-quenching. In addition, not only the root and root, but also the tooth surface is polished,
Noise may be prevented. However, in such a case, it is necessary to take care that the area ratio of the carbide on the tooth surface after polishing is 5% or more.

[0044]

According to the gear manufacturing method of the present invention, it is possible to improve all of the fatigue resistance, pitting resistance and impact resistance of the gear.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a procedure of a plasma carburizing process in Examples and Comparative Examples.

FIG. 2 is an explanatory diagram showing a procedure of a gas carburizing process in Examples and Comparative Examples.

FIG. 3 is an explanatory diagram showing a configuration and a usage method of an impact tester.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Fixed gear, 2 ... Rotating gear, 3 ... Impact tester, 4 ... Body, 5 ... Moment arm, 6 ... Instrumentation hammer.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shinji Fushimi 2 Nissan Motor Co., Ltd., Nissan Motor Co., Ltd. (72) Inventor Noriko Uchiyama Nissan Motor Co., Ltd. 2 Takaracho, Kanagawa Ward, Yokohama City, Kanagawa Prefecture (72) Inventor Masayoshi Ogura 2 Takara-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. (56) References JP-A-2-160428 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) B23P 15/14

Claims (6)

(57) [Claims] A gear made of steel for machine structural use is subjected to a high-concentration carburizing treatment for precipitating a carbide having an area ratio of 5 to 30% at a depth of 50 μm from the surface, and then the tooth is formed. A method for manufacturing a gear, comprising cutting or grinding a bottom and a root portion. 2. The method for manufacturing a gear according to claim 1, wherein the amount of cutting or grinding of the root and the root is 100.
A method for manufacturing a gear, characterized in that the diameter is at least μm. 3. The method of manufacturing a gear according to claim 2, wherein after the cutting or grinding, a shot peening of 0.5 mm or more at an arc height is performed. 4. The method for manufacturing a gear according to claim 3, wherein after the shot peening, a tooth bottom and a root portion are further cut or ground. 5. A gear made of steel for machine structural use is subjected to a high-concentration carburizing treatment at a depth of 50 μm from a surface thereof to precipitate carbide having an area ratio of 5 to 30%. Give shot peening of 0.5mm or more at height
A method for manufacturing a gear, comprising cutting or grinding a rear tooth bottom and a root portion. 6. A gear made of steel for machine structural use is provided with a surface
From 5 to 30% by area at a depth of 50 to 50 μm
After high concentration carburizing treatment to precipitate
The root of the tooth is cut or ground.
Apply shot peening of 0.5 mm or more, and then
Then, the bottom and root are cut or ground,
A method for manufacturing a gear , wherein a total amount of the cutting or grinding before and after the peening is 100 μm or more.