JP3781172B2 - Gear manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a gear used for, for example, a differential of an automobile.
[0002]
[Prior art]
In general, gears used in automobile differentials are formed with a center hole in a blank made of steel, etc., and a carburizing process is performed on the blank after forming a tooth profile by cutting or forging. A carburized layer having a uniform depth is formed.
[0003]
On the other hand, in this type of gear, as a characteristic of each part, the tooth surface portion of the tooth profile is required to have wear resistance for meshing with the other gear, and the tooth root portion of the tooth profile has impact fatigue due to repeated impact input. Strength is required, and the inner wall portion of the center hole is required to have wear resistance and seizure resistance for contact with the shaft inserted into the center hole.
[0004]
In response to such a characteristic request, when carburizing treatment is performed after forming a tooth profile or the like, the depth of the carburized layer C is uniform as a whole as shown in FIG. Although the depth of the carburized layer C is sufficiently obtained and wear resistance is improved, the depth of the carburized layer C is excessive in the tooth root portion Gb, and the input increases with the recent increase in output of the power transmission system. On the other hand, there is a problem that the impact fatigue strength of the tooth root portion Gb is lowered. In order to solve this problem, carburizing treatment is applied to the tooth base part, and as shown in FIG. 4B, the carburized layer of the tooth base part Gb without changing the depth of the carburized layer C of the tooth surface part Ga. An attempt was made to make C thinner. However, in this case, the cost of the carburizing treatment is high, and it is difficult to accurately control the depth of the carburized layer C.
[0005]
Therefore, as disclosed in Japanese Patent Application Laid-Open No. 9-38747, a method has been proposed in which a carburized blank is subjected to a carburizing process, and the blank is warm-forged and formed into a gear. According to this method, it is possible to make the carburized layer C of the tooth base part Gb thin while maintaining the depth of the carburized layer C of the tooth surface part Ga, as shown in FIG. Became.
[0006]
[Problems to be solved by the invention]
By the way, in the conventional gear manufacturing method as described above, the amount of plastic deformation of the tooth root when the blank is forged is large, whereby the carburized layer of the tooth root is maintained while maintaining the depth of the carburized layer of the tooth surface. Although the thickness of the carburized layer at the tooth surface and the root portion is determined by the depth of the carburized layer formed on the blank and the amount of deformation of the plastic working, the formation pattern of both carburized layers, i.e. The ratio between the depth of the carburized layer and the depth of the carburized layer at the root is almost limited. For this reason, if the depth of the carburized layer of the tooth root part is made appropriate, the depth of the carburized layer of the tooth surface part may become excessive, and conversely, the depth of the carburized layer of the tooth surface part is intended. Therefore, since the depth of the carburized layer at the tooth base portion may become excessive if it is attempted to increase the size, conventionally, a carburized layer having an appropriate depth is obtained by each of the tooth surface portion and the tooth root portion. Further improvement has been demanded.
[0007]
OBJECT OF THE INVENTION
The present invention has been made in view of the above-described conventional situation, and in particular, provides a gear manufacturing method capable of obtaining a carburized layer having an appropriate depth by each of a tooth surface portion and a tooth root portion of a tooth profile. It is an object.
[0008]
[Means for Solving the Problems]
Method of manufacturing a gear according to the present invention, the intermediate shape between a claim 1, when preparing a tooth wheel having a center hole, and a cylindrical blank in the first forging step initial shape and the final gear shape shaping the recess in the portion corresponding to both sides of the blank center hole of the well as formed shape to, after carburized to this intermediate product, Rutotomoni both sides to mold the preform into a gear shape in the second forging step Following a recess for molding the center hole having an inner burr during both the configuration you remove the inner beams of the center hole, as claimed in claim 2, the tooth surface of the intermediate shape of the medium between the molded body, a structure is a curved surface smoothly continuous to and outwardly similar to a gear shape of the final, as a third aspect, before the first forging step, has a structure carburized blank, with the construction of the As a means to solve the conventional problems That.
[0009]
[Effects of the Invention]
In the gear manufacturing method according to claim 1 of the present invention, a carburized layer having a predetermined depth is secured in the tooth surface portion of the tooth profile to obtain wear resistance, and an impact fatigue strength is obtained in the tooth base portion. It is intended to secure a carburized layer thinner than the carburized layer of the tooth surface part. As the process, the blank is appropriately heated, and the blank is intermediate between the initial shape and the final gear shape in the first forging process. It shape | molds in a shape and makes this an intermediate molded object. At this time, the intermediate molded body may have a substantially gear shape having an incomplete tooth profile . At the time of forming this intermediate formed body, concave portions are formed in portions corresponding to both sides of the center hole of the blank. In the following, carburize the intermediate molded body to form a carburized layer of uniform depth throughout the preform. Then, the intermediate formed body is appropriately reheated, and the intermediate formed body is formed into a gear shape in the second forging step, thereby securing a carburized layer having a predetermined depth on the tooth surface portion of the tooth profile, and on the tooth base portion. A carburized layer thinner than the carburized layer on the tooth surface is secured . When the intermediate formed body is formed into a gear shape in the second forging step, the concave portions on both sides are formed into a center hole having an inner beam between both sides. At this time, in the gear manufacturing method, in particular, a carburized layer having a uniform depth is formed in the concave portions on both sides, and both the concave portions are formed into a center hole with an inner flash, so the carburized layer on the inner wall portion of the center hole. Is substantially continuous from one center hole to the other center hole through the inner beam. Therefore, by subsequently removing the inner beam, the carburized layer is kept well along the inner wall portion of the center hole that has penetrated, and this carburized layer makes it possible to wear and seize the shaft inserted into the center hole. Is secured. Na us, the gear was molded by the second forging step, if necessary, hardening, etc. shot blasting and machining is performed.
[0010]
Here, in the process of forming the blank into a gear shape, since the amount of plastic deformation of the tooth root portion of the tooth profile is particularly large, when the blank subjected to carburizing treatment is formed into a gear shape by one forging, the deformation amount of the carburized layer The carburization layer at the tooth root may become too thin, and the depth of the carburization layer at the tooth surface may be increased by forming a deep initial carburization layer to secure the carburization layer at the tooth root. May become excessive.
[0011]
On the other hand, in the gear manufacturing method, the blank is formed into an intermediate formed body, and the intermediate formed body is subjected to carburizing treatment and then the intermediate formed body is formed into a gear shape. The amount of plastic deformation of the tooth root in the forging process is small, and accordingly, the amount of deformation of the carburized layer is small. Therefore, it is prevented that the carburized layer of the tooth root is too thin, and the initial carburizing is performed. Since the carburized layer of the tooth root is secured without forming a deep layer, the depth of the carburized layer of the tooth surface does not become excessive, and the appropriate depth for each of the tooth surface and the tooth root A carburized layer is secured.
[0013]
In the gear manufacturing method according to claim 2 of the present invention, the intermediate tooth surface of the intermediate molded body is approximated to the final gear shape, and the tooth surface is formed into a curved surface shape that smoothly continues outward. Then, through the carburizing process and the second forging process performed thereafter, a carburized layer having a predetermined depth is more easily and reliably secured in the tooth surface portion, and the tooth base portion than the carburized layer of the tooth surface portion. A thin carburized layer is more easily and reliably ensured.
[0014]
In the gear manufacturing method according to claim 3 of the present invention, the blank is carburized before the first forging step, and then the blank is formed into an intermediate formed body in the first forging step, and the intermediate formed body is carburized. Since the intermediate formed body is formed into a gear shape in the second forging process, the opportunity to control the formation pattern of the carburized layer in the tooth surface portion and the tooth root portion of the tooth profile is increased. For example, the carburized layer in the tooth root portion It is also possible to intentionally increase the depth of the carburized layer of the tooth surface portion while preventing it from becoming too thin.
[0015]
That is, when the first forging process is performed after carburizing the blank, the carburized layer of the tooth root portion can be made thin while maintaining the depth of the carburized layer of the tooth surface portion. Form the carburized layer of the base part thinner than the appropriate depth. Thereafter, if the carburizing treatment is performed on the intermediate formed body and the second forging step is performed, the depth of the carburized layer at the tooth surface portion is further increased, and the carburized layer at the tooth base portion becomes an appropriate depth.
[0016]
【The invention's effect】
According to the gear manufacturing method according to claim 1 of the present invention, the blank is formed into an intermediate formed body in the first forging step, and the intermediate formed body is subjected to carburizing treatment, and then the intermediate formed body is formed in the second forging step. By adopting a method of forming a gear shape, a carburized layer of a predetermined depth is secured on the tooth surface portion of the tooth profile to obtain wear resistance, and a tooth surface portion is obtained on the tooth base portion to obtain impact fatigue strength. When a carburized layer that is thinner than the carburized layer is secured, it is possible to prevent the carburized layer at the tooth root portion from becoming too thin, and even if the initial carburized layer in the intermediate formed body is not deeply formed, As the carburized layer is secured, the carburization cost can be reduced, and the carburized layer depth of the tooth surface can be prevented from becoming excessive. A carburized layer with a sufficient depth can be secured. Further, if the shape of the intermediate formed body is selected, it is possible to intentionally increase the depth of the carburized layer at the tooth surface while making the carburized layer at the tooth base portion appropriate. And when manufacturing the gear used for the differential of a motor vehicle, it is possible to obtain a gear having individual characteristics in the tooth surface portion and the tooth root portion and capable of sufficiently responding to high output of the power transmission system.
[0017]
In addition, the gear manufacturing method according to claim 1 of the present invention does not require a step of forming a center hole in advance in a solid blank, and can reduce the number of man-hours and the manufacturing cost. In addition, a good carburized layer with almost no carburized layer breakage can be obtained on the inner wall of the center hole, and the carburized layer ensures sufficient wear resistance and seizure resistance for the shaft inserted into the center hole. can do.
[0018]
According to the manufacturing method of the gear according to claim 2 of the present invention, on top that can obtain the same effect as claim 1, to approximate the tooth surface of the intermediate shape of the preform into the final gear shape and outer By making the curved surface shape smoothly continuous, a carburized layer having a predetermined depth can be more easily and surely secured on the tooth surface portion through a carburizing process and a second forging process performed thereafter. In addition, a carburized layer that is thinner than the carburized layer on the tooth surface can be more easily and reliably secured at the tooth base.
[0019]
According to the gear manufacturing method according to claim 3 of the present invention, the same effects as in claims 1 and 2 can be obtained, and after carburizing the blank, the first forging step, carburizing treatment and Through the second forging process, the formation pattern of the carburized layer of the tooth surface portion and the tooth root portion can be changed more widely, and a carburized layer having a desired depth is formed on each of the tooth surface portion and the tooth root portion. For example, a gear in which the carburized layer is greatly changed between the tooth surface portion and the tooth root portion can be manufactured.
[0020]
【Example】
1 and 2 are diagrams for explaining an embodiment of a gear manufacturing method according to the present invention. In this embodiment, the gear G shown in FIG. 1 (g) is a bevel gear used for a differential of an automobile, and has a tooth profile A from a small diameter portion to a large diameter portion, and along the axial direction. A center hole H is provided, and a back spherical surface R is provided on the large diameter side.
[0021]
In order to manufacture the gear G, a solid cylindrical blank B as shown in FIG. 1A is used, and the blank B is heated to about 900 to 1100 ° C., and then the blank B is first forged. In the process, an intermediate shape between the initial shape and the final gear shape is formed, and as shown in FIG. 1B, a substantially gear-shaped intermediate formed body F having an incomplete tooth shape is obtained. The intermediate shape of the intermediate molded body F has a curved surface shape in which the tooth surface approximates the final gear shape and the tooth surface smoothly continues to the outside.
[0022]
In the first forging step, a forging die as shown in FIG. The forging die includes an upper die 2 having an upper punch 1 inserted in the center and a lower die 4 having a lower punch 3 inserted in the center. The upper die 2 has a molded part 5 of a tooth profile A, and the lower 4 die has a molded part 6 of a back spherical surface R. Each of the upper and lower punches 1 and 3 has hemispherical convex portions 1a and 3a at the tip. In the first forging step, the tooth profile A and the back spherical surface R are primarily formed using the forging die described above, and the punches 1 and 3 are used to form recesses 7 in portions corresponding to both sides of the center hole H of the blank B. , 8 are molded to obtain an intermediate molded body F. At this time, the concave portions 7 and 8 are formed into a hemispherical bottom by the convex portions of the punches 1 and 3, and the vicinity of the opening is formed into a curved surface that is smoothly continuous to the outside.
[0023]
The intermediate molded body F molded as described above is subjected to carburizing treatment to form a uniform carburized layer C as shown in FIGS. 1C and 1D. The carburization depth at this time is appropriately set according to the required carburization depth as a part, the amount of plastic deformation in the second forging process, and the like. Thereafter, the intermediate formed body F is reheated to about 900 to 1100 ° C., and the intermediate formed body F is formed into a gear shape shown in FIGS. 1E and 1F in the second forging step.
[0024]
In the second forging step, a forging die as shown in FIG. 2B is used. The forging die includes an upper die 12 having an upper punch 11 inserted at the center and a lower die 14 having a lower punch 13 inserted at the center. The upper die 12 has a molded part 15 of a tooth profile A, and the lower 14 die has a molded part 16 of a back spherical surface R. Each of the upper and lower punches 11 and 13 has a flat tip portion. In the second forging step, the tooth profile A and the back spherical surface R are secondarily formed using the forging die described above, and the concave portions 7 and 8 on both sides are inserted between the two by the punches 11 and 13. The bottomed cylindrical center holes 7H and 8H are formed.
[0025]
At this time, the center holes 7H and 8H are formed by forming the recesses 7 and 8 in the intermediate formed body F in the first forging process, carburizing, and then forming the center holes 7H and 8H into the state with the inner flash V in the second forging process. As a result, the carburized layer C on the inner wall portion is in a state of being substantially continuous from the one center hole 7H to the other center hole 8H through the inner flash V.
[0026]
Thereafter, in the gear manufacturing method, the inner beam V of the center holes 7H and 8H is punched and removed using a piercing die or the like to obtain the gear G shown in FIG. Thereby, the carburized layer C is well maintained along the inner wall portion of the penetrating center hole H. Thereafter, the gear G is quenched (block B1) as shown in FIG. 1 (h), then shot blasted (B2), and further subjected to appropriate machining (B3).
[0027]
Thus, in the gear manufacturing method described above, the tooth surface portion (Ga) has a predetermined depth as in the tooth profile having the ideal carburized layer C shown in FIG. The carburized layer C is secured, the carburized layer C thinner than the carburized layer C of the tooth surface portion is secured at the tooth base portion (Gb), and a good carburized layer C is secured also at the inner wall portion of the center hole H.
[0028]
That is, in the process of forming the blank B into a gear shape, the amount of plastic deformation of the tooth root portion of the tooth profile is particularly large, and a problem such as the carburized layer C of the tooth root portion becoming too thin may occur. In this manufacturing method, the blank B is formed into an intermediate formed body F, and in particular, the intermediate-shaped tooth surface of the intermediate formed body F has a curved surface shape that approximates the final gear shape and smoothly continues to the outside. The intermediate formed body F is subjected to carburizing treatment, and then the intermediate formed body F is formed into a gear shape so that the amount of plastic deformation of the tooth root portion in the second forging step after the carburizing treatment is reduced. Accordingly, the deformation amount of the carburized layer C is reduced. Therefore, the carburized layer C of the tooth base portion does not become too thin, and the carburized layer C of the tooth root portion is ensured without forming the initial carburized layer C deeply. Therefore, the carburized layer C having an appropriate depth is ensured in each of the tooth surface portion and the tooth root portion.
[0029]
And the gear G has a wear resistance secured by maintaining the depth of the carburized layer C at the tooth surface portion meshing with the gear of the other, and the carburized layer is thinned at the tooth base portion that receives impact input during rotation. The impact fatigue strength is ensured, and furthermore, the carburized layer C is well maintained on the inner wall portion of the center hole that comes into contact with the shaft inserted in the inner wall portion of the center hole, so that wear resistance and seizure resistance are ensured. Therefore, as a gear used for a differential of an automobile, it has characteristics for each part and can sufficiently cope with a high output of a power transmission system.
[0030]
The gear manufacturing method according to the present invention may be carburized on the blank B before the first forging step, as described in the above embodiment. That is, the blank B shown in FIG. 1A is subjected to carburizing treatment, and then the blank B is formed into an intermediate formed body F in the first forging step, and the intermediate formed body F is subjected to carburizing treatment, and then the second forging step. Then, the intermediate formed body F is formed into a gear shape.
[0031]
In such a gear manufacturing method, the same effects as in the previous embodiment can be obtained, and in addition, the opportunity to control the formation pattern of the carburized layer C in the tooth surface portion and the tooth root portion of the tooth profile is increased. It is also possible to intentionally increase the depth of the carburized layer C at the tooth surface while preventing the carburized layer C at the base from becoming too thin. That is, when the first forging process is performed after the blank B is subjected to the carburizing process, the carburized layer C of the tooth base portion can be made thin while maintaining the depth of the carburized layer C of the tooth surface portion. In addition, the carburized layer C of the tooth base is formed thinner than an appropriate depth. After that, if the carburizing treatment is performed on the intermediate formed body F and the second forging process is performed, the depth of the carburized layer C in the tooth surface portion further increases, and the carburized layer C in the tooth root portion has an appropriate depth.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view (a) to (g) and a block diagram (h) illustrating a manufacturing process in an embodiment of a gear manufacturing method according to the present invention.
2 is a cross-sectional view (a) showing an example of a forging die used in the first forging step of the method for manufacturing the gear shown in FIG. 1, and a cross-sectional view (b) showing an example of the forging die used in the second forging step. .
FIG. 3 is a cross-sectional view of a tooth profile when carburizing is performed after the tooth formation (a), a cross-sectional view of the tooth profile when carburizing is performed after the tooth formation is carburized and carburized (b), and carburizing. It is sectional drawing (c) of a tooth profile at the time of forging a tooth profile after a process.
[Explanation of symbols]
B Blank C Carburized layer F Intermediate compact G Gear H Center hole V Inner beam 7 8 Recess 7H 8H Center hole before removing inner beam

Claims (3)

Upon manufacturing a tooth wheel having a center hole, the portion corresponding to both sides of the blank center hole of the well as formed form an intermediate shape between the cylindrical blank the initial shape and the final gear shape in the first forging step in molding the recess, then subjected to carburizing treatment to the intermediate product, forming an intermediate formed body in a second forging step in the center hole having an inner burr between both recesses Rutotomoni sides be molded to the gear shape to Following the method of manufacturing a gear which is characterized that you remove the inner beams of the center hole.  The gear manufacturing method according to claim 1, wherein the intermediate-shaped tooth surface of the intermediate formed body has a curved surface shape that approximates the final gear shape and smoothly continues to the outside.  The gear manufacturing method according to claim 1 or 2, wherein the blank is subjected to a carburizing process before the first forging step.

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