JP3785913B2 - 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 for each part, the tooth surface portion is required to have wear resistance for meshing with the other gear, and the tooth root portion is required to have impact fatigue strength against repeated impact input. 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 is performed after forming the tooth profile or the like, the depth of the carburized layer C is uniform as shown in FIG. However, there is a problem that the impact fatigue strength of the tooth root portion Gb is reduced with respect to the increase in input accompanying the increase in output of the power transmission system in recent years. In order to solve this problem, carburizing treatment is applied to the tooth base part, and as shown in FIG. 6B, the carburized layer of the tooth base part Gb is left 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 Laid-Open No. 9-38747, there is a method in which a blank formed into a hollow shape is subjected to carburizing treatment, the blank is warm-forged into a gear, and then the gear is quenched. Proposed. According to this method, the carburized layer C of the tooth root portion Gb can be made thin while maintaining the depth of the carburized layer C of the tooth surface portion Ga, as shown in FIG. Became.
[0006]
[Problems to be solved by the invention]
However, in the conventional gear manufacturing method as described above, the wear resistance of the tooth surface portion is ensured by maintaining the depth of the carburized layer of the tooth surface portion, and the carburized layer of the tooth base portion is thinned to reduce the tooth. The impact fatigue strength of the base is ensured, so it is possible to obtain gears that are suitable for higher power transmission systems, but wear resistance and seizure resistance by maintaining the carburized layer on the inner wall of the center hole Therefore, it is necessary to make the inner flash formed in the center hole as thin as possible in the forging process.
[0007]
In other words, in the conventional gear manufacturing method, when a hollow blank subjected to carburizing treatment is forged, the material flows into the center hole to form an inner flash. If the inner flash is thick, this is performed later. Since the carburized layer may be cut off in the inner wall portion of the center hole with the removal of the inner beam, it is necessary to make the inner beam thinner. In order to form the inner beam thinly, it is necessary to use a forging die having a higher pressure. In this case, the flow of the material with respect to the die surface becomes faster, so that the life of the die is reduced.
[0008]
OBJECT OF THE INVENTION
The present invention has been made in view of the above-described conventional situation. When a gear having a center hole is manufactured through a forging process after the carburizing process, the carburized layer on the inner wall portion of the center hole is improved by a simpler process. It is an object of the present invention to provide a method of manufacturing a gear that can be maintained at the same level and that can obtain a gear having individual characteristics at each portion of the tooth profile.
[0009]
[Means for Solving the Problems]
According to a first aspect of the present invention, a gear manufacturing method according to the present invention corresponds to both sides of a blank center hole in a first forging process after carburizing a solid blank when manufacturing a gear having a center hole. Forming a conical recess in a portion to be formed, forming a recess on both sides into a center hole having an inner flash between the two in the second forging step, and thereafter removing the inner flash of the center hole. 2, the concave portion to be formed in the first forging step has a conical shape with an apex angle as an acute angle, and the center hole including the removed portion of the inner beam after removing the inner beam of the center hole according to claim 3 the inner wall has a structure for shaping the annular recess to have a means for solving the conventional problems with the configuration described above.
[0010]
[Effects of the Invention]
In the gear manufacturing method according to claim 1 of the present invention, a solid blank is subjected to carburizing treatment to form a carburized layer having a uniform depth over the entire blank. No center hole is formed on the blank, and the blank is appropriately heated, and conical recesses are formed at portions corresponding to both sides of the center hole of the blank in the first forging step. At this time, the tooth profile is also formed. In the first forging step, the carburized layer of the recess is in a state along the recess without being cut at the top of the recess.
[0011]
And the molded object which passed through the 1st forge process is reheated suitably, and the recessed part of both sides is shape | molded in the center hole which has an internal flash between both in the 2nd forge process. At this time, the tooth profile is also formed and forging is performed after carburizing treatment, so the tooth surface portion of the tooth profile meshing with the gear of the other party maintains the depth of the carburized layer and ensures wear resistance, during rotation A carburized layer is thinned at the root portion of the tooth profile that receives impact input, and impact fatigue strength is secured. In the second forging process, the carburized layer on the inner wall portion of the center hole is substantially continuous from one of the center holes to the other of the center holes through the inner beam. Then, by removing the inner beam, the carburized layer is kept well along the inner wall of the center hole that penetrates, and this carburized layer ensures wear resistance and seizure resistance to the shaft inserted into the center hole. Is done.
[0012]
Thus, after carburizing the solid blank, forming a recess in the first forging process, forming the recess into a center hole with an inner flash in the second forging process, and then removing the inner flash. In addition to ensuring an appropriate carburized layer on the tooth surface portion and the tooth root portion, the carburized layer on the inner wall portion of the center hole is maintained well. In addition, after removing the inner beam, the gear is subjected to quenching, shot blasting, machining, and the like.
[0013]
In the gear manufacturing method according to claim 2 of the present invention, in the first forging step, by forming conical concave portions with acute angles at the apex angles at the portions corresponding to both sides of the center hole of the blank, Cutting of the carburized layer at the top is more reliably prevented.
[0014]
In the gear manufacturing method according to claim 3 of the present invention, after removing the inner beam of the center hole, an annular recess is formed on the inner wall of the center hole including the removed portion of the inner beam. Even if the carburized layer breakage occurs in the removed portion of the beam, the carburized layer cut portion is removed along with the formation of the annular recess, and the contact between the carburized layer cut portion and the shaft is eliminated, and the shaft The carburized layer is kept well on the inner wall of the center hole that comes into contact with the center hole.
[0017]
【The invention's effect】
According to the gear manufacturing method according to claim 1 of the present invention, a solid blank is subjected to carburizing treatment to form a conical recess, and the recess is formed into a center hole with an inner flash. Since the inner flash is removed after the second forging step, the step of forming the center hole in advance in the solid blank is not necessary, and the number of man-hours and the manufacturing cost can be reduced. In addition, since forging is performed after carburizing treatment, the tooth surface portion of the tooth profile that meshes with the other gear can maintain the carburized layer depth to ensure wear resistance, and the tooth profile tooth that receives impact input during rotation. The carburized layer can be thinned at the base to ensure impact fatigue strength. In particular, the carburized layer is formed on the inner wall of the center hole that contacts the shaft inserted into the center hole by the above-described simple process. It is possible to ensure good wear resistance and seizure resistance. Furthermore, for example, when manufacturing a gear for use in a differential of an automobile, it is possible to obtain a gear that has sufficient characteristics for each part of the tooth profile as described above and can sufficiently cope with high output of the power transmission system. it can.
[0018]
According to the gear manufacturing method according to claim 2 of the present invention, the same effect as in claim 1 can be obtained, and a conical recess having an acute angle in the first forging step is formed. Therefore, it is possible to more reliably prevent the carburized layer from being cut off at the top of the concave portion, to keep the carburized layer at the inner wall portion of the center hole better, and to further improve wear resistance and seizure resistance. .
[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 an annular recess is formed on the inner wall of the center hole including the inner-burr removal portion. Therefore, even if the carburized layer breakage occurs in the inner flash removal part, the carburized layer cut part can be removed to completely eliminate the contact with the shaft, and the center hole contacting the shaft can be removed. The carburized layer can be kept well on the inner wall, and further improvement in wear resistance and seizure resistance can be realized. Further, since the portion of the carburized layer cut is removed by the annular recess, it is possible to form a thick inner beam while allowing the occurrence of a certain amount of carburized layer cut without using a higher pressure forging die, Thereby, the flow of the material with respect to the mold surface is relaxed, and the life of the mold can be improved.
[0022]
【Example】
1 and 3 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 (e) 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.
[0023]
In order to manufacture the above gear G, a solid blank B which is a cylindrical body as shown in FIG. 1A is used, and the blank B is subjected to carburizing treatment. Thereby, as shown in FIG.1 (b), the carburized layer C of the substantially uniform depth is formed in the blank B as a whole. Next, blank B is heated to about 900-1100 degreeC, and this blank B is shape | molded by the 1st forge process shown in FIG.1 (c).
[0024]
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 a conical tip having an acute apex angle. In the first forging step, the tooth profile A and the back sphere R are primarily formed using the forging die described above, and the punches 1 and 3 form a conical shape at portions corresponding to both sides of the center hole H of the blank B. The concave portions 7 and 8 are molded to obtain a primary molded body F1 shown in FIG.
[0025]
Thus, in the first forging step, by forming the conical recesses 6 and 7 having an acute apex angle, the carburized layer C of the recesses 7 and 8 is not cut at the tops of the recesses 7 and 8. It will be in the state which follows the recessed parts 7 and 8. FIG. Further, in the tooth profile A, since forging is performed after the carburizing treatment, similarly to the tooth profile having the ideal carburized layer C shown in FIG. The depth of the carburized layer C of the tooth surface part (Ga) is maintained, and the carburized layer C of the tooth base part (Gb) becomes thin.
[0026]
Next, the primary molded body F1 molded as described above is appropriately reheated and then molded in the second forging step shown in FIG.
[0027]
In the second forging step, a forging die as shown in FIG. 3B 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. Are formed in the center holes 7H and 8H to obtain a secondary molded body F2 shown in FIG.
[0028]
In this way, in the second forging process, by forming the recesses 7 and 8 formed in the first forging process into the center holes 7H and 8H with the inner flash V, the carburized layer C on the inner wall portion of the center holes 7H and 8H. Is substantially continuous from one center hole 7H through the inner beam V to the other center hole 8H. In the tooth profile A, similarly to the first forging step, the carburized layer C of the tooth surface portion and the tooth root portion is maintained at a predetermined thickness.
[0029]
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 (f), then shot blasted (B2), and further subjected to appropriate machining (B3).
[0030]
The gear G manufactured in this manner has a tooth surface portion of the tooth profile A meshing with the gear of the other side, the depth of the carburized layer C is maintained and wear resistance is ensured, and the tooth profile A of the tooth profile A that receives an impact input during rotation. The carburized layer is thinned at the root portion to ensure impact fatigue strength, and the carburized layer C is well maintained on the inner wall portion of the center hole that contacts the shaft inserted into the inner wall portion of the center hole. As a result, the wear resistance and seizure resistance are ensured, and the gears used in the differential gears of automobiles can be fully compatible with the high output of the power transmission system by providing the characteristics of each part. Yes.
[0031]
Here, in the gear G manufactured as described above, after removing the inner beam V of the center hole H, as shown in FIG. 4, the inner wall of the center hole H including the removed portion of the inner beam is machined. An annular recess D can be formed.
[0032]
The formation of the annular recess D is more effective when a carburized layer break occurs in the removal portion of the inner beam in the second forging step, and the carburized layer cut portion is removed along with the formation of the annular recess D. The contact between the carburized layer cut portion and the shaft is eliminated, and the carburized layer C is well maintained on the inner wall portion of the center hole H that contacts the shaft.
[0033]
In addition, the fact that the portion of the carburized layer cut can be removed by forming the annular recess D means, in other words, that the inner flash can be formed thick while allowing a certain amount of carburized layer cut to occur. When forming the inner beam thickly, it is not necessary to use a higher pressure forging die, and in the forging die, the flow of material to the die surface is relaxed, thereby improving the life of the die.
[0034]
2 and FIG. 5 is a diagram illustrating an Example of the method for manufacturing the tooth wheel. Incidentally, the gear G to produce the reference example of this is the same as that of the previous embodiment, which has a tooth form A extending from the small diameter portion to the large diameter portion has a center hole H along the axial direction, The large diameter side has a back spherical surface R.
[0035]
In order to manufacture the gear G, a hollow blank B which is a cylindrical body as shown in FIG. 2A is used, and the blank B is subjected to carburizing treatment. Thereby, as shown in FIG.2 (b), in the blank B, the carburized layer C of the substantially uniform depth is formed in the whole outer surface and the inner surface of the hollow part Ho. Next, blank B is heated to about 900-1100 degreeC, and this blank B is shape | molded by the forge process shown in FIG.2 (c).
[0036]
In the forging process, a forging die as shown in FIG. The forging die includes an upper die 22 having a mandrel 21 inserted in the center, and a lower die 24 having a receiving hole 23 for the mandrel 21 in the center. The upper die 22 has a molded part 25 tooth profile A of the back sphere R, and the lower 24 die has a molded part 26 of the tooth profile A. Then, in the forging step, as shown in FIG. 5B, the blank B is forged with the mandrel 21 inserted into the hollow portion Ho of the blank B to obtain the gear G shown in FIG. . Thereafter, the gear G is quenched (block B1) as shown in FIG. 2 (e), then shot blasted (B2), and further subjected to appropriate machining (B3).
[0037]
Thus, even if the manufacturing method of the gear in the reference example of this, since performing forging after carburization, to the tooth surface of the tooth, the wear resistance is maintained the depth of the carburized layer C is ensured, The carburized layer C is thinned at the root portion of the tooth profile, and impact fatigue strength is ensured. Further, in the forging process, the hollow portion Ho of the blank B becomes the center hole H. At this time, since the mandrel 21 is inserted into the hollow portion Ho, the center hole H does not generate an inner flash. An initial good carburized layer C is maintained on the inner wall, and the carburized layer C ensures wear resistance and seizure resistance. Therefore, in the case of a gear used for an automobile differential device, it has characteristics for each part and can sufficiently cope with a high output of the power transmission system.
[0038]
Furthermore, in the manufacturing method of the above Symbol Reference Example gears, it is more desirable to use a closed forging die in the forging process. In other words, the use of the mandrel 21 prevents the occurrence of internal flash in the center hole H, and in addition to this, the use of a closed forging die also prevents the occurrence of flash on the outside of the gear. The work for removing the outer flash is not required at all, and the material yield is also improved, thereby reducing the number of man-hours and the manufacturing cost.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view (a) to (e) and a block diagram (f) illustrating a manufacturing process in an embodiment of a gear manufacturing method according to the present invention.
[Figure 2] In one Example of the manufacturing method of the tooth wheel is a sectional view for explaining a manufacturing process (a) ~ (d) and block diagram (e).
3 is a cross-sectional view (a) showing an example of a forging die used in a first forging step of the gear manufacturing method shown in FIG. 1, and a cross-sectional view (b) showing an example of a forging die used in a second forging step. .
FIG. 4 is a cross-sectional view illustrating a gear having an annular recess formed in a center hole.
5 is a view showing an example of a forging die used in the forging step of the gear manufacturing method shown in FIG. 2, and is a cross-sectional view (a) showing a die open state and a cross-sectional view (b) showing a die closed state. .
FIG. 6 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 by carburizing the base of the tooth after the tooth formation (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 D Annular recess G Gear H Center hole
V inner beam 7 8 Recess 7H 8H Center hole before removing inner beam

Claims (3)

 When manufacturing a gear having a center hole, after carburizing the solid blank, in the first forging step, conical recesses are formed in portions corresponding to both sides of the center hole of the blank, and the second forging step A method of manufacturing a gear, comprising: forming recesses on both sides into a center hole having an inner beam between the two, and then removing the inner beam of the center hole.  The gear manufacturing method according to claim 1, wherein the recess formed in the first forging step has a conical shape with an acute angle.  3. The method of manufacturing a gear according to claim 1, wherein after the inner beam of the center hole is removed, an annular recess is formed on the inner wall of the center hole including the inner beam removed portion.

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