JPH0679392A - Gear forging method - Google Patents

Abstract

PURPOSE:To provide a method to forge a spur gear with excellent dimensional accuracy by adding a cold or hot coining process to use a tooth profile whose draft is gentle. CONSTITUTION:A method to forge a tooth profile 41 having a draft 17 through the hot forging consists of the first process, i.e., the hot forging process to form the tooth profile, and the second process where, after completion of the first process, the cold or hot coining is executed by using a tooth profile 141 having a tooth profile surface which is slightly larger than the hot forging tooth profile 41 and whose draft 17 is gentle. The gear forging method also consists of the third process where cold sizing is executed and the product is formed by using the tooth profile which further eliminates the draft 17 for an intermediate product whose draft 17 eliminated by is this second process.

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 spur gears used in, for example, a speed reducer or a differential of an automobile.

[0002]

2. Description of the Related Art Generally, when hot forging is performed, molding is performed so as to match the specifications of a thick gear product, but one mold is hot (for example, a lower mold, the other mold is In order to prevent the shape of the molded intermediate product from collapsing when extracting the intermediate product from the upper mold), the slope that is slightly wider than the size of the planned product called "draft" is one of the molds. It is designed to improve the releasability of the intermediate product from the mold. The term "product" is used to distinguish it from "product". In this case, in the above example, the gear, which is a product, refers to a product that has been finished so that it can be mounted on an automobile, etc., and a product is a product that has been completed by a certain stage, in this case, forged. Refers to the finished gear. Conventionally, in the case of forging the gear of the above example, it is an intermediate product with a large draft and a draft for the cold sizing molding step in the next step, by hot forging, relative to the gear specifications of the product. After molding the gear, punch out the inner diameter of the intermediate product to a small size, then insert a wedge-shaped molding punch into this inner diameter and expand it, and press the excess thickness of the inner diameter toward the tooth profile by cold sizing. Molding
After that, by performing cold coining that presses the outer peripheral surface of the tooth profile in the thickness direction, it is added to the flesh part at the upper end of the tooth profile to finish the product specifications and improve the dimensional accuracy of the tooth profile. Is known (see Japanese Patent Application Laid-Open No. 59-39442, "Method for manufacturing gears").

[0003]

According to the above conventional method,
At the time of hot forging, a draft is provided to improve the releasability. However, when a gear having a large tooth width is forged, this draft remains in the product after the finish cold sizing. As a result, the gear tooth error, the tooth profile error, etc. of the gear as a product become large, and the precision of the gear as a product is reduced. Therefore, the tooth profile of the forged product is machined to make it a product with the expected accuracy. However, since the machining of the tooth profile is complicated and requires high machining accuracy, the cost of the gear product obtained is high. Further, in the method of manufacturing a gear of the above-mentioned conventional method, it is necessary that the inner diameter be drilled in advance, and if it is not drilled, there is no place to insert the cold sizing molding punch, so that there is no excess of the inner diameter portion. Since it is not possible to send the meat to the tooth profile and form it, in this conventional method, in the case of cold sizing a gear in which the boss portion and the tooth profile portion are constricted (with a web portion) in the axial cross section, Even if cold sizing of the surplus of the inner diameter in the part is restricted, the movement of the meat is restricted at the web part, and there is a risk that the surplus may not reach the tip of the tooth profile in the tooth width direction and the meat may be lacking. there were. Further, in the above-mentioned conventional method, it is necessary to leave the extra thickness calculated in advance in the inner diameter portion, and when this calculation is insufficient,
The tooth profile becomes defective and becomes a defective product. Furthermore, in the above-mentioned conventional method, the excess thickness of the inner diameter in the boss portion is squeezed with a cold sizing molding punch, but in this case, depending on the lubricant or the coating amount thereof, seizure occurs and the punch cannot be used. Each time, the mold has to be renewed, which increases the cost of the manufactured product.

[0004]

The present invention has been made in order to solve the problems of the above-mentioned conventional method, and the gist thereof is as follows. That is, in the method of forging a tooth profile having a draft by hot forging, in the hot forging step of the tooth forming shape and after the completion of this first step, the draft is slightly larger than the hot forging tooth profile and the draft is loosened. A second step of coining cold or warm using a tooth profile having a tooth profile surface, and a tooth profile surface having a draft angle removed from an intermediate product having a draft angle made gentle by the second step And a third step of forming a product by cold sizing using a tooth mold having the above. According to the present invention, in the middle of the above-mentioned conventional hot-forging step of forming a tooth and the step of forming a product by performing cold sizing, "a slightly larger size than the hot-forging tooth profile and the draft is loosened. It has the greatest feature in that "a step of performing coining in cold or warm by using a tooth mold having a tooth profile surface" is inserted. Generally, coining is not only intended to correct the deformation, but also to correct the unevenness of the wall thickness in the pressing direction to improve the accuracy of the forged product. However, here, instead of correcting uneven thickness, the meat is moved in the width direction of the product (in the direction perpendicular to the press direction), molded (with a reduced draft), and the dimensional accuracy is improved. I will point to something that improves. Therefore, the prior art (Japanese Patent Laid-Open No. 59-39442)
No. "Gear manufacturing method"), the technology indicated as "coining" (lines 8 to 9 in the upper right part of page 2 of the same publication, FIG. ), And FIG. 3), even if the excess thickness is moved by a press in the thickness direction to improve the dimensional accuracy, it is not molding (relaxing the draft). The term "coining" as used in the present invention corresponds to the term "coining" generally referred to in
is not. Note that the difference between the two "coining" effects will be described later. The "sizing" referred to here is not a special one, but is a generally used concept, in the outer shape or the inner shape in the same direction as the pressing direction,
It is intended to improve the dimensional accuracy in the direction perpendicular to the pressing direction by passing a pre-applied surplus through a mold or a punch through an inner shape (inner hole). Therefore, in the prior art (Japanese Patent Laid-Open No. 59-39442 “Gear manufacturing method”), leaving a surplus in the inner diameter and expanding it with a punch is called “sizing”.
It corresponds to "sizing" here.

[0005]

According to the present invention, in the method for forging a tooth profile having a draft by hot forging, first, the first step for hot forging a tooth forming shape is the same as the conventional method. This is a process to be performed, and the high
The standard length round bar steel billet heated to 0 ° C. is continuously processed through the first rough land process, the second rough ground process and the finishing process to the internal deburring process. In this case, the finishing process is forged with a draft having a draft. Therefore, the mold releasability is good, and the tooth profile formed in the finishing process or the like is preserved even if it is released by the knock-out mold. Further, since it is carried out hot, it is possible to easily form a tooth profile having large irregularities. Next, the intermediate product after the completion of the first process is subjected to a heat treatment process for normalizing and a shot blasting process for removing the scale on the surface of the processed product as in the conventional process, and then the tooth Go through the process of cutting burrs of width. The intermediate product that has undergone such a step enters the second step of the present invention. This second step is the greatest feature of the present invention. In this case, similarly to the conventional method, a lubricant coating or bonder treatment step is further performed in advance. The intermediate product that has undergone this step is cold coined using a tooth mold having a tooth profile surface slightly larger than the finish hot forging tooth profile of the first step and having a gentle draft. By the second step, the draft of the intermediate product is made gentle. Next, the third step is performed. In this step, the coined intermediate product is subjected to cold sizing using a tooth mold having a tooth profile surface with no draft, to mold the product. Therefore, in the product of the conventional method, the draft is attempted to be removed in the cold sizing step, but a small amount remains, and sufficient gear accuracy cannot be obtained, and the cutting process is performed. Since the product of the present invention is subjected to coining for loosening the draft in the second step, no such draft remains, and therefore, even if the cutting process for removing the draft is not performed,
Sufficient gear accuracy can be obtained. Although the second and subsequent steps are described as cold in the above description, the description is omitted because the intermediate product is the same except for the step of applying the lubricant or the bonder treatment when it is warm.

[0006]

[Effect] The present invention, as described above, has a
Although the number of processes is increased by one compared with the conventional method, it is much more efficient than the removal of the residual draft by cutting, and the production cost can be reduced, from the viewpoint of the entire process of manufacturing gear products. In addition, since coining in the second step is performed cold or warm, the product is molded by the knock-out mold when it is separated from the mold even if the draft is less gentle than in the first step. The tooth profile is not deformed.
Further, in the method of manufacturing a gear of the above-mentioned conventional method, it is necessary that the inner diameter be drilled in advance, and if it is not drilled, there is no place to insert the cold sizing molding punch, so that there is no excess of the inner diameter portion. According to the method of the present invention, it is not possible to insert the forming punch into a gear that has not been pre-drilled, so that it is possible to form the meat by cold coining, while the meat cannot be formed by sending it to the tooth profile. It is also possible. Further, in the conventional method, in the case of cold sizing a gear having a boss portion and a tooth profile portion (with a web portion) in an axial cross section, the excess thickness of the inner diameter of the boss portion is cold sized. However, since the movement of the meat is hindered by this web portion, there was a risk that the excess meat would not turn around even to the tip portion in the tooth width direction of the tooth profile, but according to the method of the present invention. Even in the case of such a constricted one (gear with a web part), the meat moves regardless of the web part that hinders the movement of the meat, so that the excess meat is sufficiently rotated by cold coining to each tip in the tooth width direction. As a result, a product having a tooth profile with high dimensional accuracy can be obtained. Further, in the conventional method, it is necessary to leave a calculated excess thickness in the inner diameter portion in advance, and when this calculation is insufficient, the tooth profile becomes defective and becomes a defective product. According to this, it is possible to obtain the necessary extra thickness by cold coining just by setting the tooth width a little thicker in advance, and even if there is a design error, adjustment can be made within the range of variation in the cutting allowance in the thickness direction. It is possible. Furthermore, in the above-mentioned conventional method, the excess thickness of the inner diameter in the boss portion is squeezed with a cold-sizing molding punch, but in this case, depending on the amount of the lubricant or its application, seizure occurs and the punch can be used. However, according to the method of the present invention, seizure of the punch to be inserted does not occur because the punch is not used. Therefore, the upper and lower dies and the side die for tooth profile (tooth die) have a long life and the production cost is low. There is an effect to finish.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, one embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a partially omitted axial sectional view showing the shape of a gear product to be manufactured in this embodiment. 1
Is a gear that is a product. 2 is a boss portion, 3 is a web portion, 4 is a tooth profile, and 5 is an inner diameter. Also, this gear 1
The tooth width 6 is 40 mm, the diameter 7 is 120 mm, and the angle R formed by the tooth profile 4 with the diameter direction of the gear 1 is 90 °. The base material is JIS-SC with a diameter of 65 mm and a length of 117 mm.
It is a standard length round bar steel piece of R20. This is inserted into a high-frequency heating furnace and taken out when the temperature is raised to 1200 ° C. in 1 to 2 minutes. The first barren forging step and then the second barren forging step are successively applied to the round bar steel piece. Figure 2
The left half and the right half are vertical sectional views showing the hot forging step before and after the finishing step. The intermediate product 11 formed in the second rough forging step is inserted into the blank 15 formed by the lower die 12 for forging, the tooth die 14 and the knock-out die 16 in the finishing step, and the upper die 13 Press,
As a result of finishing forging, the tooth profile 41 closely attached to the tooth model 14
A finished forged product (intermediate product 111) was obtained. Tooth profile 41 of the finished forged gear (intermediate product 111) at this time
Is the angle R1 with the diameter direction of the gear (intermediate product 111)
Was 89 ° 30 '. As described above, the draft 17
Since the tooth mold 14 provided with is used, the intermediate product 111 is
Releasability is good even in the hot state, and even if it is pushed up by the knock-out mold 16, the tooth profile 41 molded up to this point
Is never transformed. Subsequently to this, in the inner deburring step, the bottom portion 51 (the lower center portion of the right half in FIG. 2) of the inner diameter 5 of the gear 111 is removed. next,
After finishing the first step, the intermediate product 111 has a tooth width after a heat treatment step of normalizing and a shot blasting step of removing the scale on the surface of the processed article, as in the conventional method. 6 burr 61 (the upper right part in FIG. 2)
To cut. Next, the intermediate product 112 that has undergone such steps is
Bonding process is performed in advance. The left half and the right half of FIG. 1 are longitudinal sectional views showing before and after cold coining.
In FIG. 1, this intermediate product 112 is a tooth mold 14 having a tooth profile surface slightly larger than the hot forged tooth profile 41 of the intermediate product 112 of the first step and having a tooth drafting surface with a loosened draft 17.
It is put in a blank 151 formed by the lower die 121, the lower die 121 and the knock-out die 161, and is pressed by the upper die 131 to perform cold coining. As a result, the tooth profile 42 of the intermediate product 113 is modified more loosely than the draft 17. The left half and the right half of FIG. 3 are views showing before and after cold sizing. Intermediate product 113 that has undergone the cold coining process described above
On the other hand, cold sizing is performed. This cold sizing is the same process as the conventional method in that the tooth mold 142 having a tooth profile surface having no draft (the angle formed by the diametrical direction of the gear is at a right angle) is used. The difference is that the intermediate product 113 in which the gradient 17 is loosely modified is inserted. Therefore, product 11 obtained by cold sizing
No. 4, unlike the case of the conventional method, almost no draft 17 remained (see FIG. 5). Also, the upper and lower molds 132,
The seizure does not occur on the 122 and the tooth mold 142 and the life is extended. Conventionally, the residual draft 17 was removed by cutting, but in the present embodiment, the gear component 11
The angle R formed by the diameter 7 of No. 4 and the tooth profile 43 is substantially right angle.
Therefore, it is not necessary to remove the draft 17 by cutting. Further, since the sizing is performed in the cold, the knock-out die 162 does not deform the tooth profile 43 formed so far even when the intermediate product 112 is separated from the tooth profile 142. Therefore, it was far more efficient than the conventional method and the production cost could be reduced.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional explanatory view showing left and right of a center line as a representative view of one embodiment of the present invention showing before and after a coining step.

FIG. 2 is a vertical cross-sectional explanatory view showing the left and right of the center line showing before and after the hot forging step.

FIG. 3 is a vertical cross-sectional explanatory view showing left and right of a center line before and after a cold sizing step.

FIG. 4 is a vertical cross-sectional view showing a shape of a product, with a part thereof omitted.

FIG. 5 is a graph showing the remaining state of the draft of this embodiment.

[Explanation of symbols]

1 Product Gear 2 Boss Part 3 Web Part 4 Tooth Profile 5 Inner Diameter 6 Tooth Width 7 Diameter 11 Intermediate Product 12 Lower Model 13 Upper Model 14 Tooth Model 15 Blank 16 Knock Out Model 17 Draft 41 Tooth Profile 42 Same as 43 Same as above 51 Bottom 61 Burr 111 Intermediate product 112 Same as above 113 Same as above 114 Same as product 121 Lower mold 122 Same as above 131 Same as upper mold 132 Same as above 141 Tooth mold 142 Same as above 151 Blank 152 Same as above 161 Knock-out type 162 Same as above R Angle between the tooth profile 4 of the product gear and the diameter direction of the gear 1 R1 The angle 41 between the tooth profile 41 of the intermediate product 111 after hot forging and the diametrical direction of the gear 111 R2 The tooth profile 42 of the intermediate product 113 after cold coining
Is the angle formed with the diameter direction of the gear 113

Claims (1)

[Claims] 1. A method for forging a tooth profile having a draft by hot forging, comprising a hot forging step of forming a tooth,
After the completion of the first step, a second step of coining in cold or warm by using a tooth profile having a tooth profile surface slightly larger than the hot forged tooth profile and having a gentle draft, By two steps, an intermediate product having a gentle draft is subjected to cold sizing using a tooth mold having a tooth profile surface without a draft to form a finished product.
A method for forging a gear, comprising: