JPH04135034A - Method for forming internal gear - Google Patents

Abstract

PURPOSE:To improve the accuracy of a between-ball diameter by reducing the diameter of a cylindrical, forming plural teeth on its inner peripheral surface, then, pressing it into a die hole as it is fitted to a punch. CONSTITUTION:The cylindrical stock 22 is fitted to the punch 12. The descending amount of a composite section blanking die 42 is increased gradually and the surface 28 of a forming die 20 is pressed by a tapered surface 38 to cress out the forming die 20. The forming die 20 presses the cylindrical stock 22 by a fixed amount at every rise and fall of an upper die 36 to work the stock 22. While the upper die 36 rises, the punch 12 and the cylindrical stock 22 are rotated by a motor 17 to pressurize all the parts of the outer peripheral surface of the cylindrical stock 22. After about 60% of a working allowance is formed, an extruding device 30 is actuated and the cylindrical stock 22 is pressed into a die 64 as the cylindrical stock 22 is fitted to the punch 12. At the same time that the outer peripheral surface of the cylindrical stock 22 is finished to a prescribed dimension, the remainder of the inner teeth is formed. A gear having a high accuracy between ball diameter can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for forming an inner gear, and particularly to improving the accuracy of the between-ball diameter of an inner gear.

BACKGROUND OF THE INVENTION One of the methods for forming a gear having a plurality of teeth on its inner circumferential surface and a cylindrical outer circumferential surface is disclosed in Japanese Patent Application No. 1-265860. In this method, a cylindrical material is fitted onto a punch that has a tooth pattern corresponding to the teeth of a punching gear on its outer peripheral surface, and is movable in the radial direction of the punch, and the surface on the punch side is attached to the outer peripheral surface of the punching gear. The diameter of a cylindrical material is reduced using a plurality of molds having a concave surface approximately corresponding to the diameter of the cylindrical material, and a plurality of teeth are formed on the inner circumferential surface of the cylindrical material. The diameter reduction of the cylindrical material is
This is done gradually by increasing the amount of approach of the mold to the punch while repeating multiple times that the mold approaches the punch, presses the cylindrical material, and then moves away. Alternatively, the mold rotates and the portion of the outer peripheral surface of the cylindrical material corresponding to the gap between adjacent molds changes, so that the entire outer peripheral surface of the material is pressed uniformly.

Therefore, the degree of adhesion of the inner circumferential surface of the cylindrical material to the punch is improved, and the stress distribution within the material becomes uniform, improving the dimensional accuracy of the gear as a product. In addition, since the diameter of the material is gradually reduced and the part of the outer peripheral surface of the cylindrical material that corresponds to the gap between adjacent molds changes, it is possible to form gears with relatively large teeth while avoiding the generation of burrs. can do. Further, since the outer peripheral surface of the cylindrical material is uniformly pressed by the concave surface of each mold, the outer peripheral surface of the material is molded into a substantially cylindrical shape.

Problems to be Solved by the Invention However, the gear formed by this molding method has a problem in that the accuracy of the between-ball diameter (the same applies to the between-bin diameter) is insufficient.

For example, as shown in Figure 4, when we measured the gear after molding, we found that the between-ball diameter of the part pressed by the center of each mold at the end of the molding process and the pressure applied by the vicinity of the dividing part of each mold. There is a difference of about 0.16 mm between the ball diameters of the parts that are pressed, and there is also variation in the between ball diameters of the parts that are pressed near the dividing parts of the mold, especially among the gears. was occurring. Since the pressing force of the cylindrical material is different between the center of the mold and the area near the dividing part, at the end of the molding process, there will be a difference in the diameter of the between balls depending on which part of the mold is pressed. .

In view of this problem, the present invention has been made with the object of providing a method for improving the accuracy of the between-ball diameter of a gear.

Means for Solving the Problems And the gist of the present invention is to provide a cylindrical material whose diameter has been reduced by the method of the above application, so that the material has a radius smaller than the maximum radius of its outer circumferential surface while still fitted with a punch. The purpose is to improve the accuracy of the diameter of the between balls by pushing them into the circular die hole.

A cylindrical material may be pushed into a circular die hole with almost 100% of the machining allowance on the outer circumferential surface processed by the mold, or when 60% or more of the machining allowance on the outer peripheral surface has been processed but not yet completed. You can also push it in.

Function: In the method of the present invention, the mold approaches the punch, presses the cylindrical material, and then moves away, which is repeated multiple times to increase the amount of approach to the punch, gradually reducing the diameter of the material and causing the gear to be removed. Shape. Thereafter, the cylindrical material whose diameter has been reduced by forming the inner gear is pushed into the circular die hole while being fitted with the punch, and the outer peripheral surface is finished and formed. This improves the dimensional accuracy of the outer circumferential surface of the cylindrical material and also improves the accuracy of the between-ball diameter.

The machining allowance for the outer peripheral surface of the cylindrical material using a mold is approximately 10%.
After processing 0%, when pressing into a circular die hole whose radius is smaller than the maximum radius of the outer circumference and larger than the minimum radius, the part of the outer circumference with a large radius, that is, the part pressed near the dividing part of the mold. Since a compressive force is intensively applied to and the diameter of the between ball is reduced in that portion, variations in the diameter of the between ball depending on the location are reduced, and the dimensional accuracy of the diameter of the between ball is improved.

On the other hand, when almost 100% of the cylindrical material is not processed using a mold, and the remaining processing is performed by pushing it into a circular die hole with a radius smaller than the minimum radius of the outer peripheral surface,
Compressive force is applied almost uniformly to the entire circumference of the cylindrical material, and the inner peripheral surface is pressed against the punch almost uniformly over the entire circumference, improving the dimensional accuracy of the between-ball diameter.

In this case, the larger the difference between the minimum radius of the cylindrical material after being formed by the mold and the radius of the circular die hole, the stronger and more uniformly the cylindrical material will be pressed against the punch over its entire circumference. It is difficult to form a gear by simply pushing it into a circular die hole without using a mold at all, due to the strength of the punch teeth.
It is desirable to process at least about 60% of the machining allowance on the outer circumferential surface using a mold, and then push it into a circular die hole for finishing.

Effects of the Invention Therefore, according to the present invention, it is possible to obtain a gear with high accuracy in the diameter of the between balls.

Further, since a die for extrusion molding may be provided in a conventional press device, an increase in device cost can be avoided.

If the forming of the inner gear is not yet completed and it is pushed into the die hole, the remaining part of the forming of the inner gear is performed simultaneously with the finishing of the outer circumferential surface. Therefore, the number of times the cylindrical material is pressed by the mold can be reduced, and the processing time for gears can be shortened. Furthermore, the number of strokes and movements of the ram and latch mold for operating the mold can be reduced compared to the conventional method, so the entire device can be downsized. Furthermore, since the bending stress applied to the punch can be reduced compared to when finishing by pressing the outer circumferential surface with a mold, the life of the mold can be improved.

EXAMPLE Hereinafter, a method according to an embodiment of the present invention will be explained in detail based on the drawings.

FIG. 1 is a diagram showing the main parts of a press device used in the method of this embodiment. In the figure, numeral 10 indicates a lower mold;
This lower die 10 is attached to a bolster (not shown). A mandrel punch (hereinafter simply referred to as punch) 12 is attached to the center of the lower die 10. punch 1
2 has a circular cross section, and tooth patterns 14 corresponding to a plurality of teeth to be formed on the inner peripheral surface of the helical gear to be molded are formed on its outer peripheral surface. A shaft member 15 extends from the lower end of the punch 12. The shaft member 15 has a spline shaft portion 16, and is fitted into a spline hole 19 formed in a rotating shaft 18 of a motor 17 fixed to the lower mold 10. Therefore, the rotation of the rotating shaft 18 due to the drive of the motor 17 is transmitted to the punch 12 via the shaft member 15, and the punch 12 is rotated. Further, the punch 12 can move up and down by sliding the spline shaft portion 16 in the spline hole 19 in the axial direction.

A plurality of molds 20 are disposed around the outer periphery of the punch 12 and are movable in the radial direction of the punch 12.

The surface of the 12 punches of each mold 20 is a pressing surface 24 that approaches the punch 12 and presses the cylindrical material 22 fitted to the punch 12. As shown in FIG. 3, these pressing surfaces 24 consist of a partial cylindrical surface 25 at the center and relief surfaces 26 at both sides. The partial cylindrical surface 25 has a radius of curvature approximately equal to the outer peripheral surface of the helical gear, and the relief surfaces 26 are planes extending tangentially from both ends of the partial cylindrical surface. It is desirable that these partial cylindrical surface 25 and relief surface 26 be formed to satisfy the condition of equation (1).

However, θ: Central angle of the pressing surface 24 θ: Central angle of the partial cylindrical surface 25 Also, the surface 28 of the mold 20 opposite to the pressing surface 24 forms a part of the Taber surface where the diameter of the lower part increases. It is said to be the shape. Although not shown, these molds 20 are pressed against the punch 1 by a biasing member made of an elastic material such as a steel spring or rubber.
It is urged in a direction away from the outer circumferential surface of No. 2.

Further, an extrusion device 30 is disposed below the punch 12 in the lower die IO. The extrusion device 30 includes a cylindrical extrusion member 32 fitted to the outer peripheral surface of the punch 12, and a hydraulic cylinder (not shown) that moves the extrusion member 32 up and down via a rod 34. The hydraulic cylinder is provided on a member below the lower mold 10, and is always connected to the rod 3.
4 is retracted into the cylinder, the pushing member 32 is located in an inactive position near the lower end of the punch 12 as shown. In this inactive position, the pusher member 32
The upper end surface supports the cylindrical material 22 fitted into the punch 12, and when forming is completed, the rod 34 is extended by the operation of the hydraulic cylinder, and the extrusion member 32 is raised to remove the gear after forming. Remove it from Punch 12. The extrusion member 32 has a slightly smaller diameter at the upper part of the outer circumferential surface so as not to interfere with the pressing surface 24 of the mold 20 during molding of the cylindrical material 22.

An upper die 36 is disposed above the punch 2. The upper mold 36 includes a latch mold 42. which is provided with a latch portion 40 having a tapered surface 38 corresponding to the surface 28 of the mold 20. It consists of a support mold 44 above a latch mold 42, etc., and is repeatedly raised and lowered with a constant stroke by a ram (not shown). The lower surface of the support mold 44 is an inclined surface 47, and the inclined surface 47
A wedge member 48 is disposed between the upper surface of the latch mold 42 and the upper surface of the latch mold 42 . The wedge member 48 is movable in a direction perpendicular to the moving direction of the upper mold 36 by a hydraulic cylinder 50, and the surface of the supporting mold 44 is moved from the tip side toward the cylinder 50 side in correspondence with the inclined surface 47. It is an inclined surface 49 that rises. Therefore, by gradually advancing the wedge member 48 with each stroke of the ram, the amount by which the latch mold 42 is lowered is gradually increased. Note that the latch mold 42 is guided by a guide (not shown) so that it cannot move relative to the support mold 44 in the horizontal direction, but can move relative to the support mold 44 in the vertical direction, and
In order to prevent a gap from forming between the wedge member 48 and the latch mold 42, the wedge member 48 is constantly pulled up by a lifting plate 54 which is urged upward by a hydraulic cylinder 52.

The above support type 44. Through holes 56, 58 and 60 are formed in the wedge member 48 and the latch mold 42, respectively, and a presser mold 61 is disposed through these holes. The presser die 61 is the above-mentioned latch die, 42. It is designed to be raised and lowered by a hydraulic cylinder (not shown) that is separate from the ram that supports the support mold 44 and the like, and is lowered during molding so that it comes into contact with the upper end surface of the punch 12 and is molded together with the extrusion member 32. This prevents the end face of the gear from bulging in the vertical direction. The presser die 61 reaches the lower end before the latch die 42 acts on the mold 20 by the operation of the hydraulic cylinder, and starts rising after the latch die 42 is separated from the mold 20. Furthermore, another hydraulic cylinder (not shown) is disposed within the presser die 61, and a piston rod 62 (see FIG. 2) can protrude and retract from the tip surface of the presser die 61. . piston rod 6
The diameter of the tip surface of the punch 2 is smaller than the diameter of the punch 12. Note that the through hole 58 of the wedge member 48 is made long so that the pressing die 61 and the wedge member 48 do not interfere with each other due to the movement of the wedge member 48.

A die 64 is disposed inside the shifting die 42 above the shifting section 40 . A circular die hole 66 concentric with the punch 12 is formed in the center of the die 64. The inner diameter of the die hole 66 is equal to the outer diameter of the gear after molding, and is smaller than the minimum radius of the outer peripheral surface of the cylindrical material 22 when the diameter is reduced by pressing the mold 20. have. Further, the opening of the punch 12 of the die hole 66 allows the cylindrical material 22 to be inserted into the die hole 66.
A tapered surface 68 is used to guide the user.

The method for forming helical gears will be explained below.

First, the extrusion member 32 is positioned at the lowered end, a non-operating position, and the upper mold 36 is raised.

In this state, the cylindrical material 22 is fitted into the punch 12, and the presser mold 61 is lowered to come into contact with the punch 12. At this time, the piston rod 62 is in a retracted state within the holding die 61.

Next, by lowering the upper die 36, the tapered surface 38 of the latch portion 40 of the latch die 42 moves the mold 20 into the punch 12.
approach. During this first stroke, the wedge member 4
8 is positioned at the retreat end, and from the second stroke, the wedge member 48 is gradually advanced to gradually increase the amount of descent of the latch mold 42 at the bottom dead center of the upper mold 36. Along with this, the smaller diameter portion of the tapered surface 38 engages with the surface 28 of the mold 20 and pushes out the mold 20, so the amount of approach of the mold 20 to the punch 12 gradually increases, causing the upper mold 36 to move closer to the punch 12. The mold 20 presses the cylindrical material 22 by a certain amount each time it goes up and down, and the material 2
Process 2. Further, while the upper die 36 is being raised, the latch die 42 is separated from the forming die 20, the forming die 20 is separated from the punch 12 by the urging force of the urging member, and the presser die 61 is raised to move the punch 12 and Cylindrical material 2
separated from 2. Therefore, while the upper mold 36 is rising, the punch 12 can be rotated, and for example, by rotating the punch 12 by half an angle of the central angle corresponding to each mold 20, 20 is changed so that all parts of the outer peripheral surface of the cylindrical material 22 are pressed, and each part of the outer peripheral surface is not pressed only by the same part of the same mold 20. do it like this.

At this time, in the initial stage of processing, the pressing surface 2 of the mold 20
The portion near the boundary between the partial cylindrical surface 25 and the relief surface 26 in No. 4 presses the outer peripheral surface of the cylindrical material 22, but since the partial cylindrical surface 25 and the relief surface 26 are smoothly continuous, the cylindrical Both sides of the partial cylindrical surface 25 bite into the outer circumferential surface of the shaped material 22, preventing unevenness from forming.

The outer diameter of the cylindrical material 22 is from φ144'an to φ137m.
m (outside diameter of the gear is φ132 mm), and when about 60% of the machining allowance has been formed, the rod 34 of the extrusion device 30 is extended with the ram positioned at the bottom dead center. At the same time, the extrusion member 32 is raised with the pressing die 61 in contact with the punch 12, and the cylindrical material 22 is pushed up while being fitted with the punch 12, and the die is pressed along the tapered surface 68 of the die 64. Push into hole 66.

As a result, the outer peripheral surface of the cylindrical material 22 is finished formed into a perfect circle equal to the outer diameter of the gear as a product by the inner peripheral surface of the die hole 66, and the punch 1 of the cylindrical material 22 is
The part on the second side is brought into close contact with the tooth mold 14, and the rest of the tooth is molded. At this time, since the presser die 61 is in contact with the punch 12 and the cylindrical material 22, the cylindrical material 22 is effectively prevented from expanding toward the presser die 61 side.

When the molding is completed, the upper mold 36 is raised while the presser mold 61 and the extrusion member 32 are kept stationary, and the product, the gear, is pulled out from the die hole 66 while being fitted with the punch 12. Next, the piston rod 62 is made to protrude from the presser die 61, and the punch 12 is pushed down by the piston rod 62. Since the inner gear is held between the upper and lower sides by the extrusion member 32 and the press die 61 and is prevented from moving together with the punch 12, only the punch 12 is rotated and lowered, and is separated from the inner gear.

Thereafter, the piston rod 62 is retracted into the presser mold 61, and after the presser mold 61 is raised, the gear on the extrusion member 32 is taken out.

As described above, in this embodiment, after being molded by the mold 20, the cylindrical material 22 is pushed into the die hole 66, so that it is compressed strongly and uniformly from the entire circumference, and the punch 12
Since the ball is brought into close contact with the mold 20, the dimensional accuracy of the between-ball diameter of the tooth is improved compared to when molding is performed only by the mold 20.

In addition, in this embodiment, the cylindrical material 22 with 60% or more of the machining allowance processed is pushed into the die hole 66 and the remaining machining is performed, so the number of times the ram is raised and lowered is small, and the time is shortened. Molding can be done in hours.

However, the cylindrical material 22 is molded into approximately 100% by the mold 20.
% machining, it is possible to finish the outer peripheral surface by pushing it into the die hole 66 having a radius slightly smaller than the minimum radius.Also, if the die hole is at least smaller than the maximum radius, the outer periphery It is possible to improve the roundness of the surface and the accuracy of the between pole diameters.

Further, in this embodiment, another piston rod 62 is provided in the holding die 61 to push down the punch 12 so that the gear can be separated from the punch 12, but the spline shaft of the punch 12 A mechanism is provided to prevent the part 16 from being pulled out by more than a certain amount from the rotating shaft 18, and after the gear and punch 12 are removed from the die hole 66, the extrusion member 32 is further raised to punch the gear. It is also possible to separate it from 12.

In addition, various modifications may be made based on the knowledge of those skilled in the art.

The invention can be practiced in modified forms.

[Brief explanation of drawings]

FIG. 1 is a front cross-sectional view showing the main parts of a press device used for forming a helical gear according to an embodiment of the present invention. FIG. 2 is a partially enlarged front sectional view showing the operating state of the device. FIG. 3 is a partially planar sectional view showing an enlarged molding die of the above device. FIG. 4 is a graph showing the results of measuring between-ball diameters of gears molded by conventional molding methods. 12: Mandrel punch 14: Tooth mold

Claims (1)

[Claims] A method for forming a gear having a plurality of teeth on its inner circumferential surface and a cylindrical outer circumferential surface, the method comprising: forming a gear with a tooth pattern corresponding to the teeth on the outer circumferential surface; The materials are fitted together, and a plurality of molds, which are movable in the radial direction of the punch and whose punch-side surface is a concave surface substantially corresponding to the outer peripheral surface of the inner gear, are gradually brought closer to the punch. While approaching and separating multiple times,
By rotating the punch, the cylindrical material, and the mold relative to each other while the mold is separated from the cylindrical material, and changing the portion of the outer peripheral surface of the cylindrical material that corresponds to the gap between adjacent molds, the cylindrical material can be removed. After reducing the diameter and forming the plurality of teeth on the inner peripheral surface of the cylindrical material, a circular shape having a radius smaller than the maximum radius of the outer peripheral surface of the cylindrical material after the diameter reduction is kept fitted with the punch. A method for forming an inner gear, characterized by improving the diameter accuracy of the between balls by pushing them into a die hole.