Method for manufacturing helical gear

Abstract

To provide a helical gear having a tooth of a large helix angle or a tooth of a large module value and made of a hard material such as iron, and a method for manufacturing the same.SOLUTION: This method for manufacturing the helical gear comprises a helical gear molding step of molding the helical gear using a mold by pushing a workpiece into the mold by a pushing-in member and holding and twisting the workpiece by a twisting member. In the helical gear molding step, back pressure is applied to the workpiece by a back pressure application unit against the workpiece pushing-in force of the pushing-in member.SELECTED DRAWING: Figure 13

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a helical gear. [Background technology]

[0002] Forward extrusion cold forging for forming helical gears with a helix angle has been known (see, for example, Patent Document 1). In a gear forming die for cold forging, a first die is used to form teeth with a helix angle of 20°, and the formed teeth are then formed into teeth with a helix angle of 30° by a second die. When teeth with predetermined helix angles are formed by the first and second dies, the material from which the teeth are to be formed is rotated according to the respective helix angles of the tooth profile of the first die and the tooth profile of the second die used to form the teeth. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 58-43842 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned conventional cold forging by forward extrusion method, when iron is used as a material, it is practically impossible to form teeth with a large helix angle of 20° or more, let alone 30° or more, or to form teeth with a module of 2 or more. This is because when the helix angle is large, the load on the die becomes too large due to the forming load, and the die is damaged. In addition, when forming teeth with a large module, the load on the die becomes large, and the die is damaged or its lifespan is extremely shortened. In addition, problems arise in that the workpiece is not filled up to the tip of the die teeth, making it impossible to form the desired shape, and the workpiece cannot be released from the die.

[0005] An object of the present invention is to provide a helical gear made of a hard material such as iron and having teeth with a large helix angle and / or a large module value, and a method for manufacturing such a helical gear. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention provides a helical gear manufacturing method which includes a helical gear forming process in which a workpiece (e.g., workpiece W described below) is pressed into a die (e.g., die section 300 described below) by a pressing member (e.g., actuator 230 described below) while the workpiece is held and twisted by a twisting member (e.g., work twisting section 400 described below) to form it into a helical gear by the die, and in the helical gear forming process, back pressure is applied to the workpiece by a back pressure application section (e.g., actuator 460 described below) against the force of the pressing member pressing the workpiece.

[0007] It is also preferable that the back pressure applying portion applies back pressure to the workpiece from a portion of the twisting member that holds the workpiece.

[0008] It is also preferable that the back pressure application portion be applied to the position of the axis of the workpiece in a portion of the twisting member that holds the workpiece.

[0009] In the helical gear forming step, it is preferable that a back pressure applying section applies back pressure to the workpiece at a predetermined timing against a force of the pushing member pushing the workpiece.

[0010] It is also preferable that the back pressure applying unit applies back pressure to the workpiece from before the contact area between the die and the workpiece increases and a peak axial load occurs, until after the peak axial load occurs. It is also preferable that the back pressure applying unit applies a constant back pressure to the workpiece. It is also preferable that the twisting member starts twisting the workpiece at a predetermined timing. Effect of the Invention

[0011] According to the present invention, it is possible to provide a helical gear made of a hard material such as iron and having teeth with a large helix angle or a large module value, and a method for manufacturing such a helical gear. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a front view showing a helical gear according to an embodiment of the present invention. [Diagram 2] FIG. 1 is an explanatory diagram showing fiber flow appearing on a pressed surface of a helical gear according to an embodiment of the present invention. [Diagram 3] FIG. 1 is an explanatory diagram showing fiber flows appearing on a surface opposite to a pressed surface of a helical gear according to an embodiment of the present invention. [Figure 4] FIG. 1 is a diagram showing a gear mechanism including a helical gear according to an embodiment of the present invention. [Diagram 5] FIG. 2 is a schematic side view showing a state in which a workpiece is set in a die portion in a manufacturing method of a helical gear according to an embodiment of the present invention. [Figure 6] FIG. 11 is a schematic side view showing a state in which forming of a helical gear is completed in a manufacturing method of a helical gear according to one embodiment of the present invention. [Figure 7] FIG. 2 is a schematic side view showing a die portion used in the manufacturing method of a helical gear according to one embodiment of the present invention. [Figure 8] FIG. 4 is a schematic side view showing the configuration of a portion that applies back pressure to a workpiece in a manufacturing method for a helical gear according to one embodiment of the present invention. [Figure 9] FIG. 2 is a schematic top view showing a work twisting unit used in the method for manufacturing a helical gear according to one embodiment of the present invention. [Figure 10] 1A to 1C are side views showing a state before and a state after the teeth are formed in a manufacturing method of a helical gear according to an embodiment of the present invention. [Figure 11]1A to 1C are plan views showing a state before and a state after the teeth are formed in a manufacturing method of a helical gear according to an embodiment of the present invention. [Figure 12] 10A to 10C are diagrams illustrating how the teeth extend as they are formed in a manufacturing method for a helical gear according to one embodiment of the present invention. [Figure 13] FIG. 11 is a diagram showing how forming progresses and the shape changes over time in a manufacturing method for a helical gear according to an embodiment of the present invention. [Figure 14] FIG. 4 is a diagram showing the timing of applying a rotational force in a manufacturing method for a helical gear according to one embodiment of the present invention. [Figure 15] FIG. 4 is a diagram illustrating a back pressure applied to a tooth being formed in a manufacturing method for a helical gear according to an embodiment of the present invention. [Figure 16] 1A to 1C are diagrams illustrating an increase in the contact area between a tooth formed in a manufacturing method for a helical gear according to an embodiment of the present invention and a die part. [Figure 17] FIG. 11 is a diagram illustrating a state in which back pressure is applied to teeth being formed in a manufacturing method for a helical gear according to one embodiment of the present invention. [Figure 18] FIG. 4 is a diagram showing the timing of applying back pressure in the manufacturing method of a helical gear according to one embodiment of the present invention. [Figure 19] FIG. 11 is a diagram showing test results of a gear mechanism including a helical gear according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. First, a helical gear 1 according to the present embodiment will be described.

[0014] The helical gear 1 is a helical gear for transmitting power used in a vehicle transmission or the like, and as shown in Fig. 1, has a gear portion 10, a rotating shaft portion 20, and a parallel tooth spline 30. The gear portion 10, the rotating shaft portion 20, and the parallel tooth spline 30 are formed by integrally molding a workpiece W made of structural carbon steel material (SCM material, SCR material, SNCM material, carbon steel, etc.) suitable for gears and having a Vickers hardness of Hv150 or more by cold forging using a forward extrusion method according to a manufacturing method for helical gears described below.

[0015] As shown in FIG. 1, the rotating shaft portion 20 has a cylindrical shape and extends from one end in the longitudinal direction of the helical gear 1 (the upper end shown in FIG. 1) to the other end in the longitudinal direction (the lower end shown in FIG. 1).

[0016] The gear portion 10 is formed in the vicinity of one end of the rotating shaft portion 20 and at a position slightly lower than the one end of the rotating shaft portion 20. As described above, the gear portion 10 and the rotating shaft portion 20 are integrally molded, so the gear portion 10 is not formed in a hollow cylindrical (annular) shape but is formed as a solid shape. The gear portion 10 does not have to be solid. The gear portion 10 has teeth 11 formed on its outer circumferential surface, which have a module value of 2 or more and a helix angle of 20° or more, for example, a helix angle of 31.5° in this embodiment, to form a helical gear 1. The module value is set to 2 or more and the helix angle is set to 20° or more because it is not possible to form a helical gear with a module value of 2 or more and a helix angle of 20° or more in the conventional cold forging by forward extrusion method.

[0017] 2 and 3, fiber flows 131, 132 are formed on the surfaces of teeth 11 of gear section 10. Specifically, on press receiving surface 111, which is one side surface of tooth 11, i.e., the surface where workpiece W is pressed against die 312 of die section 300, which will be described later, in a manufacturing method of helical gears, which will be described later, fiber flows 131 are formed which extend from the base (lower part in FIG. 2), which is the base of tooth 11, to the cutting edge (upper part in FIG. 2), which is the tip of tooth 11, and which extend in a gentle curve in the tooth width direction toward the back side shown in FIG. 2 as tooth 11 becomes higher. On the other side of tooth 1, that is, the anti-press surface 112, i.e., the side of tooth 11 opposite the press receiving surface, as shown in Figure 3, a fiber flow 132 is formed that extends from the base of tooth 11 (lower part in Figure 3), which is the base of tooth 11, to the cutting edge (upper part in Figure 3), which is the tip of tooth 11, and as the height of tooth 11 becomes higher, it gently curves in the tooth width direction toward the front side as shown in Figure 3.

[0018] The parallel tooth spline 30 is formed in the vicinity of the other end (the lower end shown in FIG. 1) of the rotating shaft portion 20, slightly closer to one end than the other end of the rotating shaft portion 20, at a predetermined distance from the gear portion 10 in the axial direction of the rotating shaft portion 20. As described above, the parallel tooth spline 30 and the rotating shaft portion 20 are integrally molded, so the parallel tooth spline 30 is not formed in a hollow cylindrical (annular) shape, but is formed solid. A plurality of parallel teeth 31 parallel to the axis of the rotating shaft portion 20 are formed on the outer circumferential surface of the parallel tooth spline 30.

[0019] As shown in Fig. 4, the gear mechanism including helical gears is configured so that the gear portion 10 and the gear portion 10a mesh with each other in a positional relationship in which the press receiving surface 111 abuts against one side of the tooth 11a that receives a larger load from the tooth 11a of the other gear portion 10a that meshes with the gear portion 10 to the tooth 11. That is, when the other gear portion 10a rotates counterclockwise in Fig. 4, the tooth 11a of the gear portion 10a applies a larger load to the tooth 11 of the gear portion 10 than when the other gear portion 10a rotates clockwise. In this case, the press receiving surface 111 is located on the right side of the tooth 11 of the gear portion 10 that meshes with the gear portion 10a, as indicated by the reference numeral in Fig. 4, and the opposite press surface 112 is located on the left side of the tooth 11 of the gear portion 10 that meshes with the gear portion 10a, as indicated by the reference numeral in Fig. 4.

[0020] Next, a cold forging device 100 used in the manufacturing method of a helical gear will be described. As shown in Fig. 5 etc., the cold forging device 100 has a press unit 200 as a pressing member, a die unit 300, and a work twisting unit 400 as a twisting member. The press unit 200 has a work guide pin 210, a support unit 220, an actuator 230, and an upper guide 240.

[0021] The actuator 230 has a drive shaft 231 that is movable in the vertical direction, and the actuator 230 drives the drive shaft 231 in the vertical direction by being driven. The work guide pin 210 has a cylindrical shape extending in the vertical direction. The lower end of the work guide pin 210 abuts against the upper end of the workpiece W as the workpiece to be formed into the helical gear 1 and presses it downward. The upper end of the work guide pin 210 is fixed to the drive shaft 231 of the actuator 230 via a support part 220. The position of the work guide pin 210 is detected by a position detection sensor (not shown).

[0022] The support part 220 has a base part 221 and a pin fixing part 225. A through hole 232 is formed in the base part 221, and a drive shaft 231 of an actuator 230 passes through the through hole 232. A cylindrical part 223 is provided at a lower opening of the through hole 232 of the base part 221 so as to extend downward. A connection part between an upper end part of the work guide pin 210 and a lower end surface of the drive shaft 231 of the actuator 230 is located inside the cylindrical part 223.

[0023] The pin fixing part 225 is fixed to the lower end of the drive shaft 231 of the actuator 230, which has an axis oriented in the vertical direction and drives in the vertical direction, and moves up and down integrally with the drive shaft 231 as the drive shaft 231 of the actuator 230 drives up and down. The upper guide 240 has a cylindrical shape, and an upper end of the upper guide 240 is fixed to the support part 220 and extends downward from the support part 220. The upper guide 240 is movable in the vertical direction integrally with the support part 220.

[0024] 7, the mold section 300 has a storage section 301, an annular section 302, a front mold 311, and a mold 312. The storage section 301 has a cylindrical shape. The front mold 311 and the mold 312 are stored in the internal space of the storage section 301 while being stacked in this order from top to bottom. The annular section 302 is fixed to an opening at the upper end of the storage section 301, thereby fixing the front mold 311 and the mold 312 to the internal space of the storage section 301.

[0025] The front die 311 has a workpiece setting section 3111 in which a workpiece support through hole 3112 capable of supporting a workpiece W is formed. The die 312 has a forming section 3121. In the forming section 3121, a through hole 3122 in which a plurality of spiral grooves 3123 having a helical helix angle are formed in order to form the gear portion 10 (see FIG. 1) of the helical gear 1 having a helix angle. The value of the helix angle here is module 2 or more and 20° or more, and in this embodiment, for example, 31.5°. The reason why the module is 2 or more and 20° or more is that it is not possible to form a helical gear having a module of 2 or more and a helix angle of 20° or more in the conventional cold forging by forward extrusion method.

[0026] As shown in FIG. 5, FIG. 6, and FIG. 9, the work twisting unit 400 has a die support unit 410, a rotating columnar unit 420, an actuator 430, a work connection unit 440, and a lower guide 450. The die support unit 410 has a substantially cylindrical outer shape, and the upper end of the die support unit 410 is fixed to the lower end of the die 312 (see FIG. 7) to support the die unit 300 in a fixed state relative to the die support unit 410. As described later, when the rotating columnar unit 420 rotates, the rotating columnar unit 420 exerts a rotation stop function so that the front die 311 and the die 312 do not rotate. The rotating columnar unit 420 is disposed in the internal space of the die support unit 410 in a coaxial positional relationship with the die support unit 410. As shown in FIG. 9, the rotating columnar unit 420 has a pinion 422, and the pinion 422 is supported rotatably. A cross-shaped through hole 423 extending in the axial direction of the pinion 422 is formed in the center of the pinion 422 .

[0027] As shown in FIG. 9, a pair of actuators 430 are provided in a positional relationship that is point symmetrical about the axis of the rotating columnar portion 420 (axis of the cross through hole 423). Each actuator 430 has an actuator body 431 and a drive shaft 432 that can move away from or approach the actuator 430, and a rack 433 having a plurality of teeth is provided at the tip of the drive shaft 432. The rack 433 meshes with the pinion 422 of the rotating columnar portion 420, and when the actuator 430 is driven and the drive shaft 432 moves away from or toward the actuator 430 body, the pinion 422 of the rotating columnar portion 420 rotates integrally with the cross through hole 423 relative to the fixed member 421, centering on the axis of the cross through hole 423. The positions of the drive shaft 432 and the rack 433 are detected by a position detection sensor 435.

[0028] As shown in Fig. 5, the workpiece connecting part 440 rotates by engaging with a parallel tooth spline 30 (see Fig. 1) provided on a rotating shaft part 20 integrally molded with the workpiece W. Specifically, the workpiece connecting part 440 has a joint pin 441 and a spline sleeve 445. The joint pin 441 has a cylindrical part 4411 having a cylindrical shape, and a cross-shaped part 4412 fixed to the cylindrical part 4411 in the vicinity of the lower end part of the cylindrical part 4411. The upper end part of the cylindrical part 4411 is integrally connected to the spline sleeve 445 as described later.

[0029] The cross-shaped portion 4412 is fixed to the cylindrical portion 4411 and is composed of four cylindrical portions each protruding from the cylindrical portion 4411 in a radial direction of the cylindrical portion 4411. The cross-shaped portion 4412 and the cylindrical portion 4411 are movable in the vertical direction, which is the axial direction of the rotating cylindrical portion 420, in the cross through hole 423 (see FIG. 9) of the rotating cylindrical portion 420. That is, when the workpiece W is pushed downward by the work guide pin 210 of the press section 200 and moves, the joint pin 441 having the cross-shaped portion 4412 and the cylindrical portion 4411 moves downward integrally with the workpiece W while supporting the workpiece W below. The cross-shaped portion 4412 engages with the cross-shaped through hole 423, and when the rotating cylindrical portion 420 rotates in this engaged state, the cylindrical portion 4411 and the cross-shaped portion 4412 rotate integrally with the rotating cylindrical portion 420, while the joint pin 441 can move in the vertical direction.

[0030] The spline sleeve 445 has a cylindrical shape. A large number of grooves extending in the axial direction of the spline sleeve 445 are formed on the inner peripheral surface of the spline sleeve 445. The lower end of the spline sleeve 445 is integrally connected and fixed to the upper end of the cylindrical portion 4411. The parallel tooth spline 30 (see FIG. 1) of the workpiece W is inserted into the internal space of the spline sleeve 445 while meshing with the parallel tooth spline 30 in the groove at the upper end of the spline sleeve 445, and the upper end of the spline sleeve 445 and the lower end of the workpiece W are fixed.

[0031] 5, the lower guide 450 has a cylindrical shape, is fixed to the mold support part 410, and extends upward from the mold support part 410. The upper end part of the lower guide 450 is inserted into the internal space of the lower end part of the upper guide 240. With this configuration, the upper guide 240 is slidable relative to the lower guide 450, and the upper guide 240 is guided by the lower guide 450 and can move vertically together with the support part 220.

[0032] The die support part 410 is provided with an actuator 460. The actuator 460 is connected to a lower part of the joint pin 441, which is configured to be movable in the up-down direction relative to the cylindrical part 4411 in a coaxial positional relationship with the cylindrical part 4411, at the axial position of the cylindrical part 4411 having a cylindrical shape of the joint pin 441. The joint pin 441 is configured to apply a back pressure to the workpiece W by pressing a part at the axial position of the rotating shaft part 20 upward by driving the actuator 460.

[0033] Next, a method for manufacturing a helical gear will be described. The method for manufacturing a helical gear includes a helical gear forming process. In the helical gear forming process, the workpiece W is held and twisted by the workpiece twisting unit 400 around the axis of the rotating shaft unit 20 while back pressure is applied from below the workpiece W by the actuator 460. Also, the workpiece W is pressed into the die unit 300 by the press unit 200, and the helical gear 1 is formed by the die unit 300.

[0034] Specifically, first, the work W from which the helical gear 1 is to be formed is set in the front die 311 in a positional relationship in which it is located above the parallel tooth spline 30, and the work W is supported by the work setting section 3111. Note that the positional relationship of the spline 30 of the work W is not limited as long as a rotational force can be applied to the work W. Next, the actuator 230 of the press section 200 is driven to lower the work guide pin 210, and the lower end of the work guide pin 210 is brought into contact with the upper end of the rotating shaft section 20 of the work W. At the same time, the joint pin 441 and the spline sleeve 445 of the work connection section 440 are moved upward, and the parallel tooth spline 30 of the work W is inserted relatively to the upper end of the spline sleeve 445, and the lower end of the work W is supported by the spline sleeve 445.

[0035] Next, the helical gear forming process is performed. In the helical gear forming process, first, the actuator 230 of the press unit 200 is driven to press the workpiece W into the die 312 with an axial pressure P, as shown by "1" in Fig. 13. Then, the axial pressure P is gradually increased, and then the actuator 430 of the workpiece twisting unit 400 is driven to move the drive shaft 432 constituting the rack 433, thereby starting to rotate the rotating columnar portion 420 and the workpiece connecting portion 440 of the workpiece twisting unit 400 with a rotational force h around the cross through hole 423 of the rotating columnar portion 420. At this time, the gear portion 10 starts to be formed in the workpiece W, as shown by "2" in Fig. 13.

[0036] Next, the rotational force h is rapidly increased, and then a constant rotational force, i.e., a rotational force h equal to or greater than a predetermined ratio smaller than the yield stress at which the helical teeth 10 of the workpiece W are twisted in the circumferential direction, is applied. During this time, the axial pressure P continues to increase. At this time, the gear part 10 is being formed in the workpiece W, but since this is plastic deformation by cold forging, the volume of the left side of the workpiece W shown in FIG. 10 before the teeth 11 are formed is the same as the volume of the right side after the teeth 11 are formed. Therefore, on the right side of FIG. 10 after the teeth 11 are formed, the part indicated by "B" is formed by extending downward from the part indicated by "A".

[0037] In this way, the portion of the workpiece W where the teeth 11 are formed tends to stretch, so that the teeth 11 of the gear portion 10 beginning to be formed in the workpiece W should be formed with a helix angle of angle β as shown in Figures 11 and 12, but in reality, the helix angle tends to become β2, which is smaller than the angle β, as shown in the tooth 11 shown by the dashed line in Figure 12. Then, as shown in Figure 16, the tooth 11 slides while being strongly pressed against the press surface 3125 of the forming portion 3121 of the die 312, and the resistance due to friction between the portion of the workpiece W where the teeth 11 are formed and the press surface 3125 increases, as shown by the dashed line in Figure 18.

[0038] Therefore, at this timing, that is, as shown in Fig. 13 and Fig. 18, after the constant rotational force h starts to be applied and the axial pressure P is equal to or less than a predetermined ratio smaller than the upper limit of the axial pressure required for molding, when the upper limit is 100%, the actuator 460 starts to be driven, and the axial center position of the rotating shaft portion 20 is pressed upward to start applying back pressure, and as shown by the arrow in Fig. 17, the frictional resistance of the teeth 11 is reduced, so that the teeth 11 do not become the dot-dash line teeth 11 but become the solid line teeth 11 as shown in Fig. 15. The back pressure continues to be applied at a constant pressure until the gear portion 10 is formed in the helical gear forming process. In other words, the back pressure continues to be applied at a constant pressure from before the contact area between the die 312 and the workpiece W increases and a peak axial load (peak of the axial pressure P) occurs, until after the peak axial load occurs.

[0039] As shown in Fig. 13, as the forming of the gear portion 10 progresses, the slope of the increase in the axial pressure P gradually decreases. At this time, for example, as shown by "3" in Fig. 13, the gear portion 10 is formed in about one-third of the workpiece W.

[0040] Then, at "4", when the remaining portion of the helical tooth 10 falls below a predetermined ratio smaller than the tip diameter of the helical tooth 10 taken as 100%, the slope of the increase in the axial pressure P becomes negative and the axial pressure P decreases. As the axial pressure P decreases, the rotational force h is gradually decreased until it finally reaches a low value that is a predetermined ratio smaller than the torsional yield stress of the helical tooth 10 taken as 100%, and the gear portion 10 is formed in the helical gear forming process, as shown at "5" in Figure 13. This completes the helical gear forming process.

[0041] Next, a test was conducted on the effect of a gear mechanism having a helical gear manufactured by the manufacturing method of the helical gear according to the above configuration. In the test, a gear mechanism having a helical gear according to the above embodiment was prepared as the product of the present invention, and a gear mechanism having a helical gear manufactured by gear cutting was prepared as a comparative product. The gear specifications used in the test were module 2.3, helix angle 31.5 degrees, and number of teeth 17. Since the strength comparison was a destructive test, the length of the gear part 10 was made short so that the bending stress applied to the tooth base was set to be large. All of the gears constituting the gear mechanism were carburized gears made of structural carbon steel SCM420H. The helical gears constituting the product of the present invention and the comparative product were subjected to torque loads of 285 Nm, 300 Nm, and 350 Nm, and the number of cycles (time to failure) until failure was measured. The test results are shown in FIG. 19 and Table 1.

[0042] [Table 1]

[0043] It can be seen that the products of the present invention have a higher number of cycles than the comparative products, improving by 25% to 152%. From these results, it can be seen that good results can be obtained by configuring a gear mechanism equipped with helical gears so that the press receiving surface 111 abuts against one side of the tooth 11a that receives a larger load from the tooth 11a of the other gear portion 10a that meshes with the gear portion 10, as shown in Figure 4, and the gear portion 10 and the gear portion 10a mesh with each other.

[0044] According to this embodiment, the following effects are achieved. In this embodiment, in the gear mechanism equipped with a helical gear, a fiber flow 131 is formed on one side surface 111 of the tooth 11 of the gear portion 10, which extends toward the tip of the tooth 11 at the base of the tooth, and curves so as to extend in the tooth width direction as the height of the tooth 11 increases, and one side surface of the tooth 11a of the gear portion 10a abuts against the press surface 111 of the tooth 11 of the helical gear 1, where the tooth 11a of the gear portion 10a applies a large load to the tooth 11 of the helical gear portion 10.

[0045] As a result, even if a large load is applied to the press receiving surface 111 on which the characteristic fiber flow 131 is formed, the teeth 11 of the pinion 10 can be used without being damaged, the toughness and impact resistance of the helical gear 1 can be improved, and a gear mechanism can be provided with a high-strength helical gear 1.

[0046] In this embodiment, the helical gear forming process includes a helical gear forming process in which the workpiece W is held and twisted by the workpiece twisting unit 400 as a twisting member while being pushed into the die unit 300 by the drive shaft 231 of the actuator 230 as a pushing member, and the workpiece W is formed into the helical gear 1 by the die unit 300. The workpiece twisting unit 400 starts twisting the workpiece W at a predetermined timing. The workpiece twisting unit 400 starts twisting the workpiece W after a predetermined time has elapsed since the die unit 300 started forming the helical gear 1. This makes it possible to prevent the shape of the teeth 11 of the gear unit 10 from being distorted. In addition, since the gear unit 10 of the helical gear 1 is integrally formed with the rotating shaft unit 20, it is possible to obtain a helical gear 1 with high accuracy.

[0047] In the present embodiment, in the helical gear forming process, the actuator 460 as a back pressure applying unit applies back pressure to the workpiece W against the force of the actuator 230 pressing the workpiece W. This makes it possible to suppress a sudden increase in resistance due to friction between the portion of the workpiece W where the teeth 11 are formed and the press surface 3125, thereby making it possible to suppress an increase in forming resistance and suppress the load on the die section 300.

[0048] Also, in this embodiment, the actuator 460 applies back pressure to the workpiece W from the portion of the workpiece twisting unit 400 that holds the workpiece W. This makes it possible to miniaturize the configuration that applies back pressure to the workpiece W. Furthermore, in this embodiment, the back pressure applying member 462 applies back pressure to the position of the axis of the workpiece W in the portion of the workpiece twisting unit 400 that holds the workpiece W. This makes it possible to apply back pressure to the workpiece W in an appropriate direction with high accuracy.

[0049] In the present embodiment, in the helical gear forming process, the actuator 460 as a back pressure applying unit applies back pressure to the workpiece W at a predetermined timing against the force of the actuator 230 pressing the workpiece W. More specifically, the actuator 460 applies back pressure to the workpiece W from before the contact area between the die section 300 and the workpiece W increases and a peak axial load occurs, until after the peak axial load occurs.

[0050] This makes it possible to reliably prevent an increase in the contact area between the mold section 300 and the workpiece W and a sudden increase in resistance due to friction, thereby making it possible to prevent the molding resistance from increasing and to reduce the load on the mold section 300.

[0051] Furthermore, in this embodiment, the actuator 460 applies a constant back pressure to the workpiece W. This makes it possible to prevent the shaft 20 of the workpiece W, which receives back pressure from the back pressure applying member 462 that applies the back pressure, from exceeding its material rigidity yield strength, and prevents the shaft 20 of the workpiece W from deforming, preventing the necessary back pressure from being applied to the helical teeth 10 of the workpiece W, and thus preventing the forming of the helical gear from being hindered.

[0052] The present invention is not limited to the above-described embodiment, and includes modifications and improvements within the scope of the present invention that can achieve the object of the present invention. For example, in the present embodiment, the helical gear 1 has the gear portion 10, the rotating shaft portion 20, and the parallel tooth spline 30, but is not limited to this configuration. For example, the helical gear may not have the rotating shaft portion 20 and the parallel tooth spline 30, and may only have a gear portion having a hollow cylindrical shape. Even in this case, the gear portion has teeth with a helix angle of 20° or more and teeth with a module value of 2 or more.

[0053] In this case, the manufacturing method of the helical gear only requires that internal splines, grooves, protrusions, etc. are formed on the inner surface, outer surface, or end surface of the workpiece so that a torsional force (rotational force) can be applied to the workpiece.

[0054] Furthermore, the helical gear 1 according to the present embodiment has the parallel tooth spline 30, but is not limited to this configuration. For example, the helical gear may have a hexagonal column portion or a two-face width portion instead of the parallel tooth spline 30, as long as it has a configuration that allows the workpiece W that becomes the helical gear 1 to be rotated by these.

[0055] In the present embodiment, the gear portion 10, the rotating shaft portion 20, and the parallel tooth spline 30 are configured by integrally molding a workpiece W made of structural carbon steel material (SCM material), but this is not limiting. For example, the gear portion 10, the rotating shaft portion 20, and the parallel tooth spline 30 may be configured by integrally molding a workpiece W made of carbon steel and structural carbon steel material (SCR material, SCM material, SNCM material, etc.). In addition, in this embodiment, the helical gear 1 is manufactured by cold forging using the forward extrusion method, but it may also be manufactured, for example, by manufacturing the workpiece W by warm forging or hot forging, etc., and finally performing cold forging in a process to form the helical gear.

[0056] Furthermore, the configuration of each part of the helical gear, the configuration of the gear mechanism including the helical gear, and each step of the manufacturing method of the helical gear are not limited to the configuration of each part of the helical gear 1, the configuration of the gear mechanism including the helical gear 1, and each step of the manufacturing method of the helical gear in this embodiment. [Explanation of symbols]

[0057] 1…Helical gear 10, 10a...Gear section 11, 11a…tooth 20...Rotating shaft portion (rotating shaft) 111... Press receiving surface (one side) 131…Fiberflow 200…Press Department 230...Actuator (push-in member) 300…Mold section 312…Mold 400...Work twisting part (twisting member) 460...Actuator (back pressure application part) W…Work

Claims

1. a helical gear forming step of forcing a workpiece into a die by a pushing member while holding and twisting the workpiece by a twisting member, thereby forming the workpiece into a helical gear by the die; In the helical gear forming process, a back pressure application section applies back pressure to the workpiece against the force of the pushing member pushing the workpiece.

2. 2. The method for manufacturing a helical gear according to claim 1, wherein the back pressure applying portion applies back pressure to the workpiece from a portion of the torsion member that holds the workpiece.

3. 2. The method for manufacturing a helical gear according to claim 1, wherein the back pressure application portion is applied to a position of an axis of the workpiece in a portion of the torsion member that holds the workpiece.

4. 2. The method for manufacturing a helical gear according to claim 1, wherein in the helical gear forming step, a back pressure applying section applies back pressure to the workpiece at a predetermined timing against a force of the pushing member pushing the workpiece.

5. 5. The method for manufacturing a helical gear according to claim 4, wherein the back pressure applying section applies back pressure to the workpiece from before a contact area between the die and the workpiece increases to generate a peak axial load, until after the peak axial load has been generated.

6. 6. The method for manufacturing a helical gear according to claim 4, wherein the back pressure applying section applies a constant back pressure to the workpiece.

7. The method for manufacturing a helical gear according to claim 6, wherein the twisting member starts twisting the workpiece at a predetermined timing.

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