Method for manufacturing gear member, gear member, and forging mold used for method for manufacturing gear member

Abstract

To provide a method for a gear member, a gear member, and a forging mold which ease the push-in of a workpiece into a molding hole and enable an increase in helical strength.SOLUTION: A gear member 1 comprises an axial part 2 having a helical section 23. A plurality of flow lines 231 are present inside the helical section 23. The flow lines 231 continue over a plurality of helical gears 230. A tooth bottom 233 has a higher flow line density than a tooth tip 232. A method for manufacturing the gear member 1 includes: a partial heating process for heating a section including a heating section 24a of a workpiece 1a, but not including a heat transfer section 25a; and a forging process for heating the heat transfer section 25a from the front side to the rear side by pushing the axial part 2a of the workpiece 1a into a molding hole 500A having a plurality of gear molds 500B matching the helical gears 230, and by utilizing heat transfer to the heat transfer section 25a from the heating section 24a heated in the partial heating process, so as to mold the helical gear 230 in a helical scheduled section 23a.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a gear member, a gear member, and a forging die used in the method for manufacturing a gear member. [Background technology]

[0002] Helical gear members are manufactured, for example, by cutting. The helix is ​​formed by cutting the outer surface of a workpiece with a hob (a cutting tool with multiple spiral teeth). However, cutting generates chips from the workpiece, resulting in poor material yield. In addition, the processing time increases in proportion to the number of helical teeth and the feed width.

[0003] In this regard, Patent Document 1 discloses a method for manufacturing helical gear members by cold forging. The manufacturing method described in this document does not generate chips from the workpiece, resulting in good material yield. In addition, the processing time is short, regardless of the number of helical teeth or the feed width.

[0004] The manufacturing method described in this document includes a spur gear forming process and a helical gear forming process. In the spur gear forming process, a spur gear is formed on a workpiece by forcing the workpiece into a front-stage die. In the helical gear forming process, a helical gear is formed by forcing the spur gear formed in the front-stage die into a rear-stage die while twisting the workpiece. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-171402 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the manufacturing method in this document uses cold forging. When the inventors studied the formation of gear members by cold forging, they found that when a workpiece is forced into a forming hole in a die, an increase in the forming load causes the unformed portion of the workpiece (the portion that has not yet interfered with the tooth form) to expand radially outward outside the forming hole, making it difficult to force the workpiece into the forming hole.

[0007] Therefore, an object of the present disclosure is to provide a method for manufacturing a gear member, a gear member, and a forging die used in the manufacturing method of a gear member, which makes it easy to press a workpiece into a forming hole and can increase the strength of the helix. [Means for solving the problem]

[0008] (1) In order to solve the above-mentioned problems, the present disclosure provides a method for manufacturing a gear member, the method comprising: a shank portion having a helical section in which a plurality of helical bars are arranged; a plurality of grain flows are present within the helical section; the grain flows are continuous between the plurality of helical bars; and the grain flow density is higher at the roots of the helical bars than at the tips of the helical bars. The method comprises: a partial heating step of heating a section of a workpiece including the shank portion having a planned helical section that corresponds to the helical section and that includes a heating section and a heat transfer section connected to the rear of the heating section, the section including the heating section but not the heat transfer section; and a forging step of forging the shank portion of the workpiece into a forming hole having a plurality of tooth forms corresponding to the helical bars, and heating the heat transfer section from the front side to the rear side by utilizing heat transfer from the heating section heated in the partial heating step to the heat transfer section, thereby forming the helical bar into the planned helical section.

[0009] The method for manufacturing a gear member according to the present invention includes a partial heating step and a forging step. In the partial heating step, a heating section of a planned helical section (heating section, heat transfer section) of a workpiece is heated.

[0010] In the forging process, as the shaft portion is pressed into the forming hole, the material of the shaft portion held back by the tooth dies moves relatively from the front side (the front side in the pushing direction (the direction in which the shaft portion is pressed into the forming hole)) to the rear side (the rear side in the pushing direction). As a result, heat from the heating section is transferred to the heat transfer section via this material. Furthermore, this heat moves from the front side to the rear side in the heat transfer section.

[0011] This heat transfer allows the forming section (the part of the shaft that is being formed by the toothed die) in the heat transfer section to be heated while being formed, which makes it possible to suppress an increase in forming load compared to forming the part without heating it (e.g., cold forging).

[0012] Furthermore, the unformed portion behind the formed portion (the portion of the shank that has not yet come into contact with the tooth form) is at a lower temperature and has a higher hardness than the formed portion. Therefore, when forming the formed portion, the unformed portion outside the forming hole can be prevented from expanding radially outward. Therefore, compared to forming the workpiece without heating the entire workpiece (e.g., cold forging) or forming the entire workpiece by heating it to a uniform temperature (e.g., warm forging), the workpiece can be easily pushed into the forming hole. In other words, a helix can be easily formed on the shank.

[0013] Let us assume that a gear member is manufactured by cutting. In this case, the grain flows are broken between the multiple helical grooves of the gear member. In contrast, with the present configuration, the grain flows of the gear member are continuous across the multiple helical grooves. This increases the strength of the tooth surface. Furthermore, the grain flow density is higher at the root of the helical groove than at the tip of the helical groove. This increases the strength of the root. Furthermore, because no cutting is used in forming the helical grooves, no chips are generated from the workpiece. This increases the material yield of the workpiece. This ultimately reduces the manufacturing costs of the gear member.

[0014] (1-1) In the configuration of (1) above, it is preferable that the total length of the planned helical section in the front-to-rear direction is 100%, the front end position of the planned helical section is 0% position, and the rear end position of the planned helical section is 100% position, and that the front end position of the heating section is the 0% position and the rear end position of the heating section is included in a section between the 20% position and the 50% position.

[0015] The rear end position of the heating section is included in the section equal to or greater than the 20% position, which makes it possible to suppress insufficient heating during forming of the planned helical section, compared to when the rear end position of the heating section is included in the section below the 20% position.

[0016] The rear end position of the heating section is included in the section below the 50% position, which makes it possible to prevent the entire planned helical section from being heated, compared to when the rear end position of the heating section is included in the section above the 50% position.

[0017] (1-2) In any of the above configurations, it is preferable that in the partial heating process, the heating section is heated so that the temperature difference between the heating section and the heat transfer section at the start of the forging process is 200°C or more.

[0018] The temperature difference between the heating section and the heat transfer section at the start of the forging process is 200°C or more. Therefore, compared to when the temperature difference is less than 200°C, a hardness difference suitable for the forging process can be set between the heating section and the heat transfer section. This makes it possible to soften the formed portion and harden the unformed portion. Therefore, when forming the formed portion, it is possible to suppress radially outward expansion of the unformed portion outside the forming hole.

[0019] (1-3) In any of the above configurations, it is preferable that the partial heating step heats the heating section so that the temperature of the heating section at the start of the forging step is 400° C. or higher. With this configuration, the heating section can be softened sufficiently compared to when the temperature of the heating section at the start of the forging step is less than 400° C.

[0020] (1-4) In any of the above configurations, it is preferable that the forming speed, which is the speed at which the shank of the workpiece is forced into the forming hole in the forging process, is 60 mm / s or more. The heat transfer rate increases in proportion to the forming speed. Therefore, with this configuration, the heat in the heating section can be transferred more quickly to the heat transfer section compared to when the forming speed is less than 60 mm / s. Furthermore, in the heat transfer section, the heat can be transferred more quickly from the front side to the rear side.

[0021] (2) Preferably, in any of the above configurations, a step portion arranging step is provided in which a step portion whose diameter decreases from the front side to the rear side is arranged in the intended helical section before the partial heating step.

[0022] Let us assume that the helical section has the same diameter over its entire vertical length (this case is also included in the concept of the manufacturing method of the gear member disclosed herein). In the forging process, as the shank is forced into the forming hole, the material of the shank blocked by the tooth dies moves relatively from the front to the rear of the shank. At this time, the material expands radially outward. Here, the helical section has the same diameter over its entire longitudinal length. Therefore, the expanded material comes into pressure contact with the inner circumferential surface of the forming hole (the tooth grooves between a pair of adjacent tooth dies (hereinafter referred to as "tooth grooves on the tooth die side")). This increases the frictional force of the material against the inner circumferential surface of the forming hole, resulting in a large forming load. To reduce the frictional force, the workpiece diameter must be reduced. However, reducing the workpiece diameter reduces the material thickness at the tooth tips.

[0023] In this regard, according to the present configuration, in the step-portion arranging step, a step portion whose diameter decreases from the front side to the rear side is arranged in the intended helical section, so that the expansion of the material in the forging step can be absorbed by the step portion.

[0024] To explain in more detail, the meat held back by the tooth mold (specifically, the meat in the portion forward of the step portion of the stem (hereinafter referred to as the "front body portion")) moves relatively from the front to the rear in the portion rear of the step portion of the stem (hereinafter referred to as the "rear body portion") from the front. At this time, the meat expands radially outward. Here, the rear body portion has a smaller diameter than the front body portion. Therefore, the expanded meat is less likely to press against the inner circumferential surface of the forming hole (the tooth grooves on the tooth mold side). Therefore, the frictional force of the meat against the inner circumferential surface of the forming hole can be reduced. This improves the fluidity of the meat, allowing the meat to be filled up to the rear end position of the helical planned section. In other words, the meat tension can be improved.

[0025] (2-1) In the configuration of (2) above, it is preferable that the extending direction of the shank is the axial direction, the direction perpendicular to the axial direction is the radial direction, the part of the shank rearward of the stepped portion is the rear trunk portion, and the radial cross-sectional area of ​​the helix is ​​100%, and the outer peripheral surface of the rear trunk portion is included in an area ranging from the 40% position to the 60% position, starting from the tooth bottom of the helix, as viewed from the axial direction.

[0026] According to this configuration, the outer peripheral surface of the rear barrel portion is included in a section that is 40% or more from the tooth root (the radial inner end of the helical bar) (a position that occupies 40% of the radial cross-sectional area of ​​the helical bar). Therefore, compared to when the outer peripheral surface of the rear barrel portion is included in a section that is less than 40% from the tooth root of the helical bar, the filler material can reliably reach the inner peripheral surface of the forming hole (the tooth groove on the tooth die side). Therefore, the filler material can be reliably filled up to the tooth tip of the helical bar.

[0027] According to this configuration, the outer peripheral surface of the rear barrel portion is included in the section below 60% from the tooth root of the helical bar (a position occupying 60% of the radial cross-sectional area of ​​the helical bar). Therefore, compared to when the outer peripheral surface of the rear barrel portion is included in the section beyond 60% from the tooth root of the helical bar, the material is less likely to press against the inner peripheral surface of the forming hole (the tooth groove on the tooth die side). Therefore, the frictional force of the material against the inner peripheral surface of the forming hole can be reliably reduced.

[0028] (3) Preferably, in any of the above configurations, after the forging step, a discharging step is further included in which the helical grooves filled in the tooth grooves between a pair of adjacent tooth dies are extruded from the front side along the extending direction of the tooth grooves to discharge the gear member, which is the workpiece after the helical forming, from the forming hole. Here, the "gear member" refers to the workpiece after the helical forming. The gear member may be a finished product or an intermediate product (a product before becoming a finished product).

[0029] Let's assume that during the ejection process, the entire workpiece is extruded linearly from the front side along the front-to-rear direction (the stroke direction of the punch during the forging process). The helices and tooth grooves on the tooth die side extend in a spiral direction (a direction intersecting the front-to-rear direction). Therefore, when the entire gear member is extruded linearly from the front side, frictional force is likely to be applied to the helices from the tooth grooves on the tooth die side. This makes the helices more likely to deform.

[0030] In this regard, according to the present configuration, in the ejection step, the helical portion of the gear member is pushed out spirally from the front side along the extension direction of the tooth grooves on the tooth die side. Therefore, compared to when the entire gear member is pushed out linearly from the front side, it is possible to suppress the frictional force applied to the helical portion from the tooth grooves on the tooth die side, and therefore it is possible to suppress deformation of the helical portion.

[0031] (4) Preferably, in any of the above configurations, the gear member and the workpiece are each integral with the shaft portion and have a flange portion protruding radially outward from the shaft portion. The gear member and the workpiece in this configuration each have a shaft portion and a flange portion. The gear member is a one-piece member. The shaft portion and the flange portion are integrally connected. Similarly, the workpiece is a one-piece member. The shaft portion and the flange portion are integrally connected.

[0032] Let's assume that a helix is ​​formed on the shank of a workpiece by cutting. In this case, when the hob is brought close to the shank, the hob is likely to interfere with the flange. This makes it difficult to form the helix.

[0033] In this regard, according to the present configuration, a helix can be formed in the workpiece by forging. Therefore, even if the workpiece has a flange portion, a helix can be easily formed. Thus, the manufacturing method of the gear member of the present disclosure is particularly suitable for manufacturing a gear member having a flange portion.

[0034] (4-1) In the configuration described in (4) above, it is preferable that the rear end position of the planned helical section be within a section 10 mm or less from the front end of the radially inner end of the flange portion. The rear end position of the planned helical section (the helical section of the gear member) is within a section 10 mm or less from the front end of the radially inner end of the flange portion. Therefore, compared to when the rear end position is within a section exceeding 10 mm, the hob is more likely to interfere with the flange portion, making it difficult to form the helical section by cutting. With this configuration, the helical section can be formed by forging. Therefore, even when the rear end position of the planned helical section is within a section 10 mm or less from the front end of the radially inner end of the flange portion, the helical section can be easily formed. As such, the manufacturing method of the gear member disclosed herein is particularly suitable for manufacturing a gear member whose helical section begins near the radially inner end of the flange portion.

[0035] (5) In the configuration of (4) or (4-1) above, before the partial heating process, it is preferable that the shaft portion of the workpiece has a flange lower body portion connected to the front end of the radially inner end of the flange portion, and the flange lower body portion of the workpiece has, from the front side to the rear side, a front side body portion, a step portion, and a rear side body portion, the front side body portion has a larger diameter than the rear side body portion, the step between the front side body portion and the rear side body portion is 1 mm or more, the tip circles of the multiple helices of the gear member have a larger diameter than the outer diameter of the front side body portion of the workpiece, and the diameter difference between the diameter of the tip circle and the outer diameter of the front side body portion is 2 mm or less.

[0036] The step between the front and rear body portions of the workpiece (hereinafter referred to as "step") is set to 1 mm or more. The diameter difference between the diameter of the tooth tip circle of the gear member and the outer diameter (diameter) of the front body portion of the workpiece (hereinafter referred to as "diameter difference") is set to 2 mm or less. The diameter of the tooth tip circle of the gear member corresponds to the inner diameter (diameter) of the inner peripheral surface of the forming hole (the bottom of the tooth groove on the tooth die side).

[0037] With this configuration, compared to when the above-mentioned conditions for step and diameter difference are not met, the material of the workpiece can more easily reach the groove bottom of the tooth groove on the tooth die side during the forging process. Therefore, forming defects such as closing flaws are less likely to occur in the helix. In other words, the forming accuracy (shape accuracy) of the helix can be improved.

[0038] If the shape of the workpiece is designed with priority given to the step and diameter difference conditions, it will be difficult for the mass of the workpiece to meet the desired specifications. In this case, the axial length (length in the front-to-back direction) of the front body of the workpiece can be adjusted so that the mass of the workpiece meets the desired specifications.

[0039] (6) In any of the above configurations, it is preferable that the partial heating step heats the heating section so that the temperature of the heating section at the start of the forging step is 400°C or higher and lower than 520°C.

[0040] According to this configuration, the temperature of the heating section at the start of the forging process is set to 400° C. or higher. Therefore, the heating section can be softened sufficiently compared to when the temperature of the heating section is less than 400° C.

[0041] On the other hand, if the temperature of the heating section is increased, the deformation resistance of the workpiece during the forging process decreases. This makes it easier for the tooth dies to remove the workpiece, resulting in the generation of burrs. In this regard, with this configuration, the temperature of the heating section at the start of the forging process is set to less than 520°C. This makes it possible to suppress the generation of burrs compared to when the temperature of the heating section is 520°C or higher.

[0042] In this way, by satisfying the temperature condition of the heating section of this configuration (400°C or higher and lower than 520°C), it is possible to optimize the deformation resistance of the wall of the workpiece during the forging process, thereby improving the forming accuracy (shape accuracy) of the helix.

[0043] (7) In any of the above configurations, it is preferable that the entire length in the fore-aft direction of the planned helical section is defined as 100%, the front end position as 0%, and the rear end position as 100%. In the partial heating process, at the start of the forging process, the heating section corresponding to the section from the 0% position to the 18% position is heated so that the temperature difference between the 0% position and the 18% position is 0°C or more and 90°C or less, the temperature difference between the 18% position and the 25% position is 90°C or more and 150°C or less, the temperature difference between the 25% position and the 33% position is 150°C or more and 200°C or less, and the temperature difference between the 33% position and the 100% position is 200°C or more.

[0044] According to this configuration, the above-described temperature distribution is set in the planned helical section (heating section, heat transfer section). Therefore, a hardness difference suitable for the forging process can be set between the heating section and the heat transfer section. Therefore, the formed portion can be made soft and the unformed portion can be made hard. Therefore, when forming the formed portion, the unformed portion can be prevented from expanding radially outward outside the forming hole.

[0045] (8) In order to solve the above problems, the present disclosure provides a gear member comprising a shank portion having a helical section in which a plurality of helical beams are arranged, and a flange portion integral with the shank portion and projecting radially outward from the shank portion, wherein a plurality of grain flows exist within the helical section, the grain flows are continuous between the plurality of helical beams, and the grain flow density is higher at the roots of the helical beams than at the tips of the helical beams. The gear member of this configuration comprises a shank portion and a flange portion. The gear member is a single piece. The shank portion and the flange portion are integrally connected.

[0046] According to this configuration, the grain flows of the gear member are continuous across multiple helical teeth, which increases the strength of the tooth surface. Furthermore, the grain flow density is higher at the roots of the helical teeth than at the tips of the helical teeth, which increases the strength of the roots.

[0047] (8-1) In the configuration of (8) above, it is preferable that the rear end position of the helical section be included in a section that is 10 mm or less from the front end of the radially inner end of the flange portion. The rear end position of the helical section is included in a section that is 10 mm or less from the front end of the radially inner end of the flange portion. Therefore, compared to when the rear end position is included in a section that is more than 10 mm, the rear end position of the helical section can be positioned closer to the radially inner end of the flange portion. Therefore, the total length of the helical section in the front-to-rear direction can be increased. Furthermore, the total length of the helical section in the front-to-rear direction can be positioned closer to the flange portion.

[0048] (9) Preferably, in the configuration of (8) or (8-1) above, the grain flows extend along the surface shape of the helical bar. With this configuration, the grain flows extend along the surface shape (contour) of the helical bar. This increases the resistance to bending stress (stress acting in the direction of bending the surface of the helical bar).

[0049] (10) In order to solve the above problem, the forging die used in the manufacturing method of the gear member of the present disclosure has the configuration of (3) above, and is a forging die used in the forging process and the ejection process, and includes a die having the forming hole, a punch that pushes the workpiece into the forming hole from the rear side, and a knockout pin that pushes the gear member out of the forming hole from the front side, wherein the knockout pin has an ejection tooth that moves along the tooth groove between a pair of adjacent tooth dies, and the ejection tooth pushes the helix filled in the tooth groove from the front side along the extension direction of the tooth groove, thereby pushing the gear member out of the forming hole.

[0050] According to this configuration, in the ejection step, the ejection teeth of the knockout pin push the helical portion of the gear member from the front side in a spiral shape along the extension direction of the tooth grooves. Therefore, compared to when the entire gear member is pushed out linearly from the front side by a knockout pin without ejection teeth, it is possible to suppress the friction force applied to the helical portion from the tooth grooves, thereby suppressing deformation of the helical portion. [Effects of the Invention]

[0051] The gear member manufacturing method, gear member, and forging die used in the gear member manufacturing method of the present disclosure make it easier to press the workpiece into the forming hole and also increase the strength of the helix. [Brief explanation of the drawings]

[0052] [Figure 1] FIG. 1 is a partial cross-sectional view of a gear member taken in the vertical direction. [Figure 2] FIG. 2 is a cross-sectional view taken along the line II-II in FIG. [Figure 3] FIG. 3 is an enlarged view of the area within the frame III in FIG. [Figure 4] FIG. 4 is a partial cross-sectional view of the workpiece taken in the vertical direction. [Figure 5] FIG. 5 is a front view of a high-frequency induction heating device used in the partial heating step. [Figure 6] FIG. 6 is a vertical cross-sectional view of the forging die at the beginning of the forging process. [Figure 7] FIG. 7 is a vertical cross-sectional view of the forging die in the middle of the forging process. [Figure 8] FIG. 8 is an enlarged view of the area within the frame VIII in FIG. [Figure 9] FIG. 9 is a cross-sectional view taken along the line IX-IX in FIG. [Figure 10] FIG. 10 is a vertical cross-sectional view of the forging die at the end of the forging process. [Figure 11] FIG. 11 is a vertical cross-sectional view of the forging die in the ejection step. [Figure 12]FIG. 12 is an enlarged view of the area within the frame XII in FIG. [Figure 13] FIG. 13 is a cross-sectional view taken along the line XIII-XIII in FIG. [Figure 14] FIG. 14 is a contour diagram showing the analysis results (first stage) of Example 1. [Figure 15] FIG. 15 is a contour diagram showing the analysis results (second stage) of Example 1. [Figure 16] FIG. 16 is a contour diagram showing the analysis results (third stage) of Example 1. [Figure 17] FIG. 17 is a contour diagram showing the analysis results (fourth stage) of Example 1. [Figure 18] FIG. 18 is a contour diagram showing the analysis results (first stage) of Example 2. [Figure 19] FIG. 19 is a contour diagram showing the analysis results (second stage) of Example 2. [Figure 20] FIG. 20 is a contour diagram showing the analysis results (third stage) of Example 2. [Figure 21] FIG. 21 is a contour diagram showing the analysis results (fourth stage) of Example 2. [Figure 22] FIG. 22 is a contour diagram showing the analysis results (first stage) of Example 3. [Figure 23] FIG. 23 is a contour diagram showing the analysis results (second stage) of Example 3. [Figure 24] FIG. 24 is a contour diagram showing the analysis results (third stage) of Example 3. [Figure 25] FIG. 25 is a contour diagram showing the analysis results (first stage) of Comparative Example 1. [Figure 26] FIG. 26 is a contour diagram showing the analysis results (second stage) of Comparative Example 1. [Figure 27] FIG. 27 is a contour diagram showing the analysis results (first stage) of Comparative Example 2. [Figure 28] FIG. 28 is a contour diagram showing the analysis results (second stage) of Comparative Example 2. [Figure 29]FIG. 29 is a graph showing the relationship between the remaining stroke of the punch and the forming load. [Figure 30] FIG. 30 is a contour diagram showing the analysis results at the end of the forging process in Example 6. [Figure 31] FIG. 31 is a photograph of the workpiece in Example 7 at the end of the forging process. [Figure 32] FIG. 32 is a contour diagram showing the temperature distribution of the workpiece in the early stage of the forging process in Example 8. [Figure 33] FIG. 33 is a contour diagram showing the analysis results at the end of the forging process in Example 8. DETAILED DESCRIPTION OF THE INVENTION

[0053] Hereinafter, embodiments of a manufacturing method for a gear member, a gear member, and a forging die used in the manufacturing method for a gear member according to the present disclosure will be described. In the following drawings, the up-down direction corresponds to the "front-rear direction" in the present disclosure. The up-down direction also corresponds to the stroke direction of a punch. The up-down direction also corresponds to the axial direction of the gear member and the workpiece. The lower side corresponds to the "front side" in the present disclosure. The lower side also corresponds to the forward movement direction (direction in which the shank is inserted into the forming hole) of the stroke direction (up-down direction) of the punch. The upper side corresponds to the "rear side" in the present disclosure. The upper side also corresponds to the backward movement direction (direction in which the shank is removed from the forming hole) of the stroke direction (up-down direction) of the punch.

[0054] Corresponding parts between the gear member and the workpiece are designated by related symbols. For example, if a part of a gear member is designated by the symbol "○" (○ is a number or letter), the part of the workpiece that corresponds to that part is designated by the symbol "○a."

[0055] [Gear component configuration] First, the configuration of the gear member of this embodiment will be described. Fig. 1 shows a partial cross-sectional view of the gear member of this embodiment in the vertical direction. Fig. 2 shows a cross-sectional view taken along the II-II direction in Fig. 1. Fig. 3 shows an enlarged view of the area within box III in Fig. 2. Note that Fig. 1 shows an external view of the left side of the central axis Y, and a cross-sectional view of the right side of the central axis Y (the helical tooth 230 is shown schematically as a straight line).

[0056] The gear member 1 is a so-called flanged gear member. The gear member 1 is incorporated into a transmission unit of a vehicle. As shown in FIG. 1, the gear member 1 includes a shaft portion 2 and a flange portion 3. The gear member 1 is an integral part. That is, the shaft portion 2 and the flange portion 3 are made of the same material (for example, alloy steel for mechanical structures (SCM material)) and are integrally connected.

[0057] Shank 2 as a whole has the shape of a solid round bar extending in the up-down direction (front-rear direction). Shank 2 comprises a lower end (front end) 20, a shaft main body 21, an upper end (rear end) 22, and a helical section 23. Lower end 20 comprises, from the lower side (front side) to the upper side (rear side), a lower tapered section 200, a body section 201, and an upper tapered section 202. Lower tapered section 200 and upper tapered section 202 each have a tapered shape (partial cone shape) that becomes pointed from the upper side to the lower side. Body 201 is cylindrical.

[0058] Shaft main body portion 21 comprises, from bottom to top, a flange lower body portion 210 and a flange base body portion 211. Flange lower body portion 210 is continuous with the upper side of upper tapered portion 202. Flange lower body portion 210 has a cylindrical shape. A rounded lower chamfered portion 2100 is disposed on the outer peripheral surface of the upper end of flange lower body portion 210. Lower chamfered portion 2100 is continuous with the lower end of a radial inner end 300 of flange portion 3, which will be described later. Note that, for ease of explanation, radial inner end 300 is shown by a dotted line in FIG. 1, but shaft portion 2 and flange portion 3 are integrally connected. Flange base body portion 211 is continuous with the upper side of flange lower body portion 210. Flange base body portion 211 has a cylindrical shape.

[0059] The upper end portion 22 is continuous with the upper side of the flange base body portion 211. The upper end portion has a cylindrical shape. A rounded upper chamfered portion 220 is disposed on the outer peripheral surface of the lower end of the upper end portion 22. The upper chamfered portion 220 is continuous with the upper side of the flange base body portion 211.

[0060] 1 and 2, the helical section 23 is set on the outer peripheral surface of the flange lower body portion 210. A plurality of helical bars 230 are arranged in the helical section 23. The helical bars 230 extend in a spiral shape around the central axis Y of the shaft portion 2.

[0061] An upper end position (rear end position) 234 of the helical section 23 is set at the lower end of the lower chamfered portion 2100. The upper end position 234 is included in a section that is 10 mm or less from the lower end of the radially inner end 300 of the flange portion 3.

[0062] The lower end position (front end position) 235 of the helical section 23 is set at the lower part of the flange lower body portion 210 (a position spaced a predetermined distance above the boundary between the lower end portion 20 and the flange lower body portion 210).

[0063] As shown schematically in FIG. 3 , multiple grain flows 231 exist within the helical section 23. The grain flows 231 are continuous across the multiple helical bars 230. The grain flows 231 extend along the surface of the helical bars 230. The grain flows 231 extend in an endless loop shape centered on the central axis Y shown in FIG. 2 . The multiple grain flows 231 are arranged radially in the shape of tree rings. Focusing on the density of the grain flows 231, the grain flow density is higher at the roots 233 of the helical bars 230 than at the tips 232 of the helical bars 230.

[0064] 1, the flange portion 3 includes a disk portion 30 and a tubular portion 31. The disk portion 30 protrudes radially outward from the entire circumference of the radially outer end of the flange base body portion 211. The tubular portion 31 extends in the vertical direction from the entire circumference of the radially outer end of the disk portion 30.

[0065] [Work configuration] Next, the configuration of the workpiece of this embodiment will be described. A gear member is manufactured from the workpiece by a gear member manufacturing method described below. Fig. 4 shows a vertical partial cross-sectional view of the workpiece of this embodiment. Note that Fig. 4 shows an external view of the left side of the central axis Ya, and a cross-sectional view of the right side of the central axis Ya.

[0066] Except for the configuration of the flange lower body portion 210a, the configuration of the workpiece 1a is similar to that of the gear member 1 described above. That is, the workpiece 1a includes a shaft portion 2a and a flange portion 3a. The workpiece 1a is a single piece. The shaft portion 2a and the flange portion 3a are made of the same material and are integrally connected. The shaft portion 2a includes a lower end portion 20a, a shaft main portion 21a, and an upper end portion 22a. The lower end portion 20a includes a lower tapered portion 200a, a body portion 201a, and an upper tapered portion 202a. The shaft main portion 21a includes a flange lower body portion 210a and a flange base body portion 211a. A rounded lower chamfered portion 2100a is disposed on the outer peripheral surface of the upper end of the flange lower body portion 210a. A rounded upper chamfered portion 220a is disposed on the outer peripheral surface of the lower end of the upper end portion 22a. The flange portion 3a includes a disk portion 30a and a cylindrical portion 31a.

[0067] The workpiece 1a shown in FIG. 4 and the gear member 1 shown in FIG. 1 have different configurations of flange lower body portions 210a, 210. The flange lower body portion 210a of the workpiece 1a includes, from bottom to top, a lower body portion (front body portion) 2101a, a tapered portion 2102a, and an upper body portion (rear body portion) 2103a. The lower body portion 2101a is connected to the upper side of the upper tapered portion 2102a. The lower body portion 2101a has a cylindrical shape. The tapered portion 2102a has a tapered shape that becomes sharper from bottom to top. The tapered portion 2102a is included in the concept of a "step portion" in this disclosure. The upper body portion 2103a has a cylindrical shape. The upper body portion 2103a has a smaller diameter than the lower body portion 2101a.

[0068] The planned helical section 23a is set on the outer peripheral surface of the flange lower body portion 210a. The planned helical section 23a corresponds to the helical section 23 shown in FIG. 1. An upper end position (rear end position) 234a of the planned helical section 23a is set at the lower end of the lower chamfered portion 2100a. The upper end position 234a is included in a section that is 10 mm or less from the lower end of the radially inner end 300a of the flange portion 3a. A lower end position (front end position) 235a of the planned helical section 23a is set at the boundary between the lower end portion 20a and the flange lower body portion 210a. Note that in FIG. 4, for ease of explanation, the radially inner end 300a is shown by a dotted line, but the shaft portion 2a and the flange portion 3a are integrally connected.

[0069] The helical planned section 23a includes a heating section 24a and a heat transfer section 25a. The entire length of the helical planned section 23a in the vertical direction is defined as 100%, with the lower end position 235a defined as the 0% position and the upper end position 234a defined as the 100% position. The upper end position (rear end position) 240a of the heating section 24a is included in the section between the 20% position and the 50% position. The upper end position 240a is set at the boundary between the tapered section 2102a and the upper body section 2103a. The lower end position (front end position) of the heating section 24a is set at the 0% position (lower end position 235a). The heat transfer section 25a is connected to the upper side of the heating section 24a. The upper end position of the heat transfer section 25a is set at the 100% position (upper end position 234a).

[0070] [Manufacturing method for gear components] Next, a method for manufacturing a gear member according to this embodiment will be described. The method for manufacturing a gear member includes a step-forming step, a partial heating step, a forging step, and a discharging step. The steps will be described in order below.

[0071] {Step portion arrangement process} In this step, a workpiece 1a is produced in the shape shown in Fig. 4. That is, a lower body portion 2101a, a tapered portion 2102a, and an upper body portion 2103a are arranged on a flange lower body portion 210a of a shaft portion 2a of the workpiece 1a.

[0072] {Partial heating process} This process is performed after the step arrangement process. In this process, the device-side heating section A of the workpiece 1a is heated. That is, the section of the workpiece 1a that includes the heating section 24a but does not include the heat transfer section 25a is heated. Focusing on the helical planned section 23a, only the heating section 24a is locally heated.

[0073] (Configuration of high frequency induction heating device) First, the configuration of the high-frequency induction heating device used in this process will be described. Figure 5 shows a front view of the high-frequency induction heating device used in this process. The base 410 is shown in a vertical cross-sectional view. The high-frequency induction heating device 4 comprises a device main body 40, a workpiece support part 41, and a heating coil 42. The device main body 40 and the workpiece support part 41 are arranged side by side in the left-right direction (horizontal direction).

[0074] The workpiece support portion 41 includes a base portion 410, a frame portion 411, and four legs 412. The base portion 410 is annular. The frame portion 411 is annular. The frame portion 411 is disposed on the upper surface of the base portion 410. The four legs 412 support the base portion 410 from below. The heating coil 42 is disposed in the space below the base portion 410 (the space between the four legs 412). The heating coil 42 is cylindrical and extends in the vertical direction. When viewed from the vertical direction, the heating coil 42 is disposed at the radial center of the base portion 410 and the frame portion 411.

[0075] (Process details) Next, the contents of this step will be explained. First, the workpiece 1a is set on the workpiece support part 41. That is, the lower part of the shaft part 2a of the workpiece 1a (the part below the flange part 3a) is inserted from above into the space below the pedestal part 410. At this time, the shaft part 2a of the workpiece 1a is inserted radially inside the heating coil 42. Next, the tubular part 31a of the flange part 3a of the workpiece 1a is placed on the pedestal part 410. At this time, the outer peripheral surface of the tubular part 31a is brought into contact with the inner peripheral surface of the frame part 411. In this way, the workpiece 1a is positioned relative to the workpiece support part 41 (axial (vertical) positioning and radial (horizontal) positioning).

[0076] In this state, the heating coil 42 covers the "section from the vertical middle of the body portion 201a to the upper end position 240a of the heating section 24a" (apparatus-side heating section A) shown in Fig. 4 from the radial outside. Here, the apparatus-side heating section A includes the heating section 24a. The apparatus-side heating section A does not include the heat transfer section 25a.

[0077] Next, the device main body 40 shown in Figure 5 is started, and a magnetic field is formed in the heating coil 42. This magnetic field induces an eddy current in the device-side heating section A of the workpiece 1a. This eddy current and the electrical resistance of the device-side heating section A cause Joule heat to be generated in the device-side heating section A. This Joule heat causes the device-side heating section A to self-heat.

[0078] {Forging process} This step is performed after the partial heating step. In this step, the helical portion 230 (i.e., the helical portion 23) shown in Fig. 1 is formed in the helical portion planned portion 23a shown in Fig. 4 by forward extrusion. In other words, the gear member 1 is produced from the workpiece 1a.

[0079] (Configuration of forging die) First, the configuration of the forging die used in this process and the next process (discharging process) will be described. FIG. 6 shows a vertical cross-sectional view of the forging die at the beginning of the forging process. FIG. 7 shows a vertical cross-sectional view of the forging die at the middle of the forging process. FIG. 8 shows an enlarged view of the area within frame VIII in FIG. 7. FIG. 9 shows a cross-sectional view along the line IX-IX in FIG. 8. FIG. 10 shows a vertical cross-sectional view of the forging die at the end of the forging process. Note that in FIGS. 6 to 8 and 10, the helical protrusion 230, tooth profile 500B, and tooth groove 500C are shown as straight lines. For ease of explanation, in FIG. 9, the tooth root 233 of the helical protrusion 230 is shown by a dotted line, but the helical protrusion 230 and the shank 2a are integrally connected.

[0080] 6 to 10, the forging die 5 includes a lower die (fixed die) 50, an upper die (movable die) 51, and a knockout pin 53. The lower die 50 includes a die 500, a die holder 501, and a die plate 502.

[0081] The die holder 501 has a cylindrical shape with a bottom. That is, the die holder 501 has a recess 501A that opens upward. A pin support hole 501C is defined at the radial center of a bottom wall portion 501B of the die holder 501. The pin support hole 501C penetrates the bottom wall portion 501B in the vertical direction.

[0082] The die 500 has a cylindrical shape. The die 500 is accommodated in a recess 501A. A forming hole 500A is defined in the radial center of the die 500. The forming hole 500A penetrates the die 500 in the vertical direction. A plurality of tooth dies 500B are arranged on the inner peripheral surface of the forming hole 500A. The tooth dies 500B correspond to the helical teeth 230 shown in FIG. 1. A tooth groove 500C is arranged between a pair of tooth dies 500B adjacent to each other in the circumferential direction. The tooth groove 500C has a shape symmetrical to the helical teeth 230.

[0083] The die plate 502 has a thick plate shape. A pin insertion hole 502A is defined in the radial center of the die plate 502. The pin insertion hole 502A passes through the die plate 502 in the vertical direction. From the top to the bottom, the molding hole 500A of the die 500, the pin support hole 501C of the die holder 501, and the pin insertion hole 502A of the die plate 502 are linearly connected.

[0084] The knockout pin 53 is inserted from below into the pin insertion hole 502A, the pin support hole 501C, and the forming hole 500A. The knockout pin 53 is reciprocable in the up-and-down direction (one axial direction). The knockout pin 53 is rotatable around the central axis Ya. However, during the forging process, the knockout pin 53 is immobile.

[0085] The knockout pin 53 includes a shaft portion 530 and an upper end portion 531. The shaft portion 530 extends in the vertical direction. The upper end portion 531 is disposed above the shaft portion 530. The upper end portion 531 has a cylindrical shape with a bottom. That is, the upper end portion 531 includes a recessed portion 531A that opens upward. The inner surface of the recessed portion 531A has a shape that is symmetrical to the outer surface of the lower end portion 20 of the gear member 1 shown in FIG. 1. The inner surface of the recessed portion 531A is a forming surface that forms the lower end portion 20a of the workpiece 1a. A plurality of ejection teeth 531C are disposed on a side peripheral wall portion 531B of the upper end portion 531. The ejection teeth 531C have a shape (spiral shape) similar to that of the helical tooth 230 shown in FIG. 1. The ejection teeth 531C are capable of moving spirally along the tooth groove 500C.

[0086] The upper die 51 includes a punch 510. The punch 510 extends in the vertical direction. The punch 510 is reciprocable in the vertical direction (one axial direction). The punch 510 is movable from above into the recess 501A of the die holder 501. The punch 510 and the knockout pin 53 face each other in the vertical direction.

[0087] (Process details) Next, the contents of this step will be described. First, the workpiece 1a, whose device-side heating section A (the section including the heating section 24a) has been heated in the previous step (partial heating step), is set in the recess 501A of the die holder 501 of the lower mold 50. At this time, the outer peripheral surface (guided surface) of the cylindrical portion 31a of the flange portion 3a abuts against the inner peripheral surface (guiding surface) of the recess 501A.

[0088] Next, the punch 510 of the upper die 51 is inserted into the recess 501A from above. The punch 510 presses the portion of the shank 2a below the flange 3a (specifically, the lower end 20a of the shank 2a and the flange lower body portion 210a) into the forming hole 500A from above. This pressing causes the helical intended section 23a to interfere with the tooth die 500B. As a result, the helical 230 (i.e., the helical section 23) shown in FIG. 1 is formed in the helical intended section 23a.

[0089] When the punch 510 reaches the bottom dead center of the stroke, the lower end 20a of the shank 2a abuts against the inner surface of the recess 531A of the knockout pin 53. The shape of the inner surface of the recess 531A is transferred to the lower end 20a. The flange 3a abuts against the upper surface of the die 500. In the tooth groove 500C, the helical tooth 230 abuts against the ejection tooth 531C of the knockout pin 53. The helical tooth 230 and the ejection tooth 531C face each other in the extension direction of the tooth groove 500C.

[0090] {Discharge process} This process is performed after the forging process. Fig. 11 shows a vertical cross-sectional view of the forging die in the ejection process. Fig. 12 shows an enlarged view of the area within frame XII in Fig. 11. Fig. 13 shows a cross-sectional view taken along the line XIII-XIII in Fig. 12. In Figs. 11 and 12, the helical tooth 230, tooth shape 500B, and tooth groove 500C are shown schematically as straight lines.

[0091] In this step, the gear member 1 (workpiece 1a after forming the helical tooth 230) is ejected from the forming hole 500A. That is, as shown in FIG. 12, in the tooth groove 500C, the helical tooth 230 abuts against the ejection tooth 531C of the knockout pin 53. In this step, in the tooth groove 500C, the ejection tooth 531C pushes the helical tooth 230 from below along the extension direction (spiral direction) of the tooth groove 500C. While remaining in abutment with each other, the knockout pin 53 and the gear member 1 move upward within the forming hole 500A while rotating around the central axis Y along the extension direction of the tooth groove 500C. The knockout pin 53 pushes the gear member 1 upward from the forming hole 500A.

[0092] [Action and effect] Next, the effects of the manufacturing method of the gear member, the gear member, and the forging die used in the manufacturing method of the gear member according to this embodiment will be described. The manufacturing method of the gear member 1 according to this embodiment includes a partial heating step and a forging step. As shown in FIG. 5, in the partial heating step, only the heating section 24a of the intended helical section 23a (heating section 24a, heat transfer section 25a) is selectively and locally heated. As shown in FIGS. 6 to 10, in the forging step, as the shank portion 2a is pressed into the forming hole 500A, the material of the shank portion 2a blocked by the tooth die 500B moves relatively from the lower side (the front side of the pressing direction (the direction in which the shank portion 2a is pressed into the forming hole 500A)) to the upper side (the rear side of the pressing direction). Therefore, heat from the heating section 24a is transferred to the heat transfer section 25a via the material. The heat also moves from the lower side to the upper side of the heat transfer section 25a. Furthermore, in the forging process, as the shaft portion 2a is pressed into the forming hole 500A, the formed portion B shown in Figure 7 (the portion of the shaft portion 2a being formed by the tooth mold 500B) expands the shaft portion 2a from the bottom to the top.

[0093] In this way, in the forging process, the formed portion B expands from the bottom to the top in response to the transfer of heat from the bottom to the top. Therefore, the helical part 230 can be formed while continuously heating the formed portion B. Therefore, compared to when the formed portion B is formed without being heated (e.g., cold forging), an increase in the forming load can be suppressed.

[0094] Furthermore, the unformed portion C shown in FIG. 7 (the portion of the shank 2a that is located above the formed portion B and has not yet come into contact with the tooth die 500B) has a lower temperature and a higher hardness than the formed portion B. Therefore, when forming the formed portion B, the unformed portion C can be prevented from expanding radially outward outside the forming hole 500A. Therefore, compared to forming the workpiece 1a without heating the entire workpiece 1a (e.g., cold forging) or forming the workpiece 1a by heating the entire workpiece 1a to a uniform temperature (e.g., warm forging), the workpiece 1a can be easily pressed into the forming hole 500A. In other words, the helix 230 can be easily formed in the shank 2a.

[0095] Assume that the gear member 1 is manufactured by cutting. In this case, the grain flows 231 shown in FIG. 3 are broken between the helical segments 230 of the gear member 1. This reduces the strength of the helical segments 230. In contrast, with the manufacturing method of the gear member of this embodiment, the grain flows 231 of the gear member 1 are continuous across the helical segments 230, as shown in FIG. 3. This increases the strength of the tooth flanks. Furthermore, the distance between adjacent grain flows 231 is narrower at the tooth root 233 than at the tooth tip 232. This means that the grain flow density is higher at the tooth root 233 than at the tooth tip 232. This increases the strength of the tooth root 233. Furthermore, because cutting is not used to form the helical segments 230, chips generated from the workpiece 1a are reduced. This increases the material yield of the gear member 1. This, in turn, reduces the manufacturing cost of the gear member 1.

[0096] 4, assuming that the entire length of the helical intended section 23a in the up-down direction is 100%, the lower end position 235a of the helical intended section 23a is the 0% position, and the upper end position 234a of the helical intended section 23a is the 100% position, the upper end position 240a of the heating section 24a is included in a section equal to or greater than the 20% position. Therefore, compared to a case where the upper end position 240a of the heating section 24a is included in a section less than the 20% position (a case where the vicinity of the lower end position 235a of the helical intended section 23a is locally heated), it is possible to suppress insufficient heating of the helical intended section 23a during forming.

[0097] With the entire length of the planned helical section 23a in the up-down direction as 100%, a lower end position 235a of the planned helical section 23a as the 0% position, and an upper end position 234a of the planned helical section 23a as the 100% position, the upper end position 240a of the heating section 24a is included in a section below the 50% position. Therefore, compared to when the upper end position 240a of the heating section is included in a section beyond the 50% position (when a section exceeding the lower half of the planned helical section 23a is heated), it is possible to prevent the planned helical section 23a from being heated as a whole.

[0098] In the partial heating process, the heating section 24a is heated so that the temperature difference between the heating section 24a and the heat transfer section 25a at the start of the forging process is 200°C or more. Therefore, compared to when the temperature difference is less than 200°C, a hardness difference suitable for the forging process can be set between the heating section 24a and the heat transfer section 25a. That is, the hardness of the formed section B shown in FIG. 7 can be reduced to an extent that makes it easy to form. In addition, the hardness of the unformed section C above the formed section B can be increased to an extent that it does not expand radially outward outside the forming hole 500A.

[0099] In the partial heating process, the heating section 24a is heated so that the temperature of the heating section 24a at the start of the forging process is 400° C. or higher. Therefore, the heating section 24a can be softened sufficiently compared to when the temperature is lower than 400° C.

[0100] In the forging process, the descending speed of the punch 510 (the pressing speed of the workpiece 1a), i.e., the forming speed, is set to 60 mm / s or more. Therefore, compared to when the forming speed is less than 60 mm / s, the heat in the heating section 24a can be transferred more quickly to the heat transfer section 25a. Furthermore, in the heat transfer section 25a, the heat can be transferred more quickly from the lower side to the upper side.

[0101] The manufacturing method of the gear member 1 of this embodiment includes a step arranging step before the partial heating step. In the step arranging step, a tapered portion 2102a whose diameter decreases from the bottom to the top is arranged in the intended helical section 23a shown in FIG.

[0102] Assume that the helical intended section 23a has the same diameter (the same diameter as the lower body section 2101a shown in FIG. 4) along its entire vertical length. In the forging process, as the shank 2a is forced into the forming hole 500A, the wall of the shank 2a blocked by the tooth die 500B moves relatively upward from the lower side of the shank 2a. At this time, the wall expands radially outward. Here, the helical intended section 23a has the same diameter along its entire vertical length. Therefore, the expanded wall presses against the inner circumferential surface (tooth groove 500C) of the forming hole 500A shown in FIG. 8. This increases the frictional force of the wall against the inner circumferential surface of the forming hole 500A, resulting in a large forming load. To reduce the frictional force, the diameter of the workpiece must be reduced. However, reducing the diameter of the workpiece reduces the wall thickness of the tooth tip 232.

[0103] In this regard, according to the manufacturing method of the gear member 1 of this embodiment, in the step arranging step, a tapered portion 2102a whose diameter decreases from the lower side to the upper side is arranged in the intended helical section 23a shown in Fig. 4. Therefore, the above-mentioned wall expansion during the forging step can be absorbed by the tapered portion 2102a.

[0104] More specifically, the material of the lower body portion 2101a blocked by the toothed mold 500B shown in FIG. 8 moves relatively from the lower side to the upper body portion 2103a. At this time, the material expands radially outward. Here, the upper body portion 2103a has a smaller diameter than the lower body portion 2101a. Therefore, the expanded material is less likely to press against the inner circumferential surface (tooth groove 500C) of the forming hole 500A. This reduces the frictional force of the material against the inner circumferential surface of the forming hole 500A. This improves the fluidity of the material, allowing the material to be filled up to the upper end position 234a of the intended helical section 23a. In other words, the material tension can be improved.

[0105] As shown in Fig. 9, when the radial cross-sectional area of ​​the helical bit 230 is taken as 100%, the outer peripheral surface of the upper body portion 2103a is included in a section that is 40% or more from the tooth bottom 233 (the radial inner end of the helical bit 230) of the helical bit 230 (a position that occupies 40% of the radial cross-sectional area of ​​the helical bit 230). Therefore, compared to a case where the outer peripheral surface of the upper body portion 2103a is included in a section that is less than 40% from the tooth bottom 233, the filler material can reliably reach the inner peripheral surface (tooth groove 500C) of the forming hole 500A shown in Fig. 8. Therefore, the filler material can be reliably filled up to the tooth tip 232 of the helical bit 230.

[0106] As shown in Fig. 9, when the radial cross-sectional area of ​​the helical bar 230 is taken as 100%, the outer peripheral surface of the upper body portion 2103a is included in a section not exceeding 60% from the tooth root 233 of the helical bar 230 (a position occupying 60% of the radial cross-sectional area of ​​the helical bar 230). Therefore, compared to when the outer peripheral surface of the upper body portion 2103a is included in a section exceeding 60% from the tooth root 233, the material is less likely to be pressed against the inner peripheral surface (tooth groove 500C) of the forming hole 500A shown in Fig. 8. Therefore, the frictional force of the material against the inner peripheral surface of the forming hole 500A can be reliably reduced.

[0107] The manufacturing method of the gear member 1 of this embodiment includes a forging step followed by an ejection step. Assume that in the ejection step, the entire gear member 1 is pushed out linearly from below along the vertical direction (the stroke direction of the punch 510 in the forging step) using a knockout pin 53 without ejection teeth 531C shown in FIGS. 11 to 13 . The helical grooves 230 and the tooth spaces 500C extend in a spiral direction (a direction intersecting the vertical direction). Therefore, if the entire workpiece 1a is pushed out linearly from below, frictional force is likely to be applied to the helical grooves 230 from the tooth spaces 500C. Therefore, the helical grooves 230 are likely to deform.

[0108] In this regard, as shown in Figures 11 to 13, the knockout pin 53 of the forging die 5 of this embodiment is provided with an ejection tooth 531C that moves along the tooth groove 500C. In the ejection process, the ejection tooth 531C pushes out the helical tooth 230 of the gear member 1 from below in a spiral shape along the extension direction of the tooth groove 500C. Therefore, compared to when the entire gear member 1 is pushed out linearly from below, it is possible to suppress the friction force applied to the helical tooth 230 from the tooth groove 500C. Therefore, it is possible to suppress deformation of the helical tooth 230.

[0109] In this embodiment, the gear member 1 and the workpiece 1a each include a shaft portion 2, 2a and a flange portion 3, 3a. The gear member 1 is a one-piece member. The shaft portion 2 and the flange portion 3 are integrally connected. Similarly, the workpiece 1a is a one-piece member. The shaft portion 2a and the flange portion 3a are integrally connected.

[0110] Let us assume that the helical bore 230 shown in FIG. 1 is formed by cutting the shank 2a of the workpiece 1a shown in FIG. 4. In this case, when the hob is brought close to the shank 2a, the hob is likely to interfere with the flange 3a. This narrows the movable range of the hob. Furthermore, the degree of freedom of the hob's trajectory is reduced. This makes it difficult to form the helical bore 230.

[0111] In this regard, according to the manufacturing method of the gear member 1 of this embodiment, the helical joint 230 can be formed in the workpiece 1a by the forging process. Therefore, even though the workpiece 1a has a flange portion 3a, the helical joint 230 can be easily formed. In this way, the manufacturing method of the gear member 1 of this embodiment is particularly suitable for manufacturing a gear member 1 having a flange portion 3.

[0112] As shown in FIG. 4 , in the workpiece 1a, the upper end position 234a of the intended helical section 23a is located within a section 10 mm or less from the lower end of the radially inner end 300a of the flange portion 3a. Therefore, forming the helical section 230 by cutting is more difficult than when the upper end position 234a is located within a section greater than 10 mm. In contrast, the manufacturing method of the gear member 1 of this embodiment allows the helical section 230 to be formed by a forging process. Therefore, even when the upper end position 234a is located within a section 10 mm or less from the lower end of the radially inner end 300a, the helical section 230 can be easily formed. Thus, the manufacturing method of the gear member of this embodiment is particularly suitable for manufacturing a gear member 1 in which the helical section 23 begins near the base (radially inner end 300a) of the flange portion 3.

[0113] As shown in FIG. 3 , in the gear member 1, multiple grain flows 231 exist within the helical section 23. The grain flows 231 are continuous across multiple helical bars 230, which increases the strength of the tooth surface. Furthermore, the distance between adjacent grain flows 231 is narrower at the roots 233 of the helical bars 230 than at the tips 232 of the helical bars 230. In other words, the grain flow density is higher at the roots 233 than at the tips 232. This increases the strength of the roots 233.

[0114] In the gear member 1, the grain flows 231 extend along the surface shape (contour) of the helical bar 230. This increases the resistance to bending stress (stress acting in the direction in which the surface of the helical bar 230 bends).

[0115] As shown in FIG. 1 , in the gear member 1, the upper end position 234 of the helical section 23 is included in a section that is 10 mm or less from the lower end of the radially inner end 300 of the flange portion 3. Therefore, compared to when the upper end position is included in a section that is more than 10 mm, the upper end position 234 can be located closer to the base (radially inner end 300) of the flange portion 3. This makes it possible to increase the overall length of the helical section 23 in the vertical direction. In addition, the overall length of the helical section 23 in the vertical direction can be located closer to the base of the flange portion 3.

[0116] As shown in FIGS. 6 to 10, in the forging process, heat from the heating section 24a diffuses through the helical section 23a. Specifically, as shown in FIG. 4, heat diffuses from the heating section 24a toward the upper end position 234a. Here, in the heat diffusion path, the temperature is higher on the upstream side (the heating section 24a side, i.e., the lower side of the workpiece 1a) than on the downstream side (the upper side of the workpiece 1a). In other words, the lower side of the helical section 23a becomes softer during processing than the upper side of the helical section 23a. Due to this thermal history in the forging process, residual stress increases in the helical section 23 of the gear member 1 from the lower end position 235 toward the upper end position 234. Thus, the gear member 1 of this embodiment may have a characteristic stress distribution after the forging process.

[0117] [others] The above describes embodiments of the gear member manufacturing method, gear member, and forging die used in the gear member manufacturing method according to the present disclosure. However, the embodiments are not particularly limited to the above-described embodiments. Various modifications and improvements that can be made by those skilled in the art are also possible.

[0118] {Work 1a, gear component 1} The shape of the workpiece 1a is not particularly limited. The workpiece 1a may or may not include a flange portion 3a. The vertical length and position of the planned helical section 23a on the shank portion 2a are not particularly limited. The planned helical section 23a may be located in close proximity to the flange portion 3a. The planned helical section 23a may also be located away from the flange portion 3a. A plurality of planned helical sections 23a may be located on a single shank portion 2a. A gear (for example, a spur gear whose tooth trace extends in the direction of the central axis Ya) may be located on the outer peripheral surface of the cylindrical portion 31a of the flange portion 3a.

[0119] The vertical length and position of the heating section 24a in the intended helical section 23a are not particularly limited. The heating section 24a may be located close to the flange portion 3a. Alternatively, the heating section 24a may be located away from the flange portion 3a. The same applies to the heat transfer section 25a. The occupancy ratio of the heating section 24a to the heat transfer section 25a in the intended helical section 23a is not particularly limited.

[0120] The material of the workpiece 1a is not particularly limited. For example, it may be iron, steel (stainless steel, manganese steel, nickel steel, nickel chromium steel, chromium steel, etc.), titanium, titanium alloy, nickel, nickel alloy, aluminum, aluminum alloy, copper, copper alloy, or other metal. It is sufficient that heat is transferred within the workpiece 1a by thermal conduction. The above lists modified and improved forms of the workpiece 1a, but the same applies to the gear member 1.

[0121] There is no particular limitation on the use of the gear member 1. For example, it may be used as a stepped pinion type planetary gear or a counter driven gear in a transmission unit of a vehicle (gasoline vehicle, diesel vehicle, hybrid vehicle, electric vehicle, etc.).

[0122] {Regarding the manufacturing method of gear member 1} In the step arranging step, the method for arranging the lower body portion 2101a, the tapered portion 2102a, and the upper body portion 2103a on the flange lower body portion 210a is not particularly limited. For example, first, a workpiece 1a having a cylindrical flange lower body portion 210a may be fabricated, and then the flange lower body portion 210a of the workpiece 1a may be subjected to appropriate diameter reduction processing (cutting processing) to form the lower body portion 2101a, the tapered portion 2102a, and the upper body portion 2103a. Alternatively, first, a workpiece 1a having a cylindrical flange lower body portion 210a may be fabricated, and then the flange lower body portion 210a of the workpiece 1a may be subjected to appropriate diameter increase processing to form the lower body portion 2101a, the tapered portion 2102a, and the upper body portion 2103a. Alternatively, the workpiece 1a may be formed by forging or casting, and may include the flange lower body portion 210a, the lower body portion 2101a, the tapered portion 2102a, and the upper body portion 2103a.

[0123] The temperature conditions set in the partial heating step at the start of the forging step are not particularly limited. For example, the temperature difference between the heating section 24a and the heat transfer section 25a at the start of the forging step is not particularly limited. It may be 200°C or higher or lower than 200°C. Furthermore, the temperature of the heating section 24a at the start of the forging step may be 400°C or higher or lower than 400°C.

[0124] However, the temperature setting is not necessarily unlimited. The key point of the manufacturing method of the gear member 1 of the present disclosure is to reduce the deformation resistance of the heated section 24a by heating, thereby reducing the load required for processing, while preventing the deformation resistance of the unheated heat transfer section 25a from decreasing by not heating it, thereby preventing the heat transfer section 25a from expanding radially outward while the heated section 24a is being formed.

[0125] The appropriate temperature difference for preventing expansion in the heat transfer section 25a varies depending on the type of steel and the magnitude of processing distortion of the formed portion B, and therefore must be determined appropriately by conducting prototypes for each part (gear member 1). As a result, the appropriate temperature difference varies for each part. The same applies to selecting appropriate temperature conditions for the heating section 24a. Therefore, it is necessary to set an appropriate temperature in accordance with the above-mentioned concept.

[0126] The temperature of the heating section 24a at the start of the forging process may be lower than the transformation point of the material of the workpiece 1a. This allows for higher forming accuracy of the helical bar 230. The temperature of the heating section 24a at the start of the forging process may be higher than the transformation point of the material of the workpiece 1a. This allows for densifying the structure of the helical bar 230.

[0127] In the partial heating step, the vertical length and position of the heating section 24a in the device-side heating section A heated by the high-frequency induction heating device 4 are not particularly limited. The vertical total length of the device-side heating section A need only be equal to or greater than the vertical total length of the heating section 24a. The heating section 24a need only be included in the device-side heating section A. The method for heating the heating section 24a is not particularly limited. The heating section 24a may be heated using a halogen lamp or the like. To adjust the temperature difference between the heating section 24a and the heat transfer section 25a, the heat transfer section 25a may be cooled using a cooling means such as air.

[0128] The forming conditions in the forging process are not particularly limited. For example, the lubrication conditions, the stroke length, stroke direction, speed (forming speed), and forming load of the punch 510 are not particularly limited. The configuration and material of the forging die 5 are not particularly limited. The lower die 50 may be fixed and the upper die 51 may be movable. The lower die 50 may be movable and the upper die 51 may be fixed. Both the lower die 50 and the upper die 51 may be movable. The speed of the punch 510 may be constant or variable. The drive mechanism for the punch 510 is not particularly limited. It may be a hydraulic press (such as a hydraulic press), a mechanical press (such as a crank press), or the like.

[0129] The ejection conditions in the ejection process are not particularly limited. For example, the lubrication conditions, the stroke length, stroke direction, speed, and forming load of the knockout pin 53 are not particularly limited. The number of ejection teeth 531C is not particularly limited. The number of ejection teeth 531C may be the same as the number of tooth grooves 500C (i.e., helical grooves 230). In this case, all of the helical grooves 230 can be pushed out by the ejection teeth 531C. The number of ejection teeth 531C may be fewer than the number of tooth grooves 500C (i.e., helical grooves 230). In this case, the ejection teeth 531C may be arranged at predetermined intervals in the circumferential direction (e.g., every third tooth groove 500C). The knockout pin 53 does not need to have ejection teeth 531C. In this case, the upper end 531 of the knockout pin 53 may push up the workpiece 1a from below.

[0130] Other processes may be performed before, after, or between each process (step portion arrangement process, partial heating process, forging process, and ejection process) in the manufacturing method of the gear member 1. For example, an additional forming process (such as a forging process) or a finishing process (such as a polishing process or a painting process) may be performed after the ejection process. In addition, a cooling process may be performed between the partial heating process and the forging process to adjust the temperatures of the heating section 24a and the heat transfer section 25a. [Example]

[0131] Below, analyses 1 to 4 performed on the manufacturing method of the gear member, the gear member, and the forging die used in the manufacturing method of the gear member according to the present disclosure will be described.

[0132] <Analysis 1 (Examples 1 to 3, Comparative Examples 1 and 2)> First, analysis 1 (CAE (Computer Aided Engineering) analysis) will be described with reference to Fig. 4 and Fig. 9. In the analysis, the step arrangement step, partial heating step, and forging step of the above-described manufacturing method for a gear member were simulated for the workpieces of Examples 1 to 3 and Comparative Examples 1 and 2 shown below.

[0133] [Regarding Workpieces 1a of Examples 1 to 3 and Comparative Examples 1 and 2] {Example 1} Example 1 has a configuration similar to that of the workpiece 1a shown in Figure 4. The entire vertical length of the planned helical section 23a shown in Figure 4 is defined as 100%, the lower end position 235a of the planned helical section 23a is defined as the 0% position, and the upper end position 234a of the planned helical section 23a is defined as the 100% position. The lower end position of the heating section 24a is the 0% position (lower end position 235a). The upper end position 240a of the heating section 24a is defined as the 33% position. That is, in the case of Example 1, the lower 33% of the planned helical section 23a is set as the heating section 24a to be heated in the partial heating process.

[0134] The outer peripheral surface of the upper body portion 2103a shown in FIG. 9 is set at a 56.6% position (a position occupying 56.6% of the radial cross-sectional area of ​​the helical bar, starting from the tooth bottom 233 of the helical bar) with the tooth bottom 233 as the starting point.

[0135] {Example 2} The only difference between Example 2 and Example 1 is the upper end position 240a of the heating section 24a shown in Figure 4. In Example 2, the upper end position 240a is at the 11% position. That is, in Example 2, the lower 11% section of the planned helical section 23a is set as the heating section 24a to be heated in the partial heating step.

[0136] {Example 3} The only difference between Example 3 and Example 1 is that the lower body portion 2101a, the tapered portion 2102a, and the upper body portion 2103a shown in Fig. 4 are not set. In Example 3, the flange lower body portion 210a has the same diameter over the entire vertical length (the same diameter as the lower body portion 2101a shown in Fig. 4).

[0137] {Comparative Example 1} Similar to Example 1, Comparative Example 1 includes a flange lower body portion 210a (lower body portion 2101a, tapered portion 2102a, and upper body portion 2103a) shown in Fig. 4. Comparative Example 1 is not a publicly known example. The only differences between Comparative Example 1 and Example 1 are the heating section 24a and the heat transfer section 25a.

[0138] The manufacturing method of Comparative Example 1 does not include a partial heating step. In the case of Comparative Example 1, the entire workpiece 1a is not heated. In other words, Comparative Example 1 is a workpiece 1a for cold forging. Therefore, Comparative Example 1 does not have a heating section 24a or a heat transfer section 25a.

[0139] {Comparative Example 2} Similar to Example 1, Comparative Example 2 includes a flange lower body portion 210a (lower body portion 2101a, tapered portion 2102a, upper body portion 2103a) shown in Fig. 4. Comparative Example 2 is not a publicly known example. The only differences between Comparative Example 2 and Example 1 are the heating section 24a and the heat transfer section 25a.

[0140] The manufacturing method of Comparative Example 2 does not include a partial heating step. In Comparative Example 2, the entire workpiece 1a is heated, not just a portion of it. In other words, Comparative Example 2 is a workpiece 1a for warm forging. Therefore, in Comparative Example 2, the entire intended helical section 23a, i.e., 100% of the section, corresponds to the heating section 24a. In Comparative Example 2, no heat transfer section 25a is set.

[0141] [Analysis conditions] The analysis was performed using FORGE (manufactured by Transvalor; the same applies below), a plastic processing simulation software. The material of the workpiece 1a was SCr420 (JIS G 4053). The diameter of the shaft portion 2a was 32.8 mm. The total axial length of the planned helical section 23a was 38.2 mm. The total axial length of the lower body portion 2101a was 5.5 mm. The step between the lower body portion 2101a and the upper body portion 2103a (the difference in radius between the radially outer end and the radially inner end of the tapered portion 2102a) was 1 mm. In the analysis, the thickness, temperature (forming temperature), and forming load in the forging process when gear members were formed from the workpieces of Examples 1 to 3 and Comparative Examples 1 and 2 shown below were calculated.

[0142] In Examples 1 to 3 and Comparative Examples 1 and 2, the forming speed in the forging process (lowering speed of the punch 510) was 80 mm / s. In Examples 1 to 3, the temperature of the heating section 24a at the start of the forging process, which is imparted in the partial heating process, was 500°C. The temperature difference between the heating section 24a and the heat transfer section 25a at the start of the forging process was 480°C. In Comparative Example 2, the temperature of the entire workpiece 1a at the start of the forging process was 20°C.

[0143] [About the analysis results] {About meat firmness and temperature} Example 1 14 to 17 show the analysis results (first to fourth stages) of Example 1 in contour diagrams. The left diagram shows thickness. In Fig. 15 (left diagram) to Fig. 17 (left diagram), the parts with the same color as Fig. 14 (left diagram) are unprocessed parts. Also, the parts with a different color from Fig. 14 (left diagram) are processed parts, that is, parts with reduced thickness. The right diagram shows temperature. In Fig. 14 (right diagram) to Fig. 17 (right diagram), the light-colored parts are high-temperature parts. The dark-colored parts are low-temperature parts.

[0144] As the forging process progresses, a portion of the workpiece moves relatively upward (rearward) as shown in Figure 15 (left). Also, as shown in Figure 15 (right), a helix is ​​formed in the forming portion of the workpiece, and heat is diffused upward.

[0145] As shown in FIG. 4, the upper body portion 2103a has a smaller diameter than the lower body portion 2101a. Due to this difference in diameter (step) (i.e., due to the tapered portion 2102a), when a helix is ​​formed in the lower body portion 2101a, the material of the lower body portion 2101a rises radially outward of the upper body portion 2103a. This suppresses the radial expansion deformation of the lower body portion 2101a. As shown in FIGS. 16 and 17, heat is distributed throughout the entire helical section. Furthermore, a helix is ​​formed throughout the entire helical section.

[0146] As shown in Figures 14 (right) to 16 (right), there is a significant difference in shading between the formed and unformed portions. In other words, the unformed portions are at a lower temperature than the formed portions. Therefore, when the formed portions are processed, the unformed portions do not expand radially outward outside the forming hole. This makes it easy to push the workpiece into the forming hole. As a result, the helix can be formed over the entire intended helix section.

[0147] Example 2 18 to 21 are contour diagrams showing the analysis results (first to fourth stages) of Example 2. The diagrams can be read in the same way as in the above-mentioned FIGS.

[0148] The helical forming process is the same as in the first embodiment described above. According to Example 2, the helical can be formed over the entire intended helical section. However, as shown in FIG. 14 (right), the heating section 24a (see FIG. 4) in Example 1 is a section covering 33% of the lower portion of the intended helical section 23a, whereas as shown in FIG. 18 (right), the heating section 24a in Example 2 is a section covering 11% of the lower portion of the intended helical section 23a. That is, Example 2 has a smaller heating section 24a than Example 1. Therefore, as shown in FIG. 19 (right), the temperature of the formed section (especially the upper portion) is likely to decrease due to heat diffusion. Therefore, compared to Example 1, the forming load is likely to increase.

[0149] Example 3 Figures 22 to 24 show the analysis results (first to third stages) of Example 3 in contour diagrams. Figures 22 to 24 correspond to the left diagrams of Figures 14 to 21. That is, Figures 22 to 24 show thickness thickening. In Figures 23 to 24, the parts that have changed color compared to Figure 22 are the processed parts (thinned parts). Also, the spiral parts are the tooth forms of the formed holes.

[0150] The helical forming process is the same as in the first embodiment. According to Example 3, a helical can be formed over the entire intended helical section while suppressing an increase in forming load. However, while the flange lower body portion 210a (see FIG. 4) of Example 1 includes a lower body portion 2101a, a tapered portion 2102a, and an upper body portion 2103a, the flange lower body portion 210a of Example 3 has the same diameter (the same diameter as the lower body portion 2101a) over its entire vertical length. Therefore, as shown in FIG. 24, an unprocessed portion is more likely to appear in the helical as compared to Example 1.

[0151] (Comparative Example 1) 25 and 26 show contour diagrams of the analysis results (first and second stages) of Comparative Example 1. The diagrams can be read in the same way as in the above-mentioned Figs. 22 to 24. As shown in Fig. 26, in the case of Comparative Example 1, the unformed portion expands radially outward and cannot be pushed into the forming hole. Therefore, although the analysis indicates that forming can continue, in reality, forming is impossible.

[0152] (Comparative Example 2) 27 and 28 show contour diagrams of the analysis results (first and second stages) of Comparative Example 2. The diagrams can be read in the same way as in the above-mentioned Figs. 22 to 26. As shown in Fig. 28, in the case of Comparative Example 2, the unformed portion expands radially outward and cannot be pushed into the forming hole. For this reason, although the analysis indicates that molding can continue, in reality, molding is impossible.

[0153] {About forming load} Figure 29 is a graph showing the relationship between the remaining stroke of the punch and the forming load. The horizontal axis shows the remaining stroke of the punch 510 (see Figure 6) up to the bottom dead center. The vertical axis shows the load (forming load; the load applied by the punch 510 to the workpiece 1a; the reaction force received by the punch 510 from the workpiece 1a). The data for Example 1 is shown by a solid line. The data for Comparative Examples 1 and 2 are shown by dotted lines.

[0154] 29, the forming load is, in order of decreasing, Example 1 (partially hot forging), Comparative Example 2 (warm forging), and Comparative Example 1 (cold forging). Compared to Comparative Examples 1 and 2, Example 1 has a lower forming load throughout the entire period of the forging process.

[0155] In Comparative Examples 1 and 2, an increase in the forming load causes the unformed portion of the shank 2a to expand radially outward outside the forming hole during forming. Therefore, although the analysis shows that the punch 510 can reach bottom dead center (remaining stroke = 0 mm), in reality, it is impossible to form the helical bore 230 (see FIG. 4) over the entire helical bore-designated section 23a. In contrast, Example 1 can suppress an increase in the forming load. Therefore, the unformed portion of the shank 2a does not expand radially outward outside the forming hole during forming. Therefore, the helical bore 230 can be formed over the entire helical bore-designated section 23a.

[0156] <Analysis 2 (Examples 4 to 6)> Next, Analysis 2 (CAE analysis) will be described with reference to Figures 1 to 9. In the analysis, the step arrangement step, partial heating step, and forging step of the above-described gear member manufacturing method were simulated for the workpieces of Examples 4 to 6 shown below.

[0157] [Regarding Work 1a in Examples 4 to 6] {Example 4} The tooth tip circle is an imaginary circle formed by connecting the tooth tips 232 of the multiple helical teeth 230 of the gear member 1 shown in Fig. 2. The diameter of the tooth tip circle corresponds to the inner diameter of the inner circumferential surface (tooth grooves 500C) of the forming hole 500A of the forging die 5 shown in Figs.

[0158] The difference between Example 4 and Example 1 is that the difference in diameter between the tip circle diameter (=36.7 mm) shown in Fig. 2 and the diameter (=35.2 mm) of the lower body portion 2101a shown in Fig. 4 is set to 1.5 mm. Also, the difference in radius between the lower body portion 2101a radius (=17.6 mm) and the upper body portion 2103a radius (=16.4 mm) shown in Fig. 4 (the difference in radius between the radially outer end and the radially inner end of the tapered portion 2102a) is set to 1.2 mm.

[0159] {Example 5} The difference between Example 5 and Example 4 is that the step between the radius of the lower body portion 2101a (=17.6 mm) and the radius of the upper body portion 2103a (=16.45 mm) shown in FIG. 4 is set to 1.15 mm.

[0160] {Example 6} The difference between Example 6 and Example 4 is that the step between the radius of the lower body portion 2101a (=17.6 mm) and the radius of the upper body portion 2103a (=16.5 mm) shown in FIG. 4 is set to 1.1 mm.

[0161] [Analysis conditions] The analysis was performed using FORGE. The material of the workpiece 1a, the diameter of the shaft portion 2a, the total axial length of the intended helical section 23a, and the total axial length of the lower body portion 2101a in Examples 4 to 6 were the same as those in Examples 1 to 3 and Comparative Examples 1 and 2 described above.

[0162] As for the step between the lower body portion 2101a and the upper body portion 2103a (the difference in radius between the radially outer end and the radially inner end of the tapered portion 2102a), as described above, the step was 1.2 mm in Example 4, 1.15 mm in Example 5, and 1.1 mm in Example 6. In the analysis, the thickness in the forging process when forming gear members from the workpieces of Examples 4 to 6 was calculated.

[0163] The forming speed (lowering speed of the punch 510) in the forging process was 80 mm / s. The temperature of the heating section 24a at the start of the forging process, which was imparted in the partial heating process, was 500°C. The temperature difference between the heating section 24a and the heat transfer section 25a at the start of the forging process was 480°C.

[0164] [About the analysis results] Fig. 30 shows a contour diagram of the analysis results at the end of the forging process for Example 6, which is representative of Examples 4 to 6. In the diagram, the light-colored parts are parts that do not come into contact with the tooth dies 500B and tooth spaces 500C shown in Figs. 8 and 9 during forging (hereinafter referred to as "non-contact parts"). On the other hand, the dark-colored parts are parts that come into contact with the tooth dies 500B and tooth spaces 500C shown in Figs. 8 and 9 during forging (hereinafter referred to as "contact parts").

[0165] As a result of the analysis, it was found that optimizing the dimensions of the workpiece 1a improves the forming accuracy (shape accuracy) of the helical bob 230 after the forging process. Specifically, it was found that optimizing the difference in diameter between the diameter of the tip circle shown in Fig. 2 and the diameter of the lower body portion 2101a shown in Fig. 4, and the step difference between the radius of the lower body portion 2101a and the radius of the upper body portion 2103a shown in Fig. 4 (the difference in radius between the radially outer end and the radially inner end of the tapered portion 2102a) improves the forming accuracy of the helical bob 230.

[0166] As shown in Fig. 30 (see the symbols in Figs. 1 to 3), a pair of tooth grooves is arranged on both sides of any given helical protrusion 230. In the forging process, the convex helical protrusion 230 corresponds to the tooth groove 500C of the concave forging die 5 shown in Figs. 8, 12 to 13. In addition, the concave tooth groove corresponds to the tooth shape 500B of the convex forging die 5 shown in Figs. 8, 12 to 13.

[0167] During the forging process, the material of the workpiece 1a (material forming the helical joint 230) flows along the tooth grooves 500C of the forging die 5. Here, the tooth grooves 500C extend spirally around the central axis Ya, which also extends in the vertical direction, rather than in the vertical direction (the opening and closing direction of the forging die 5). Therefore, the flow conditions of the material of the workpiece 1a are different between a pair of tooth grooves 500C adjacent to each other in the circumferential direction across any tooth shape 500B. Therefore, between a pair of tooth grooves 500C, a phenomenon may occur in which material flowing through one tooth groove 500C overlaps with material flowing through the other tooth groove 500C. As a result, forming defects such as "closing flaws" may occur in the helical joint 230.

[0168] The tendency for molding defects to occur is more pronounced when the difference in diameter between the tip circle diameter shown in Figure 2 and the diameter of the lower body portion 2101a shown in Figure 4 is large, or when the difference in step between the radius of the lower body portion 2101a and the radius of the upper body portion 2103a shown in Figure 4 is small.

[0169] In this regard, in the case of Example 6, the difference in diameter between the diameter of the tip circle (=36.7 mm) shown in Fig. 2 and the diameter (=35.2 mm) of the lower body portion 2101a shown in Fig. 4 is set to 1.5 mm. In addition, the difference in step between the radius (=17.6 mm) of the lower body portion 2101a and the radius (=16.5 mm) of the upper body portion 2103a shown in Fig. 4 is set to 1.1 mm.

[0170] Therefore, in the case of Example 6, as shown by the dark-colored portions in FIG. 30, the workpiece 1a is in full contact with the tooth dies 500B and tooth grooves 500C shown in FIGS. 8 and 9. That is, the material of the workpiece 1a reaches the groove bottom of the tooth grooves 500C. Therefore, it is possible to prevent the occurrence of forming defects such as "closing flaws" between a pair of tooth grooves 500C adjacent in the circumferential direction across any tooth die 500B. That is, it is possible to improve the forming accuracy (shape accuracy) of the helical tooth 230.

[0171] In the cases of Examples 4 and 5, the same analysis results as those in Fig. 30 are obtained. Therefore, in the cases of Examples 4 and 5, as in Example 6, it is possible to suppress the occurrence of forming defects such as "closing flaws" and improve the forming accuracy of the helical tooth 230.

[0172] <Analysis 3 (Example 7)> Next, Analysis 3 (analysis based on experiments) will be described with reference to Figures 1 to 9. In the analysis, the step arrangement step, partial heating step, and forging step of the above-described gear member manufacturing method were performed on the workpiece of Example 7 shown below.

[0173] [About Work 1a of Example 7] The material of the workpiece 1a, the diameter of the shank 2a, the overall axial length of the intended helical section 23a, and the overall axial length of the lower body portion 2101a of Example 7 are the same as those of the above-described Example 6. That is, the materials and dimensions of Example 7 and Example 6 are the same.

[0174] [Analysis conditions] 5 had an output of 15 kW, a frequency of 3 to 80 kHz, and a single turn of the heating coil 42. In the analysis, the thickness of the workpiece in Example 7 during the forging process was evaluated when a gear member was formed.

[0175] The forming speed (lowering speed of the punch 510) in the forging process was 80 mm / s. The temperature of the heating section 24a at the start of the forging process, which was imparted in the partial heating process, was 420°C. The temperature difference between the heating section 24a and the heat transfer section 25a at the start of the forging process was 480°C.

[0176] [About the analysis results] Fig. 31 shows a photograph (viewed from the radial outside) of the workpiece at the end of the forging process of Example 7. As shown in Fig. 31 (see the symbols in Fig. 4), the lower chamfered portion 2100 (near the upper end position 234 of the helical section 23) has a smooth arc-shaped surface (cylindrical outer peripheral surface). As a result of the analysis, it was found that setting the temperature of the heating section 24a at the start of the forging process to 420°C improves the forming accuracy (shape accuracy) of the lower chamfered portion 2100 after the forging process.

[0177] <Analysis 4 (Example 8)> Next, Analysis 4 (CAE analysis) will be described with reference to Figures 1 to 9. In the analysis, the step arrangement step, partial heating step, and forging step of the above-described gear member manufacturing method were performed on the workpiece of Example 8 shown below.

[0178] [About Work 1a of Example 8] The first difference between Example 8 and Example 1 is the upper end position 240a of the heating section 24a shown in Fig. 4. In Example 8, the upper end position 240a is at the 18% position. That is, in Example 8, the lower 18% section of the planned helical section 23a is set as the heating section 24a to be heated in the partial heating step.

[0179] The second difference between Example 8 and Example 1 is that at the start of the forging process, the heating section 24a is heated in the partial heating process so that the planned helical section satisfies the following temperature distribution.

[0180] The specific temperature distribution is as follows: The temperature difference between the 0% position (lower end position 235a) and the 18% position (upper end position 240a of the heating section 24a) is 0°C or more and 90°C or less. The temperature difference between the 18% position and the 25% position is 90°C or more and 150°C or less. The temperature difference between the 25% position and the 33% position is 150°C or more and 200°C or less. The temperature difference between the 33% position and the 100% position (upper end position 234a of the planned helical section 23a) is 200°C or more.

[0181] [Analysis conditions] The analysis was performed using FORGE. The material of the workpiece 1a, the diameter of the shaft portion 2a, the total axial length of the intended helical section 23a, the total axial length of the lower body portion 2101a, and the step between the lower body portion 2101a and the upper body portion 2103a (the difference in radius between the radial outer end and the radial inner end of the tapered portion 2102a) in Examples 4 to 6 were the same as those in Examples 6 and 7. In the analysis, the thickness in the forging process when a gear member was formed from the workpiece of Example 8 described below was calculated.

[0182] The forming speed (lowering speed of the punch 510) in the forging process was 80 mm / s. The temperature of the heating section 24a at the start of the forging process, which was imparted in the partial heating process, was 500°C.

[0183] [About the analysis results] Figure 32 shows a contour diagram of the temperature distribution of the workpiece at the beginning (start) of the forging process in Example 8. In Figure 32, the light-colored areas are high-temperature areas, and the dark-colored areas are low-temperature areas. Figure 33 shows a contour diagram of the analysis results at the end of the forging process in Example 8. As with Figure 30 above, the light-colored areas in Figure 32 are non-contact areas, and the dark-colored areas are contact areas.

[0184] As shown in FIG. 32 (see the symbols in FIG. 4), a predetermined temperature distribution is ensured in the helical section 23a at the start of the forging process. Specifically, the entire vertical length of the helical section 23a is defined as 100%, the lower end position 235a as the 0% position, and the upper end position 234a as the 100% position. The temperature difference between the 0% position (lower end position 235a) and the 18% position is set to 90°C, the temperature difference between the 18% position and the 25% position is set to 150°C, the temperature difference between the 25% position and the 33% position is set to 200°C, and the temperature difference between the 33% position and the 100% position (upper end position 234a) is set to 200°C. In this way, a predetermined temperature distribution is ensured in the helical section 23a at the start of the forging process. Therefore, when the formed portion is machined, the unformed portion does not expand radially outward outside the forming hole. This makes it easier to press the workpiece 1a into the forming hole.

[0185] Therefore, as shown in Fig. 33, the thickness of the workpiece 1a can be distributed over the entire helical section 23a. Therefore, the helical section 230 can be reliably formed over the entire helical section 23a. As a result of the analysis, it was found that the forming accuracy (shape accuracy) of the helical section 230 can be improved by ensuring the above-mentioned temperature distribution at the start of the forging process. [Explanation of symbols]

[0186] 1: gear member, 2: shaft portion, 20: lower end portion, 200: lower tapered portion, 201: body portion, 202: upper tapered portion, 21: shaft main body portion, 210: flange lower body portion, 2100: lower chamfered portion, 211: flange base body portion, 22: upper end portion, 220: upper chamfered portion, 23: helical section, 230: helical, 231: grain flow line, 232: tooth tip, 233: tooth root, 234: upper end position, 235: lower end position, 3: flange portion, 30: disc portion, 300: radial inner end, 31: cylindrical portion 1a: workpiece, 2a: shaft portion, 20a: lower end portion, 200a: lower tapered portion, 201a: body portion, 202a: upper tapered portion, 21a: shaft main body portion, 2100a: lower chamfered portion, 2101a: lower body portion, 2102a: tapered portion (step portion), 2103a: upper body portion, 210a: flange lower body portion, 211a: flange base body portion, 220a: upper chamfered portion, 22a: upper end portion, 23a: helical intended section, 234a: upper end position, 235a: lower end position, 24a: heating section, 240a: upper end position, 25a: heat transfer section, 3a: flange portion, 30a: disc portion, 300a: radial inner end, 31a: cylindrical portion 4: High frequency induction heating device, 40: Device body, 41: Work support part, 410: Base part, 411: Frame part, 412: Leg part, 42: Heating coil 5: forging die, 50: lower die, 500: die, 500A: forming hole, 500B: tooth shape, 500C: tooth groove, 501: die holder, 501A: recess, 501B: bottom wall portion, 501C: pin support hole, 502: die plate, 502A: pin insertion hole, 51: upper die, 510: punch, 53: knockout pin, 530: shaft portion, 531: upper end portion, 531A: recess, 531B: side peripheral wall portion, 531C: ejection tooth A: Heating section on the device side, B: Formed part, C: Unformed part, Y: Central axis, Ya: Central axis

Claims

1. A method for manufacturing a gear member comprising: a shank having a helical section in which a plurality of helical bars are arranged; a plurality of grain flows exist within the helical section; the grain flows are continuous between the plurality of helical bars; and the grain flow density is higher at the roots of the helical bars than at the tips of the helical bars, a partial heating step of heating a section of the workpiece including the shank portion having a helical planned section in which a heating section and a heat transfer section connected to a rear side of the heating section are arranged, the section including the heating section but not including the heat transfer section; a forging process in which the shank of the workpiece is forced into a forming hole having a plurality of tooth forms corresponding to the helix, and the heat transfer section is heated from the front side to the rear side by utilizing heat transfer from the heating section heated in the partial heating process to the heat transfer section, thereby forming the helix in the helix planned section; A method for manufacturing a gear member, comprising:

2. 2. The method for manufacturing a gear member according to claim 1, further comprising a step providing step of providing a step having a diameter that decreases from the front side to the rear side in the predetermined helical section before the partial heating step.

3. 2. The method for manufacturing a gear member according to claim 1, further comprising, after the forging step, a discharging step of extruding the helices filled in the tooth grooves between a pair of adjacent tooth dies from a front side along an extending direction of the tooth grooves, thereby discharging the gear member, which is the workpiece after the helical forming, from the forming hole.

4. 2. The method for manufacturing a gear member according to claim 1, wherein the gear member and the workpiece are each integral with the shaft portion and have a flange portion that protrudes radially outward from the shaft portion.

5. Before the partial heating step, the shaft portion of the workpiece has a flange lower body portion connected to a front end of a radially inner end of the flange portion, The flange lower body portion of the workpiece includes, from the front side to the rear side, a front body portion, a step portion, and a rear body portion, the front body portion has a larger diameter than the rear body portion, a step between the front body portion and the rear body portion is 1 mm or more; an addendum circle of the plurality of helical teeth of the gear member has a diameter larger than an outer diameter of the front trunk portion of the workpiece; 5. The method for manufacturing a gear member according to claim 4, wherein the difference in diameter between the tip circle and the outer diameter of the front body portion is 2 mm or less.

6. 2. The method for manufacturing a gear member according to claim 1, wherein in the partial heating step, the heating section is heated so that the temperature of the heating section at the start of the forging step is 400°C or higher and lower than 520°C.

7. The total length of the planned helical section in the fore-and-aft direction is set to 100%, the front end position is set to 0% position, and the rear end position is set to 100% position, In the partial heating step, at the start of the forging step, The temperature difference between the 0% position and the 18% position is 0°C or more and 90°C or less. The temperature difference between the 18% position and the 25% position is 90°C or more and 150°C or less. The temperature difference between the 25% position and the 33% position is 150°C or more and 200°C or less, The temperature difference between the 33% position and the 100% position is 200°C or more, As each one is, 2. The method for manufacturing a gear member according to claim 1, wherein the heating section corresponds to a section from the 0% position to the 18% position.

8. a shaft portion having a helical section in which a plurality of helical grooves are arranged; a flange portion integral with the shaft portion and protruding radially outward from the shaft portion; A gear member comprising: a plurality of grain flows are present within the helical section, the grain flow is continuous between the plurality of helices, A gear member, characterized in that the grain flow density is higher at the root of the helical tooth than at the tip of the helical tooth.

9. 9. The gear member according to claim 8, wherein the plurality of grain flows extend along the surface shape of the helical groove.

10. A forging die used in the forging step and the discharging step in the method for manufacturing a gear member according to claim 3, a die having the shaping hole; a punch that pushes the workpiece into the forming hole from the rear side; a knockout pin that pushes the gear member out of the molding hole from the front side; Equipped with The knockout pin has an ejection tooth that moves along a tooth groove between a pair of adjacent tooth dies, the ejection tooth pushes the helical teeth filled in the tooth grooves from the front side along an extension direction of the tooth grooves, thereby pushing the gear member out of the forming hole.

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