JP4383151B2 - Manufacturing method of helical gear - Google Patents

Description

  The present invention relates to a method for manufacturing a helical gear by cold forging.

  A method of manufacturing a gear by cold forging using a metal material is known as disclosed in Patent Document 1.

  1A and 1B show a conventional spur gear manufacturing method by cold forging described in Patent Document 1. FIG. The cylindrical metal material 10 has a size close to the desired outer diameter of the gear. The lower end of the cylindrical metal material 10 is inserted into the hole 11A of the mold 11, pushed in from the direction of the arrow X, and the metal material 10 is pressed by a punch (not shown). A male tooth profile is formed on the outer periphery of the. The male tooth profile formed on the outer periphery of the material 10 corresponds to the tooth profile 12 of the mold 11. The relationship between the tooth root and the tooth tip of the tooth profile is reversed between the material 10 and the mold 11. The tooth profile 12 of this mold 11 has a regular full tooth bamboo H. Therefore, the tooth profile formed on the outer periphery of the material 10 has the regular full tooth bamboo H as well.

  1A and 1B, reference numeral 13 denotes a pitch circle. Reference numeral 14 indicates a tip circle of the tooth profile 12 of the mold 11, and reference numeral 15 indicates the root circle.

  In the conventional method of manufacturing a gear by cold forging, the end surface 16 of the tooth forming shape start portion of the tooth profile 12 of the die 11 is inclined, but the inclination angle B of the end surface 16 with respect to the surface perpendicular to the axis of the die 11 is 30. ° or less. The smaller the inclination angle B, the fewer incomplete tooth profile portions.

  In addition, the material 10 may be cold forged in a single process, but after being preformed hot or warm in advance, it is annealed, surface lubricated, etc., and then finished by cold forging. Sometimes.

  In the conventional method of manufacturing a gear by cold forging shown in FIG. 1, the quality of the final product gear is considered to account for 50 to 80% of the factors related to the forging die.

  In the method shown in FIG. 1, molding is performed inside a female mold, which is called in-die molding. The material of the metal material used in this manufacturing method is a solid round bar, a ring-shaped material, a pre-processed product by hot or warm forging, or the like.

In the conventional method shown in FIG. 1, the finished dimension is obtained by cold forging the gear in one step. Therefore, the load (pressure) applied to the inclined end surface 16 of the tooth forming shape start portion of the tooth profile 12 is 200 kgf / mm ² to 280 kgf / mm ² . This load (pressure) is 70 to 90% of the breaking strength of the mold even if the material has the highest level as the mold material.

  On the other hand, as shown in Patent Document 2, it is swept into a primary working gear having a gear shape in which both the tooth tip and the tooth thickness are set smaller than the tooth profile of the gear shape of the spur gear from which the material is to be obtained. A first machining step, a second machining step in which the material is freely flowed in a portion other than the tooth profile in the primary machining gear, and compression molding into a secondary machining gear, and the secondary machining gear is ironed into a final product. A spur gear forging method is also known, which includes a third processing step, and performs each of these steps by cold forging.

  2A to 2E show the method described in Patent Document 2, FIG. 2A is a first processing step, and FIG. 2B is a gold for performing the second processing step. Represents a type.

  2A, reference numeral 200 denotes a die, and 201 denotes a tooth profile portion of the die 200. A punch 202 fitted into the die 200 and a knockout pin 204 inserted into the through hole 203 corresponding to the punch 202 are provided. Yes. Reference numeral 205 denotes a material, and 206 denotes a primary processing gear processed by the die 200.

  2B, 210 is a die, 211 is a tooth profile portion of the die 210, 212 is a through hole that communicates with the tooth profile portion 211 and penetrates the die 210, 213 is a punch that fits into the die 210, and 214 is a die 210. A knockout pin inserted into the through hole 212. Reference numeral 215 denotes a secondary machining gear machined by the die 200, and a material raised portion 216 is formed toward the through hole 212.

  In FIG. 2 (A), the primary working gear 206 upset from the raw material 205 is insufficiently filled in the die of the material, resulting in a lacking wall 207. Next, the primary working gear 206 is put into the die of FIG. 2B, the material is filled in the tooth profile portion 211 by compression molding with the punch 213, and the secondary processing gear 215 is molded.

  The secondary processing gear 215 formed in the compression molding by the punch 213 is formed by forming the raised portion 216 by freely flowing the material in a portion where the material is not restrained to a portion other than the tooth shape during the molding processing. Fills the tooth profile part 211 and eliminates the lack of thickness that occurs in the tooth tip part.

2 (C) to 2 (E) are diagrams comparing the tooth profile shapes of the primary processing gear 206 formed and processed in the first processing step and the primary processing gear 215 formed and processed in the second processing step. The tooth profile contour 206A formed in the first processing step is set so that the tooth tip and the tooth thickness are smaller than the tooth profile contour 215A formed in the second processing step.
Japanese Patent Laid-Open No. 9-300041 Japanese Patent No. 2913522

  In the method described in Patent Document 1, the maximum load during cold forging is often generated on the inclined end surface 16 of the tooth forming shape starting portion on the inner surface of the die. Conventionally, the life of the mold 11 was short because there was not enough device to reduce the maximum load. As a result, there is a drawback that product accuracy deteriorates.

  In particular, when a helical gear is manufactured by cold forging, a load for applying the tooth profile 12 of the die 11 to only one side is applied, so the probability of breakage near the inclined surface 16 tends to increase. . As a result, the life of the mold 11 was shortened.

  According to the knowledge of the present inventor, in the case of processing a helical gear by cold forging, a load is intensively applied to one surface (front surface) of the mold tooth profile, and the back surface thereof is not much. No load is applied. Therefore, the difference in load between the front side and the back side of the tooth profile is remarkable, and there are many tooth profile defects caused by the difference.

  The method described in Patent Document 2 has the following problems.

  As shown in FIG. 2 (E), since the entire tooth profile including both the tooth tip and the tooth thickness is formed into a smaller (decreased) shape and size than the contour of the completed helical tooth profile, the plastic working rate is increased.

  When the processing rate increases, plastic work hardening of the processed product proceeds, deformation resistance increases, and molding becomes difficult.

  Furthermore, the shape factor increases, the overhang forming pressure (molding load) increases, and the distortion of the mold increases. Therefore, the accuracy of the processed product is lowered. Molds can be easily damaged by increasing the processing speed.

  As shown in FIG. 2 (E), the method of enlarging (thickening) the tooth profile formed small by primary processing is not preferable in terms of accuracy. For example, as the tooth width increases, the difference between the center width and the end face portion of the tooth width (formation degree) increases. The tooth profile becomes uneven and the cylindricity becomes worse.

  In particular, the method described in Patent Document 2 is not suitable as a method for mass-producing high-precision gears.

  When the molding load is increased in order to increase the accuracy, the distortion of the processed product increases, and the processing distortion during the subsequent heat treatment increases. The greater the load, the easier the mold breaks.

  Therefore, an object of the present invention is to provide a method of manufacturing a helical gear by cold forging, which can prolong the life of a working die and manufacture a good tooth profile.

  The solution of the present invention is exemplified by the following helical gear manufacturing method.

(1) In a method of manufacturing a helical gear by cold forging,
A material formed in a cylindrical shape with a metal material is inserted into an initial mold, and the end surface of the material is pressurized to project the material in the radial direction to form an initial processed product having an initial helical tooth shape, and then the initial An initial step of removing the initial workpiece from the initial mold while rotating the workpiece relative to the initial helical tooth profile in the initial mold;
By pressing the end face of the initial workpiece, the initial workpiece is moved in the intermediate mold while rotating relatively along the intermediate helical tooth profile of the intermediate mold, and is almost the same as the tooth thickness of the initial helical tooth profile. to either maintain the tooth thickness decreases the tooth thickness in the range of 10% or less than the tooth thickness of the initial helical teeth, and, together with to project the addendum radially outward than the initial helical tooth profile, tooth the bottom is compressed radially inward by molding the intermediate workpiece, this time, the addendum of the intermediate helical tooth profile of the intermediate workpiece, to an intermediate helical teeth of the intermediate mold, leaving a space without contacting The thickness of the intermediate helical tooth profile and the root of the intermediate workpiece are brought into contact with the intermediate helical tooth profile of the intermediate mold , and then the intermediate workpiece is relatively moved along the intermediate helical tooth profile in the intermediate mold. Remove from the intermediate mold while rotating And the intermediate step,
A completion process of forming a finished helical tooth profile by sizing the intermediate helical tooth profile of the intermediate product;
The manufacturing method of the helical gear characterized by including these.

  A preferred embodiment of the present invention will be described.

  The helical gear manufactured by the method of the present invention is preferably a helical gear of a power train for automobiles that is particularly required for mass production and high dimensional accuracy, and a method of manufacturing such a helical gear by cold forging, At least the following three types of processes are included.

(1) An initial step of forming an initial processed product having an initial helical tooth profile by cold forging by inserting a metal material into an initial mold and pressurizing the end face of the material.

(2) Insert the initial processed product into the intermediate mold while relatively rotating, and maintain the tooth thickness at a predetermined position substantially the same as the initial helical tooth profile, While reducing the tooth thickness within a range of 10% or less than the tooth thickness, the intermediate workpiece having the intermediate helical tooth profile is formed by one or more cold forgings by protruding the tip of the tooth from the initial helical tooth profile. Intermediate process.

(3) A completion process of forming a completed helical tooth profile by sizing the intermediate helical tooth profile of the intermediate processed product.

  The tooth thickness dimension of the processed product after the initial process (initial processed product) is set so as to increase the tooth thickness within the range equal to or less than 10% of the completed helical tooth profile. Moreover, the roundness of the bottom of the initial helical tooth profile of the initial processed product is set larger than that of the completed helical tooth profile. In this case, if the processing rate between the initial process and the intermediate process is appropriately distributed, even if the molding process pressure (molding load) is reduced by 10 to 50% compared to the case of conventional stretch molding alone, A desired completed helical tooth profile can be obtained by finishing (sizing finishing).

  The outer diameter of the tooth profile of the intermediate workpiece after the intermediate process is formed to be slightly larger than the completed helical tooth profile. This makes it easy to obtain an accurate tooth profile in the subsequent sizing process (finish drawing process).

  In order to avoid increasing the working pressure in the initial process and the intermediate process, it is preferable not to approach the fully closed state (that is, non-closed forging) during each cold forging. For example, after each cold forging, a space remains between the root of the tooth profile of the mold and the tip of the tooth tip of the tooth profile of the workpiece.

  After each cold forging, the tooth tip of the processed product is rounded, and the roundness is set to an arc or other chevron-shaped curved surface (a shape in which the top is located in the middle) and large. By increasing the roundness of the tooth tip of the processed product, the strength against cracking of the mold is improved.

  As described above, the present invention makes it possible to obtain a lower molding load by rounding the tooth tip of the tooth profile of the processed product by non-closed forging.

  If it carries out as follows, it can process by a lower load in each cold forging.

(1) Applying a molybdenum sulfide coating or a lubricating film for bonding.

(2) In the case of steel, soft annealing is performed at 600 to 650 ° C. for 90 to 240 minutes.

(3) Adjust the tooth profile. The tooth thickness is almost the same between the initial machining and the intermediate machining. The combination of the height of the tooth tip (tooth bamboo), the roundness of the tooth base (bottom) and the roundness of the tooth tip is combined.

(4) In the case of a material having a high work hardening rate, the dimensions are distributed in consideration of an intermediate additional tertiary processing setting.

(5) Setting and distribution of shapes and dimensions other than the tooth profile portion.

(6) A guide portion is provided at the mouth portion of the mold for initial machining. The length of the guide portion is approximately the tooth width of the processed product. The loss of the dimensional difference between the intermediate machining die and the initial machining die is eliminated, and the increase (protrusion) of the tip height is effectively obtained. This is a practically effective method in mass production.

  It is preferable to start with a long coil material, form a large number of cylindrical materials by cutting or other automatic processing, and cold forge them in 3 to 7 stages with a parts homer to form a finished helical tooth profile. In this case, the best mass production form can be taken in terms of cost.

  In the case of a helical tooth profile, the torsion angle can be formed accurately and accurately, so that it can be used as a reference surface for accuracy in the subsequent process.

  An example of another preferred processing procedure according to the present invention will be described as follows.

(1) The initial process of tooth molding is a process in which a cylindrical material is placed in a mold and both ends of the material are pressed with a punch to project the side surface of the material outward. Further, extrusion molding is performed as an intermediate process, and the molding pressure at that time is lowered. In this way, the accuracy and the effect of improving the mold life are great.

(2) Softening annealing and lubrication coating are performed immediately after the initial process. The main purpose of this is to obtain a good surface roughness.

(3) In extrusion molding in the intermediate process, 0.02 to 0.10 sizing allowance (finish drawing allowance) is provided on each surface of the tooth outer diameter, tooth surface, and tooth bottom of the processed product. The extrusion molding may be performed three times on a case-by-case basis.

(4) Sizing (finish drawing) in the completion process to finish the tooth profile. The mold for sizing is provided with a guide part at the base of the hole of the mold, the tooth trace is fixed to the entire length of the blank, and the blank and the tooth surface of the mold are applied. As a result, it is possible to prevent the tooth traces from deviating due to sizing pressure. In this case, since the working pressure required for finishing the tooth profile is low, the internal stress is reduced and the accuracy is high.

(5) The end face and hole of the helical gear are cut. The processing reference surface is the tooth surface or the tooth outer diameter. Furthermore, chamfer cutting of the end face corner may be performed.

(6) A gear designated for heat treatment is quenched.

(7) Improve surface roughness and remove minute burrs. For example, barrel polishing or shot peening is performed. Electropolishing or chemical polishing may be performed.

(8) Grind the hole and end face of the helical gear. If not specified, grinding is not performed.

(9) Clean the helical gear.

(10) The helical gear is rust-proofed (generally with rust-preventing oil applied).

  The present invention is an improvement of a method for manufacturing a helical gear by cold forging, and has a remarkable effect on a helical gear. Although it has been recognized that the helical gear is extremely difficult to manufacture by cold forging, according to the present invention, the helical gear can be manufactured efficiently and with high accuracy. For example, according to the manufacturing method of the present invention, the product accuracy of the helical gear can be JIS standard class 2 to class 5.

  The present invention includes a method of performing preforming by cold forging after preforming hot or warm, and a method of adding cutting or the like before or during forging as necessary. That is, the present invention is not limited to a method of manufacturing a final product of a helical gear from the beginning to the end only by cold forging.

  The material used in the present invention is not limited to a cylinder in the strict sense, and may be in the broadest column shape, including a ring-shaped material and the like.

  The material may have no holes, but may have holes before the tooth profile is formed. When there is a hole, a cored bar pin may be arranged at the center. In this case, the material length is longer for the material with holes than for the material without holes. During the initial overhanging process, the tooth profile can be formed by pressurizing both end faces while plastically processing the hole. A material preferable from the viewpoint of cost is a long metal coil material cut at a predetermined interval. In principle, materials that are normally used as gear materials can be used.

  In the present invention, by using a metal material, it is possible to use a combination of overhanging, drawing, and extrusion. If the tooth width of the gear becomes relatively large and it is difficult to obtain cylindricity only by overhang molding and extrusion, a good effect can be obtained by performing a drawing with an appropriate distribution of the processing rate. Even in the case of a material with poor spreadability, it is effective to use drawing together. The processing rate is set in consideration of dimensions and materials.

  In any of the above-described embodiments, the overhang molding and the extrusion molding are preferably compression molding using a punch or a pin to press the end face of a material or a processed product.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  3-6 illustrate one preferred embodiment of the present invention. FIG. 6 shows each processing state of FIGS. Reference numeral 50 in the figure denotes a gear. Reference numeral 54 denotes a pitch circle of a regular tooth profile.

  Hereinafter, each process will be described.

  In the initial step, a cylindrical material made of a metal material is inserted into the first mold 30 (only the tooth bottom and the vicinity thereof are shown), and overhanging is performed. Thereby, the initial helical tooth profile 51 of the initial processed product shown in FIG. 3 is obtained. The initial helical tooth profile 51 has a rounded tip 51a.

  In the intermediate process, the initial helical tooth profile 51 with the rounded tooth tip shape obtained in the initial process is inserted into the second mold 40 (only the tooth bottom and the vicinity thereof are shown in FIG. 4) to perform extrusion molding. To do. As a result, an intermediate processed product having the intermediate tooth profile 52 having a rounded tooth tip shape in the intermediate process shown in FIG. The intermediate tooth profile 52 has a rounded tip 52a.

  The tooth thickness is kept the same in the initial process and the intermediate process. At the same time, the tooth tips 51a and 52a protrude stepwise while changing the rounded shape by a plurality of cold forgings and approach the tooth tip of the completed helical tooth shape. In the intermediate process, the shape of the tooth tip may be rounded by one cold forging, but in order to reduce the forming pressure, the shape of the tooth tip is rounded by multiple cold forgings. It is preferable to do this.

  In both of the initial process and the intermediate process, a space is left between the tooth tips 51a and 52a of the tooth profiles 51 and 52 of the workpiece 50 and the tooth bottoms of the tooth profiles of the molds 30 and 40. In other words, it is not hermetic forging but non-hermetic forging.

  The shape of the tooth tips 51a and 52a of the tooth profiles 51 and 52 of the processed product 50 is set to have a large roundness.

  In the completion process, the tooth profile 52 obtained in the intermediate process is finish-molded by sizing (that is, drawing). Thereby, the completed helical tooth profile 53 shown in FIG. 5 is obtained.

  The obtained completed helical tooth profile 53 is a regular tooth profile, and the fiber flow is good and no crack is generated.

  FIG. 6 shows the above-described various tooth profiles 51, 52, and 53 together.

  An important point about a series of cold forging processes of such a helical gear will be described below.

(1) The initial process of forming the helical tooth profile is overhang forming. As a result, the twist angle can be accurately transferred, and the molding pressure can be lowered from intermediate processing.

(2) Softening annealing and lubricating film application are performed immediately after the initial process. This process is mainly employed to obtain surface roughness.

(3) The initial processed product is extracted from the mold in the initial process while rotating along the twist angle. This can be done by pushing the end face of the workpiece from one direction.

(4) The initial processed product is inserted into the intermediate process mold while being rotated along the twist angle, set at a predetermined position, and then subjected to extrusion molding in the intermediate process. At this time, 0.02 to 0.10 mm sizing (finish drawing) is given to the outer diameter, tooth surface, and tooth bottom surface of the helical tooth profile of the intermediate processed product. Extrusion molding may be performed three times on a case-by-case basis. Thereafter, the intermediate workpiece is extracted from the intermediate mold while rotating along the twist angle. This can be done by pushing the end face of the workpiece from one direction.

(5) In the completion process, sizing is performed so as to reduce the thickness of the tooth profile surface by 0.02 to 0.2 mm, and the helical tooth profile is finished. The sizing mold is preferably provided with a guide portion at the base of the hole. A tooth streak is applied over the entire length of the blank (metal material). This prevents the tooth streak from being distorted by sizing pressure. Since the processing pressure required for tooth profile finishing is low, the internal stress is small and the accuracy is high.

(6) The end face and hole of the helical gear are processed by cutting. The processing reference surface is the tooth surface or the tooth outer diameter.

(7) The gears designated for heat treatment are hardened.

(8) Barrel polishing and shot peening are performed for the purpose of improving the surface roughness and removing minute burrs. Electropolishing or chemical polishing may be performed.

(9) The gear hole and end face are ground. If not specified, no grinding is performed.

(10) Wash the finished product.

(11) Rust-proof the finished product.

  FIG. 7 shows another embodiment of the present invention. In the second embodiment, a helical tooth pinion is formed.

  An example of a method for forming the helical tooth pinion 90 will be described.

  A cylindrical metal material provided with holes in advance is placed in a predetermined mold (not shown). In a state where a pin (not shown) having a shape corresponding to the shape of the hole is inserted into the hole, the end surface of the material is pressed along the axial direction. The pressed material is stretched and formed in the circumferential direction. Then, extrusion molding is performed using the same mold. Thereby, the tooth profile of the corresponding mold is formed excluding the tooth tip portion.

  After the extrusion molding, the helical tooth pinion 90 is extracted from the mold while rotating along the twist angle.

  An example of the helical tooth pinion 90 is that the twist angle (twist direction) is 25 ° (left) and the tooth accuracy is JIS grade 4 or grade 5.

  Such a helical tooth pinion 90 can be manufactured by the method of Example 3 described below.

  In Example 3 of FIGS. 8 to 9, the relative movement distance between the mold and the processed product is reduced, and a processed product closer to the accuracy of the mold is obtained.

  FIG. 8 shows a state immediately before processing the material, that is, a state where the processed product is started to be formed. FIG. 9 shows the completed state of the processed product.

  A common mold 101 for forming the initial tooth profile and the intermediate tooth profile is used. In order to make it easy to understand, in FIG. 8, the mold 101 is of a fixed type. The mold 101 may be moved.

  The mold 101 has a hole 101a penetrating in the axial direction. A female tooth profile 107 is formed on the peripheral surface of the hole 101a. The tooth profile 107 is a regular tooth profile, but other tooth profiles may be used.

  In FIG. 8, an upper push-out pin 108 is provided above the metal material 100 as a pressing member. The upper extruding pin 108 presses the end surface of the material 100 from above.

  An upper sleeve 102 is provided around the upper push pin 108. The upper sleeve 102 supports the material 100 and the upper pushing pin 108 from the side.

  Below the material 100, a lower extrusion pin 109 is provided as a pressing member. The lower extrusion pin 109 presses the material 100 from below.

  A lower sleeve 104 is provided around the lower push pin 109. The lower sleeve 104 is fixed and supports the material 100 and the lower extrusion pin 109 from the side.

  An example of a method for forming the initial tooth profile and the intermediate tooth profile of the helical gear by cold forging in the initial process and the intermediate process using the mold 101 will be described.

  A cylindrical material 100 is put into the center of the mold 101. Thereafter, the upper push-out pin 108 and the upper sleeve 102 move downward to confine the metal material 100, and the upper sleeve 102 and the lower sleeve 104 are stopped.

  Pressure is applied to the upper push pin 108 in the direction of arrow C (FIG. 9). Pressure is applied to the lower push pin 104 in the direction of arrow D (FIG. 9). The upper sleeve 102 and the lower sleeve 104 are stopped in a state where the mold 101 is sandwiched by hydraulic pressure or spring pressure. In such a state, a cylindrical material 100 is projected in the radial direction toward the tooth profile 107 of the mold 101 and molded. As a result, an initial tooth profile corresponding to the tooth profile 107 of the mold 101 is formed on the initial processed product 110. However, the tooth profile 107 of the mold 101 and the tooth profile of the initial processed product 110 correspond to the portion excluding the tooth tip 103 of the tooth profile of the initial processed product 110, and the tooth tip 103 corresponds to the tooth profile 107 of the mold 101. Not done. A space remains between the tooth profile 107 of the mold 101 and the tooth tip 103 of the tooth profile of the initial processed product 110.

  Using the same die 101 used in the initial process, cold forging is performed a plurality of times as an intermediate process. At that time, forging conditions (such as molding pressure and speed) are changed. Even when cold forging is performed a plurality of times in the intermediate process, the forging conditions (molding pressure, speed, etc.) need not be changed for each molding.

  In addition, various molds can be used for each molding in the initial process and the intermediate process.

  At the end of each cold forging performed in the intermediate process, the tooth tip of the intermediate tooth profile of the intermediate workpiece is not shown in the figure, but the tooth tip 103 of the initial tooth profile of the initial workpiece and the tooth profile 107 of the die 101 are Located between the tooth bottom. Therefore, a small space remains between the tooth tip of the intermediate tooth profile of the intermediate processed product and the tooth bottom of the tooth profile 107 of the mold 101.

  In the example of FIG. 9, the tooth tip of the intermediate tooth profile of the intermediate processed product at the final stage and the tooth bottom of the tooth profile 107 of the mold 101 are in contact, but the present invention is not limited to this example.

  An arrow E in FIG. 9 schematically shows the flow of the metal material during each cold forging.

  In order to take out the intermediate molded product 110 from the mold 101, first, the upper extrusion pin 108 and the upper sleeve 102 are moved upward. Thereafter, the lower extruding pin 109 is moved upward to extract the molded product 110 out of the mold 101 while rotating relative to the mold 101.

  If molded in this way, the relative movement distance between the molded gear and the mold is extremely small, so that the gear can be molded with high accuracy.

  FIG. 10 shows yet another embodiment of the present invention. In Example 4, after the tooth tip portion of the processed product is protruded in the mold in the intermediate process, the tooth profile is further formed by drawing as finishing sizing.

  The drawing die 111 has a hole 111 a penetrating in the direction of the axis 116. A female helical tooth profile 114 is formed on the peripheral surface of the hole 111a. Reference numeral 117 indicates a pitch circle.

  The drawing die 111 includes a guide part 112 and a drawing part 113.

  The guide portion 112 is provided for copying the mouth of the drawing die 111. The diameter of the pitch circle 117 of the guide portion 112 is preferably slightly larger than the diameter of the pitch circle of the previous process product that has been extruded. For example, it may be 0.05 to 0.2 mm larger. The axial length of the guide part 112 is preferably 5 times or more of the tooth module.

  The aperture portion 113 is provided at the lower end of the guide portion 112. The tooth profile 114 of the restrictor 113 is a regular tooth profile.

  When forming the finished helical tooth profile, the initial process is an overhanging process in which the peripheral surface of the metal material is raised as a whole, and then a protruding process in which only the tooth tip portion of the processed product is raised. This makes it easy to form a precise tooth stripe. Further, the intermediate processed product is inserted into the hole 111a. Then, the metal material is drawn by 0.05 to 0.2 mm by the drawing unit 113 using the protruding tooth surface as a copying surface. As a result, the tooth profile error can be extremely reduced.

  Also in the above-described Examples 2 to 4, it is preferable to adopt the important points (1) to (11) described with respect to the above-described Example 1. In particular, for each of multiple cold forgings (at least between overhanging and extrusion molding), the processed product is removed from the mold, and a lubricating coating or softening annealing is applied to enable forging with a low load. Is preferred.

  Further, in any of the above-described Examples 1 to 4, the closed forging is not performed, that is, the tooth tip of the work tooth shape reaches the tooth bottom of the tooth shape of the die in each of multiple stages (a plurality of cold forgings). It is preferable to stop the molding before starting to avoid an increase in molding load. The shape of the tooth tip of the workpiece is rounded so that a small space remains between it and the bottom of the mold. The shape of the top portion of the tooth tip of the tooth profile formed by the protrusion is not limited to the circular arc, and can be various rounded shapes and other free shapes as long as the protrusion is advantageous.

  In addition, this invention is not limited to the above-mentioned Example.

FIG. 1A is a cross-sectional view taken along line 1-1 of FIG. 1B and shows a conventional spur gear manufacturing method by cold forging. FIG. 1 (B) shows the tooth-forming start portion of the mold as seen from the direction of arrow A in FIG. 1 (A). (A) is sectional drawing of the metal mold | die used at the 1st processing process in another other conventional method. (B) is sectional drawing of the metal mold | die used at a 2nd manufacturing process. (C)-(E) are the comparison figures of the tooth profile shape-molded by the above-mentioned 1st process process and a 2nd process process. The tooth profile 51 obtained in yet another embodiment of the present invention is shown. The tooth profile 52 obtained in the next step of FIG. 3 is shown. The tooth profile 53 obtained in the next step of FIG. 4 is shown. 3 to 5 are shown together. Yet another embodiment of the present invention will be described. It is another Example of this invention, and the shaping | molding start state of a processed article is shown. FIG. 9 shows a completed state of the processed product of FIG. Yet another embodiment of the present invention will be described.

Explanation of symbols

30 type 40 type 50 helical gear 51 helical tooth profile 51a tooth tip 52 helical tooth profile 52a tooth tip 53 helical tooth profile 54 pitch circle 90 helical tooth profile pinion 100 metal material 101 mold 102 upper sleeve 104 lower sleeve 105 tooth bottom 107, 114 female Tooth profile 108 Upper extruding pin 109 Lower extruding pin 111 Drawing die 112 Guide part 113 Drawing part 116 Center axis 117 Pitch circle

Claims (1)

In a method of manufacturing a helical gear by cold forging,
A material formed in a cylindrical shape with a metal material is inserted into an initial mold, and the end surface of the material is pressurized to project the material in the radial direction to form an initial processed product having an initial helical tooth shape, and then the initial An initial step of removing the initial workpiece from the initial mold while rotating the workpiece relative to the initial helical tooth profile in the initial mold;
By pressing the end face of the initial workpiece, the initial workpiece is moved in the intermediate mold while rotating relatively along the intermediate helical tooth profile of the intermediate mold, so that it is almost the same as the tooth thickness of the initial helical tooth profile. to either maintain the tooth thickness decreases the tooth thickness in the range of 10% or less than the tooth thickness of the initial helical teeth, and, together with to project the addendum radially outward than the initial helical tooth profile, tooth the bottom is compressed radially inward by molding the intermediate workpiece, this time, the addendum of the intermediate helical tooth profile of the intermediate workpiece, to an intermediate helical teeth of the intermediate mold, leaving a space without contacting The thickness of the intermediate helical tooth profile and the root of the intermediate workpiece are brought into contact with the intermediate helical tooth profile of the intermediate mold , and then the intermediate workpiece is relatively moved along the intermediate helical tooth profile in the intermediate mold. Remove from the intermediate mold while rotating And the intermediate step,
A completion process of forming a finished helical tooth profile by sizing the intermediate helical tooth profile of the intermediate product;
The manufacturing method of the helical gear characterized by including these.

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