JP2007051354A - Method and apparatus for manufacturing gear - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform a shot-peening process to compensate the decrease of strength in the vicinity of a tooth surface edge caused by vacuum carburizing. <P>SOLUTION: When performing the shot-peening process after subjecting a hypoid gear 1 to vacuum carburizing and quenching treatment, a shot jetting direction of a shot jetting nozzle 5 is shifted radially outward relative to a plane containing a central axis 7 of the hypoid gear 1. In this way, shot-peening is performed on a tooth bottom 1a as well as the vicinity of the tooth surface edge 1c of the hypoid gear 1 to thereby increase a residual compression stress in the vicinity of the tooth surface edge 1c and compensate the decrease of strength. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gear manufacturing method and a manufacturing apparatus that perform shot peening after vacuum carburizing and quenching of a gear.

  The gas carburizing and quenching process for hypoid gears used in automobile transmissions, etc. requires a significant reduction in processing time so that gear parts of various specifications, such as the number of teeth, can be produced according to the assembly procedure of automobiles, etc. It has been. However, in the gas carburizing method that is generally performed, technological development related to shortening the processing time has already reached its limit, and it is difficult to significantly reduce the time.

  In addition, the vacuum carburizing method that has been introduced in recent years is a direct / non-equilibrium reaction in which a small amount of gas is blown in a vacuum in contrast to the gas carburizing method, which is always an equilibrium reaction in a gas atmosphere of a certain concentration. Therefore, it is possible to greatly reduce the processing time, but on the other hand, it has been found that the carbon concentration distribution of the processed parts becomes non-uniform, and it is difficult to ensure the same strength as gas carburizing.

  At this time, due to the non-uniformity of the carbon concentration that is a feature of the vacuum carburization method corresponding to the rapid carburization described above, the carbon concentration is increased in the vicinity of the end of the tooth surface, particularly in the tooth width direction, compared to the tooth bottom, In the vicinity of the portion where the carbon concentration is increased, retained austenite is increased, the mechanical properties are deteriorated, and the fatigue strength is reduced.

On the other hand, for example, the following Patent Document 1 describes increasing the fatigue strength by performing shot peening after vacuum carburizing and quenching.
Japanese Examined Patent Publication No. 6-72254

  As described in the above-mentioned Patent Document 1, it is effective to perform shot peening to increase fatigue strength after vacuum carburizing and quenching. However, a shot peening method that is usually applied is a hypoid gear. Since the center of the shot projection nozzle is aligned with the bottom of the tooth, which is the strength neck, it is not possible to compensate for the strength reduction in the vicinity of the end of the tooth surface in the tooth width direction due to vacuum carburization.

  Therefore, an object of the present invention is to perform shot peening so as to compensate for strength reduction in the vicinity of the end of the tooth surface in the width direction of the tooth surface in vacuum carburization.

  The present invention relates to a gear manufacturing method for performing shot peening after vacuum carburizing and quenching on a circular gear having teeth on an outer peripheral surface, and performing shot peening on the tooth surface together with the tooth bottom of the gear. It is most important that the shot projection direction of the shot projection nozzle is shifted to the outer side in the radial direction of the gear with respect to the plane including the central axis of the gear, as performed on the outer end portion in the tooth width direction. Features.

  According to the present invention, after the vacuum carburizing and quenching process, which can significantly reduce the processing time as compared with a normal gas carburizing and quenching process, the carbon concentration at the outer edge in the tooth width direction on the tooth surface is compared with the tooth bottom. Even if fatigue strength decreases due to an increase in retained austenite, shot peening after vacuum carburizing and quenching is performed so that the shot projection direction of the shot projection nozzle is on the radially outer side of the gear with respect to the plane including the central axis of the gear. Since the deviation direction is performed on the outer end portion of the tooth surface in the tooth width direction together with the tooth bottom of the gear, the decrease in fatigue strength at the outer end portion of the tooth surface in the tooth width direction can be compensated.

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

  FIG. 1 shows a circular shape having teeth on the outer peripheral surface shown in FIG. 3 when a vacuum carburizing and quenching process (hereinafter simply referred to as vacuum carburizing) and a normal gas carburizing and quenching process (referred to as gas carburizing) are performed. The surface carbon concentration in the vicinity of a tooth surface edge portion (tooth surface ridge line portion) 1c corresponding to the end portion of the hypoid gear 1 which is the gear of the tooth and the tooth surface 1b, particularly the outer end portion in the tooth width direction, is shown. In FIG. 1, the solid line corresponds to gas carburization, and the broken line corresponds to vacuum carburization.

  In FIG. 1, when vacuum carburizing is applied to the hypoid gear 1, the carbon concentration is equivalent to that of gas carburizing (0.75 to 0.85%) in order to ensure the fatigue strength of the root 1a equivalent to that of gas carburizing. ) Is set. At this time, with respect to the carbon concentration in the vicinity of the tooth surface edge portion 1c, vacuum carburization is 0.2 to 0.25% higher than gas carburization due to the carbon concentration non-uniformity described above.

  When the carbon concentration in the vicinity of the tooth surface edge portion 1c increases, the amount of retained austenite (γ) in the vicinity of the tooth surface edge portion 1c increases due to a decrease in the Ms (Martensite Start) point by 70 to 88 ° C, and the mechanical characteristics deteriorate. This causes a decrease in fatigue strength.

  FIG. 2 compares the meshing fatigue strength of hypoid gears when the current shot peening is performed on the hypoid gears after gas carburizing and vacuum carburizing.

  In the current shot peening process, as shown in FIG. 3, in a state where the hypoid gear 1 is horizontally installed on the rotary drive shaft 3 and rotated, the shot projection nozzle 5 is moved 45 to the horizontal plane from the outside of the hypoid gear 1. The light is projected toward the tooth portion on a plane P (see FIG. 5) that is tilted and includes the central axis 7 of the hypoid gear 1. Thereby, a shot is reliably projected on the root 1a which is the strength neck of the hypoid gear 1.

  In FIG. 2, the horizontal axis is the number of breaks and the vertical axis is the input shaft torque. The solid line is “gas carburized + current (normal) shot” and the broken line is “vacuum carburized + current (normal) shot”. It corresponds to.

  According to this, it is understood that the mesh fatigue strength is lower in “vacuum carburizing + current (normal) shot” than in “gas carburizing + current (normal) shot”. Here, the number of breaks T corresponds to a strength of 100,000 times. At this time, the former has a fatigue strength that is about 10% lower than the latter.

  As described above, after the vacuum carburization corresponding to the rapid carburization is performed, when the current (normal) shot peening process shown in FIG. 3 is performed, the shot is projected toward the root 1a which is the strength neck. Therefore, the fatigue strength in the vicinity of the tooth surface edge portion 1c is reduced. The vicinity of the tooth surface edge portion 1c is a portion that receives stress particularly when engaged with another gear, and high fatigue strength is required.

  Therefore, in the present embodiment, shot peening is performed as shown in FIG. 4 in order to compensate for the fatigue strength reduction in the vicinity of the tooth surface edge portion 1c.

  FIG. 4A is a perspective view corresponding to FIG. 3 showing a state in which shot peening processing according to an embodiment of the present invention is performed, and FIG. 4B is a front view thereof. Here, the same parts as those in FIG.

  This embodiment is different from the current shot method shown in FIG. 3 in that the shot projection direction of the shot projection nozzle 5 is set in the radial direction of the hypoid gear 1 with respect to the plane P including the central axis 7 of the hypoid gear 1 (see FIG. 5). The direction is shifted to the outside (lower side in FIG. 5). At this time, a plurality of shot projection nozzles 5 may be provided along the circumferential direction in order to direct the tip of the shot projection nozzle 5 in the shifted direction and project a shot over the entire tooth width H.

  By setting the shot projection direction of the shot projection nozzle 5 as described above, it is possible to perform shots on the vicinity of the tooth surface edge portion 1c where the strength is reduced by vacuum carburization together with the root 1a which is the strength neck of the hypoid gear 1. Can be sufficiently irradiated to increase the fatigue strength.

  Here, the amount of deviation of the shot projection nozzle 5 from the plane P including the central axis 7 in the shot projection direction is preferably 15 to 25% of the outer diameter of the hypoid gear 1. The shift amount here corresponds to the length in the vertical direction in FIG. 5 from the plane P to the point where the extension line at the center of the projection port of the shot projection nozzle 5 intersects the tooth portion.

  FIG. 5 is a plan view when the shot direction of the shot projection nozzle 5 is changed with respect to the hypoid gear 1. Level 1 corresponds to the current shot method shown in FIG. The level 2 corresponds to a state in which the amount of deviation described above is 5% of the outer diameter of the hypoid gear 1. Thereafter, levels 3 to 5 increase the amount of deviation sequentially by 5% with respect to level 2.

  FIG. 6 shows residual compressive stress values according to the distance from the tooth surface after shot peening, in the vicinity of the tooth bottom 1a and tooth surface edge portion 1c in level 1 and in the tooth bottom 1a and tooth surface edge in level 5. The vicinity of the portion 1c is shown. According to this, for the tooth bottom 1a, the residual compressive stress values are almost the same in the level 1 and the level 5, but in the vicinity of the tooth surface edge portion 1c, the deviation amount of the shot projection nozzle 5 is set to 20%. 5 has a residual compressive stress value of about 25 to 30% higher than level 1. This is the same level as when the level 1 shot technique is applied to gas carburizing.

  The residual compressive stress in the vicinity of the tooth surface edge portion 1c is increased by increasing the deviation amount of the shot projection nozzle 5 with respect to the plane P including the central axis 7 in the shot projection direction from 25% to 25%. However, since the amount of shot projection onto the tooth bottom 1a is reduced, the residual compressive stress of the tooth bottom 1a is lowered and a decrease in strength is expected. Therefore, by setting the amount of deviation to 20%, the tooth bottom 1a and the tooth Both fatigue strengths in the vicinity of the surface edge portion 1c can be ensured as desired.

  Thus, in this embodiment, the carbon concentration near the tooth surface edge portion 1c is increased compared to the tooth bottom 1a after the vacuum carburizing and quenching processing, which can significantly reduce the processing time compared to the normal carburizing and quenching processing. Even if the fatigue strength decreases due to an increase in retained austenite, the shot peening process after the vacuum carburizing and quenching process is performed, and the shot projection direction of the shot projection nozzle 5 is shifted radially outward from the plane P including the central axis 7 of the hypoid gear 1. Since it is performed on the vicinity of the tooth surface edge portion 1c together with the tooth bottom 1a of the hypoid gear 1, the decrease in fatigue strength near the tooth surface edge portion 1c can be compensated.

It is explanatory drawing which shows the surface carbon density | concentration of the hypoid gear near the tooth bottom and tooth surface edge part at the time of performing gas carburization and vacuum carburization. It is explanatory drawing which shows the meshing fatigue strength of a hypoid gear at the time of performing the present shot peening process to the hypoid gear after gas carburizing and vacuum carburizing. It is a perspective view which shows the present shot peening process. (A) is the perspective view equivalent to FIG. 3 which shows the state which is performing the shot peening process concerning one Embodiment of this invention, (b) is the same front view. It is a top view at the time of changing the shot direction of a shot projection nozzle with respect to a hypoid gear. It is explanatory drawing which showed the residual compressive-stress value according to the distance from the surface after shot peening about the tooth bottom and tooth surface edge part in level 1, and the tooth bottom and tooth surface edge part in level 5, respectively.

Explanation of symbols

1 Hypoid gear (circular gear)
1a Tooth base 1b Tooth surface 1c Tooth surface edge part (end part on the tooth surface in the tooth width direction)
5 Shot projection nozzle 7 Center axis of hypoid gear P Plane including the center axis of hypoid gear

Claims (2)

  In a gear manufacturing method in which shot peening is performed after vacuum carburizing and quenching is performed on a circular gear having teeth on an outer peripheral surface, the shot peening is performed on the tooth surface in the tooth width direction along with the tooth bottom of the gear. The shot projection direction of the shot projection nozzle is set to a direction shifted radially outward of the gear with respect to the plane including the central axis of the gear, as is performed on the end of the gear. Method.   In a gear manufacturing apparatus that performs shot peening after vacuum carburizing and quenching for a circular gear having teeth on an outer peripheral surface, the shot peening is performed on the tooth surface in the tooth width direction along with the tooth bottom of the gear. A gear having a shot projection nozzle in which the shot projection direction is shifted to the outer side in the radial direction of the gear with respect to a plane including the central axis of the gear, as performed on the end of the gear. Manufacturing equipment.

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