JP2005271102A - Sintered gear and manufacturing method of the gear - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sintered gear, heightening the fatigue strength and wear resistance of a tooth part by a method advantageous in cost, and a manufacturing method of the gear. <P>SOLUTION: In this sintered gear 1, the carbonized quenched tooth flank has skin subjected to shot-peening, and the texture of a part 0.06 mm deep from the surface of the tooth flank is made as dense as hole percentage of 3% or less. This sintered gear 1 is manufactured by a method of peening the tooth flank with a shot whose particle diameter is ϕ0.3 mm or less. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a sintered gear with improved tooth fatigue strength and wear resistance and a method of manufacturing the gear.

  In order to increase the fatigue strength of the tooth portion of the sintered gear, particularly the tooth root, Patent Document 1 below heats a material of an iron-based sintered body provided with a tooth profile forming portion serving as a tooth portion, and forms a rolling mold on this material. A method of manufacturing a sintered gear is proposed in which a tooth portion with a dense structure is created in the tooth profile forming portion by applying high pressure.

  Furthermore, this patent document 1 describes that densification of the surface of the tooth profile forming part of the material is performed by sizing or strong pressure of a rotating roll before the hot rolling process, or hot rolling, quenching, and tempering. It also describes that shot peening is performed as necessary after each step.

  However, the manufacturing method of Patent Document 1 requires a hot rolling process, which is disadvantageous in terms of cost.

  Further, when shot peening is performed after heat treatment as described in Patent Document 1, the fatigue strength of the teeth can be further increased, but the particle diameter described in Patent Document 1 is 0.3 to 0.00. When an 8 mm shot is used, the reduction in the surface roughness of the tooth surface and the reduction in the accuracy of the gear increase.

Here, Patent Document 2 described below uses a shot having a particle diameter smaller than the surface roughness pitch of a ferrous sintered alloy member machined after heat treatment to prevent surface roughness and scratches. . However, the shot shown in this embodiment by Patent Document 2 is extremely small with a particle size of 0.044 mm, and there is a concern about an increase in cost.
JP-A-7-112231 JP-A-6-49509

  An object of the present invention is to provide a sintered gear capable of increasing the fatigue strength and wear resistance of a tooth portion in a cost-effective manner, and a method for manufacturing the gear.

  In order to solve the above-described problems, in the present invention, a carburized and hardened tooth surface has a ground surface shot-peened, and a structure having a depth of 0.06 mm or less from the surface of the tooth surface has a porosity of 3 % To provide a sintered gear densified to less than or equal to%.

  Further, the present invention provides a sintered gear having a measured value of residual compressive stress at the bottom of the tooth by a minute X-ray stress measuring device of −500 MPa or more.

  These sintered gears, after carburizing and quenching, peening the tooth surface using a shot having a particle diameter of φ0.3 mm or less, and the structure of a portion having a depth of 0.06 mm or less from the tooth surface has a porosity of 3%. It can manufacture by the method of densifying below. In this invention, the manufacturing method of this sintered gear is also provided. In the shot used in this method, the lower limit of the particle diameter is preferably limited to about φ0.1 mm in consideration of the processing cost.

  In addition, the porosity mentioned here is the ratio of the void | occupy to the area of the cross section of a surface and a parallel position, and the part whose porosity is 3% or less is called a densified layer below. The thickness of the densified layer is obtained by polishing the cross section of the tooth portion and examining the depth until the porosity is 3% or less from the tooth surface layer of the polished cross section observed with an optical microscope. Can be measured.

  The sintered gear of the present invention is manufactured by a general method of powder metallurgy, that is, a method of forming a powder into a shape close to the final product and sintering the compact. According to this method, there is no hot rolling process, and no cost increase occurs due to an increase in the number of processes. However, on the other hand, densification of the tooth structure by hot rolling described in Patent Document 1 is not performed.

  Therefore, shot peening is performed after carburizing and quenching to form a densified layer with few voids in the surface layer portion of the tooth surface. Densification of the surface layer portion of the tooth surface is also performed by sizing performed after sintering, but it is not sufficient by itself, so shot peening is performed after carburizing and quenching.

  From the test conducted by the inventors, it was found that the compressive residual stress applied to the tooth surface decreases as the thickness of the densified layer (depth from the surface) increases. When the thickness of the densified layer (depth from the surface of the tooth surface) is 0.06 mm or less, a compressive residual stress of slightly less than −600 MPa is obtained, and the fatigue strength of the tooth portion is sufficiently satisfied.

  Also, depending on the conditions of peening, if the conditions such as shot hardness, injection pressure, and injection time are the same, the dimensional accuracy and surface roughness of the tooth surface increase as the particle size of the shot used increases. It has also been found that the thickness of the densified layer tends to increase when a shot having a large particle size is used. By using shots with a particle size of φ0.1 mm or more, the cost increase due to shot peening can be kept small, and by using shots of 0.3 mm or less, the dimensional accuracy and surface roughness of the tooth surface are acceptable. It is easy to control the thickness of the densified layer within 0.06 mm.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an example of a sintered gear of the present invention. The illustrated sintered gear 1 is a spur gear, but the type of gear is not particularly limited. The present invention can be applied to all of the gears that are manufactured by creating a tooth portion by powder molding and then sintering.

  A sintered gear 1 according to the present invention is a method of compressing a powder constituting an iron-based sintered alloy with a mold to form a molded body having a shape close to the final product, and forming the molded body into a sintering furnace such as a pusher furnace. And sintered at a required temperature, for example, 1300 ° C. Thereafter, carburizing and quenching is performed, and the tooth surface 2 is manufactured by performing shot peening.

  The powder is preferably molded at a high pressure, for example, a pressure of 600 MPa or more, so that the theoretical density of the compact is 88% or more.

  In order to increase dimensional accuracy, it is desirable to perform sizing before carburizing and quenching.

  The carburizing quenching or tempering method performed after sizing may be a generally performed method.

  Further, if the shot peening process for strengthening the tooth part is performed using a shot having a hardness higher than the hardness of the tooth surface of the carburized and quenched gear, the processing efficiency does not decrease. In addition, the use of shots with a particle size of φ0.1 mm or more can suppress the cost increase due to shot peening, and the use of shots with a particle size of 0.3 mm or less reduces the reduction in tooth surface accuracy and surface roughness. Can be suppressed.

  FIG. 2 shows an outline of an example of shot peening. A work table 5 that is rotated by a motor 4 is provided in the processing chamber 3 of the processing machine. The work table 5 has a support shaft 6 standing at the center of the upper surface. The support shaft 6 is passed through the shaft hole at the center of the workpiece, and the workpiece (sintered gear 1) is held so as not to move. In this state, a plurality of workpieces (sintered gear 1) are stacked on the workpiece table 5. Then, after the work setting is completed, the work table 5 is rotated, the nozzle 7 in the processing chamber 3 is reciprocated along the support shaft 6, and the shot 8 is moved from the nozzle 7 to the work, that is, the sintered gear 1. A small depression is generated in the tooth surface 2 by spraying the outer tooth surface 2 at a high speed.

More detailed examples are given below.
Sintered gears were manufactured using iron-based sintered alloy HMC-90 (Fe-Mn-C) as a material. In this sintered gear, a powder compact formed at a pressure of 800 MPa is put in a pusher furnace and sintered at 1300 ° C., and then sizing is performed at an ironing cost of 0.02%, followed by carburizing and tempering. It is carried out.

Next, a peening process is performed on the tooth surfaces of the carburized and quenched sintered gear by the method shown in FIG. 2 using four types of shots having particle diameters of φ0.10 mm, φ0.17 mm, φ0.3 mm, and φ0.6 mm. did. The conditions for peening were unified at an injection pressure of 0.5 MPa and an injection time of 60 seconds regardless of the shot particle size. The shot hardness was also H _R C53 ± 2.

  FIG. 3 shows a cross-sectional hole photograph of the tooth tip of the gear after shot peening. FIG. 3A shows a shot using a shot having a particle size of φ0.17 mm (hereinafter referred to as sample B), and FIG. 3B shows a shot using a shot having a particle size of φ0.3 mm (hereinafter referred to as sample C). ), FIG. 3C shows a shot using a shot having a particle diameter of φ0.6 mm (hereinafter referred to as sample D).

  The thickness (depth from the surface) of the densified layer 9 having a porosity of 3% or less generated on the tooth surface of each sample is 0.04 mm for sample B, 0.06 mm for sample C, and 0. It was 1 mm. In addition, although what used the shot of particle diameter (phi) 0.1mm (sample A) omitted the hole photograph of a cross section, the densification layer thickness was 0.02 mm.

  The residual compressive stress at the tooth root of the gear tooth surface was −55 MPa before the shot peening process, but sample A was −1024 MPa, sample B was −896 MPa, sample C was −594 MPa, and sample D. Increased to -485 MPa. As a result, the gear subjected to shot peening was found to have improved fatigue strength by about 30% compared to the gear before being subjected to shot peening in a tooth overload bending fatigue test.

  In the overload bending fatigue test, the servo pulsar 10 shown in FIG. 4 is used, the member locked to the teeth of the fixed sintered gear 1 is reciprocated up and down, and the reciprocating movement is taken as one cycle, and the tooth portion is Evaluation was based on the difference in the number of cycles until fatigue failure.

  Next, the accuracy of each sample was examined. As a result of examining the tooth shape error and the tooth trace error as the gear accuracy, the samples A, B and C satisfy both the tooth shape error standard 0.02 mm and the tooth trace error standard 0.03 mm. D exceeded the standard value for both the tooth type error and the tooth trace error.

  The surface roughness of the tooth surface was good for samples A and B, and sample C was within the allowable range, but sample D was outside the allowable range.

  On the other hand, the processing cost by shot peening was not different between the samples C and D, but the costs of the samples A and B were higher than those of the samples C and D.

  The above test results are summarized in Table 1. In Table 1, ◎ indicates satisfaction, ○ indicates almost satisfactory, Δ indicates normal, and X indicates unsatisfactory.

  From this test result, it is recommended that the thickness of the densified layer in the surface layer is 0.06 mm or less in terms of improving the fatigue strength of the teeth, and the upper limit of the shot particle size is 0.3 mm in terms of the accuracy of the tooth surfaces. From the viewpoint of processing cost, it is understood that the lower limit of the shot particle size should be limited to about φ0.1 mm.

The perspective view which shows an example of the sintered gear of this invention Diagram showing an example of shot peening Cross-sectional hole photo of gear teeth after shot peening Diagram showing the testing machine used for the overload bending fatigue test

Explanation of symbols

1 Sintered gear 2 Tooth surface 3 Processing chamber 4 Motor 5 Worktable 6 Support shaft 7 Nozzle 8 Shot 9 Densified layer 10 Servo pulser

Claims (3)

  A sintered gear having a ground surface that has been shot peened on a carburized and hardened tooth surface, and the structure of a portion having a depth of 0.06 mm or less from the surface of the tooth surface is densified to a porosity of 3% or less.   The sintered gear according to claim 1, wherein a measured value of residual compressive stress in the tooth bottom portion by a minute X-ray stress measuring device is -500 MPa or more.   Claims wherein the tooth surface is peened using a shot having a particle size of φ0.3 mm or less after carburizing and quenching, and the structure of a portion having a depth of 0.06 mm or less from the tooth surface is densified to a porosity of 3% or less. 2. A method for producing a sintered gear according to 1.