JPH10176203A - Method for making dense surface of sintered gear parts - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely form a sufficiently dense layer on the surface of gear parts by form-rolling. SOLUTION: A working blank 1 composed of a sintered body having the gear parts with plural teeth constituted of tips of teeth 1c, surfaces of teeth 1a and bottoms of teeth 1b is subjected to form-rolling by using a form-rolling die 2 meshable with the gear parts to make the dense surface of the gear part. At this time, in at least a part of the teeth, desirably, in many teeth as much as possible in the gear part of the working blank 1, the relations of the shape and the position between the working bland 1 and the form-rolling die 2 are defined so that the surfaces of teeth 1a and the bottoms of teeth 1b of the gear parts are press-contacted with the form-rolling die 2 and the interval between the form-rolling die 2 and the tips of teeth 1c of the gear parts becomes zero for execution of the form-rolling. By the method, the thickness of the working blank 1 crushed with the form-rolling die 3 is surely fluidized into the inner part of the working blank 1 (pressurizing direction by the form-rolling die 2) and the dense layer can surely be formed on the surface of the gear parts press-contacted with the form-rolling die 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for densifying a surface of a sintered gear part.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication No. 6-501988 discloses a gear rolling technique for densifying the surface of a sintered gear part. This involves pressing a metal powder into a predetermined shape to form a green compact having a gear portion, and sintering the green compact to form a sintered material obtained by sintering. Is used to roll-process the gear portion.

[0003] According to this rolling process, the surface of the gear portion is densified, so that the wear resistance and strength of the gear portion can be improved by surface hardening.

[0004]

However, in the technique disclosed in the above publication, the formation of a dense layer on the surface of the gear portion by rolling is insufficient, and the diameter of the tooth tip circle of the gear portion is reduced by rolling. It was confirmed by the inventor's experiment that it increased after processing. That is, in the rolling technology of the above publication,
As shown in FIG. 3A, a method of pressing a rolling die 90 against a tooth surface 81 of a gear portion of a workpiece 80 to densify the surface of the tooth surface 81. As shown in FIG. Workpiece material 80
A method in which a rolling die 90 is pressed against the tooth surface 81 and the tooth bottom 82 of the gear portion to make the surfaces of the tooth surface 81 and the tooth bottom 82 dense, and as shown in FIG. The rolling die 90 is pressed into contact with the tooth bottom 82 of the gear portion to make the surface of the tooth bottom 82 dense. However, in any of these methods, there is a clearance between the tooth tip 83 of the gear portion of the workpiece 80 and the rolling die 90. For this reason, the meat of the workpiece 80 crushed by the rolling dies 90 tends to flow not only inside the workpiece 80 but also toward the tooth tip 83. As a result, the formation of the dense layer is insufficient at the portion where the surface of the rolling die 90 is to be pressed to make the surface dense, and the circular diameter of the tooth tip 83 of the gear portion increases.

The present invention has been made in view of the above-mentioned circumstances, and a sufficient dense layer can be formed on the surface of a gear portion by rolling, and the diameter of the addendum circle of the gear after rolling is reduced. An object of the present invention is to provide a method for densifying a surface of a sintered gear component that can prevent the increase in the number of the sintered gear components.

[0006]

According to a first aspect of the present invention, there is provided a method for densifying a surface of a sintered gear part, comprising a gear portion having a plurality of teeth formed by a tooth tip, a tooth surface and a tooth bottom. A method in which a work material made of a sintered body is rolled by a rolling die that meshes with the gear portion to densify the surface of the gear portion. The rolling die is pressed against the tooth surface and the tooth bottom, and the shape of the material to be processed and the rolling die is such that the interval between the rolling die and the tooth tip is zero. The rolling process is performed by determining the positional relationship.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for densifying a surface of a sintered gear component according to the present invention, a material to be processed formed of a sintered body having a gear portion is rolled. The gear portion of the material to be processed has a plurality of teeth including a tooth tip, a tooth surface, and a tooth bottom. The material to be processed can be prepared by compression molding a metal powder raw material into a green compact having a gear portion having a tooth tip, a tooth surface and a tooth bottom by press working or the like, and sintering the compact.

The shape of the gear portion can be a spur gear, a helical gear, or the like. The rolling dies used for the rolling process are prepared according to the shape of the gear portion of the material to be processed. That is, it is possible to use a gear-shaped rolling die having a tooth bottom and a tooth tip that mesh with the tooth tip and the tooth bottom of the gear portion of the workpiece, respectively. To elaborate,
At the time of rolling, at least a part of the teeth of the gear portion of the material to be processed has a tooth surface and a tooth tip shape that can be pressed against the tooth surface and the tooth bottom of the gear portion of the material to be processed, respectively, and The gap between the tooth tip of the gear portion of the workpiece and the tooth bottom of the rolling die becomes zero, that is, a gear-shaped rolling die having a tooth bottom shape that can be brought into contact with the tooth tip of the gear portion. Can be used.

The rolling die may be provided with one rolling die on one side of the material to be processed or a pair of rolling dies on both sides of the material to be processed. In the rolling process, the material to be processed and the rolling die are rotatably supported, respectively, and the rotation axis of the material to be processed and the rotation axis of the rolling die that can be approached or remoted from each other are relatively set. In a state where the gear portion of the material to be processed and the gear portion of the rolling die are meshed with each other, the rotation axis of the rolling die can be rotated by a driving source. In addition, the rotation direction of the rolling die may be only one direction, or may be both forward and reverse directions.

[0010] In the above rolling process, at least a part of the teeth of the gear portion of the workpiece is pressed with the tooth surface and the tooth tip of the rolling die against the tooth surface and the tooth bottom of the gear portion of the workpiece. In addition, the positional relationship between the workpiece and the rolling die is determined so that the distance between the tooth tip of the gear portion of the workpiece and the root of the rolling die becomes zero. That is, the interval between the rotation axis of the workpiece and the rotation axis of the rolling die at the time of the rolling is at least part of the teeth of the gear of the workpiece, The tooth surface and the tooth tip of the rolling die are pressed against the tooth surface and the tooth bottom, respectively, and
The distance between the tooth tip of the gear portion of the workpiece and the root of the rolling die is set to be zero.

In a preferred embodiment, the rolling dies are pressed against the tooth surfaces and the tooth bottoms of the gear portion of the material to be processed for all the teeth of the gear portion of the material to be processed, and It is most preferable to determine the shape of the rolling dies and the positional relationship between the work material and the rolling dies so that the distance between the tooth tip and the tooth bottom of the rolling dies is zero. It is preferable to determine the shape of the rolling die and the positional relationship between the material to be processed and the rolling die so as to satisfy the following relationship. However, due to the dimensional variation of the material to be processed and the rolling dies, a minute gap is inevitably formed between the tooth tip of the gear portion and the rolling die for some teeth of the gear portion of the material to be processed. It is permissible to do so.

Conventionally, the rolling process is performed in a state where there is a clearance between the tooth tip of the gear portion of the workpiece and the rolling die. Therefore, the workpiece crushed by the rolling die during the rolling process. There was a tendency for the flesh of the material to flow in the tooth tip direction of the gear portion (the clearance direction). In contrast,
In the method for densifying the surface of the sintered gear component of the present invention, the rolling dies are formed on at least some of the teeth of the gear portion of the material to be processed, in a preferred embodiment, on as many teeth as possible. The shape and positional relationship between the material to be processed and the rolling die are determined so as to be pressed so as to be pressed against the root of the tooth and that the distance between the tooth tip of the gear portion and the rolling die is zero. Therefore, in a tooth satisfying such a relationship, the meat of the workpiece crushed by the rolling die during the rolling process surely flows into the workpiece (in the direction of pressing by the rolling die). However, unlike the conventional case, there is no possibility that the fluid flows toward the tooth tip of the gear portion. Therefore, it is possible to reliably form a dense layer on the surface of the gear portion on which the rolling dies are pressed, and to prevent the tip diameter of the gear portion from increasing after rolling. Become.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for densifying the surface of a sintered gear part according to the present invention will be described below in detail. (Example) Iron-based alloy powder raw material is pressed into teeth,
A compact having a gear portion having a tooth surface and a tooth bottom was compression-molded and sintered to prepare a workpiece 1 having a spur gear shape. Further, a rolling die 2 having a gear shape corresponding to the shape of the gear portion of the workpiece 1 was prepared.
The rolling die 2 is provided with a tooth surface 2a and a tooth surface 2a that can be pressed against the tooth surface 1a and the tooth bottom 1b of the gear portion of the material 1 during rolling, for all the teeth of the gear portion of the material 1 to be processed. The gear has a tip 2b shape and a root shape such that the distance between the tooth tip 1c of the gear portion of the workpiece 1 and the tooth bottom 2c of the rolling die 2 is zero.

The workpiece 1 and the rolling die 2 are rotatably supported on a rotating shaft (not shown). The rotation axis of the rolling die 2 is relatively movable with respect to the rotation axis of the workpiece 1 in a direction approaching or remote from the rotation axis, and is rotatable by a driving source (not shown). Have been. Then, the rotation axis of the rolling die 2 is brought close to the rotation axis of the workpiece 1 by a predetermined distance, and the gear portion of the rolling die 2 is placed on the tooth tip 1c and the tooth bottom 1b of the gear portion of the workpiece 1. In a state where the tooth bottom 2c and the tooth tip 2b are meshed with each other, the rotating shaft of the rolling die 2 is rotationally driven to perform rolling.
At the time of this rolling, the tooth surface 2a and the tooth tip 2b of the rolling die 2 are pressed against the tooth surface 1a and the tooth bottom 1b of the gear portion of the workpiece 1 for all the teeth of the gear portion of the workpiece 1. In addition, the rotation axis of the workpiece 1 and the rotation axis of the rolling die 2 are adjusted so that the distance between the tooth tip 1c of the workpiece 1 and the root 2c of the rolling die 2 becomes zero. The interval was set.

As described above, in this embodiment, for all the teeth of the gear portion of the workpiece 1, the rolling dies 2 are pressed against the tooth surface 1 a and the tooth bottom 1 b of the gear portion of the workpiece 1. The shape of the rolling die 2 and the material 1 and the rolling die 2 are adjusted so that the distance between the tooth tip 1c of the gear portion of the raw material 1 and the root of the rolling die 2 becomes zero. However, due to the dimensional variations of the workpiece 1 and the rolling dies 2, some of the teeth of the gear portion of the workpiece 1 have a tooth tip 1c of the gear and the rolling dies. It can also be assumed that an inevitable minute gap is formed between them.

(Comparative Example) The workpiece 1 has a tooth surface 2a and a tooth tip 2b that can be pressed against the tooth surface 1a and the tooth bottom 1b of the gear portion of the workpiece 1 during rolling.
In addition to using a rolling die having a tooth bottom shape such that the distance between the tooth tip 1c of the gear portion and the root 2c of the rolling die 2 is 0.5 mm, the rolling die 2 The tooth surface 2a and the tooth tip 2b of the workpiece 1 are pressed against the tooth surface 1a and the tooth bottom 1b of the gear portion of the workpiece 1 and the distance between the tooth tip 1c of the workpiece 1 and the root 2c of the rolling die 2 Is 0.5m
It is the same as the above embodiment except that the distance between the rotation axis of the workpiece 1 and the rotation axis of the rolling die 2 is set to m.

(Evaluation) Each sample 1 of the above Examples and Comparative Examples
For 0 pieces, the change in the tip diameter of the tip 1c of the workpiece 1 before and after the rolling was examined. In addition, the diameter of the addendum circle of the addendum portion 1c of the workpiece 1 was also measured after the heat treatment at 900 ° C. for 150 minutes after the rolling. These results are shown in FIG.

As is clear from FIG. 2, the diameter of the addendum circle increased by about 0.7 mm after the rolling in the comparative example, but increased only about 0.02 mm in the present example. In addition, in the comparative example, after the rolling and the heat treatment, the variation in the tip diameter was large, whereas in the present example, the variation in the tip diameter was small.

[0019]

As described above in detail, in the method for densifying the surface of a sintered gear component according to the present invention, the meat of the workpiece crushed by the rolling dies at the time of the rolling process is surely used as the workpiece. Since it is possible to flow inside (in the direction in which the rolling dies are pressed), it is possible to reliably form a dense layer on the surface of the gear portion to which the rolling dies are pressed, and to add the tip circle of the gear portion. It is possible to prevent the diameter from increasing after rolling. Therefore, according to the method of the present invention, the surface of the gear portion can be sufficiently densified to sufficiently improve the fatigue strength and the like, and the dimensional accuracy of the tooth tip portion and the like can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a method for densifying a surface of a sintered gear component of the present embodiment.

FIG. 2 is a diagram showing a state of a change in a tooth tip circle diameter before and after a rolling process, and the like.

FIG. 3 is an explanatory view schematically showing a conventional method for densifying the surface of a sintered gear component.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Work material, 1a ... Tooth surface, 1b ... Tooth bottom, 1c ... Tooth tip, 2 ... Rolling die

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Haruo Otsuka 1-1-1 Fujikoshi Honcho, Toyama City, Toyama Prefecture

Claims (1)

[Claims] 1. A work material comprising a sintered body having a gear portion having a plurality of teeth constituted by a tooth tip, a tooth surface and a tooth bottom is rolled by a rolling die engaged with the gear portion. A method of densifying the surface of the gear portion, wherein at least a part of the teeth of the gear portion, the rolling die is pressed against the tooth surface and the tooth bottom, and
As the interval between the rolling die and the tooth tip becomes zero,
A method for densifying the surface of a sintered gear component, comprising: determining the shape and positional relationship between the material to be processed and the rolling dies and rolling.