JPH0671520A - Manufacture of mechanical member with high strength - Google Patents

Abstract

PURPOSE:To improve the fatigue strength of a mechanical member by providing higher compressive residual stress to the mechanical member. CONSTITUTION:A method for manufacturing a mechanical member with high strength consists of the CBN grinding process 12 to execute the CBN grinding of the surface part of the mechanical member to be carburized in the carburizing process 11, and the shot peening process 13 to execute the shot peening treatment to the surface part of the mechanical member to be ground in this CBN grinding process 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing high strength mechanical members such as gears and shafts which require high strength.

[0002]

2. Description of the Related Art Conventionally, mechanical members such as gears and shafts which are required to have high strength have been subjected to surface hardening treatment by carburizing, for example. However, a grain boundary oxide layer is usually formed on the surface of the carburized machine member over a depth of about 10 to 40 μm from the surface, and this grain boundary oxide layer is a factor that reduces the fatigue strength of the machine member. It was one of the.

The following techniques have been proposed in order to prevent a decrease in fatigue strength of carburized mechanical members. (1) The grain boundary oxide layer is removed from the carburized machine member by grinding wheel grinding, CBN (cubic boron nitride) grinding or the like. By these grindings, the grain boundary oxide layer does not exist on the surface portion of the mechanical member, so that the fatigue strength of the mechanical member is prevented from lowering. In CBN grinding, a compressive residual stress is applied to the surface of the mechanical member, so the fatigue strength of this mechanical member is increased. (2) A shot peening process (for example, an arc height value of 0.6 to 1.0 mmA) is performed on the carburized mechanical member. By this shot peening treatment, a compressive residual stress higher than that of the CBN grinding is applied to the surface portion of the mechanical member, so that the fatigue strength of the mechanical member is increased.

It is generally known that the fatigue strength of a mechanical member increases as the integral value of the compressive residual stress generated in the mechanical member increases (see FIG. 4). Therefore, in order to increase the fatigue strength of the mechanical member, it is sufficient to increase the integral value of the compressive residual stress generated in the mechanical member.

However, in (1) grinding with a grindstone, a compressive residual stress is not applied to the surface of a mechanical member, and conversely, a tensile residual stress may be applied. Further, in CBN grinding, the range of compressive residual stress applied to the surface portion of a mechanical member is up to a depth of about 50 μm from the surface, and the fatigue strength in the deep portion of the mechanical member cannot be increased. (2) In the shot peening process, the range of the compressive residual stress applied to the surface of the mechanical member is 20 from the surface.
Although the depth of the compressive residual stress is up to about 0 μm, the peak of the compressive residual stress is usually located at a depth of about 50 to 100 μm from the surface of the mechanical member, and the compressive residual stress at the outermost surface of the mechanical member is equal to Less than half.

The following techniques have been proposed to solve these problems. (3) After subjecting the carburized mechanical member to shot peening, the surface portion having a low compressive residual stress is removed by CBN grinding to expose the portion having a high compressive residual stress on the surface portion of the mechanical member (special feature). See Kaihei 1-264727). (4a) After the carburized mechanical member is subjected to shot peening, the surface portion having a low compressive residual stress is removed by electrolytic polishing to expose a portion having a high compressive residual stress on the surface portion of the mechanical member. (4b) After removing a portion having a low compressive residual stress existing on the surface portion of the carburized mechanical member by electrolytic polishing to expose a portion having a high compressive residual stress on the surface portion of the mechanical member, Perform shot peening (4
For a and 4b, refer to JP-A-2-160428).

[0007]

However, (3) the carburized mechanical member is generally distorted, and the high (peak) portion of the compressive residual stress imparted by the shot peening treatment is caused by the shot peening treatment. 20 to 10 from the surface of the mechanical member depending on the conditions
Since it changes in the depth range of 0 μm, it is difficult to expose a portion having a high compressive residual stress on the surface portion of the mechanical member by CBN grinding. Further, even if a portion having a high compressive residual stress can be exposed on the surface portion of the mechanical member, since the portion of the mechanical member to which the compressive residual stress is applied is ground by the CBN grinding, The portion of the mechanical member to which the compressive residual stress is applied is reduced, and the fatigue strength of the mechanical member is not sufficiently high.

The relationship between the depth from the surface of the mechanical member that has been CBN ground after the shot peening treatment and the compressive residual stress generated in the mechanical member will be described in detail with reference to FIG. The compressive residual stress applied to the carburized mechanical member is shown by the broken line, and when the carburized mechanical member is subjected to shot peening, the compressive residual stress on the surface of the mechanical member increases and As shown by the chain line. When the surface portion of the mechanical member that has been subjected to shot peening is ground by CBN grinding, for example, to 20 μm, a compressive residual stress is applied to the surface portion of the mechanical member by the CBN grinding. Will be indicated by.

As can be seen from FIG. 5, a grain boundary oxide layer is formed on the surface of the carburized mechanical member. The grain boundary oxide layer is soft and the mechanical member has a buffer during the shot peening treatment. Since it acts as a material, the compressive residual stress imparted by the shot peening treatment in the deep part of the carburized mechanical member does not become high. Further, the shaded portion in the figure is the portion to which a high compressive residual stress is originally given by the shot peening process, and the portion to which this high compressive residual stress is given is ground by the CBN grinding. As a result, the fatigue strength of the mechanical member cannot be increased.

(4a, 4b) In general, electrolytic polishing improves the appearance of a mechanical member by preferentially removing the convex portion on the surface of the carburized mechanical member over the concave portion, that is, on the surface of the mechanical member. It is one of means for imparting smoothness and glossiness, and it is difficult to maintain the precision of the mechanical member and to uniformly remove the grain boundary oxide layer. Therefore,
It is not practical to apply it to mechanical members such as gears.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method for manufacturing a high-strength mechanical member that increases fatigue strength of the mechanical member that requires high strength. To do.

[0012]

A method of manufacturing a high-strength mechanical member according to the present invention comprises a CBN grinding step of performing CBN grinding on a surface portion of a carburizing machine member in the carburizing step, and the CB grinding step.
And a shot peening step of performing a shot peening treatment on the surface portion of the machine member to be ground in the N grinding step.

[0013]

In the method for manufacturing a high-strength mechanical member of the present invention, first, the grain boundary oxide layer formed on the surface portion of the carburized mechanical member in the carburizing step is CBN ground in the CBN grinding step.
By this CBN grinding, the precision of the mechanical member is increased and a compressive residual stress is applied to the mechanical member to increase the fatigue strength of the mechanical member. Next, in the shot peening step, a shot peening process is performed on the surface portion of the machine member that has been CBN ground. Therefore,
By this shot peening treatment, compressive residual stress is further applied to the mechanical member, so that the fatigue strength of the mechanical member is further increased.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a specific embodiment of the present invention will be described with reference to the drawings. The steps of the method for manufacturing a high strength mechanical member of the present invention are shown in FIG. According to this process, the surface portion of the mechanical member carburized in the carburizing process 11 is subjected to CBN grinding in the CBN grinding process 12, and then shot peening is performed in the shot peening process 13.

FIG. 2 shows the relationship between the depth from the surface of the mechanical member which has been shot peened after the above-mentioned CBN grinding and the compressive residual stress applied to the mechanical member. In FIG. 2, the compressive residual stress applied to the carburized mechanical member is shown by a broken line. When the carburized mechanical member is subjected to CBN grinding and the surface portion of the mechanical member is ground by, for example, 20 μm, the compressive residual stress on the surface portion of the mechanical member becomes high and is shown by a chain double-dashed line. . When this mechanical member is subjected to shot peening, the compressive residual stress applied to the mechanical member is indicated by the thick solid line.

As can be seen from FIG. 2, a grain boundary oxide layer is formed on the surface of the carburized mechanical member. The grain boundary oxide layer is soft and the mechanical member has a buffer during the shot peening treatment. CB because it acts as a material
The grain boundary oxide layer is first removed by N grinding. At this time, C is formed by carburizing on the surface of the mechanical member.
The compressive residual stress removed by BN grinding (shown by diagonal lines in the figure) is extremely small compared to the compressive residual stress applied by CBN grinding. Also, this CBN
The precision of the mechanical member is increased by the grinding. When shot peening treatment is applied to a mechanical member in which the grain boundary oxide layer has been removed by CBN grinding and the compressive residual stress has been increased, this shot peening treatment imparts compressive residual stress to the deep part of the mechanical member. . As a result, the fatigue strength of the mechanical member can be increased deep inside the mechanical member.

Next, FIG. 3 shows the results of the rotary bending fatigue strength test of the mechanical member manufactured by the method for manufacturing a high-strength mechanical member of the present invention and the mechanical member manufactured by the conventional manufacturing method. The test results are carburization + CBN grinding, carburization + shot peening treatment, carburization + shot peening treatment + CBN grinding, carburization + CBN grinding + shot peening treatment (invention) with the limit of the rotary bending fatigue strength of the carburized machine member being 1. The rotational bending fatigue strength of the machined member is shown in correspondence with the number of times the rotational bending is repeated.

According to the test results, the rotational bending fatigue strength of the mechanical member manufactured by using the method for manufacturing a high-strength mechanical member according to the present invention is higher than that of the mechanical member manufactured by using the conventional manufacturing method. This value is at least 1.1 times that of the conventional one.

[0019]

According to the present invention configured as described above, since a high compressive residual stress is applied from the surface of the mechanical member to the deep portion, the fatigue strength of the mechanical member can be increased. Further, the precision of the mechanical member can be improved by CBN grinding the mechanical member.

[Brief description of drawings]

FIG. 1 is a diagram showing steps of a method for manufacturing a high-strength mechanical member according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a compressive residual stress in a mechanical member manufactured by a method for manufacturing a high-strength mechanical member according to an embodiment of the present invention.

FIG. 3 is a diagram showing a comparison of rotational bending fatigue strength between a mechanical member manufactured by a method for manufacturing a high-strength mechanical member according to an embodiment of the present invention and a mechanical member manufactured by a conventional manufacturing method.

FIG. 4 is a diagram illustrating a relationship between a compressive residual stress and a fatigue strength of a mechanical member.

FIG. 5 is a diagram illustrating compressive residual stress in a mechanical member manufactured by a conventional method for manufacturing a high-strength mechanical member.

[Explanation of symbols]

 11 Carburizing process 12 CBN grinding process 13 Shot peening process

Claims (1)

[Claims] 1. A CBN grinding step of performing CBN grinding on a surface portion of a machine member carburized in the carburizing step, and the CB
A method for producing a high-strength mechanical member, comprising: a shot peening step of performing a shot peening treatment on a surface portion of the mechanical member ground in the N grinding step.