JP2019111613A - Shot-peening method - Google Patents

Abstract

To provide a shot-peening method that improves the surface roughness of a metal product by having an increased number of stages, and prevents deterioration in compressive residual stress that occurs in the metal product.SOLUTION: Before projecting a projection material (large) of a prescribed grain diameter as a first stage to a test piece T, a projection material (small) with a grain diameter half or less of the grain diameter of the projection material (large) is projected to the test piece T as a preceding stage. With this projection, a surface of the test piece T can be hardened while restraining deterioration of the surface roughness of the test piece T. Thus, the surface roughness of the test piece T can be improved by restraining deterioration in the surface roughness of the test piece T by the projection at the first stage and onward. Meanwhile, since there is no change in the projection material of the final stage (the last stage in the case of a plurality of stages after the first stage or the first stage in the case of only the first stage), compressive residual stress that occurs in the test piece T is prevented from deteriorating.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a shot peening method.

  Conventionally, in metal products requiring fatigue strength, such as gears and springs, if the surface roughness is large, cracks resulting from the surface roughness may lower the fatigue strength of the metal product.

  On the other hand, there has been proposed a method of reducing the surface roughness of a metal product by shot peening. However, when the surface of the metal product is undulated, it has been difficult to improve the surface roughness.

  Therefore, when there is a large unevenness such as waviness on the part surface, the surface roughness or peak count value of the metal product is first made larger than the initial surface of the metal product, that is, relatively strong so as to be rougher than the surface initial state. The first step shot peening is applied, and the second step shot peening is slower than the first step in projection speed, or the particle diameter of the projection material is smaller, or the hardness of the projection material is lowered to make the surface uniformly flat What makes it smooth is proposed (refer patent document 1).

JP 2002-361559 A

  In the case of the above prior art, if the number of steps is further increased to improve the surface roughness of the treated surface of the metal product, the surface roughness of the metal product is improved but the compressive residual stress on the surface of the metal product is deteriorated. And other inconveniences may occur.

  An object of the present invention is to provide a shot peening method in which the number of stages is increased to improve the surface roughness of a metal product and the deterioration of the compressive residual stress produced in the metal product is prevented.

  The shot peening method according to the invention of claim 1 comprises, as a first stage, a step of projecting a first projectile having a predetermined particle diameter onto the surface of a metal product, and, as a first stage, the first stage. And 1) projecting a second projectile having a particle size equal to or less than half the particle size of the projectile onto the surface of the metal product.

  In this shot peening method, before projecting the first projectile having a predetermined particle diameter as the first stage onto the surface of the metal product, the second projection having a particle diameter equal to or less than half the particle diameter of the first projectile as the former stage Project material onto the surface of metal products. This projection can harden the surface of the metal product while suppressing the deterioration of the surface roughness of the metal product. Therefore, the surface roughness of the metal product can be improved by suppressing the deterioration of the surface roughness of the metal product due to the projection after the first stage.

  On the other hand, since there is no change in the projection material of the final stage (the final stage in the case of a plurality of stages after the first stage, and the first stage in the case of only the first stage), the compression residue applied to metal products Deterioration of stress is prevented.

  The shot peening method according to the invention of claim 2 is the shot peening method according to the invention of claim 1, wherein the particle diameter of the second projectile is 0.3 mm or less, and the Vickers of the second projectile The hardness is a Vickers hardness of -100 or more of the metal product.

  If the Vickers hardness of the second projectile is 100 or more lower than the Vickers hardness of the metal product, the surface of the metal product can not be sufficiently work hardened even if the second projectile is projected onto the metal product as a former stage. As a result, the surface roughness of the metal product may be deteriorated by projecting the first projectile onto the surface of the metal product as the first stage.

  However, if the Vickers hardness of the second projectile is the Vickers hardness of the metal product-100 or more, the surface of the metal product is sufficiently work hardened by the projection in the previous stage, and the surface roughness of the metal product in the first and subsequent projections Can be sufficiently suppressed.

  Moreover, since the particle diameter of a 2nd projection material is 0.3 mm or less, it is suppressed that the surface roughness of a metal product worsens by the projection of a front | former stage.

  The shot peening method according to the invention of claim 3 is the shot peening method according to the invention of claim 1 or 2, wherein the coverage of the first stage is 300% or more.

  In this shot peening method, since the coverage of the former stage is 300% or more, the surface of the metal product by the projection of the former stage can be stably work hardened.

  The shot peening method according to the invention of claim 4 is the shot peening method according to the invention of any one of claims 1 to 3, wherein the metal product is heat-treated and has a Vickers hardness of 600 or more. It is.

  The surface of a metal product that has not been heat treated has less work hardening by projection. Therefore, this shot peening method is heat treated and applied to the surface of a metal product having a Vickers hardness of 600 or more. Thereby, work hardening of the surface of the metal product by the projection in the former stage is sufficiently achieved.

  The shot peening method according to the invention as set forth in claim 5 is the shot peening method according to the invention according to any one of claims 1 to 4, wherein the second shot after the first step is the first shot material. A third projectile having a particle size smaller than the particle size is projected on the surface of the metal product.

  In this shot peening method, after the first projectile is projected on the surface of the metal product as the first stage, the third projectile having a particle size smaller than the particle size of the first project material is projected on the surface of the metal product The surface roughness of the metal product is further improved and the compressive residual stress is improved, as compared with the case where the processing is finished in the first stage projection.

  Since the shot peening method according to the invention of claim 1 or 2 is configured as described above, it is possible to improve the surface roughness by increasing the number of steps and to prevent the deterioration of the compressive residual stress imparted to the metal product.

  In the shot peening method according to the third and fourth aspects of the present invention, the surface of the metal product can be sufficiently work-hardened by the projection in the previous stage because of the above configuration.

  In the shot peening method according to the fifth aspect of the present invention, the number of steps can be increased to improve the surface roughness and the compressive residual stress imparted to the metal product can be improved.

It is a schematic block diagram of the shot peening apparatus which concerns on one Embodiment. (A) and (B) are tables which show the projection conditions of a 1st test. It is a graph which shows arithmetic mean coarseness Ra of each specimen which is the 1st test result. It is a graph which shows maximum height Rz of each specimen which is the 1st test result. It is a graph which shows maximum section height Pt of each specimen which is the 1st test result. It is a graph which shows the ten-point average roughness Rzjis of each test piece which is a 1st test result. No. 1 of the first test. It is a graph which shows the relationship between the depth from the surface in a test piece of 1-3, and a compressive residual stress. No. 1 of the first test. 4-NO. It is a graph which shows the relationship between the depth from the surface in the test piece of 6, and a compressive residual stress. (A) and (B) are tables which show the projection conditions of a 2nd test. It is a graph which shows arithmetic mean coarseness Ra of each specimen which is the 2nd test result. It is a graph which shows maximum height Rz of each specimen which is the 2nd test result. It is a graph which shows maximum section height Pt of each specimen which is the 2nd test result. It is a graph which shows the ten-point average roughness Rzjis of each test piece which is a 2nd test result. No. 2 of the second test. 7-NO. It is a graph which shows the relationship between the depth from the surface and compressive residual stress in the test piece of 9.

  A shot peening method according to an embodiment of the present invention will be described with reference to FIGS.

[Constitution]
First, an (air type) shot peening apparatus 10 to which a shot peening method is applied will be described.

  The shot peening apparatus 10 is, as shown in FIG. 1, a projection chamber 12 for projecting the projection material S onto the test piece T, and a pressure chamber provided below the projection chamber 12 for mixing the projection material S and air. 14 and the supply hose 18 which supplies the projection material S and air mixed in the pressure chamber 14 to the projection chamber 12 and projects the test piece T from the nozzle 16 attached to the tip.

  Further, in the projection chamber 12, a rotating shaft 20 which is configured to be capable of attaching the test piece T at its tip and which is rotatably provided is provided. Furthermore, below the projection chamber 12, a tapered portion 22 for supplying the projected projection material S to the pressure chamber 14 is provided.

  That is, the projection material S mixed with the air pressurized in the pressure chamber 14 is projected from the tip of the nozzle 16 onto the test piece T supported by the rotating shaft 20.

[Effect]
In order to explain the action of the shot peening method according to the present embodiment, the first test and the second test were conducted on comparative examples and examples. In addition, the test piece in a 1st test and a 2nd test, a projectile, and projection conditions are common. Moreover, the non-processing of FIGS. 3-6 and FIGS. 10-13 shows the state before the projection of the surface of the test piece T. FIG.

(contents of the test)
1. Test piece Test piece T is chromium molybdenum steel SCM420H (JIS standard) (vacuum carburized and quenched), initial surface roughness Ra is about 0.4 μm, and surface hardness (Vickers hardness) is about HV700. The test piece T is a cylindrical body having a diameter of 25 mm and a length of 100 mm.

2. The following three types of projection materials are used as the projection materials S.

(1) Made of iron-based material, diameter 0.6 mm and Vickers hardness HV 650 to 750
(2) Made of iron-based material, diameter 0.1 mm and Vickers hardness HV 700 to 830
(3) It is made of an iron-based material and has a diameter of 0.05 mm and a Vickers hardness of HV 900 to 950.

  The projectiles of (1) to (3) may be described as "large", "medium" and "small" in the drawings and the like.

3. Projection Conditions As shown in FIGS. 2A and 9A, the air pressure is 0.2 MPa for the projectiles "small" and "medium", and 0.3 MPa for the projectiles "large". Further, coverage is 300% or 500% in the former stage described later, and is 300% in each of the first and second stages.

4. Contents of the first test As shown in FIG. 2 (B), NO. Each of the projectiles is projected onto the surface of the test piece T in the order of the respective projections in the order of 1 to 6, and the arithmetic average roughness Ra (see FIG. 3) and the maximum height Rz of the surface of the projected test piece T 4), maximum cross-sectional height Pt (see FIG. 5), ten-point average roughness Rzjis (see FIG. 6), and compressive residual stress applied to the test piece T was measured (FIG. 7, figure) 8). In addition, NO. 1 and 4 are comparative examples, and NO. 2, 3, 5, 6 are examples.

  First, NO. 1 and NO. Compare 2 and 3. In the case of NO. No. 1 to 1. 2 and 3 project the projection material "small" as a front stage before the projection material "large" to obtain the arithmetic average roughness Ra, maximum height Rz, maximum section height Pt, ten-point average roughness of the test piece T It was confirmed that Rzjis is improved (see FIGS. 3 to 6).

  This is the projection material "small" with a particle size (0.05 mm) less than half (0.3 mm) of the particle size (0.6 mm) of the particle size (0.6 mm) of the first stage project material as the former stage Therefore, it is considered that the surface can be work-hardened while suppressing roughening of the surface roughness of the test piece T before the first stage projection material "large" is projected.

  In addition, since the Vickers hardness of the projectile "small" to be projected in the former stage is HV900 and the Vickers hardness HV700-HV100 = HV600 or more of the test piece T, the surface of the specimen T is sufficiently It is thought that it is because it can be work hardened.

  That is, because the arithmetic mean roughness Ra, the maximum height Rz, the maximum cross-section height Pt, and the ten-point average roughness Rzjis of the test piece T are suppressed by the first-stage projection material "large" projection It is believed that there is.

  Moreover, NO. NO. Although the former and the latter have added the former stage, as shown in FIG. 7, the deterioration of the compressive residual stress imparted to the test piece T is not observed.

  This is because the compressive residual stress imparted to the test piece T depends on the particle size of the shot material "large" in the final stage (the first stage for NO. 1 to 3). Here, NO. 2 and 3 are NO. As the first stage is added to 1 only, the final stage (the first stage for NO. 1 to 3) is NO. It is identical to 1. Therefore, NO. The compressive residual stress imparted to a few test pieces T is NO. Deterioration compared to 1 is prevented.

  Furthermore, NO. 2 and NO. When 3 is compared, the arithmetic mean roughness Ra of the test piece T, maximum height Rz, maximum section height Pt, ten-point average roughness are obtained by setting coverage of the projection material “small” in the former stage to 300% to 500%. It was confirmed that Rzjis is further improved (see FIGS. 3 to 6).

  Next, NO.1 which is a comparative example which projects a projection material "large" in the 1st stage, and projects a projection material "inside" in the 2nd stage. 4 and NO. Compare 5 and 6 Also in this case, NO. No. 4 in comparison with 4. It was confirmed that the arithmetic average roughness Ra, the maximum height Rz, the maximum cross-sectional height Pt, and the ten-point average roughness Rzjis of the test pieces T are improved in the cases 5 and 6 (see FIGS. 3 to 6). . In particular, NO. 2 and NO. When 3 is compared, the arithmetic mean roughness Ra of the test piece T, maximum height Rz, maximum section height Pt, ten-point average roughness are obtained by setting coverage of the projection material “small” in the former stage to 300% to 500%. It was confirmed that Rzjis is further improved (see FIGS. 3 to 6).

  Moreover, NO. In comparison with No. 4, NO. Although 5 and 6 added the former stage, as shown in FIG. 8, the deterioration of the compressive residual stress given to the test piece T is not seen.

  This NO. Also in the test results of 4 to 6, NO. It is considered to be the same reason as 1 to 3.

5. Details of the second test The second test is also performed in the same manner as the first test. 7-9 is NO. 4-NO. It is what changed the projection material "middle" of the 2nd step | stage in 6 into the projection material "small." That is, the projectiles of the front stage and the second stage are the same as the projectile "small". This NO. For each of 7 to 9, each projectile is projected onto the test piece T in the order of projection, and the arithmetic average roughness Ra (refer to FIG. 10) and the maximum height Rz (refer to FIG. 11) for the projected test pieces T The maximum cross-sectional height Pt (see FIG. 12) and the ten-point average roughness Rzjis (see FIG. 13) were determined, and the compressive residual stress imparted to the test piece T was measured (see FIG. 14). In addition, NO. 7 is a comparative example, NO. 8, 9 are examples.

  In addition, NO. 7 projects the projection material "small" onto the surface of the metal product as the second stage after the first stage projection material "large", so the arithmetic average roughness Ra (see Fig. 10), the maximum height Rz (see FIG. 11), maximum cross-sectional height Pt (see FIG. 12), and ten-point average roughness Rzjis (see FIG. 13) are suppressed.

  Next, with respect to the test piece T, the projection material "large" as the first stage and the projection material "small" as the second stage are projected. No.7 and the projection material "small" to project the projection material "small" as a further front before the projection material "large" Compare 8 and 9 NO. In comparison with No. 7, NO. As for 8 and 9, it was confirmed that arithmetic mean roughness Ra of test piece T, maximum height Rz, maximum section height Pt, and ten-point average roughness Rzjis are improved (see FIGS. 10 to 13). In particular, NO. 8 and NO. In comparison with 9, the arithmetic mean roughness Ra, maximum height Rz, maximum cross-section height Pt, and ten-point average roughness of the test piece T are obtained by setting the coverage of the projectile “small” at the former stage to 300% to 500%. It was confirmed that Rzjis is further improved (see FIGS. 10 to 13).

  Moreover, NO. In comparison with No. 7, NO. 8 and 9 added the former stage, but as shown in FIG. 14, the deterioration of the compressive residual stress imparted to the test piece T is not observed.

  This NO. Also in the test results of 7 to 9, NO. It is considered to be the same reason as 1 to 3.

(Others)
Although the shot peening method of this embodiment was applied to the air type shot peening apparatus 10, as long as it is a shot peening method of projecting a projectile onto the test piece T, it may be applied to another apparatus.

T test piece (metal products)

Claims (5)

Projecting a first projectile of a predetermined particle size onto the surface of a metal product as the first stage;
Projecting a second projectile having a particle diameter equal to or less than half of the particle diameter of the first projectile on the surface of the metal product as a former stage before the first stage;
Shot peening method comprising.   The shot peening method according to claim 1, wherein a particle diameter of the second projectile is 0.3 mm or less, and a Vickers hardness of the second projectile is a Vickers hardness of -100 or more of the metal product.   The shot peening method according to claim 1 or 2, wherein the coverage of the former stage is 300% or more.   The shot peening method according to any one of claims 1 to 3, wherein the metal product is heat-treated and has a Vickers hardness of 600 or more.   The 3rd projection material which has a particle size smaller than the particle size of the said 1st projection material is projected on the surface of the said metal product as a 2nd stage after the said 1st stage. Shot peening method.