JP5609106B2 - Manufacturing method of shaft with holes with excellent fatigue characteristics - Google Patents

Description

  The present invention relates to a technique for improving the fatigue strength of a shaft with a hole, that is, a shaft having a hole for allowing oil to pass through, for example, on the axis and side of the shaft.

  Some parts for machine structures, particularly automobile transmission shafts and crankshafts, are imparted with characteristics as machine structure parts by induction hardening and tempering after being processed into a part shape. Such a shaft is generally provided with a lateral hole called an oil hole on its side surface for ejecting oil supplied into the shaft to the outside of the shaft. Moreover, the oil hole which ejects this oil is connected with the shaft hole opened in parallel with the shaft near the shaft center of the shaft, and oil is supplied through this shaft hole.

  However, the stress around the wall surface that divides the oil hole (hereinafter referred to as the oil hole wall surface) is more concentrated than the adjacent part, so fatigue cracks can occur from this point, leading to shaft breakage. Not a few. Generally, the fracture from the wall surface of the oil hole occurs from the vicinity of the outlet side of the oil hole. This is because the load stress increases as the distance from the central axis of the shaft increases. However, fatigue cracks may occur from the boundary between the induction-quenched portion on the wall surface of the oil hole and the base material (non-quenched portion), that is, the quenching boundary, and may break. In this case, not only the soft base material side is the starting point, but also tensile residual stress is generated in this vicinity, so the fatigue strength is lower than when the oil hole inlet side vicinity is the starting point. It is common.

  As a measure for preventing a decrease in fatigue strength due to a crack starting from the vicinity of the inlet side of the oil hole wall surface, Patent Document 1 discloses that the oil hole wall surface is formed by so-called shot peening, in which a small hard ball collides with the side wall surface. A method for increasing the residual compressive stress of is described. However, in this method, since the hard ball is projected obliquely toward the oil hole, the force acting perpendicularly to the wall surface of the oil hole (force component for increasing the residual compressive stress) is small and inefficient. Shot peening is possible with parts with a relatively large horizontal hole diameter, such as a crankshaft, but shot parts clog the oil hole with a small oil hole diameter of about 1-2 mm, such as a transmission shaft. However, since shot peening itself becomes difficult, it becomes difficult to increase the residual compressive stress on the inner surface.

  On the other hand, in recent years, attempts have been made to modify the surface of mechanical parts by utilizing the crushing impact force of bubbles in cavitation (see, for example, Patent Document 2), which is called cavitation peening. This cavitation peening is performed by jetting a jet water flow having low pressure water around the high pressure water to the surface of the material. However, with a shaft having an oil hole on the side surface, in the case where cracks occur from the burning boundary on the inner surface of the oil hole, how to apply the crushing impact force of cavitation bubbles to the inner surface of the oil hole, In order to improve fatigue strength by applying cavitation peening to a shaft having an oil hole that has not been considered, there is room for improvement in the method of cavitation peening.

Japanese Patent No. 2766488 JP 2003-62492 A

  An object of the present invention is to provide a method of manufacturing a shaft that uses cavitation peening to increase the residual compressive stress of the side wall surface of a shaft having a side hole such as an oil hole, thereby improving fatigue strength, particularly torsional fatigue strength. And

The inventors have conducted intensive research on a method for uniformly distributing a high residual compressive stress on the wall surface of the lateral hole, and have developed the following solution.
That is, the gist configuration of the present invention is as follows.
(1) A method of manufacturing a shaft having a shaft hole provided parallel to the axial direction of the shaft, and a lateral hole penetrating from the side surface of the shaft to the shaft hole,
After inserting a rod-shaped stopper into the shaft hole, and closing the opening on the shaft hole side of the horizontal hole with the peripheral surface of the rod-shaped stopper, from the side of the side hole to the periphery of the high-pressure water low pressure water decor, injected water jet method excellent holed shaft torsional fatigue characteristics characterized by imparting residual compressive stress due to cavitation peening wall partitioning the lateral hole.

(2) In the above (1), a shaft with a hole with excellent torsional fatigue characteristics, characterized in that the shaft hole side is closed with respect to the region to which the residual compressive stress of the wall surface is applied, and a pin is inserted into the lateral hole. Manufacturing method.

( 3 ) In any one of (1) or (2) , the pressure of the high pressure water is 10 to 20 MPa and the pressure of the low pressure water is 0.02 to 0.06 MPa. A method for producing a shaft with a hole excellent in torsional fatigue characteristics, characterized in that the distance to the center position of the region to which the residual compressive stress is applied is 30 to 40 mm. (4) In any one of the above (1) to (3), the hole diameter of the lateral hole is 2 mm or less, and the manufacturing method of a shaft with a hole excellent in torsional fatigue characteristics.

  According to the present invention, since the residual compressive stress is appropriately applied to the side wall surface of the shaft, the fatigue strength of the shaft with a hole can be remarkably improved. In particular, when there is a burning boundary on the wall surface of the side hole, torsional fatigue failure starting from the burning boundary is less likely to occur, and a shaft having high fatigue strength can be manufactured.

It is sectional drawing which shows the example of the shaft manufactured by this invention. It is sectional drawing which shows the point which implements cavitation peening to a shaft. It is sectional drawing which shows the point which implements cavitation peening to the shaft which concerns on embodiment of this invention. It is sectional drawing which shows the point which implements the cavitation peening to the shaft which concerns on another embodiment of this invention, (a) is schematic and (b) is an enlarged view of a side hole part. It is sectional drawing which shows the point which implements cavitation peening to the shaft which concerns on another embodiment of this invention. It is a figure which shows the shape of the shaft of the Example of this invention. It is a figure which shows the point which gives the residual compressive stress to the horizontal hole wall surface of the shaft of the Example of this invention, (a) is an invention example, (b) is another invention example, (c) is another invention. For example, (d) shows a comparative example.

  FIG. 1 is a cross-sectional view showing an example of a shaft targeted by the present invention. The shaft 1 has a lateral hole 2 penetrating from its side surface toward the axial center, and further has an axial hole 3 parallel to the axial direction. The lateral hole 2 penetrates from the outer surface of the shaft 1 to the shaft hole 3. In such a shaft with a hole, the present invention applies a residual compressive stress to the side wall surface 2a defining the side hole 2 to improve the fatigue strength of the shaft.

Here, cavitation peening is a process in which bubbles called cavitation are generated when a high-pressure water flow is generated inside a low-pressure water flow, and residual compressive stress is imparted to the material by the impact force generated when the bubbles collapse. is there.
As described above, in conventional shot peening, it is difficult to hit the inner surface of a small-diameter hole, and since it is injected from an oblique direction with respect to the opening of the hole, it is perpendicular to the inner surface of the hole. The force acting from the direction was small, and it was not efficient for applying the residual compressive stress. In this respect, in the cavitation peening, the impact force when the bubbles collapse spreads in all directions, so that it is possible to effectively apply the impact force to the side wall surface 2a, and the residual compressive stress can be applied thereto. Is possible.

Therefore, in the present invention, residual compressive stress is applied to the side wall surface 2a using cavitation peening. That is, as shown in FIG. 2 in which the cavitation peening is performed on the wall surface 2 a of the horizontal hole, the jet water flow 10 is ejected from the nozzle 11 disposed opposite to the opening of the horizontal hole 2 provided on the outer surface of the shaft 1. The jet water stream 10 is set to be a water stream that is arranged around the low-pressure water stream 10 a around the high-pressure water stream 10 b, and is jetted toward the center of the opening of the horizontal hole 2. Cavitation peening is performed on the wall surface 2a of the horizontal hole by injecting the jet water flow 10 toward the center of the horizontal hole 2 from the outer surface side of the shaft 1.
Here, in the jet water stream 10, the pressure of the low pressure water stream is preferably 0.02 to 0.10 MPa, and the pressure of the high pressure water stream is preferably 10 to 20 MPa.
The distance from the nozzle tip to the center of the region to which the residual compressive stress is applied is preferably 30 to 40 mm.

  At this time, it is important to close the opening of the horizontal hole 2 on the side of the axial hole 3 and close the outlet side of the jet water flow 10. FIG. 3 is a diagram illustrating an example of a technique for closing the opening of the horizontal hole 2 on the shaft hole 3 side. That is, in performing the cavitation peening, in order to close the opening of the horizontal hole 2 on the side of the shaft hole 3, in the example of FIG. 3, a rod-shaped stopper 12 is inserted into the shaft hole 3 and the opening of the horizontal hole 2 on the side of the shaft hole 3. Is closed by the peripheral surface of the stopper 12.

  By doing in this way, the escape place of the bubble generated by the cavitation accompanying jet water flow injection is lost, and the inside of the side hole is filled and collapsed. Therefore, the residual compressive stress can be uniformly applied to the side wall surface 2a.

  Further, as shown in FIG. 4, a cylindrical pin 15 is inserted into the horizontal hole 2 so as to close the axial hole 3 side of the region 14 to which the residual compressive stress of the wall surface 2 a defining the horizontal hole 2 is to be applied. When the cavitation peening is performed (see FIG. 4B), higher residual compressive stress can be applied due to the effect of the cavitation peening bubbles rebounding on the upper surface of the pin 15.

  Further, when it is difficult to close the opening of the side hole 2 on the side of the shaft hole 3, as shown in FIG. 5, a plug 13 is provided at the opening 3a of the shaft hole 3 at the end of the shaft so You may try to eliminate the escape. At this time, when cavitation peening is performed on a shaft provided with a plurality of lateral holes 2 as shown in FIG. 1, the holes 2 not in the state of cavitation peening are plugged from the outer surface side of the shaft. It is preferable to keep it. This is to prevent bubbles from escaping from escaping from the holes 2 that are not in the state of performing cavitation peening. Further, by performing cavitation peening for all the holes 2 at the same time, the escape space for the cavitation bubbles may be eliminated.

For example, the transmission shaft has a structure in which a lateral hole is connected to a shaft hole (main hole) provided in the center of the shaft. In such a case, as shown in FIG. 3, the plug is plugged from the shaft hole side of the oil hole, or as shown in FIG. 5, the plug 13 is plugged into the opening 3a of the shaft hole 3 at the end of the shaft. With this, air bubbles caused by cavitation can be contained.
In addition, when there are many horizontal holes for oil, it is possible to shorten the working time by arranging a large number of nozzles.

C: 0.45 mass%, Si: 0.40 mass%, Mn: 0.80 mass%, Al: 0.024 mass%, Mo: 0.20% mass, Ti: 0.022% mass, B: 0.0019 mass%, balance Fe and inevitable impurities A shaft 1 having the shape shown in FIG. 6 was manufactured using a steel material. This shaft 1 has a shaft hole 3 (hole diameter 10 mmφ) parallel to the axial direction, and further has a parallel portion of 90 mm in length at the center in the longitudinal direction of the shaft. Further, the central portion in the longitudinal direction of the parallel portion has a hole 2 (hole diameter 2 mmφ) connected to the shaft hole 3 from the outer surface. This shaft was quenched by induction moving quenching under the condition that the maximum surface heating temperature was 950 ° C. and tempered at 170 ° C. for 30 minutes. The thickness of the quenched part was an average of 2.5 mm.
About the obtained shaft, the process with respect to the horizontal hole 2 was performed on the conditions shown below.

[Invention Example 1]
For the shaft after induction hardening and tempering, as shown in FIG. 7A, a rod-like stopper 12 was inserted into the shaft hole 3 to close the shaft hole side opening of the horizontal hole 2. Next, cavitation peening was performed with the distance from the tip of the nozzle 11 to the entrance of the horizontal hole 3 being 20 mm. The nozzle 11 injects a jet water flow around the low-pressure water 10b around the high-pressure water 10a. The high-pressure water pressure is 15 MPa and the low-pressure water pressure is 0.04 MPa. Arranged so that the center position matches.

[ Reference Example 2]
As for the shaft after induction hardening and tempering, as shown in FIG. 7 (b), a plug 13 is plugged into the opening 3a of the shaft hole 3 at one end of the shaft, and the distance from the tip of the nozzle 11 to the inlet of the horizontal hole Cavitation peening was performed at 20 mm. The nozzle 11 injects a jet water stream around the low-pressure water 10b around the high-pressure water 10a. The high-pressure water pressure is 15 MPa and the low-pressure water pressure is 0.04 MPa. Arranged to fit.

[Invention Example 3]
For the shaft after induction hardening and tempering, a rod-like stopper 12 is inserted into the shaft hole 3 in the same manner as in [Invention Example 1], and then the distance from the tip of the nozzle 11 to the inlet of the side hole 2 is 33 mm (from the tip of the nozzle 11). Cavitation peening was performed at the position where the residual compressive stress in the induction-hardened part was most desired (35 mm from the side hole entrance to a depth of 2 mm). The nozzle 11 injects a jet water flow around the low-pressure water 10b around the high-pressure water 10a. The high-pressure water pressure is 15 MPa and the low-pressure water pressure is 0.04 MPa. Arranged so that the center position matches.

[Invention Example 4]
With respect to the shaft after induction hardening and tempering, as shown in FIG. 7C, a rod-like stopper 12 was inserted into the shaft hole 3 to close the opening of the side hole 2 on the shaft hole side. Furthermore, the pin 15 was inserted so that the side of the axial hole 3 might be plugged up with respect to the horizontal hole 2 rather than the area | region which wants to provide a residual compressive stress. Then, cavitation peening was performed with the distance from the tip of the nozzle 11 to the inlet of the horizontal hole 33 mm (35 mm from the tip of the nozzle 11 to the position where the highest residual compressive stress in the induction-hardened portion is desired (35 mm from the side of the side hole to a depth of 2 mm)). The nozzle 11 injects a jet water flow around the low-pressure water 10b around the high-pressure water 10a. The high-pressure water pressure is 15 MPa and the low-pressure water pressure is 0.04 MPa. Arranged so that the center position matches.

[Comparative Example 1]
The shaft after induction hardening and tempering was subjected to cavitation peening with the distance from the tip of the nozzle 11 to the entrance of the side hole being 20 mm without plugging as in Examples 1 to 4. The nozzle 11 is designed to inject a jet water stream around low-pressure water, mainly high-pressure water. The high-pressure water pressure is 15 MPa, the low-pressure water pressure is 0.04 MPa, and the center position of the jet water stream is aligned with the center of the opening of the horizontal hole 2. Arranged.

[Comparative Example 2]
About the shaft after induction hardening and tempering, as shown in FIG.7 (d), the hard ball 21 whose diameter is 0.5 mm was injected diagonally with respect to the side wall surface 2a, and shot peening was performed. At this time, the injection direction of the injection nozzle 20 of the hard ball 21 was adjusted so as to be a direction of 20 ° with respect to the central axis of the opening of the horizontal hole 2, and injection was performed with an injection pressure of 0.5 MPa. Further, shot peening was performed by rotating the shaft little by little as indicated by arrows in the drawing so that the hard sphere collides with the entire side wall surface 2a.

A plurality of shafts subjected to the above treatments were prepared, and a torsional fatigue test was conducted using these shafts, and the 1 × 10 ⁵ times torsional fatigue strength was investigated from the SN curve. In addition, a plurality of shafts that were subjected to induction hardening and tempering were prepared, and the fatigue strength was similarly investigated.

As a result, the shaft of Invention Example 1 is 930 Nm, the shaft of Invention Example 2 is 890 Nm, the shaft of Invention Example 3 is 960 Nm, the shaft of Invention Example 4 is 1010 Nm, the shaft of Comparative Example 1 is 780 Nm, and the shaft of Comparative Example 2 is 835 Nm The induction-quenched-tempered shaft had a fatigue strength of 780 Nm.
From the above, it can be seen that the cavitation peening method of the present invention can effectively reinforce the periphery of the side hole provided on the side surface of the shaft.

DESCRIPTION OF SYMBOLS 1 Shaft 2 Horizontal hole 2a Horizontal hole wall surface 3 Shaft hole 10 Jet water flow 10a Low pressure water 10b High pressure water 11 Nozzle 12 Bar-shaped plug 13 Plug 14 Area | region which wants to give residual compressive stress 15 Pin 20 Hard ball injection nozzle 21 Hard ball

Claims (4)

A method of manufacturing a shaft having a shaft hole provided parallel to the axial direction of the shaft, and a lateral hole penetrating from the side surface of the shaft to the shaft hole,
After inserting a rod-shaped stopper into the shaft hole, and closing the opening on the shaft hole side of the horizontal hole with the peripheral surface of the rod-shaped stopper, from the side of the side hole to the periphery of the high-pressure water low pressure water decor, injected water jet method excellent holed shaft torsional fatigue characteristics characterized by imparting residual compressive stress due to cavitation peening wall partitioning the lateral hole.   2. The method for manufacturing a shaft with a hole with excellent torsional fatigue characteristics according to claim 1, wherein a pin is inserted into the side hole that closes the shaft hole side of the wall surface from the region to which the residual compressive stress is applied.   3. The residual compressive stress of the wall surface is applied from the tip of a nozzle that injects the jet water flow, with the pressure of the high-pressure water being 10 to 20 MPa and the pressure of the low-pressure water being 0.02 to 0.06 MPa. A method for manufacturing a shaft with a hole excellent in torsional fatigue characteristics, wherein the distance to the center position of the region to be made is 30 to 40 mm.   4. The method of manufacturing a shaft with a hole excellent in torsional fatigue characteristics according to claim 1, wherein a hole diameter of the horizontal hole is 2 mm or less.

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