JP2005125458A - Device and method for water jet peening - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device capable of easily and accurately imparting compressive residual stress to a screw hole. <P>SOLUTION: The water jet peening device is provided with a high-pressure water feeding means 12 for feeding high-pressure water, a nozzle hole 7 for jetting the high-pressure water fed from the high-pressure water feeding means 12, a nozzle 5 with a screw, which can be screwed with the screw hole 3, a tensile force imparting means 21, which imparts tensile stress to the screw hole 3 in a state that the nozzle 5 with a screw is screwed with the screw hole 3, and an actuator 32 which relatively rotates the nozzle 5 with a screw and the screw hole 3 in a state that the tensile stress is imparted to the screw hole 3 by the tensile force imparting means 21. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a water jet peening apparatus and method, and more particularly to a water jet peening apparatus and method for applying compressive residual stress to a screw hole.

  Conventionally, screws are used for fastening various members. For example, in an automobile engine, screw fastening is used for fixing a cylinder head and a cylinder block, fixing a bearing support (body and cap) that supports a crankshaft, and the like.

  These screw fastening portions have been subjected to higher loads as the engine output increases, and higher strength is desired.

  However, in recent years, for the purpose of reducing the weight of the engine and the like, there is a tendency that a member made of an aluminum alloy having a strength lower than that of a steel material is used. It has become.

  An example of a screw hole breakage mechanism will be described with reference to FIG.

  FIG. 3 is a partially enlarged view of a screw fastening member for fixing a bearing support that supports the crankshaft, where B is a body disposed above the crankshaft (not shown), and S is a body B. This is a bolt that is screwed into a screw hole (female screw) N formed on the body and fixes a cap (not shown) to the body B.

  In the combustion process of the engine, as the piston descends, a downward pressing force acts on the crankshaft and the cap that supports the crankshaft. Then, a large tensile stress is generated in the bolt S and the screw hole N, particularly in the valley portion T of the screw hole N. Since this tensile stress repeatedly acts while the engine is driven, there is a possibility that a fatigue crack C may occur in the valley portion T of the screw hole N.

  In particular, since the tensile residual stress due to tapping and the tensile stress due to tightening of the bolt S are originally present in the screw hole N, fatigue failure due to the tensile stress is likely to occur.

  Therefore, it has been proposed to apply compressive residual stress by performing shot peening on the inner surface of the screw hole N (see, for example, Patent Document 1).

JP 2002-346677 A (2nd page, paragraph 0004)

  However, this method has the following problems.

  1) Since shot grains (such as steel balls) remaining in the screw holes N after shot peening need to be removed, this leads to an increase in processes and an increase in manufacturing costs.

  2) The thread may be deformed by shot grains.

  3) It is difficult to accurately hit the shot grains against the valley T which is a stress concentration site.

  Accordingly, an object of the present invention is to provide an apparatus that can easily and accurately apply a compressive residual stress to a screw hole.

  In order to achieve the above object, the present invention provides a water jet peening apparatus for applying compressive residual stress to a screw hole, the high pressure water supply means for supplying high pressure water, and the supply from the high pressure water supply means A nozzle hole for injecting the generated high-pressure water, a threaded nozzle that can be screwed into the screw hole, and a tensile stress applied to the screw hole in a state where the threaded nozzle is screwed into the screw hole. A tension applying means for applying, and an actuator for rotating the threaded nozzle and the screw hole relative to each other in a state where a tensile stress is applied to the screw hole by the tension applying means.

  Here, the tension applying unit may include a detecting unit for detecting a tensile stress acting on the screw hole.

  Furthermore, the present invention is a water jet peening method for imparting compressive residual stress to a screw hole, the step of screwing a screw nozzle that jets high-pressure water from a tip portion into the screw hole, and the screw hole. The step of spraying high-pressure water from the tip of the screwed nozzle onto the inner surface of the screw hole, the step of applying a tensile stress to the screw hole, and the state of applying the tensile stress to the screw hole And a step of relatively rotating the attached nozzle and the screw hole in a direction in which the screwing is released.

  Here, the injection of the high-pressure water may be performed on one to three valleys from the screwing position with the tip of the threaded nozzle in the screw hole.

  Further, it is preferable that the tensile stress applied to the screw hole is constant while the threaded nozzle and the screw hole are relatively rotated.

  Further, it is preferable that the tensile stress applied to the screw hole is set equal to the tensile stress acting on the screw hole in actual use.

  According to the present invention, an excellent effect that compressive residual stress can be easily and accurately applied to a screw hole is exhibited.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  The present invention is to apply compressive residual stress to a screw hole in order to improve the fatigue strength of the screw hole, and uses water jet peening as the means. In addition, when water jet peening is applied to a screw hole, a contrivance has been made to effectively improve the stress of the screw hole.

  FIG. 1 is a front sectional view of a water jet peening apparatus according to the present embodiment, and FIG. 2 is a perspective view of a threaded nozzle.

  A water jet peening apparatus 1 (hereinafter abbreviated as an apparatus) includes a fixing means 2 for fixing a workpiece W (for example, an aluminum alloy cylinder block), which is a stress improvement target member, to a fixed side such as a table (not shown). It has. The fixing means 2 is composed of a pair of claw members provided so as to be movable up and down with respect to the fixed side and capable of adjusting the distance between them (the distance in the left-right direction in FIG. 1). The work W can be fixed at an appropriate position by being engaged with the upper surface and pressing it toward the fixed side (downward).

  The apparatus 1 includes a threaded nozzle 5 that can be screwed into the screw hole 3 of the workpiece W. That is, the threaded nozzle 5 is formed with a male screw 6 that can be screwed into the screw hole 3 on the outer periphery thereof. The threaded nozzle 5 is formed in a hollow shape, and a nozzle hole 7 is formed in the inner space of the threaded nozzle 5 so as to communicate with both ends in the longitudinal direction of the threaded nozzle 5. The nozzle hole 7 is formed in a tapered shape so that the cross-sectional area gradually increases at the tip of the threaded nozzle 5 (the front end in the insertion direction when screwed into the screw hole 3). In the present embodiment, the nozzle hole 7 has a circular cross section and is gradually expanded in diameter at the tip.

  Further, a discharge groove 9 for discharging high-pressure water sprayed from the nozzle hole 7 is formed on the outer peripheral portion of the threaded nozzle 5. In the present embodiment, the discharge grooves 9 have a circular arc shape in cross section, and four discharge grooves 9 are formed at substantially equal intervals (90 °) in the circumferential direction of the male screw 6 (see FIG. 2). Each discharge groove 9 is formed over the entire longitudinal direction of the male screw 6.

  A rod 8 having a diameter substantially equal to the diameter of the valley of the male screw 6 is provided at the rear end (upper end) of the male screw 6. A larger cross section than the rod 8 and the male screw 6 is provided at the rear end of the rod 8. A flange 10 is provided. In the present embodiment, the flange 10 has a disk shape, and the engagement groove 11 is formed on the lower surface thereof. Two engaging grooves 11 are formed so as to extend from the radially outer end of the flange 10 toward the center by a predetermined distance and to be 180 degrees apart in the circumferential direction of the flange 10, that is, to face each other.

  A high-pressure water supply means 12 can be connected to the upper surface of the flange 10 of the threaded nozzle 5. The high-pressure water supply means 12 includes a connecting member 13 detachably attached to the upper surface of the flange 10, a high-pressure water pipe 15 connected to the connecting member 13, and a high-pressure water supply source (pump connected to the other end of the high-pressure water pipe 15. Etc.) 16.

  In this embodiment, the connection member 13 is made of a coupler and includes a seal member 17 that seals between the flange 10 of the threaded nozzle 5. A communication hole 19 that is aligned with the nozzle hole 7 of the threaded nozzle 5 is formed at the center of the coupler 13, and the high-pressure water pipe 15 is connected to the communication hole 19 via a rotary joint 20. Therefore, the high-pressure water pipe 15 and the coupler 13 can rotate relative to each other. When high-pressure water is supplied into the pipe 15 from the high-pressure water supply source 16, the high-pressure water is jetted from the tip (lower end) of the threaded nozzle 5 through the communication hole 19 and the nozzle hole 7.

  The apparatus 1 further includes tension applying means 21 that pulls up the screwed nozzle 5 screwed into the screw hole 3 of the workpiece W and applies tensile stress to the screwed nozzle 5 and the screw hole 3. .

  The tension applying means 21 includes an engagement jig 22 that engages with the flange 10 of the threaded nozzle 5 in a relatively non-rotatable manner, a base 23 provided on the upper portion of the engagement jig 22 so as to be relatively rotatable, and a base 23. Drive means 25 (here, a hydraulic cylinder) that moves up and down is provided.

  The engagement jig 22 includes a pair of U-shaped members 26, 26 that can adjust the distance between them (the distance in the left-right direction in FIG. 1). The U-shaped members 26, 26 are formed on the lower surface of the flange 10. By engaging with the mating groove 11, the engagement jig 22 and the threaded nozzle 5 can be engaged with each other so as not to rotate relative to each other.

  The base 23 is connected to the upper surface of the engagement jig 22 via a bearing 27, and a hydraulic cylinder 25 is interposed between the upper surface of the base 23 and the reaction force receiver 29.

  The hydraulic cylinder 25 has a main body 25 a fixed to the reaction force receiver 29 and a rod 25 b fixed to the base 23. By retracting the rod 25b of the hydraulic cylinder 25, the base 23, the engaging jig 22 and the threaded nozzle 5 engaged therewith are pulled upward, and pulled to the threaded nozzle 5 and the threaded hole 3 of the workpiece W. Stress can be applied.

  The tension applying means 21 includes a detecting means 30 (here, a load cell) that detects tensile stress acting on the threaded nozzle 5 and the screw hole 3. In the present embodiment, the load cell 30 is provided on the rod 25b of the hydraulic cylinder 25, and detects the tensile stress acting on the threaded nozzle 5 and the screw hole 3 from the strain generated in the rod 25b. However, the load cell 30 may be attached to the threaded nozzle 5 or the like.

  Control means 31 for controlling expansion and contraction of the rod 25 b of the hydraulic cylinder 25 is provided, and a detection value of the load cell 30 is input to the control device 31. The control device 31 controls the expansion and contraction of the rod 25b of the hydraulic cylinder 25 based on the detection value from the load cell 30, and appropriately controls the tensile stress acting on the screwed nozzle 5 and the screw hole 3.

  The apparatus 1 further includes an engagement jig 22 and an actuator 32 that rotationally drives the threaded nozzle 5 engaged therewith.

  The actuator 32 includes a driven gear 33 connected to the upper surface of the engagement jig 22 and a driving device 35 (here, a motor) that rotationally drives the driven gear 33.

  The driven gear 33 is provided at the upper end of a rod 37 that extends upward from the upper surface of the engagement jig 22 through a through hole 36 formed in the center of the base 23, and is disposed above the base 23. The motor 35 is fixed to the upper surface of the base 23, and a drive gear 39 provided on the rotation shaft meshes with the driven gear 33. When the driven gear 33 is rotationally driven by the motor 35, the rod 37, the engagement jig 22 and the threaded nozzle 5 engaged therewith rotate, and rotate relative to the workpiece W and its screw hole 3.

  The high-pressure water pipe 15 extends through a hole (not shown) formed in the engagement jig 22, the rod 37 and the driven gear 33.

  Next, a water jet peening method using this water jet peening apparatus will be described.

  First, using the fixing members 2 and 2, the workpiece W, which is a stress improvement target member, is fixed to a table (not shown) with the screw hole 3 facing upward.

  Next, the threaded nozzle 5 is inserted into the screw hole 3 of the workpiece W and screwed together. This screwing may be performed using a spanner or nutrunner, and at this time, the engagement jig 22 is engaged with the flange 10 of the threaded nozzle 5 and the threaded nozzle 5 is driven by the actuator 32 (motor 35). May be rotated. The screwing (insertion) depth of the threaded nozzle 5 is set to be the same as the screwing depth of a bolt screwed into the screw hole 3 when the workpiece W is actually used.

  Next, if the engagement work between the engagement jig 22 and the threaded nozzle 5 is not yet performed, the U-shaped members 26 and 26 of the engagement jig 22 are moved to the engagement grooves 11 of the flange 10 of the threaded nozzle 5. 11, the threaded nozzle 5 and the engagement jig 22 are engaged so as not to be relatively rotatable. As a result, the threaded nozzle 5 is connected to the tension applying means 21 and the actuator 32.

  Next, the rod 25 b of the hydraulic cylinder 25 is retracted (raised), the threaded nozzle 5 is pulled upward, and tensile stress is applied to the threaded nozzle 5 and the screw hole 3 of the workpiece W. At this time, the tensile stress acting on the screw nozzle 5 and the screw hole 3 is detected by the load cell 30, and the tensile stress generated when the workpiece W is actually used (tensile residual stress due to tapping + bolt tightening). The tensile stress generated by Specifically, the control device 31 controls the expansion / contraction amount of the rod 25b based on the detection value of the load cell 30.

  Next, the coupler 13 is connected to the upper surface of the flange 10 of the threaded nozzle 5, and the nozzle hole 7 of the threaded nozzle 5 and the high pressure water supply means 12 are connected.

  Then, high pressure water is supplied into the nozzle hole 7 of the screwed nozzle 5 by the high pressure water supply source 16. As a result, high-pressure water is ejected from the tip of the threaded nozzle 5 and supplied to the gap between the threaded nozzle 5 and the screw hole 3. Since the diameter of the tip of the nozzle hole 7 is increased, the injected high-pressure water is directed radially outward and actively flows into the valley of the screw hole 3. When high-pressure water is jetted from the threaded nozzle 5, cavitation (bubbles) is generated between the threaded nozzle 5 and the threaded hole 3, and the inner surface of the threaded hole 3 (impact pressure generated when the cavitation collapses) In particular, plastic deformation is caused in the valleys, and compressive residual stress is applied. The jetted high-pressure water is discharged upward through a gap between the discharge groove 9 and the screw hole 3 formed in the outer peripheral portion of the threaded nozzle 5, and is collected by a collecting means (not shown).

  In a state where high-pressure water is being sprayed from the threaded nozzle 5 and a tensile stress is applied to the threaded nozzle 5 and the threaded hole 3, the threaded nozzle 5 is connected to the threaded hole 3 by the actuator 32 (motor 35). It is rotated in the direction in which the screwing is released, that is, the direction in which the threaded nozzle 5 is removed. When the threaded nozzle 5 rotates, the threaded nozzle 5 gradually moves upward, and the thread that has been screwed with the male thread 6 (the thread of the threaded hole 3) is sequentially exposed from below. Accordingly, water jet peening is sequentially applied to the continuously exposed threads, and compressive residual stress is applied.

  While the threaded nozzle 5 is rotated, the hydraulic cylinder 25 is controlled by the control device 31 so that the tensile stress acting on the threaded nozzle 5 and the threaded hole 3 is always constant. Thereby, the compressive residual stress is always applied under the same conditions as when the workpiece W is used.

  If the application of the compressive residual stress to the inner surface of the screw hole 3 is performed within a predetermined range, the supply of high-pressure water is stopped and the application of the tensile stress by the tension applying means 21 is stopped, and the screwed nozzle 5 is connected to the screw hole. Remove from 3. By releasing the tensile stress applied by the tension applying means 21, a large compressive residual stress is generated on the inner surface of the screw hole 3.

  According to the water jet peening apparatus and method of the present embodiment, the following effects can be obtained.

  1) Since the removal operation of shot grains can be omitted, the process and the manufacturing cost can be reduced.

  2) Since the peening is performed with high-pressure water, there is no possibility that the threads are deformed.

  3) Since the peening is performed with high-pressure water, the stress can be easily and accurately improved with respect to the valley of the screw, which is a stress concentration site. In particular, since the diameter of the tip of the nozzle hole 7 is increased, high-pressure water can easily flow in the radially outer side, and can be effectively supplied to the thread valley.

  4) The compressive residual stress can be applied under the actual use conditions of the workpiece W. Therefore, when the workpiece W is actually used as a product and a bolt is tightened in the screw hole 3, it is possible to leave compressive stress in the screw hole 3, which is very effective for improving the fatigue strength of the screw hole 3. It is.

  5) Since the peening is performed while the threaded nozzle 5 is rotated, the peening can be continuously performed along the thread valleys of the screw holes 3 and the efficiency is high.

  Here, the present applicant has found through experiments and the like that stress is concentrated in the threaded portion between the screw hole and the bolt from the screwing position with the bolt tip in the screw hole. Referring to FIG. 3 as an example, the first thread is the thread N1 that is screwed with the thread SN of the tip of the bolt S, and the second thread N2 and the third thread that are continuous to the thread N1. Stress concentrates in a valley T of a mountain (not shown) and cracks are likely to occur. Therefore, if the stress improvement by the water jet peening described above is performed at least from the screwing position with the tip of the threaded nozzle 5 to the valleys of 1 to 3 ridges, a great effect can be obtained. In other words, after the threaded nozzle 5 is screwed into the threaded hole 3 to a predetermined depth, the threaded nozzle 5 is rotated until 1-3 threads are exposed to perform water jet peening.

  The present invention is not limited to the embodiment described above.

  For example, the fixing means 2 is not limited to that shown in FIG. For example, the workpiece W may be fixed using a bracket and a bolt.

  Further, the tension applying means 21 and the actuator 32 are not limited to those shown in FIG. For example, the tension applying means 21 may be of a type that pushes the engagement jig 22 upward from the bottom, or may be a type that pushes the work W downward while fixing the threaded nozzle 5. The actuator 32 may rotate the workpiece W with the screwed nozzle 5 fixed.

  Further, high pressure water including cavitation in advance may be supplied to the screwed nozzle 5 by the high pressure water supply source 16.

  In addition, in the water jet peening method, the order of the steps is not necessarily limited to that described above. For example, the threaded nozzle 5 and the high-pressure water supply means 12 may be connected after the threaded nozzle 5 is screwed into the screw hole 3 of the workpiece W and before the tensile stress is applied by the tension applying means 21.

  In the above embodiment, the compressive residual stress is applied to the screw hole 3. However, the fatigue strength improvement effect can be obtained only by eliminating or reducing the tensile residual stress existing in the screw hole 3.

  Furthermore, the water jet peening apparatus and method described above can be applied to any screw such as a screw hole formed in a cylinder block made of an aluminum alloy and a screw hole formed in a support body (body) of a bearing that supports a crankshaft. It can be used to improve the fatigue strength of holes.

It is front sectional drawing of the water jet peening apparatus which concerns on one Embodiment of this invention. It is a perspective view of a nozzle with a screw. It is a figure for demonstrating the damage mechanism of a screw fastening member.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Water jet peening apparatus 3 Screw hole 5 Nozzle with screw 7 Nozzle hole 12 High pressure water supply means 21 Tension provision means 30 Detection means 32 Actuator

Claims (6)

A water jet peening apparatus for applying compressive residual stress to a screw hole,
High-pressure water supply means for supplying high-pressure water;
A nozzle with a screw for injecting the high-pressure water supplied from the high-pressure water supply means, and a screwed nozzle that can be screwed into the screw hole;
Tension applying means for applying a tensile stress to the screw hole in a state where the screw nozzle is screwed with the screw hole;
An actuator that relatively rotates the threaded nozzle and the screw hole in a state in which a tensile stress is applied to the screw hole by the tension applying unit;
A water jet peening apparatus comprising:   The water jet peening apparatus according to claim 1, wherein the tension applying means includes a detecting means for detecting a tensile stress acting on the screw hole. A water jet peening method for applying compressive residual stress to a screw hole,
Screwing a threaded nozzle for injecting high-pressure water from the tip into the screw hole;
Spraying high-pressure water onto the inner surface of the screw hole from the tip of the threaded nozzle screwed into the screw hole;
Applying a tensile stress to the screw hole;
In a state where a tensile stress is applied to the screw hole, the step of relatively rotating the screwed nozzle and the screw hole in a direction in which the screwing is released;
A water jet peening method characterized by comprising:   The water jet peening method according to claim 3, wherein the injection of the high-pressure water is performed on one to three valleys from a screwed position with the tip of the threaded nozzle in the screw hole.   The water jet peening method according to claim 3 or 4, wherein a tensile stress applied to the screw hole is constant while the threaded nozzle and the screw hole are relatively rotated. The water jet peening method according to any one of claims 3 to 5, wherein a tensile stress applied to the screw hole is set equal to a tensile stress acting on the screw hole under actual use.

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