A turbine shaft bolt hole projectile type ultrasonic impact strengthening device and strengthening method thereof

Abstract

The present invention belongs to the part surface treatment technology, and relates to a turbine shaft bolt hole projectile type ultrasonic impact strengthening device and a strengthening method thereof. The device comprises a fuselage bracket (1), a projectile sealed cavity groove (2), a cavity base (3), a variable amplitude rod (4), a transducer fixing clamp (5), and a transducer (6); the device of the present invention completely seals the semi-open bolt holes of the structure to form a closed cavity, and then places a hard projectile in the cavity, and uses an ultrasonic source to amplify the amplitude to excite the hard projectile in the closed cavity to perform Brownian motion, so that the projectile impacts the cavity and the inner wall of the bolt hole at high speed under ultrasonic excitation, so that the inner wall surface undergoes elastic-plastic deformation, and the inner wall surface of the bolt hole is indiscriminately impacted by the projectile, so that a uniform strengthening effect is obtained at all places on the inner wall of the bolt hole.

Description

Technical Field

[0001] The invention belongs to the part surface treatment technology and relates to a turbine shaft bolt hole projectile type ultrasonic impact strengthening device and a strengthening method thereof. Background Art

[0002] The turbine shaft has a harsh service environment and is subjected to multiple loads such as its own cyclic load and high-temperature corrosion of gas. It is prone to low-cycle fatigue failure and has become one of the "life-limited parts" of aircraft engines, which has attracted great attention. Among them, the bolt hole is one of the main areas where fatigue crack failure occurs. The reason is that, on the one hand, the bolt hole of the turbine disk has a high structural stress concentration factor. Under the action of alternating loads, the actual stress level borne by the hole mouth and the hole wall area is much higher than the external load, and even exceeds the yield strength of the material, which can easily cause low-cycle fatigue failure; on the other hand, the bolt hole wall is in contact with the bolt assembly. If the assembly is improper, under the action of alternating loads, alternating thermal expansion and contraction, etc., there will be micro-wear between the two, which can easily cause micro-motion fatigue failure of the hole wall.

[0003] At present, the commonly used strengthening methods for bolt holes are shot peening or cold extrusion. The former uses compressed gas to drive the projectile to hit the hole wall surface, and the latter uses an interference core rod to squeeze the hole wall to form a residual compressive stress layer and a structural strengthening layer to improve the fatigue performance of the bolt hole. However, due to the structural interference problem of some bolt holes in the turbine shaft, the projectile accessibility of the hole mouth and the hole wall is poor. This structural interference mainly comes from two aspects: 1) The bolt hole is a small hole with a large depth-to-diameter ratio (the diameter is less than 10mm, and the depth / diameter ratio is greater than 2), and the hole wall is easily blocked and difficult to be hit by the projectile; 2) There is a long axis and an installation edge near the hole mouth of the bolt hole, and the movement of the spray gun is restricted. Therefore, it is difficult for the middle part of the inner wall of the bolt hole along the axial direction to reach the shot peening intensity specified in the drawing, resulting in uneven shot peening effect on the inner wall of the bolt hole. On the one hand, the anti-fatigue effect of shot peening cannot reach the expected effect, and on the other hand, it causes the bolt hole to deform beyond the tolerance, affecting assembly. In addition, for these bolt holes, the cold extrusion strengthening method cannot be used to strengthen the hole wall due to the obstruction of the long axis and the installation edge near the hole mouth.

[0004] At present, there are also ultrasonic impact strengthening devices and methods for shaft parts or deep holes. For example, the CN104846187A patent discloses a device and method for ultrasonic impact strengthening of shaft parts welds. This method is to ultrasonically impact strengthen the welds on the outer surface of shaft parts, and it uses a pin-type method, which cannot be applied to the strengthening requirements of the inner wall of the bolt hole of shaft parts. The CN114107633A patent discloses a rotating workpiece ultrasonic impact strengthening device and method. Although it uses a projectile method, this method is to ultrasonically impact strengthen the outer surface of the gear, which cannot be applied to the strengthening requirements of the inner wall of the bolt hole of shaft parts. The CN112975765A patent discloses a deep hole V-type ultrasonic shot peening device, which uses two transducers to achieve surface strengthening of the inner wall of the hole. The horn 105 of the device is perpendicular to the axial direction of the deep hole, not coaxial, and cannot meet the strengthening requirements of the inner wall of the bolt hole of shaft parts. In summary, the devices and methods of the above three patents cannot meet the strengthening requirements of the inner wall of the bolt hole of shaft parts with structural interference problems. Summary of the invention

[0005] The purpose of the present invention is to propose a projectile-type ultrasonic impact strengthening device for the inner wall of a turbine shaft chassis bolt hole and a method of using the device, so as to solve the problems of hole mouth structure interference of bolt holes with a large aspect ratio and poor projectile accessibility to the hole wall, and to improve the uniformity of the strengthening effect of the hole wall.

[0006] The technical solution of the present invention is:

[0007] A turbine shaft bolt hole ultrasonic impact strengthening device comprises a fuselage bracket 1, a projectile-sealed cavity groove 2, a cavity base 3, a variable amplitude rod 4, a transducer fixing clamp 5, and a transducer 6; the cavity base 3 is fixed to the upper end surface of the fuselage bracket 1 and is positioned by a locating pin; a square through hole is provided in the center of the cavity base 3; the projectile-sealed cavity groove 2 is an integrated structure, consisting of a conduit 201 and a base cavity 202; the conduit 201 is at the upper end of the base cavity 202; a square hole is provided on the lower end surface of the base cavity 202, the size of which is consistent with the size of the square through hole in the center of the cavity base 3, and is fixed to the upper end surface of the cavity base 3 after corresponding; the square tool head at the upper end of the variable amplitude rod 4 is inserted into the square through hole of the cavity base 3, the transducer 6 is connected to the variable amplitude rod 4 by an internal thread, and the transducer 6 is connected and fixed to the fuselage bracket 1 by the transducer fixing clamp 5.

[0008] The projectile sealed cavity groove 2 is made of resin, the interior of the base cavity 202 is a cavity, the cavity wall thickness is 2-3 mm, the bolt hole diameter is the same as the inner diameter of the catheter 201, and the wall thickness of the catheter 201 is 1-2 mm.

[0009] The length of the catheter 201 is 50-100 mm.

[0010] The square tool head at the upper end of the amplitude changing rod 4 is inserted into the square through hole of the cavity base 3 , and the tool head and the square through hole are clearance-matched, and the clearance size is 0.05-0.5 mm; the square tool head and the square through hole of the cavity base 3 are coaxial.

[0011] The upper opening of the bolt hole of the chassis of the turbine shaft 8 is equipped with an opening plug 9.

[0012] The ultrasonic frequency generated by the transducer 6 is 20-25 KHz, the resonance frequency of the horn 4 is 18-21 KHz, and the amplitude amplification factor is 12-16.

[0013] The angle between the upper end surface of the tool head at the upper end of the amplitude transformer 4 and the normal line of the horizontal plane does not exceed 5°.

[0014] A strengthening method for a turbine shaft bolt hole ultrasonic impact strengthening device:

[0015] 1) First, insert the long axis of the turbine shaft 8 into the buckled cylinder 702 of the turbine shaft clamping tool 7, fix the chassis support rod 703 of the turbine shaft clamping tool 7 on the chassis of the turbine shaft 8, and connect and fix the buckled cylinder flange 701 of the turbine shaft clamping tool 7 with the robot flange 704 of the turbine shaft clamping tool 7;

[0016] 2) Putting a pellet into the conduit 201 of the pellet-enclosed cavity 2;

[0017] 3) Operate the robot handle to move the turbine shaft 8 through the robot so that the lower opening of the bolt hole of the chassis of the turbine shaft 8 is close to the upper end of the guide tube 201 of the projectile closed cavity groove 2, and the gap size is 0.05-0.5mm.

[0018] 4) Turn on the power supply, and the horn 4 performs high-speed up-and-down reciprocating motion under the drive of ultrasonic waves, driving the projectile to hit the inner wall of the bolt hole, and the processing time is 10 to 120 seconds.

[0019] 5) After strengthening is completed, turn off the power, move the robot to raise the turbine shaft, rotate the turbine shaft, repeat steps 2) to 4) to complete the strengthening of the next bolt hole until all bolt holes are strengthened.

[0020] The turbine shaft clamping tool 7 includes a snap-fitting cylinder flange 701, a snap-fitting cylinder 702, a chassis support rod 703, and a robot flange 704; the snap-fitting cylinder flange 701 is connected and fixed to the robot flange 704 and positioned by a locating pin; the snap-fitting cylinder 702 is sleeved on the outer surface of the long axis of the turbine shaft 8 and is connected and fixed to the snap-fitting cylinder flange 701; there are two chassis support rods 703, the upper end of which is connected to the lower end of the snap-fitting cylinder 702, and the lower end is connected to the chassis of the turbine shaft 8.

[0021] The projectiles are spherical in shape, with a quantity of 10 to 80, a diameter of Φ1mm to Φ2mm, and are made of ceramic or cast steel shots with a hardness of HRC55 to 62.

[0022] The advantages of the present invention are:

[0023] (1) The semi-open bolt holes of the structure are completely closed by using the device of the present invention to form a closed cavity, and then hard projectiles are placed in the cavity. The hard projectiles in the closed cavity are excited to perform Brownian motion by using an ultrasonic source through variable amplitude amplification, so that the projectiles impact the cavity and the inner wall of the bolt hole at high speed under ultrasonic excitation, thereby causing elastic-plastic deformation of the inner wall surface, achieving indiscriminate impact of the inner wall surface of the bolt hole by the projectile, thereby obtaining a uniform strengthening effect at all locations on the inner wall of the bolt hole.

[0024] (2) This method consumes only a small amount of shot (10 to 80 shots), which is far less than traditional shot peening, resulting in lower processing costs, less dust, and less noise.

[0025] (3) Since the ultrasonic frequency is as high as 20-25 kHz and the resonance frequency of the horn is as high as 18-21 kHz, the surface strengthening processing efficiency is high.

[0026] (4) This method improves the uniformity of the strengthening effect on the inner wall surface of the bolt hole, which is not only beneficial to improving the fatigue performance of the turbine shaft, but also beneficial to reducing the deformation of the bolt hole and realizing coordinated control of shape and property. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the whole device

[0028] Figure 2 Turbine shaft installation diagram

[0029] Figure 3 Schematic diagram of the cross section of the closed projectile cavity DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with the accompanying drawings:

[0031] like Figure 1As shown, a turbine shaft bolt hole ultrasonic impact strengthening device includes a fuselage bracket 1, a projectile-sealed cavity groove 2, a cavity base 3, a variable amplitude rod 4, a transducer fixing clamp 5, and a transducer 6; the cavity base 3 is fixed to the upper end surface of the fuselage bracket 1 and is positioned by a locating pin; a square through hole is provided in the center of the cavity base 3; the projectile-sealed cavity groove 2 is an integrated structure, consisting of a conduit 201 and a base cavity 202; the conduit 201 is at the upper end of the base cavity 202; a square hole is provided on the lower end surface of the base cavity 202, and its size is consistent with that of the square through hole in the center of the cavity base 3, and is fixed to the upper end surface of the cavity base 3 after corresponding; the square tool head at the upper end of the variable amplitude rod 4 is inserted into the square through hole of the cavity base 3, the transducer 6 is connected to the variable amplitude rod 4 by an internal thread, and the transducer 6 is connected and fixed to the fuselage bracket 1 by the transducer fixing clamp 5. The ultrasonic frequency generated by the transducer 6 is 20-25 KHz, the resonance frequency of the horn 4 is 18-21 KHz, and the amplitude amplification factor is 12-16.

[0032] like Figure 3 As shown, the projectile closed cavity groove 2 is made of resin, the base cavity 202 is hollow inside, the cavity wall thickness is 2 to 3 mm, the bolt hole diameter is the same as the inner diameter of the catheter 201, the wall thickness of the catheter 201 is 1 to 2 mm, and the length is 50 to 100 mm.

[0033] The square tool head at the upper end of the amplitude changing rod 4 is inserted into the square through hole of the cavity base 3, and the tool head and the square through hole are clearance-matched, and the clearance size is 0.05-0.5mm; the square tool head is coaxial with the square through hole of the cavity base 3, and the normal angle between the upper end face of the tool head and the horizontal plane does not exceed 5°.

[0034] The upper openings of the bolt holes of the chassis of the turbine shaft 8 are generally equipped with opening plugs 9.

[0035] A strengthening method for a turbine shaft bolt hole ultrasonic impact strengthening device:

[0036] 1) First, insert the long axis of the turbine shaft 8 into the buckled cylinder 702 of the turbine shaft clamping tool 7, fix the chassis support rod 703 of the turbine shaft clamping tool 7 on the chassis of the turbine shaft 8, and connect and fix the buckled cylinder flange 701 of the turbine shaft clamping tool 7 with the robot flange 704 of the turbine shaft clamping tool 7;

[0037] 2) Putting a pellet into the conduit 201 of the pellet-enclosed cavity 2;

[0038] 3) Operate the robot handle to move the turbine shaft 8 through the robot so that the lower opening of the bolt hole of the chassis of the turbine shaft 8 is close to the upper end of the guide tube 201 of the projectile closed cavity groove 2, and the gap size is 0.05-0.5mm.

[0039] 4) Turn on the power supply, and the horn 4 performs high-speed up-and-down reciprocating motion under the drive of ultrasonic waves, driving the projectile to hit the inner wall of the bolt hole, and the processing time is 10 to 120 seconds.

[0040] 5) After strengthening is completed, turn off the power, move the robot to raise the turbine shaft, rotate the turbine shaft, repeat steps 2) to 4) to complete the strengthening of the next bolt hole until all bolt holes are strengthened.

[0041] like Figure 2 As shown, the turbine shaft clamping tool 7 includes a snap-fitting cylinder flange 701, a snap-fitting cylinder 702, a chassis support rod 703, and a robot flange 704; the snap-fitting cylinder flange 701 is connected and fixed to the robot flange 704 and positioned by a locating pin, the snap-fitting cylinder 702 is sleeved on the outer surface of the long axis of the turbine shaft 8, and is connected and fixed to the snap-fitting cylinder flange 701; there are two chassis support rods 703, the upper end of which is connected to the lower end of the snap-fitting cylinder 702, and the lower end is connected to the chassis of the turbine shaft 8.

[0042] The projectiles are spherical in shape, with a quantity of 10 to 80, a diameter of Φ1mm to Φ2mm, and are made of ceramic or cast steel shots with a hardness of HRC55 to 62.

[0043] The working principle of the present invention is:

[0044] In addition to pneumatic shot peening machines, ultrasonic waves have the advantages of high frequency, high energy, and high power density, and are also one of the ideal power sources for high-energy surface strengthening. Therefore, the present invention first closes all the semi-open bolt holes of the structure to form a closed cavity, and then places hard projectiles in the cavity, and uses an ultrasonic source to amplify the hard projectiles in the closed cavity to perform Brownian motion, so that the projectiles hit the cavity and the inner wall of the bolt hole at high speed under ultrasonic excitation, thereby causing elastic-plastic deformation on the inner wall surface to achieve surface strengthening. It has been calculated that the maximum height of the projectile moving through the catheter can reach 25 cm, and the maximum height of the catheter + bolt hole in the present invention does not exceed 13 cm. Therefore, the projectile still has a large kinetic energy when reaching the lowest end of the bolt hole. The impact force and direction of each projectile when colliding in the closed cavity are different, and the number and strength of each part of the cavity being hit by the projectile are the same. Therefore, the strengthening effect of the inner wall surface of the hole is uniform, thereby solving the structural interference problem of the strengthening of the inner wall of the hole, and improving the uniformity of the strengthening effect of the inner wall surface of the bolt hole, which is not only beneficial to improving the fatigue performance of the turbine shaft, but also beneficial to reducing the deformation of the bolt hole, and realizing the coordinated control of the shape and properties.

[0045] Embodiment 1:

[0046] A turbine shaft bolt hole ultrasonic impact strengthening device consists of a fuselage bracket 1, a projectile-sealed cavity groove 2, a cavity base 3, a horn 4, a transducer fixing clamp 5, a transducer 6, a clamping tool 7, a turbine shaft 8 and an orifice plug 9. The cavity base 3 is fixed to the upper end surface of the fuselage bracket 1, and the two are positioned by a locating pin and fixed by screws. There is a square through hole in the center of the cavity base 3. The projectile-sealed cavity groove 2 consists of a conduit 201 and a base cavity 202. The base cavity 202 is fixed to the upper end surface of the cavity base 3 by screws. The base cavity 202 is made of resin, and the interior is a cavity with a cavity wall thickness of 2 mm. There is a square hole on the lower end surface, and the size is consistent with the size of the square through hole in the center of the cavity base 3. There is a circular hole on the upper end surface, which is connected to the conduit 201, and the diameter of the circular hole is the same as the inner diameter of the conduit 201. The square tool head at the upper end of the amplitude change rod 4 is inserted into the square through hole of the cavity base 3, and the tool head and the square through hole are clearance-matched, and the clearance size is 0.5 mm. The square tool head is coaxial with the square through hole. The transducer 6 is connected to the amplitude change rod 4 by an internal thread. The transducer 6 is connected and fixed to the fuselage bracket 1 by a transducer fixing clamp 5. The turbine shaft clamping tool 7 consists of four parts: a buckling cylinder flange 701, a buckling cylinder 702, a chassis support rod 703, and a robot flange 704. The buckling cylinder flange 701 is connected and fixed to the robot flange 704, positioned by a locating pin, and fixed by a screw connection. The buckling cylinder 702 is sleeved on the outer surface of the long axis of the turbine shaft 8, and is connected to the buckling cylinder flange 701 by screws. The number of chassis support rods 703 is 2, the upper end is connected to the lower end of the buckling cylinder 702, and the lower end is connected to the chassis of the turbine shaft 8. The orifice plug 9 is placed on the upper orifice of the bolt hole of the chassis of the turbine shaft 8 .

[0047] The ultrasonic frequency generated by the transducer 6 is 25 KHz, the resonance frequency of the horn is 21 KHz, and the amplitude amplification factor is 16.

[0048] The angle between the upper end surface of the tool head at the upper end of the horn 4 and the normal line of the horizontal plane does not exceed 5°.

[0049] A method for strengthening a turbine shaft bolt hole ultrasonic impact strengthening device,

[0050] (1) First, insert the long axis of the turbine shaft 8 into the snap-fit ​​cylinder 702, fix the chassis support rod 703 on the chassis of the turbine shaft 8, and connect and fix the snap-fit ​​cylinder flange 701 and the robot flange 704.

[0051] (2) Put the pellets into the conduit 201 of the pellet-enclosed cavity 2.

[0052] (3) Operate the robot handle and use the robot to move the turbine shaft so that the lower opening of the bolt hole of the chassis of the turbine shaft 8 is close to the upper end of the guide tube 201 of the projectile closed cavity groove 2, and the gap size is 0.5mm.

[0053] (4) Turn on the power supply, and the horn 4 moves up and down at high speed under the drive of ultrasonic waves, driving the projectile to hit the inner wall of the bolt hole. The processing time is 120 seconds.

[0054] (5) After strengthening is completed, turn off the power, move the robot to raise the turbine shaft, rotate the turbine shaft, and repeat steps (2) to (4) to complete the strengthening of the next bolt hole until all bolt holes are strengthened.

[0055] The projectiles are spherical in shape, with a number of 80 and a diameter of Φ2mm. They are made of ceramic pellets with a hardness of HRC55-62.

[0056] Embodiment 2:

[0057] The wall thickness of the base cavity 202 is 3mm, the square tool head of the horn 4 is gap-matched with the square through hole, and the gap size is 0.05mm. The ultrasonic frequency generated by the transducer 6 is 20KHz, the resonance frequency of the horn is 18KHz, and the amplitude amplification factor is 12.

[0058] The clearance between the lower opening of the bolt hole of the chassis of the turbine shaft 8 and the upper end of the guide tube 201 of the projectile closed cavity groove 2 is 0.05 mm. Turn on the power supply, and the processing time is 10 seconds. The number of projectiles is 10, the diameter is Φ1 mm, and the material is cast steel shot.

[0059] Through the above method, the shot coverage rate of the inner wall of the bolt hole along the axial direction is basically the same, the surface residual compressive stress value is basically equivalent, the surface roughness is basically the same, and the depth difference of the hardened layer is no more than 20μm.

Claims

1. A turbine shaft bolt hole ultrasonic impact strengthening device, characterized in that: The invention comprises a body support (1), a projectile-sealed cavity groove (2), a cavity base (3), a horn (4), a transducer fixing clamp (5), and a transducer (6); the cavity base (3) is fixed to the upper end surface of the body support (1) and positioned by a positioning pin; a square through hole is provided in the center of the cavity base (3); the projectile-sealed cavity groove (2) is an integrated structure, and is composed of a guide tube (201) and a base cavity (202); the guide tube (201) is at the upper end of the base cavity (202); a square hole is provided on the lower end surface of the base cavity (202), and the size is consistent with the size of the square through hole in the center of the cavity base (3), and is fixed to the upper end surface of the cavity base (3) after being aligned; a square tool head at the upper end of the horn (4) is provided. Inserted into the square through hole of the cavity base (3), the transducer (6) is connected to the amplitude change rod (4) through an internal thread, and the transducer (6) is connected and fixed to the fuselage bracket (1) through a transducer fixing clamp (5); the square tool head at the upper end of the amplitude change rod (4) is inserted into the square through hole of the cavity base (3), and the tool head and the square through hole are clearance-matched, and the clearance size is 0.05-0.5 mm; the square tool head is coaxial with the square through hole of the cavity base (3); the upper end surface of the tool head at the upper end of the amplitude change rod (4) and the normal of the horizontal plane do not exceed 5°; the ultrasonic frequency generated by the transducer (6) is 20-25 kHz, the resonance frequency of the amplitude change rod (4) is 18-21 kHz, and the amplitude amplification factor is 12-16.

2. The turbine shaft bolt hole ultrasonic impact strengthening device according to claim 1, characterized in that: The projectile sealed cavity groove (2) is made of resin, the interior of the base cavity (202) is a hollow cavity, the cavity wall thickness is 2 to 3 mm, the bolt hole diameter is the same as the inner diameter of the catheter (201), and the catheter (201) wall thickness is 1 to 2 mm.

3. The turbine shaft bolt hole ultrasonic impact strengthening device according to claim 1, characterized in that: The length of the catheter (201) is 50 to 100 mm.

4. The turbine shaft bolt hole ultrasonic impact strengthening device according to claim 1, characterized in that: The upper opening of the bolt hole of the chassis of the turbine shaft 8 is equipped with an opening plug (9).

5. A strengthening method for a turbine shaft bolt hole ultrasonic impact strengthening device according to any one of claims 1 to 4, characterized in that: 1) First, insert the long axis of the turbine shaft (8) into the buckling cylinder (702) of the turbine shaft clamping tool (7), fix the chassis support rod (703) of the turbine shaft clamping tool (7) on the chassis of the turbine shaft (8), and connect and fix the buckling cylinder flange (701) of the turbine shaft clamping tool (7) and the robot flange (704) of the turbine shaft clamping tool (7); 2) placing a pellet into the guide tube (201) of the pellet-enclosed cavity (2); 3) operating the robot handle to move the turbine shaft (8) through the robot so that the lower opening of the bolt hole of the chassis of the turbine shaft (8) is closely attached to the upper end of the guide tube (201) of the projectile sealed cavity groove (2), with a gap size of 0.05 to 0.5 mm; 4) Turn on the power supply, and the horn (4) performs high-speed up-and-down reciprocating motion under the drive of ultrasonic waves, driving the projectile to hit the inner wall of the bolt hole, and the processing time is 10 to 120 seconds; 5) After strengthening is completed, turn off the power, move the robot to raise the turbine shaft, rotate the turbine shaft, repeat steps 2) to 4) to complete the strengthening of the next bolt hole until all bolt holes are strengthened.

6. A strengthening method for a turbine shaft bolt hole ultrasonic impact strengthening device according to claim 5, characterized in that: The turbine shaft clamping tool (7) comprises a buckling cylindrical flange (701), a buckling cylinder (702), a chassis support rod (703), and a robot flange (704); The snap-fitting cylinder flange (701) is connected and fixed to the robot flange (704) and positioned by a positioning pin. The snap-fitting cylinder (702) is sleeved on the outer surface of the long axis of the turbine shaft 8 and is connected and fixed to the snap-fitting cylinder flange (701). There are two chassis support rods (703), the upper end of which is connected to the lower end of the snap-fitting cylinder (702) and the lower end of which is connected to the chassis of the turbine shaft (8).

7. The strengthening method of a turbine shaft bolt hole ultrasonic impact strengthening device according to claim 5, characterized in that: The projectiles are spherical in shape, with a quantity of 10 to 80, a diameter of Φ1mm to Φ2mm, and are made of ceramic or cast steel shots with a hardness of HRC55 to 62.

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