Hydraulic spring auxiliary vibration device for linear friction welding

Abstract

The invention provides a hydraulic spring auxiliary vibration device for linear friction welding, which comprises an electro-hydraulic excitation system and a vibration platform, the vibration platform is used for clamping a workpiece to be welded, the electro-hydraulic excitation system is used for applying linear reciprocating motion to the workpiece to be welded, and the hydraulic spring auxiliary vibration device is characterized by further comprising a hydraulic spring, the hydraulic spring is located below the vibration platform, a piston rod is arranged in the hydraulic spring, one end of the piston rod makes contact with the vibration platform, and the piston rod does linear reciprocating motion under the action of the vibration platform; elastic dampers acting on the two sides of the piston rod are arranged in the hydraulic spring and used for widening the excitation frequency of the electro-hydraulic excitation system. By changing the rigidity of the system, the resonant frequency of the linear friction welding electro-hydraulic excitation system is widened, the tracking control performance of the electro-hydraulic excitation system is improved, and it is guaranteed that the linear friction welding performance is more reliable.

Description

Technical Field

[0001] The invention relates to the field of linear friction welding equipment, in particular to a hydraulic spring auxiliary vibration device used for linear friction welding. Background Art

[0002] Heavy-duty linear friction welding equipment is a key manufacturing equipment for my country's new generation of high thrust-to-weight ratio aero-engine integral blades. It mainly applies linear reciprocating motion and upsetting force to the contact interface of the workpiece to be welded through the electro-hydraulic excitation system and the electro-hydraulic upsetting system to generate friction heat and complete welding. When the linear friction welding equipment is welding materials of different materials, cross-sectional areas, and masses, its electro-hydraulic excitation system needs to be able to provide vibrations of different amplitudes and frequencies.

[0003] However, the existing linear friction welding electro-hydraulic excitation system is a second-order mechanical system with a low damping ratio. It has poor high-frequency tracking performance, a narrow vibration bandwidth, and is prone to resonance. The prior art proposes a resonance suppression method based on a speed loop LADRC controller; on the basis of the traditional (position loop, speed loop, current loop), the prior art proposes a four-closed-loop self-disturbance-rejection resonance suppression method based on the actuator position closed loop. The prior art needs to use a resonant frequency identification method to construct an identification model of the system and adjust the resonant frequency according to the identification parameters. However, the quality and process parameters (frequency, amplitude) of the existing control object will change according to the welding requirements, the reliability of the controller cannot be guaranteed, and a large number of repetitive experiments are required to adjust. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a hydraulic spring-assisted vibration device for linear friction welding, which directly broadens the resonant frequency of the linear friction welding electro-hydraulic excitation system by changing the stiffness of the system, improves the tracking control performance of the electro-hydraulic excitation system, and ensures that the linear friction welding performance is more reliable.

[0005] The present invention achieves the above technical objectives through the following technical means.

[0006] A hydraulic spring-assisted vibration device for linear friction welding, comprising an electro-hydraulic excitation system and a vibration platform, wherein the vibration platform is used to clamp the workpiece to be welded, and the electro-hydraulic excitation system is used to apply linear reciprocating motion to the workpiece to be welded. The invention is characterized in that it also includes a hydraulic spring, wherein the hydraulic spring is located below the vibration platform, wherein a piston rod is provided inside the hydraulic spring, wherein one end of the piston rod is in contact with the vibration platform, and under the action of the vibration platform, the piston rod performs linear reciprocating motion; wherein the hydraulic spring has elastic damping acting on both sides of the piston rod, which is used to broaden the excitation frequency of the electro-hydraulic excitation system.

[0007] Furthermore, the hydraulic spring includes a shell, a liquid chamber and a gas chamber; the piston on the piston rod is located in the shell, dividing the inner cavity of the shell into two left and right oil chambers, one end of the piston rod extending from one oil chamber is in contact with the vibration platform, and each oil chamber is separated into a gas chamber by an air chamber piston, and the gas chamber stores gas of set pressure.

[0008] Furthermore, the piston divides the inner cavity of the shell into a left oil chamber and a right oil chamber that are not connected to each other. The left oil chamber is separated into a left gas chamber by a left air chamber piston, and the right oil chamber is separated into a right gas chamber by another right air chamber piston; one end of the piston rod extending from the left oil chamber is in contact with the vibration platform.

[0009] Furthermore, the rod diameters on both sides of the piston rod are the same, and the effective areas of the left air chamber piston and the right air chamber piston are the same, which are used to balance the pressure of the gas chamber and the oil chamber.

[0010] Furthermore, it also includes a pressure sensor and a displacement sensor. The pressure sensor is used to detect the pressure of the oil chamber; the displacement sensor is located at the other end of the piston rod and is used to obtain the displacement of the piston.

[0011] Furthermore, when the electro-hydraulic excitation system is subjected to symmetrical friction resistance, the pressures of the two left and right oil chambers are both P0, and the gas pressure in the gas chamber is the oil chamber pressure P0.

[0012] Furthermore, when the electro-hydraulic excitation system is subjected to asymmetric frictional resistance, the frictional resistances experienced by the electro-hydraulic excitation system in different movement directions are made equal by changing the pressure of an oil chamber.

[0013] Furthermore, by regulating the oil chamber pressure of the hydraulic spring, the equivalent stiffness of the electro-hydraulic excitation system is changed to avoid resonance of the electro-hydraulic excitation system.

[0014] A method for adjusting a hydraulic spring-assisted vibration device for linear friction welding comprises the following steps:

[0015] The maximum resistance of the electro-hydraulic excitation system in the direction of linear reciprocating motion is obtained through the force sensor, where the maximum resistance in the positive direction is recorded as F max,v+ , the maximum resistance in the negative direction is recorded as F max,v- ;

[0016] When the difference between the maximum resistance in the positive direction and the maximum resistance in the negative direction exceeds the set value, the electro-hydraulic excitation system is subjected to asymmetric friction resistance;

[0017] The pressure difference αP between the left and right oil chambers is determined according to the maximum resistance of the electro-hydraulic excitation system in the direction of linear reciprocating motion, specifically: ΔP = (Fmax,v+ -F max,v- ) / A0, where A0 is the effective action area of ​​the piston rod;

[0018] The hydraulic system is used to pressurize an oil chamber corresponding to one end of the piston rod in contact with the vibration platform, so that the oil chamber pressure P1 = P0 + ΔP; while the pressure of the other oil chamber is maintained at P0, where P0 is the pressure of the oil chamber when the electro-hydraulic excitation system is subjected to symmetrical friction resistance.

[0019] The beneficial effects of the present invention are:

[0020] 1. The hydraulic spring-assisted vibration device for linear friction welding described in the present invention can change the stiffness of the linear friction welding electro-hydraulic excitation system and increase the resonant frequency of the system through the elastic damping acting on both sides of the piston rod in the hydraulic spring.

[0021] 2. The hydraulic spring-assisted vibration device for linear friction welding described in the present invention will produce asymmetric friction resistance to the electro-hydraulic vibration system during linear friction welding due to the asymmetric or tilted shape of the cross-section of the workpiece to be welded, which can easily cause the displacement of the reciprocating motion to drift. When the electro-hydraulic vibration system is subjected to asymmetric friction resistance, the present invention changes the pressure of one oil chamber to make the pressure of the oil chamber on one side higher than that of the other side, so that the friction resistance of the electro-hydraulic vibration system in different movement directions is the same.

[0022] 3. The hydraulic spring auxiliary vibration device for linear friction welding described in the present invention requires an excitation frequency of up to 50Hz for difficult-to-weld materials (such as titanium alloys, nickel-based alloys, etc.). At this time, the electro-hydraulic excitation system is prone to resonance under such a high excitation frequency. In order to broaden the bandwidth of the electro-hydraulic excitation system, the pressure of the hydraulic spring oil chamber is adjusted to change the equivalent stiffness of the electro-hydraulic excitation system, thereby avoiding resonance of the electro-hydraulic excitation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. The drawings described below are some embodiments of the present invention. For ordinary technicians in this field, it is obvious that other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 This is a schematic diagram of the hydraulic spring assisted vibration device for linear friction welding according to the present invention.

[0025] Figure 2 This is a schematic diagram of the working principle of the hydraulic spring device described in the present invention.

[0026] Figure 3 The control principle diagram of the hydraulic system described in the present invention.

[0027] Figure 4 This is the stiffness curve of the hydraulic spring under different pressures described in the present invention.

[0028] Figure 5 This is the change process of the vibration table displacement during the excitation process described in the present invention.

[0029] Figure 6 This is the change process of the hydraulic spring force during the vibration process described in the present invention.

[0030] In the figure:

[0031] 1-Hydraulic spring; 1A-Left oil chamber; 1B-Right oil chamber; 1C-Left gas chamber; 1D-Right gas chamber; 2A-Left gas chamber piston; 2B-Right gas chamber piston; 3-Piston rod; 4-Displacement sensor; 5A-First stop valve; 5B-Second stop valve; 6A-First pressure sensor; 6B-Second pressure sensor; 7-First servo valve; 8-Second servo valve; 9-Oil tank; 10-Constant pressure oil source; 11-Vibration platform; 12-Electro-hydraulic excitation system; 13-Electro-hydraulic upsetting system; 14-Frame; 15-Pressure controller; 16-Position controller; 17-Force sensor. DETAILED DESCRIPTION

[0032] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0033] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "axial", "radial", "vertical", "horizontal", "inner", "outer" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0034] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] like Figure 1 As shown, the hydraulic spring auxiliary vibration device for linear friction welding of the present invention comprises a vibration platform 11, an electro-hydraulic excitation system 12, an electro-hydraulic upsetting system 13, a frame 14 and a hydraulic spring 1. The vibration platform 11 is used to clamp the workpiece to be welded, and the electro-hydraulic excitation system 12 is used to apply linear reciprocating motion to the workpiece to be welded. The electro-hydraulic excitation system 12 and the electro-hydraulic upsetting system 13 apply linear reciprocating motion and upsetting force to the contact interface of the workpiece to be welded to generate friction heat and complete welding. The electro-hydraulic upsetting system 13 is horizontally mounted on the frame 14, and the electro-hydraulic excitation system 12 is vertically mounted on the frame 14. The hydraulic spring 1 is mounted at the lower end of the vibration platform 11 that can reciprocate vertically. The hydraulic spring 1 has a piston rod 3, one end of which is in contact with the vibration platform 11. Under the action of the vibration platform 11, the piston rod 3 performs linear reciprocating motion; the hydraulic spring 1 has elastic damping acting on both sides of the piston rod 3, which is used to widen the excitation frequency of the electro-hydraulic excitation system 12. During the welding process, the vibration platform 11 performs linear reciprocating motion under the drive of the electro-hydraulic excitation system 12. During the excitation process, the piston rod 3 of the hydraulic spring 1 also performs linear reciprocating motion under the action of the vibration platform 11.

[0036] like Figure 2 As shown, the hydraulic spring 1 includes a housing, a liquid chamber and a gas chamber; the piston on the piston rod 3 is located in the housing, dividing the inner cavity of the housing into a left oil chamber 1A and a right oil chamber 1B which are not connected to each other, the left oil chamber 1A is separated into a left gas chamber 1C by a left gas chamber piston 2A, and the right oil chamber 1B is separated into a right gas chamber 1D by another right gas chamber piston 2B; one end of the piston rod 3 extending from the left oil chamber 1A is in contact with the vibration platform 11. The volume of the oil chambers on both sides of the hydraulic spring 1 is mainly affected by the position of the piston rod 3 and the gas chamber piston. The rod diameters on both sides of the piston rod 3 are the same, and the effective areas of the left gas chamber piston 2A and the right gas chamber piston 2B are the same, which are used to balance the pressure of the gas chamber and the oil chamber. The gas chamber stores gas of set pressure, which is used to store hydraulic energy.

[0037] The pre-charge pressure in the left gas chamber 1C and the right gas chamber 1D is generally 0.6 to 0.7 times the working pressure P0. Then the hydraulic system is used to pressurize the left oil chamber 1A and the right oil chamber 1B respectively, so that the left gas chamber 1C, the right gas chamber 1D, the left oil chamber 1A and the right oil chamber 1B all reach the required working pressure P0. At the same time, in order to ensure that the oil volume of the left oil chamber 1A and the right oil chamber 1B is the same when the hydraulic spring 1 is working, the hydraulic system is required to adjust the piston rod 3 to the middle working position x0 of the hydraulic spring 1.

[0038] like Figure 2 The hydraulic system in the embodiment includes a left oil circuit and a right oil circuit, wherein the left oil circuit and the right oil circuit share a constant pressure oil source 10, and the left oil circuit and the right oil circuit have the same structure. The left oil circuit is taken as an example below, including the first servo valve 7, the oil tank 9 and the first stop valve 5A. The constant pressure oil source 10 can provide the circuit with oil with constant pressure and sufficient flow. The oil outlet of the constant pressure oil source 10 is connected to the P port of the first servo valve 7, and the T port of the first servo valve 7 is connected to the return oil tank 9; the A port of the first servo valve 7 is connected to the left oil chamber 1A through the first stop valve 5A, and the B port of the first servo valve 7 is blocked and not connected to the outside. A first pressure sensor 6A is provided in the left oil chamber 1A for detecting the oil pressure of the left oil chamber 1A.

[0039] Combination Figure 2 and Figure 3 As shown, the displacement sensor 4 is installed at the end of the piston rod 3 to detect the real-time position of the piston rod 3. When the working pressure of the hydraulic spring 1 chamber needs to be P0 and the working position of the piston 3 needs to be x0, the control scheme of the hydraulic system is as follows:

[0040] Left oil chamber 1A: First close the first stop valve 5A, at this time, the A port of the first reversing solenoid valve 7 is not connected to the left oil chamber 1A. Use a pneumatic tool to apply 0.6 to 0.7 times the working pressure P0 to the left gas chamber 1C. Then open the first stop valve 5A to connect the A port of the first reversing solenoid valve 7 to the left oil chamber 1A. Figure 3As shown, the oil pressure collected from the left oil chamber 1A is subtracted from the working pressure P0, and then combined with the obtained pressure tracking error, the first servo valve 7 is adjusted through the traditional pressure controller 15 to pressurize and release the left oil chamber 1A, so as to keep the pressure of the left oil chamber 1A at P0. Specifically: when the pressure of the left oil chamber 1A is insufficient, the right position of the first servo valve 7 works, the A port of the first servo valve 7 is connected to the P port, and the constant pressure oil source 10 supplies oil to the left chamber 1A under the precise control of the first servo valve 7, and the pressure increases; when the pressure of the left oil chamber 1A is too high, the left position of the first reversing solenoid valve 7 works, the A port of the first reversing solenoid valve 7 is connected to the T port, and the left chamber 1A releases oil to the oil tank 9 under the precise control of the first reversing solenoid valve 7, and the pressure decreases;

[0041] Right oil chamber 1B: The real-time feedback signal of the displacement sensor 4 is subtracted from the ideal working position x0, and then combined with the obtained position tracking error, the second servo valve 8 is adjusted through the traditional position controller 16 to pressurize and release the right oil chamber 1B to keep the position of the control piston 3 at x0. Under the joint control of the first servo valve 7 and the second servo valve 8, since the effective area on both sides of the piston 3 is the same, the pressure of the oil chambers on both sides is the same. Similarly, since the effective effective area of ​​the piston 2 in the gas chamber and the oil chamber is also the same, the pressure of the oil chamber and the gas chamber is the same. In this way, the pressure of the four chambers of the hydraulic spring 1 can be guaranteed to be the same, and better linear stiffness can be obtained during operation.

[0042] Combined with the feedback signals of the first pressure sensor 6A, the second pressure sensor 6B and the position sensor 4, when the pressures of the left oil chamber 1A and the right oil chamber 1B are equal and the position of the piston rod is at x0, the stop valves 5A and 5B are closed, so that the oil chambers on both sides of the hydraulic spring 1 are not connected to the outside and are in a closed state. At this time, the hydraulic spring 1 is in a working state.

[0043] like Figure 4 , provides the stiffness curves of the hydraulic spring device of the present invention under pressures of 4MPa, 10MPa, 12MPa, and 15MPa. It can be seen that under different pressures, the hydraulic spring force and displacement are linearly related, and the greater the pressure, the greater the hydraulic spring stiffness. The measurement results of the present invention meet the design requirements and can achieve the expected effect.

[0044] like Figure 5-6 , provides a curve of the change of the exciting displacement of the vibration table and the output force of the hydraulic spring. With the rapid change of the exciting displacement, the output force of the hydraulic spring also changes rapidly. When the vibration table quickly returns to the origin, the output force of the hydraulic spring also quickly returns to zero. The effect diagram of the above hydraulic spring shows that the present invention has a rapid response, good applicability, and meets the design requirements.

[0045] In addition, due to the asymmetry or tilt of the cross-section of the welded parts, the friction resistance of the electro-hydraulic excitation system 12 during linear friction welding will be asymmetric, which can easily cause the displacement of the reciprocating motion to drift. At this time, the stiffness of the hydraulic spring 1 can be adjusted to make the pressure of the oil chamber on one side higher than that of the oil chamber on the other side, so that the friction resistance of the electro-hydraulic excitation system in different movement directions is the same. The details are as follows:

[0046] The maximum resistance of the electro-hydraulic excitation system 12 in the linear reciprocating motion direction is obtained by the force sensor 17, where the maximum resistance in the positive direction is recorded as F max,v+ , the maximum resistance in the negative direction is recorded as F max,v- ; Figure 1 As shown, the upward direction is the positive direction and the downward direction is the negative direction.

[0047] When the difference between the maximum resistance in the positive direction and the maximum resistance in the negative direction exceeds the set value, the electro-hydraulic excitation system 12 is subjected to asymmetric friction resistance;

[0048] The pressure difference ΔP between the left and right oil chambers is determined according to the maximum resistance of the electro-hydraulic excitation system 12 in the linear reciprocating motion direction, specifically: ΔP = (F max,v+ -F max,v- ) / A0, where A0 is the effective action area of ​​the piston rod 3;

[0049] The hydraulic system is used to pressurize an oil chamber corresponding to one end of the piston rod 3 in contact with the vibration platform 11, so that the oil chamber pressure P1 = P0 + ΔP; while the pressure of the other oil chamber is maintained at P2 = P0, where P0 is the pressure of the oil chamber when the electro-hydraulic excitation system 12 is subjected to symmetrical friction resistance.

[0050] When the pressure in the asymmetric oil pressure chamber needs to be adjusted, the actual working position of the piston rod 3 is mainly maintained by the electro-hydraulic excitation system 12. Figure 3 As shown, the ideal working position x0 is subtracted from the actual working position fed back by the displacement sensor 4, and combined with the position tracking error, the position controller 4 regulates the electro-hydraulic excitation system 12 so that the piston position is maintained at x0.

[0051] Among them, the pressure difference ΔP between the left and right oil chambers can be a negative number. When ΔP is a positive value, that is, the maximum resistance in the positive direction is greater than the maximum resistance in the negative direction, so the hydraulic system is pressurized to make the pressure of the left oil chamber 1A greater than the pressure of the right oil chamber 1B; when ΔP is a negative value, that is, the maximum resistance in the positive direction is less than the maximum resistance in the negative direction, so the hydraulic system is pressurized to make the pressure of the right oil chamber 1B greater than the pressure of the left oil chamber 1A.

[0052] The hydraulic spring auxiliary vibration device for linear friction welding described in the present invention requires an excitation frequency of up to 50Hz for difficult-to-weld materials (such as titanium alloys, nickel-based alloys, etc.). At this time, the electro-hydraulic excitation system is prone to resonance under such a high excitation frequency. In order to broaden the bandwidth of the electro-hydraulic excitation system, the equivalent stiffness of the electro-hydraulic excitation system is changed by adjusting the oil chamber pressure of the hydraulic spring to avoid resonance in the electro-hydraulic excitation system.

[0053] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0054] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. All equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A hydraulic spring-assisted vibration device for linear friction welding, comprising an electro-hydraulic vibration system (12) and a vibration platform (11), wherein the vibration platform (11) is used to clamp a workpiece to be welded, and the electro-hydraulic vibration system (12) is used to apply linear reciprocating motion to the workpiece to be welded, characterized in that: The invention also comprises a hydraulic spring (1), wherein the hydraulic spring (1) is located below the vibration platform (11), wherein a piston rod (3) is provided inside the hydraulic spring (1), wherein one end of the piston rod (3) is in contact with the vibration platform (11), and under the action of the vibration platform (11), the piston rod (3) performs linear reciprocating motion; and wherein the hydraulic spring (1) has elastic damping acting on both sides of the piston rod (3) for widening the excitation frequency of the electro-hydraulic excitation system (12).

2. The hydraulic spring-assisted vibration device for linear friction welding according to claim 1, characterized in that: The hydraulic spring (1) comprises a housing, a liquid chamber and a gas chamber; the piston on the piston rod (3) is located in the housing, dividing the inner cavity of the housing into two left and right oil chambers, one end of the piston rod (3) extending out of one oil chamber contacts the vibration platform (11), and each oil chamber is separated into a gas chamber by an air chamber piston, and the gas chamber stores gas at a set pressure.

3. The hydraulic spring-assisted vibration device for linear friction welding according to claim 2, characterized in that: The piston divides the inner cavity of the shell into a left oil chamber (1A) and a right oil chamber (1B) which are not connected to each other; the left oil chamber (1A) is separated into a left gas chamber (1C) by a left gas chamber piston (2A); the right oil chamber (1B) is separated into a right gas chamber (1D) by another right gas chamber piston (2B); one end of the piston rod (3) extending from the left oil chamber (1A) is in contact with the vibration platform (11).

4. The hydraulic spring-assisted vibration device for linear friction welding according to claim 3, characterized in that: The rod diameters on both sides of the piston rod (3) are the same, and the effective areas of the left air chamber piston (2A) and the right air chamber piston (2B) are the same, which are used to balance the pressure of the gas chamber and the oil chamber.

5. The hydraulic spring assisted vibration device for linear friction welding according to claim 2, characterized in that: It also includes a pressure sensor and a displacement sensor (4), wherein the pressure sensor is used to detect the pressure of the oil chamber; the displacement sensor (4) is located at the other end of the piston rod (3) and is used to obtain the displacement of the piston.

6. The hydraulic spring assisted vibration device for linear friction welding according to claim 2, characterized in that: When the electro-hydraulic excitation system (12) is subjected to symmetrical friction resistance, the pressures in the two left and right oil chambers are both P0, and the gas pressure in the gas chamber is the oil chamber pressure P0.

7. The hydraulic spring assisted vibration device for linear friction welding according to claim 2, characterized in that: When the electro-hydraulic excitation system (12) is subjected to asymmetric frictional resistance, the frictional resistances experienced by the electro-hydraulic excitation system in different movement directions are made equal by changing the pressure of an oil chamber.

8. The hydraulic spring assisted vibration device for linear friction welding according to claim 2, characterized in that: By regulating the oil chamber pressure of the hydraulic spring, the equivalent stiffness of the electro-hydraulic excitation system (12) is changed, thereby preventing the electro-hydraulic excitation system (12) from generating resonance.

9. A method for adjusting a hydraulic spring-assisted vibration device for linear friction welding according to any one of claims 2 to 8, characterized in that: The steps include: The maximum resistance of the electro-hydraulic excitation system (12) in the direction of linear reciprocating motion is obtained by a force sensor (17), wherein the maximum resistance in the positive direction is recorded as F max,v+ , the maximum resistance in the negative direction is recorded as F max,v- ; When the difference between the maximum resistance in the positive direction and the maximum resistance in the negative direction exceeds a set value, the electro-hydraulic excitation system (12) is subjected to asymmetric friction resistance; The pressure difference ΔP between the left and right oil chambers is determined according to the maximum resistance of the electro-hydraulic excitation system (12) in the linear reciprocating motion direction, specifically: ΔP = (F max,v+ -F max,v- ) / A0, wherein A0 is the effective action area of ​​the piston rod (3); Pressurizing an oil chamber corresponding to one end of a piston rod (3) in contact with a vibration platform (11) through a hydraulic system so that the pressure of the oil chamber is P1 = P0 + ΔP; The pressure of the other oil chamber is maintained at P0, where P0 is the pressure of the oil chamber when the electro-hydraulic excitation system (12) is subjected to symmetrical friction resistance.

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