EP2918690A1

EP2918690A1 - Method and system for locally regulating and controlling metal member residual stress

Info

Publication number: EP2918690A1
Application number: EP13871844.0A
Authority: EP
Inventors: Chunguang Xu; Wentao SONG; Qinxue PAN; Dingguo XIAO; Lang Xu; Xiao Li; Haiyang Liu
Original assignee: Beijing Institute of Technology BIT
Current assignee: Beijing Institute of Technology BIT
Priority date: 2013-01-21
Filing date: 2013-03-11
Publication date: 2015-09-16
Also published as: WO2014110864A1; EP2918690A4; JP6373935B2; JP2016505856A; JP2017071860A

Abstract

A method and system for locally regulating and controlling a metal member residual stress, the method comprising: arranging one or more high-energy ultrasonic wave transducers (1) in or around a metal member area that the residual stress needs to be regulated and controlled, fixing the ultrasonic wave transducers (1) and controlling the ultrasonic wave transducers to emit high-energy ultrasonic waves, regulating and controlling the magnitude and direction of the residual stress value in the area by adjusting the parameters such as frequency, amplitude, phase and energy. The method and system effectively eliminate, inhibit and reestablish in situ local metal member residual stress, and have simple structure, easy operation, high efficiency, low cost, and reduced pollution.

Description

Background of the invention

The present invention relates to a method and system for regulating and controlling in situ local metal member residual stress, which eliminates, inhibits and reestablishes in situ local residual stress of metal member still having service life. The achievement of the present invention can be widely applied to several fields, such as industries of aerospace, ship, machine tool, construction machinery, coal-mine machinery, foundry, forging, welding, molding, nuclear power, wind power and etc.

Description of the related art

The residual stress is a kind of stress which is retained after deformation, due to uneven of stress field, uneven strain field, uneven temperature field and heterogeneity of structure. The residual stress influences reliability of metal member very much, particularly fatigue life, dimensional stability and resistance to corrosion, of structural member, and may result in stress concentration, so as to cause cracks on material. These cracks may lead to breakage of material under a certain condition. For this, it is urgently necessary to eliminate, regulate and control the residual stress of the member. However, the generation of residual stress is very common and hard to be predicted. There is no method and system for better controlling residual stress in order to satisfy practical requirements of manufacture.
Conventionally, methods, such as natural aging, thermal treatment, are used for weakening and eliminating the residual stress. However, the natural aging has many disadvantages like time consuming, low efficient, large space occupying, difficult regulation and control. The thermal treatment has many disadvantages like long period, high power consuming, high economic cost, easily oxidizing workpiece, serious pollution, and is not suitable to process large member or quick-wear member due to heat.
The vibration aging is a technique developing in last fifty years for eliminating residual stress by adopting mechanical method. The microscopic and macroscopic plastic deformation occurs in workpiece to reduce and uniform residual stress, when the member is suffered from stronger mechanical vibration and superposition of vibration stress and residual stress inside of material is greater than yield limit of the material. The disadvantages of this technique are as follows: 1) narrower application, nearly 77% of members cannot be vibrated due to high rigid and high natural frequency; 2) bad effect, hardly eliminating multi-dimension residual stress, the effect thereof cannot be compare favourably with the effect of the thermal aging; 3) complicated operation, when conventional vibration aging device processes a workpiece, there are tedious operations for adjusting excitation point, supporting point and vibration pick-up point; 4) serious noise pollution, the vibration of workpiece is occurred around the natural frequency, which generates much louder noise, resulting in poor environment condition of work site. This method is also hard to be applied to eliminate residual stress of a member still having service life.
There are tow further typical method for eliminating residual stress by adopting mechanical method, which are respectively so-called explosion method and static action-force method. The theory of the methods is as follows: by superposing outside applied load and inside residual stress to plastically deform inside of material and release the residual stress. The disadvantages are in that the explosion method is only suitable for materials which cannot be damaged by strong blast wave, and the static action-force method has special requirements for static load capacity of member.
The pulse-current process method is a new method for partially or even completely eliminating residual stress in material. However, the disadvantages is in that mono pulse current is only be adopted, the pulse current has greater peak value, and has a short action time.
The electromagnetic-complex processing method processes metal material with ferromagnetism by pulse current and pulse-magnetic field. The disadvantages of this method are in that there are more factors affecting elimination of residual stress, and implementation is complicated, so that in situ residual stress of member still having service life is hard to be eliminated.
A method for impacting and eliminating residual stress in welding by ultrasonic wave transmits mechanical vibration of ultrasonic frequency to wielding joint on a workpiece by means of an impact device of ultrasonic wave to produce a plastic deformation layer on a surface of the welding joint. The disadvantage of this method is in that an impacting damage, even cracks or tiny cracks are often brought about while ultrasonic wave impact is uniforming residual stress of member still having service life. These cracks will significantly influence safety and reliability of mechanical structure.

Summary of the invention

For aforementioned problems, the purpose of the present invention is to provide a method and system for regulating and controlling residual stress, which effectively eliminates, inhibits and reestablishes in-situ local residual stress of metal member still having service life.
In a method for regulating and controlling residual stress according to the present invention, one or more ultrasonic wave transducers are arranged in or around an area where residual stress needs to be regulated and controlled. The ultrasonic wave transducer is fixed and controlled to generate ultrasonic wave for eliminating residual stress in the area.
According to aforementioned method, the present invention has characteristics like convenient implementation, improved working efficiency, low cost and low pollution.
A system for regulating and controlling residual stress according to the present invention, includes IPC (Industrial Personal Computer), an excitation controller for ultrasonic wave signal, a ultrasonic wave amplifier, a ultrasonic wave transducer, which are connected to each other successively. The excitation controller for ultrasonic wave signal serves to receive control instruction issued by the IPC and emits a signal for regulating and controlling to the ultrasonic wave amplifier. The ultrasonic wave amplifier excites the ultrasonic wave transducer to generate ultrasonic wave beam for regulating residual stress of workpiece, on the basis of the signal for regulating and controlling.
The present invention is a reasonable design, simple and useful, easily implemented. Further, the system can be configured to be small, light-weight, easily to be carried.

Brief description of the drawings

Fig. 1 (a) shows a sound field model of single ultrasonic wave transducer and a coordinate system thereof.
Fig. 1 (b) shows a focused array sound field model of multiple ultrasonic wave transducers and a coordinate system thereof.
Fig. 2 is a schematic view of far-field focusing for high-energy sound field.
Fig. 3 is a schematic view of a multichannel high-energy ultrasonic wave sound field processing device for weld-residual stress.
Fig. 4 is a schematic view of a high-energy sound field closed-loop system for regulating and controlling residual stress, according to the present invention.
Fig. 5 is a schematic view of a holding device during single ultrasonic wave transducer working.
Fig. 6 (a) is a side view of guiding head of ultrasonic wave transducer according to the present invention.
Fig. 6 (b) is a plan view of guiding head of ultrasonic wave transducer according to the present invention.

Introduction for reference number

1: ultrasonic wave transducer; 3: residual stress concentrating area; 4: workpiece; 7: excitation signal; 8: high-power ultrasonic wave amplifier; 9: regulation and control signal; 10: ultrasonic wave signal excitation controller; 11: instruction signal; 12: IPC; 13: coupling agent; 14: centre fixation rod; 15: elongated support rod; 16: threaded rod; 17: compression plate; 19: magnetic base; 21: welding joint; 22: ultrasonic wave signal excitation multichannel controller; 23: residual stress closed-loop controller; 24: ultrasonic wave signal processing module; 25: residual stress detection transducer.

Detailed description of the invention

The present invention adopts high-energy ultrasonic wave sound field to regulate and control residual stress. The so-called regulation and control for residual stress by high-energy ultrasonic wave sound field is in that providing a solid mechanical member still having service lift in high-energy sound field, locally and quantitatively regulating and controlling the residual stress state by use of additional high-power sound energy applied from outside, while detecting macroscopic residual stress of member in time by the acoustoelastic effect, and forming a closed-loop control system for residual stress, and finally the ultrasonic wave detection and closed-loop control are achieved for local residual stress state of member.
The embodiments of the present invention will be described in detail with reference to drawings.
Fig. 1(a) shows a sound field model of single ultrasonic wave transducer and a coordinate system thereof. Fig. 1(b) shows a focused array sound field model of multiple ultrasonic wave transducers and a coordinate system thereof. In Fig. 1, 'P' represents any point in sound field, 'r' represents distance between 'P' and sound source, 'θ' represents an angle between 'P' and the sound source, 'φ' represents an angle at which an anchor point for transducer surface.
First, a method for regulating and controlling residual stress by high-energy ultrasonic wave sound field will be described.
The theory of the method for regulating and controlling residual stress by high-energy ultrasonic wave sound field is: the elimination of residual stress is substantively a process in which elastic strain stored in material is gradually released via microscopic or local plastic deformation, that is, it is relative to the dislocation movement. In order to eliminate residual stress, dislocation atom is gave enough power to overcome its resistance. The lattice distortion is reduced by sliding the atom out of inside of lattice, so that residual stress is eliminated.
The energy obtained by mass element is as follows, wherein, the mass element is provided by high-energy ultrasonic wave, and distance between the mass element and power ultrasonic wave source is x: $E = \frac{1}{2} ρ_{0} V_{0} c^{2} + \frac{1}{2} \frac{{(A \sin 2 π ft)}^{2} V_{0}}{ρ_{0} c^{2}} \exp [- 2 x (CF d^{3} f^{3} + \frac{2 π^{2} f^{2} K^{2}}{ρ_{0} c^{3}} (\frac{1}{c_{v}} + \frac{1}{c_{p}}))]$
It can be seen from above that residual stress inside of metal will be released, when energy E provided to inner mass element of a workpiece 4 by high-energy ultrasonic wave sound field, is greater than the binding energy W produced by dislocation. This initially demonstrates that the utilization of high-energy ultrasonic wave can control residual stress in theory, but the efficiency and effect of the control relates to some factors, such as material property, excitation frequency, coupling way and local position of the control.
It has been known according to the formula (1), the high-energy ultrasonic-wave provided energy of metal inner mass element is proportional to the natural properties of metal material, such as density ρ ₀, constant-volume specific heat c_v , constant-pressure specific heat c_p and etc, and is inversely proportional to a speed c with which the ultrasonic wave is spread in the metal material, while the aforementioned energy is proportional to square of ultrasonic-wave provided sound pressure amplitude A and frequency f. Because the natural properties of a material is constant, such as density ρ ₀, constant-volume specific heat c_v , constant-pressure specific heat c_p and etc, when residual stress inside the material is regulated and controlled, an ultrasonic wave transducer 1 with high power should be used for providing higher sound pressure amplitude A to a workpiece 4 having larger residual stress in order to achieve the best effect of regulation and control, and the transducer can excitation an ultrasonic wave sound field having higher frequency f.
Fig. 2 is a schematic view of far-field focusing for high-energy sound field. In Fig. 2, a plurality of ultrasonic wave transducers 1 are adopted to generate high-energy ultrasonic wave focusing in stress area of workpiece 4. In a normal temperature condition, the high-energy ultrasonic wave having a certain frequency and power is continuously used to regulate for a period of time under a certain temperature allowing of heating. The ultrasonic wave transducers 1 in Fig. 2 form focusing in a residual stress concentrating area 3 by using an inclining cylinder having a slope surface. The ultrasonic wave transducer may have various shapes like cylinder (as Fig. 5 shown), flaring shape (as Fig. 3 shown), cylinder of which the middle part has a joint, which are not specially limited. The ultrasonic wave transducer 1 can have any shape in the following description and drawings, and is not limited by the shapes represented in the specification and drawings, if there is no special declaration. The shapes represented in the specification and drawings are only examples for convenient explaining.
The ultrasonic wave transducer 1 includes a housing, a matching layer, a transducer with piezoelectric ceramics disk, a back lining, an outgoing cable, and Cymbal array receiver, where a part of back lining forms a guiding head (as Fig. 6 shown).
Fig. 5 is a schematic view of a holding device during a cylindrical ultrasonic wave transducer 1 (to which the flaring-shape ultrasonic wave transducer is identical) working. When an area on which residual stress of welding workpiece concentrates is regulated and controlled, two strong magnetic bases 19 are attached on a welding body portion to be regulated and controlled. An elongated support rod 15 is fixed on the upper end of two strong magnetic bases 19. The ultrasonic wave transducer 1 is adjusted to a wielding joint 21 (the area on which residual stress concentrates) by adjusting a centre fixation rod and a threaded rod 16. The workpiece 4 is held to fixedly contact with the ultrasonic wave transducer 1 by a compression plate 17. Both ends of the ultrasonic wave transducer 1 are then connected to a power supply so as to switch on the high-energy ultrasonic wave excitation system. The device is designed to have a multichannel circuit board so as to control a plurality of ultrasonic wave transducers 1 simultaneously via a control cabinet. The assistance holding device supplies a certain holding force to keep the workpiece to fixedly contact with the ultrasonic wave transducer 1. A layer of coupling agent 13 is coated on a holding surface so as to reduce the energy lost of ultrasonic wave and lower temperature during the regulation and control for residual stress by high-energy sound field.
As Fig. 5 shown, the two magnetic bases 19 are attached on the welding body portion to be regulated and controlled. The ultrasonic wave transducer is adjusted to the residual stress concentrating area of the wielding joint 21 (the area on which residual stress concentrates) by adjusting a centre fixation rod and a threaded rod 16. The ultrasonic wave transducer 1 is applied with a certain pretightening force by means of the compression plate 17 so as to be fixed on the surface of welding body portion. A layer of coupling agent 13 is coated on a holding surface so as to reduce the energy lost of ultrasonic wave and lower temperature during the regulation and control for residual stress by high-energy sound field.
Further, Figs. 6 (a) and (b) show a guiding head of ultrasonic wave transducer 1 which is shaped as an inclining cylinder having a slope surface (as Fig. 2 shown). The guiding head is configured to control incident angle of high-energy sound beam and locally, quantitatively focusing the sound beam inside the workpiece 4. The focusing ultrasonic wave transducer is designed by means of Snell principle to control incident angle of high-energy sound beam and locally, quantitatively focusing the sound beam inside a member. In order to achieve convenient holding, a gap 20 is formed on side surface of periphery of the guiding head to assist the holding of the holding device. Similarly, a layer of coupling agent 13 is coated on a holding surface so as to reduce the energy lost of ultrasonic wave and lower temperature during the regulation and control for residual stress by high-energy sound field.
The system for regulating and controlling residual stress by high-energy ultrasonic wave sound field will be described.
Fig. 3 is a schematic view of a multichannel high-energy ultrasonic wave sound field processing device for weld-residual stress. The processing device includes an IPC 12, an ultrasonic wave signal excitation controller 10, a high-power ultrasonic wave amplifier 8, an ultrasonic wave transducer 1 and assistance devices. In Fig. 3, the ultrasonic wave transducer 1 is configured to be flaring shape.
Fig. 3 shows a multichannel high-energy ultrasonic wave sound field processing system, where the IPC 12 issues a control instruction by coordinating with system software. After receiving the control instruction signal 11, the ultrasonic wave signal excitation controller 10 sends a regulation and control signal 9 to the high-power ultrasonic wave amplifier 8. The high-power ultrasonic wave amplifier 8 excites the ultrasonic wave transducer 1 on the basis of the regulation and control signal to generate high-energy ultrasonic wave beam. The energy of high-energy ultrasonic wave beam is injected to the residual stress concentrating area 3 according to predetermined requirement so as to adjust the residual stress. During working, high-energy sound field spreads in medium of workpiece so that particles of the medium alternatively vibrates or wriggles, and causes stress or sound pressure in the medium continuously or discontinuously change so as to trigger a serious of secondary effects, such as wriggle between crystal particles or lattices. The constraining force between lattices is destructed, reduced or reestablished by means of stronger wave energy of inner sound field of workpiece, which serves to regulate and control residual stress field.
The system for regulating and controlling residual stress by using high-energy ultrasonic wave sound field can adopt an ultrasonic wave detection and closed-loop control system for residual stress, as Fig. 4 shown.
As Fig. 4 shown, the ultrasonic wave detection and closed-loop control system for residual stress includes ultrasonic wave transducers 1, high-power ultrasonic wave amplifier 8, ultrasonic wave signal excitation multichannel controller 22, residual stress closed-loop controller 23, ultrasonic wave signal processing module 24, and residual stress detection transducer 25, which are successively connected to each other. This connection relationship is showed in Fig. 4, where the ultrasonic wave transducers 1 are fixedly connected to a workpiece 4 via coupling agent 13.
If a workpiece 4 is suffered from regulation and control of residual stress, the ultrasonic wave signal excitation multichannel controller 22 controls a plurality of ultrasonic wave amplifiers 8 to generate excitation signal by coordinating with software. The excitation signal excites a plurality of ultrasonic wave transducer 1 to generate high-energy ultrasonic wave beam having different frequency and phase. The energy of high-energy ultrasonic wave beam is focused to regulate residual stress, while the residual stress of workpiece 4 is detected by using the residual stress detection transducer 25, and an ultrasonic wave signal (ultrasonic transit time) is transmitted to the ultrasonic wave signal processing module 24. The ultrasonic wave signal processing module 24 transmits the detected residual stress information to the residual stress closed-loop controller 23 in real time. The residual stress closed-loop controller 23 is connected to the ultrasonic wave signal excitation multichannel controller 22 so as to form a residual stress closed-loop control system.
The in situ sound energy control method for elastic solid residual stress field will be described in detail as follows.
First, one or more focusing ultrasonic wave transducers 1 are arranged in or around an area where residual stress needs to be regulated and controlled. This arrangement is defined by actual tooling condition and amount of ultrasonic wave transducer 1 in work place. The ultrasonic wave transducers 1 is connected to a workpiece 4 via a holding device. The contact surface is coated with coupling agent 13 to reduce energy lost of ultrasonic wave and working temperature. The positive and negative poles of the transducers are connected to positive and negative output ends of ultrasonic wave excitation multichannel control cabinet. The control cabinet is connected to a high-energy ultrasonic wave generator. The power supply of the ultrasonic wave generator is switched on so that the ultrasonic wave transducers 1 generate ultrasonic wave energy and the residual stress concentrating area is focused by sound field at far-field. The preferred current range of a single transducer is 0.1∼1A. The processing temperature is within normal temperature. The continuously focusing is kept for a certain time.
The key technique of high-energy ultrasonic wave focusing is focusing control mode. The present invention takes advantage of a focusing system composed by ultrasonic wave transducer 1 and multi-array element focusing acoustic lens, which is an effective and practical focusing way. A plurality of ultrasonic wave transducers 1 is used for exciting focusing simultaneously in order to better control local residual stress inside material. The high-energy wave is generated at focusing position by means of geometrical focusing theory of sound field as Fig. 1(b) shown. This high-energy ultrasonic wave focusing method solves a problem that the power of single ultrasonic wave transducer 1 is not enough, very well. The ultrasonic wave is focused on an area where residual stress needs to be regulated and controlled, by means of automatic control technique to coordinate each ultrasonic wave transducer 1 is coordinated with each other by automatic control technique to focus the ultrasonic wave in the same coordinate system onto an area where residual stress needs to be regulated and controlled.
The relatively high-energy focusing areas are formed on positions at different depth within the workpiece 4 by controlling different excitation parameters, such as incident angle, frequency and phase, so as to regulate and control residual stress state of surface and sub-surface of member and residual stress state of different depth inside the member. The high-energy sound field distribution of sound lens is described by the diffraction theory, which can acquire more accuracy result.
After high-energy ultrasonic wave focusing for a period of time, the real-time state of residual stress is accurately detected in time by residual stress detection system, which depends on a computer control system and some devices, such as a workbench, holding tools and etc, coordinating with computer control system. The real-time state of residual stress is fed back to the control system. The control system controls processing time on the basis of real-time effect of regulation and control, so as to achieve the purpose of accurately, quantitatively and locally regulating and controlling residual stress.
A test is made for high-energy ultrasonic wave sound field's eliminating weld residual stress of metal material, such as steel 45# plate, by means of multichannel high-energy ultrasonic wave sound field processing system. The steel 45# workpiece 4 is processed with a high-energy sound field for a certain time by means of a plurality of focusing transducers having a certain power and frequency. Eight measure areas on measure surface are measured by means of ultrasonic wave residual stress measurement system, before testing. The value of stress of the measure areas is measured again, after testing. The test acts transducer power, transducer frequency and loading time as factors of influence.
The result of test represents that the value of residual stress in the residual stress concentrating area 3 does not change a lot. This means that the regulation and control for local residual stress of elastic solid workpiece 4 may be achieved effectively and quantitatively by regulating and controlling the excitation rule and far-field focusing, so that the purpose of eliminating and restraining undesirable residual stress and increasing desirable residual stress. The stress value of steel 45# plate is improved overall after eliminating stress by high power ultrasonic wave for a period of time. By properly introducing pressure stress, the strength of surface and entire structure of the steel plate is increased, and the corrosion and wear resistance of weld area surface is improved. The technique for regulating and controlling state of residual stress field by ultrasonic wave energy has expansively practical applications.
The implementation steps will be described in detail.

1) measuring residual stress value of area of workpiece 4 to be regulated and controlled, where adopting ultrasonic wave transducer 1 with higher excitation frequency and power for a workpiece having higher residual stress; adopting ultrasonic wave transducer 1 with lower excitation frequency and power for regulating and controlling a workpiece 4 having lower residual stress.
2) re-measuring residual stress value of the regulated and controlled area, after being processed by high-energy sound field.
3) comparing current residual stress value to a desirable value of regulation and control, if the effect of regulation and control is achieved, then stopping continuous regulation and control, if not, then repeating step 2) until the effect of regulation and control is achieved, after then stopping regulation and control.

Embodiment 1

The steel 45# sample is locally quenched to generate residual stress. The residual stress concentrating portion is provided with four ultrasonic wave transducers 1. The ultrasonic wave generator is powered on, after then the four ultrasonic wave transducers 1 are excited to focus simultaneously, which brings about high-energy action on focusing position to implement residual stress regulation for the residual stress concentrating area. The current of single focusing transducer is 0.1∼1A, and the power and frequency have three match combinations: 60W/28KHz, 60W/20KHz, 40W/28Kz. The time for maintaining action is respectively 10mins, 20mins, 40mins, and 80mins.

Embodiment 2

The material to be acted is H62 copper sample. The current of single sound wave transducer 1 is 0.1∼1A, and the power and frequency have three match combinations: 60W/28KHz, 60W/20KHz, 40W/28Kz. The time for maintaining action is respectively 40mins, 80mins, and 160mins.

Embodiment 3

The difference from the embodiment 1 is in that:
The material to be acted is aluminium alloy 6061 sample. The current of single sound wave transducer 1 is 0.1∼1A, and the power and frequency are 60W/28KHz. The time for maintaining action is respectively 30mins, and 60mins.
Through aforementioned tests, by means of high-energy ultrasonic wave sound field device for regulating and controlling residual stress, the average stress value of tested area is respectively 239Mpa and 125Mpa before and after being processed by high-energy ultrasonic wave, degree of reduction reaches up to 47.8%, the residual stress value of local area reduces to 162Mpa from 408Mpa, decline of stress reaches to 246Mpa. Through aforementioned tests, the frequency range 20KHz∼600KHz can bring about better effect. Further, the power range of sound field generated by wave transducer is preferable 40W∼1000W. The action time range of sound field generated by ultrasonic wave transducer is preferable 10mins∼10hrs.
The method for quantitatively regulating and controlling local residual stress of material by means of ultrasonic wave focusing has the following advantages:

(1) Advanced theory and better processing effect. The present invention starts with the generation reason of residual stress, and injects the energy of high-power ultrasonic wave to an area in which stress is regulated and controlled. The original dislocation structure is properly changed so that the dislocation is moved to relative stable position of low-energy location from unstable high-energy location. The original dislocation structure is broke, and a new structure with low impedance energy and low elastic property is rebuilt, that is, residual stress is redistributed, level of residual stress is reduced, so as to eliminate residual stress of workpiece and increase size stability of material.
(2) Low power consumption, faster processing speed. The present invention controls different excitation parameters of high-energy ultrasonic wave beam by means of the system for regulation and controlling, such as incident angle, frequency and phase of the high-energy ultrasonic wave beam, and forms a residual stress concentrating area having high-energy on a portion where residual stress needs to be regulated and controlled in a short time, and changes slippage caused by dislocation and plastic strain in the area, so as to regulate and control the residual stress.
(3) Simple device, easy operation, low cost. The lowest configuration for the present invention includes high-power ultrasonic wave generator, focusing ultrasonic wave transducer and corresponding assistance holding device.
(4) No pollution. The ultrasonic wave is harmless to human body. The processing of high-energy ultrasonic wave has small noise, and is safe and reliable, cannot substantially produce pollution.
(5) Suitable for plurality of materials. The present invention is suitable for all elastic solid workpieces, including metal or nonmetal material, such as glass.

The protection scope of the present invention is not limited by the aforementioned embodiments. It is obvious that a person skilled in the art can make any change and variant for the present invention without leave from the scope and spirit of the present invention. If these changes and variants belong to the claims of the present invention and the equivalent technical scope, intention of the present invention includes these changes and variants as well.

Claims

A method for regulating and controlling residual stress, characterized in that,
arranging one or more ultrasonic wave transducers in or around an area in which residual stress needs to be regulated and controlled;
fixing said ultrasonic wave transducer and making it emitting ultrasonic wave to eliminate residual stress in said area.
The method according to claim 1, characterized in that, further comprising the following steps:
step 1: measuring magnitude of residual stress value of a workpiece's area to be regulated and controlled, selecting excitation frequency and power of said ultrasonic wave transducer on the basis of said stress value, and implementing regulation and control;

step 2: re-measure magnitude of residual stress value of said area to be regulated and controlled after said regulation and control lasting for a period of time;

step 3: comparing current residual stress value to a desirable value of regulation and control, if a desirable effect of regulation and control is achieved, then stopping continuous regulation and control, if not, then repeating said step 2 until the desirable effect of regulation and control is achieved, after then stopping regulation and control.
The method according to claim 1, characterized in that, a frequency range of sound field generated by said ultrasonic wave transducer is 20KHz∼600KHz.
The method according to claim 1, characterized in that, a frequency range of sound field generated by said ultrasonic wave transducer is 40KHz∼1000KHz.
The method according to claim 1, characterized in that, an action-time range of sound field generated by said ultrasonic wave transducer is 10mins∼10hrs.
The method according to claim 1, characterized in that, fixing said ultrasonic wave transducer by way of coupling and holding, wherein, said coupling is a solid coupling or a liquid coupling, said holding is a magnetic type and thread fastened holding.
The method according to claim 1, characterized in that, current range of a single ultrasonic wave transducer is 0.1∼1A, a processing temperature is normal temperature.
A system for regulating and controlling residual stress, characterized in that, comprising:
an IPC (12), an ultrasonic wave signal excitation controller (10), an ultrasonic wave amplifier (8), and an ultrasonic wave transducer (1), which are successively connected with each other,

said ultrasonic wave signal excitation controller (10) is used for receiving an control instruction issued by said IPC (12) and sends a signal for regulating and controlling to said ultrasonic wave amplifier (8);

said ultrasonic wave amplifier (8) excites said ultrasonic wave transducer (1) to generate ultrasonic wave beam for regulating and controlling residual stress of a workpiece, on the basis of said signal for regulating and controlling.
The system according to claim 8, characterized in that, further comprising:
a residual stress closed-loop controller (23), an ultrasonic wave signal processing module (24), and a residual stress detection transducer (25), which are successively electrically connected to each other,

said residual stress detection transducer (25) is used for detecting residual stress of a workpiece and transmits a detection signal to said ultrasonic wave signal processing module (24);

said ultrasonic wave signal processing module (24) transmits detected information of residual stress to said residual stress closed-loop controller (23);

said residual stress closed-loop controller (23) is electrically connected to an ultrasonic wave signal excitation multichannel controller (22) to form a closed-loop control system for residual stress.
The system according to claim 8, characterized in that, further comprising a holding device which connects and fixes said ultrasonic wave transducer (1) to a workpiece, an area in which said ultrasonic wave transducer (1) is in contact with a workpiece is coated with coupling agent.
The system according to claim 8, characterized in that, said residual stress detection transducer (25) adopts pitch-catch mode and acquires a residual stress ultrasonic wave signal of said area to be regulated and controlled by exciting and receiving critical refraction longitudinal wave, said ultrasonic wave signal is input to said ultrasonic wave signal processing module (24) in which residual stress of said area to be regulated and controlled is calculated.
The system according to claim 8, characterized in that, a guiding head of a focusing transducer is designed to have a structure in which there is a certain inclining angle between axis of said guiding head and bottom surface.
The system according to claim 12, characterized in that, said focusing transducer is grooved at a side of said guiding head to have a right-angle groove.