CN113977190A - Ultrasonic vibration auxiliary hole extrusion strengthening device, design method and operation process thereof - Google Patents
Ultrasonic vibration auxiliary hole extrusion strengthening device, design method and operation process thereof Download PDFInfo
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Abstract
The invention provides an ultrasonic vibration auxiliary hole extrusion strengthening device, a design method and an operation process thereof. The relative amplitude of the working ring position of the extrusion core rod is large, and the relative amplitude of the threaded connection position of the extrusion core rod and the ultrasonic transducer is minimum. In the ultrasonic vibration hole extrusion strengthening process, the ultrasonic vibration converts the linear motion of the extrusion core rod in the assembly hole into sine motion or cosine motion, changes the motion track of the extrusion core rod, increases the extrusion times of the extrusion core rod working ring on the hole wall of the assembly hole of the structural member, can obviously improve the surface quality of the hole wall of the assembly hole of the extruded workpiece, and improves the fatigue performance of the structural member with the hole.
Description
Technical Field
The invention discloses an ultrasonic vibration auxiliary hole extrusion strengthening device, a design method and an operation process thereof, belongs to the technical field of hole extrusion strengthening precision machining, and particularly relates to an ultrasonic vibration composite hole extrusion strengthening technology which combines an ultrasonic vibration technology and a hole extrusion strengthening technology to improve the quality of the assembled hole wall of a porous structural member and improve the fatigue strength of the porous structural member.
Background
Most structures on the airplane are assembled by installing fasteners in the assembly holes of the structural parts, and the structural parts have the assembly holes, so that stress concentration is easy to generate, fatigue cracks are initiated or the crack propagation rate is accelerated, the fatigue performance of the structural parts with holes is reduced, and the service life is shortened.
The slotting bush hole extrusion strengthening process is an advanced hole extrusion strengthening technology, belongs to indirect extrusion strengthening, and avoids the damage of the extrusion strengthening process to the surface quality of a hole wall. Therefore, the slotting bush hole extrusion strengthening process is widely applied to the extrusion strengthening of the aircraft structural member assembly holes, and after the structural member assembly holes are subjected to extrusion strengthening, the hole walls form a residual stress field, so that the fatigue performance of the structural member with holes can be improved, and the fatigue strengthening is improved. However, after the extrusion strengthening of the split bush of the assembly hole of the large-thickness structural member, the problems of uneven residual stress field formed on the hole wall, low extrusion strengthening efficiency and the like are solved, so that the extrusion strengthening of the assembly hole of the large-thickness structural member faces a dilemma.
The problems that after the assembly hole of the large-thickness structural part is extruded and reinforced by using the slotted bushing, the hole wall forms uneven residual stress, the extrusion reinforcement efficiency is low and the like are solved. The inventor proposes 2020.12.09 a process for cold extrusion strengthening of assembly holes using a split bushing (CN202011447798.6), wherein the split bushing is inserted through one end of an extrusion mandrel and placed on a guide section, and is fixed to a fixture by a thread at the tail part; the extrusion core rod and the slotted bush penetrate through the workpiece with the hole to complete installation; when the extrusion core rod is pulled out of the assembly hole of the workpiece with the hole at a constant speed, the extrusion core rod working ring extrudes the slotted bush, the slotted bush is elastically expanded under the action of extrusion force, and the hole wall of the assembly hole of the workpiece with the hole is extruded to cause the plastic deformation of the hole wall of the assembly hole, thereby realizing the strengthening effect; more than one slot is symmetrically arranged on the slot bushing. The invention has simple structure and can realize the repeated use of the slotted bush, thereby reducing the cost of the hole extrusion strengthening process. The wall of the assembly hole of the workpiece with the hole forms a uniform residual stress field, and the fatigue life of the workpiece with the hole is prolonged. The inventor proposes 2021.03.19 a multi-split bushing diameter variable device with a threaded sleeve and a method of using the same (CN202110296927.4), wherein a rotating handle is installed on the threaded sleeve, the threaded sleeve with the rotating handle is installed in the middle of the multi-split bushing, and the middle of the multi-split bushing has a taper angle and is threaded. Rotating the rotary handle, and gradually narrowing the slit width on the multi-slit bushing in the process that the threaded sleeve gradually moves from the middle of the multi-slit bushing to the tail of the bushing to cause the diameter of the front end of the multi-slit bushing to be reduced; the rotating handle is rotated anticlockwise, the threaded sleeve moves from the middle of the multi-slotted bushing to the front end of the bushing gradually, and the width of the slot on the multi-slotted bushing is restored to the original width. The diameter of the front end of the multi-slotted bushing can be freely changed by clockwise and anticlockwise rotating the rotating handle. The multi-split-slot bushing cold extrusion strengthening process is simple in structure and convenient to operate, and the diameter of the front end of the multi-split-slot bushing can be changed, so that the multi-split-slot bushing cold extrusion strengthening process is smoothly realized. The inventor proposes 2021.07.21 a method for machining a multi-split bush (CN202110824573.6), which includes the following steps: (1) the material selected for preparing the multi-split bushing is 0Cr17Ni7 Al; (2) blanking 0Cr17Ni7Al bar stock based on the structural parameters of the extruded workpiece; (3) performing rough machining on the 0Cr17Ni7Al bar stock after blanking according to the design size of the multi-slot bushing; (4) performing heat treatment on the rough-machined bar stock by using a TH565 heat treatment system; (5) drilling and forming the heat-treated 0Cr17Ni7Al bar stock into a bushing; (6) the bushing slots form a multi-split bushing. The invention has high production efficiency and high processing precision, can improve the surface quality of the hole wall of the assembly hole of the extruded workpiece and improve the fatigue performance of the extruded workpiece.
However, there is no literature report combining ultrasonic vibration technology with hole extrusion strengthening technology.
Disclosure of Invention
The invention provides an ultrasonic vibration auxiliary hole extrusion strengthening device, a design method and an operation process thereof, aiming at solving the problems of stable hole wall surface quality, uneven residual stress and the like after the existing slotted liner hole is extruded and strengthened to the assembling hole of the perforated structural member and seriously influencing the fatigue performance and the service life of the perforated structural member.
The ultrasonic vibration technology and the hole extrusion strengthening technology are combined with each other, the linear application of the extrusion core rod in the assembly hole is changed into sine or cosine motion, the extrusion times of the extrusion core rod working ring on the hole wall of the assembly hole are increased, and therefore the surface quality of the hole wall can be improved, and the fatigue performance of the structure with holes is improved.
Meanwhile, the inventor proposes an improved scheme of different structures of the extrusion core rod, preferably selects the hole extrusion strengthening device with the ultrasonic vibration auxiliary hole extrusion strengthening device with the resonant frequency approaching to the design frequency and the maximum relative amplitude being larger, and realizes the remarkable improvement of the extrusion strengthening effect of the structure with the holes.
Technical scheme
In order to realize the purpose of the invention, the invention adopts the following technical scheme:
the utility model provides an ultrasonic vibration assists hole extrusion reinforcing means, is including the extrusion plug, amplitude transformer and the ultrasonic transducer who connects gradually, and ultrasonic transducer is connected to the power, wherein:
the extrusion plug from preceding to back includes in proper order: a front end 11, a front section 13 and a rear section 12 of the core rod;
the ultrasonic transducer comprises from front to back: a front end cover 6, a piezoelectric ceramic piece 8 and a rear end cover 9.
The size of the ultrasonic transducer is calculated based on a half-wavelength theory, the node of the ultrasonic transducer is arranged on the right side of the piezoelectric ceramic plate, and the size of the front end cover is 1/4 of the longitudinal wave wavelength.
The front end 11 of the extrusion core rod is connected with the front end cover 6 of the ultrasonic transducer, and in order to avoid ultrasonic energy loss, the diameter of the front end 11 of the extrusion core rod is the same as that of the front end of the ultrasonic transducer. Therefore, the relative amplitude of the threaded connection part of the extrusion core rod and the ultrasonic transducer is minimum, and the phenomenon that the threads of the connection part of the extrusion core rod are loosened or the bolts at the connection part are broken by ultrasonic vibration energy in the extrusion strengthening process of the ultrasonic hole is prevented.
The amplitude transformer and the front end cover of the ultrasonic transducer are integrated, so that threaded connection is reduced, and ultrasonic energy attenuation is avoided.
The extrusion core rod is a solid extrusion core rod, preferably, the extrusion core rod is in a sectional type, wherein the front section is in threaded connection with the front end cover of the ultrasonic transducer, and the rear section is in threaded connection with the front section of the extrusion core rod.
Wherein, extrusion plug back end includes: rear cone section 1, working ring 2, front cone section 3, direction section 4. The front conical section, the working ring and the rear conical section are working parts of an extrusion core rod, the diameter of the rear section (12) of the extrusion core rod is smaller than that of an assembly hole of an extruded workpiece, and the extruded workpiece is placed on a guide section of the extrusion core rod from the rear section of the extrusion core rod.
In order to make the relative amplitude at the position of the working ring of the extrusion core rod large, it is preferable that the extrusion core rod is provided with protrusions, the number of which is preferably 1-2, and more preferably 2.
An operation process of an ultrasonic vibration auxiliary hole extrusion strengthening device is characterized in that the principle is as follows:
(1) turning on an ultrasonic power supply to output a high-frequency oscillation electric signal, and receiving the electric signal and converting the electric signal into mechanical vibration by a piezoelectric ceramic transducer; the amplitude transformer transmits the vibration to the extrusion core rod;
(2) the diameter of the rear section (12) of the extrusion core rod is smaller than that of the assembly hole of the extruded workpiece, and the extruded workpiece is placed on the guide section of the extrusion core rod from the rear section of the extrusion core rod;
(3) in the process of ultrasonic vibration hole extrusion strengthening, the ultrasonic vibration converts the linear motion of the extrusion core rod in the assembly hole into sine motion or cosine motion, changes the motion track of the extrusion core rod, increases the extrusion times of the extrusion core rod working ring on the hole wall of the assembly hole of the structural member, obviously improves the extrusion strengthening effect of the assembly hole and improves the fatigue performance of the structural member with the hole;
the relative amplitude of the working ring position of the extrusion core rod is large, and the relative amplitude of the threaded connection position of the extrusion core rod and the ultrasonic transducer is minimum.
The design method of the ultrasonic vibration auxiliary hole extrusion strengthening device comprises the following steps:
(1) determining the size of the extrusion core rod;
(2) ultrasonic transducer sizing;
(3) simulating the mode of the ultrasonic transducer;
(4) an improved scheme of the extrusion core rod structure;
(5) performing modal simulation on the ultrasonic vibration auxiliary hole extrusion strengthening device;
(6) the ultrasonic vibration auxiliary hole extrusion strengthening device with the best hole extrusion effect is preferred.
Specifically, the design method includes the following steps:
(1) extrusion core rod sizing
The extrusion plug that uses in the supplementary hole extrusion reinforcing apparatus of ultrasonic vibration is solid extrusion plug, and the back end of solid extrusion plug mainly includes: front cone section, working ring, back cone section, direction section. The front conical section, the working ring and the rear conical section are working parts of the extrusion core rod, and the machining precision and the size of the working parts are closely related to the extrusion strengthening of the extruded workpiece.
And calculating the diameter of the working ring of the extrusion core rod based on the nominal aperture and the relative extrusion amount of the extruded workpiece.
The final hole diameter of the extruded workpiece can be obtained by unit conversion according to the nominal hole diameter. When the reaming amount of the hole wall of the assembly hole of the structural member after extrusion strengthening is not more than 0.2mm, the reaming processing has no influence on the residual stress field formed on the hole wall, so that the reaming amount of the hole wall of the assembly hole of the structural member after extrusion strengthening is 0.2mm, and the aperture of the assembly hole of the structural member after extrusion strengthening is obtained.
Knowing the amount of absolute reaming Ra, the final hole diameter DfPrimary pore diameter D0Relative extrusion amount ErThe rebound amount h is in the relationship shown in the formula (1).
Ra＝Df-D0(1+Er)+h (1)
The formula (1) is finished to obtain the change relation of the initial pore diameter as shown in the formula (2).
Obtaining a functional relation between the initial hole diameter and the resilience amount through a fitting formula, substituting the functional relation into the formula (2), and obtaining the initial hole diameter D of the structural member assembling hole0。
In the extrusion strengthening process of the direct hole of the extrusion core rod, the diameter D of the working ring of the extrusion core rod and the diameter D of the initial hole exist without using a lining0Relative extrusion amount ErThe relationship between them is shown in formula (3).
D＝D0+Ea＝D0(1+Er) (3)
The diameter D of the working ring of the extrusion core rod is calculated by the initial hole diameter and the relative extrusion amount of the assembly hole of the structural member by using the formula (3).
The design frequency of the ultrasonic vibration hole extrusion strengthening device is set, and the sound velocity of the material is calculated by the formula (4) according to the mechanical property of the extrusion core rod material.
Wherein c is the material sound velocity; e is the elastic modulus of the material; ρ is the density of the material.
The longitudinal wave wavelength is calculated by using the design frequency of the hole extrusion strengthening device and the sound velocity of the material according to the formula (5).
In the formula, lambda is the longitudinal wave wavelength; f is the design frequency.
And determining the longitudinal ultrasonic vibration wavelength of the extrusion core rod material by using a wavelength theorem, namely the propagation distance of the wave in one vibration period, and obtaining the length of the extrusion core rod.
(2) Ultrasound transducer sizing
The ultrasonic transducer consists of a front end cover, a piezoelectric ceramic piece and a rear end cover. And selecting the material, the size specification and the number of the piezoelectric ceramic pieces according to the working requirements of the ultrasonic vibration auxiliary hole extrusion strengthening device. The node of the ultrasonic transducer is arranged on the right side of the piezoelectric ceramic piece, the ultrasonic transducer is used as a continuous elastic body, waves are reflected on the end face of the uniform rod, the reflected waves and the existing waves are superposed, and the ultrasonic vibration energy is increased. The wave equation of the uniform rod vibration is shown in equation (6).
In the formula, xi is an axial coordinate of a certain point on the uniform rod; t is time; c is the longitudinal wave velocity.
The solution of the longitudinal wave equation can be obtained as shown in equation (7):
ξ(x,t)＝(A2 cosωt+B2 sinωt)·(Acoskx+Bsinkx) (7)
the ultrasonic transducer is a continuous elastomer, and the elastomer meets Hooke's law F ═ keΔ x, yielding the relationship shown in formula (8):
in the formula, F is the stress of a certain point in the uniform rod; s is the cross-sectional area of the uniform rod; k is the number of circles, k is omega/c is 2 pi/lambda; λ is the longitudinal wave wavelength.
Let m (t) be A2cosωt+B2sin ω t, m (t) is a function of t, indicating that the vibration of the uniform rod varies with time. The vibration at different points on the uniform rod with a constant time is expressed by the following equations (9) and (10):
ξ(x)＝m(Acoskx+Bsinkx) (9)
in the formula, m is a constant.
The ultrasonic transducer is designed by using the half-wavelength theorem, and an ultrasonic transducer design model is established as shown in figure 3.
Regard as the stiff end with nodal plane one side, the even elastic rod of free end is regarded as to one side, and the free end displacement volume of even pole is big, and the power that receives is little, and the displacement of stiff end is zero, sets up the origin of coordinates on the contact surface of rear end cap and piezoceramics piece, and the boundary condition of elasticity even pole is shown as formula (11):
the frequency formula of the ultrasonic transducer obtained by substituting the boundary conditions into the equations (9) and (10) is shown as the formula (12):
where Z ═ ρ cS is the acoustic characteristic impedance of each part of the ultrasonic transducer. Equation (13) is the design equation for the transducer.
Based on the design equation of the ultrasonic transducer, the length of the rear end cover can be obtained. The nodal plane is arranged on the right side of the piezoelectric ceramic plate, and the size of the front end cover is 1/4 of the wavelength of the longitudinal wave, so that the size of each part of the ultrasonic transducer can be obtained.
(3) Ultrasound transducer modal simulation
Based on the obtained sizes of the front end cover, the piezoelectric ceramic piece and the rear end cover and the material properties of all parts of the ultrasonic transducer, an ultrasonic transducer three-dimensional finite element simulation model is constructed, the established ultrasonic transducer is subjected to modal simulation, the resonant frequency of the ultrasonic transducer is compared with the design frequency of the ultrasonic vibration auxiliary hole extrusion strengthening device, and when the resonant frequency of the ultrasonic transducer deviates from the design frequency of the hole extrusion strengthening device, the resonant frequency of the ultrasonic transducer can be approached to the design frequency of the device by properly adjusting the sizes of the front end cover and the rear end cover.
(4) Improved scheme of extrusion core rod structure
In order to change the amplitude of the ultrasonic vibration auxiliary hole extrusion strengthening device, the ultrasonic vibration effect in the hole extrusion strengthening process is obviously improved. By optimizing the structure of the extrusion core rod, the resonant frequency of the hole extrusion strengthening device is controlled to approach to the design frequency, and the ultrasonic amplitude of the hole extrusion strengthening device is increased.
1) The first improvement scheme of the extrusion core rod is as follows: the diameter of the working ring of the extrusion mandrel is larger than the aperture of the assembly hole of the extruded workpiece, the front end of the extrusion mandrel is connected with the front end cover of the ultrasonic transducer, in order to avoid ultrasonic energy loss, the diameter of the front end of the extrusion mandrel is the same as that of the front end of the ultrasonic transducer, the diameter of the front end of the extrusion mandrel is larger than that of the assembly hole of the extruded workpiece, therefore, the extrusion mandrel needs to be disconnected, the extrusion mandrel is divided into an extrusion mandrel front section and an extrusion mandrel rear section, the extruded workpiece is placed at the extrusion mandrel guide section from the extrusion mandrel rear section, the diameter of the extrusion mandrel is smaller than that of the assembly hole of the structural member, and the extrusion mandrel is disconnected and connected by threads.
2) The second improvement scheme of the extrusion core rod: based on the first improvement scheme of the extrusion core rod, the protrusions are added on the extrusion core rod, the diameter and the length of the protrusions are controlled to be unchanged, the number of the protrusions is changed, and the influence of the number of the protrusions on the maximum relative amplitude of the hole extrusion strengthening device is analyzed;
3) the third improvement scheme of the extrusion core rod is as follows: based on the first extrusion core rod improvement scheme, the number of the bulges and the length of the bulges are controlled to be unchanged, the diameter of the bulges added on the extrusion core rod is changed, and the influence of the diameter of the bulges on the maximum relative amplitude of the hole extrusion strengthening device is analyzed;
4) the extrusion core rod is improved in the following scheme: based on the first extrusion core rod improvement scheme, the number and the diameter of the protrusions are controlled, the length of the protrusions added on the extrusion core rod is changed, and the influence of the length of the protrusions on the maximum relative amplitude of the hole extrusion strengthening device is analyzed;
5) the extrusion core rod is improved in the fifth scheme: based on the first improvement scheme of the extrusion core rod, the front end of the extrusion core rod and the front end cover of the ultrasonic transducer are combined into a whole, so that threaded connection is reduced, and ultrasonic energy attenuation is reduced. The relative amplitude of the joint of the rear section of the extrusion core rod and the front end cover of the ultrasonic transducer is minimized by adjusting the rear section of the extrusion core rod.
(5) Modal simulation of ultrasonic vibration auxiliary hole extrusion strengthening device
Assembling an ultrasonic transducer and extrusion core rods of different improved schemes together to form an ultrasonic vibration auxiliary hole extrusion strengthening device, establishing a three-dimensional finite element simulation analysis model of the ultrasonic amplitude auxiliary hole extrusion strengthening device, carrying out modal analysis on the hole extrusion strengthening device, and exploring the relative amplitudes of the hole extrusion strengthening devices of different extrusion core rod structures.
(6) Ultrasonic vibration auxiliary hole extrusion strengthening device with optimal hole extrusion strengthening effect
The ultrasonic vibration auxiliary hole extrusion strengthening device with the best extrusion strengthening effect is preferably selected based on the indexes of small number of threaded connections, small relative amplitude at the threaded connections, large relative amplitude at the position of the extrusion core rod working ring and the like as the preferable standards.
The optimized ultrasonic vibration auxiliary hole extrusion strengthening device can improve the surface quality of the hole wall of the assembly hole of the porous structural member, improve the fatigue performance and prolong the service life.
Compared with the prior art, the invention has the following advantages:
1. the ultrasonic vibration auxiliary hole extrusion strengthening device combines the ultrasonic vibration technology and the hole extrusion strengthening technology, changes the linear motion of the extrusion core rod in the assembling hole into sine or cosine motion, increases the extrusion strengthening times of the hole wall of the assembling hole, and can improve the surface quality of the hole wall of the assembling hole.
2. In the ultrasonic vibration auxiliary hole extrusion pressure device, the amplitude transformer and the front end cover are integrated, so that the number of threaded connections is reduced, and the attenuation of ultrasonic energy is reduced.
3. The ultrasonic vibration auxiliary hole extrusion strengthening device has the advantages that the relative amplitude of the threaded connection part of the extrusion core rod and the front end cover is small, the thread loosening can be prevented, and the damage of ultrasonic vibration energy to the hole extrusion strengthening device is avoided.
4. The resonant frequency of the ultrasonic vibration auxiliary hole extrusion strengthening device and the resonant frequency of the ultrasonic transducer are close to the design frequency, and the relative amplitude of the hole extrusion strengthening device is maximum.
Drawings
FIG. 1 is a three-dimensional view of a solid extrusion core rod;
FIG. 2 is a flow chart of extrusion mandrel work ring diameter determination;
FIG. 3 is a half-wavelength ultrasonic transducer design model;
FIG. 4 is a schematic view of an ultrasound transducer;
FIG. 5 is an ultrasound transducer modality;
FIG. 6 is a mode shape of an ultrasound transducer after size optimization
FIG. 7 is a schematic view of a first modification of the extrusion core rod;
FIG. 8 is a schematic view of a second extrusion core rod modification;
FIG. 9 is a schematic view of a third extrusion core rod modification;
FIG. 10 is a schematic view of a fourth extrusion core rod modification;
FIG. 11 is a schematic view of a fifth extrusion mandrel modification;
FIG. 12 illustrates the mode of an ultrasonic vibration assisted hole extrusion enhancement device according to a first embodiment of the extrusion core rod;
FIG. 13 is a mode shape of the ultrasonic vibration assisted hole extrusion enhancement device after the extrusion core rod size is optimized;
FIG. 14 is a rule of the maximum relative amplitude of the ultrasonic vibration assisted hole extrusion enhancing apparatus influenced by the number of protrusions;
FIG. 15 is a maximum relative amplitude law of the impact of the convex radius on the ultrasonic vibration assisted hole extrusion strengthening device;
FIG. 16 is a rule of the maximum relative amplitude of the ultrasonic vibration assisted hole extrusion strengthening device affected by the length of the protrusions;
fig. 17 shows the mode of the ultrasonic vibration assisted hole extrusion strengthening device of the fifth extrusion core rod modification.
Wherein, the rear cone section-1; a working ring-2; a front cone section-3; a guide section-4; a connecting section-5; front end cover-6; an ultrasonic transducer flange-7; a piezoelectric ceramic piece-8; rear end cap-9; nodal surface-10; core rod front end-11; extruding the rear section-12 of the core rod; extruding the front section-13 of the core rod; a projection-14.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
Example 1 extrusion core rod sizing
FIG. 1 is a three-dimensional view of a solid extrusion core rod. The solid extrusion core rod mainly comprises: front cone section, working ring, back cone section, direction section. The front cone section 3, the working ring 2 and the rear cone section 1 are main parts for realizing extrusion strengthening of the assembly hole of the porous structural member.
Fig. 2 is a flow chart of the extrusion core rod sizing. The dimensions of the extrusion core rod are determined using fig. 2 based on the nominal bore diameter of the extruded workpiece and the relative extrusion amount. The dimensions of the extrusion mandrel were calculated taking as an example a nominal bore diameter 16/32in, with a relative extrusion amount of 5%.
The nominal hole diameter 16/32in is converted into a unit of 1in 25.4mm, and 16/32in 12.7mm is the final hole diameter D of the assembly hole of the extruded workpiecef12.7 mm. When the reaming amount of the hole wall of the assembly hole of the structural member after extrusion strengthening is less than 0.2mm, the reaming processing has small influence on the residual stress field formed on the hole wall after extrusion strengthening, so that the reaming amount of the hole wall after extrusion strengthening of the hole is 0.2mm, and the aperture of the assembly hole of the structural member after extrusion strengthening is 12.5 mm.
Knowing the amount of absolute reaming Ra, the final hole diameter DfPrimary pore diameter D0Relative extrusion amount ErThe rebound amount h has a relationship shown in formula (1):
Ra＝Df-D0(1+Er)+h (1)
the formula (1) is finished to obtain the variation relation of the initial pore diameter as shown in the formula (2):
based on the existing research results, when the relative extrusion amount is 5%, the functional relationship shown in the following formula exists between the initial hole diameter and the rebound amount:
h＝0.0175D0+0.015
will type initial hole diameter D0Substituting the functional relation between the elastic quantity h and the initial hole diameter D of the extruded workpiece into the formula (2)0＝12.12mm。
In the extrusion strengthening process of the direct hole of the extrusion core rod, a lining is not used, and the diameter D of the working ring of the extrusion core rod and the diameter D of the initial hole exist0Relative extrusion amount ErThe relationship between them is shown in formula (3):
D＝D0+Ea＝D0(1+Er) (3)
the diameter of an initial hole of a structural member assembling hole is 12.12mm, the relative extrusion amount is 5%, and the diameter D of the extrusion core rod working ring obtained by the formula (3) is 12.73 mm.
When the design frequency of the ultrasonic vibration hole extrusion strengthening device is set to be 30kHz, the material of the extrusion core rod in the ultrasonic vibration hole extrusion strengthening device is W6Mo5Cr4V2, and the sound velocity of the material is calculated by using the formula (4).
Wherein c is the material sound velocity; e is the elastic modulus of the material; ρ is the density of the material.
The elastic modulus E of the W6Mo5Cr4V2 material is 218GPa, and the density rho is 7.75g/cm3The sound velocity of the W6Mo5Cr4V2 material is 5303.68 m/s.
The design frequency of the hole extrusion strengthening device is 30kHz, the sound velocity c of the W6Mo5Cr4V2 material is 5303.68m/s, and the longitudinal wave wavelength is calculated by using the formula (5).
In the formula, lambda is the longitudinal wave wavelength; f is the design frequency.
The wavelength λ of the longitudinal wave acoustic wave obtained by the formula (5) was 176.789 mm.
Determining the longitudinal ultrasonic vibration wavelength of the extrusion core rod material by a wavelength theorem, namely the propagation distance of the wave in one vibration period, and obtaining the length of the extrusion core rod:
when the fixed frequency of the hole extrusion strengthening device is 30kHz, the longitudinal wave wavelength lambda of the W6Mo5Cr4V2 material is 176.789mm, namely the length of the extrusion core rod is 176.789 mm.
When the fixed frequency of the hole extrusion strengthening device is 25kHz, the longitudinal wave wavelength lambda of the W6Mo5Cr4V2 material is 212.147mm, namely the length of the extrusion core rod is 212.147 mm.
When the fixed frequency of the hole extrusion strengthening device is 20kHz, the longitudinal wave lambda of the W6Mo5Cr4V2 material is 265.184mm, and the length of the extrusion core rod is 265.184 mm.
Based on the size of the extruded workpiece, the stroke of the ultrasonic vibration auxiliary hole extrusion strengthening device in the clamp is selected, the fixed frequency of the ultrasonic vibration auxiliary hole extrusion strengthening device is 20kHz, and the length of the extrusion core rod is 265.184 mm.
Example 2 ultrasound transducer sizing
Fig. 3 is a design model of a half-wavelength ultrasonic transducer, and referring to fig. 3, the ultrasonic transducer is composed of a front end cover 6, a piezoelectric ceramic plate 8 and a rear end cover 9.
According to the working requirements of the ultrasonic vibration auxiliary hole extrusion strengthening device, the material of the piezoelectric ceramic piece is PZT-8, the diameter of the piezoelectric ceramic piece is 25mm, the inner diameter of the piezoelectric ceramic piece is 10mm, the thickness of the piezoelectric ceramic piece is 4mm, and the number of the piezoelectric ceramic pieces is 4. The node of the ultrasonic transducer is arranged on the right side of the piezoelectric ceramic piece, the ultrasonic transducer is regarded as a uniform and continuous elastic body (namely a uniform elastic rod), waves are reflected on the end face of the uniform elastic rod, the reflected waves and the existing waves are superposed, and the ultrasonic vibration energy is increased.
The wave equation of the uniform rod vibration is shown in equation (6).
In the formula, xi is an axial coordinate of a certain point on the uniform rod; t is time; c is the longitudinal wave velocity.
The solution of the longitudinal wave equation can be obtained as shown in equation (7):
ξ(x,t)＝(A2 cosωt+B2sinωt)·(Acoskx+Bsinkx) (7)
the ultrasonic transducer is a uniform and continuous elastomer, and the elastomer meets Hooke's law F ═ keΔ x, yielding the relationship shown in formula (8):
in the formula, F is the stress of a certain point in the uniform rod; s is the cross-sectional area of the uniform elastic rod; k is the number of circles, k is omega/c is 2 pi/lambda; λ is the longitudinal wave wavelength.
Let m (t) be A2cosωt+B2sin ω t, m (t) is a function of t, indicating that the vibration of the uniform rod varies with time. The vibration at different points on the uniform elastic rod with a constant time is expressed by the following equations (9) and (10):
ξ(x)＝m(Acoskx+Bsinkx) (9)
in the formula, m is a constant.
Regard as the stiff end with nodal plane 10 one side, the even elastic rod of free end is regarded as to the opposite side, and the free end displacement volume of even elastic rod is big, and the power that receives is little, and the displacement of stiff end is zero, sets up the origin of coordinates on the contact surface of rear end cap 9 and piezoceramics piece 8, and the boundary condition of the even pole of elasticity is shown as formula (11):
the frequency formula of the ultrasonic transducer obtained by substituting the boundary conditions into the equations (9) and (10) is shown as the formula (12):
where Z ═ ρ cS is the acoustic characteristic impedance of each part of the ultrasonic transducer.
Equation (12) is a design equation of the ultrasonic transducer. Based on equation (12), the length of the ultrasonic transducer rear end cap 9 is 36.7835 mm. Since the nodal plane 10 is on the right side of the piezoceramic wafer 8, the size of the front end cap 6 is 1/4 of the longitudinal wave wavelength, i.e. the size of the front end cap 6 is 64.4455 mm.
Example 3 ultrasound transducer Modal simulation
Fig. 4 is a schematic view of an ultrasound transducer. Based on the size and material of each part of the ultrasonic transducer, a three-dimensional finite element simulation model of the ultrasonic transducer is established, the established model is subjected to modal simulation, and the modal simulation result of the ultrasonic transducer is shown in fig. 5.
From the results of the ultrasonic transducer modal simulation, it can be seen that when the length of the rear end cover 9 is 36mm and the size of the front end cover 6 is 64mm, the resonant frequency of the ultrasonic transducer is 21717.3Hz, and deviates from the set design frequency. By optimizing the sizes of the front end cover and the rear end cover, the resonant frequency of the ultrasonic transducer approaches to the design frequency. The mode of the ultrasound transducer after size optimization is shown in fig. 6.
Optimized ultrasonic transducer dimensions: when the rear end cover 9 is 36mm and the front end cover 6 is 73mm, the resonant frequency of the ultrasonic transducer is 19958.3Hz, and the resonant frequency of the ultrasonic transducer approaches the design frequency.
EXAMPLE 4 extrusion core rod modifications
In order to change the amplitude of the ultrasonic vibration auxiliary hole extrusion strengthening device, the ultrasonic vibration effect in the hole extrusion strengthening process is obviously improved. By optimizing the structure of the extrusion core rod, the resonant frequency of the hole extrusion strengthening device is controlled to approach to the design frequency, and the ultrasonic amplitude of the hole extrusion strengthening device is increased.
1) The first improvement scheme of the extrusion core rod is as follows: the diameter of the extrusion mandrel working ring 2 is larger than the diameter of an assembly hole of an extruded workpiece, the front end 11 of the extrusion mandrel is connected with the front end cover 6 of the ultrasonic transducer, in order to avoid ultrasonic energy loss, the diameter of the front end of the extrusion mandrel is the same as that of the front end of the ultrasonic transducer, the diameter of the front end 11 of the extrusion mandrel is larger than that of the assembly hole of the extruded workpiece, therefore, the extrusion mandrel needs to be disconnected, the extrusion mandrel is divided into an extrusion mandrel front section 13 and an extrusion mandrel rear section 12, the extruded workpiece is placed to an extrusion mandrel guide section 4 from the disconnected position, and the disconnected position of the extrusion mandrel is connected by threads. A schematic diagram of a first extrusion mandrel modification is shown in fig. 7.
2) The second improvement scheme of the extrusion core rod: based on the first extrusion core rod improvement scheme, the protrusions 14 are added on the extrusion core rod, the diameter and the length of the protrusions are controlled to be unchanged, the number of the protrusions is changed, the influence of the number of the protrusions on the maximum relative amplitude of the hole extrusion strengthening device is analyzed, and a schematic diagram of the second extrusion core rod improvement scheme is shown in fig. 8. In fig. 8, the number of the protrusions of the extrusion core rod is 3, the diameter of the protrusions is 14mm, the length of the protrusions is 6mm, and the distance between the protrusions is 8 mm.
3) The third improvement scheme of the extrusion core rod is as follows: based on the first extrusion core rod improvement scheme, the number of the protrusions and the protrusion length are controlled to be unchanged, the diameter of the protrusions added on the extrusion core rod is changed, the influence of the protrusion diameter on the maximum relative amplitude of the hole extrusion strengthening device is analyzed, and a third extrusion core rod improvement scheme is schematically illustrated in fig. 9. In FIG. 9, the number of the protrusions of the extrusion core rod is 1, the diameter of the protrusion is 14mm, and the length of the protrusion is 6 mm.
4) The extrusion core rod is improved in the following scheme: based on the first extrusion core rod improvement scheme, the number of the protrusions and the diameter of the protrusions are controlled, the length of the protrusions added on the extrusion core rod is changed, the influence of the length of the protrusions on the maximum relative amplitude of the hole extrusion strengthening device is analyzed, and a schematic diagram of a fourth extrusion core rod improvement scheme is shown in fig. 10. In FIG. 10, the number of projections of the extrusion core rod is 1, the diameter of the projection is 14mm, and the length of the projection is 20 mm.
5) The extrusion core rod is improved in the fifth scheme: based on the first improvement scheme of the extrusion core rod, the front end of the extrusion core rod and the front end cover of the ultrasonic transducer are combined into a whole, so that threaded connection is reduced, and ultrasonic energy attenuation is reduced. The relative amplitude of the joint of the rear section of the extrusion core rod and the front end cover of the ultrasonic transducer is minimized by adjusting the rear section of the extrusion core rod. A schematic diagram of a modified extrusion core rod is shown in fig. 11.
Example 5 extrusion core rod configuration optimization
Assembling an ultrasonic transducer with the extrusion core rods of different improved schemes recorded in the embodiment 4 to form an ultrasonic vibration auxiliary hole extrusion strengthening device, establishing a three-dimensional finite element simulation analysis model of the ultrasonic vibration auxiliary hole extrusion strengthening device, performing modal analysis on the hole extrusion strengthening device, and exploring the maximum relative amplitudes of the hole extrusion strengthening devices of different extrusion core rod structures.
1) Improved scheme one of extrusion core rod
The mode of the ultrasonic vibration assisted hole extrusion strengthening device of the first extrusion core rod modification is shown in fig. 12, and the resonant frequency of the hole extrusion strengthening device is 18693.2Hz, which is greatly different from the set design frequency. The size of the extrusion core rod is optimized, so that the resonant frequency of the hole extrusion strengthening device approaches to the design frequency. The mode of the ultrasonic vibration assisted hole extrusion strengthening device after the extrusion core rod is optimized in size is shown in fig. 13.
2) Improved scheme two of extrusion core rod
Based on the first improvement scheme of the extrusion mandrel, the number of the protrusions is changed by adding the protrusions on the extrusion mandrel, controlling the diameter and the length of the protrusions to be unchanged, and obtaining a rule that the maximum relative amplitude of the number of the protrusions on the hole extrusion strengthening device is influenced is shown in fig. 14.
With the increasing number of the protrusions, the maximum relative amplitude of the hole extrusion strengthening device is increased gradually and then decreased sharply. When the number of the bulges is 2, the position of the bulges is at the position with the minimum relative amplitude, the maximum relative amplitude of the hole extrusion strengthening device reaches the maximum, and when the position of the bulges is far away from the position with the minimum relative amplitude, the maximum relative amplitude of the hole extrusion strengthening device shows a decreasing trend.
3) Improved scheme three of extrusion core rod
Based on the second improved scheme of the extrusion core rod, the number of the protrusions is controlled to be 2, the length of the protrusions is controlled to be 6mm, the radius of the protrusions added on the extrusion core rod is changed, and the rule of the maximum relative amplitude influence of the obtained radius of the protrusions on the hole extrusion strengthening device is shown in fig. 15.
Along with the gradual increase of the radius of the bulge, the maximum relative amplitude of the hole extrusion strengthening device is in positive correlation with the radius of the bulge, and the maximum relative amplitude increase amplitude of the hole extrusion strengthening device is small.
4) Improved scheme of extrusion core rod
Based on the first improvement scheme of the extrusion core rod, the number of the protrusions is controlled to be 1, the diameter of each protrusion is 10mm, the length of the protrusion added on the extrusion core rod is changed, and the rule of the maximum relative amplitude influence of the obtained protrusion length on the hole extrusion strengthening device is shown in fig. 16.
The maximum relative amplitude of the hole extrusion strengthening device is gradually increased and then sharply decreased along with the gradual increase of the length of the protrusion, and when the diameter of the protrusion is 10mm and the length of the protrusion is 25mm, the maximum relative amplitude of the hole extrusion strengthening device is assisted by ultrasonic amplitude to reach the maximum value.
5) Improved scheme five of extrusion core rod
The first to the fourth extrusion core rod improvement schemes are that two parts of the ultrasonic vibration auxiliary hole extrusion strengthening device are in threaded connection, the front section of the extrusion core rod is in threaded connection with the front end cover of the ultrasonic transducer, and the rear section of the extrusion core rod is in threaded connection with the front section of the extrusion core rod. The screw joint between the rear end of the extrusion mandrel and the front end of the extrusion mandrel is a position at which the relative amplitude of the hole extrusion reinforcement device is maximum. The threaded connection attenuates ultrasonic energy, reduces the maximum relative amplitude of the hole extrusion strengthening device, and reduces the extrusion strengthening effect of the structural member assembly hole. The threaded connection is at the maximum relative amplitude position of the hole extrusion strengthening device, so that the threaded connection is loosened or the bolt is broken, and the hole extrusion strengthening device is damaged.
Therefore, the front section of the extrusion core rod and the front end cover of the ultrasonic transducer are combined into a whole, and threaded connection is reduced. By optimizing the size of the extrusion core rod, the relative amplitude of the threaded connection part of the extrusion core rod and the front end cover of the ultrasonic transducer is minimized. The mode of the ultrasonic vibration auxiliary hole extrusion strengthening device of the fifth extrusion core rod improvement scheme is shown in fig. 17.
In the fifth extrusion core rod improvement scheme, only one threaded connection is arranged, the relative amplitude of the threaded connection is small, the resonant frequency of the hole extrusion strengthening device approaches to the design frequency, and the relative amplitude of the position of the working ring of the extrusion core rod is 2.93586 micrometers.
In summary, the ultrasonic vibration hole extrusion strengthening device for obtaining the fifth extrusion core rod improvement scheme is optimal and the hole extrusion strengthening effect of the structural member assembly hole is optimal by taking the indexes of small number of threaded connections, small relative amplitude at the threaded connections, large relative amplitude at the position of the extrusion core rod working ring and the like as the optimal standards.
Claims (10)
1. The utility model provides an ultrasonic vibration auxiliary hole extrusion reinforcing apparatus which characterized in that, is including the extrusion plug, amplitude transformer and the ultrasonic transducer who connects gradually, and ultrasonic transducer is connected to the power, wherein:
the extrusion core rod is a solid extrusion core rod; the extrusion plug from preceding to back includes in proper order: a front end (11), a front section (13) and a rear section (12) of the core rod;
the ultrasonic transducer comprises from front to back: the piezoelectric ceramic and rear end cover (9);
the front end (11) of the extrusion core rod is connected with the front end cover (6) of the ultrasonic transducer, and in order to avoid ultrasonic energy loss, the diameter of the front end of the extrusion core rod is the same as that of the front end of the ultrasonic transducer;
the amplitude transformer and the front end cover of the ultrasonic transducer are integrated.
2. The ultrasonic vibration assisted hole extrusion strengthening device of claim 1, wherein the extrusion core rod is segmented, wherein the front section is in threaded connection with the front end cover of the ultrasonic transducer, and the rear section is in threaded connection with the front section of the extrusion core rod.
3. The ultrasonic vibration assisted hole extrusion strengthening device of claim 1, wherein the extrusion core rod is provided with 1-2 protrusions, the diameter of the protrusions and the length of the protrusions are suitable for achieving the maximum relative amplitude of the ultrasonic amplitude assisted hole extrusion strengthening device to the maximum value.
4. The ultrasonic vibration auxiliary hole extrusion strengthening device as claimed in claim 1, wherein the size of the ultrasonic transducer is calculated based on a half-wavelength theory, the node of the ultrasonic transducer is on the right side of the piezoelectric ceramic plate, and the size of the front end cover is 1/4 of the longitudinal wave wavelength.
5. The operation process of the ultrasonic vibration assisted hole extrusion strengthening device of claim 1, which is characterized by comprising the following steps:
(1) turning on an ultrasonic power supply to output a high-frequency oscillation electric signal, and receiving the electric signal and converting the electric signal into mechanical vibration by a piezoelectric ceramic transducer; the amplitude transformer transmits the vibration to the extrusion core rod;
(2) the diameter of the thread of the rear section (12) of the extrusion core rod is smaller than that of the assembly hole of the extruded workpiece, and the extruded workpiece is placed on the guide section of the extrusion core rod from the rear section of the extrusion core rod;
(3) in the process of extruding and strengthening the ultrasonic vibration hole, the ultrasonic vibration converts the linear motion of the extrusion core rod in the assembly hole into sine motion or cosine motion, changes the motion track of the extrusion core rod and increases the extrusion times of the working ring of the extrusion core rod on the hole wall of the assembly hole of the structural member;
the relative amplitude of the position of the working ring of the extrusion core rod is large, and the relative amplitude of the threaded connection position of the extrusion core rod and the ultrasonic transducer is minimum.
6. The design method of the ultrasonic vibration assisted hole extrusion strengthening device of claim 1 is characterized by comprising the following steps:
(1) determining the size of the extrusion core rod;
(2) ultrasonic transducer sizing;
(3) simulating the mode of the ultrasonic transducer; constructing a three-dimensional finite element simulation model of the ultrasonic transducer based on the size and material properties of the ultrasonic transducer obtained in the step (2), performing modal simulation on the established ultrasonic transducer, comparing the resonant frequency of the ultrasonic transducer with the design frequency of the ultrasonic vibration auxiliary hole extrusion strengthening device, and approaching the resonant frequency of the ultrasonic transducer to the design frequency of the device by adjusting the sizes of the front end cover and the rear end cover of the ultrasonic transducer when the resonant frequency of the ultrasonic transducer deviates from the design frequency of the hole extrusion strengthening device;
(4) optimizing and improving the structure of the extrusion core rod: by optimizing the structure of the extrusion core rod, the resonant frequency of the hole extrusion strengthening device is controlled to approach to the design frequency, and the ultrasonic amplitude of the hole extrusion strengthening device is increased;
(5) performing modal simulation on the ultrasonic vibration auxiliary hole extrusion strengthening device; assembling an ultrasonic transducer with the extrusion core rods of different improved schemes in the step (4) to form an ultrasonic vibration auxiliary hole extrusion strengthening device, establishing a three-dimensional finite element simulation analysis model of the ultrasonic amplitude auxiliary hole extrusion strengthening device, carrying out modal analysis on the hole extrusion strengthening device, and exploring the relative amplitudes of the hole extrusion strengthening devices of different extrusion core rod structures;
(6) the ultrasonic vibration auxiliary hole extrusion strengthening device with the best hole extrusion effect is preferred.
7. The design method of ultrasonic vibration assisted hole extrusion strengthening device of claim 6, wherein the step (1) of determining the size of the extrusion core rod comprises the following steps:
(1.1) calculating the diameter of the working ring of the extrusion core rod based on the nominal aperture and the relative extrusion amount of the extruded workpiece;
the final hole diameter of the extruded workpiece can be obtained by unit conversion according to the nominal hole diameter. When the reaming amount of the hole wall of the assembly hole of the structural member after extrusion strengthening is not more than 0.2mm, the reaming processing has no influence on the residual stress field formed on the hole wall, so that the reaming amount of the hole wall of the assembly hole of the structural member after extrusion strengthening is 0.2mm, and the aperture of the assembly hole of the structural member after extrusion strengthening is obtained;
knowing the amount of absolute reaming Ra, the final hole diameter DfPrimary pore diameter D0Relative extrusion amount ErThe rebound amount h has a relationship shown in formula (1):
Ra＝Df-D0(1+Er)+h (1)
the formula (1) is finished to obtain the variation relation of the initial pore diameter as shown in the formula (2):
obtaining a functional relation between the initial hole diameter and the resilience amount through a fitting formula, substituting the functional relation into the formula (2), and obtaining the initial hole diameter D of the structural member assembling hole0；
In the extrusion strengthening process of the direct hole of the extrusion core rod, the diameter D of the working ring of the extrusion core rod and the diameter D of the initial hole exist without using a lining0Relative extrusion amount ErThe relationship between them is shown in formula (3):
D＝D0+Ea＝D0(1+Er) (3)
calculating the diameter D of the working ring of the extrusion core rod by using the formula (3) according to the initial hole diameter and the relative extrusion amount of the assembly hole of the structural member;
(1.2) setting the design frequency of the ultrasonic vibration hole extrusion strengthening device, and calculating the sound velocity of the material by using the formula (4) according to the mechanical property of the extrusion core rod material:
wherein c is the material sound velocity; e is the elastic modulus of the material; ρ is the density of the material;
calculating the longitudinal wave wavelength by using the design frequency of the hole extrusion strengthening device and the sound velocity of the material according to the formula (5):
in the formula, lambda is the longitudinal wave wavelength; f is the design frequency;
and determining the longitudinal ultrasonic vibration wavelength of the extrusion core rod material by using a wavelength theorem, namely the propagation distance of the wave in one vibration period, and obtaining the length of the extrusion core rod.
8. The design method of ultrasonic vibration assisted hole extrusion coating apparatus of claim 6, wherein (2) ultrasonic transducer sizing comprises the steps of:
the node of the ultrasonic transducer is arranged on the right side of the piezoelectric ceramic piece, the ultrasonic transducer is used as a continuous elastomer, and the wave equation of the vibration of the uniform rod of the continuous elastomer is shown as the formula (6):
in the formula, xi is an axial coordinate of a certain point on the uniform rod; t is time; c is the longitudinal wave velocity;
the solution of the longitudinal wave equation can be obtained as shown in equation (7):
ξ(x,t)＝(A2cosωt+B2sinωt)·(Acoskx+Bsinkx) (7)
the ultrasonic transducer is a continuous elastomer, and the elastomer meets Hooke's law F ═ keΔ x, yielding the relationship shown in formula (8):
in the formula, F is the stress of a certain point in the uniform rod; s is the cross-sectional area of the uniform rod; k is the number of circles, k is omega/c is 2 pi/lambda; λ is the longitudinal wave wavelength;
let m (t) be A2cosωt+B2sin ω t, m (t) is a function of t, indicating that the vibration of the uniform rod varies with time; the vibration at different points on the uniform rod with a constant time is expressed by the following equations (9) and (10):
ξ(x)＝m(Acoskx+Bsinkx) (9)
wherein m is a constant;
designing an ultrasonic transducer by utilizing a half-wavelength theorem, and establishing an ultrasonic transducer design model;
regard as the stiff end with nodal plane one side, the even elastic rod of free end is regarded as to one side, and the free end displacement volume of even pole is big, and the power that receives is little, and the displacement of stiff end is zero, sets up the origin of coordinates on the contact surface of rear end cap and piezoceramics piece, and the boundary condition of elasticity even pole is shown as formula (11):
the frequency formula of the ultrasonic transducer obtained by substituting the boundary conditions into the equations (9) and (10) is shown as the formula (12):
where Z ═ ρ cS is the acoustic characteristic impedance of each part of the ultrasonic transducer. Equation (13) is the design equation for the transducer;
based on the design equation of the ultrasonic transducer, the length of the rear end cover can be obtained; the nodal plane is arranged on the right side of the piezoelectric ceramic plate, and the size of the front end cover is 1/4 of the wavelength of the longitudinal wave, so that the size of each part of the ultrasonic transducer can be obtained.
9. The design method of the ultrasonic vibration assisted hole extrusion strengthening device of claim 6, wherein (4) the extrusion core rod structure is optimized and improved, and the method comprises the following steps:
1) the first improvement scheme of the extrusion core rod is as follows: the extrusion core rod is disconnected, the extrusion core rod is divided into two parts, namely a front extrusion core rod section and a rear extrusion core rod section, an extruded workpiece is placed to the extrusion core rod guide section from the position, where the diameter of the rear extrusion core rod section is smaller than that of the structural member assembling hole, of the extrusion core rod, and the extrusion core rod is connected at the disconnected position by using threads;
2) the second improvement scheme of the extrusion core rod: based on the first improvement scheme of the extrusion core rod, the protrusions are added on the extrusion core rod, the diameter and the length of the protrusions are controlled to be unchanged, the number of the protrusions is changed, and the influence of the number of the protrusions on the maximum relative amplitude of the hole extrusion strengthening device is analyzed;
3) the third improvement scheme of the extrusion core rod is as follows: based on the first extrusion core rod improvement scheme, the number of the bulges and the length of the bulges are controlled to be unchanged, the diameter of the bulges added on the extrusion core rod is changed, and the influence of the diameter of the bulges on the maximum relative amplitude of the hole extrusion strengthening device is analyzed;
4) the extrusion core rod is improved in the following scheme: based on the first extrusion core rod improvement scheme, the number and the diameter of the protrusions are controlled, the length of the protrusions added on the extrusion core rod is changed, and the influence of the length of the protrusions on the maximum relative amplitude of the hole extrusion strengthening device is analyzed;
5) the extrusion core rod is improved in the fifth scheme: based on the first improvement scheme of the extrusion core rod, the front end of the extrusion core rod and the front end cover of the ultrasonic transducer are combined into a whole, so that threaded connection is reduced, and ultrasonic energy attenuation is reduced; the relative amplitude of the joint of the rear section of the extrusion core rod and the front end cover of the ultrasonic transducer is minimized by adjusting the rear section of the extrusion core rod.
10. The design method of the ultrasonic vibration auxiliary hole extrusion strengthening device according to claim 6, wherein the step (6) of optimizing the ultrasonic vibration auxiliary hole extrusion strengthening device with the best hole extrusion effect is based on the indexes of small number of threaded connections, small relative amplitude at the threaded connections, large relative amplitude at the position of the extrusion core rod working ring and the like as the optimization standards, and the optimized ultrasonic vibration auxiliary hole extrusion strengthening device can improve the surface quality of the wall of the assembly hole of the porous structural member, improve the fatigue performance and prolong the service life.
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