Two-dimensional adjustable ultrasonic vibration assisted cutting device

Abstract

The application relates to a two-dimensional adjustable ultrasonic vibration auxiliary cutting device which comprises a vibration flat plate, a supporting base, four supporting columns, a stepped horn a, a stepped horn b, a longitudinal vibration piezoelectric transducer a and a longitudinal vibration piezoelectric transducer b. The vibration flat plate is of a stepped structure. The four supporting columns are vertically arranged, the upper ends of the four supporting columns are fixedly connected with the four corners of the vibration flat plate respectively, and the lower ends of the four supporting columns are fixedly connected with the supporting base simultaneously. The stepped horn a and the stepped horn b are horizontally arranged. The small end of the stepped horn a is fixedly connected with the center position of the left side surface of the vibration flat plate perpendicularly, and the large end is fixedly connected with the longitudinal vibration piezoelectric transducer a. The small end of the stepped horn b is fixedly connected with the center position of the back side surface of the vibration flat plate perpendicularly, and the large end is fixedly connected with the longitudinal vibration piezoelectric transducer b. The device has the characteristics of simple structure, less energy dissipation and good machining stability, and can realize efficient and low-damage milling and pin machining.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of ultrasonic machining, and relates to a two-dimensional adjustable ultrasonic vibration auxiliary cutting device. BACKGROUND

[0002] A two-dimensional ultrasonic vibration cutting system is generally composed of an ultrasonic transducer, an amplitude transformer, a workpiece and a tool, and functions to convert high-frequency electrical signals output by an ultrasonic power supply into high-frequency mechanical vibration displacement through the transducer, and then amplify the high-frequency mechanical vibration displacement through the amplitude transformer, so as to form high-frequency vibration between the workpiece and the tool, and then complete ultrasonic cutting. According to different positions of ultrasonic excitation application, the ultrasonic vibration cutting system can be divided into two forms of tool vibration and workpiece vibration.

[0003] In actual production process, a strategy more widely adopted is to apply ultrasonic vibration to the tool, that is, to use a rotary ultrasonic tool holder to perform cutting machining. However, the cutting edge motion trajectory under this strategy is more complex, and it is difficult to effectively analyze the influence of each factor separately.

[0004] Patent CN109227152A discloses a two-dimensional vibration table for precise ultrasonic machining, which comprises two ultrasonic vibration devices, a vibration table, and a clamp. One ultrasonic vibration device is fixed on each of the two adjacent side surfaces of the vibration table, the two ultrasonic vibration devices are perpendicular to each other and are supported by vibration device support frames, the bottom of each vibration device support frame is fixed to a base, and the clamp is fixed on the node surface of the ultrasonic waves emitted by the two ultrasonic vibration devices on the top surface of the vibration table. The clamp is a group and cannot be too large in size. The vibration table realizes elliptical motion under the excitation of the two ultrasonic vibration devices. A vibration table support frame is installed between the bottom surface of the vibration table and the base. The vibration table support frame is a point support frame or a plate support frame. The point support frame is installed at the center of the bottom surface of the vibration table and is composed of a column and a support ball. The support ball is fixed to the top surface of the column, the bottom surface of the column is fixed to the base, and the support ball is in contact with the bottom surface of the vibration table but is not fixedly connected thereto. The plate support frame is a support plate fixed to one side of the bottom surface of the vibration table. The bottom surface of the support plate is fixed to the base, and the top surface of the support plate is in contact with the bottom surface of the vibration table but is not fixedly connected thereto.

[0005] Since the vibration table support frame of patent CN109227152A is a point support frame or a plate support frame, energy dissipation is small, but there is a problem of poor machining stability, which affects the machining quality and makes it difficult to realize efficient and low-damage milling and pin machining.

[0006] Therefore, it is necessary to study a two-dimensional ultrasonic vibration cutting system with the characteristics of small energy dissipation and good machining stability, so as to realize efficient and low-damage milling and pin machining. SUMMARY

[0007] The application aims to solve the problems in the prior art and provide a two-dimensional adjustable ultrasonic vibration auxiliary cutting device.

[0008] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0009] The two-dimensional adjustable ultrasonic vibration auxiliary cutting device comprises a vibration plate, a supporting base, four supporting columns, a stepped amplitude transformer a, a stepped amplitude transformer b, a longitudinal vibration piezoelectric transducer a and a longitudinal vibration piezoelectric transducer b.

[0010] The vibration plate is a square plate placed horizontally and comprises a front side, a back side, a left side and a right side.

[0011] The vibration plate is provided with square grooves I and II arranged symmetrically and at intervals.

[0012] The square groove I has an upward opening, and is surrounded by a left side wall, a back side wall and a bottom wall located below the two walls. The front edge of the bottom wall is coplanar with the front side of the vibration plate, the intersection of the front edge and the right edge of the bottom wall is located on the intersection line of the front side and the right side of the vibration plate, and the length of the front edge of the bottom wall is less than the side length of the vibration plate.

[0013] The supporting base is located below the vibration plate and is arranged at an interval therefrom.

[0014] The four supporting columns are vertically placed, the upper ends of the four supporting columns are fixedly connected with the four corners of the vibration plate respectively, and the lower ends of the four supporting columns are fixedly connected with the supporting base simultaneously.

[0015] The stepped amplitude transformer a and the stepped amplitude transformer b are placed horizontally. The small end of the stepped amplitude transformer a is fixedly connected with the center position of the left side of the vibration plate vertically, and the large end is fixedly connected with the longitudinal vibration piezoelectric transducer a. The small end of the stepped amplitude transformer b is fixedly connected with the center position of the back side of the vibration plate vertically, and the large end is fixedly connected with the longitudinal vibration piezoelectric transducer b.

[0016] The present application solves the problem of poor machining stability of the patent CN109227152A by designing four vertically placed supporting columns, the upper ends of the four supporting columns are fixedly connected with the four corners of the vibration plate respectively, and the lower ends of the four supporting columns are fixedly connected with the supporting base simultaneously. However, this will cause more energy dissipation, only by combining the characteristics of less energy dissipation and good machining stability can high-efficiency low-damage milling and pinning be realized. Therefore, the amplitude transformer is designed as a stepped amplitude transformer, and the vibration plate is designed as a stepped vibration plate, forming a two-stage amplitude modulation effect, which makes up for the energy dissipation caused by the four supporting columns.

[0017] The workpiece vibration form is adopted in the application, high-frequency ultrasonic vibration movement is separated from tool rotation movement, and the stability of the whole system is improved. The two-dimensional adjustable ultrasonic vibration auxiliary cutting device designed in the application adopts a double-excitation-source ultrasonic vibration system. Two groups of longitudinal vibration piezoelectric transducers are arranged orthogonally to generate two mutually perpendicular simple harmonic vibrations, and the two groups of transducers are driven respectively. By adjusting the phase difference between the two vibration signals of the ultrasonic vibration system and the output power of each, the purpose of changing the two-direction ultrasonic vibration parameters and form can be achieved. The two groups of longitudinal vibration piezoelectric transducers are connected with two-direction amplitude-varying rods respectively to drive the amplitude-varying rods to vibrate longitudinally. The vibration signals are amplified by the amplitude-varying rods and then transmitted to the vibration platform. The two-direction vibration signals are coupled on the vibration platform to make the vibration platform generate the required movement track through the vibration superposition principle. The amplitude-varying rods and the vibration platform are fixedly connected, and the whole platform works in a harmonic mode. Compared with a non-harmonic mode, the harmonic mode can give the ultrasonic vibration platform a higher working frequency and energy efficiency.

[0018] In actual ultrasonic vibration, the vibration amplitude directly output by the ultrasonic transducer is very small and far from the actual application requirement, so the amplitude-varying rod is needed to concentrate and amplify the ultrasonic amplitude. In order to maximize the amplification effect of the amplitude and reduce the half-wave resonance length, the stepped amplitude-varying rod is adopted in the application. The stepped amplitude-varying rod is the simplest to design and manufacture. When the area coefficient (the large-end diameter / small-end diameter) is constant, the amplitude amplification coefficient is maximum and the half-wave resonance length is shortest. Figure 1 As shown in the figure, the large-end diameter of the stepped amplitude-varying rod is D, the length is a, the cross-sectional area is A1, the small-end diameter is d, the length is b, the cross-sectional area is A2, and the total length of the amplitude-varying rod is l=a+b. K is the circular wave number, K=ω / c, ω is the circular frequency, and c is the propagation speed of the longitudinal wave in the thin rod. Therefore, the amplitude amplification coefficient of the stepped amplitude-varying rod is: Mp=(A1sin(Ka)) / (A2sin(Kb)).

[0019] In order to expand the adjustment range of the two-direction ultrasonic amplitude, the vibration platform is also designed in a stepped form, so as to cooperate with the stepped amplitude-varying rod to form a two-stage amplification effect and amplify the vibration signal output by the amplitude-varying rod again.

[0020] The vibration platform is in a stepped form, that is, square grooves I and square grooves II of a certain size are arranged symmetrically and at intervals at a certain position of the square plate-shaped vibration platform. The vibration energy can also be amplified when passing through different cross-sectional positions of the vibration platform, so as to realize two-stage amplification.

[0021] In addition, the fixed connection of the stepped amplitude-varying rod and the vibration platform can also withstand a higher working frequency, so as to reduce the half-wave resonance length.

[0022] The two-dimensional adjustable ultrasonic vibration auxiliary cutting device of the application is characterized in that the effective ultrasonic vibration region is a two-dimensional plane, and the vibration is a typical two-dimensional elliptical motion; the vibration amplitude is adjustable, and the vibration signal is amplified through a variable amplitude rod and a stepped vibration plate to form two-stage amplitude modulation.

[0023] As a preferred technical solution,

[0024] The two-dimensional adjustable ultrasonic vibration auxiliary cutting device is characterized in that the edge length of the vibration plate is 203 mm, and the thickness is 32 mm.

[0025] The two-dimensional adjustable ultrasonic vibration auxiliary cutting device is characterized in that the front edge length of the bottom wall of the square groove I is 142 mm, and the depth of the square groove I is 8 mm.

[0026] The two-dimensional adjustable ultrasonic vibration auxiliary cutting device is characterized in that the left side wall and the rear side wall, the left side wall and the bottom wall, and the rear side wall and the bottom wall of the square groove I are circularly transitioned.

[0027] The two-dimensional adjustable ultrasonic vibration auxiliary cutting device is characterized in that the length of the four supporting columns is 115 mm.

[0028] The structure and size design idea of the vibration plate (as shown in Figure 2 and Figure 3 ) of the application will be described below:

[0029] The size of the vibration plate is 203 mm x 203 mm x 32 mm, which has good symmetry when the vibration signal is input from the two sides, and is conducive to realizing stable elliptical motion; at the same time, the vibration plate adopts a stepped shape, which cooperates with the variable amplitude rod to form two-stage amplitude modulation, so as to improve the vibration energy; the effective vibration region size is 142 mm x 142 mm, so that the energy is more concentrated; the length of the four supporting columns of the bottom surface of the plate is 115 mm, which can effectively control the position of the vibration plate and improve the processing stability.

[0030] The two-dimensional adjustable ultrasonic vibration auxiliary cutting device is characterized in that the four supporting columns are double-headed studs; each of the four corners of the vibration plate is provided with a threaded hole a, and the area corresponding to the four corners of the vibration plate in the supporting base is provided with a threaded hole b; one end of the double-headed stud is inserted into the threaded hole a, and the other end is inserted into the threaded hole b.

[0031] The two-dimensional adjustable ultrasonic vibration auxiliary cutting device is characterized in that the center distance between any two adjacent threaded holes a is 160 ± 0.25 mm.

[0032] The two-dimensional adjustable ultrasonic vibration auxiliary cutting device is characterized in that the supporting base is a horizontally placed square plate with a side length of 203 mm and a thickness of 32 mm.

[0033] The two-dimensional adjustable ultrasonic vibration auxiliary cutting device as described above, a U-shaped groove is opened on the support base, the size of which matches the machine tool workbench, thereby realizing the fixation of the two-dimensional adjustable ultrasonic vibration auxiliary cutting device.

[0034] The two-dimensional adjustable ultrasonic vibration auxiliary cutting device as described above, the shapes and sizes of the stepped horn a and the stepped horn b are the same.

[0035] The two-dimensional adjustable ultrasonic vibration auxiliary cutting device as described above, the stepped horn a is composed of a cylinder I, a flange plate and a cylinder II; the diameter of the cylinder I is larger than that of the cylinder II, the cylinder I is coaxial with the cylinder II and the two are fixedly connected; the flange plate is fixedly sleeved on the cylinder II, the outer diameter of the flange plate is larger than that of the cylinder I, and the flange plate is attached to the end face of the cylinder I close to the cylinder II.

[0036] The two-dimensional adjustable ultrasonic vibration auxiliary cutting device as described above, the length of the cylinder I is 62 mm and the diameter is 50 mm; the outer diameter of the flange plate is 79 mm and the thickness is 6 mm; the length of the cylinder II is 68 mm and the diameter is 30 mm.

[0037] The two-dimensional adjustable ultrasonic vibration auxiliary cutting device as described above, the materials of the stepped horn a and the stepped horn b are 45 steel with smaller acoustic impedance.

[0038] The two-dimensional adjustable ultrasonic vibration auxiliary cutting device as described above, the stepped horn a and the stepped horn b are connected with the vibration plate and the longitudinal vibration piezoelectric transducer a and b through stud bolts.

[0039] The design idea of the structure and size of the stepped horn of the present application will be described as follows:

[0040] In actual ultrasonic vibration, the vibration amplitude directly output by the ultrasonic transducer is very small and far from meeting the actual application requirements, so the horn is needed to concentrate and amplify the ultrasonic amplitude. In order to maximize the amplification effect of the amplitude and reduce the half-wave resonance length, the stepped horn is adopted in the present application, and the material is selected as 45 steel with smaller acoustic impedance.

[0041] For a uniform cross-section rod as shown in Figure 4 , the wave equation of one-dimensional vibration thereof is:

[0042]

[0043] In the formula, ξ = ξ (x) is a displacement function, k is a wave number, k = ω / c, ω is a circular frequency, and c is a wave speed.

[0044] The solution is:

[0045]

[0046] where A1, A2, B1, B2 are undetermined coefficients;

[0047] From the boundary condition we have:

[0048] A1=ξ1cos ka, B1=-ξ1sin ka (2-43);

[0049] From the other boundary condition we have:

[0050]

[0051] Substituting equations (2-43) and (2-44) into equation (2-42), we have the displacement of the mass point:

[0052]

[0053] The displacement node is When , the node x=0, i.e. the center position.

[0054] At the section surface of x=0, the situation is more complicated due to the change of cross-sectional area. If the cross-sectional area ratio S1 / S2 is less than 5, the force can be considered continuous, i.e.

[0055]

[0056] Using this condition, we have from equation (2-43):

[0057] S1B1=S2B2 (2-47);

[0058] Without load, i.e. ZL=0, substituting equations (2-43) and (2-44) into equation (2-47), we have the amplification factor:

[0059]

[0060] From the above equation, we can see that when b=a=λ / 4, the amplification factor reaches the maximum, and at this time the wave node is at x=0. Now let the amplitude bar D1=50mm, D2=30mm, the material be 45# steel, and the designed resonant frequency be 20kHZ. The wave propagation speed in the 45# steel rod is:

[0061]

[0062] where E is the elastic modulus and p is the material density.

[0063] Therefore, the half-wave resonant length is:

[0064]

[0065] The node position is:

[0066]

[0067] At the same time, considering the assembly problem with the outside world, a flange with a thickness of 6 mm and a diameter of 80 mm is added at the pitch surface.

[0068] The designed amplitude lever is verified by modal analysis using ANSYS Workbench. The first 20 modes of the amplitude lever are extracted, and the 8th mode is determined as the required longitudinal vibration mode, as shown in Figure 5 The resonant frequency of the amplitude lever is 20539 Hz, which is very close to the design frequency. Most of the force transmission curves are concentrated at the end of the amplitude lever tool, and there is almost no force escape at the flange, and the energy dissipation is less. At the same time, the frequency response analysis is carried out, and the simulation shows that the frequency response curve is smooth transition, and the amplitude reaches the maximum at the frequency of 20530 Hz, which is basically consistent with the modal simulation frequency. After connecting the amplitude lever with the ultrasonic transducer and the vibrating plate at both ends, the overall modal analysis is carried out again in ANSYS Workbench, and the result is shown in Figure 6 The vibration is strong in the red area in the center of the plate, and the shape is approximately circular, which is a typical two-dimensional elliptical vibration. The overall vibration frequency of the system after adding the vibrating plate is 20515 Hz, which matches the amplitude lever.

[0069] After theoretical calculation and finite element simulation verification, the two-dimensional adjustable ultrasonic vibration assisted cutting device is assembled and the vibration performance is tested. The physical object of the two-dimensional adjustable ultrasonic vibration assisted cutting device is shown in Figure 7 (a), in which the transducer and the amplitude lever, the amplitude lever and the vibrating plate are connected by double-headed studs, and the vibrating plate material is SKD11 die steel, which is connected to the bottom plate through threaded struts at the four corners. Vaseline oil is applied at all connections to avoid air gaps affecting vibration transmission.

[0070] To realize the precise collaborative control of two ultrasonic waves, the two-dimensional adjustable ultrasonic vibration assisted cutting device is equipped with a JZT2V1.1 intelligent ultrasonic generator, as shown in Figure 7 (b). Its frequency range is 14 kHz-70 kHz, with a step of 0.1 kHz, which can realize the input of sinusoidal wave voltage with the same frequency and certain phase to the two groups of longitudinal ultrasonic vibrators, and the phase adjustment range is 0-180°. The resonant frequency of the two-dimensional adjustable ultrasonic vibration assisted cutting device is tested by using an ultrasonic impedance analyzer, and the initial frequency is 18 kHz and the terminal frequency is 22 kHz, and the impedance test result is shown in Figure 7(c) shown. From the impedance test results, it can be seen that after connecting the working base plate, the actual resonant frequency of the two-dimensional adjustable ultrasonic vibration assisted cutting device is shifted to 19833.6Hz, which is only decreased by 3.32% compared with the simulation results, and has good consistency. In addition, the admittance circle is very close to the standard normal circle at this time, which shows that the designed amplitude rod and ultrasonic transducer have very good matching.

[0071] Advantages:

[0072] The two-dimensional adjustable ultrasonic vibration assisted cutting device has the advantages of simple structure, less energy dissipation, good machining stability, and can realize efficient and low-damage milling and pin machining. BRIEF DESCRIPTION OF DRAWINGS

[0073] Figure 1 It is a schematic view of the structure of the stepped amplitude rod;

[0074] Figure 2 It is a top view of the vibration platform;

[0075] Figure 3 It is a front view of the vibration platform;

[0076] Figure 4 It is a schematic view of the stepped amplitude rod with uniform cross section;

[0077] Figure 5 It is a design size diagram of the ultrasonic amplitude rod;

[0078] Figure 6 It is the simulation results of the two-dimensional adjustable ultrasonic vibration assisted cutting device: (a) amplitude rod harmonic response analysis results; (b) whole machine modal analysis results;

[0079] Figure 7 It is the ultrasonic equipment building and verification: (a) vibration platform; (b) ultrasonic wave generator; (c) impedance analysis results;

[0080] Figure 8 It is a schematic view of the three-dimensional structure of the two-dimensional adjustable ultrasonic vibration assisted cutting device (the longitudinal vibration piezoelectric transducer a and the longitudinal vibration piezoelectric transducer b are not shown in the figure);

[0081] Figure 9 It is a verification experiment: (a) experimental setup; (b) milling schematic diagram; (c) and (d) PCD cutter used;

[0082] Figure 10 It is conventional milling: (A) crack propagation state in simulation; (B) surface topography of 3Y-TZP sample; (I) and (II) are the topography of the enlarged area in (B);

[0083] Figure 11For low-frequency ultrasonic elliptical vibration milling: (A) Crack propagation state in simulation; (B) Surface morphology of 3Y-TZP sample; (I) and (II) are magnified morphologies of the region in (B);

[0084] Figure 12 For medium-frequency ultrasonic elliptical vibration milling: (A) Simulation of crack propagation state; (B) Surface morphology of 3Y-TZP sample; (I) Enlarged morphology of (B);

[0085] Figure 13 For high-frequency ultrasonic elliptical vibration milling: (A) Crack propagation state in simulation; (B) Surface morphology of 3Y-TZP sample; (I) Morphology of the magnified area in (B);

[0086] Among them, 1-vibrating plate, 2-support base, 3-support column, 4-stepped amplitude transformer a, 4.1-cylinder I, 4.2-flange, 4.3-cylinder II, 5-stepped amplitude transformer b, 6-square groove I, 7-square groove II, 8-U-shaped groove. Detailed Implementation

[0087] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0088] Two-dimensional adjustable ultrasonic vibration assisted cutting device, such as Figure 8 As shown, it includes a vibrating plate 1, a support base 2, four pillars 3, a stepped amplitude transformer a 4, a stepped amplitude transformer b 5, a longitudinal vibration piezoelectric transducer a and a longitudinal vibration piezoelectric transducer b;

[0089] Vibrating plate 1 is a horizontally placed square plate (e.g.) Figures 2-3 As shown, the side length is 203mm and the thickness is 32mm, including the front side, rear side, left side and right side;

[0090] The vibrating plate 1 has two square grooves, I 6 and II 7, arranged symmetrically and at intervals, as shown below. Figures 2-3 As shown, the front edge length of the bottom wall of the square groove I 6 is 142mm, and the depth of the square groove I 6 is 8mm.

[0091] The notch of the square groove I 6 is upward, the square groove I 6 is surrounded by a left side wall, a back side wall and a bottom wall below the two walls, the bottom wall includes a front edge, a back edge, a left edge and a right edge; the front edge of the bottom wall is coplanar with the front side of the vibrating flat plate 1, the intersection of the front edge and the right edge of the bottom wall is on the intersection line of the front side and the right side of the vibrating flat plate 1, and the length of the front edge of the bottom wall is less than the length of the side of the vibrating flat plate 1;

[0092] The left side wall and the back side wall of the square groove I 6, the left side wall and the bottom wall, and the back side wall and the bottom wall are transitioned by rounded corners; as shown in the figure, the distance between the upper edge of the left side wall of the square groove I 6 and the right side of the vibrating flat plate 1 is 150 mm; Figure 2

[0093] The support base 2 is arranged below the vibrating flat plate 1 with a certain distance; the support base 2 is a square plate horizontally placed, with a length of 203 mm and a thickness of 32 mm; a U-shaped groove 8 is opened on the support base 2;

[0094] The four supporting columns 3 are vertically placed, the upper ends of the four supporting columns 3 are fixedly connected with the four corners of the vibrating flat plate 1 respectively, the lower ends of the four supporting columns 3 are fixedly connected with the support base 2 simultaneously, and the length of the four supporting columns 3 is 115 mm; the four supporting columns 3 are all double-headed studs; each of the four corners of the vibrating flat plate 1 is provided with a threaded hole a, and each of the regions corresponding to the four corners of the vibrating flat plate 1 in the support base 2 is provided with a threaded hole b; one end of the double-headed stud is inserted into the threaded hole a, and the other end is inserted into the threaded hole b; as shown in the figure, the center distance of any two adjacent threaded holes a is 160±0.25 mm; Figure 2

[0095] The stepped amplitude rods a 4 and b 5 are horizontally placed; the small end of the stepped amplitude rod a 4 is fixedly connected with the center position of the left side of the vibrating flat plate 1 through a double-headed stud, and the large end is fixedly connected with the longitudinal vibration piezoelectric transducer a through a double-headed stud; the small end of the stepped amplitude rod b 5 is fixedly connected with the center position of the back side of the vibrating flat plate 1 through a double-headed stud, and the large end is fixedly connected with the longitudinal vibration piezoelectric transducer b through a double-headed stud;

[0096] The stepped amplitude rods a 4 and b 5 are the same in shape and size; the stepped amplitude rod a 4 is composed of a cylinder I 4.1, a flange plate 4.2 and a cylinder II 4.3; the diameter of the cylinder I 4.1 is greater than that of the cylinder II 4.3, the cylinder I 4.1 is coaxial with the cylinder II 4.3 and the two are fixedly connected; the flange plate 4.2 is fixedly sleeved on the cylinder II 4.3, the outer diameter of the flange plate 4.2 is greater than that of the cylinder I 4.1, and the flange plate 4.2 is in close contact with the end face of the cylinder I 4.1 close to the cylinder II 4.3; as shown in the figure, the stepped amplitude rod b 5 is the same in shape and size as the stepped amplitude rod a 4; Figure 5 ​​As shown, the length of the cylinder I 4.1 is 62mm, and the diameter is 50mm; the outer diameter of the flange plate 4.2 is 79mm, and the thickness is 6mm; the length of the cylinder II 4.3 is 68mm, and the diameter is 30mm; the materials of the stepped amplitude bar a 4 and the stepped amplitude bar b 5 are 45 steel.

[0097] The two-dimensional adjustable ultrasonic vibration assisted cutting device of the application has the characteristics of less energy dissipation and good machining stability, and can realize efficient and low-damage milling machining. The following experiments are combined to illustrate:

[0098] (1) Experimental setup

[0099] The ultrasonic milling experiment was completed on the DMU 70V vertical machining center produced by Demag Company. The main performance parameters of the machine tool are given in Table 1.

[0100] Table 1 Machine tool performance parameters

[0101]

[0102] Figure 9 (a) gives the test site layout. The sample used in the test is a fully sintered 3Y-TZP ceramic provided by Zhuhai Jiawei Ceramics Technology Co., Ltd., and its physical and mechanical properties are shown in Table 2. The two-dimensional adjustable ultrasonic vibration assisted cutting device developed by the application has a clamping groove on the side, the 3Y-TZP ceramic sample is placed on the clamping groove on the side of the vibration platform, and the pressure plate is pressed against the side of the workpiece through the tightening bolt to realize the clamping of the workpiece. Before the test, vaseline was applied to the connecting parts and clamping parts of the platform to eliminate air gaps and ensure stable vibration transmission.

[0103] Table 2 Physical and mechanical properties of 3Y-TZP ceramic

[0104]

[0105] It is worth noting that orthogonal cutting is used in the simulation, and it is difficult to directly realize ultrasonic elliptical vibration orthogonal cutting in the test, therefore, the application adopts side milling method to mill the ceramic sample along the machine tool x axis. In order to simulate the simulation conditions to the greatest extent, the feed per tooth during milling in the test is set to 27.5μm, and the radial depth of cut is set to 50μm, at this time the corresponding maximum undeformed chip thickness is about 5μm, as shown in Figure 9 (b). The tool is a double-tooth PCD milling cutter with a diameter of 6mm, a rake angle of 4°, and a relief angle of 6°, as shown in Figure 9(c) and (d). Therefore, the radial depth of cut in the experiment is extremely small compared to the tool radius, so the direction of tool cutting speed is considered not to change, achieving similar cutting conditions as in the simulation. Ultrasonic vibrations are applied along the tool feed direction and perpendicular feed direction with a phase difference of π / 2 to obtain the expected elliptical vibration trajectory.

[0106] On the other hand, since the working frequency of the two-dimensional adjustable ultrasonic vibration assisted cutting device is fixed, the tool rotational speed (nominal cutting speed) is adjusted to obtain different equivalent Rs values. The experimental parameters are shown in Table 3. It is worth noting that at a maximum undeformed chip thickness of 5 μm, brittle fracture of the ceramic has occurred in conventional cutting and low-frequency UEVC (ultrasonic elliptical vibration cutting) simulation, while in medium- and high-frequency UECV, the material is still removed in a plastic manner, so it has a control significance.

[0107] Table 3 Ultrasonic vibration assisted milling experiment parameters

[0108]

[0109]

[0110] After the experiment, the 3Y-TZP sample was ultrasonically cleaned in acetone for 10 min, and then the sample milling surface morphology was observed using a TESCAN MIRA3 scanning electron microscope to analyze the material removal behavior of 3Y-TZP ceramic under different ultrasonic speed ratios.

[0111] (2) Results and analysis

[0112] 3Y-TZP ceramic is a typical difficult-to-machine material after complete sintering, with a very small ductile removal scale, so its machinability is very poor. From the 3Y-TZP conventional cutting simulation results in section 2.2, the ductile removal scale is only 2.9 μm without two-dimensional ultrasonic vibration excitation. Under the current test settings, the maximum undeformed chip thickness produced during side milling is 5 μm, at which time the conventional cutting process of 3Y-TZP ceramic will cause the material removal to enter the brittle domain category, inducing long cracks in the material, thus promoting the ceramic material to be removed in a brittle fracture manner, as shown in Figure 10 (A). Figure 10 (B) is the surface morphology of the 3Y-TZP sample after milling without ultrasonic vibration assistance, a large number of furrows with different widths and depths parallel to the cutting direction appear on the workpiece milling surface, and the furrow edges have poor integrity. In addition, there are numerous pit defects on the milling surface caused by brittle fracture of the material, and the surface quality is extremely poor, as shown in Figure 10(B) shows. It can be seen that, without the assistance of ultrasonic vibration, when the maximum undeformed chip thickness is 5 μm, the machined surface topography is consistent with the characteristics of brittle cutting, which is consistent with the simulation results. In addition, this also explains why the mechanical surface micro-texture machining method is less applied in ceramic materials, that is, the machining parameters are greatly limited when using mechanical machining, which easily makes the ceramic material enter the brittle domain removal category, resulting in the deterioration of the quality of the subsequently machined surface micro-texture.

[0113] After applying low-frequency ultrasonic vibration excitation, due to the variable speed effect and the variable angle effect, the crack propagation degree in the 3Y-TZP ceramic cutting process is inhibited to a certain extent under the same maximum undeformed chip thickness, and the original long cracks are converted into multiple short cracks, as shown in Figure 11 (A). However, the ceramic material removal process still belongs to the brittle domain cutting range. In the low-frequency UEVC process, the machined surface topography of 3Y-TZP ceramic is mainly composed of numerous cutting streaks, brittle fracture pits on the streaks, and micro-cracks, as shown in Figure 11 (B), which is consistent with the characteristics of brittle cutting. Compared with conventional milling process, the large area brittle fracture pits of 3Y-TZP ceramic surface disappear under low-frequency UEVC, and are replaced by a large number of micro-cracks extending into the material, which shows that the variable speed effect and the variable cutting angle effect of ultrasonic vibration cutting help to improve the stress distribution in the 3Y-TZP ceramic machining process, convert long cracks into multiple short cracks, and inhibit the transverse crack propagation to the free surface of the workpiece, thereby refining the overall macroscopic fracture into numerous local microscopic fractures, and improving the machining surface quality. However, the low-frequency UEVC has limited ability to improve the ductile-brittle transition critical depth of 3Y-TZP ceramic, only 3.7 μm, and still belongs to the brittle domain cutting range under the maximum undeformed chip thickness of 5 μm, and the machining quality is still not ideal, which is consistent with the simulation results.

[0114] When the medium-frequency ultrasonic excitation is applied, the 3Y-TZP ceramic has shown ductile removal characteristics in the simulation, as shown in Figure 12(A) is shown. Brittle fracture features are also not observed on the workpiece milled surface, and the machined surface has clear ultrasonic vibration lines, cutting texture and a relatively smooth machined surface, showing similar cutting features of metal materials, indicating that 3Y-TZP ceramic has entered the ductile removal mode at this time, which is consistent with the simulation results. It is worth noting that since the ultrasonic vibration platform frequency is fixed, the preset Rs can only be achieved by reducing the spindle speed, which means that the instantaneous cutting speed is reduced compared to low-frequency UEVC. But even without the effect of speed change, the ceramic milling surface quality is still significantly improved, which can be attributed to the reduction of the maximum effective undeformed chip thickness and the effect of crack secondary removal after the tool path overlap. This shows that these two crack suppression mechanisms play a dominant role in improving the critical depth of the ductile-brittle transition of 3Y-TZP. Further reducing Rs to 0.03183 to achieve high-frequency UEVC, the material removal process is more stable. Figure 13 (B) gives the 3Y-TZP ceramic milling surface morphology under high-frequency UEVC, since it is completely in the ductile domain removal scale as the medium-frequency UEVC, the workpiece surface morphology is not much different from Figure 12 (B), both are flat surfaces with ultrasonic vibration lines.

[0115] Therefore, the following conclusions can be drawn: the crack suppression effect of UEVC on 3Y-TZP ceramic is highly dependent on the ultrasonic velocity ratio Rs. Many scholars have pointed out that UEVC has a significant effect on the improvement of the ductile domain of brittle materials, but most of the research is carried out for scratching process. The scratching speed is low, so Rs can be less than the critical value 0.128 under conventional ultrasonic vibration frequency, and thus significant crack suppression effect can be obtained. But for milling process, the linear velocity in the cutting process is much higher than that in the scratching experiment, so Rs exceeds its critical value, and then the crack suppression effect at this time is relatively limited.

Claims

1. A two-dimensional adjustable ultrasonic vibration-assisted cutting device, characterized in that, It includes a vibrating plate, a support base, four pillars, a stepped amplitude transformer a, a stepped amplitude transformer b, a longitudinal vibration piezoelectric transducer a, and a longitudinal vibration piezoelectric transducer b; The vibrating plate is a horizontally placed square plate, which includes a front side, a rear side, a left side, and a right side. The vibrating plate has two square grooves, I and II, arranged symmetrically and at intervals. The square groove I has its opening facing upwards. The square groove I is formed by a left side wall, a rear side wall, and a bottom wall located below both of them. The bottom wall includes a front edge, a rear edge, a left edge, and a right edge. The front edge of the bottom wall is coplanar with the front side of the vibrating plate. The intersection of the front edge and the right edge of the bottom wall is located on the intersection line of the front side and the right side of the vibrating plate. The length of the front edge of the bottom wall is less than the side length of the vibrating plate. The support base is located below the vibrating plate and is spaced apart from the vibrating plate. Four pillars are placed vertically, with the upper ends of the four pillars fixedly connected to the four corners of the vibrating plate, and the lower ends of the four pillars fixedly connected to the support base. The stepped amplitude transformer a and stepped amplitude transformer b are placed horizontally; the small end of stepped amplitude transformer a is vertically and fixedly connected to the center of the left side of the vibrating plate, and the large end is fixedly connected to the longitudinal vibration piezoelectric transducer a; the small end of stepped amplitude transformer b is vertically and fixedly connected to the center of the rear side of the vibrating plate, and the large end is fixedly connected to the longitudinal vibration piezoelectric transducer b.

2. The two-dimensional adjustable ultrasonic vibration-assisted cutting device according to claim 1, characterized in that, The vibrating plate has a side length of 203mm and a thickness of 32mm.

3. The two-dimensional adjustable ultrasonic vibration-assisted cutting device according to claim 2, characterized in that, The front edge length of the bottom wall of square groove I is 142mm, and the depth of square groove I is 8mm.

4. The two-dimensional adjustable ultrasonic vibration-assisted cutting device according to claim 2, characterized in that, The length of the four support pillars is 115mm.

5. The two-dimensional adjustable ultrasonic vibration-assisted cutting device according to claim 2, characterized in that, All four support pillars are double-ended studs; each of the four corners of the vibrating plate has a threaded hole a, and each area of ​​the support base corresponding to the four corners of the vibrating plate has a threaded hole b; one end of the double-ended stud is inserted into the threaded hole a, and the other end is inserted into the threaded hole b.

6. The two-dimensional adjustable ultrasonic vibration-assisted cutting device according to claim 1, characterized in that, The support base is a horizontally placed square plate with a side length of 203mm and a thickness of 32mm.

7. The two-dimensional adjustable ultrasonic vibration-assisted cutting device according to claim 1, characterized in that, The stepped amplitude transformer a and the stepped amplitude transformer b have the same shape and size.

8. The two-dimensional adjustable ultrasonic vibration-assisted cutting device according to claim 7, characterized in that, The stepped amplitude transformer a consists of cylinder I, a flange, and cylinder II; the diameter of cylinder I is larger than that of cylinder II, cylinder I and cylinder II are coaxial and fixedly connected; the flange is fixedly fitted on cylinder II, the outer diameter of the flange is larger than that of cylinder I, and the flange is in contact with the end face of cylinder I near cylinder II.

9. The two-dimensional adjustable ultrasonic vibration-assisted cutting device according to claim 8, characterized in that, Cylindrical I has a length of 62mm and a diameter of 50mm; the flange has an outer diameter of 79mm and a thickness of 6mm; Cylindrical II has a length of 68mm and a diameter of 30mm.

10. The two-dimensional adjustable ultrasonic vibration-assisted cutting device according to claim 1, characterized in that, The stepped amplitude transformer a and stepped amplitude transformer b are made of 45 steel.

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