An ultrasonic internal broaching test platform and ultrasonic vibration mode control method

Abstract

The present invention belongs to the field of machining technology, and specifically relates to an ultrasonic internal broaching test platform and an ultrasonic vibration mode control method, wherein the test platform includes a base, a broach and a clamping mechanism, the clamping mechanism including a support ring and a clamping sleeve; the broach is provided with a clamping groove, and the clamping sleeve is provided with a protrusion that matches the clamping groove; the base is provided with support columns, and the support columns are multiple and arranged in a circular shape; the broach is set in a space enclosed by multiple support columns; and a piezoelectric actuator is provided on the broach. Based on the above platform, the present invention provides a control method for ultrasonic vibration mode, which can optimize and reduce modal drift by adjusting the preload force and the ultrasonic power supply driving frequency, and use the preload force to adjust the stable contact stiffness to reduce energy loss; through frequency tracking and real-time matching of the resonance point, energy transfer can be maximized; the two methods are controlled synergistically, taking into account both response speed and stability, and adapting to high dynamic loads.

Description

Technical Field

[0001] The present invention relates to the technical field of machining, and in particular to an ultrasonic internal broaching test platform and an ultrasonic vibration mode control method. Background Art

[0002] In the field of precision machining, high-strength and high-hardness materials such as titanium alloys, hardened steel, and nickel-based superalloys, due to their excellent mechanical properties, have become the materials of choice in key areas such as aerospace, energy equipment, and high-end mold manufacturing. These materials not only possess exceptional strength, enabling them to withstand enormous loads under extreme conditions, but also possess exceptional hardness, ensuring wear resistance and stability under complex operating conditions. However, these same exceptional properties also present significant challenges for traditional cutting processes. Machining high-strength and high-hardness materials places extremely high demands on the rigidity and stability of machine tools, and the machining process is also more susceptible to vibration and deformation of components such as cutting tools, which in turn affects machining accuracy. Furthermore, cutting tools wear rapidly when in contact with high-strength and high-hardness materials, significantly shortening tool life and increasing machining costs. Furthermore, the increased heat generated during cutting of high-strength and high-hardness materials creates high temperatures in the machining area, further exacerbating tool wear and potentially causing thermal damage to the workpiece surface, impacting surface quality. The surface roughness after processing is difficult to control, and defects such as cracks and residual stress are prone to occur. These defects not only affect the appearance of the workpiece, but are more likely to become the source of fatigue cracks, thereby reducing the service life of the workpiece.

[0003] To address these issues, ultrasonic-assisted machining (UAM) has been proposed. Ultrasonic-assisted machining (UAM) superimposes high-frequency vibrations (20–40 kHz) on the tool or workpiece, leveraging the "contact-separation" effect to reduce cutting forces and inhibit cutting heat accumulation. This has become an important technical means of improving the machinability of these difficult-to-machine materials. However, in some special machining scenarios, such as internal broaching of high-strength and high-hardness workpieces, the broaching load is extremely high, potentially exceeding 500N, far exceeding the 200N of conventional cutting. This high load directly alters the resonant characteristics of the ultrasonic vibration system, significantly changing the vibration mode and amplitude of the ultrasonic vibration, significantly reducing the broaching performance and machining accuracy of UAM.

[0004] In order to achieve the goal of ensuring that the ultrasonic-assisted system can maintain a stable amplitude under special scenarios (higher loads), the present invention aims to provide an ultrasonic internal broaching test platform and an ultrasonic vibration mode control method. By measuring the broaching vibration mode and vibration amplitude of the broach, a closed-loop control method is optimized based on preload and frequency to achieve high-load stable output amplitude, ensure that its vibration mode meets the broaching working conditions, and significantly improve broaching accuracy and efficiency. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art and provide an ultrasonic internal broaching test platform and an ultrasonic vibration mode control method, so as to achieve high-load stable output amplitude during the broaching process, ensure that the vibration mode meets the broaching working conditions, and significantly improve the broaching accuracy and efficiency.

[0006] To achieve the above-mentioned objectives, the present invention first provides an ultrasonic internal broaching test platform, comprising a base, a broach and a clamping mechanism, the clamping mechanism being used to fix the broach to the base, the clamping mechanism comprising a support ring and a clamping sleeve; the broach is provided with a clamping groove, and the clamping sleeve is provided with a protrusion matching the clamping groove; the base is provided with support columns, and there are multiple support columns arranged in a circular shape; the broach is arranged in a space enclosed by multiple support columns; the upper end of the broach is connected to the support columns through a clamping mechanism; the lower end of the broach is connected to the base through a clamping mechanism; and a piezoelectric actuator is provided on the broach.

[0007] Furthermore, the position where the clamping mechanism clamps the broach is exactly at the vibration node of the broach.

[0008] Furthermore, the clamping sleeve is annular and the broach is cylindrical; when the broach is installed vertically, the upper end groove angle of the clamping groove is recorded as , the lower end groove angle of the clamping groove is recorded as , the raised angle of the clamping sleeve is recorded as , the raised angle of the lower end of the clamping sleeve is recorded as , then the following requirements are met:

[0009] , ; > .

[0010] These angles ensure that the clamping sleeve contacts the broach at the bottom and the outer side, reducing radial vibration. Furthermore, because the groove angle on the inside of the broach is greater than that on the outside, radial vibration on the inside is lower than on the outside, improving broaching accuracy. Furthermore, they increase the axial transmission rate of ultrasonic energy, thereby increasing the axial vibration amplitude and enhancing ultrasonic-assisted broaching performance.

[0011] Furthermore, the piezoelectric actuator is formed by connecting multiple piezoelectric ceramic sheets in series, the polarization directions of the multiple piezoelectric ceramic sheets are consistent with the axial direction of the broach, and the polarization directions are alternating + / -. Preferably, the piezoelectric ceramic sheets are PZT sheets.

[0012] Furthermore, the number of the support columns can be 4 or 3. Considering the stability of the test, 3 are preferred and they are evenly arranged in a circle at intervals of 120°.

[0013] Furthermore, according to the height of vertical installation, the support ring is divided into an upper support ring and a lower support ring, and the clamping sleeve is divided into an upper clamping sleeve and a lower clamping sleeve. The upper support ring is annular, the outer side of the upper support ring is connected to the support column, and the inner side is connected to the upper clamping sleeve; the lower support ring is cylindrical, the inner side of the lower support ring is connected to the lower clamping sleeve, and the lower end of the lower support ring is connected to the base.

[0014] Furthermore, a bottom plate is provided below the base.

[0015] Furthermore, the bottom plate is an adjustable structure, and there are multiple bottom plates arranged in a circular shape. The base can be kept level by adjusting the height of each bottom plate.

[0016] Furthermore, the base is cylindrical and can be a truss structure or a cast iron structure. The support column and the lower support ring can be fixed to the base by countersunk bolts, and the gasket at the bolt connection is a three-layer sandwich structure of high manganese steel and rubber.

[0017] The present invention also provides an ultrasonic vibration mode control method; utilizing the above-mentioned internal broaching test platform, the method comprises the following steps:

[0018] S1. Build a three-dimensional model of the broach, perform modal analysis, select the axial resonant frequency, and avoid adjacent radial modes;

[0019] S2, piezoelectric actuator layout design;

[0020] The piezoelectric actuator uses multiple PZT annular plates stacked symmetrically. The polarization direction of the PZT annular plates is consistent with the axial direction of the broach, and the polarization direction of the PZT annular plates is designed to alternate between + and -.

[0021] S3, multi-physics coupling simulation;

[0022] Analyze the vibration stability of the ultrasonic broaching system under the interaction of broaching force and ultrasonic vibration to avoid the modal drift of the ultrasonic broaching system; specifically include:

[0023] S3-1. Establish a multi-physics coupling model integrating structural mechanics, piezoelectric effect, and contact mechanics in finite element software;

[0024] S3-2. Set the boundary conditions of the broach according to the broaching working conditions, including the clamping conditions at both ends of the broach;

[0025] S3-3, load condition simulation;

[0026] S3-4, modal and harmonic response analysis;

[0027] 1) Prestressed modal analysis;

[0028] Determine the stress distribution under static broaching forces; calculate modal frequencies and vibration shapes based on the prestressed state; compare modal parameters with those under no load and identify frequency drift;

[0029] 2) Harmonic response analysis;

[0030] Frequency sweep: Apply a sweep voltage in the target frequency band and observe the amplitude-frequency curve;

[0031] Comparative analysis of axial amplitude attenuation: observe whether the vibration amplitude under load still meets the processing requirements;

[0032] Radial vibration suppression: Verify whether non-target modes are excited;

[0033] S3-5, stability assessment and optimization;

[0034] 1) Set the criteria for modal drift determination;

[0035] 2) Modal drift detection and diagnosis;

[0036] Use a laser vibrometer to measure the axial / radial amplitude of the tool tip or a current sensor to monitor the output current phase of the ultrasonic power supply. If the current phase angle suddenly increases and the amplitude decreases, it indicates a resonance mismatch (frequency drift). Use FFT analysis of the vibration spectrum to confirm the location of the new resonance peak.

[0037] 3) Adjustment and optimization after modal drift occurs;

[0038] a. Dynamic adjustment of preload force;

[0039] Adjust the preload torque of the PZT. The adjustment logic is: when the preload force is insufficient, increase the preload force; when the preload force is excessive and exceeds the PZT stress limit, reduce the preload force to a safe range;

[0040] b. Adaptive tracking of driving frequency;

[0041] A frequency-adjustable signal is generated using a DSP or FPGA and output to the PZT via a high-voltage amplifier. A phase-locked loop (PLL) is used to track the resonant frequency in real time, and a phase detector compares the phase difference between current and voltage. The frequency adjustment range is limited to the PZT operating frequency band. A voltage-controlled oscillator (VCO) dynamically adjusts the drive frequency, using a gradient descent method to iteratively search for the optimal frequency with the goal of maximizing the amplitude.

[0042] ;

[0043] in is the step size, and A1 is the amplitude.

[0044] Furthermore, in step S3-1, the multi-physics coupling model includes:

[0045] (1) Piezoelectric-structural coupling model;

[0046] Used to define the relationship between the voltage input of the PZT and the structural vibration response;

[0047] (2) Contact nonlinear model;

[0048] Used to set the preload and friction conditions of the PZT-broach interface;

[0049] (3) Damping model;

[0050] Use Rayleigh damping or structural damping to simulate energy dissipation;

[0051] (4) Grid accuracy model;

[0052] Used to set the mesh accuracy. The contact interface needs to be meshed finely, with at least 3 layers of elements.

[0053] (5) Nonlinear convergence model;

[0054] Enable the Geometric Nonlinearity option and set the Damping Factor to improve convergence.

[0055] Furthermore, in step S3-3, the following operations are performed:

[0056] 1) Static broaching force simulation;

[0057] Apply static force to the broach cutting edge, analyze the superposition effect of preload force and broaching force, and evaluate the stability of the contact interface;

[0058] 2) Dynamic load simulation;

[0059] Broaching is divided into the cutting-in stage, the stable cutting stage and the cutting-out stage. Therefore, the broaching force fluctuates periodically, and the following time function can be defined:

[0060] ,

[0061] in, is the cutting force determined by the number of teeth in stable cutting, and t is the time; Indicates the broaching force;

[0062] is the number of teeth that cut in and out during cutting, that is, the cutting force determined by the changing number of teeth.

[0063] It is the frequency of fluctuation in the number of teeth cut in and out during cutting, which is determined by the ratio of tooth spacing to broaching speed;

[0064] 3) Boundary conditions;

[0065] Clamping constraint: fix the broach clamping end, and the clamping end is located at the axial vibration mode node;

[0066] Preload force implementation: Bolt preload, applying force or displacement through the "Bolt Preload" interface in the finite element software (COMSOL).

[0067] Furthermore, in step S3-5, the judgment standard of modal drift adopts the threshold standard, that is, if the calculated modal frequency is , the measured modal frequency is ,when , it is determined that modal drift has occurred.

[0068] Furthermore, in step S3-5, the adjustment method after modal drift further includes:

[0069] c. Combined adjustment of preload force and frequency;

[0070] The vibration frequency of the ultrasonic broach is measured in real time. When the broach frequency drifts, if the vibration frequency is lower than the target frequency and the phase angle is greater than the threshold, the broach ultrasonic vibration has a frequency mismatch. Drive frequency tracking is used. If the vibration frequency is lower than the target frequency and the phase angle is not greater than the threshold, the broach clamping nonlinearity is dominant, and the preload force is increased.

[0071] Furthermore, in the process of joint adjustment of preload force and frequency, the frequency is adjusted to the new resonance point first. If the amplitude is still insufficient after the frequency adjustment, the preload force is adjusted.

[0072] Compared with the existing technology, the present invention has the following advantages: the ultrasonic internal broaching test platform and ultrasonic vibration mode control method provided by the present invention can optimize and reduce modal drift by adjusting the preload force and the ultrasonic power supply drive frequency. The use of preload force to adjust the stable contact stiffness can reduce energy loss. Through frequency tracking and real-time matching of the resonance point, energy transfer can be maximized. The two methods are controlled synergistically, taking into account both response speed and stability, and adapting to high dynamic loads. For example, the optimal preload force range (e.g., 800–1200N) and the drive frequency are determined through parametric scanning. The simulation results guide the dynamic adjustment of the drive frequency to track the resonance point. Increasing the preload force from 800N to 1200N and adjusting the drive frequency to 19.9kHz compensates for frequency drift. This method can improve processing efficiency by more than 20%. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 Schematic diagram of the longitudinal section of the ultrasonic internal broaching test platform in an embodiment of the present invention;

[0074] Figure 2 A schematic cross-sectional view of the connection between the broach and the clamping sleeve in an embodiment of the present invention;

[0075] Figure 3 This is a frequency tracking control block diagram in the control method of the present invention;

[0076] In the figure: 1. Upper clamping sleeve; 2. Broach; 3. Upper support ring; 4. Support column; 5. Piezoelectric actuator; 6. Lower clamping sleeve; 7. Lower support ring; 8. Base; 9. Bottom plate. DETAILED DESCRIPTION

[0077] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is described below through specific embodiments. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. The structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions under which the present invention can be implemented. Therefore, they have no technical significance. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed in the present invention without affecting the efficacy and purpose that can be achieved by the present invention.

[0078] Furthermore, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily obscuring the concepts in the present invention. Example

[0079] like Figure 1-2 As shown, this embodiment provides an ultrasonic internal broaching test platform, including a base 8, a broach 2 and a clamping mechanism, the clamping mechanism is used to fix the broach 2 to the base 8, and the clamping mechanism includes a support ring and a clamping sleeve; the broach 2 is provided with a clamping groove, and the clamping sleeve is provided with a protrusion that matches the clamping groove; the base 8 is provided with support columns 4, and there are 4 support columns 4 and they are arranged in a circular shape; the broach 2 is arranged in a space enclosed by multiple support columns 4; the upper end of the broach 2 is connected to the support column 4 through a clamping mechanism; the lower end of the broach 2 is connected to the base 8 through a clamping mechanism; a piezoelectric actuator 5 is provided on the broach 2.

[0080] In this embodiment, the position of the clamping mechanism holding the broach is exactly at the vibration node of the broach. The clamping sleeve is annular and the broach is cylindrical. When the broach is installed vertically, the upper end groove angle of the clamping groove is recorded as , the lower end groove angle of the clamping groove is recorded as , the raised angle of the clamping sleeve is recorded as , the raised angle of the lower end of the clamping sleeve is recorded as , then the following requirements are met: , ; > .

[0081] In this embodiment, the piezoelectric actuator 5 is composed of four piezoelectric ceramic sheets connected in series. The piezoelectric ceramic sheets are PZT annular sheets. The polarization directions of the four piezoelectric ceramic sheets are consistent with the axial direction of the broach 2, and the polarization directions are alternating + / -.

[0082] In this embodiment, according to the vertical installation height, the support ring is divided into an upper support ring 3 and a lower support ring 7, and the clamping sleeve is divided into an upper clamping sleeve 1 and a lower clamping sleeve 6. The upper support ring 3 is annular, and the outer side of the upper support ring 3 is connected to the support column 4, and the inner side is connected to the upper clamping sleeve 1; the lower support ring 7 is cylindrical, and the inner side of the lower support ring 7 is connected to the lower clamping sleeve 6, and the lower end of the lower support ring 7 is connected to the base 8.

[0083] In this embodiment, a bottom plate 9 is provided below the base 8. The bottom plate 9 is an adjustable structure, and there are six bottom plates 9 arranged in a circular shape. The base 8 can be kept level by adjusting the height of each bottom plate 9.

[0084] In this embodiment, the base 8 is cylindrical and adopts a truss structure. The support column 4 and the lower support ring 7 can be fixedly connected to the base 8 by countersunk bolts, and the gasket at the bolt connection is a three-layer sandwich structure of high manganese steel and rubber.

[0085] The method for realizing ultrasonic vibration mode control using the above-mentioned internal broaching test platform includes the following steps:

[0086] S1. Establish a three-dimensional model of the broach and perform modal analysis;

[0087] Considering that the target vibration mode of the broach is axial vibration, the radial vibration should be reduced as much as possible; therefore, the axial resonant frequency (such as 20kHz) should be selected and the adjacent radial modes should be avoided.

[0088] S2, piezoelectric actuator layout design;

[0089] The piezoelectric actuator uses four symmetrically stacked PZT rings with alternating polarization directions of + / -. That is, the PZT rings are symmetrically arranged along the broach axis, with the polarization direction of the PZT rings aligned with the broach axis. Adjacent PZT rings are polarized in opposite directions (alternating + / -) to enhance axial strain consistency.

[0090] S3, multi-physics coupling simulation;

[0091] Multiphysics coupled simulation is used to analyze the vibration stability of an ultrasonic broaching system under the interaction of broaching force (mechanical load) and ultrasonic vibration (piezoelectric excitation) to avoid modal drift in the ultrasonic broaching system. Specifically, the following operations are involved:

[0092] S3-1. In finite element software (e.g., COMSOL Multiphysics), establish a multi-physics coupling model that integrates structural mechanics, piezoelectric effects, and contact mechanics. The multi-physics coupling model includes:

[0093] (1) Piezoelectric-structural coupling model;

[0094] Used to define the relationship between the voltage input of the PZT and the structural vibration response;

[0095] (2) Contact nonlinear model;

[0096] Used to set the preload and friction conditions of the PZT-broach interface;

[0097] (3) Damping model;

[0098] Use Rayleigh damping or structural damping to simulate energy dissipation;

[0099] (4) Grid accuracy model;

[0100] Used to set the mesh accuracy. The contact interface needs to be meshed finely, with at least 3 layers of elements.

[0101] (5) Nonlinear convergence model;

[0102] Enable the Geometric Nonlinearity option and set the Damping Factor to improve convergence.

[0103] S3-2. Set the boundary conditions of the broach according to the broaching working conditions, including the clamping conditions at both ends of the broach.

[0104] S3-3, load condition simulation;

[0105] 1) Static broaching force simulation;

[0106] Apply a static force (e.g., 500N axial force) to the broaching edge to analyze the superposition effect of the preload force and the broaching force and evaluate the stability of the contact interface.

[0107] 2) Dynamic load simulation;

[0108] Time-varying load: The broaching force fluctuates periodically (the cutting teeth are subjected to alternating forces). A time function can be defined:

[0109] ,

[0110] in, is the cutting force determined by the number of teeth in stable cutting, t is the time;

[0111] is the number of teeth that cut in and out during cutting, that is, the cutting force determined by the changing number of teeth.

[0112] It is the frequency of fluctuation in the number of teeth cut in and out during cutting, which is determined by the ratio of tooth spacing to broaching speed;

[0113] 3) Boundary conditions;

[0114] Clamping constraint: fix the broach clamping end, and the clamping end is located at the axial vibration mode node;

[0115] Preload force implementation: Bolt preload, applying force or displacement through the "Bolt Preload" interface in the finite element software (COMSOL).

[0116] S3-4, modal and harmonic response analysis;

[0117] 1) Prestressed modal analysis;

[0118] Determine the stress distribution under static broaching force; calculate the modal frequency and vibration shape based on the prestressed state;

[0119] Compare the modal parameters under no load to identify frequency drift; for example, from 20kHz to 19.8kHz;

[0120] 2) Harmonic response analysis;

[0121] Frequency sweep: Apply a sweep voltage in the target frequency band (e.g., 18–22 kHz) and observe the amplitude-frequency curve.

[0122] Comparative analysis of axial amplitude attenuation: Observe whether the vibration amplitude under load still meets the processing requirements (e.g. ≥8μm);

[0123] Radial Vibration Suppression: Verifies whether non-target modes are excited.

[0124] S3-5, stability assessment and optimization;

[0125] Set the modal drift judgment criteria;

[0126] The threshold standard is used, that is, if the resonant frequency offset, such as: the calculated modal frequency is , the measured modal frequency is ,when , it is determined to be modal drift. Optimization design is required. The main reasons are that the broaching force causes the change of contact stiffness and the preload force is insufficient.

[0127] 2) Modal drift detection and diagnosis;

[0128] Use a laser vibrometer to measure the axial / radial amplitude of the tool tip, or a current sensor to monitor the output current phase of the ultrasonic power supply. If the current phase angle suddenly increases and the amplitude decreases, it indicates a resonance mismatch (frequency drift). Use FFT (Fast Fourier Transform) to analyze the vibration spectrum and confirm the location of the new resonance peak.

[0129] 3) Adjustment and optimization after modal drift occurs;

[0130] a. Dynamic adjustment of preload force;

[0131] The PZT preload torque is adjusted using a torque wrench, and bolt preload compensation is achieved using a servo motor to fine-tune the bolts (accuracy ±10N). The adjustment logic is as follows: if the preload is insufficient (contact slip), increase the preload, for example, from 800N to 1200N. If the preload exceeds the PZT stress limit, reduce the preload to a safe level. The preload cannot exceed the PZT compressive strength (e.g., 80MPa for PZT-8).

[0132] b. Driving frequency tracking;

[0133] Generate a frequency-adjustable signal using DSP or FPGA technology; output it to the PZT through a high-voltage amplifier; use a PLL phase-locked loop to track the resonant frequency in real time, and a phase detector to compare the current and voltage phase difference. Limit the frequency adjustment range to the PZT operating frequency band; dynamically adjust the drive frequency through a voltage-controlled oscillator (VCO), and use a gradient descent method to iteratively search for the optimal frequency with the goal of maximizing the amplitude. ;

[0134] ;

[0135] in is the step size, and A1 is the amplitude.

[0136] c. Combined adjustment of preload force and frequency;

[0137] The vibration frequency of the ultrasonic broach is measured in real time. When the broach frequency does drift, if the vibration frequency is lower than the target frequency and the phase angle is greater than the threshold, it indicates that there is a frequency mismatch in the ultrasonic vibration of the broach, and the drive frequency tracking method is used for adjustment; if the vibration frequency is lower than the target frequency and the phase angle is not greater than the threshold, it is dominated by the nonlinearity of the broach clamping, and the preload force is increased.

[0138] During the joint adjustment of preload force and frequency, the frequency is adjusted to the new resonance point first (fast response, ms level). If the amplitude is still insufficient after the frequency adjustment, the preload force is adjusted (slow response, seconds level).

[0139] Joint preload-frequency optimization effectively suppresses modal drift. Using preload to stabilize contact stiffness reduces energy loss. Frequency tracking allows for real-time matching of resonance points, maximizing energy transfer. Coordinated control of these two factors balances response speed and stability, adapting to high dynamic loads. For example, a parametric sweep determines the optimal preload range (e.g., 800–1200 N) and adaptively adjusts the drive frequency. Simulation results guide dynamic adjustment of the drive frequency to track the resonance point. Increasing the preload from 800 N to 1200 N and adjusting the drive frequency to 19.9 kHz compensates for frequency drift. This approach can improve machining efficiency by over 20%.

[0140] The above are only some embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have combinations and variations of the aforementioned technical features. Without departing from the spirit and scope of the present invention, those skilled in the art can improve, modify, or replace the present invention with equivalents, or apply the structure or method of the present invention to other fields to achieve the same effect, which all fall within the scope of protection included in the present invention.

Claims

1. A method for controlling ultrasonic vibration mode; the ultrasonic internal broaching test platform used includes a base, a broach and a clamping mechanism, the clamping mechanism is used to fix the broach to the base, and the clamping mechanism includes a support ring and a clamping sleeve; the broach is provided with a clamping groove, and the clamping sleeve is provided with a protrusion that matches the clamping groove; the base is provided with support columns, and the support columns are multiple and arranged in a circular shape; the broach is set in a space enclosed by multiple support columns; the upper end of the broach is connected to the support column through the clamping mechanism; the lower end of the broach is connected to the base through the clamping mechanism; a piezoelectric actuator is provided on the broach; it is characterized in that, The following steps are involved: S1. Build a three-dimensional model of the broach, perform modal analysis, select the axial resonant frequency, and avoid the adjacent radial modes; S2, piezoelectric actuator layout design; The piezoelectric actuator uses multiple PZT annular plates stacked symmetrically. The polarization direction of the PZT annular plates is consistent with the axial direction of the broach, and the polarization direction of the PZT annular plates is designed to alternate between + and -. S3, multi-physics coupling simulation; Analyze the vibration stability of the ultrasonic broaching system under the interaction of broaching force and ultrasonic vibration to avoid the modal drift of the ultrasonic broaching system; specifically include: S3-1. Establish a multi-physics coupling model integrating structural mechanics, piezoelectric effect, and contact mechanics in finite element software; S3-2. Set the boundary conditions of the broach according to the broaching working conditions, including the clamping conditions at both ends of the broach; S3-3, load condition simulation; S3-4, modal and harmonic response analysis; (1) Prestressed modal analysis; Determine the stress distribution under static broaching forces; calculate modal frequencies and vibration shapes based on the prestressed state; compare modal parameters with those under no load and identify frequency drift; (2) Harmonic response analysis; Frequency sweep: Apply a sweep voltage in the target frequency band and observe the amplitude-frequency curve; Comparative analysis of axial amplitude attenuation: observe whether the vibration amplitude under load still meets the processing requirements; Radial vibration suppression: Verify whether non-target modes are excited; S3-5, stability assessment and optimization; (1) Setting the criteria for modal drift determination; (2) Modal drift detection and diagnosis; Use a laser vibrometer to measure the axial / radial amplitude of the tool tip or a current sensor to monitor the output current phase of the ultrasonic power supply. If the current phase angle suddenly increases and the amplitude decreases, it indicates frequency drift. Use FFT analysis to analyze the vibration spectrum and confirm the location of the new resonance peak. (3) Adjustment and optimization after modal drift occurs; a. Dynamic adjustment of preload force; Adjust the preload force of PZT. When the preload force is insufficient, increase the preload force. When the preload force is excessive and exceeds the PZT stress limit, reduce the preload force to a safe range. b. Adaptive tracking of driving frequency; A frequency-adjustable signal is generated using a DSP or FPGA and output to the PZT via a high-voltage amplifier. A phase-locked loop (PLL) is used to track the resonant frequency in real time, and a phase detector compares the phase difference between current and voltage. The frequency adjustment range is limited to the PZT operating frequency band. A voltage-controlled oscillator dynamically adjusts the drive frequency, using a gradient descent method to iteratively search for the optimal frequency with the goal of maximizing the amplitude. ； in is the step size, and A1 is the amplitude.

2. The ultrasonic vibration mode shape control method according to claim 1, characterized in that: In step S3-1, the multi-physics coupling model includes: Piezoelectric-structural coupling model, used to define the relationship between the voltage input of the PZT and the structural vibration response; Contact nonlinear model, used to set the preload and friction conditions of the PZT-broach interface; Damping model: Rayleigh damping or structural damping is used to simulate energy dissipation; Mesh precision model, used to set mesh precision. The contact interface needs to be meshed finely, with at least 3 layers of elements. For nonlinear convergence models, enable the Geometric Nonlinearity option and set the Damping Factor to improve convergence.

3. The ultrasonic vibration mode shape control method according to claim 1, characterized in that: In step S3-3, the following operations are performed: (1) Static broaching force simulation; Apply static force to the broach cutting edge, analyze the superposition effect of preload force and broaching force, and evaluate the stability of the contact interface; (2) Dynamic load simulation; When the broaching force fluctuates periodically, the following time function is defined: ， in, Indicates the broaching force; is the cutting force determined by the number of teeth in stable cutting, and t is the time; is the number of teeth that cut in and out during cutting, that is, the cutting force determined by the changing number of teeth. It is the frequency of fluctuation in the number of teeth cut in and out during cutting, which is determined by the ratio of tooth spacing to broaching speed; (3) Boundary conditions; Clamping constraint: fixed broach clamping end; Preload force realization: Bolt preload, apply force or displacement through the "bolt preload" interface in the finite element software.

4. The ultrasonic vibration mode shape control method according to claim 1, characterized in that: In step S3-5, the judgment standard of modal drift adopts the threshold standard, that is, if the calculated modal frequency is , the measured modal frequency is ,when , it is determined that modal drift has occurred.

5. The ultrasonic vibration mode shape control method according to claim 1, characterized in that: In step S3-5, the adjustment method after modal drift further includes: c. Joint adjustment of preload force and frequency; The vibration frequency of the ultrasonic broach is measured in real time. When the broach frequency drifts, if the vibration frequency is lower than the target frequency and the phase angle is greater than the threshold, the broach ultrasonic vibration has a frequency mismatch. Drive frequency tracking is used. If the vibration frequency is lower than the target frequency and the phase angle is not greater than the threshold, the broach clamping nonlinearity is dominant, and the preload force is increased.

6. The ultrasonic vibration mode shape control method according to claim 5, characterized in that: In the process of joint adjustment of preload force and frequency, the frequency is adjusted to the new resonance point first. If the amplitude is still insufficient after the frequency adjustment, the preload force is adjusted.

7. The ultrasonic vibration mode shape control method according to claim 1, wherein: The position where the clamping mechanism clamps the broach is exactly on the vibration node of the broach.

8. The ultrasonic vibration mode shape control method according to claim 1, characterized in that: When the broach is installed vertically, the upper groove angle of the clamping groove is recorded as , the lower end groove angle of the clamping groove is recorded as , the raised angle of the clamping sleeve is recorded as , the raised angle of the lower end of the clamping sleeve is recorded as , then: ， ； > 。 9. The ultrasonic vibration mode shape control method according to claim 1, wherein: The piezoelectric actuator is composed of a plurality of piezoelectric ceramic sheets connected in series. The polarization directions of the plurality of piezoelectric ceramic sheets are consistent with the axial direction of the broach, and the polarization directions are alternating between + and -.

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