Process for the precision sheet metal chipless forming

Abstract

The present application relates to the technical field of metal plate non-cutting processing, and discloses a precision metal plate non-cutting forming machining process, which comprises the following steps: maintaining the system stiffness chain load balance state in the forming pressure maintaining stage, so that the internal elastic strain energy is stably distributed; acquiring the driving main motor bus current sample value in real time, and extracting the load fluctuation signal representing the intrinsic vibration of the mold; determining the real-time elastic recovery phase of the mold based on the load fluctuation signal, and calculating the initial phase and loading rate of the reverse compensation load required to offset the system elastic hysteresis; and applying pulse load to the precision metal plate according to the initial phase and loading rate in the stepped unloading process, and neutralizing the internal residual strain energy in situ through phase counterattack, so that the dynamic mechanical response of the current characteristic closed-loop sensing system is realized, the stress and strain energy is precisely neutralized, the distortion of the formed part is effectively inhibited, and the forming precision is improved.

Description

Technical Field

[0001] This invention relates to a precision metal sheet non-cutting forming process, belonging to the field of non-cutting metal sheet processing technology. Background Technology

[0002] Currently, in the non-cutting process of precision metal sheet, the elastic rebound of the material is a physical obstacle that restricts the forming accuracy. Existing technologies usually adopt geometric compensation methods, which correct the mold surface according to the preset rebound amount and offset the shape deviation after unloading by reserving compensation allowance. However, the plastic flow of metal sheet involves dislocation accumulation and strain hardening behavior. These physical evolution laws are affected by material batch fluctuations, microstructure uniformity and processing environment, and exhibit nonlinear characteristics.

[0003] Existing static geometric compensation paths are difficult to adapt to the dynamic drift of material properties. Current displacement control or constant load control schemes only focus on achieving the macroscopic shape of the material and fail to address the in-situ adjustment of the residual stress field at the end of forming. This results in uneven distribution of elastic recovery energy released at the moment of unloading. For example, Chinese invention patent CN120587310A discloses a non-cutting automatic processing equipment for metal plates and its usage method. It uses a PLC in conjunction with pressure and position sensors to realize an automated closed loop of feeding, forming and mechanical clamping. Essentially, it belongs to macroscopic quasi-static control. At the moment of unloading, it cannot sense the evolution of microscopic stress caused by work hardening and system elastic hysteresis. It cannot actively intervene in the internally accumulated residual strain energy and lacks a high-frequency capture and phase compensation mechanism for intrinsic dynamic signals such as the drive motor bus current. The adjustment action lags behind the elastic recovery of the material, resulting in uncontrollable distortion during the stress release of the formed part, which is difficult to meet the springback suppression requirements of precision components such as high-strength steel.

[0004] Therefore, the technical problem to be solved by this invention is how to address the uncontrollable dynamic evolution of residual stress field at the end of precision metal sheet forming and the limitation of forming accuracy caused by the inability to offset elastic rebound potential energy in situ. Summary of the Invention

[0005] To address the problems mentioned in the background art, the technical solution of the present invention is as follows: A precision metal plate non-cutting forming process, comprising the following steps:

[0006] Step S1: In the precision metal plate forming and pressure holding stage, the system stiffness chain consisting of the press actuator, forming mold and precision metal plate is in a load balance state. The preset forming load is maintained by the actuator so that the elastic strain energy inside the system stiffness chain can reach a stable distribution state.

[0007] Step S2: Real-time acquisition of the bus current sampling value of the main motor driving the press actuator, and extraction of the load fluctuation signal characterizing the elastic recovery characteristics of the system stiffness chain. The load fluctuation signal originates from the micro-amplitude pulsation characteristics of the current induced by the intrinsic vibration of the molding die in the reverse electromotive force of the main motor driving the press.

[0008] Step S3: Determine the real-time elastic recovery phase of the forming mold based on the load fluctuation signal, and calculate the starting phase and loading rate of the reverse compensation load required to counteract the elastic hysteresis of the stiffness chain of the precision metal plate according to the material hardening index of the precision metal plate.

[0009] Step S4: Perform a stepped unloading action consisting of two return strokes. During the step unloading action, apply a pulse-shaped reverse compensation load to the precision metal plate according to the initial phase and loading rate. Utilize the phase offset generated by the reverse compensation load and the elastic recovery phase of the forming mold to neutralize the residual strain energy inside the precision metal plate in situ, thereby achieving precision forming of the precision metal plate.

[0010] Preferably, in step S2, the bus current sampling value is acquired at a sampling frequency of not less than 100kHz, and the high-frequency pulsating signal superimposed on the steady-state current component is extracted to identify the dynamic mechanical response frequency of the system stiffness chain under the pressure-holding state, and the dynamic mechanical response frequency is used as the carrier reference for generating the reverse compensation load.

[0011] Preferably, step S3 specifically includes: in the initial unloading stage of the stepped unloading action, collecting the transient unloading displacement and load change rate of the precision metal plate, determining the real-time stiffness deviation coefficient of the current precision metal plate, and correcting the amplitude of the reverse compensation load according to the real-time stiffness deviation coefficient.

[0012] Preferably, the amplitude of the reverse compensation load Satisfy the following formula: Where α is the preset load conversion gain, The rate of change of the bus current sampling value over time. This is the real-time stiffness deviation coefficient. This is the preset standard stiffness reference value for materials.

[0013] Preferably, during step S4, an alternating micro-vibration load with a frequency of 15kHz to 25kHz is applied to the contact interface between the forming mold and the precision metal plate to reduce the transient friction coefficient of the contact interface and eliminate interface lock-up during the stress neutralization process.

[0014] Preferably, step S4 further includes: according to the preset vector compensation parameters of the rolling direction of the precision metal plate, when the reverse compensation load is applied, the horizontal component force is superimposed by the actuator to guide the reverse strain energy generated by the reverse compensation load to the deep cavity forming area of ​​the precision metal plate, so as to suppress the anisotropic distortion of the formed part.

[0015] Preferably, the stepped unloading action includes: performing the first stage of return unloading to release the system elastic deformation energy of the press actuator and maintain the clamping state between the forming mold and the precision metal plate; and performing the second stage of constant speed unloading during the period of applying the reverse compensation load.

[0016] Preferably, in step S3, the initial phase is determined by: detecting the peak of the load fluctuation signal and setting the phase difference between the loading start time of the reverse compensation load and the peak. To achieve phase offset at the physical level, the angles must be between 170° and 190°.

[0017] Preferably, the process also includes a real-time monitoring step: comparing the power spectral density changes of the load fluctuation signal before and after the application of the reverse compensation load, and stopping the application of the reverse compensation load when the amplitude attenuation ratio of the power spectral density at the dynamic mechanical response frequency reaches a preset threshold.

[0018] Preferably, in step S1, the duration of the load balance state is dynamically preset based on the thickness tolerance and material hardening characteristics of the precision metal plate, so that the elastic strain energy inside the system stiffness chain reaches a stable distribution state.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. In the non-cutting forming of metal sheets, the in-situ neutralization of the residual stress field and the in-situ absorption of elastic potential energy within the sheet are achieved. The inflection point of the material's work hardening rate is identified in real time using the second derivative of the applied load with respect to displacement, accurately capturing the physical moment when the metal sheet enters global plastic rheology. Combined with the micro-creep induced during the holding pressure stage, some lattice distortion energy is released in the form of heat. On this basis, by applying a reverse pulse load opposite to the main forming direction and matching the Bauschinger effect of the material before the main load is unloaded, micro-reverse slip of the lattice is induced, and a reverse internal stress field is constructed. This reverse internal stress field physically cancels out the forming residual stress field, causing the elastic recovery potential energy at the moment of unloading to be dissipated by the plastic energy dissipation within the sheet, effectively suppressing the springback of precision metal parts and improving the surface fidelity under non-cutting conditions.

[0021] 2. Eliminating the implicit interference of the elastic hysteresis of the closed stiffness chain of the processing system on the molding accuracy, this invention collects the feedback load signal of the servo actuator and extracts the intrinsic elastic vibration frequency of the mold system from it. It calculates the phase difference angle caused by the elastic hysteresis of the system and determines the trigger phase of the reverse pulse load. This makes the rising edge of the reverse pulse load cancel each other out with the elastic recovery peak of the mold system. Through this system-level momentum impedance matching, the phase drift and amplitude attenuation of the pulse energy when passing through the interface between the press slide and the mold are avoided. This ensures that the reverse strain energy acts directly on the dislocation pile-up region in the thickness direction of the sheet metal. This solves the problem of uneven energy transfer caused by insufficient stiffness of the mechanical system in traditional processes and enhances the mobility and stability of the molding process on different equipment.

[0022] 3. Achieving adaptive high-precision compensation for fluctuations in intrinsic properties of materials across batches: This invention utilizes the initial slope of the load and displacement curves collected during the initial exploratory unloading stage after the main forming action is completed. By comparing this real-time slope with the standard elastic modulus online, the transient elastic resistance deviation coefficient of the current sheet is calculated, and the peak value and duration of the reverse pulse load are corrected in real time accordingly. This ensures that the generated reverse strain energy is physically equivalent to the actual elastic recovery requirements of the current material. This mechanism transforms the dynamic drift of material properties into feedback input for the control system, eliminating the failure of springback suppression caused by fluctuations in material hardening index or thickness tolerance. It realizes the transformation of precision forming from relying on manual mold-making experience to relying on logical closed-loop shape control. Attached Figure Description

[0023] Figure 1 This is a flow chart of the precision metal plate non-cutting forming process of the phase-counting precision metal plate of the present invention;

[0024] Figure 2 This is a diagram of the molding control data processing architecture for multimodal feature fusion according to the present invention. Detailed Implementation

[0025] The technical solution provided by the present invention will be described in detail below with reference to the accompanying drawings. The following embodiments are intended to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0026] The precision metal sheet forming process provided by this invention consists of several stages, including precision metal sheet forming and holding pressure, high-frequency sampling of the drive motor bus current, calculation of reverse compensation load parameters, and application of stepped unloading load. These stages interact in a closed loop through real-time data streams from a servo control system. The press actuator, forming die, and precision metal sheet form a system stiffness chain. By monitoring the micro-amplitude pulsations in the current induced by the reverse electromotive force of the main motor, the physical parameters required to counteract the system's elastic hysteresis are determined, achieving in-situ neutralization of residual strain energy at the end of plastic forming. During the precision metal sheet forming and holding pressure stage, the system stiffness chain consisting of the press actuator, forming die, and precision metal sheet is in a load-balanced state. The actuator maintains the preset forming load, ensuring the system stiffness... The elastic strain energy inside the stiffness chain is stably distributed. During this process, the actuator drives the forming head to reach the displacement endpoint and performs a dwell, inducing micro-creep inside the precision metal plate, causing the lattice distortion energy to be released in the form of heat energy, and realizing the initial relaxation of the stress field inside the plate. The bus current sampling value of the main motor driving the press actuator is acquired in real time, and the load fluctuation signal characterizing the elastic recovery characteristics of the system stiffness chain is extracted. The load fluctuation signal comes from the micro-amplitude pulsation characteristics of the current induced by the intrinsic vibration of the forming die in the reverse electromotive force of the main motor. In the specific acquisition process, the system acquires the bus current sampling value at a sampling frequency of not less than 100kHz, and extracts the high-frequency pulsation signal superimposed on the steady-state current component to identify the dynamic mechanical response frequency of the system stiffness chain under the pressure holding state.

[0027] The system determines the real-time elastic recovery phase of the molding die based on the load fluctuation signal, and calculates the starting phase and loading rate of the reverse compensation load required to counteract the elastic hysteresis of the system stiffness chain based on the material hardening index of the precision metal plate. The method for determining the starting phase includes: detecting the peak of the load fluctuation signal, setting the phase difference ϕ between the loading start time of the reverse compensation load and the peak to satisfy the range of 170° to 190°, and the system uses a formula... Determine the amplitude of the reverse compensation load, where, α represents the amplitude of the reverse compensation load; α represents the load conversion gain. The rate of change of the bus current sampling value over time; This is the real-time stiffness deviation coefficient; The material standard stiffness reference value is preset; a stepped unloading action consisting of two stages of return is performed. During the stepped unloading action, a pulse-form reverse compensation load is applied to the precision metal plate according to the determined initial phase and loading rate. The phase offset generated by the reverse compensation load and the elastic recovery phase of the forming die is used to neutralize the residual strain energy inside the precision metal plate in situ. The stepped unloading action includes: performing the first stage of return unloading to release the system elastic deformation energy of the press actuator and maintain the clamping state between the forming die and the precision metal plate; performing the second stage of constant speed unloading during the period of applying the reverse compensation load; during the above unloading action, an alternating micro-vibration load with a frequency of 15kHz to 25kHz is applied to the contact interface between the forming die and the precision metal plate. This load is generated by a high-frequency piezoelectric transducer integrated in the die support plate. The critical frequency point when the friction coefficient transitions from static friction to dynamic friction is identified by frequency sweep test. And set the frequency used in formal production as the critical frequency point. It is 1.1 times that of the static friction equilibrium of the contact interface by using micro-amplitude alternating stress, so that the contact interface transitions to the dynamic friction state, thereby reducing the transient friction coefficient of the contact interface and eliminating interface lock-up during the stress neutralization process.

[0028] To address the anisotropic distortion generated during the rolling process of precision metal sheets, the system presets vector compensation parameters based on the rolling direction of the precision metal sheet. When a reverse compensation load is applied, a horizontal component force is superimposed via a lateral auxiliary cylinder of the actuator to guide the reverse strain energy generated by the reverse compensation load to the deep cavity forming area of ​​the precision metal sheet. The system utilizes an ultrasonic detection unit to obtain the sound velocity deviation of the precision metal sheet in the parallel and perpendicular rolling directions, and calculates the anisotropic strength coefficient. Based on this, a bias operator is introduced into the vector decomposition path of the reverse compensation load to maintain the ratio of the horizontal component force to the main forming load in the range of 0.05 to 0.08. The power spectral density change of the load fluctuation signal before and after the application of the reverse compensation load is compared. When the peak energy attenuation ratio at the dynamic mechanical response frequency reaches the preset power spectral density attenuation threshold Γ, it is determined that the internal dislocation pile-up has reached a stable state and the application of the reverse compensation load is stopped. The power spectral density attenuation threshold Γ is determined by the correlation curve between the residual stress neutralization rate and the signal amplitude attenuation established by the offline controlled stress relaxation experiment. This monitoring logic ensures that the reverse loading action always occurs within the time window of the material rheological properties.

[0029] Example 1: In the forming process of a deep-drawn curved surface component of ultra-high strength steel with a thickness of 1.2mm and a tensile strength of 980MPa, the strain hardening caused by dislocation accumulation inside the material exhibits nonlinear variation with batch fluctuations. This leads to the energy distribution within the closed stiffness chain of the processing system deviating from the preset model, resulting in uneven release of elastic recovery energy after unloading. To address the forming accuracy challenge caused by material performance fluctuations, when the press actuator drives the forming head to the displacement endpoint and enters the non-isothermal holding pressure stage, the system collects the bus current sampling value of the drive main motor and extracts the high-frequency pulsating signal superimposed on the steady-state current component at a sampling frequency of 100kHz. From this, the load fluctuation signal characterizing the intrinsic vibration of the forming mold is identified. During the execution of the first-stage return unloading action, the control unit determines the real-time stiffness deviation coefficient based on the transient unloading displacement and load change rate of the precision metal plate. And according to the preset material standard stiffness benchmark value The magnitude of the reverse compensation load used to neutralize residual stress is determined using the following formula. : ,in, The magnitude of the reverse compensation load is expressed in nanoseconds (N), and α is the preset load conversion gain. The rate of change of the bus current sampling value over time, in A / s. This refers to the real-time stiffness deviation coefficient determined during the initial unloading phase, expressed in N / mm. The material stiffness reference value is set in N / mm. A 200N test pulse is applied during the dwell phase of the servo actuator at the end of the displacement. Synchronously acquire the effective value of the bus current response According to the formula The load conversion gain α is calibrated, and the calibration procedure is based on the principle of energy equivalence to eliminate the influence of motor torque constant and transmission efficiency fluctuations.

[0030] The system performs three displacement detection actions 0.5 mm before the preset endpoint, applying a pressure increment of 150 N each time and collecting the displacement feedback variable Δs, according to the formula... Determine the real-time stiffness reference value for the current batch of sheet metal. Alternating micro-vibration loads of 15kHz to 25kHz were applied to the high-frequency piezoelectric transducer of the mold support plate. Frequency sweep tests were used to identify the critical frequency point for the transition from static friction to dynamic friction. The production frequency is set to 1.1 times the critical point to ensure that the transient friction coefficient is reduced to the range of 0.05 to 0.08 during unloading, thereby eliminating stress neutralization and interface lock-up. The system detects the peak of the load fluctuation signal to determine the real-time elastic recovery phase of the molding die, and sets the phase difference ϕ between the loading start time of the reverse compensation load and the peak to 180°. While performing the second-stage constant-speed unloading action, a pulsed reverse compensation load is applied. The microscopic reverse slip of the lattice induced by the reverse compensation load interacts destructively with the elastic recovery phase of the system stiffness chain, neutralizing the residual strain energy inside the precision metal plate in situ. During this process, the contact interface is subjected to an alternating micro-vibration load with a frequency of 20kHz through a high-frequency piezoelectric transducer to reduce the transient friction coefficient during unloading and eliminate interface lock-up during stress release, so that the springback of the molded part after unloading is controlled within 0.01mm.

[0031] Example 2: Verifying the effectiveness of precision metal sheet non-cutting forming process in suppressing springback of ultra-high strength steel; the experiment used a multi-axis servo stamping verification platform, which integrates a pressure sensor with 10N force resolution and a displacement monitoring unit with repeatability better than 0.002mm; the experimental data came from real-time signals collected by the physical experimental platform; to simulate a real industrial electromagnetic environment, random pulse interference with a signal-to-noise ratio of 20dB was superimposed in the signal acquisition path; the core parameter sampling frequency was set to 100kHz, and the value of this parameter depends on the technical trade-off between the completeness of capturing the intrinsic vibration frequency of the forming die and the computational load of the servo control system; when the sampling frequency is below 50kHz, the high-frequency characteristics in the bus current sampling value are aliased, resulting in the inaccurate extraction of the load fluctuation signal; when the sampling frequency exceeds 200kHz, the data flow surge causes the controller calculation cycle to time out; under the working conditions of an ambient temperature of 25℃ and an ambient humidity of 45%, for a thickness of The decision logic was applied to 1.2mm thick duplex DP980 steel plates, with a sampling frequency of 100kHz to ensure signal fidelity. A problem strength gradient control system was constructed to evaluate process stability. Three gradients were set according to the material's tensile strength: 590MPa, 780MPa, and 980MPa. Experimental group one applied the phase-counting in-situ strain energy neutralization procedure described in the specific implementation. Control group one removed the reverse compensation load application step and adopted a static pressure holding process. Control group two removed the load fluctuation signal extraction step and applied a fixed-amplitude reverse pulse only at the moment of unloading. Under the DP980 gradient condition, the original rebound displacement observed in control group one was distributed between 0.125mm and 0.142mm, exhibiting non-uniform characteristics. In experimental group one, during the first stage of return unloading, a load fluctuation signal with a center frequency of 3.2kHz was extracted from the feedback load signal of the main motor, and the real-time stiffness deviation coefficient was calculated based on the initial unloading slope. for .

[0032] During the period of applying the reverse compensation load, the system monitors the changing trend of the residual stress field inside the precision metal plate; using the formula... Determine the output amplitude; where, The magnitude of the reverse compensation load is expressed in nanometers (N); α is the preset load conversion gain. The time-varying rate of change of the bus current sampling value is expressed in A / s. The real-time stiffness deviation coefficient is determined during the initial exploratory unloading phase, and its unit is N / mm; This is a preset standard material stiffness reference value, with units of N / mm; in this example, the preset standard material stiffness reference value is... for The load conversion gain α is set to 0.85, and the time change rate of the real-time acquired bus current sampling value is... The value is 12.4 A / s; the amplitude of the reverse compensation load is calculated. The normal stress at the contact interface of the precision metal plate decreased instantaneously at the moment of opposition when the phase difference ϕ was maintained at 180°. Data recording showed that as the tensile strength increased from 590MPa to 980MPa, the springback suppression rate of control group 2 decreased from 65% to 42%, showing performance degradation. However, the springback amount of test group 1 remained stably within the range of 0.008mm to 0.012mm, and its springback suppression effect did not deteriorate linearly with the increase of material strength. Boundary verification of key parameters was carried out, and the influence of the micro-vibration frequency of the contact interface on the interface locking phenomenon was investigated. When the micro-vibration frequency was set below 10kHz, the transient friction coefficient of the contact interface remained above 0.18. During the stress neutralization process, the local friction coefficient was reduced. Stress buildup occurs in certain areas, leading to scratches on the sidewalls of the molded part. When the frequency is increased to the 15kHz to 25kHz range, the transient friction coefficient decreases to 0.05 to 0.08, and the dislocation slip path inside the sheet metal is unobstructed. When the frequency exceeds 30kHz, power spectral density monitoring shows that energy is dissipated at high frequency at the mold support plate, and the molding accuracy no longer increases with frequency, exhibiting a performance saturation effect. Finally, the contour deviation of the DP980 molded part was reduced from 0.086mm in the original state to 0.009mm. The experimental results confirm that by sensing the mechanical response of the high-frequency current characteristic closed loop and implementing phase offset, the machining accuracy limitation caused by the coupling effect of intrinsic springback and system elastic hysteresis in precision metal forming can be solved.

[0033] Example 3: This example combines Figures 1 to 2 A description of the machining process for precision metal sheet forming without cutting, such as... Figure 1As shown, in step S1, during the pressure holding stage of precision metal plate forming, the system stiffness chain consisting of the press actuator, forming mold, and precision metal plate is in a load balance state. The actuator maintains the preset forming load so that the elastic strain energy inside the system stiffness chain reaches a stable distribution state. Step S2 is then executed to acquire the current sampling value of the drive main motor bus in real time and extract the load fluctuation signal that characterizes the elastic recovery characteristics of the system stiffness chain to identify the current micro-amplitude pulsation induced by the intrinsic vibration of the forming mold. Step S3 is then executed to determine the real-time elastic recovery phase of the forming mold based on the load fluctuation signal and to calculate the starting phase and loading rate of the reverse compensation load required to offset the elastic hysteresis of the system stiffness chain according to the material hardening index. Finally, step S4 is executed to perform a stepped unloading action, applying a pulse-shaped reverse compensation load according to the starting phase and loading rate, and using phase offset to neutralize the residual strain energy inside the precision metal plate in situ to achieve precision forming.

[0034] like Figure 2 As shown, the real-time bus current sequence is received as time-series data input and its fluctuation features are captured through a one-dimensional convolutional layer. Then, it is input into a long short-term memory layer for time-series dependency modeling. At the same time, the system stiffness chain parameters are received as static data and material property data are received as auxiliary data. The stiffness and material mapping is completed through the first fully connected encoding layer and the high-dimensional feature abstraction is performed through the second fully connected encoding layer. The time-series features output by the long short-term memory layer and the abstract features output by the fully connected encoding layer converge in the multi-modal feature fusion layer. The fused data stream enters the deep feature mapping layer 1. Finally, the system outputs in parallel the generation of a stepped unloading strategy for sequence decision-making, the elastic recovery phase determination for classification and phasing, and the reverse compensation load amplitude for regression prediction. The generated stepped unloading strategy will act on the physical system and affect the input at the next time step, forming a closed-loop control logic.

[0035] Example 4: In the deep drawing and non-cutting forming process of precision stainless steel shielding cavities for 5G communication base stations, the viscosity of the press guide rail lubricating oil fluctuates due to the increase in ambient temperature with continuous operation time. This induces nonlinear phase drift in the system stiffness chain, causing a phase mismatch between the reverse pulse load at the moment of unloading and the real-time elastic recovery phase of the forming die. The neutralization efficiency of residual stress at the bottom of the formed part decreases from the initial 92% to 78%. To compensate for the accuracy loss caused by the hysteretic dynamic evolution of the system, the system executes an initial state definition procedure before starting production, that is, controlling the actuator to perform 50 no-load cycles, so that the press... The main motor temperature rise is stabilized within the range of 45±2℃, and zero-point static calibration is performed using an integrated displacement sensor to ensure that the system stiffness chain is in a thermodynamic quasi-equilibrium state. After entering the molding and holding pressure stage, the system executes a load fluctuation signal extraction algorithm. A second-order Butterworth bandpass filter is applied to the bus current sampling value acquired at a frequency of 100kHz, with the lower cutoff frequency set to 1kHz and the upper cutoff frequency set to 8kHz to eliminate electromagnetic noise generated by inverter switching. The zero-crossing point of the filtered signal is identified by executing a zero-crossing detection algorithm, and the reciprocal of the time interval between adjacent zero-crossing points is calculated to determine the intrinsic vibration frequency of the molding die system. .

[0036] For load conversion gain To determine the accuracy, the system employs an energy equivalent calibration procedure. During the detection phase following the completion of the main deformation, a test pulse with an amplitude of 200N is applied via an actuator. Synchronously acquire the response amplitude of the bus current According to the formula Calculate the gain; where α is the load conversion gain, in N / A. The preset test pulse amplitude is 200N. The observed effective value of the response current is expressed in amperes (A). This procedure eliminates the influence of motor torque constant and mechanical transmission efficiency fluctuations on load calculation. During the execution of stepped unloading, the control unit identifies the peak moment of the load fluctuation signal. And calculate the pulse trigger time based on the determined initial phase ϕ. The specific calculation formula is as follows: ,in, The starting time of the reverse compensation load is expressed in seconds. ϕ represents the peak time of the load fluctuation signal, measured in seconds; ϕ is the preset starting phase, with a value of 180°. The intrinsic vibration frequency is expressed in Hz. While performing the phase-counteracting action, the system monitors the acoustic emission signal energy distribution at the interface between the precision metal plate and the forming mold. When a steep decay of the high-frequency acoustic emission characteristic energy above 200kHz is detected and the power spectral density tends to flatten, it is determined that the internal residual strain energy has been dissipated in situ through microscopic reverse slip. At this time, the system automatically terminates the second-stage constant-speed unloading and exits the mold. Through the execution of the above procedure, the flatness error at the bottom of the shielding cavity is reduced from 0.12mm to 0.015mm. This process transforms phase matching into triggering logic based on the time-domain characteristics of the bus current, solving the uncertainty of the stress response caused by mechanical wear and thermal deformation, and maintaining the process consistency under large-scale continuous production.

[0037] Example 5: In the deep drawing process of 5083 aluminum alloy sheet, due to the differences in grain orientation and work hardening characteristics between different batches of sheet, the system establishes control parameters through on-site pre-calibration procedures before continuous production. The on-site pre-calibration procedures include: controlling the press actuator to perform three displacement detection actions 0.5mm before the forming displacement reaches the preset endpoint, with each displacement detection applying a pressure increment of 150N, and simultaneously collecting the displacement feedback variable Δs; the control unit then uses the formula... Determine the real-time stiffness reference value of the current batch of plates. and the real-time stiffness reference value The values ​​are stored in the system stiffness chain database as input parameters for calculating the reverse compensation load; the system is based on real-time stiffness reference values. The correlation with the material hardening index was used to determine the loading rate of the reverse compensation load. When the real-time stiffness reference value for Furthermore, when the material hardening index is 0.18, the determined loading rate is... for .

[0038] During the application of a reverse compensation load to the aforementioned aluminum alloy sheet, the system monitors the power spectral density of the load fluctuation signal in real time using a high-frequency sampling unit. The pre-set power spectral density attenuation threshold Γ is 35%. The power spectral density attenuation threshold Γ is determined by measuring the correlation curve between the residual stress neutralization rate and the attenuation of the load fluctuation signal amplitude through offline stress relaxation experiments, identifying the dynamic mechanical response frequency corresponding to the residual stress decreasing to below 10 MPa. The energy component at the location; when the dynamic mechanical response frequency is monitored. When the peak energy attenuation ratio reaches the power spectral density attenuation threshold Γ, the control unit commands the main motor to stop outputting reverse pulses and initiates the second-stage constant-speed unloading. The peak residual stress in the plate forming area decreases from 186.4 MPa to 7.8 MPa, and the flatness error of the plate forming surface remains within 0.012 mm. The control unit compares the power spectral density changes of the load fluctuation signal before and after the application of the reverse compensation load in real time. Using offline controlled stress relaxation experiments, the correlation curve between the residual stress neutralization rate and the signal amplitude attenuation is established, and the dynamic mechanical response frequency corresponding to the residual stress dropping below 10 MPa is identified. At the energy component, determine the power spectral density at frequency. When the peak energy attenuation ratio reaches a preset threshold Γ of 35%, the command drives the main motor to stop outputting reverse pulses and starts the second-stage constant speed unloading. The system synchronously monitors the energy distribution of high-frequency acoustic emission characteristics above 200kHz, determines that the acoustic emission signal has a steep attenuation and the spectrum tends to flatten, confirms that the internal residual strain energy is dissipated in situ through the microscopic reverse slip of dislocations, and transforms the phase matching into triggering logic based on the time domain characteristics of the bus current to ensure that the springback consistency of the molded parts meets the preset deviation requirements under large-scale continuous production.

[0039] Example 6: In the precision stretch forming process of 6061-T6 aluminum alloy components, the yield strength ratio of different material batches fluctuates, causing changes in the lattice reverse slip resistance in the unloading path. Before continuous production, the system executes a control benchmark correction procedure. The control benchmark correction procedure includes: selecting a sample of the sheet material to be processed to perform a loading and unloading test, and determining the Bauschinger influence factor β of the current batch by calculating the ratio of the reverse yield stress to the forward flow stress; the system applies an excitation signal with a frequency sweeping from 500Hz to 5000Hz by driving the main motor and monitors the response amplitude of the bus current sampling value, locking the frequency corresponding to the peak value of the response current as the intrinsic vibration frequency. When the Bauschinger influence factor β is 0.72 and the intrinsic vibrational frequency... At 2850Hz, the control unit uses the formula Determine the loading rate of the reverse compensation load ;in, The loading rate of the reverse compensation load is expressed in N / s, η is the preset energy coupling coefficient with a value of 1.55, and β is the Bauschinger influence factor. The intrinsic vibration frequency is expressed in Hz.

[0040] During the aluminum alloy sheet forming process, the system extracts the power spectral density of the load fluctuation signal in real time during the 5ms dwell period after the first-stage return unloading action is completed. This power spectral density is used as a dynamic baseline and its correlation with the reference energy spectrum in the system stiffness chain database is calculated. When the cross-correlation coefficient is lower than the threshold of 0.85, the system adjusts the amplitude of the reverse compensation load in 1% increments. The real-time force response of the contact interface recovers to the resonant state; after applying a reverse pulse load with an initial phase ϕ of 180°, the normal stress distribution range of the precision metal plate forming area is reduced from 32.5MPa to 4.2MPa, and the measured profile deviation of the component is stable within the range of 0.008mm; when processing precision metal plates with rolling anisotropy, the system applies a reverse pulse load while simultaneously superimposing a horizontal component force through the lateral auxiliary cylinder of the actuator; the magnitude of the horizontal component force is determined by the preset vector compensation parameter of the rolling direction; the extraction procedure of the preset vector compensation parameter of the rolling direction includes: using an ultrasonic detection unit to obtain the sound velocity deviation of the precision metal plate in the direction parallel to and perpendicular to the rolling direction, and calculating the anisotropic strength coefficient. ;when When the value is 1.12 and the angle between the rolling centerline of the precision metal sheet and the axis of symmetry of the die is 30°, the system is based on the anisotropic strength coefficient. An offset operator is introduced into the vector decomposition path of the reverse compensation load to maintain the ratio of the horizontal component force to the main forming load in the range of 0.05 to 0.08. This horizontal component force generates a reverse shear stress flow to compensate for the difference in plastic flow rate of the sheet in different crystal orientations and eliminate the torsion distortion phenomenon of cavity-type components at the forming end.

[0041] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A machining process for precision metal sheet forming without cutting, characterized in that, Includes the following steps: Step S1: In the precision metal plate forming and pressure holding stage, the system stiffness chain consisting of the press actuator, forming mold and precision metal plate is in a load balance state. The preset forming load is maintained by the actuator so that the elastic strain energy inside the system stiffness chain can reach a stable distribution state. Step S2: Real-time acquisition of the bus current sampling value of the main motor driving the press actuator, and extraction of the load fluctuation signal characterizing the elastic recovery characteristics of the system stiffness chain. The load fluctuation signal originates from the micro-amplitude pulsation characteristics of the current induced by the intrinsic vibration of the molding die in the reverse electromotive force of the main motor driving the press. Step S3: Determine the real-time elastic recovery phase of the forming mold based on the load fluctuation signal, and calculate the starting phase and loading rate of the reverse compensation load required to counteract the elastic hysteresis of the stiffness chain of the precision metal plate according to the material hardening index of the precision metal plate. Step S4: Perform a stepped unloading action consisting of two return strokes. During the step unloading action, apply a pulse-shaped reverse compensation load to the precision metal plate according to the initial phase and loading rate. Utilize the phase offset generated by the reverse compensation load and the elastic recovery phase of the forming mold to neutralize the residual strain energy inside the precision metal plate in situ, thereby achieving precision forming of the precision metal plate.

2. The machining process for precision metal plate forming without cutting according to claim 1, characterized in that, In step S2, the bus current sampling value is acquired at a sampling frequency of not less than 100kHz, and the high-frequency pulsating signal superimposed on the steady-state current component is extracted to identify the dynamic mechanical response frequency of the system stiffness chain under the pressure holding state, and the dynamic mechanical response frequency is used as the carrier reference for generating the reverse compensation load.

3. The machining process for precision metal plate forming without cutting according to claim 1, characterized in that, Step S3 specifically includes: in the initial unloading stage of the stepped unloading action, collecting the transient unloading displacement and load change rate of the precision metal plate, determining the real-time stiffness deviation coefficient of the current precision metal plate, and correcting the amplitude of the reverse compensation load based on the real-time stiffness deviation coefficient.

4. The machining process for precision metal plate forming without cutting according to claim 3, characterized in that, amplitude of reverse compensation load Satisfy the following formula: Where α is the preset load conversion gain, The rate of change of the bus current sampling value over time. This is the real-time stiffness deviation coefficient. This is the preset standard stiffness reference value for materials.

5. The machining process for precision metal sheet forming without cutting according to claim 1, characterized in that, During step S4, an alternating micro-vibration load with a frequency of 15kHz to 25kHz is applied to the contact interface between the forming mold and the precision metal plate to reduce the transient friction coefficient of the contact interface and eliminate interface lock-up during the stress neutralization process.

6. The machining process for precision metal sheet forming without cutting according to claim 5, characterized in that, Step S4 further includes: according to the preset vector compensation parameters based on the rolling direction of the precision metal plate, when the reverse compensation load is applied, the horizontal component force is superimposed by the actuator to guide the reverse strain energy generated by the reverse compensation load to the deep cavity forming area of ​​the precision metal plate.

7. The machining process for precision metal plate forming without cutting according to claim 1, characterized in that, The stepped unloading action includes: performing the first stage of return unloading to release the system elastic deformation energy of the press actuator and maintain the clamping state between the forming mold and the precision metal plate; and performing the second stage of constant speed unloading during the cycle of applying the reverse compensation load.

8. The machining process for precision metal plate forming without cutting according to claim 1, characterized in that, In step S3, the initial phase is determined by detecting the peak of the load fluctuation signal and setting the phase difference ϕ between the loading start time of the reverse compensation load and the peak to satisfy 170° to 190°, so as to achieve phase offset at the physical level.

9. The machining process for precision metal plate forming without cutting according to claim 1, characterized in that, The process also includes a real-time monitoring step: comparing the power spectral density changes of the load fluctuation signal before and after the application of the reverse compensation load, and stopping the application of the reverse compensation load when the amplitude attenuation ratio of the power spectral density at the dynamic mechanical response frequency reaches a preset threshold.

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