Electrical discharge-electrolytic combined machining proportion closed-loop regulation method and system

Abstract

This invention belongs to the field of special processing technology, specifically relating to a closed-loop control method and system for the proportion of EDM in electro-discharge-electrolysis composite machining. This invention adopts a hierarchical closed-loop control approach with hydraulic master control, addressing the process requirements of different stages—roughing, semi-finishing, and finishing—by formulating layered control strategies: high-proportion EDM-dominated, medium-proportion synergistic, and low-proportion ECM-dominated. Using inlet pressure as the main control variable, it achieves continuous switching of the EDM proportion within a wide range of 0.2~0.9, elevating high-pressure microbubbles to an active and precise control variable. It enables continuous stepless adjustment of the proportion within the same processing area and process, with rapid response to operating condition changes. A real-time high-frequency acquisition module collects voltage and current waveforms, and waveform feature recognition and a piecewise charge integration algorithm are used to calculate the actual EDM processing proportion online. This invention simplifies the process flow, reduces processing costs, significantly reduces harmful gas emissions, and is easy to promote in engineering projects.

Description

Technical Field

[0001] This invention belongs to the field of special processing technology, specifically relating to a closed-loop control method and system for the proportion of electrical discharge machining (EDM) and electrolytic composite machining, and more particularly to a closed-loop control method and system for the proportion of EDM and electrolytic machining based on high-pressure microbubbles. Background Technology

[0002] Electrical Discharge Machining (EDM) removes material based on the instantaneous high temperature of inter-electrode pulsed discharge. It is not limited by the hardness or strength of the workpiece material and can perform precision machining of complex surfaces and cavities. However, it easily produces a recast layer and microcracks on the workpiece surface after machining, degrading the workpiece's surface integrity and service performance. Electrochemical Machining (ECM) removes material based on the principle of electrochemical anodic dissolution. The process involves no cutting force and no residual stress, effectively eliminating the recast layer produced by EDM and resulting in excellent surface quality. However, the electrolytic process is accompanied by gas evolution side reactions, and strong electrolytic machining throughout produces a large amount of harmful gases, leading to high costs for environmental treatment and occupational health protection. Furthermore, excessive electrolysis can easily cause stray corrosion, resulting in decreased machining contour accuracy and damage to non-target areas.

[0003] Electrochemical Discharge Machining (ECDM) is a key technology for the precision manufacturing of difficult-to-machine metals such as titanium alloys, high-temperature alloys, and hardened steel, combining the advantages of both EDM and electrochemical machining. The instantaneous high temperature generated by EDM can locally disrupt the passivation film on the workpiece surface, providing reaction sites for electrolytic dissolution, thus ensuring the stable progress of the electrolytic process. Electrolytic dissolution can repair discharge defects and optimize surface integrity. However, this hybrid machining mode also has inherent process contradictions. In the roughing stage, which involves removing large allowances, it is necessary to increase the proportion of EDM machining to fully utilize the efficient etching capability of EDM. In the finishing stage, which involves surface polishing, it is necessary to increase the proportion of ECM machining to obtain a highly intact machined surface through electrolytic dissolution. Existing processes make it difficult to flexibly and continuously switch the proportion of each process within the same operation based on changes in machining allowance. The two mechanisms, EDM and ECM, exist in a competitive and mutually restrictive relationship within the inter-electrode gap. Increasing the proportion of EDM makes the workpiece more prone to recast layers and microcracks, exacerbating surface damage. Conversely, increasing the proportion of ECM leads to stray corrosion and harmful gas emissions. Neither mechanism can be maximized simultaneously through a single parameter adjustment, making it difficult to balance forming accuracy, surface quality, processing efficiency, and environmental friendliness within the same process. Therefore, achieving online, continuous, and quantitative control of the proportions of EDM and ECM to fully leverage their synergistic effect is a key technical challenge hindering the large-scale industrial application of this technology.

[0004] Current methods for controlling the proportion of EDM / ECM machining mainly revolve around three aspects: electrical parameter optimization, electrolyte formulation adjustment, and inter-electrode gap control. Modifying electrical parameters such as voltage, pulse width, and duty cycle can directly change the energy distribution during machining. However, this method is highly coupled between the two machining mechanisms, making decoupling control difficult. Mode switching often requires rematching the entire set of parameters, easily leading to decreased discharge stability and machining quality fluctuations, and the adjustment range is limited. Changing the electrolyte formulation and concentration can alter the intensity of electrolysis, but this method has a lag response, and switching between different electrolytes can easily introduce cross-contamination, significantly increasing process complexity and operating costs, and making online continuous adjustment during machining impossible. Adjusting the inter-electrode gap to change the electric and flow field distribution can also achieve a change in machining mode, but the inter-electrode gap in composite machining is typically only tens of micrometers, placing extremely high demands on the dynamic accuracy and stability of the machine tool feed system. The control window is narrow, making it difficult to adapt to complex dynamic machining processes.

[0005] Patent CN103480926A discloses a micro-hole EDM-Electrolysis heterogeneous synchronous composite machining method and its dedicated tool. It employs a spatial partitioning strategy, applying pulsed voltage to the tube electrode. Under high-voltage pulses, axial feed perforation is achieved at the end face via EDM, while radial electrolytic finishing is performed on the hole wall under low-voltage pulses. However, this scheme is essentially a "time-sharing / regional" machining approach, where EDM and electrolysis occur at different locations or times within the machining area. It cannot achieve online, continuous, and quantitative control of the proportion of the two mechanisms within the same machining area, and it does not address the active control of the machining medium by air bubbles. Patent CN114700568A discloses a method and apparatus for composite machining of groove structures using strip electrodes and electro-discharge. By controlling the voltage amplitude to vary within a range above or below the critical voltage of the electro-discharge, it initially achieves switching and control of the machining ratio. However, this scheme relies on voltage as an electrical parameter to achieve ratio switching, and can only achieve ratio adjustment within a limited range. Voltage switching is an open-loop control method, lacking a real-time feedback correction mechanism based on the machining state, and cannot adjust the ratio according to dynamic changes such as passivation film formation and product accumulation during machining. Patent CN212552139U discloses an inverted bubble-assisted chip removal ultrasonic vibration micro-electro-discharge composite system, utilizing bubble-assisted chip removal to improve the removal of eroded material during deep hole machining. Although this scheme introduces the concept of "bubble assistance," the bubbles only play a passive auxiliary role in chip removal, not for actively controlling the machining ratio of EDM and ECM. Furthermore, this patent is an open-loop auxiliary system; bubble parameters (pressure, flow rate) are supplied only according to preset values, lacking a closed-loop adjustment mechanism based on machining state feedback.

[0006] In summary, existing technologies cannot achieve continuous online adjustment of the processing ratio, making it difficult to simultaneously consider processing quality and environmental protection. The processing ratio control is mostly open-loop control, lacking a dynamic correction mechanism, resulting in insufficient process stability. Corresponding control logic and feedback rules have not been formulated for different process objectives of roughing, semi-finishing, and finishing. It is impossible to achieve multi-objective synergistic optimization of excess material removal, passivation film removal, and surface finishing. Furthermore, there is a lack of a technical solution for continuous online quantitative adjustment of the processing ratio using high-pressure microbubbles as the core control medium.

[0007] Therefore, there is an urgent need to develop a complete EDM / ECM ratio control method and system that combines closed-loop control and synergistic effects to achieve synergistic optimization of composite processing efficiency, quality and environmental protection. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a closed-loop control method and system for the proportion of EDM / ECM composite machining. Through the technical solution of high-pressure microbubble medium and hydraulic main control hierarchical closed-loop control, closed-loop feedback correction and staged differentiated control, the proportion of EDM / ECM machining can be controlled in a wide range, with high precision and online continuous control. The process is simplified, the processing cost is reduced, and the emission of harmful gases is greatly reduced, thus improving the environmental friendliness of the process.

[0009] The technical solution adopted is as follows: A closed-loop control method for the proportion of electrical discharge machining (EDM) and electrolytic composite machining includes the following steps: S1. Assembly and setting of fixed process parameters: Clamp the workpiece and tool electrode, turn on the liquid supply booster module and microbubble generation module, divide the process into three stages: roughing, semi-finishing and finishing, and preset the target EDM ratio range and corresponding initial liquid inlet pressure for each stage. S2. Roughing stage: Adjust the inlet pressure to the high pressure range, and use electric spark discharge erosion as the main method to achieve rapid material removal. By real-time current acquisition and online calculation of the proportion, the EDM proportion is kept stable within the target range. During the roughing stage, the inlet pressure is adjusted to 0.7~0.8 MPa, and the target EDM proportion is controlled at 0.85~0.9. The closed-loop control logic in the roughing stage is as follows: real-time high-frequency acquisition of inter-electrode current waveform, online calculation of the current actual EDM ratio using the current waveform integration method, and comparison of the deviation with the target ratio range; when the actual ratio is lower than the lower limit of the target range, the control system automatically increases the inlet pressure, increases the bubble volume fraction, reduces the equivalent conductivity of the medium, and enhances the local electric field distortion to increase the EDM discharge probability; when the actual ratio is higher than the upper limit of the target range, the control system reduces the inlet pressure, reduces the bubble volume fraction, and causes the ratio to fall back to the target range. S3. Semi-finishing stage: Gradually reduce the inlet pressure to the medium pressure range, so that EDM can break the passivation film and ECM can dissolve and repair in a synergistic way, taking into account both forming accuracy and surface quality. The target EDM ratio and the inlet pressure benchmark value are linearly adjusted down with the processing depth. In the semi-finishing stage, the inlet pressure is adjusted to 0.4~0.6 MPa, and the target EDM ratio is controlled at 0.45~0.78. The control strategy for adjusting the target EDM ratio and the reference value of the inlet pressure as the machining depth changes is as follows: for each preset step increase in machining depth, the target EDM ratio and the reference value of the inlet pressure are linearly adjusted downwards, while the hydraulic pressure is dynamically corrected in conjunction with real-time current feedback. S4. Finishing stage: Reduce the inlet pressure to the low pressure range, mainly remove the recast layer and microcracks by electrolytic dissolution, and rely on hydraulic closed-loop adjustment to compensate for the proportion drift fluctuation; during the finishing stage, adjust the inlet pressure to 0.2~0.3 MPa, and control the target EDM proportion at 0.2~0.3. The closed-loop control logic of the finishing stage is as follows: maintain the inlet pressure reference value constant, monitor the proportion fluctuation through real-time current, and when the proportion rises or falls abnormally, achieve closed-loop compensation by finely adjusting the inlet pressure to ensure that the electrolytic dissolution process is uniform and smooth. S5. By continuously adjusting the inlet pressure online, the three process modes of roughing, semi-finishing, and finishing can be smoothly switched to complete the workpiece processing; In the aforementioned control method, an electrolyte containing uniform microbubbles is delivered to the processing gap through a high-pressure microbubble generator. The inlet pressure is used as the main control variable to achieve continuous switching between the EDM and ECM processing ratios within the range of 0.2 to 0.9. Combined with synchronous acquisition of inter-electrode voltage and current, the ratio is calculated online through interval identification, filtering and noise reduction, cubic spline interpolation, and piecewise charge integration. This constructs a closed-loop control logic with target preset, real-time feedback, and dynamic correction.

[0010] Preferably, in step S1, the fixed process parameters include: applied voltage 70 V, pulse frequency 2 kHz, pulse duty cycle 50%, and electrolyte being a 2% NaNO3 aqueous solution. The electrolyte can be selected according to actual needs, such as NaCl, CaCl2, Ca(NO3)2, etc.

[0011] Preferably, the equivalent diameter of the microbubbles generated by the microbubble generation module is stably controlled within the range of 20~80μm; the pressure adjustment range is 0.2~0.8 MPa, and the high-pressure environment inhibits bubble coalescence and rupture, ensuring the stability of the flow field and dielectric properties of the medium.

[0012] Preferably, in step S3, the strategy corresponding to the linear reduction of the target EDM ratio and the inlet pressure benchmark value is as follows: The total number of processing layers is preset. Based on the total number of layers, the total processing depth of the workpiece is divided into several processing layers arranged in sequence. All processing layers are divided into roughing area, semi-finishing area and finishing area according to the processing feed sequence. The processing proceeds layer by layer from the first layer downwards. In each processing layer corresponding to the rough processing area, the preset target EDM ratio and the inlet pressure benchmark value are kept unchanged. After entering the semi-finishing area, as the number of processing layers increases, the target EDM ratio and the inlet pressure reference value decrease synchronously and linearly according to a preset ratio until the last layer of this area is processed; after entering the finishing area, the preset target EDM ratio and inlet pressure reference value for finishing are locked and maintained until the processing is completed. When each layer of processing is completed or the preset depth step is reached, the target EDM ratio and the inlet pressure benchmark setting value are updated. The setting value is used as the expected input, and combined with the actual EDM processing ratio collected in real time, the inlet pressure is dynamically corrected and compensated through closed-loop control.

[0013] Preferably, the inlet pressure and the proportion of EDM processing are monotonically positively correlated: the higher the inlet pressure, the larger the bubble volume fraction, the lower the equivalent conductivity of the medium, the stronger the electric field distortion, the higher the EDM discharge breakdown probability, and the larger the proportion of EDM processing; conversely, the proportion of ECM action increases.

[0014] Preferably, the online calculation of the proportion adopts the following method: The inter-electrode voltage waveform and the inter-electrode total current waveform are synchronously collected within a complete statistical period T, where the statistical period T is an integer multiple of the pulse period; the time-series sampling data for the entire time period is analyzed point by point; when the inter-electrode voltage experiences continuous fluctuations and the synchronous inter-electrode current rises, the continuous sampling period that simultaneously satisfies voltage drop and current rise is defined as the EDM discharge processing main interval; the period with only stable base current and no significant voltage drop is defined as the ECM electrolytic processing main interval; median filtering and noise reduction are performed on the discrete current sampling points in the EDM dominant interval to remove abrupt abnormal noise points; for the effective discrete current sampling points after noise reduction, cubic spline interpolation is used to construct a continuous instantaneous current function i. EDM (t); The piecewise definite integral of the fitted EDM discharge current function is performed, and the total charge of all spark discharges within the statistical period is accumulated. Then, the total inter-electrode current at all times within the complete statistical period is integrated to obtain the total inter-electrode charge within the period. The ratio of the total EDM discharge charge to the total charge of the period is calculated, and finally, the actual proportion coefficient of the current EDM is calculated online using the current waveform integration method. The formula is as follows: ; In the formula, R EDM EDM processing ratio coefficient, %; iEDM (t) represents the instantaneous EDM discharge current, A; i total (t) represents the instantaneous total inter-electrode current, in A; T is the statistical period, taken as an integer multiple of the pulse period to ensure statistical accuracy, in s; t is the time variable, in s; The ECM processing ratio is obtained by subtracting the EDM ratio from the total processing ratio.

[0015] This invention also provides a closed-loop control system for the proportion of electrical discharge machining (EDM) and electrolytic composite machining, used to implement the closed-loop control method, including a controller, and further comprising: The liquid supply booster module is used to receive industrial control output signals to steplessly adjust the liquid inlet pressure, change the bubble content in the electrolyte, and realize the range switching of EDM / ECM ratio; The microbubble generation module, connected downstream of the liquid supply and pressurization module, is capable of preparing a gas-liquid two-phase electrolyte and can achieve a wide range of changes in bubble volume fraction by adjusting the inlet pressure. The inter-electrode signal acquisition module can acquire and identify inter-electrode voltage and current waveforms at high frequency, and calculate the actual EDM processing ratio in real time through the built-in integration algorithm; The industrial control closed-loop control module is connected to the liquid supply booster module and the inter-electrode signal acquisition module respectively. It can receive the actual EDM processing ratio fed back by the inter-electrode signal acquisition module, compare it with the target ratio, output a pressure adjustment signal to the liquid supply booster module, and collect the electrode processing depth in real time, and switch the three-level processing conditions as needed.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention achieves wide-range, online, continuous, and quantitative control of the EDM / ECM processing ratio. It adopts a hierarchical closed-loop control approach with hydraulic main control. The inlet pressure is used as the main control means to achieve continuous switching of the EDM ratio within a wide range of 0.2~0.9; it can achieve continuous stepless adjustment of the ratio within the same processing area and the same process, and there is no need to stop the machine to change electrical parameters, change electrolyte, or adjust the inter-electrode gap. The working condition switching response is fast and there is no cross-contamination, which solves the defects of strong coupling and obvious lag in traditional single-parameter control.

[0017] (2) This invention constructs a closed-loop feedback control mechanism, which significantly improves process stability and reproducibility. Voltage and current waveforms are acquired in real-time at high frequency through an inter-electrode signal acquisition module. Waveform feature recognition and a piecewise charge integration algorithm are used to calculate the actual EDM processing ratio online, constructing a complete closed-loop control logic of "target preset → real-time acquisition → deviation comparison → dynamic correction". Furthermore, this invention can sense processing state fluctuations such as passivation film formation, product accumulation, and flow field changes in real time, and dynamically compensates for these fluctuations by automatically adjusting the inlet pressure. This effectively suppresses the phenomenon of the actual ratio deviating from the target value during processing, reduces the probability of abnormal discharge and stray corrosion, and improves the consistency of processing quality.

[0018] (3) This invention achieves efficient, high-quality, and environmentally friendly multi-objective synergistic optimization. For the differentiated process objectives of the three stages of roughing, semi-finishing, and finishing, a layered control strategy was formulated, with high EDM dominance, medium EDM synergy, and low ECM dominance respectively. In the roughing stage, an EDM proportion of 0.85-0.9% was used to achieve rapid removal of large allowances, avoiding the slow dissolution of the entire electrolytic machining process and significantly shortening the processing cycle. In the finishing stage, an ECM proportion of 0.7-0.8% was used as the dominant factor to effectively remove the recast layer and microcracks generated by EDM, obtaining a machined surface with excellent surface integrity, avoiding the drawback of requiring additional subsequent processing steps after EDM in the prior art. The ECM-dominant mode was used in the finishing stage, significantly shortening the duration of strong electrolytic machining, reducing the emission of harmful gases generated by the side reactions of electrolytic gas desorption from the source, while avoiding stray corrosion and damage to non-target areas caused by strong electrolysis throughout the process, reducing environmental protection and occupational health protection costs, and breaking through technical bottlenecks.

[0019] (4) This invention establishes for the first time a quantitative monotonic mapping relationship between the inlet pressure (0.2~0.8 MPa) and the EDM processing ratio (0.2~0.9), elevating high-pressure microbubbles from a passive role of merely assisting chip removal in existing technologies to a core control variable for actively and precisely regulating the processing mechanism. Simultaneously, this invention relies on the inlet pressure to achieve closed-loop adjustment of the ratio under all operating conditions, realizing wide-range ratio switching and fine-grained compensation under various operating conditions. The equivalent diameter of the microbubbles is stably controlled within the range of 20~80 μm, and the high-pressure environment inhibits bubble aggregation and collapse, ensuring the long-term stability of the inter-electrode flow field and the dielectric properties of the medium.

[0020] (5) This invention proposes a complete online quantitative characterization algorithm for EDM proportion: waveform synchronous acquisition → EDM / ECM interval feature identification → median filtering noise reduction → cubic spline interpolation to construct a continuous current function → piecewise charge integration → proportion calculation. This algorithm effectively solves the problems of misjudgment of interval division and distortion of charge calculation caused by the burr noise of the current waveform under continuous disturbance of high-voltage microbubbles. Cubic spline interpolation can completely restore the steep discharge peak of electric spark, adapt to the varied discharge waveforms under all working conditions of roughing, semi-finishing and finishing, and at the same time take into account the calculation accuracy and the real-time operation requirements of industrial control equipment, providing reliable real-time feedback data support for closed-loop control.

[0021] (6) The system of the present invention has strong compatibility and is easy to promote in engineering. The control method can be directly connected to the existing EDM-Electrolysis composite processing equipment without modifying the main body of the machine tool. It only needs to be equipped with a high-pressure microbubble generating unit and a current acquisition module, which has low modification cost and strong engineering implementation. Attached Figure Description

[0022] Figure 1 This invention provides the structure and schematic diagram of a closed-loop control system for the proportion of electrical discharge machining (EDM) and electrolysis composite machining.

[0023] Figure 2 This is a flowchart of a closed-loop control method for the proportion of electrical discharge-electrolysis composite processing according to the present invention.

[0024] Figure 3 The curves show the changes in the EDM / ECM processing ratio under different inlet pressures.

[0025] Figure 4 This is a typical voltage-current timing waveform diagram between electrodes in an electrical discharge-electrolysis composite machining process. Detailed Implementation

[0026] The accompanying drawings are for illustrative purposes only. The invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings and specific embodiments, as the advantages of the invention in the above and / or other aspects will become clearer.

[0027] It should be understood that some common knowledge or prior art in the accompanying drawings may be omitted or simplified.

[0028] Example 1, such as Figure 1 As shown, this embodiment provides a closed-loop control system for the proportion of electrical discharge machining (EDM) and electrolytic composite machining, including a controller 1. The controller 1 has an industrial control closed-loop control module and also includes: The liquid supply boosting module includes a water pump 8 and a hydraulic sensor 9 installed on the liquid line. The hydraulic sensor 9 is connected to the industrial control closed-loop control module in the controller 1. The liquid supply boosting module is used to receive industrial control output signals to steplessly adjust the liquid inlet pressure, change the bubble content in the electrolyte, and realize the range switching of EDM / ECM ratio. The microbubble generation module 2, connected downstream of the liquid supply and pressurization module, is capable of preparing a gas-liquid two-phase electrolyte 7, and can achieve a wide range of changes in bubble volume fraction by adjusting the liquid inlet pressure. The inter-electrode signal acquisition module 3 is capable of high-frequency acquisition and identification of inter-electrode voltage and current waveforms, and calculates the actual EDM processing ratio in real time through a built-in integration algorithm; it also includes a digital oscilloscope 6 for displaying waveforms, etc. The industrial control closed-loop control module is connected to the liquid supply booster module and the inter-electrode signal acquisition module 3 respectively. It can receive the actual EDM processing ratio fed back by the inter-electrode signal acquisition module 3, compare it with the target ratio, output a pressure adjustment signal to the liquid supply booster module, and collect the processing depth of electrode 5 in real time, and switch the three-level processing conditions as needed.

[0029] The controller 1 is also connected to the control spindle 10, which is installed above the electrolytic cell containing the electrolyte 7. Electrodes 5 are installed below the control spindle 10. The workpiece 4 is placed on the mounting platform in the electrolyte 7. The workpiece mounting platform is connected to a digital oscilloscope 6 to display the waveform changes of the workpiece 4 in real time.

[0030] like Figure 2 As shown, this embodiment provides a closed-loop control method for the proportion of EDM / ECM composite machining, specifically a closed-loop control method for the proportion of EDM / ECM composite machining based on high-pressure microbubbles. An electrolyte containing uniform microbubbles is supplied to the machining gap through a high-pressure microbubble generation module. The inlet pressure is used as the main control variable to achieve continuous switching of the machining proportion over a wide range. Combined with real-time current acquisition and online proportion calculation, a closed-loop control logic of target preset, real-time feedback, and dynamic correction is constructed. Differentiated proportion control strategies are formulated for the three stages of roughing, semi-finishing, and finishing, achieving continuous and precise control of the machining proportion within the range of 0.2 to 0.9, simultaneously considering processing efficiency, surface quality, and environmental friendliness. Specifically, the method includes the following steps: S1. Clamp the workpiece and tool electrode, and set fixed process parameters. Set the applied voltage parameters, turn on the liquid supply booster module and microbubble generation module, and divide the process into three stages: roughing, semi-finishing, and finishing. Preset the target EDM ratio range and corresponding initial liquid inlet pressure for each stage.

[0031] S2. Coarse processing stage: Residual material removal dominated by high proportion of EDM.

[0032] Adjust the inlet pressure to the high pressure range (0.7~0.8MPa), and control the target EDM ratio at 0.85~0.9.

[0033] Process objective: To quickly remove most of the machining allowance from the workpiece by using electrical discharge erosion as the main material removal method; the electrolytic effect accounts for a low proportion in this stage, which greatly shortens the time of strong electrolytic machining and reduces the emission of harmful gases generated by electrolytic gas separation reaction from the source.

[0034] Closed-loop control logic: Real-time high-frequency acquisition of inter-electrode current waveforms; online calculation of the current actual EDM percentage using current waveform integration; comparison of this actual percentage with the target percentage range: When the actual percentage is lower than the lower limit of the target range, the control system automatically increases the inlet pressure, increases the bubble volume fraction, reduces the equivalent conductivity of the medium, and enhances local electric field distortion to increase the EDM discharge probability, thus raising the percentage back to the target range; when the actual percentage is higher than the upper limit of the target range, the control system slightly reduces the inlet pressure, decreases the bubble volume fraction, and lowers the percentage back to the target range. By dynamically correcting the inlet pressure, the percentage is maintained stable within the target range, ensuring the discharge erosion efficiency during the roughing stage.

[0035] S3. Semi-finishing stage: Moderate EDM / ECM collaborative transition control.

[0036] As the processing allowance gradually decreases, the control system gradually reduces the inlet pressure to the medium pressure range (0.4~0.6MPa), with the target EDM ratio controlled at 0.45~0.78, and the bubble size moderate and the distribution uniform.

[0037] Process Objective: EDM and ECM work synergistically to balance molding accuracy and surface quality. EDM periodically breaks the passivation film, maintaining the active surface for electrolytic dissolution and ensuring processing efficiency; ECM gradually refines the processing contour, eliminating surface defects left by roughing and preparing for the finishing stage, while continuously controlling the intensity of electrolysis to avoid the generation of large amounts of harmful gases.

[0038] Closed-loop control logic: The proportion control strategy changes with the processing depth. For each preset step increase in processing depth, the target EDM proportion and the reference value of the inlet pressure are linearly reduced. At the same time, the hydraulic pressure is dynamically corrected by real-time current feedback to offset the proportion drift caused by processing state fluctuations, ensure a smooth transition of proportion, avoid processing quality fluctuations caused by mode switching, and achieve simultaneous improvement of forming accuracy and surface quality.

[0039] S4.ECM-dominated finishing mode (low-pressure operation).

[0040] When the machining allowance is close to the finished product size, the control system reduces the inlet pressure to a low pressure range (0.2~0.3MPa), the bubble distribution is sparse, the equivalent conductivity of the medium is high, and the target EDM ratio is controlled at 0.2~0.3%.

[0041] Process objectives: The process is primarily based on electrolytic dissolution to remove the recast layer and microcracks generated in previous processes, refine the final machining contour, and minimize machining allowance. The low proportion of EDM only plays an auxiliary role in intermittently breaking the passivation film, ensuring uniform and stable electrolytic dissolution. Furthermore, the electrolysis time in this stage is short to avoid stray corrosion and the generation of a large number of harmful gases caused by strong electrolysis throughout the process. Ultimately, a machined surface with excellent surface integrity is obtained, balancing machining quality and environmental protection.

[0042] Closed-loop control logic: With surface quality stability as the core control objective, the liquid inlet pressure benchmark value is kept constant, and the proportion fluctuation is monitored in real time. When the proportion increases or decreases abnormally, the liquid inlet pressure can be finely adjusted to achieve closed-loop compensation, ensuring that the electrolytic dissolution process is uniform and smooth, and ensuring the quality consistency of the final processed surface.

[0043] S5. Switch to online mode.

[0044] During processing, the inlet pressure can be continuously adjusted according to process requirements, achieving smooth switching between roughing, semi-finishing, and finishing modes without machine shutdown, electrolyte replacement, or modification of electrical parameters. The EDM ratio variation curves under different hydraulic pressures are shown below. Figure 3 As shown, based on the change curve, by adjusting the inlet pressure, the proportion of EDM processing can be continuously and steplessly controlled in the range of 0.2 to 0.9, corresponding to the continuous transition and switching between three processing modes: rough processing dominated by EDM, semi-finishing processing with EDM / ECM synergy, and finishing processing dominated by ECM.

[0045] This embodiment relies on synchronously acquired dual-channel time-series waveforms of inter-electrode voltage and total inter-electrode current. It employs an integrated algorithm process encompassing waveform feature recognition, noise preprocessing, waveform interpolation fitting, and piecewise charge integration to achieve accurate online quantitative calculation of the EDM (Electronic Degradation) processing proportion. The ECM (Enhanced Mechanism of Processing) processing proportion is directly obtained by subtracting the EDM proportion from the total processing contribution proportion. During processing, the inter-electrode signal acquisition module synchronously acquires the inter-electrode voltage and total inter-electrode current waveforms within a complete statistical period T. The statistical period T is uniformly selected as an integer multiple of the pulse period to eliminate calculation deviations caused by random disturbances from single pulses, ensuring stable and representative statistical results.

[0046] Analyzing the time-series sampling data point by point throughout the entire process, the typical inter-electrode voltage-current timing waveforms in electrical discharge machining (EDM) are shown below. Figure 4As shown, the main EDM discharge processing and main ECM electrolytic processing regions are distinguished by the unique electrical signal characteristics of electrical spark breakdown discharge. When EDM breakdown discharge occurs, the inter-electrode voltage exhibits significant and continuous fluctuations, while the inter-electrode current rises significantly. The continuous sampling period that simultaneously satisfies a significant voltage drop and a significant current rise is defined as the main EDM discharge processing region. The period with only a stable base current and no significant voltage drop is defined as the main ECM electrolytic processing region. Because high-voltage microbubbles continuously disturb the inter-electrode electrolyte, the acquired current waveform is prone to a large amount of random spike noise. This noise can cause misjudgment of the region division and distortion of the integrated charge calculation. Therefore, this invention prioritizes median filtering to denoise the discrete current sampling points of the divided EDM dominant regions, eliminating abrupt and abnormal noise points and fully preserving the true trend of the discharge peak changes. After completing the waveform denoising preprocessing, for each effective discrete current sampling point within the main EDM discharge processing region, this invention preferably uses cubic spline interpolation to construct a continuous instantaneous current function i. EDM (t).

[0047] A piecewise cubic polynomial is constructed within the time interval of adjacent sampling points. The piecewise function is constrained to have continuous function values, first derivatives, and second derivatives at the nodes. All polynomial coefficients are solved with natural boundary conditions. The interpolation curve strictly passes through all effective sampling points and is second-order continuous and smooth. It can completely reproduce the steep discharge peaks of electric sparks and is suitable for the varied discharge waveforms under all working conditions of roughing, semi-finishing, and finishing. At the same time, it takes into account the calculation accuracy and the real-time computing requirements of industrial control equipment.

[0048] Piecewise definite integrals are performed on the fitted EDM discharge current function, and the total charge of all spark discharges within the statistical period is accumulated. Then, the total inter-electrode current at all times within the complete statistical period is integrated to obtain the total inter-electrode charge within the period. The ratio of the total EDM discharge charge to the total charge of the period is calculated to obtain the EDM processing proportion coefficient. The calculation formula is as follows: ; In the formula, R EDM EDM processing ratio coefficient, %; i EDM (t) represents the instantaneous EDM discharge current, in A; i total (t) represents the instantaneous total inter-electrode current in A; T represents the statistical period, which is an integer multiple of the pulse period to ensure statistical accuracy in seconds; t represents the time variable in seconds.

[0049] The ECM processing ratio is obtained by subtracting the EDM ratio from the total processing ratio.

[0050] Example 2: This example uses the irregular surface of a titanium alloy blade for an aero-engine as the processing object. The workpiece material is TC4 titanium alloy, and the total processing depth of the surface is 5mm. It is used to implement the closed-loop control method of EDM / ECM composite processing ratio based on high-pressure microbubbles of the present invention.

[0051] Step 1: Preset basic process parameters.

[0052] Clamp the TC4 titanium alloy workpiece and the contouring tool electrode, and set the fixed preset process parameters: applied voltage 70 V, pulse frequency 2 kHz, pulse duty cycle 50%, and electrolyte is 2% NaNO3 aqueous solution. Turn on the electrolyte circulation system and high-pressure microbubble generator, and start the industrial control closed-loop control module. Based on the workpiece allowance distribution and surface quality requirements, divide the process into three stages: roughing, semi-finishing, and finishing. The preset EDM ratio target range for the roughing stage is 0.85~0.90, and the initial inlet pressure is set to 0.78 MPa; the preset EDM ratio target range for the semi-finishing stage is 0.55~0.75, and the initial inlet pressure is set to 0.50 MPa; the preset EDM ratio target range for the finishing stage is 0.20~0.30, and the initial inlet pressure is set to 0.22 MPa.

[0053] Step 2: In the rough processing stage, a high proportion of EDM (Electronic Direct Mail) is used to quickly remove excess material.

[0054] The industrial control system outputs a pressure control signal to the liquid supply booster module, adjusting the inlet pressure to 0.78 MPa. Under this pressure, the high-pressure microbubble generator stably prepares a gas-liquid two-phase electrolyte containing microbubbles. The equivalent diameter of the microbubbles stabilizes in the range of 20–50 μm, with a high bubble volume fraction. The equivalent conductivity of the medium decreases to a low level, and the distortion of the inter-electrode electric field is enhanced. Under these conditions, the EDM discharge breakdown probability is significantly increased. The current waveform acquired in real-time by the inter-electrode signal acquisition module shows dense discharge pulses. The industrial control system calculates the actual EDM ratio to be 0.87 through real-time ratio calculation, stabilizing within the target range (0.85–0.90). In this stage, electric spark discharge erosion is the main material removal method, achieving a material removal rate of 18–24 mm. 3 The process achieves rapid removal of most of the workpiece's excess material at a speed of [speed / min]. Electrolysis serves only as a supplementary means to break the passivation film, shortening the duration of strong electrolysis and reducing the generation of harmful gases from electrolytic gas separation. During processing, the inter-electrode signal acquisition module acquires voltage and current waveforms at high frequency. The industrial control system performs online percentage calculation and deviation comparison every 100 ms. When the percentage drops to 0.84 due to passivation film formation, the control system automatically fine-tunes the inlet pressure to 0.80 MPa, and the percentage recovers to around 0.86 within hundreds of milliseconds, ensuring material removal efficiency in the roughing stage.

[0055] Step 3: Semi-finishing stage, medium proportion of EDM / ECM collaborative transition control.

[0056] When the machining depth reaches 4.0 mm, the industrial control system, based on the machining depth-dependent control strategy, linearly reduces the target EDM ratio to approximately 0.65, while simultaneously gradually decreasing the inlet pressure from 0.78 MPa to 0.50 MPa. During this stage, the microbubble volume fraction decreases, the equivalent conductivity of the medium increases, the EDM discharge probability decreases moderately, and the ECM dissolution effect gradually strengthens. The EDM pulse discharge periodically breaks down the dense passivation film on the titanium alloy surface, providing continuous reaction sites for the ECM; the ECM simultaneously dissolves and removes the discharge recast layer and microcracks generated during the roughing stage, performing preliminary trimming of the machining contour. The industrial control system maintains closed-loop real-time feedback: when the actual ratio deviates from the target range, it automatically fine-tunes the inlet pressure (adjustment range ±0.02 MPa) for dynamic compensation, ensuring the ratio control deviation remains stably within ±0.03. During this stage, the processing depth increased from 4.0 mm to 4.7 mm, the surface roughness Ra decreased from about 4~6 μm after rough machining to about 2~3 μm, and the recast layer thickness decreased from an average of 19~24 μm after rough machining to 6~8 μm. The processing was stable with no abnormal discharge, and the amount of harmful gas generated was at a moderate and controllable level.

[0057] Step 4: Finishing stage, with a low proportion of ECM dominating surface finishing.

[0058] When the processing depth approaches the finished product size (approximately 4.85 mm), the industrial control system further reduces the inlet pressure to 0.22 MPa, lowering the target EDM ratio to 0.25. At this stage, microbubble distribution is sparse, the equivalent conductivity of the medium is high, and ECM dissolution dominates. The inter-electrode signal acquisition module monitors the ratio fluctuation in real time. When the EDM ratio abnormally rises above 0.34 due to inter-electrode product accumulation, the industrial control system fine-tunes the inlet pressure to quickly return the ratio to the target range. This stage removes surface defects left over from previous processing, suppresses the recast layer to a low level, essentially eliminates microcracks, and reduces the surface roughness Ra to 0.5~1 μm after processing, obtaining a processed surface with good integrity. Simultaneously, it avoids stray corrosion and the release of large amounts of harmful gases caused by prolonged strong electrolysis.

[0059] Step 5: Smooth mode switching and completion.

[0060] The two mode switches from roughing to semi-finishing and from semi-finishing to finishing are both achieved through online continuous adjustment of the inlet hydraulic pressure. The entire switching process requires no machine stoppage, no electrolyte replacement, and no resetting of pulse electrical parameters, ensuring a stable and undisturbed inter-electrode discharge. This invention, through layered closed-loop control of the EDM and ECM processing ratios, completes large-scale material removal and surface finishing within the same set of processes, balancing processing efficiency and workpiece surface quality while reducing the environmental impact of electrolytic gas.

[0061] This invention enables quantitative control of the EDM to ECM ratio within the range of 0.2 to 0.9, and allows for smooth online switching between three processing modes: rough, semi-finish, and finish. This significantly shortens processing time while achieving a highly intact surface, and effectively reduces harmful gas emissions at the source.

[0062] Comparative Example 1: Pure Electrical Discharge Machining.

[0063] This comparative example uses a typical pure electrical discharge machining (EDM) scheme in the prior art to process the same irregular surface of aero-engine titanium alloy blade (workpiece material: TC4 titanium alloy, total surface machining depth 5 mm) as in the example, and compares the processing effect with that of Example 1.

[0064] (1) Processing parameter settings: The same EDM machine tool and contouring electrode (material: copper) as in the embodiment are used, and the workpiece clamping method is consistent with that in the embodiment. No electrolyte is introduced during the machining process, and no high-pressure microbubble generator or industrial control closed-loop control module is configured. Only conventional EDM working fluid (kerosene-based working fluid) is used for flushing, cooling and chip removal.

[0065] The processing is carried out in three stages: roughing, semi-finishing, and finishing. The discharge parameters (peak current, pulse width, pulse interval, etc.) of each stage are set to the optimal values ​​based on common knowledge in the field and the equipment operation manual.

[0066] The inlet pressure is fixed throughout the entire processing, with no percentage adjustment or real-time feedback closed-loop control. After each processing stage, the operator judges based on experience whether it is necessary to stop the machine to replace electrodes or adjust parameters.

[0067] (2) Processing procedure: The machining process proceeds gradually from roughing. In the initial stage of machining, the discharge condition is good, and the material removal rate is approximately 8-10 mm. 3 / min. As the machining depth increases, the chip removal conditions between electrodes gradually deteriorate. Especially after machining to a depth of 3 mm, the discharge state becomes unstable, and abnormal discharge phenomena such as arcing and short circuits occur frequently, requiring multiple machine shutdowns to clean the carbon deposits between electrodes and to repair the tool electrodes.

[0068] In the semi-finishing stage, due to the reduction in discharge energy, the processing speed further decreases, and the material removal rate drops to 3~5 mm. 3 / min. At this stage, obvious recast layer and heat-affected layer have appeared on the workpiece surface, the tool electrode tip shows obvious wear, the shape preservation of the profile decreases, and the machining accuracy is significantly affected.

[0069] During the finishing stage, a low discharge energy is used for surface finishing. Due to severe electrode wear, the electrode needs to be replaced and the tool re-set twice during the process, with each stop taking about 15 to 20 minutes. When the final depth of 5 mm is reached, a recast layer with a thickness of about 18 to 22 μm still exists on the surface, with many microcracks and a surface roughness Ra of about 8.0 to 14.0 μm.

[0070] The entire processing process generates a large amount of harmful gases from the thermal decomposition of the working fluid (mainly CO, CH4 and volatile hydrocarbons), resulting in a noticeable pungent odor in the processing workshop. High-power exhaust and purification devices are required to meet environmental emission requirements.

[0071] Comparative Example 1 shows a low material removal rate during rough machining. In the finishing stage, the efficiency further decreases due to limited discharge energy, and the electrode wear is severe, requiring multiple electrode replacements and tool resetting, which affects machining accuracy and process continuity.

[0072] This invention achieves a layered control strategy through closed-loop regulation of the proportion of electrical discharge machining (EDM) and electrolytic machining (ECM). This strategy enables rapid material removal dominated by EDM in roughing, a synergistic transition between EDM and ECM in semi-finishing, and surface finishing dominated by ECM in finishing. The entire process, from large material removal to high-quality surface finishing, can be completed within a single operation. Material removal rate is significantly improved, processing time is greatly shortened, electrode wear is effectively suppressed, and the formation of recast layers and microcracks is effectively inhibited after processing, resulting in a high-integrity surface. Simultaneously, harmful gas emissions are significantly reduced at the source. This invention represents a substantial advancement in processing efficiency, surface quality, electrode wear, process continuity, and environmental friendliness.

[0073] Example 3: This example describes the use of electrical discharge machining (EDM) and electrolytic machining (ECM) for the cavity of a precision mold made of hardened steel. The workpiece material is Cr12MoV hardened mold steel, and the total removal depth of the cavity is 2.5 mm. The method of closed-loop control of the proportion of EDM / ECM composite machining based on high-pressure microbubbles is adopted.

[0074] Step 1: Basic process parameters and layer presets.

[0075] Clamp the Cr12MoV hardened steel workpiece and forming tool electrode, and set the preset process parameters: applied voltage 65V, pulse frequency 2kHz, pulse duty cycle 45%, and 2% NaNO3 aqueous solution as electrolyte. Turn on the electrolyte supply booster module and high-pressure microbubble generator, and start the industrial control closed-loop control module.

[0076] The total number of machining layers is preset. Based on this, the total machining removal depth of the cavity is divided into several machining layers, and all machining layers are categorized into roughing, semi-finishing, and finishing areas. The preset target EDM ratio range for each layer in the roughing area is 0.82~0.88, corresponding to an initial inlet pressure of 0.75MPa. The preset target EDM ratio range for each layer in the semi-finishing area is 0.48~0.72, with an inlet pressure reference range of 0.42~0.58MPa. The preset target EDM ratio range for each layer in the finishing area is 0.20~0.28, with an inlet pressure reference of 0.22MPa.

[0077] Step 2: The rough machining area is processed in layers, and the high EDM ratio quickly removes the cavity excess.

[0078] The system controls the electrodes to feed layer by layer into the corresponding processing layers of the roughing area, maintaining the target EDM ratio and inlet pressure benchmark during the roughing stage. The liquid supply booster module outputs an inlet pressure of 0.75 MPa, while the microbubble generation module generates a large number of uniform microbubbles, increasing the probability of EDM discharge breakdown between electrodes. The inter-electrode signal acquisition module acquires the inter-electrode voltage and current waveforms at high frequency, and calculates the actual EDM processing ratio in real time online through waveform feature recognition and a piecewise charge integration algorithm. When product accumulation or flow field disturbance causes the actual ratio to deviate from the target range, the system dynamically corrects the inlet pressure through real-time feedback control, maintaining the EDM ratio within the target range and efficiently removing most of the processing allowance from the cavity. Electrolysis accounts for a relatively low percentage during this stage, reducing the duration of strong electrolysis and mitigating the environmental impact of electrolytic gas removal.

[0079] Step 3: Layered collaborative transition processing of semi-finished areas.

[0080] The processing layers progress to the processing layer corresponding to the semi-finishing area. As the number of processing layers increases, the target EDM ratio and the reference value of the inlet pressure decrease linearly in sync. The reference setting is refreshed after each processing layer is completed. During this stage, the bubble volume fraction gradually decreases, and the ECM electrolytic dissolution effect gradually strengthens. EDM discharge continuously updates the workpiece processing interface, providing reaction conditions for electrolytic dissolution; ECM gradually corrects surface defects left by roughing. The layered output is only the reference expected value. Combined with the actual EDM processing ratio obtained from real-time feedback, the system dynamically compensates for the inlet pressure to offset the ratio drift caused by inter-electrode disturbances, ensuring a smooth ratio transition and balancing cavity forming accuracy and surface quality. After semi-finishing, surface defects in the cavity are improved, and the recast layer generated by roughing is effectively thinned and suppressed.

[0081] Step 4: Layered finishing process in the finishing area.

[0082] The processing layers progress to the corresponding processing layer in the finishing area, locking in the preset target EDM ratio and inlet pressure benchmark value for finishing. With the reduction of microbubble numbers, ECM electrolytic dissolution becomes the primary material removal method. The industrial control closed-loop module continuously monitors the actual EDM processing ratio; when an abnormal increase in the ratio occurs, the inlet pressure is finely adjusted to change the bubble volume fraction and size, bringing the ratio back to the target range. Electrolytic dissolution removes surface defects remaining from previous processes, suppressing the recast layer to a low level, essentially eliminating microcracks, and obtaining a mold cavity with good molding accuracy and high surface integrity, while avoiding the problem of stray corrosion at the cavity edges and corners caused by prolonged strong electrolysis.

[0083] Step 5: Smooth mode switching and processing completion.

[0084] The entire machining process relies on continuous adjustment of the inlet pressure to smoothly switch between roughing, semi-finishing, and finishing modes, without requiring machine downtime, changes to electrical parameters, or electrolyte replacement. The finished product is a hardened steel mold cavity with excellent contour consistency.

[0085] This embodiment demonstrates that the layered closed-loop control method of the present invention is not only applicable to titanium alloy blade parts, but also to hardened steel mold cavity components. It can achieve continuous control of the EDM processing ratio within the range of 0.2 to 0.9, and realize the removal of large allowances and surface finishing in the same process.

[0086] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A closed-loop control method for the proportion of electrical discharge machining (EDM) and electrolytic composite machining, characterized in that, Includes the following steps: S1. Assembly and setting of fixed process parameters: Clamp the workpiece and tool electrode, turn on the liquid supply booster module and microbubble generation module, divide the process into three stages: roughing, semi-finishing and finishing, and preset the target EDM ratio range and corresponding initial liquid inlet pressure for each stage. S2. Rough processing stage: Adjust the liquid inlet pressure to the high pressure range, and use electric spark discharge erosion as the main method to achieve rapid material removal. Through real-time current acquisition and online calculation of proportion, maintain the EDM proportion stable within the target range. During the roughing stage, the inlet pressure is adjusted to 0.7~0.8 MPa, and the target EDM ratio is controlled at 0.85~0.

9. The closed-loop control logic in the roughing stage is as follows: real-time high-frequency acquisition of inter-electrode current waveform, online calculation of the current actual EDM ratio using the current waveform integration method, and comparison of the deviation with the target ratio range; when the actual ratio is lower than the lower limit of the target range, the control system automatically increases the inlet pressure, increases the bubble volume fraction, reduces the equivalent conductivity of the medium, and enhances the local electric field distortion to increase the EDM discharge probability; when the actual ratio is higher than the upper limit of the target range, the control system reduces the inlet pressure, reduces the bubble volume fraction, and causes the ratio to fall back to the target range. S3. Semi-finishing stage: Gradually reduce the inlet pressure to the medium pressure range, so that EDM can break the passivation film and ECM can dissolve and repair in synergy, taking into account both forming accuracy and surface quality. The target EDM ratio and the inlet pressure benchmark value are linearly adjusted down with the processing depth. During the semi-finishing stage, the inlet pressure is adjusted to 0.4~0.6 MPa, and the target EDM ratio is controlled at 0.45~0.

78. The control strategy for adjusting the target EDM ratio and the reference value of the inlet pressure as the machining depth changes is as follows: for each preset step increase in machining depth, the target EDM ratio and the reference value of the inlet pressure are linearly adjusted downwards, while the hydraulic pressure is dynamically corrected in conjunction with real-time current feedback. S4. Finishing stage: Reduce the inlet pressure to the low pressure range, mainly remove the recast layer and microcracks by electrolytic dissolution, and rely on hydraulic closed-loop adjustment to compensate for the proportion drift fluctuation; during the finishing stage, adjust the inlet pressure to 0.2~0.3 MPa, and control the target EDM proportion at 0.2~0.

3. The closed-loop control logic of the finishing stage is as follows: maintain the inlet pressure reference value constant, monitor the proportion fluctuation through real-time current, and when the proportion rises or falls abnormally, achieve closed-loop compensation by finely adjusting the inlet pressure to ensure that the electrolytic dissolution process is uniform and smooth. S5. By continuously adjusting the inlet pressure online, the three process modes of roughing, semi-finishing, and finishing can be smoothly switched to complete the workpiece processing; In the aforementioned control method, an electrolyte containing uniform microbubbles is delivered to the processing gap through a high-pressure microbubble generator. The inlet pressure is used as the main control variable to achieve continuous switching between the EDM and ECM processing ratios within the range of 0.2 to 0.

9. Combined with synchronous acquisition of inter-electrode voltage and current, the ratio is calculated online through interval identification, filtering and noise reduction, cubic spline interpolation, and piecewise charge integration. This constructs a closed-loop control logic with target preset, real-time feedback, and dynamic correction.

2. The closed-loop control method for the proportion of electrical discharge-electrolysis composite machining according to claim 1, characterized in that, In step S1, the fixed process parameters include: applied voltage 70 V, pulse frequency 2 kHz, pulse duty cycle 50%, and electrolyte is 2% NaNO3 aqueous solution.

3. The closed-loop control method for the proportion of electrical discharge-electrolysis composite machining according to claim 1, characterized in that, The equivalent diameter of the microbubbles generated by the microbubble generation module is stably controlled within the range of 20~80μm; the adaptable pressure adjustment range is 0.2~0.8 MPa.

4. The closed-loop control method for the proportion of electrical discharge-electrolysis composite machining according to claim 1, characterized in that, In step S3, the strategy corresponding to the linear reduction of the target EDM ratio and the inlet pressure benchmark value is as follows: The total number of processing layers is preset. Based on the total number of layers, the total processing depth of the workpiece is divided into several processing layers arranged in sequence. All processing layers are divided into roughing area, semi-finishing area and finishing area according to the processing feed sequence. The processing proceeds layer by layer from the first layer downwards. In each processing layer corresponding to the rough processing area, the preset target EDM ratio and the inlet pressure benchmark value are kept unchanged. After entering the semi-finishing area, as the number of processing layers increases, the target EDM ratio and the inlet pressure reference value decrease synchronously and linearly according to a preset ratio until the last layer of this area is processed; after entering the finishing area, the preset target EDM ratio and inlet pressure reference value for finishing are locked and maintained until the processing is completed. When each layer of processing is completed or the preset depth step is reached, the target EDM ratio and the inlet pressure benchmark setting value are updated. The setting value is used as the expected input, and combined with the actual EDM processing ratio collected in real time, the inlet pressure is dynamically corrected and compensated through closed-loop control.

5. The closed-loop control method for the proportion of electrical discharge-electrolysis composite machining according to claim 1, characterized in that, The inlet pressure and the proportion of EDM processing are monotonically positively correlated: the higher the inlet pressure, the larger the bubble volume fraction, the lower the equivalent conductivity of the medium, the stronger the electric field distortion, the higher the EDM discharge breakdown probability, and the larger the proportion of EDM processing; conversely, the proportion of ECM increases.

6. The closed-loop control method for the proportion of electrical discharge-electrolysis composite machining according to claim 1, characterized in that, The online calculation of the proportion adopts the following method: the inter-electrode voltage waveform and the inter-electrode total current waveform are synchronously collected within a complete statistical period T, wherein the statistical period T is an integer multiple of the pulse period; The time-series sampling data for the entire time period is analyzed point by point. When the inter-electrode voltage fluctuates continuously and the synchronous inter-electrode current rises, the continuous sampling period that simultaneously satisfies the voltage drop and current rise is defined as the main interval of EDM discharge machining. The period with only a stable base current and no significant voltage drop is defined as the main interval of ECM electrolytic machining. Median filtering is performed on the discrete current sampling points of the EDM dominant interval to remove abrupt abnormal noise points. For the effective discrete current sampling points after noise reduction, cubic spline interpolation is used to construct the continuous instantaneous current function i. EDM (t); The piecewise definite integral operation is performed on the fitted EDM discharge current function, and the total charge of all electric spark discharges within the statistical period is obtained by summing them up. Then, the total inter-electrode current at all times within the complete statistical period is integrated to obtain the total inter-electrode charge within the period. The ratio of the total EDM discharge charge to the total periodic charge is calculated, and the final calculation formula for the actual proportion coefficient of the current EDM is obtained online using the voltage and current waveform integration method: ； In the formula, R EDM i is the EDM processing ratio coefficient; EDM (t) represents the instantaneous EDM discharge current; i total (t) represents the instantaneous total inter-electrode current; T is the statistical period, which is taken as an integer multiple of the pulse period to ensure statistical accuracy; t is the time variable; The ECM processing ratio is obtained by subtracting the EDM ratio from the total processing ratio.

7. A closed-loop control system for the proportion of electrical discharge machining (EDM) and electrolytic composite machining, used to implement the closed-loop control method for the proportion of EDM and electrolytic composite machining as described in any one of claims 1 to 6, comprising a controller, characterized in that, Also includes: The liquid supply booster module is used to receive industrial control output signals to steplessly adjust the liquid inlet pressure, change the bubble content in the electrolyte, and realize the range switching of EDM / ECM ratio; The microbubble generation module, connected downstream of the liquid supply and pressurization module, is capable of preparing a gas-liquid two-phase electrolyte and can achieve a wide range of changes in bubble volume fraction by adjusting the inlet pressure. The inter-electrode signal acquisition module can acquire and identify inter-electrode voltage and current waveforms at high frequency, and calculate the actual EDM processing ratio in real time through the built-in integration algorithm; The industrial control closed-loop control module is connected to the liquid supply booster module and the inter-electrode signal acquisition module respectively. It can receive the actual EDM processing ratio fed back by the inter-electrode signal acquisition module, compare it with the target ratio, output a pressure adjustment signal to the liquid supply booster module, and collect the electrode processing depth in real time, and switch the three-level processing conditions as needed.

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