Deep cavity electrolytic machining method and device

Abstract

The application relates to a deep cavity electrolytic machining method, which is realized through a deep cavity electrolytic machining device. The deep cavity electrolytic machining device comprises an outer cathode and an inner cathode, the outer cathode is sleeved outside the inner cathode, an inner insulating layer is arranged on the inner side of the outer cathode, an outer insulating layer is arranged on the outer side of the outer cathode, a channel for electrolyte flow is arranged in the middle of the inner cathode, the deep cavity electrolytic machining method comprises the following steps: the inner cathode is controlled to keep static, the outer cathode is driven to move along the outer side of the inner cathode to feed and machine the workpiece, and the electrolyte is sprayed from the middle of the inner cathode; when the outer cathode feeding reaches a preset depth, the outer cathode is controlled to stop feeding and keep static, and the inner cathode is driven to move to feed and machine the workpiece; when the inner cathode feeding reaches a preset depth, the inner cathode is controlled to stop feeding, and the outer cathode and the inner cathode are withdrawn from the workpiece. The application can solve the problem that the size and shape are difficult to guarantee due to side wall corrosion in the process of machining a deep cavity, and improve the side wall machining precision and surface quality.

Description

Technical Field

[0001] This application relates to the field of electrochemical machining technology, and in particular to a deep cavity electrochemical machining method and apparatus. Background Technology

[0002] In the aerospace manufacturing field, a large number of deep, irregularly shaped cavities have appeared in load-bearing structures, and the machining method is generally CNC milling. The main problem is the low efficiency in machining deep cavities, and deformation due to machining stress occurs when machining the thin walls of the cavity. In recent years, electrolytic machining has become an important technological direction for deep cavity machining. Electrolytic machining is a special process that uses the principle of electrochemical anodic dissolution to remove metal. In electrolytic machining, the tool electrode is the cathode, and the workpiece is the anode. A certain gap is maintained between the workpiece anode and the tool cathode during electrolytic machining. A DC voltage is applied between the electrodes, and the electrolyte is generally a neutral salt solution. An electrochemical reaction cell is formed between the electrodes, and the high-speed flow continuously carries away the electrolysis products and heat, and depolarizes the electrolyte. The workpiece dissolves continuously as the tool cathode feeds until the cavity size of the workpiece reaches the required level.

[0003] In deep-cavity electrolytic machining, throughout the entire electrode feeding process, in addition to the electrochemical "anodic dissolution" of the cavity body, the lateral portion after machining is continuously affected by the electrochemical field and undergoes continuous corrosion, resulting in significant slope and deviations from tolerances on the finished cavity sidewalls. Although previous efforts have incorporated various technical measures such as flow field improvements, pulsed power supply, and insulation protection, the conformal preservation of the cavity sidewalls remains unresolved. The continuous "anodic dissolution" process in electrolytic machining requires establishing a stable electrolyte scouring flow field. However, in deep-cavity electrolytic machining, the electrolyte scouring channel is excessively long, leading to high flow resistance. As the electrode penetrates deeper into the workpiece, the electrolyte path becomes increasingly longer, increasing the flow resistance along the gap between the electrode and the cavity sidewalls. This slows down the scouring velocity, affecting the discharge of electrolytic products and causing electrochemical polarization in the machining area, resulting in reduced dimensional accuracy and surface quality of the cavity sidewalls. Summary of the Invention

[0004] This application provides a method and apparatus for deep cavity electrolytic machining, which solves the problem that corrosion of the cavity sidewall during the machining of deep irregular cavities makes it difficult to guarantee the forming dimensional accuracy and surface quality.

[0005] In a first aspect, this application provides a deep cavity electrolytic machining method, implemented by a deep cavity electrolytic machining apparatus; the deep cavity electrolytic machining apparatus includes an outer cathode and an inner cathode, the outer cathode being sleeved on the outside of the inner cathode; an inner insulating layer is provided on the inner side of the outer cathode, and an outer insulating layer is provided on the outer side; a channel for the flow of electrolyte is provided in the middle of the inner cathode;

[0006] The deep cavity electrolytic machining method includes:

[0007] The inner cathode is kept stationary, while the outer cathode is driven to move along the outside of the inner cathode to feed and process the workpiece, and the electrolyte is sprayed out from the middle of the inner cathode;

[0008] When the outer cathode reaches a preset depth, the outer cathode is controlled to stop feeding and remain stationary, while the inner cathode is driven to move to feed and process the workpiece.

[0009] When the inner cathode reaches the preset depth, the inner cathode is controlled to stop feeding, and the outer cathode and the inner cathode are withdrawn from the workpiece.

[0010] Furthermore, the deep cavity electrolytic machining apparatus also includes a DC power supply; the workpiece is connected to the positive terminal of the DC power supply, the inner cathode is connected to the negative terminal of the DC power supply through an inner cathode switch, and the outer cathode is connected to the negative terminal of the DC power supply through an outer cathode switch.

[0011] Before controlling the inner cathode to remain stationary and driving the outer cathode to move along the outer side of the inner cathode to feed and process the workpiece, the method further includes:

[0012] The workpiece is connected to the positive terminal of the DC power supply, the inner cathode switch is turned off, and the outer cathode switch is closed to connect the outer cathode to the negative terminal of the DC power supply.

[0013] Furthermore, the deep cavity electrolytic machining device also includes a machine tool cathode mounting plate and a cylinder, one end of which is connected to the machine tool cathode mounting plate and the other end of which is connected to the external cathode;

[0014] The method of driving the outer cathode to move along the outer side of the inner cathode to feed and process the workpiece includes:

[0015] The cylinder is controlled to move so as to drive the outer cathode to move along the outside of the inner cathode to feed and process the workpiece.

[0016] Furthermore, before controlling the outer cathode to stop feeding and remain stationary after the outer cathode has reached a preset depth, and before driving the inner cathode to move to feed and process the workpiece, the method further includes:

[0017] The external cathode switch is opened, and the internal cathode switch is closed to connect the internal cathode to the negative terminal of the DC power supply.

[0018] Furthermore, the inner cathode is connected to the machine tool cathode mounting plate;

[0019] The process of driving the inner cathode to move and feed the workpiece includes:

[0020] The movement of the machine tool cathode mounting plate is controlled to drive the movement of the inner cathode to feed and process the workpiece.

[0021] Furthermore, before controlling the inner cathode to stop feeding and retracting the outer cathode and the inner cathode from the workpiece after the inner cathode has reached the preset depth, the method further includes:

[0022] The workpiece is disconnected from the positive terminal of the DC power supply, the external cathode switch is turned off, and the internal cathode switch is turned off.

[0023] Further, the step of retracting the outer cathode and the inner cathode from the workpiece includes:

[0024] The machine tool cathode mounting plate is controlled to move so as to retract the outer cathode and the inner cathode from the workpiece.

[0025] Secondly, this application provides a deep cavity electrolytic machining apparatus for implementing the deep cavity electrolytic machining method described above; the deep cavity electrolytic machining apparatus includes an external cathode, an internal cathode, a DC power supply, a machine tool cathode mounting plate, and a cylinder;

[0026] The outer cathode is sleeved on the outside of the inner cathode; an inner insulating layer is provided on the inner side of the outer cathode, and an outer insulating layer is provided on the outer side; a channel for the flow of electrolyte is provided in the middle of the inner cathode;

[0027] The positive terminal of the DC power supply is connected to the workpiece, the inner cathode is connected to the negative terminal of the DC power supply through an inner cathode switch, and the outer cathode is connected to the negative terminal of the DC power supply through an outer cathode switch.

[0028] One end of the cylinder is connected to the machine tool cathode mounting plate, and the other end is connected to the outer cathode; the inner cathode is connected to the machine tool cathode mounting plate.

[0029] Furthermore, the deep cavity electrolytic machining apparatus also includes a liquid collection chamber, which is disposed between the machine tool cathode mounting plate and the inner cathode, and communicates with the channel in the middle of the inner cathode.

[0030] Furthermore, pipe joints are provided on both sides of the liquid collection chamber, and the pipe joints are used to connect the electrolyte pipe.

[0031] The above-mentioned technical solution of this application has the following advantages:

[0032] The deep cavity electrolytic machining method provided in the first aspect of this application is implemented using a deep cavity electrolytic machining apparatus. The apparatus includes an outer cathode and an inner cathode, with the outer cathode nested outside the inner cathode. An inner insulating layer is provided on the inner side of the outer cathode, and an outer insulating layer is provided on the outer side. A channel for electrolyte flow is provided in the middle of the inner cathode. By employing a nested arrangement of inner and outer cathodes for cavity machining, the outer cathode first feeds into the workpiece to machine a groove, forming the cavity sidewall. Then, the outer cathode remains stationary, forming a protective sleeve. The inner and outer insulating layers can block the electric field between the machined cavity sidewall and the electrode, providing insulation and protection for the machined cavity sidewall, preventing stray corrosion and secondary machining during the machining process, and improving the sidewall machining accuracy and surface quality. When the inner cathode continues to machine a complete deep cavity, it no longer corrodes the cavity sidewall, thus ensuring the shape of the machined deep cavity.

[0033] It is understandable that the beneficial effects of the second aspect mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0035] Figure 1 A schematic diagram of the deep cavity electrolytic machining apparatus provided in this application;

[0036] Figure 2 A flowchart of the deep cavity electrolytic machining method provided in this application.

[0037] Reference numerals in the attached diagram: 1. DC power supply; 2. Inner cathode switch; 3. Outer cathode switch; 4. Machine tool cathode mounting plate; 5. Pipe joint; 6. Liquid collection chamber; 7. Cylinder; 8. Inner cathode; 9. Outer cathode; 10. Inner insulation layer; 11. Outer insulation layer; 12. Workpiece. Detailed Implementation

[0038] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of this application with unnecessary detail.

[0039] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0040] Furthermore, in the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0041] References to "one embodiment" or "some embodiments" in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized. "A plurality" means "two or more."

[0042] Stray corrosion is a common phenomenon in electrochemical machining (ECM), typically occurring in low-current-density areas near the non-machined surfaces of the workpiece. It causes uneven material dissolution on these non-machined surfaces, affecting the accuracy of ECM. In cavity ECM, the use of highly reactive electrolytes such as NaCl, KBr, or composite electrolytes further exacerbates the problem by reducing the localization of material dissolution, thus intensifying stray corrosion on the cavity surface and impacting forming accuracy.

[0043] This application addresses the problems of poor machining stability due to inadequate electrolyte scouring at deep depths, large dimensional deviations caused by lateral corrosion, and difficulty in guaranteeing surface quality in electrolytic machining of deep irregular cavities. It proposes a deep cavity electrolytic machining method and apparatus to solve the problem of difficulty in guaranteeing dimensional and shape due to sidewall corrosion during the machining of deep irregular cavities.

[0044] The specific embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate this application, but are not intended to limit the scope of this application.

[0045] This application provides a deep cavity electrolytic machining method, implemented using a deep cavity electrolytic machining apparatus. For example... Figure 1As shown, the deep cavity electrolytic machining apparatus includes an outer cathode 9 and an inner cathode 8. The outer cathode 9 is sleeved on the outside of the inner cathode 8. An inner insulating layer 10 is provided on the inner side of the outer cathode 9, and an outer insulating layer 11 is provided on the outer side. A channel for the flow of electrolyte is provided in the middle of the inner cathode 8.

[0046] like Figure 2 As shown, the deep cavity electrolytic machining method includes: controlling the inner cathode 8 to remain stationary, driving the outer cathode 9 to move along the outside of the inner cathode 8 to feed and machine the workpiece 12, with electrolyte sprayed from the middle of the inner cathode 8; when the outer cathode 9 reaches a preset depth, controlling the outer cathode 9 to stop feeding and remain stationary, driving the inner cathode 8 to move to feed and machine the workpiece 12; when the inner cathode 8 reaches the preset depth, controlling the inner cathode 8 to stop feeding, and retracting the outer cathode 9 and the inner cathode 8 from the workpiece 12.

[0047] This embodiment employs two nested cathodes, an inner cathode 8 and an outer cathode 9, to divide the deep cavity machining into two stages. In the first stage, the inner cathode 8 remains stationary while the outer cathode 9 feeds towards the workpiece 12, machining a groove of a predetermined depth along the contour of the cavity to be machined, forming the cavity sidewall. The inner insulating layer 10 and the outer insulating layer 11 can block the electric field between the machined cavity sidewall and the electrode, providing insulation protection for the machined cavity sidewall, preventing stray corrosion and secondary machining during the process, and improving the machining accuracy and surface quality of the sidewall. In the second stage, the outer cathode 9 stops feeding and remains stationary while the inner cathode 8 feeds towards the workpiece 12, removing the remaining material encased inside the outer cathode 9, machining a complete deep cavity, thereby ensuring the shape of the machined deep cavity.

[0048] The cavity is machined using nested inner and outer cathodes. The outer cathode 9 is fed first and then the cavity sidewall is formed. After the outer cathode 9 stops feeding and remains stationary, it forms a protective sleeve. When the inner cathode 8 continues to machine, it will no longer have a corrosive effect on the cavity sidewall, thus ensuring the shape of the machined deep cavity.

[0049] like Figure 1 As shown, in some embodiments, the deep cavity electrolytic machining apparatus further includes a DC power supply 1; the workpiece 12 is connected to the positive terminal of the DC power supply 1, the inner cathode 8 is connected to the negative terminal of the DC power supply 1 through an inner cathode switch 2, and the outer cathode 9 is connected to the negative terminal of the DC power supply 1 through an outer cathode switch 3.

[0050] Before controlling the inner cathode 8 to remain stationary and driving the outer cathode 9 to move along the outside of the inner cathode 8 to feed and process the workpiece 12, the method further includes: controlling the workpiece 12 to be connected to the positive terminal of the DC power supply 1, the inner cathode switch 2 to be disconnected, and the outer cathode switch 3 to be closed so that the outer cathode 9 is connected to the negative terminal of the DC power supply 1.

[0051] like Figure 1 As shown, in some embodiments, the deep cavity electrolytic machining apparatus further includes a machine tool cathode mounting plate 4 and a cylinder 7, one end of which is connected to the machine tool cathode mounting plate 4 and the other end of which is connected to the external cathode 9.

[0052] The method of driving the outer cathode 9 to move along the outer side of the inner cathode 8 to feed and process the workpiece 12 includes: controlling the cylinder 7 to move so as to drive the outer cathode 9 to move along the outer side of the inner cathode 8 to feed and process the workpiece 12.

[0053] In some embodiments, after the outer cathode 9 reaches a preset depth, before controlling the outer cathode 9 to stop feeding and remain stationary, and before driving the inner cathode 8 to move to feed and process the workpiece 12, the method further includes: controlling the outer cathode switch 3 to open, and the inner cathode switch 2 to close so that the inner cathode 8 is connected to the negative terminal of the DC power supply 1.

[0054] like Figure 1 As shown, in some embodiments, the inner cathode 8 is connected to the machine tool cathode mounting plate 4. Driving the inner cathode 8 to move and feed the workpiece 12 includes: controlling the movement of the machine tool cathode mounting plate 4 to drive the inner cathode 8 to move and feed the workpiece 12.

[0055] In some embodiments, after the inner cathode 8 reaches the preset depth, before controlling the inner cathode 8 to stop feeding and retracting the outer cathode 9 and the inner cathode 8 from the workpiece 12, the method further includes: controlling the workpiece 12 to disconnect from the positive terminal of the DC power supply 1, disconnecting the outer cathode switch 3, and disconnecting the inner cathode switch 2.

[0056] In some embodiments, retracting the outer cathode 9 and the inner cathode 8 from the workpiece 12 includes: controlling the movement of the machine tool cathode mounting plate 4 to retract the outer cathode 9 and the inner cathode 8 from the workpiece 12.

[0057] The cathode for machining the cavity is divided into two parts: an outer cathode 9 and an inner cathode 8. The outer cathode 9 is connected to the machine tool cathode mounting plate 4 via symmetrically distributed cylinders 7, while the inner cathode 8 is directly fixed to the machine tool cathode mounting plate 4. During machining, the electrolyte is sprayed out from the middle of the inner cathode 8. In the first step, the inner cathode 8 is stationary, the outer cathode 9 is connected to the negative terminal of the DC power supply 1, the workpiece 12 is connected to the positive terminal of the DC power supply 1, the outer cathode 9 is fed, and after reaching the set depth, the feed stops and the power supply to the outer cathode 9 is cut off. In the second step, the inner cathode 8 is connected to the negative terminal of the DC power supply 1 and feeds for machining. At this time, the outer cathode 9 plays a protective role for the sidewall of the machined cavity.

[0058] This application also provides a deep cavity electrolytic machining apparatus for implementing the deep cavity electrolytic machining method described above. Figure 1 As shown, the deep cavity electrolytic machining device includes an outer cathode 9, an inner cathode 8, a DC power supply 1, a machine tool cathode mounting plate 4, and a cylinder 7.

[0059] The outer cathode 9 is sleeved outside the inner cathode 8; an inner insulating layer 10 is provided on the inner side of the outer cathode 9, and an outer insulating layer 11 is provided on the outer side; a channel for the flow of electrolyte is provided in the middle of the inner cathode 8; the positive terminal of the DC power supply 1 is connected to the workpiece 12, the inner cathode 8 is connected to the negative terminal of the DC power supply 1 through the inner cathode switch 2, and the outer cathode 9 is connected to the negative terminal of the DC power supply 1 through the outer cathode switch 3; one end of the cylinder 7 is connected to the machine tool cathode mounting plate 4, and the other end is connected to the outer cathode 9; the inner cathode 8 is connected to the machine tool cathode mounting plate 4.

[0060] like Figure 1 As shown, in some embodiments, the deep cavity electrolytic machining apparatus further includes a liquid collection chamber 6, which is disposed between the machine tool cathode mounting plate 4 and the inner cathode 8, and communicates with the channel in the middle of the inner cathode 8.

[0061] like Figure 1 As shown, in some embodiments, pipe joints 5 are respectively provided on both sides of the liquid collection chamber 6, and the pipe joints 5 are used to connect the electrolyte pipe.

[0062] A machining electrode can be installed on the machine tool cathode mounting plate 4. The cylinder 7 actuates to push out the outer cathode 9 and maintains the thrust. During machining, the electrolyte is sprayed out from the middle of the inner cathode 8 through the electrolyte pipe and the collecting chamber 6. When the workpiece 12 is connected to the positive terminal of the DC power supply 1, the outer cathode switch 3 is closed, connecting the outer cathode 9 to the negative terminal of the DC power supply 1, and the outer cathode 9 begins machining feed.

[0063] After the outer cathode 9 is machined to the set depth, the feed is paused, the outer cathode switch 3 is disconnected, and simultaneously, the inner cathode switch 2 is closed, connecting the inner cathode 8 to the negative terminal of the DC power supply 1. The pressure in cylinder 7 is released, and the machine tool cathode mounting plate 4 moves downwards, driving the inner cathode 8 to feed. The outer cathode 9 remains stationary, forming a protective sleeve. Its inner insulating layer 10 protects the outer cathode 9 from corrosion, while the outer insulating layer 11 isolates the machining energy field from the machined cavity sidewall, thus protecting the cavity sidewall. When the inner cathode 8 reaches the bottom of the cavity at the set depth, the DC power supply 1 is disconnected, the machine tool cathode mounting plate 4 retracts, and the machining process ends.

[0064] The deep cavity electrolytic machining method and apparatus provided in this application were used to machine a deep cavity in titanium alloy. The cavity cross-sectional dimensions were 50mm × 50mm, and the depth was 80mm. The electrolyte was a 10% KBr aqueous solution, the electrolyte temperature was 25℃, the electrolyte pressure was 0.6MPa, and the machining voltage was 20V. After machining to a given depth, the feed was stopped and the power was cut off. Testing showed that under the above parameters, the machined deep cavity had a small sidewall slope and a surface roughness of Ra3.2μm or less.

[0065] The deep cavity electrolytic machining method and apparatus provided in this application employs nested inner and outer cathodes for cavity machining. The outer cathode first feeds into the workpiece to machine grooves, forming the cavity sidewall. Then, the outer cathode remains stationary, forming a protective sleeve. The inner and outer insulating layers block the electric field between the machined cavity sidewall and the electrode, providing insulation and protection to the sidewall, preventing stray corrosion and secondary machining during the process, and improving the sidewall machining accuracy and surface quality. When the inner cathode continues to machine the complete deep cavity, it no longer corrodes the cavity sidewall, thus ensuring the shape of the machined deep cavity.

[0066] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application.

[0067] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A deep cavity electrochemical machining method, characterized by, The deep cavity electrolytic machining device comprises an outer cathode and an inner cathode, the outer cathode is sleeved outside the inner cathode, an inner insulation layer is arranged on the inner side of the outer cathode, and an outer insulation layer is arranged on the outer side of the outer cathode; A channel for flowing of electrolyte is arranged in the middle of the inner cathode; The deep cavity electrolytic machining method comprises the following steps: The inner cathode is controlled to remain stationary, the outer cathode is driven to move along the outer side of the inner cathode to feed and machine the workpiece, and the electrolyte is sprayed from the middle of the inner cathode; When the outer cathode feeding reaches a preset depth, the outer cathode is controlled to stop feeding and remain stationary, and the inner cathode is driven to move to feed and machine the workpiece; When the inner cathode feeding reaches the preset depth, the inner cathode is controlled to stop feeding, and the outer cathode and the inner cathode are withdrawn from the workpiece.

2. The deep cavity electrochemical machining method according to claim 1, wherein The deep cavity electrolytic machining device further comprises a direct current power supply; the workpiece is connected with the positive pole of the direct current power supply, the inner cathode is connected with the negative pole of the direct current power supply through an inner cathode switch, and the outer cathode is connected with the negative pole of the direct current power supply through an outer cathode switch; Before the inner cathode is controlled to remain stationary and the outer cathode is driven to move along the outer side of the inner cathode to feed and machine the workpiece, the following step is further included: The workpiece is connected with the positive pole of the direct current power supply, the inner cathode switch is turned off, and the outer cathode switch is turned on to connect the outer cathode with the negative pole of the direct current power supply.

3. The deep cavity electrochemical machining method of claim 1, wherein, The deep cavity electrolytic machining device further comprises a machine tool cathode mounting plate and a pneumatic cylinder, one end of the pneumatic cylinder is connected with the machine tool cathode mounting plate, and the other end of the pneumatic cylinder is connected with the outer cathode; The outer cathode is driven to move along the outer side of the inner cathode to feed and machine the workpiece, and the following step is included: The pneumatic cylinder is controlled to move to drive the outer cathode to move along the outer side of the inner cathode to feed and machine the workpiece.

4. The deep cavity electrochemical machining method according to claim 2, wherein After the outer cathode feeding reaches the preset depth, before the outer cathode is controlled to stop feeding and remain stationary and the inner cathode is driven to move to feed and machine the workpiece, the following step is further included: The outer cathode switch is turned off, and the inner cathode switch is turned on to connect the inner cathode with the negative pole of the direct current power supply.

5. The deep hole electrochemical machining method of claim 3, wherein The inner cathode is connected with the machine tool cathode mounting plate; The inner cathode is driven to move to feed and machine the workpiece, and the following step is included: The machine tool cathode mounting plate is controlled to move to drive the inner cathode to move to feed and machine the workpiece.

6. The deep cavity electrochemical machining method of claim 2, wherein, After the inner cathode feeding reaches the preset depth, before the inner cathode is controlled to stop feeding and the outer cathode and the inner cathode are withdrawn from the workpiece, the following step is further included: The workpiece is disconnected with the positive pole of the direct current power supply, the outer cathode switch is turned off, and the inner cathode switch is turned off.

7. The deep hole electrochemical machining method of claim 3, wherein The outer cathode and the inner cathode are withdrawn from the workpiece, and the following step is included: The machine tool cathode mounting plate is controlled to move to withdraw the outer cathode and the inner cathode from the workpiece.

8. A deep cavity electrochemical machining apparatus characterized by comprising: The deep cavity electrolytic machining device comprises an outer cathode, an inner cathode, a direct current power supply, a machine tool cathode mounting plate and a pneumatic cylinder. The outer cathode is sleeved outside the inner cathode; the inner cathode is provided with an inner insulation layer on the inner side and an outer insulation layer on the outer side; and the inner cathode is provided with a channel for electrolyte flow in the middle part; The positive pole of the direct current power supply is connected with the workpiece, the inner cathode is connected with the negative pole of the direct current power supply through an inner cathode switch, and the outer cathode is connected with the negative pole of the direct current power supply through an outer cathode switch; One end of the air cylinder is connected with the machine tool cathode mounting plate, and the other end is connected with the outer cathode; and the inner cathode is connected with the machine tool cathode mounting plate.

9. The deep hole electrochemical machining apparatus of claim 8, wherein The deep cavity electrolytic machining device further comprises a liquid collecting cavity, which is arranged between the machine tool cathode mounting plate and the inner cathode and is in communication with the channel in the middle part of the inner cathode.

10. The deep hole electrochemical machining apparatus of claim 9, wherein Pipe joints are arranged on both sides of the liquid collecting cavity, and the pipe joints are used for connecting electrolyte pipes.

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