Flexible nodular electrode and electrochemical mechanical composite finishing method for inner channel

Abstract

The invention provides a flexible nodular electrode and an electrochemical mechanical composite finishing method for an inner channel, and belongs to the technical field of electrochemical mechanical composite machining. The flexible nodular electrode comprises a plurality of similar nodular units, and each nodular unit comprises an electrode conductive substrate, a universal joint, a porous insulating layer and insulating soft abrasive particles. The adjacent nodal units are hinged through the universal joints, and good flexibility is achieved. The insulating layer on the surface of the conductive substrate of the electrode is made of loose and porous sponge, and an electric field line and electrolyte can penetrate through the insulating layer, so that an electrochemical effect is generated between the conductive substrate and the complex inner channel, and meanwhile, short-circuit burn caused by contact between the conductive substrate and the surface of the complex inner channel can be avoided; the insulating soft abrasive particles are embedded outside the insulating layer, so that a mechanical scraping effect can be applied to a complex inner channel in the machining process, and a passive film generated on the surface of a workpiece is ground away. During polishing, the electrode reciprocates, and complex inner channel polishing is completed under the composite action of electrochemical and mechanical scraping.

Description

Technical Field

[0001] The invention relates to a flexible segmented electrode and an electrochemical mechanical composite finishing inner channel method, belonging to the technical field of electrochemical mechanical composite processing. Background Art

[0002] Additive manufacturing technology, also known as 3D printing technology, is a scientific technology based on the principle of discrete-accumulation, in which the three-dimensional data of parts directly drives the manufacturing process of parts. Unlike traditional subtractive processes such as cutting, the core principle of additive manufacturing is the cumulative forming of materials. The three-dimensional model of parts is discretized to form points, lines or surfaces, and then the materials are gradually accumulated and stacked to form a three-dimensional complex structure. Due to the high flexibility, short manufacturing cycle, and near-net forming with almost no material waste, additive manufacturing technology has been widely used in the field of aerospace manufacturing. For metal components with thin walls and complex internal channel structures such as engine injectors, flat engine nozzles, and combustion chamber guide bushings, it is very difficult to manufacture them by traditional processing methods. However, additive manufacturing technology is not limited by the complex shape of the components. It uses discrete means to stack layer by layer, and can directly process the required components.

[0003] Complex internal channel components manufactured using additive manufacturing technology have a large number of protrusions on the surface of the inner channel and a large original roughness due to the spheroidization effect, ripple effect, step effect and powder adhesion generated during the processing. For complex internal channel parts, the rough surface will cause many tiny eddies and vortices, which will increase the friction resistance. The adhered powder particles have poor bonding with the matrix of the additively manufactured parts and can easily fall off the matrix surface, damaging product performance and even causing component failure. The main methods currently used to polish complex internal channels include mechanical polishing, chemical polishing, and electrochemical polishing. Mechanical polishing has poor accessibility and is only suitable for surface polishing of simple structures. Chemical polishing is to place metal parts in a chemical polishing liquid. The metal material of the protruding parts is easier to dissolve, while the concave parts are not easy to dissolve. The finishing effect is achieved by the difference in dissolution rates of concave and convex parts, but the chemical polishing effect is affected by the purity and uniformity of the workpiece. The polishing quality of some parts with higher roughness is poor, and the polishing fluid used in chemical polishing usually pollutes the environment.

[0004] Electrochemical polishing is a special processing method that uses the principle of anodic dissolution during electrochemical reactions to remove material from workpieces. During the processing, the anodic workpiece will dissolve, and the uneven parts of the workpiece will dissolve at different rates. The dissolution rate of the microscopic raised parts on the workpiece surface will be higher than that of the microscopic sunken areas. As the electrochemical reaction proceeds, the surface of the concave and convex parts of the workpiece will tend to be flat. Electrochemical polishing has high production efficiency and is not affected by the mechanical properties of the processed materials. The surface of the processed parts is smooth, and an environmentally friendly neutral green electrolyte can be used during the polishing process to avoid environmental pollution.

[0005] Electrochemical mechanical composite polishing is an innovative technology that combines the advantages of both electrochemical processing and mechanical processing by superimposing mechanical action on electrochemical action. The basic principle of processing is based on electrochemical anodic dissolution, and the mechanical scraping effect of abrasive particles is used to remove the passivation film generated on the surface of the protrusion during the processing process, accelerate the dissolution of the material at the protrusion, and thus achieve the effect of finishing processing. Compared with traditional electrochemical polishing, electrochemical mechanical composite polishing not only has the advantages of not being affected by the mechanical properties of the processed material, smooth surface of the processed parts, and good processing accessibility, but also has higher processing efficiency and better processing quality. It has broad application prospects in the field of finishing complex internal channels.

[0006] In the patent "An Electrolytic Tool Electrode and a Method for Electrolytic Finishing of the Internal Channel of a Workpiece Using the Electrolytic Tool Electrode and the Electrolytic Finishing Method of the Internal Channel of a Workpiece Using the Electrolytic Tool Electrode" (application number: 202010737210.4 applicant Nanjing University of Aeronautics and Astronautics, inventor Zhao Chenhao Zhang Qu Ningsong Tang Xiaochuan) a flexible electrolytic tool cathode is proposed. The cathode body is composed of a flexible metal wire and an elastic insulating layer fixed on the metal wire, and has good flexibility. In contrast, the electrode insulating layer used in the present invention is distributed with soft abrasive particles, which can remove the passivation film formed on the surface of the workpiece during the processing, realize electrochemical mechanical composite polishing, and have higher processing efficiency and better processing quality.

[0007] In the patent "Snake-shaped flexible cathode and inner channel electrochemical polishing method" (application number 202210578582.6 applicant Nanjing University of Aeronautics and Astronautics, inventors Zhu Di'an, Lin Chao and Wang Dengyong), a snake-shaped flexible cathode consisting of a cathode unit section, a ball joint, a cathode end cover, a cathode support ring and a fastening bolt is proposed. In comparison, the electrode used in the present invention is formed by connecting a number of similar nodular units through a universal joint, which can be bent arbitrarily in space to adapt to the shape of different complex inner channels. The soft abrasive particles distributed outside the insulating layer of the electrode conductive unit can remove the passivation film generated during the processing, realize electrochemical mechanical composite processing, and improve the processing quality.

[0008] In the patent "An electrolytic polishing device for the inner wall of a stainless steel pipe" (application number 201810407857.3 applicant Xuancheng Pinzhou Clean Technology Co., Ltd., inventor Wu Leigang Taoran), a flexible cathode is proposed, which is composed of a copper rod and a PTFE external threaded rod connected to it. In comparison, the electrode used in the present invention is formed by connecting a number of segmented units through a universal joint, has better flexibility, can adapt to complex internal channels of different shapes, and the soft abrasive particles outside the insulating layer of the electrode conductive unit can remove the passivation film during the processing, promote the electrochemical reaction, and improve the surface polishing quality.

[0009] In the patent "Electrochemical milling and grinding high-efficiency roughing and finishing integrated processing method" (application number 201810001038.9 applicant Nanjing University of Aeronautics and Astronautics, inventor Qu Ningsongyue Xiaokang Niu Li Hansong Fang Xiaolong) a tool cathode with diamond abrasive grains is proposed, which can achieve roughing and finishing of the workpiece by changing different processing parameters. In contrast, the electrode used in the present invention is formed by a number of similar nodal units connected by universal joints, can be bent arbitrarily in space, has good flexibility, and can perform electrochemical mechanical composite polishing on channels with complex shapes.

[0010] In the patent "Removable combined tool cathode and electrolytic grinding and milling method thereof" (application number 201710120203.8 applicant Nanjing University of Aeronautics and Astronautics, inventor Qu Ningsong Niu Li Hansong Fu Shuxing) a removable cathode consisting of a grinding head, a sealing ring and a tool bar is proposed, wherein the lower end side wall and the bottom surface of the grinding head are provided with liquid outlet holes and electroplated with abrasive grain layers, and the workpiece can be electrochemically mechanically composited. In contrast, the electrode used in the present invention is formed by connecting a number of segmented units through universal joints, has good flexibility and adaptability, and can realize electrochemical mechanical composite polishing of complex internal channels.

[0011] In the patent "Complex inner channel reciprocating motion electrolytic grinding composite processing method" (application number 202011047082.7 applicant Nanjing University of Aeronautics and Astronautics, inventors Zhu Di Wang Dengyong An Linchao), a complex inner channel reciprocating motion electrolytic grinding composite processing method is proposed. The tool assembly consists of a central axis and a cathode and a grinding wheel mounted thereon. During processing, the machine tool spindle pulls the hose to drive the tool assembly to reciprocate in the inner channel to achieve high-quality finishing of the inner channel surface. In comparison, the electrode used in the present invention is composed of several similar nodular units connected by a universal joint. It has a simple structure, is easy to manufacture, has better flexibility, and is suitable for small hole polishing.

[0012] In the patent "An electrolytic polishing device for the inner wall of a special-shaped microtube" (application number 202310330372.X, applicant Taiyuan University of Technology, inventor Liang Guoxing, Bai Xuechen, Hao Xinhui, Liu Donggang, Yang Shiqing, Zhang Dongdong, and Lv Ming), a flexible cathode composed of a circular polyether block, a hard sponge segment, and a circular copper core substrate is proposed, which can accurately control the area that needs electrolytic polishing. In comparison, the electrode structure used in the present invention is simple, easy to make, and has better flexibility. During the processing, the soft abrasive on the insulating layer can remove the generated passivation film, promote the electrochemical reaction, and improve the processing quality.

[0013] In the patent "A flexible liquid-conducting cathode and its application in electrochemical polishing of a closed-end tube" (application number 202311504508.0 applicant China Aviation Industry Shenyang Liming Aero Engine Co., Ltd., inventors Zhang Zhichao, Li Hanye, Wang Qifeng, Liu Zhiqiang), a flexible cathode formed by twisting a spiral capillary metal and a plurality of nylon insulating filaments is proposed, which can realize the polishing of a closed-end tube. In comparison, the soft abrasive particles on the insulating layer of the conductive substrate of the electrode of the present invention can remove the passivation film, realize electrochemical mechanical composite polishing, and improve the polishing quality.

[0014] From the above, it can be seen that the key to electrochemical mechanical composite polishing additive manufacturing of complex internal channels lies in the design of flexible tool electrodes and the realization of the combined action of electrochemical dissolution and mechanical scraping. The flexible tool electrode must not only adapt to complex internal channels of different shapes, but also avoid short-circuit burns caused by contact between the electrode and the internal channel of the workpiece during processing, and at the same time, it should ensure that the electrochemical dissolution and mechanical scraping are carried out simultaneously. Therefore, the present invention proposes a flexible segmented electrode and an electrochemical mechanical composite polishing method for internal channels. Summary of the invention

[0015] The purpose of the present invention is to provide a flexible nodular electrode and an electrochemical-mechanical composite finishing method for the internal channel that can adapt to complex internal channels of different shapes, avoid short-circuit burning caused by contact between the electrode and the internal channel of the workpiece during processing, and ensure that electrochemical dissolution and mechanical scraping are carried out simultaneously.

[0016] A flexible nodular electrode, characterized in that it is composed of a plurality of nodular unit electrodes and a universal joint for connecting adjacent nodular unit electrodes; the above-mentioned nodular unit electrodes are composed of an electrode conductive substrate, a porous insulating layer attached to the surface of the electrode conductive substrate, and insulating soft abrasive particles uniformly embedded on the outer surface of the porous insulating layer.

[0017] The flexible nodular electrode is characterized in that the porous insulating layer is a loose and porous sponge layer.

[0018] The electrochemical mechanical composite finishing method for the inner channel of the flexible nodular electrode is characterized by the following process: the adjacent nodular unit electrodes of the flexible nodular electrode are hinged by a universal joint to ensure that the electrodes can be flexibly bent and deformed to adapt to complex inner channels of different shapes; the insulating layer is a loose and porous sponge layer, which is attached to the local surface of the electrode conductive substrate. The electric field lines and the electrolyte can pass through the loose insulating layer, so that electrochemical action occurs between the electrode conductive substrate and the complex inner channel. At the same time, the porous insulating layer can prevent the electrode conductive substrate from contacting the surface of the complex inner channel and causing short circuit burns; the insulating soft abrasive particles are evenly embedded on the outer surface of the insulating layer, and can produce a mechanical scraping effect on the complex inner channel during the processing, thereby grinding off the passivation film generated on the workpiece surface, promoting electrochemical reactions, and forming electrochemical mechanical composite finishing.

[0019] The electrochemical mechanical composite finishing method of the flexible nodular electrode is characterized by the following process: step one: fix the workpiece on the machine tool workbench, and pre-place the flexible nodular electrode in the channel of the workpiece; step two: pass one end of the flexible nodular electrode through the liquid collecting cavity and connect it to the first machine tool spindle through the first conductive flexible shaft; use the same method to connect the other end of the flexible nodular electrode to the second machine tool spindle through the second conductive flexible shaft, and adjust the relative position of the machine tool spindle so that the flexible nodular electrode has a certain pre-tension; step three: connect the flexible nodular electrode to the negative pole of the power supply and the workpiece to the positive pole of the power supply. The positive pole of the power supply is turned on, and the liquid supply system is turned on. The high-speed and high-pressure flowing electrolyte enters the liquid collecting chamber from the inlets on both sides of the liquid collecting chamber. After the electrolyte is collected in the cavity, it is ejected along the outer wall of the flexible segmented electrode and flows into the processing gap; Step 4: Drive the first machine tool spindle and the second machine tool spindle to make linear motion in the same direction, drive the flexible segmented electrode to reciprocate, so that the soft abrasive particles outside the insulating layer exert mechanical scraping action on the complex inner channel of the workpiece, turn on the power, and the complex inner channel is polished under the combined action of electrochemical and mechanical scraping; Step 5: When the surface roughness of the inner channel of the workpiece meets the requirements, stop processing.

[0020] The beneficial effects of the present invention are: 1. The cathode of this patented tool is hinged by universal joints between adjacent segmented unit electrodes, which ensures that the electrodes have good flexibility and can be flexibly bent and deformed to adapt to complex internal channels of different shapes.

[0021] 2. An insulating layer is attached to the local surface of the electrode conductive substrate. The insulating layer is a loose and porous sponge layer, which is attached to the local surface of the electrode conductive substrate. The electric field lines and electrolyte can pass through the loose insulating layer, so that electrochemical reactions occur between the electrode conductive substrate and the complex internal channels. At the same time, the porous insulating layer can prevent the electrode conductive substrate from contacting the complex internal channel surface and causing short circuit burns.

[0022] 3. Insulating soft abrasive particles are distributed outside the insulating layer, which can produce mechanical scraping effect on the complex internal channels during processing, remove the passivation film generated on the workpiece surface, promote electrochemical reaction, form electrochemical mechanical composite finishing, and improve the finishing efficiency and finishing quality of the complex internal channels.

[0023] The flexible nodular electrode is characterized in that: the electrode conductive substrate is a cylindrical metal block, with bases for hinged universal joints at both ends, and the included angle between the axes of the hinge holes of the bases at both ends is 90°; the universal joint is composed of two cross-shaped shafts, and each shaft has a protruding cylindrical boss at both ends for hinged connection with the electrode conductive substrate. Through this connection method, the electrode can have better flexibility, can adapt to complex internal channels of different shapes, and complete the electrochemical finishing of complex internal channels of different shapes. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the flexible node-shaped electrode structure; Figure 2 is a schematic diagram of a universal joint; Figure 3 Schematic diagram of the electrode conductive matrix; Figure 4 Schematic diagram of the complex inner channel of the flexible nodular electrode electrochemical mechanical composite polishing; Figure 5 Schematic diagram of the electrochemical mechanical composite polishing process for the complex inner channel surface; The label names are: 1. flexible nodular electrode, 2. electrode conductive substrate, 3. universal joint, 4. insulating layer, 5. insulating soft abrasive, 6. workpiece, 7. liquid collecting chamber, 8. first conductive flexible shaft, 9. first machine tool spindle, 10. second conductive flexible shaft, 11. second machine tool spindle, 12. power supply, 13. passivation film. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0026] according to Figure 1As shown, the flexible nodular electrode 1 comprises a plurality of similar nodular units, wherein a single nodular unit comprises an electrode conductive substrate 2, a universal joint 3, a porous insulating layer 4 and insulating soft abrasive grains 5. Adjacent nodular units are hinged by the universal joint 3 to ensure that the electrode can be flexibly bent and deformed to adapt to complex internal channels of different shapes; the insulating layer 4 is a loose porous sponge layer, which is attached to the local surface of the electrode conductive substrate 2. The electric field lines and the electrolyte can pass through the loose insulating layer 4, so that an electrochemical reaction occurs between the electrode conductive substrate 2 and the complex internal channel of the workpiece 6. At the same time, the porous insulating layer 4 can prevent the electrode conductive substrate from contacting the surface of the complex internal channel and causing short circuit burns; the insulating soft abrasive grains 5 are evenly embedded on the outer surface of the insulating layer 4, and can produce a mechanical scraping effect on the complex internal channel of the workpiece 6 during the processing, thereby removing the passivation film generated on the surface of the workpiece 6, promoting the electrochemical reaction, and forming an electrochemical mechanical composite finishing.

[0027] according to Figure 2 , Figure 3 As shown, the electrode conductive substrate 2 is a cylindrical metal block, with bases for hinged universal joints at both ends, and the included angle between the axes of the hinge holes of the bases at both ends is 90°; the universal joint 3 is composed of two cross-shaped shafts, and each shaft has a protruding cylindrical boss at both ends, which is used to hinge with the electrode conductive substrate 2; according to Figure 4 As shown, the flexible nodular electrode and the electrochemical mechanical composite light-smoothing inner channel method proposed in the present invention include the following processes: Step 1: fix the workpiece 6 on the machine tool workbench, and pre-place the flexible node-shaped electrode 1 in the inner channel of the workpiece 6; Step 2: Pass one end of the flexible node-shaped electrode 1 through the liquid collecting cavity 7 and connect it to the first machine tool spindle 9 through the first conductive flexible shaft 8; use the same method to connect the other end of the flexible node-shaped electrode 1 to the second machine tool spindle 11 through the second conductive flexible shaft 10, and adjust the relative position of the machine tool spindle so that the flexible node-shaped electrode 1 has a certain pre-tension; Step 3: Connect the flexible node-shaped electrode 1 to the negative electrode of the power source 12, connect the workpiece 6 to the positive electrode of the power source 12, turn on the liquid supply system, and the electrolyte with high speed and high pressure flows into the liquid collecting chamber 7 from the inlets on both sides of the liquid collecting chamber 7. After the electrolyte is collected in the cavity, it is ejected along the outer wall of the flexible node-shaped electrode 1 and flows into the processing gap; Step 4: drive the first machine tool spindle 9 and the second machine tool spindle 11 to make linear motion in the same direction, drive the flexible segmented electrode 1 to reciprocate, so that the soft abrasive grains 5 outside the insulating layer 4 exert mechanical scraping action on the complex inner channel of the workpiece 6, turn on the power supply 12, and the complex inner channel is smoothed under the combined action of electrochemical action and mechanical scraping action; Step 5: When the surface roughness of the inner channel of the workpiece 6 reaches the requirement, stop processing.

[0028] according to Figure 5As shown, a layer of passivation film 13 is generated on the surface of the inner flow channel of the workpiece 6 during the processing, and the passivation film is thin at the protrusions and thick at the concave parts. During the processing, the flexible segmented electrode 1 makes a reciprocating motion, and the soft abrasive grains 5 on the insulating layer 4 exert a mechanical scraping action on the inner surface of the workpiece 6, and the passivation film at the protrusions is removed, exposing the base material, electrochemically dissolving, and then a new passivation film 13 is generated. The two processes of generating the passivation film and removing the passivation film by the soft abrasive grains are cyclically performed alternately until the surface roughness of the inner channel of the workpiece 6 meets the requirements.

Claims

1. A flexible node-shaped electrode, characterized in that: It is composed of a plurality of segmented unit electrodes and a universal joint (3) for connecting adjacent segmented unit electrodes; The segmented unit electrode is composed of an electrode conductive substrate (2), a porous insulating layer (4) attached to the surface of the electrode conductive substrate (2), and insulating soft abrasive particles (5) uniformly embedded on the outer surface of the porous insulating layer (4).

2. The flexible nodular electrode according to claim 1, characterized in that: The porous insulating layer (4) is a loose and porous sponge layer.

3. The flexible node-shaped electrode according to claim 1, characterized in that: The electrode conductive substrate (2) is a cylindrical metal block, with bases for hinged universal joints at both ends, and the included angle between the axes of the hinge holes of the bases at both ends is 90°; the universal joint (3) is composed of two cross-shaped shafts, and each shaft has a protruding cylindrical boss at both ends for hinged connection with the electrode conductive substrate (2).

4. The electrochemical mechanical composite finishing method of the inner channel using the flexible nodular electrode according to claim 2 is characterized by the following process: The adjacent segmented unit electrodes of the flexible segmented electrode (1) are hinged via a universal joint (3), thereby ensuring that the electrode can be flexibly bent and deformed to adapt to complex internal channels of different shapes; The insulating layer (4) is a loose and porous sponge layer, which is attached to the local surface of the electrode conductive substrate (2). The electric field lines and the electrolyte can pass through the loose insulating layer (4), so that an electrochemical reaction occurs between the electrode conductive substrate (2) and the complex inner channel. At the same time, the porous insulating layer (4) can prevent the electrode conductive substrate (2) from contacting the surface of the complex inner channel and causing short circuit burns. The insulating soft abrasive grains (5) are evenly embedded on the outer surface of the insulating layer (4), and can produce a mechanical scraping effect on the complex internal channel during the processing, remove the passivation film generated on the surface of the workpiece (6), promote electrochemical reaction, and form electrochemical mechanical composite finishing.

5. The electrochemical mechanical composite finishing method of the inner channel using the flexible nodular electrode according to claim 4 is characterized by the following process: Step 1: fix the workpiece (6) on the workbench of the machine tool, and pre-place the flexible segmented electrode (1) in the inner channel of the workpiece (6); Step 2: Pass one end of the flexible node-shaped electrode (1) through the liquid collecting chamber (7) and connect it to the first machine tool spindle (9) via the first conductive flexible shaft (8); connect the other end of the flexible node-shaped electrode (1) to the second machine tool spindle (11) via the second conductive flexible shaft (10) using the same method, and adjust the relative position of the machine tool spindle so that the flexible node-shaped electrode (1) has a certain pre-tension; Step 3: Connect the flexible segmented electrode (1) to the negative electrode of the power source (12), connect the workpiece (6) to the positive electrode of the power source (12), open the liquid supply system, and allow the electrolyte with high speed and high pressure to flow into the liquid collecting chamber (7) from the inlets on both sides of the liquid collecting chamber (7). After the electrolyte is collected in the chamber, it is ejected along the outer wall of the flexible segmented electrode (1) and flows into the processing gap; Step 4: driving the first machine tool spindle (9) and the second machine tool spindle (11) to perform linear motion in the same direction, driving the flexible segmented electrode (1) to perform reciprocating motion, so that the soft abrasive grains (5) outside the insulating layer (4) exert a mechanical scraping effect on the complex internal channel of the workpiece (6), turning on the power supply (12), and the complex internal channel is smoothed under the combined action of electrochemical and mechanical scraping; Step 5: When the surface roughness of the inner channel of the workpiece (6) reaches the requirement, stop processing.

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