Flexible segmented electrode and electrochemical-mechanical composite finishing method for inner channels

Abstract

A flexible segmented electrode (1) and an electrochemical-mechanical composite finishing method for inner channels, which belong to the technical field of electrochemical-mechanical composite machining. The flexible segmented electrode (1) comprises several similar segmented units, wherein a single segmented unit comprises an electrode conductive substrate (2), a universal joint (3), a porous insulating layer (4) and insulating soft abrasive particles (5); adjacent segmented units are hinged by means of the universal joints (3), and have a good flexibility; the insulating layer (4) on a surface of each electrode conductive substrate (2) is made of a loose and porous sponge, and electric field lines and an electrolyte can pass through the insulating layer (4), such that an electrochemical action occurs between each conductive substrate (2) and a complex inner channel, and short-circuit burns caused by contact between each conductive substrate and a surface of the complex inner channel can be also prevented; and the insulating soft abrasive particles (5) are embedded outside the insulating layers, such that a mechanical scraping effect can be applied to the complex inner channel during machining, thereby abrading a passivation film generated on the surface of a workpiece (6). During polishing, the electrode reciprocates, thereby completing polishing of the complex inner channel under the combined action of the electrochemical action and mechanical scraping.

Description

Flexible nodular electrode and electrochemical mechanical combined finishing inner channel method TECHNICAL FIELD

[0001] The present application relates to a flexible nodular electrode and electrochemical mechanical combined finishing inner channel method, belonging to the technical field of electrochemical mechanical combined machining. BACKGROUND

[0002] Additive manufacturing technology, also known as 3D printing technology, is a scientific and technological technique based on the discrete-accumulation principle, which directly drives the part manufacturing process from three-dimensional data. Unlike traditional subtractive processes such as cutting, the core principle of additive manufacturing is the accumulation of material forming, which forms points, lines or surfaces by discretizing the three-dimensional model of the part, and then gradually accumulates material stacking to form a three-dimensional complex structure. Due to the high degree of flexibility, short manufacturing cycle and near-net-shape of additive manufacturing technology, it has been widely used in the field of aerospace manufacturing. For engine nozzles, flat engine nozzles, combustion chamber guide bushings and other metal components with thin-walled and complex inner channel structures, it is very difficult to manufacture by traditional machining methods. Additive manufacturing technology can not be limited by the complex shape of the component, and can directly process the required component by layer-by-layer accumulation through discretization.

[0003] The complex inner channel component manufactured by additive manufacturing technology has a large number of protrusions on the inner channel surface due to problems such as spheroidization effect, ripple effect, step effect and powder adhesion during the machining process. The original roughness is large. For complex inner channel parts, rough surfaces can cause many small eddies and vortices, increasing frictional resistance. The adhesion of powder particles to the additive manufacturing part substrate is poor, and it is easy to fall off from the substrate surface, which can damage the performance of the product and even cause the component to fail. The methods currently used for polishing complex inner channels mainly include mechanical polishing, chemical polishing, electrochemical polishing, etc. Mechanical polishing has poor accessibility and is only suitable for surface polishing of simple structures; chemical polishing is to place the metal part in a chemical polishing solution, the protruding part of the metal material is more easily dissolved, the recessed part is not easily dissolved,

[0004] The polishing effect is achieved by the difference in dissolution rate between the protrusions and recesses, but the effect of chemical polishing is affected by the purity and uniformity of the workpiece. The polishing quality of some parts with high roughness is poor, and the polishing liquid used in chemical polishing usually pollutes the environment.

[0005] Electrochemical polishing is a special processing method that uses the principle of anode dissolution in electrochemical reaction to remove material from workpieces. During the process, the anode workpiece will dissolve, and the dissolution rate of the uneven parts of the workpiece will be different. The dissolution rate of the micro-protrusions on the workpiece surface will be higher than that of the micro-depressions. As the electrochemical reaction proceeds, the surfaces of the concave and convex parts of the workpiece will tend to be flat. Electrochemical polishing has high production efficiency, is not affected by the mechanical properties of the processed materials, and produces smooth surfaces. Moreover, environmentally friendly neutral green electrolyte can be used in the polishing process, avoiding environmental pollution.

[0006] Electrochemical mechanical compound polishing is an innovative technology that combines the advantages of electrochemical processing and mechanical processing. The basic principle of the process is to use the mechanical scraping action of abrasive particles to remove the passivation film generated on the surface of protrusions during processing, thereby accelerating the dissolution of the material at the protrusions and achieving finishing. Compared with traditional electrochemical polishing, electrochemical mechanical compound polishing not only has the advantages of not being affected by the mechanical properties of the processed materials, smooth surfaces after processing, and good accessibility, but also has higher processing efficiency and better processing quality, making it widely applicable in the field of finishing complex internal channels.

[0007] In the patent "Electrolytic tool electrode and method for electrolytic finishing of internal channels of workpieces" (Application No. 202010737210.4, Applicant: Nanjing University of Aeronautics and Astronautics, Inventors: Zhao Chenhao, Zhang Quning, Song Tangxiaochuan), a flexible electrolytic tool cathode is proposed, which 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 of the present invention is distributed with soft abrasive particles, which can remove the passivation film formed on the surface of the workpiece during processing, realize electrochemical mechanical compound polishing, and have higher processing efficiency and better processing quality.

[0008] In the patent "Snake-shaped flexible cathode and internal channel electrochemical polishing method" (Application No. 202210578582.6, Applicant: Nanjing University of Aeronautics and Astronautics, Inventors: Zhu Di, An Linchao, Wang Dengyong), a snake-shaped flexible cathode composed of cathode unit segments, spherical hinge joints, cathode end covers, cathode support rings, and fastening bolts is proposed. In contrast, the electrode of the present invention is composed of several similar segmental units connected by universal joints, which can bend arbitrarily in space and adapt to the shape of different complex internal channels. The soft abrasive particles distributed on the outer surface of the electrode conductive unit insulating layer can remove the passivation film generated during processing, realize electrochemical mechanical compound processing, and improve the processing quality.

[0009] In the patent "A stainless steel pipe inner wall electrolytic polishing equipment" (application number 201810407857.3 applicant of Xuan Cheng Pinzhou Clean Technology Co., Ltd., inventor Wu Legang Tao Ran) proposes a flexible cathode composed of a copper rod and a PTFE outer threaded rod connected to it. Compared with it, the electrode adopted in the present application is formed by connecting several nodular units through universal joints, which has better flexibility and can adapt to different shapes of complex inner channels. The soft abrasive particles outside the electrode conductive unit insulation layer can remove the passivation film during processing, promote the electrochemical reaction, and improve the surface polishing quality.

[0010] In the patent "Electrolytic milling and grinding efficient rough and finish machining integrated machining method" (application number 201810001038.9 applicant of Nanjing University of Aeronautics and Astronautics, inventor Qu Ningsong, Yue Xiaokang, Niu Yu, Li Hansong, Fang Xiaolong) proposes a tool cathode with diamond abrasive particles, which realizes rough and finish machining of workpieces by changing different machining parameters. Compared with it, the electrode adopted in the present application is formed by connecting several similar nodular units through universal joints, which can be arbitrarily bent in space and has good flexibility, and can be used for electrochemical mechanical combined polishing of complex shape inner channels.

[0011] In the patent "Dismountable combined tool cathode and its electrolytic milling and grinding machining method" (application number 201710120203.8 applicant of Nanjing University of Aeronautics and Astronautics, inventor Qu Ningsong, Niu Yu, Li Hansong, Fu Shuxing) proposes a detachable cathode composed of a grinding head, a sealing ring and a cutter bar. The lower end side wall and bottom surface of the grinding head are provided with liquid outlet holes and are plated with abrasive particle layers, which can be used for electrochemical mechanical combined machining of workpieces. Compared with it, the electrode adopted in the present application is formed by connecting several nodular units through universal joints, which has good flexibility and adaptability, and can realize electrochemical mechanical combined polishing of complex inner channels.

[0012] In the patent "Complex inner channel reciprocating electrolytic grinding composite machining method" (application number 202011047082.7 applicant of Nanjing University of Aeronautics and Astronautics, inventor Zhu Di, Wang Dengyong, An Linchao) proposes a complex inner channel reciprocating electrolytic grinding composite machining method. The tool assembly is composed of a center shaft 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, realizing high-quality finishing of the inner channel surface. Compared with it, the electrode adopted in the present application is formed by connecting several similar nodular units through universal joints, which has a simple structure, is easy to manufacture, has better flexibility, and is suitable for small hole polishing.

[0013] In the patent "a special-shaped micro-tube inner wall electrolytic polishing device" (application number 202310330372.X applicant Taiyuan University of Technology, inventors Liang Guoxing Bai Xuechen Hao Xinhui Liu Donggang Yang Shiqing Zhang Dongdong Lv Ming) proposed a flexible cathode composed of a circular polyether block, a hard sponge section and a circular copper core substrate, which can accurately control the area that needs electrolytic polishing. Compared with the above, the electrode structure adopted by the present application is simple, easy to manufacture, has better flexibility, and the soft abrasive particles on the insulating layer can remove the generated passivation film during processing, promote the electrochemical reaction and improve the processing quality.

[0014] In the patent "a flexible liquid guide cathode and its application in electrochemical polishing of one-end closed pipe" (application number 202311504508.0 applicant China Aviation Engine (Shenyang) Co., Ltd., inventors Zhang Zhichao Li Han Ye Wang Qifeng Liu Zhiquang) proposed a flexible cathode composed of a spiral capillary metal and a flexible cathode formed by twisting a plurality of nylon insulating filaments, which can realize polishing of one-end closed pipe. Compared with the above, the soft abrasive particles on the insulating layer of the electrode conductive matrix can remove the passivation film, realize electrochemical mechanical combined polishing, and improve the polishing quality.

[0015] From the above, the key to electrochemical mechanical combined polishing of complex inner channels of additive manufacturing is to design a flexible tool electrode and realize the combined effect of electrochemical dissolution and mechanical scraping. The flexible tool electrode not only adapts to different shapes of complex inner channels, but also avoids short-circuit burn phenomenon caused by contact between the electrode and the inner channel of the workpiece during processing, while ensuring that electrochemical dissolution and mechanical scraping are performed simultaneously. Therefore, the present application proposes a flexible nodular electrode and a method for electrochemical mechanical combined finishing of inner channels. SUMMARY

[0016] The purpose of the present application is to provide a flexible nodular electrode and a method for electrochemical mechanical combined finishing of inner channels, which can adapt to different shapes of complex inner channels, avoid short-circuit burn phenomenon caused by contact between the electrode and the inner channel of the workpiece during processing, and ensure that electrochemical dissolution and mechanical scraping are performed simultaneously.

[0017] Specifically, the present application provides the following technical solutions: a flexible nodular electrode composed of a plurality of nodular unit electrodes and universal joints for connecting adjacent nodular unit electrodes; the nodular unit electrode is composed of an electrode conductive matrix, a porous insulating layer attached to the surface of the electrode conductive matrix, and insulating soft abrasive particles uniformly embedded on the outer surface of the porous insulating layer.

[0018] In the flexible nodular electrode provided in an embodiment of the present application, the porous insulating layer is a loose and porous sponge layer.

[0019] In the flexible joint electrode provided in one embodiment of the present application, the electrode conductive base is a cylindrical metal block, and both ends of the electrode conductive base have bases for hinging universal joints, and the included angle between the axis of the hinging hole of the two ends of the base is 90°; the universal joint is composed of two cross shafts, and each shaft has a protruding cylindrical boss at both ends for hinging with the electrode conductive base. Through this connection mode, the electrode has better flexibility, and can adapt to different shapes of complex inner channels to complete the electrochemical finishing of different shapes of complex inner channels.

[0020] Secondly, the present application also provides an electrochemical mechanical composite finishing inner channel method of the above flexible joint electrode, which comprises the following processes: the adjacent joint electrode units of the above flexible joint electrode are hinged through the universal joints to ensure that the electrode can be flexibly bent and deformed to adapt to different shapes of complex inner channels; the above insulating layer is a loose porous sponge layer attached to the local surface of the electrode conductive base, and the electric field lines and the electrolyte can pass through the loose insulating layer to cause electrochemical action between the electrode conductive base and the complex inner channel, and at the same time, the porous insulating layer can avoid short-circuiting and burn injury caused by the contact between the electrode conductive base and the surface of the complex inner channel; the above insulating soft abrasive particles are uniformly embedded on the outer surface of the insulating layer, and can produce mechanical scraping action on the complex inner channel during the machining process to remove the passivation film generated on the surface of the workpiece, promote the electrochemical reaction, and form electrochemical mechanical composite finishing.

[0021] In the electrochemical mechanical composite finishing inner channel method of the above flexible joint electrode disclosed in one embodiment of the present application, the following steps are included: step one: fixing the workpiece on the machine tool workbench and pre-placing the flexible joint electrode in the inner channel of the workpiece; step two: passing the flexible joint electrode through the liquid collecting cavity at one end, connecting the flexible joint electrode with the first machine tool spindle through the first conductive soft shaft, and using the same method to connect the flexible joint electrode with the second machine tool spindle through the second conductive soft shaft at the other end, and adjusting the relative position of the machine tool spindles to make the flexible joint electrode have a certain pre-tension; step three: connecting the flexible joint electrode to the negative electrode of the power supply and connecting the workpiece to the positive electrode of the power supply, opening the liquid supply system, and making the high-speed and high-pressure flowing electrolyte enter the liquid collecting cavity from the entrances on both sides of the liquid collecting cavity, collecting the electrolyte in the cavity, and then making the electrolyte flow out along the outer wall of the flexible joint electrode and into the machining gap; step four: driving the first machine tool spindle and the second machine tool spindle to move linearly in the same direction to drive the flexible joint 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, and turning on the power supply to make the complex inner channel be finished under the combined action of electrochemistry and mechanical scraping; and step five: stopping the machining when the surface roughness of the inner channel of the workpiece reaches the requirement.

[0022] Compared with the prior art, the flexible joint electrode and the electrochemical mechanical composite finishing inner channel method provided in the embodiments of the present application have the following advantages:

[0023] 1. The flexible nodular electrode provided by the embodiment, the tool cathode is hinged between adjacent nodular unit electrodes through the universal joint, which ensures that the electrode has good flexibility and can be flexibly deformed to adapt to different shapes of complex internal channels.

[0024] 2. The electrode conductive base has an insulating layer attached to the local surface. The insulating layer is a loose porous sponge layer attached to the local surface of the electrode conductive base. The electric field lines and electrolyte can pass through the loose insulating layer, so that the electrode conductive base and the complex internal channel can have electrochemical action. At the same time, the porous insulating layer can avoid short circuit and burn of the electrode conductive base and the complex internal channel surface.

[0025] 3. The insulating layer is distributed with insulating soft abrasive particles, which can produce mechanical scraping effect on the complex internal channel during processing, remove the passivation film generated on the surface of the workpiece, promote electrochemical reaction, form electrochemical mechanical combined finishing, and improve the finishing efficiency and quality of the complex internal channel. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a schematic diagram of the structure of the flexible nodular electrode and a local enlarged schematic diagram;

[0027] Figure 2 is a schematic diagram of the universal joint;

[0028] Figure 3 is a schematic diagram of the electrode conductive base;

[0029] Figure 4 is a schematic diagram of the flexible nodular electrode electrochemical mechanical combined polishing of the complex internal channel;

[0030] Figure 5 is a schematic diagram of the electrochemical mechanical combined polishing process of the surface of the complex internal channel;

[0031] The reference numerals and names are as follows: 1, flexible nodular electrode, 2, electrode conductive base, 3, universal joint, 4, insulating layer, 5, insulating soft abrasive particles, 6, workpiece, 7, liquid collecting cavity, 8, first conductive soft shaft, 9, first machine tool spindle, 10, second conductive soft shaft, 11, second machine tool spindle, 12, power supply, 13, passivation film, 14, base, 15, hinge hole, 16, boss. DETAILED DESCRIPTION

[0032] The technical solutions of the present application will be further described below in combination with the drawings.

[0033] According to the embodiment shown in FIG. 1, the flexible nodal electrode 1 comprises several similar nodal units, each nodal unit comprising an electrode conductive base 2, a universal joint 3, a porous insulating layer 4 and insulating soft abrasive particles 5, the adjacent nodal units are hinged by the universal joint 3 to ensure that the electrode can be flexibly bent and deformed to adapt to the complex inner channel of different shapes; the insulating layer 4 is a loose porous sponge layer attached to the local surface of the electrode conductive base 2, the electric field lines and the electrolyte can pass through the loose insulating layer 4, so that the electrode conductive base 2 and the complex inner channel of the workpiece 6 can have electrochemical action, at the same time, the porous insulating layer 4 can avoid short-circuiting and burning of the electrode conductive base in contact with the surface of the complex inner channel; the insulating soft abrasive particles 5 are uniformly embedded on the outer surface of the insulating layer 4, which can produce a mechanical scraping effect on the complex inner channel of the workpiece 6 during processing, and can remove the passivation film generated on the surface of the workpiece 6 to promote electrochemical reaction and form electrochemical mechanical combined finishing, in FIG. 1, A is a partial enlarged view of the square frame.

[0034] According to the embodiment shown in FIG. 2 and FIG. 3, the electrode conductive base 2 is a cylindrical metal block, both ends of which have a base 14 for hinging the universal joint, the axis angle of the hinging holes 15 of the two end bases 14 is 90°; the universal joint 3 is composed of two cross axes connected, each axis has a protruding cylindrical boss 16 at both ends for hinging with the electrode conductive base 2;

[0035] According to the embodiment shown in FIG. 4, the flexible nodal electrode and the electrochemical mechanical combined finishing inner channel method comprises the following processes:

[0036] Step one: fix the workpiece 6 on the machine tool workbench, and pre-place the flexible nodal electrode 1 in the inner channel of the workpiece 6;

[0037] Step two: pass one end of the flexible nodal electrode 1 through the liquid collecting cavity 7, and connect it with the first machine tool spindle 9 through the first conductive soft shaft 8; use the same method to connect the other end of the flexible nodal electrode 1 with the second machine tool spindle 11 through the second conductive soft shaft 10, and adjust the relative position of the machine tool spindles to make the flexible nodal electrode 1 have a certain pre-tension;

[0038] Step three: connect the flexible nodal electrode 1 with the negative pole of the power supply 12, and connect the workpiece 6 with the positive pole of the power supply 12, open the liquid supply system, and high-speed high-pressure flowing electrolyte enters the liquid collecting cavity 7 from the inlet on both sides of the liquid collecting cavity 7, collects in the cavity, and then flows out along the outer wall of the flexible nodal electrode 1 and flows into the machining gap;

[0039] Step four: drive the first machine tool spindle 9 and the second machine tool spindle 11 to move linearly in the same direction, drive the flexible nodal electrode 1 to reciprocate, make the soft abrasive particles 5 outside the insulating layer 4 exert mechanical scraping effect on the complex inner channel of the workpiece 6, turn on the power supply 12, and the complex inner channel is finished under the combined action of electrochemical action and mechanical scraping action.

[0040] Step five: stop the machining when the roughness of the inner surface of the workpiece 6 reaches the required value.

[0041] According to Fig. 5, a passivation film 13 is formed on the inner surface of the workpiece 6 during the machining process. The passivation film is thin on the convex part and thick on the concave part. During the machining process, the flexible nodular electrode 1 moves back and forth, and the soft abrasive particles 5 on the insulating layer 4 exert mechanical scraping action on the inner surface of the workpiece 6. The passivation film on the convex part is removed, and the base material is exposed, which is electrochemically dissolved, and then a new passivation film 13 is formed. The two processes of forming the passivation film and removing the passivation film by the soft abrasive particles are alternately repeated until the roughness of the inner surface of the workpiece 6 reaches the required value.

Claims

1. A flexible nodular electrode, characterized by: The flexible segmented electrode (1) is composed of a plurality of segmented electrode units and universal joints (3) for connecting adjacent segmented electrode units. The segmented electrode unit is composed of an electrode conductive base (2), a porous insulating layer (4) attached to the surface of the electrode conductive base (2), and insulating soft abrasive particles (5) uniformly embedded on the outer surface of the porous insulating layer (4).

2. The flexible nodular electrode of claim 1, wherein: The porous insulating layer (4) is a loose and porous sponge layer.

3. The flexible nodular electrode of claim 1, wherein: The electrode conductive base (2) is a cylindrical metal block with two ends having seats for hinging the universal joints, and the included angle between the hinge hole axes of the two end seats is 90°; the universal joint (3) is composed of two cross-shaped shafts connected together, and each shaft has a protruding cylindrical boss at both ends for hinging with the electrode conductive base (2).

4. The electrochemical mechanical combined finishing in-hole process using the flexible nodular electrode of claim 2, characterized in that, The process includes the following steps: The adjacent segmented electrode units of the flexible segmented electrode (1) are hinged by the universal joints (3) to ensure that the electrode can flexibly bend and deform to adapt to different shapes of complex internal channels; The insulating layer (4) is a loose and porous sponge layer attached to the local surface of the electrode conductive base (2), and the electric field lines and electrolyte can pass through the loose insulating layer (4) to cause electrochemical action between the electrode conductive base (2) and the complex internal channel, while the porous insulating layer (4) can prevent the electrode conductive base (2) from contacting the surface of the complex internal channel and causing short circuit and burn; The insulating soft abrasive particles (5) are uniformly embedded on the outer surface of the insulating layer (4) and can produce mechanical scraping action on the complex internal channel during processing to remove the passivation film generated on the surface of the workpiece (6), promote electrochemical reaction, and form electrochemical mechanical combined finishing.

5. The electrochemical mechanical complex finishing in-hole process using the flexible nodular electrode of claim 4, characterized in that, The process includes the following steps: Step 1: Fix the workpiece (6) on the machine tool workbench, and pre-place the flexible segmented electrode (1) in the internal channel of the workpiece (6); Step 2: Pass one end of the flexible segmented 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 segmented electrode (1) to the second machine tool spindle (11) through the second conductive flexible shaft (10), and adjust the relative positions of the machine tool spindles to give the flexible segmented electrode (1) a certain pre-tension; Step 3: Connect the flexible segmented electrode (1) to the negative electrode of the power supply (12), and connect the workpiece (6) to the positive electrode of the power supply (12), turn on the liquid supply system, and high-speed high-pressure flowing electrolyte enters the liquid collecting cavity (7) from the entrances on both sides of the liquid collecting cavity (7), collects in the cavity, and then flows out along the outer wall of the flexible segmented electrode (1) and into the machining gap; Step 4: Drive the first machine tool spindle (9) and the second machine tool spindle (11) to move linearly in the same direction, drive the flexible segmented electrode (1) to reciprocate, and make the soft abrasive particles (5) outside the insulating layer (4) exert mechanical scraping action on the complex internal channel of the workpiece (6); turn on the power supply (12), and the complex internal channel is finished under the combined action of electrochemistry and mechanical scraping; Step 5: When the surface roughness of the internal channel of the workpiece (6) meets the requirements, stop processing.

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