Device and method for electrolytic machining of double-edge blade sandwich cathode partitioned electrification full-surface

Abstract

This invention relates to a device and method for electrolytic machining of the entire profile of a double-bladed blade with a sandwich cathode, belonging to the field of electrolytic machining technology. The blade base / back sandwich cathode in this device is an integrated cathode composed of a crown cathode, a body cathode, a tenon cathode, and two insulating layers. The cathodes in the integrated sandwich cathode are mutually insulated, allowing for zoned energization, and the energization state of each cathode is matched with the feed direction of the integrated sandwich cathode. During machining, the integrated sandwich cathode first feeds along the blade direction, with the body cathode energized and the other cathodes de-energized, to perform blade profile machining. Then, the feed direction of the integrated sandwich cathode is changed in situ to the crown or tenon direction, with the crown or tenon cathode energized and the other cathodes de-energized, to perform crown or tenon machining. This invention can complete the electrolytic machining of the entire profile of a double-bladed blade in one clamping and one machining step, significantly improving machining efficiency and quality, and has good practical significance.

Description

Technical Field

[0001] This invention relates to a device and method for electrolytic machining of the entire surface of a double-bladed blade sandwich cathode with zoned energization, belonging to the field of electrolytic machining technology. Background Technology

[0002] Aero-engines are the "heart" of aircraft and are among the most complex electromechanical products. Double-bladed blades are a core component of aero-engines, and their manufacturing precision and surface integrity directly affect the engine's performance and service life. Compared to conventional single-bladed blades, double-bladed blades, in addition to the blade body and tenon, also include the blade crown, making their structure more complex. These blades come in many varieties, require high machining precision and surface quality, and are typically made from difficult-to-machine materials such as titanium alloys, nickel-based superalloys, and TiAl intermetallic compounds, making precision and efficient manufacturing extremely difficult, especially the integrated precision and efficient manufacturing of the entire blade body, tenon, and blade crown profile.

[0003] Electrolytic machining (EMC) is a specialized machining technology that removes materials based on the principle of electrochemical anodic dissolution. It possesses inherent advantages such as independence from the mechanical properties of the workpiece material (e.g., strength and hardness), no tool electrode wear, high processing efficiency, and good surface quality, making it ideal for the precision and efficient manufacturing of aero-engine blades. As a supplementary technology to traditional machining, EMC has, after years of development, become one of the preferred machining technologies for complex structural components made from difficult-to-machine materials in aero-engines.

[0004] In traditional electrolytic machining of blades, the blade base tool cathode and the blade back tool cathode feed towards each other at a certain feed rate, gradually approaching the blade profile, which is then gradually shaped under electrochemical normal dissolution. However, in this method, the tenon and crown profiles of double-blade blades lack the feed component of the tool cathode, resulting in lateral dissolution and continuous secondary electrochemical corrosion, leading to poor machining accuracy and surface quality. Therefore, a new electrolytic machining process is urgently needed that allows the entire blade profile, including the tenon and crown, to have a feed component, ultimately achieving normal dissolution and shaping, thereby improving machining accuracy and surface quality.

[0005] In the patent "Integrated Electrolytic Molding Method for Integral Bladed Disk with Coordinated Spatial Rotation and Translation" (application number 201910800505.9, applicant: Nanjing University of Aeronautics and Astronautics, inventors: Xu Zhengyang, Wang Jingtao, Wang Jing, Zhu Di), the integrated bladed disk blade channel and blade profile electrolytic processing adopt the same tool cathode. Through the complex movement of the tool cathode and the complex movement of the integrated bladed disk, the integrated processing of the entire blade profile of the integrated bladed disk can be achieved.

[0006] In the article “An electrochemical machining method for aero-engine blades based on four-directional synchronous feeding of cathode tools” (authors Jia Liu, Libing Hui, Dongqian Jia, Yan Liu, Di Zhu, Chinese Journal of Aeronautics, 2023, 36(9): 380–391), a four-directional synchronous feeding electrochemical machining method based on four cathodes is proposed for the electrochemical machining of the blade base, blade back, leading edge and trailing edge, which can realize the machining of the entire blade surface.

[0007] In the patent "A method and electrolytic tool for integrated electrolytic processing of integral bladed disk" (application number 201911225268.4, applicant Hefei University of Technology, inventors Zhang Juchen, Li Xinglin, Chen Yuanlong, Zhang Bin), an integrated tool cathode with a hollow thin-walled structure is adopted. The integral bladed disk blade basin, blade back and hub are formed in one step through multi-axis linkage between the workpiece and the tool cathode.

[0008] In the patent "Triaxial Flexible Feed Electrolytic Machining Method for Blades" (application number 200610040556.9, applicant: Nanjing University of Aeronautics and Astronautics, inventors: Zhu Di, Xu Zhengyang, Shi Xianchuan), the full-surface machining of single-blade blades can be achieved through triaxial flexible feed electrolytic machining of the blade, blade basin cathode, and blade back cathode.

[0009] In the patent “ELECTROCHEMICAL MACHINING METHOD AND ELECTROCHEMICAL MACHINING DEVICE” (application number 06780652.1, applicants IHI Corporation and APC Aerospecialty, inventor FUJIHARA Yasuo), two tool cathodes with different feed directions are used. The two tool cathodes and the blade are driven to move in three directions through three sets of motion mechanisms, which can realize the machining of the two side rims and the full surface of the blade body of the double-rimmed blade.

[0010] In the patent “MULTIPART ELECTRODE ARRAY AND METHOD FOR THE ELECTROCHEMICALTREATMENT OF BLADES HAVING SHROUDING BANDS” (patent number US 9682437 B2, applicant MTU AeroEngines AG, inventor Albin Platz Daniela Arbinger), three mutually contacting tool cathodes are used. These three cathodes slide relative to each other through a certain angled inclined plane, so that the tool cathodes on both sides also have a feed component on the rim plates on both sides of the double-rim plate blade, realizing the full-surface machining of the blade body and the two rim plates on both sides.

[0011] In the patent "An integrated forming processing method for integral bladed disk" (application number 202311296512.2, applicant: China Aero Engine Corporation Shenyang Liming Aero Engine Co., Ltd., inventors: Lan Yingduo, Shan Kun, Liang Qiaoyun, Zhang Yashuang), a combination of three process schemes—abrasive waterjet roughing, electrolytic finishing, and adaptive belt polishing—is used to realize an integrated processing method for integral bladed disks.

[0012] In the patent "Method for Electrolytic Processing of Integrated Bladed Disk with Double-Sided Combination Double Cathode and Segmented Electricity Control" (application number 202210306217.X, applicant: Nanjing University of Aeronautics and Astronautics, inventors: Xu Zhengyang, Shen Zhenyu, Liu Jia, Zhu Dong), the processing of the blade channel and blade body of the integrated bladed disk can be completed sequentially through a pair of double-sided combined tool cathodes and two processing steps.

[0013] For double-bladed blades, the crown and tenon profiles are almost perpendicular to the blade profile and are all complex spatial curved surfaces. The efficient and precise integrated manufacturing of these entire profiles presents a significant challenge to electrolytic machining. To address these challenges, this invention proposes a device and method for electrolytic machining of the entire profile of double-bladed blades using a cathode with partitioned energization. Summary of the Invention

[0014] The purpose of this invention is to overcome the problem that traditional blade electrochemical machining of double-bladed blades lacks a feed component on the sidewall profile, making it impossible to achieve efficient and precise manufacturing of the entire profile. This invention innovatively proposes a double-bladed blade sandwich cathode partitioned energizing full-profile electrochemical machining device and method. It adopts an integrated sandwich cathode and, through a reversing feed + partitioned energizing mode, achieves efficient and precise machining of the entire profile of the blade body and both side rims of a double-bladed blade with one set of fixtures, one clamping, and one machining process, significantly improving machining efficiency and machining accuracy of the side rim profiles.

[0015] A double-bladed blade sandwich cathode zoned energized full-surface electrolytic machining apparatus, characterized in that: it includes a blade basin sandwich cathode, a blade back sandwich cathode, and a double-bladed blade electrolytic machining fixture; the blade basin sandwich cathode includes a blade basin-side crown cathode, a blade basin cathode, and a blade basin-side tenon cathode; wherein the blade basin-side crown cathode and the blade basin-side tenon cathode are respectively located on the left and right sides of the blade basin sandwich cathode; the blade basin-side crown cathode and the blade basin cathode are insulated from each other by a first left insulating layer, and the blade basin cathode and the blade basin-side tenon cathode are insulated from each other by a first right insulating layer; the blade back sandwich cathode consists of a blade back-side crown cathode, a blade back... The blade has a cathode and a tenon cathode on the back side; the tenon cathode on the back side and the crown cathode on the back side are located on the left and right sides of the blade back sandwich cathode, respectively; the crown cathode on the back side and the blade back cathode are insulated from each other by a second left insulating layer, and the blade back cathode and the tenon cathode on the back side are insulated from each other by a second right insulating layer; the above-mentioned double-edged blade electrolytic machining fixture consists of a fixture cover, a fixture body, a blade basin side water sealing plate, a blade back side water sealing plate, a blade basin side tenon insulating plate, a tenon side tenon insulating plate, a tenon clamping block, a blade basin side crown insulating plate, a blade back side crown insulating plate, and a crown clamping block; the fixture cover is provided with an electrolyte inlet. The aforementioned blade basin sandwich cathode and blade back sandwich cathode are each an integral structure; that is, the blade basin side crown cathode, blade basin cathode and blade basin side tenon cathode are fixed to each other, but are mutually insulated and energized in separate areas, and the energization state matches the feed direction; the blade back side crown cathode, blade back cathode and blade back side tenon cathode are fixed to each other, but are mutually insulated and energized in separate areas, and the energization state matches the feed direction.

[0016] The method of the double-blade blade sandwich cathode zoned energization full-surface electrolytic machining device is characterized by the following processes: 1) The blade basin sandwich cathode is installed on the Y1 axis on the left side of the machine tool, and the blade back sandwich cathode is installed on the Y2 axis on the right side of the machine tool; the double-blade blade electrolytic machining fixture is installed on the worktable above the X-axis in the middle of the machine tool; the double-blade blade blank is installed in the double-blade blade electrolytic machining fixture and pressed, then tool setting is performed, leaving a certain initial machining gap; 2) The blade basin cathode in the blade basin sandwich cathode and the blade back cathode in the blade back sandwich cathode are connected to the negative terminal of the power supply, the other cathodes are in a de-energized state, and the double-blade blade blank is connected to the positive terminal of the power supply; 3) High-pressure and high-speed electrolyte flows into the machining area from the electrolyte inlet, covering the entire surface of the double-blade blade; 4) The power supply is started, and the blade basin sandwich cathode and the blade back sandwich cathode are energized separately. Driven by the Y1 and Y2 axes of the machine tool, feed towards each other along the Y-axis at a certain speed, gradually approaching the blade body. The blade body profile gradually takes shape under the electrochemical normal dissolution action. 5) When the blade body profile is completed, the feed direction of the blade basin sandwich cathode and the blade back sandwich cathode is automatically changed to the blade crown or tenon direction, i.e., the X-axis direction. At the same time, the blade basin cathode and the blade back cathode are automatically de-energized. The blade basin side crown cathode or blade basin side tenon cathode in the blade basin sandwich cathode and the blade back side crown cathode or blade back side tenon cathode in the blade back sandwich cathode are automatically switched to the energized state. The blade crown or tenon profile gradually takes shape under the electrochemical normal dissolution action. 6) When the blade crown and tenon are completed, the machine tool spindle stops, and the electrolytic machining of the entire profile of the double-blade blade body and the two side blades is completed. The machining is finished. 7) Turn off the power and stop the electrolyte pump.

[0017] Compared with the prior art, the present invention has the following significant advantages.

[0018] (1) Innovative tool cathode structure. This invention innovatively designs an integrated sandwich cathode consisting of a crown cathode, a blade cathode, a tenon cathode, and two insulating layers. The cathodes in the integrated sandwich cathode are mutually insulated, allowing for zoned energization. Only one set of fixtures and one pair of cathodes are needed to achieve efficient and precise electrolytic machining of the entire profile of a double-bladed blade. This shortens the design and manufacturing cycle of the tool cathode and fixtures, reduces the machining cycle, and lowers production costs.

[0019] (2) Innovative electrolytic machining process. This invention utilizes an integrated sandwich-type cathode reversing feed + zoned energizing mode to ensure that the entire profile of the double-blade blade is formed by normal feed. This allows for efficient and precise manufacturing of the blade body and both side rims in a single clamping and machining operation. It avoids repeated installation errors and significantly improves machining efficiency and the machining quality of the side rims.

[0020] (3) Simple motion. The present invention can realize the full surface machining of double-bladed blades by sequentially moving the integrated sandwich cathode along the Y-axis and X-axis. The motion is simple, easy to operate, and has good practicality.

[0021] (4) It has a wide range of applications and prospects. Aero engines contain a large number of double-bladed blades of various types, and there is an urgent need for efficient and precise integrated manufacturing of the entire profile of double-bladed blades, which has good application prospects. In addition, the processing device and process proposed in this invention can also be applied to the electrolytic machining of the entire profile of components such as single-bladed blades with simple adjustments, and has a wide range of applications.

[0022] (5) The blade basin sandwich cathode and the blade back sandwich cathode mentioned above are both integral structures. Through the reversing feed + zoned energizing mode of the integral sandwich cathode, the entire profile of the double-blade blade is finally formed by normal melting. This simplifies the design of tool cathodes and tooling fixtures and greatly shortens the processing cycle.

[0023] The aforementioned double-blade blade sandwich cathode zoned energized full-surface electrolytic machining device is characterized by the following: there is a distance between the aforementioned blade basin sandwich cathode and the blade basin-side tenon insulating plate and the blade basin-side crown insulating plate; there is also a distance between the aforementioned blade back sandwich cathode and the blade back-side tenon insulating plate and the blade back-side crown insulating plate. This avoids interference with the fixture when the blade basin sandwich cathode and the blade back sandwich cathode move along the X-axis to machine the blade crown or tenon profile.

[0024] The aforementioned double-blade blade interlayer cathode partitioned energized full-surface electrolytic machining device is characterized in that: the fixture cover is provided with multiple sets of electrolyte inlets, corresponding to the blade basin / blade back machining area, the blade basin side tenon machining area, the blade basin side crown machining area, the blade back side tenon machining area, and the blade back side crown machining area, respectively. This flow field mode allows the electrolyte to cover the entire surface of the double-blade blade, avoiding areas of insufficient electrolyte; simultaneously, the machining area is discretized into multiple small channels, enhancing the flushing performance of the electrolyte and accelerating product removal.

[0025] The described method for electrolytic machining of the entire blade profile using a sandwich cathode with zoned energization is characterized by the following steps: When machining the blade base and blade back profiles, the blade base side sealing plates and blade back side sealing plates are fixed to the fixture body and do not move; when machining the blade crown or tenon profiles, the blade base side sealing plates and blade back side sealing plates are respectively fixed to the blade base sandwich cathode and blade back sandwich cathode, and move along the X-axis with the blade base sandwich cathode and blade back sandwich cathode. This method allows for reversing feed of the integrated sandwich cathode, enabling continuous machining of the blade body and both side flange profiles. Attached Figure Description

[0026] Figure 1Three-dimensional assembly drawing of a full-surface electrolytic machining device for double-bladed blade interlayer cathode zone energization;

[0027] Figure 2 Three-dimensional internal structure diagram of a full-surface electrolytic machining device for double-bladed blade interlayer cathode zone energization;

[0028] Figure 3 These are three-dimensional model diagrams of sandwich cathodes, where Figure (a) and Figure (b) are three-dimensional model diagrams of leaf back sandwich cathodes and leaf basin sandwich cathodes, respectively.

[0029] Figure 4 A schematic diagram of the full-surface electrolytic machining process for a double-bladed blade sandwich cathode with zoned energization;

[0030] Labels in the diagram: 1. Blade-pot sandwich cathode; 101. Blade-pot side crown cathode; 102. First left insulating layer; 103. Blade-pot cathode; 104. First right insulating layer; 105. Blade-pot side tenon cathode; 2. Fixture cover; 3. Electrolyte inlet storage chamber; 4. Electrolyte inlet; 5. Blade-back sandwich cathode; 501. Blade-back side crown cathode; 502. Second left insulating layer; 503. Blade-back cathode 504. Second right insulation layer; 505. Tenon cathode on blade back side; 6. Fixture body; 7. Water sealing plate on blade basin side; 8. Tenon insulation plate on blade basin side; 9. Pressing block on tenon; 10. Double-edged blade blank; 11. Tenon insulation plate on blade back side; 12. Water sealing plate on blade back side; 13. Insulating plate on blade crown on blade back side; 14. Pressing block on blade crown; 15. Insulating plate on blade basin side; 16. Bubble; 17. Product. Detailed Implementation

[0031] The present invention will now be further described with reference to the accompanying drawings.

[0032] like Figure 1-4 As shown, the double-blade blade sandwich cathode zone electrolytic machining method proposed in this invention mainly includes the following processes:

[0033] 1) The blade-basin sandwich cathode 1 is installed on the Y1 axis on the left side of the machine tool, and the blade-back sandwich cathode 5 is installed on the Y2 axis on the right side of the machine tool; the double-blade blade electrolytic machining fixture is installed on the worktable above the X axis in the middle of the machine tool; the double-blade blade blank 10 is installed in the double-blade blade electrolytic machining fixture and pressed, then the tool is set, leaving a certain initial machining gap;

[0034] 2) The blade basin cathode 103 in the blade basin sandwich cathode 1 and the blade back cathode 503 in the blade back sandwich cathode 5 are connected to the negative terminal of the power supply, while the other cathodes are in a de-energized state, and the double-edged blade blank 10 is connected to the positive terminal of the power supply.

[0035] 3) High-voltage, high-speed electrolyte flows into the processing area from electrolyte inlet 4, covering the entire profile of the double-bladed blade;

[0036] 4) Start the power supply. The blade basin sandwich cathode 1 and the blade back sandwich cathode 5 are driven by the Y1 axis and Y2 axis of the machine tool, respectively, and feed towards each other along the Y axis at a certain speed, gradually approaching the blade body. The blade body shape is gradually formed under the electrochemical normal dissolution action.

[0037] 5) When the blade profile is completed, the feed direction of the blade basin sandwich cathode 1 and the blade back sandwich cathode 5 is automatically changed from the original position to the feed direction of the blade crown or tenon, that is, the X-axis direction. At the same time, the blade basin cathode 103 and the blade back cathode 503 are automatically de-energized, and the blade basin side crown cathode 101 or blade basin side tenon cathode 105 in the blade basin sandwich cathode 1 and the blade back side crown cathode 501 or blade back side tenon cathode 505 in the blade back sandwich cathode 5 are automatically switched to the energized state. The blade crown or tenon profile is gradually formed under the electrochemical normal dissolution action.

[0038] 6) When the blade crown and tenon are finished, the machine tool spindle stops, and the electrolytic machining of the entire surface of the double-bladed blade body and the two side blades is completed, and the machining ends;

[0039] 7) Turn off the power and stop the electrolyte pump from supplying liquid.

Claims

1. A double-bladed blade sandwich cathode zoned energizing full-surface electrolytic machining device, characterized in that: Includes blade basin sandwich cathode (1), blade back sandwich cathode (5), and double-edged blade electrolytic machining fixture; The above-mentioned leaf-pot sandwich cathode (1) includes a leaf-pot side crown cathode (101), a leaf-pot cathode (103), and a leaf-pot side tenon cathode (105); wherein the leaf-pot side crown cathode (101) and the leaf-pot side tenon cathode (105) are located on the left and right sides of the leaf-pot sandwich cathode (1), respectively; the leaf-pot side crown cathode (101) and the leaf-pot cathode (103) are insulated from each other by a first left insulating layer (102), and the leaf-pot cathode (103) and the leaf-pot side tenon cathode (105) are insulated from each other by a first right insulating layer (104); The aforementioned leaf-back sandwich cathode (5) consists of a leaf-back side crown cathode (501), a leaf-back cathode (503), and a leaf-back side tenon cathode (505); wherein the leaf-back side crown cathode (501) and the leaf-back side tenon cathode (505) are located on the left and right sides of the leaf-back sandwich cathode (5), respectively; the leaf-back side crown cathode (501) and the leaf-back cathode (503) are insulated from each other by a second left insulating layer (502), and the leaf-back cathode (503) and the leaf-back side tenon cathode (505) are insulated from each other by a second right insulating layer (504); The above-mentioned double-blade blade electrolytic machining fixture consists of a fixture cover (2), a fixture body (6), a blade basin side water sealing plate (7), a blade back side water sealing plate (12), a blade basin side tenon insulation plate (8), a blade back side tenon insulation plate (11), a tenon clamping block (9), a blade basin side blade crown insulation plate (15), a blade back side blade crown insulation plate (13), and a blade crown clamping block (14); the fixture cover (2) is provided with an electrolyte inlet (4); The above-mentioned blade basin sandwich cathode (1) and blade back sandwich cathode (5) are each an integral structure; that is, the blade basin side crown cathode (101), blade basin cathode (103) and blade basin side tenon cathode (105) are fixed to each other, but are mutually insulated and energized in separate areas, and the energization state matches the feed direction; the blade back side crown cathode (501), blade back cathode (503) and blade back side tenon cathode (505) are fixed to each other, but are mutually insulated and energized in separate areas, and the energization state matches the feed direction.

2. The double-bladed blade sandwich cathode zoned energized full-surface electrolytic machining apparatus according to claim 1, characterized in that: There is a distance between the above-mentioned blade basin sandwich cathode (1) and the blade basin side tenon insulation plate (8) and the blade basin side leaf crown insulation plate (15); there is a distance between the above-mentioned blade back sandwich cathode (5) and the blade back side tenon insulation plate (11) and the blade back side leaf crown insulation plate (13).

3. The double-bladed blade sandwich cathode zoned energized full-surface electrolytic machining apparatus according to claim 1, characterized in that: The clamp cover (2) is provided with multiple sets of electrolyte inlets (4), which correspond to the leaf basin back processing area, leaf basin side tenon processing area, leaf basin side leaf crown processing area, leaf back side tenon processing area, and leaf back side leaf crown processing area, respectively.

4. The method of the double-bladed blade sandwich cathode zoned energizing full-surface electrolytic machining apparatus according to claim 1, characterized in that... Includes the following processes: 1) The blade basin sandwich cathode (1) is installed on the Y1 axis on the left side of the machine tool, and the blade back sandwich cathode (5) is installed on the Y2 axis on the right side of the machine tool; the double-blade blade electrolytic machining fixture is installed on the worktable above the X axis in the middle of the machine tool; the double-blade blade blank (10) is installed in the double-blade blade electrolytic machining fixture and pressed, then the tool is set, and a certain initial machining gap is left. 2) The leaf basin cathode (103) in the leaf basin sandwich cathode (1) and the leaf back cathode (503) in the leaf back sandwich cathode (5) are connected to the negative terminal of the power supply, while the other cathodes are in a de-energized state, and the double-edged blade blank (10) is connected to the positive terminal of the power supply. 3) High-voltage and high-speed electrolyte flows into the processing area from the electrolyte inlet (4), covering the entire profile of the double-edged blade; 4) Start the power supply. The blade basin sandwich cathode (1) and the blade back sandwich cathode (5) are driven by the Y1 axis and Y2 axis of the machine tool respectively and feed towards each other along the Y axis at a certain speed, gradually approaching the blade body. The blade body shape gradually takes shape under the electrochemical normal dissolution action. 5) When the blade profile is completed, the feed direction of the blade basin sandwich cathode (1) and the blade back sandwich cathode (5) is automatically changed to the blade crown or tenon direction, i.e., the X-axis direction. At the same time, the blade basin cathode (103) and the blade back cathode (503) are automatically de-energized. The blade basin side crown cathode (101) or blade basin side tenon cathode (105) in the blade basin sandwich cathode (1) and the blade back side crown cathode (501) or blade back side tenon cathode (505) in the blade back sandwich cathode (5) are automatically switched to the energized state. The blade crown or tenon profile is gradually formed under the electrochemical normal dissolution action. 6) When the blade crown and tenon are finished, the machine tool spindle stops, and the electrolytic machining of the entire surface of the double-bladed blade body and the two side blades is completed, and the machining ends; 7) Turn off the power and stop the electrolyte pump from supplying liquid.

5. The method for full-surface electrolytic machining of double-bladed blade sandwich cathode zones according to claim 4, characterized in that... Includes the following processes: When processing the blade basin and blade back profile, the blade basin side sealing plate (7) and the blade back side sealing plate (12) are fixed to the fixture body (6) and do not move; When processing the blade crown or tenon profile, the blade basin side sealing plate (7) and the blade back side sealing plate (12) are fixed to the blade basin sandwich cathode (1) and the blade back sandwich cathode (5) respectively, and move along the X-axis direction with the blade basin sandwich cathode (1) and the blade back sandwich cathode (5).

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