A method and apparatus for suppressing edge fringing current corrosion in electrochemical polishing / electrochemical mechanical polishing of planar workpieces

Abstract

The application discloses a method and device for inhibiting edge stray current corrosion in plane workpiece grinding or polishing, which comprises the following steps: adding an equipotential protection ring to the edge of the workpiece, and applying the same potential to the equipotential protection ring and the workpiece, so that no lateral current exists between the side surface of the workpiece and the equipotential protection ring; the device comprises: first nylon disc, second nylon disc and workpiece clamp which are arranged in sequence and concentrically from top to bottom; the second nylon disc is hollow and provided with a stepped hole, a spring copper brush is arranged in the stepped hole, the upper end of the spring copper brush is connected with a conductive slip ring arranged in the central hole of the first nylon disc through a lead wire, the lower end of the spring copper brush is provided with a copper brush head which penetrates through the middle through hole of the workpiece clamp and elastically contacts the workpiece below, the workpiece is nested in the equipotential protection ring which is placed on the same plane, and the second nylon disc is provided with a groove in the bottom, a spring graphite brush is arranged in the groove and elastically contacts the equipotential protection ring. The application inhibits the lateral current of the edge of the workpiece by a simple structure to inhibit the stray current corrosion of the edge of the workpiece, and improves the electrochemical grinding / mechanical polishing processing precision.

Description

Technical Field

[0001] The present invention belongs to the technical field of grinding and polishing, and in particular relates to a method and a device for suppressing edge stray current corrosion in electrochemical grinding / electrochemical mechanical polishing of a planar workpiece. Background Art

[0002] Planar components, as common engineering products, are widely used in fields such as electronics and information technology, energy and transportation, and materials engineering. To meet the demand for high-performance thin-plate components in these fields, precision or ultra-precision machining is often required to achieve the required quality. Examples include copper plating on silicon wafers, metal springs for voice coil motors, brake discs for motorcycles, and pure metal flying layers used in precision physics experiments such as detonation and flying layer impacts.

[0003] When machining thin plate parts made of different materials, the machining method and the unevenness of surface material removal can affect the machining quality. Furthermore, some low-thickness flat parts often experience warping, bending, and twisting due to a variety of factors, including internal stress in the blank, tooling clamping force, cutting forces and heat during machining, and residual stress on the machined surface. These complex and diverse deformations seriously affect the machining accuracy of the parts. Therefore, existing technologies currently utilize specialized composite machining technologies based on multiple chemical and electrochemical processes, such as chemical mechanical polishing, electrochemical polishing, electrochemical polishing, and electrochemical mechanical polishing. These technologies leverage the synergistic effects of chemical, electrochemical, and mechanical processes to significantly weaken or suppress the negative effects of forces during machining. Chemical mechanical polishing, through chemical reaction on the surface of the workpiece to generate easily removable substances, which are then erased by polishing pads or abrasives, can achieve sub-nanometer roughness on the surface of pure copper. However, due to deformation of the polishing pad during the material removal process, the surface shape error of thin metal plates such as pure copper plates may increase (Pan B, Kang R, Guo J, et al. Precision fabrication of thin copper substrateby double-sided lapping and chemical mechanical polishing[J]. Journal ofManufacturing Processes. 2019,44: 47-54.). Electrochemical polishing can achieve nanometer-level roughness on pure copper and has the advantage of stress-free processing, but it is easy to increase surface shape error due to stray current corrosion. Electrochemical polishing has a higher removal rate because the local high points on the machined surface of metal parts are exposed to a higher concentration of etchant, achieving stress-free preferential removal of local high points on the workpiece, thereby achieving surface flatness. However, MRRLimited, when statically processing metal sheets such as pure copper sheets (the workpiece is stationary relative to the electrode) MRR =0.107μm / h, during dynamic machining (the workpiece rotates relative to the electrode) MRR =0.618~0.756μm / h (Guo Minzheng. Development of an Electrochemical Polishing System [D]. Dalian: Dalian University of Technology, 2020.). Electrochemical mechanical polishing uses an electrochemical reaction to form a passivation film on the surface of metal parts to inhibit electrolysis. The friction of the grinding tool then erases the high points of the passivation film, preventing direct contact between the workpiece surface and the abrasive particles. However, electrolyte easily accumulates at the edges of the workpiece. The high ion concentration and low resistivity in this area can lead to preferential removal of material at the edges. Furthermore, edge corrosion caused by stray currents is a common problem in electrochemical machining / combined electrochemical machining. The tip effect at the workpiece edge can easily lead to excessive material removal at the edges, compromising machining accuracy.

[0004] At present, the research on high surface accuracy and high surface quality processing of flat metal workpieces still has the following problems:

[0005] 1. The electrolyte accumulates at the edge of the workpiece, making the ion concentration in this area high and the resistivity low, making the material at the edge of the workpiece easier to remove than in the center of the workpiece.

[0006] 2. Edge stray current corrosion is a common problem in electrochemical machining / electrochemical composite machining. The tip effect at the edge of the workpiece can easily cause the workpiece potential to be superimposed, forming a high potential, and ultimately causing excessive material removal at the edge of the workpiece during the machining process, affecting the machining accuracy. Summary of the Invention

[0007] The purpose of the present invention is to provide a method and device for inhibiting edge stray current corrosion in electrochemical grinding / electrochemical mechanical polishing of planar workpieces, so as to solve the problem of excessive removal of workpiece edge material and deterioration of machining accuracy due to edge stray current corrosion in existing electrochemical machining.

[0008] To achieve the above objectives, the present invention proposes a method for inhibiting edge stray current corrosion during electrochemical grinding / electrochemical mechanical polishing of planar workpieces. By adding an equipotential body to the edge of the planar workpiece, the electrolyte at the edge of the workpiece is reduced through the physical barrier effect of the equipotential body. In addition, the same electric potential is applied to the equipotential body and the planar workpiece, so that there is no lateral current between the side of the planar workpiece and the equipotential body, thereby inhibiting electrochemical corrosion.

[0009] The present invention provides a device for suppressing edge stray current corrosion during electrochemical grinding / electrochemical mechanical polishing processing, comprising: a first nylon disk, a second nylon disk, and a workpiece clamp, which are concentrically arranged in sequence from top to bottom; a stepped hole is provided in the hollow of the second nylon disk, a spring copper brush is provided in the stepped hole, the upper end of the spring copper brush is connected to a conductive slip ring provided in the center hole of the first nylon disk via a wire, and the copper brush head provided at the lower end passes through the central through hole of the workpiece clamp to maintain elastic contact with the workpiece below, and the workpiece is nested in an equipotential protection ring placed on the same plane.

[0010] Preferably, a plurality of grooves are provided at the bottom of the second nylon disk, and spring graphite brushes are provided in the grooves and maintain elastic contact with the equipotential protection ring.

[0011] Preferably, the three grooves are equidistantly arranged on the outer periphery of the bottom of the second nylon disk, and are matched with three spring graphite brushes.

[0012] Preferably, a through hole is provided between the groove and the stepped hole, so that the spring graphite brush and the spring copper brush are connected through a wire in the through hole.

[0013] Preferably, the workpiece fixture comprises a ceramic disk and an adsorption pad is provided at the bottom thereof, and the adsorption pad vacuum adsorbs the workpiece through the adsorption surface.

[0014] Preferably, the adsorption pad is a wax-free adsorption pad.

[0015] The present invention provides a method for suppressing edge stray current corrosion during electrochemical grinding / electrochemical mechanical polishing, comprising the following steps:

[0016] S1. Selecting an equipotential protection ring material, wherein the metallic property of the equipotential protection ring material is higher than or equal to the metallic property of the workpiece material;

[0017] S2. Place the workpiece and the equipotential protection ring on the same horizontal plane, and nest the workpiece in the equipotential protection ring, with the centroid of the bottom surface of the workpiece and the centroid of the bottom surface of the equipotential protection ring being 0-1 mm apart;

[0018] S3. Applying the same electric potential to the workpiece and the equipotential protection ring through a power supply, and performing electrochemical grinding / electrochemical mechanical polishing.

[0019] Preferably, the height of the equipotential protection ring is higher than the thickness of the workpiece, and the inner diameter of the equipotential protection ring is larger than the diameter of the workpiece fixture or larger than the longest diagonal length of the workpiece fixture.

[0020] The present invention provides an equipotential protection ring, which is made of a material with metallic properties higher than or equal to the metallic properties of a workpiece material; the height of the equipotential protection ring is higher than the thickness of the workpiece, and the diameter of the equipotential protection ring is greater than the inner diameter of a workpiece fixture or greater than the longest diagonal length of the workpiece fixture.

[0021] The present invention provides an application of an equipotential protection ring for suppressing edge stray current corrosion during electrochemical grinding / electrochemical mechanical polishing.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. Low cost: only one equipotential guard ring and several spring graphite brushes are required. The relative position of the equipotential guard ring and the workpiece is further limited to achieve lateral current suppression at the workpiece edge.

[0024] 2. Inhibit stray current corrosion at the edge of the workpiece during machining. Compared with the pure copper sheet without equipotential protection, the corrosion width at the edge of the pure copper sheet under equipotential protection is reduced by 75% and the corrosion depth is reduced by 90%, thereby improving the machining accuracy of electrochemical grinding / electrochemical mechanical polishing of the workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A comparison diagram of the prior art without equipotential protection and the equipotential protection principle of the present invention;

[0026] Figure 2 This is a diagram showing the overall structure of the electrochemical grinding / electrochemical mechanical polishing anode device of the present invention;

[0027] Figure 3 A top view of the electrochemical grinding / electrochemical mechanical polishing anode device of the present invention;

[0028] Figure 4 This is a real picture of the workpiece after grinding without adding equipotential protection in the existing technology;

[0029] Figure 5 A photo of the workpiece after grinding with equipotential protection added according to the present invention;

[0030] Figure 6 This is a physical picture of a workpiece being ground without adding equipotential protection in the prior art;

[0031] Figure 7 A real picture of workpiece grinding with equipotential protection added to the present invention;

[0032] Including: 1. Conductive slip ring, 2. Hexagon socket bolt, 3. Screw, 4. Nut, 5. First nylon disk, 6. Spring copper brush, 7. Second nylon disk, 8. Ceramic disk, 9. Adsorption pad, 10. Workpiece, 11. Equipotential protection ring, 12. Spring graphite brush. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to specific examples, but the present invention is not limited thereto in any way.

[0034] Unless otherwise specified, the instruments, reagents, and materials used in the following examples are all conventional instruments, reagents, and materials available in the prior art and can be obtained through regular commercial channels. The experimental methods and detection methods used in the following examples are all conventional experimental methods and detection methods available in the prior art, unless otherwise specified.

[0035] like Figure 1 As shown in a, it is a schematic diagram of the principle of the prior art without equipotential protection. When there is no equipotential protection, the edge of the workpiece is at a high potential due to the tip effect, the current is higher, and the material removal rate is higher.

[0036] The present invention provides a device for suppressing stray current corrosion at the edge of a planar workpiece during electrochemical grinding / electrochemical mechanical polishing. The device provides a protective ring at the edge of the workpiece. By applying the same potential as the pure copper component to form an equipotential body, the corrosion area is transferred to the equipotential protective ring (i.e., a ring-shaped equipotential body) to suppress stray current corrosion at the edge of the workpiece. Figure 1 As shown in b, it is the principle diagram of the equipotential protection of the present invention. The material of the equipotential protection ring is preferably the same as that of the workpiece to avoid the introduction of other metal ions and affecting the formation of the corrosion inhibition film. After improvement, the anode assembly and polishing pad of the electrochemical polishing device are as follows Figure 2 、 Figure 3 shown.

[0037] The device of the present invention includes a conductive slip ring 1, a hexagon socket bolt 2, a screw rod 3, a nut 4, a first nylon disk 5, a spring copper brush 6, a second nylon disk 7, a ceramic disk 8, a wax-free adsorption pad 9, a workpiece 10, an equipotential protection ring 11, and a spring graphite brush 12;

[0038] The conductive slip ring 1 is fixed to the center hole of the nylon disk 5 by the hexagon socket bolt 2. The first nylon disk 5, the second nylon disk 7 and the workpiece fixture are placed concentrically along the axis of the outer peripheral surface of the first nylon disk 5 in sequence from top to bottom and fixed by screws 3 and nuts 4; the workpiece fixture includes a ceramic disk 8 and an adsorption pad 9 provided at the bottom thereof; a stepped hole is provided at the center of the end face of the second nylon disk 7, and a spring copper brush 6 is installed in the stepped hole of the second nylon disk 7. The spring copper brush 6 is connected to the conductive slip ring 1 in the center hole of the first nylon disk 5 through a wire. Three square grooves are provided on the bottom surface of the second nylon disk 7 and are arranged in an array equidistant around the circumference of the second nylon disk 7. A through hole is provided at the center of the end face of the ceramic disk 8. The spring copper brush 6 can extend the spring to make the copper brush head pass through the through hole of the ceramic disk 8. The wax-free adsorption pad 9 is divided into a glue layer and an adsorption layer. The wax-free adsorption pad 9 is adhered to the bottom surface of the ceramic disk 8 with a glue layer. The wax-free adsorption pad 9 adsorbs the workpiece 10 with the vacuum adsorption effect of the adsorption surface. A through hole of the same size as the center hole of the ceramic disk 8 is opened in the center of the wax-free adsorption pad 9. The spring copper brush 6 passes through the through hole of the ceramic disk 8 by virtue of the spring recovery effect and maintains elastic contact with the workpiece 10 to conduct high potential. The spring graphite brush 12 is installed in the square groove on the outer periphery of the second nylon disk 7. A circular through hole is opened between the square groove and the stepped hole of the second nylon disk 7. The spring graphite brush 12 and the spring copper brush 6 are connected by wires between the through holes. The workpiece 10 is nested in the equipotential protection ring 11 placed on the same plane. The spring graphite brush 12 maintains elastic contact with the equipotential protection ring 11, so that the equipotential protection ring 11 and the spring graphite brush 12 are combined to form a concentric circular array.

[0039] The working principle of the device is as follows:

[0040] The workpiece 10 is held on the adsorption surface of the wax-free adsorption pad 9 under the vacuum adsorption effect of the wax-free adsorption pad 9, and the conductive slip ring 1 transmits the high potential E 1 is conducted to the spring copper brush 6, which passes through the ceramic plate 8 and the through hole in the center of the wax-free adsorption pad 9 to maintain elastic contact with the workpiece 10, putting the workpiece at a high potential. E 1. The spring copper brush 6 and the spring graphite brush 12 are connected by wires and are at the same potential. E 1. The spring graphite brush 12 maintains elastic contact with the workpiece 10 to be at the same electrical potential E 1. The bottom surface of the workpiece 10 and the bottom surface of the equipotential protection ring 11 are placed in the same plane and the workpiece 10 is located inside the equipotential protection ring 11. The workpiece 10 reduces the electrolyte on the edge of the workpiece through the physical barrier effect of the equipotential protection ring 11, and the same potential is applied to the workpiece 10 through the equipotential protection ring 11. E 1. There is no lateral current between the side of the workpiece and the equipotential body, which inhibits electrochemical corrosion.

[0041] The present invention provides a method for inhibiting edge stray current corrosion. By adding equipotential bodies at the edge of a workpiece, on the one hand, excessive electrolyte accumulation at the edge of the workpiece is inhibited, and on the other hand, lateral electrolysis of the edge of the workpiece during electrochemical grinding / electrochemical mechanical polishing is inhibited, thereby inhibiting stray current corrosion at the edge of the workpiece.

[0042] The specific implementation of this method is as follows:

[0043] 1. Select the material of the equipotential protection ring (i.e., annular equipotential body) based on the metallic properties of the workpiece material. The metallic properties of the equipotential protection ring material must not be lower than that of the workpiece material.

[0044] 2. When processing annular equipotential bodies, the height of the equipotential protection ring should be higher than the thickness of the workpiece, and the inner diameter of the equipotential protection ring should be larger than the diameter of the workpiece fixture or the longest diagonal length.

[0045] 3. Place the workpiece and the equipotential protection ring on the polishing pad / grinding pad on the same horizontal plane. The workpiece is nested in the equipotential protection ring. The centroid of the bottom surface of the workpiece and the centroid of the bottom surface of the equipotential protection ring are 0~1mm apart. The lowest point of the bottom surface of the equipotential protection ring during processing shall not be higher than the lowest point of the bottom surface of the workpiece.

[0046] 4. Apply the same electric potential to the workpiece and the equipotential protection ring through the power supply.

[0047] 5. Perform electrochemical grinding / electrochemical mechanical polishing.

[0048] After improving the device, in order to test the protection effect of the equipotential protection ring, the Φ100mm×3mm pure copper sheet was electrochemically polished without adding the equipotential protection ring. The results are as follows: Figure 4 、 Figure 5 Compared with the workpiece without equipotential protection, the edge of the workpiece with equipotential protection added by the method of the present invention has no obvious corrosion ring, which proves that the stray corrosion of the edge is significantly suppressed. In order to quantitatively compare the protection effect, the present invention uses a VK-X200 laser confocal microscope to perform contour scanning on the edges of different workpieces processed under two conditions, with a scanning length of 3.5mm and scanning paths a1 and a2 respectively. The contour scanning results of a1 and a2 are shown as follows: Figure 6 、 Figure 7 As shown, the corrosion width at the edge of the pure copper sheet under equipotential protection was reduced by 75% and the corrosion depth was reduced by 90% compared to the pure copper sheet without equipotential protection, verifying the protective effect of the equipotential protection ring on the workpiece edge. In summary, the improvements of the present invention effectively suppress stray corrosion defects at the edges during electrochemical machining.

[0049] For any skilled person familiar with the art, many possible variations and modifications of the technical solutions of the present application can be made using the technical content disclosed above without departing from the scope of the technical solutions of the present application, or modified as equivalent embodiments of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application without departing from the content of the technical solutions of the present application shall still belong to the scope of protection of the technical solutions of the present application.

Claims

1. A method for suppressing edge stray current corrosion during electrochemical machining, characterized in that: The following steps are involved: S1, selecting a material for the equipotential protection ring (11), wherein the metallic property of the material for the equipotential protection ring (11) is higher than or equal to the metallic property of the material for the workpiece (10); S2, placing the workpiece (10) and the equipotential protection ring (11) on the same horizontal plane, and nesting the workpiece (10) in the equipotential protection ring (11), with the centroid of the bottom surface of the workpiece (10) and the centroid of the bottom surface of the equipotential protection ring (11) being 0-1 mm apart; S3. Applying the same electric potential to the workpiece (10) and the equipotential protection ring (11) through a power supply, and performing electrochemical grinding / electrochemical mechanical polishing processing.

2. The method for suppressing edge stray current corrosion during electrochemical machining according to claim 1, characterized in that: The height of the equipotential protection ring (11) is higher than the thickness of the workpiece (10), and the inner diameter of the equipotential protection ring (11) is greater than the diameter of the workpiece fixture or greater than the longest diagonal length of the workpiece fixture.

3. A device for suppressing edge stray current corrosion during electrochemical machining, characterized in that: include: A first nylon disk (5), a second nylon disk (7), and a workpiece fixture are concentrically arranged from top to bottom; the second nylon disk (7) is hollow with a stepped hole, a spring copper brush (6) is arranged in the stepped hole, the upper end of the spring copper brush (6) is connected to a conductive slip ring (1) arranged in the center hole of the first nylon disk (5) through a wire, and the copper brush head arranged at the lower end passes through the middle through hole of the workpiece fixture to maintain elastic contact with the workpiece (10) below, and the workpiece (10) is nested in an equipotential protection ring (11) placed on the same plane.

4. The device for suppressing edge stray current corrosion during electrochemical machining according to claim 3, characterized in that: The bottom of the second nylon disk (7) is provided with a plurality of grooves, and spring graphite brushes (12) are arranged in the grooves and maintain elastic contact with the equipotential protection ring (11).

5. The device for suppressing edge stray current corrosion during electrochemical machining according to claim 3, characterized in that: Three grooves are equidistantly arranged on the outer periphery of the bottom of the second nylon disk (7), and three spring graphite brushes (12) are matched therewith.

6. The device for suppressing edge stray current corrosion during electrochemical machining according to claim 5, characterized in that: A through hole is provided between the groove and the stepped hole, so that the spring graphite brush (12) and the spring copper brush (6) are connected via a wire in the through hole.

7. The device for suppressing edge stray current corrosion during electrochemical machining according to claim 3, characterized in that: The workpiece fixture comprises a ceramic disc (8) and a suction pad (9) provided at the bottom thereof, wherein the suction pad (9) vacuum-adsorbs the workpiece (10) via the suction surface.

8. The device for suppressing edge stray current corrosion during electrochemical machining according to claim 7, characterized in that: The adsorption pad (9) is a wax-free adsorption pad.

9. An equipotential protection ring, characterized in that: The equipotential protection ring is made of a material with metallic properties higher than or equal to the metallic property of the workpiece material; the height of the equipotential protection ring is higher than the thickness of the workpiece, the inner diameter of the equipotential protection ring is larger than the diameter of the workpiece fixture or larger than the longest diagonal length of the workpiece fixture, and the equipotential protection ring is used to suppress edge stray current corrosion during electrochemical grinding / electrochemical mechanical polishing.

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