Rotating cathode and method for improving surface flatness in fly-by electrolytic milling

Abstract

The present invention relates to a rotating cathode and method for improving the surface flatness of fly-through electrolytic milling, and belongs to the field of electrolytic machining. In the present invention, the cathode is provided with a central water outlet, five large water outlets and ten small water outlets. The axis of the central water outlet coincides with the axis of the cathode, and the five large water outlets are evenly distributed around the central water outlet; the ten small water outlets are divided into five groups corresponding to the five large water outlets, and the two small water outlets in each group are symmetrically distributed with the straight line corresponding to the center of the large water outlet and the center of the central water outlet as the symmetry axis. This water outlet design adjusts the electric field distribution by reducing the metal material on the bottom surface of the cathode, and adjusts the conductivity distribution by changing the electrolyte speed in each area within the machining gap. In this way, the power supply received by the machining tank in the vertical direction tends to be consistent, resulting in the material removal amount at each location in the machining tank in the vertical direction tending to be consistent, significantly improving the flatness of the machining surface, and being simple and efficient.

Description

Technical Field

[0001] The invention relates to a rotating cathode and a method for improving the surface flatness of a fly-by electrolytic milling process, belonging to the field of electrolytic processing. Background Art

[0002] To reduce weight, large aerospace structural components often feature various elements such as slots, ribs, bosses, and holes. These components also feature thin thickness, minimal material removal depth, large dimensions, and extremely low relative stiffness. Therefore, traditional machining processes can easily cause deformation in these thin-walled aerospace components. The fly-by electrochemical milling process utilizes electrolyte ejected from the tool's cathode to contactlessly dissolve the anode workpiece surface. This eliminates cutting forces and heat, thus preventing residual stress, recast layers, microcracks, and deformation. Therefore, the fly-by electrochemical milling process holds broad application prospects in the machining of large aerospace structural components.

[0003] The use of a rotating cathode is currently a popular choice for fly-by-fly electrochemical milling (ECM). This is because the rotating cathode's simultaneous feed mode promotes rapid electrolyte renewal, maintaining high electrolyte conductivity. This not only improves machining efficiency but also eliminates the hazards of short circuits and sparks. Furthermore, the rotating cathode optimizes the flow distribution within the machining gap, reducing stagnation time in turbulent fluid flow and significantly improving machining accuracy. Most notably, the use of a rotating cathode is key to integrating ECM with other machining processes, such as electrochemical spark discharge machining (EDM), aligning with the broader trend of developing hybrid machining technologies. However, the major drawback of using a rotating cathode for fly-by-fly electrochemical milling is that the machined surface typically has a curved arc profile, resulting in poor surface flatness. Because the electric field distribution on the rotating cathode's circular base is uneven, the amount of electricity per unit area perpendicular to the feed direction decreases from the center toward the edges. Consequently, the amount of material dissolved by the electrochemical anode is greater in the center and less at the edges. Consequently, the machining depth is naturally deeper in the center and shallower at the edges, resulting in an arc-shaped profile. Furthermore, the larger the size of the rotating cathode, the greater the variation in power distribution, and the worse the surface flatness after machining. The thin thickness and limited material removal depth of large, thin-walled aerospace components mean that there's no opportunity for multiple passes during machining. Consequently, poor surface flatness not only significantly reduces machining efficiency but also easily leads to overcutting, resulting in the scrapping of the machined component. Therefore, addressing the problem of poor surface flatness after fly-by electrochemical milling using a rotating cathode is a top priority for current research.

[0004] Many scholars have conducted research on the flatness problem of electrolytic machining. The patent "Combined electrolytic machining tool cathode and method for improving the flatness of the bottom surface of the machining" (authorization announcement number: CN112091338B, inventors: Ma Xin; Li Hansong; Qu Ningsong; Yue Xiaokang) proposes a combined electrode to improve the flatness of the bottom surface of electrolytic machining. However, this combined electrode is a translational electrode, not a rotating electrode, and it is not suitable for many application scenarios of rotating cathodes. The patent "Tool cathode and method for improving the flatness of the bottom surface of electrolytic milling" (authorization announcement number: CN108080755B, inventors: Niu Ni; Qu Ningsong; Yue Xiaokang; Li Hansong) is used for electrolytic milling with a large cutting depth, that is, the bottom surface of the tool cathode is located below the surface of the anode workpiece being machined, and the outer circle and bottom surface of the tool cathode need to be processed at the same time. Therefore, the machining gap during electrochemical milling is divided into two parts: one between the outer diameter of the tool cathode and the semicircular workpiece sidewall to be machined, and the other between the bottom surface of the tool cathode and the bottom surface of the workpiece being machined. This naturally divides the flow field into two parts. During electrochemical milling, the semicircular workpiece sidewall to be machined restricts the flow field in both parts of the machining gap, causing electrolyte to converge at the bottom of the tool cathode, thereby impairing machine flatness. This patent improves bottom surface flatness during electrochemical milling by designing the tool cathode structure to suppress this convergence and diffuse the flow field distribution. However, electrochemical milling is not suitable for machining large, thin-walled aerospace components with small thicknesses and low material removal depths. Most fundamentally, the machining conditions and conditions of fly-by electrochemical milling and electrochemical milling are fundamentally different, making them incomparable. In fly-by electrochemical milling, the bottom surface of the tool cathode moves above the anode workpiece surface, while the outer diameter of the tool cathode does not participate in the machining process. Therefore, the flow field is distributed only in the machining gap between the bottom surface of the tool cathode and the machined surface of the workpiece. In addition, the low depth of fly-by electrochemical milling allows the electrolyte in the machining gap to freely overflow and diffuse in all directions, without any constraints or convergence. Therefore, the solution proposed in this patent is not applicable to fly-by electrochemical milling. The key to improving the surface smoothness of the rotating cathode machining process lies in solving the problem of uneven power supply distribution, which still requires starting from the fundamental distribution of the electric field. Summary of the Invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention proposes a rotating cathode and method for improving surface smoothness in fly-by electrolytic milling. By designing the size, number, and arrangement of the water holes, the electric field distribution can be adjusted by reducing the amount of metallic conductive material on the circular bottom surface of the rotating cathode. Furthermore, the conductivity distribution in the flow field can be adjusted by varying the electrolyte velocity in each area within the machining gap. This, from the perspectives of both the electric field and the flow field, promotes a uniform vertical distribution of power received by the machining groove from the bottom surface of the cathode, resulting in a uniform amount of material removed vertically across the machining groove, thereby improving the smoothness of the machined surface.

[0006] A rotating cathode for improving surface flatness during fly-by electrolytic milling, characterized in that: the cathode is a cylindrical structure with a height of H and an outer radius of R; the cathode is provided with a central water outlet with a radius of r1, five large water outlets with a radius of r2, and ten small water outlets with a radius of r3; the water outlets all penetrate the upper and lower end surfaces of the cathode, and their axes are all parallel to the axis of the cathode;

[0007] The axis of the central water outlet coincides with the axis of the cathode, and its radius r1 satisfies

[0008] The radius r2 of the large outlet hole satisfies The five large water holes are evenly distributed around the central water hole. Any two adjacent lines in the five straight lines that are collinear with the center of the central water hole form an angle of 72°. The distance between the center of the five large water holes and the center of the central water hole is d1, and d1 satisfies

[0009]

[0010] The radius of the small water holes is r3 = R / 9. The 10 small water holes are grouped in pairs. The five groups of small water holes correspond to the five large water holes respectively. The two small water holes in each group are symmetrically distributed with the straight line that is collinear with the center of the corresponding large water hole and the center of the central water hole as the symmetry axis. The two straight lines that are collinear with the center of the two small water holes in each group and the center of the central water hole both form an angle of 20° with the symmetry axis. The distance between the center of the 10 small water holes and the center of the central water hole is d2, and d2 satisfies

[0011]

[0012] The cathode designed in the present invention rotates and feeds at the same time during processing, so the cylindrical structure can make the most effective use of the conductive area of ​​the metal and is the most suitable. In addition, in order to facilitate structural design and reduce manufacturing costs, the overall structure should be evenly arranged with the axis as the center. Because the bottom surface of the cathode of the cylinder is circular, in the process of traditional rotating cathode electrolytic milling to process grooves, the amount of power received by the processing groove in the vertical direction from the cathode bottom surface must be the largest in the center and decreases towards the two edges, resulting in the largest amount of material removed in the center of the processing groove and decreasing towards the two edges. In this way, the processing groove presents an arc-shaped profile in the vertical direction that is deep in the middle and shallow on both sides. In order to fundamentally improve the flatness of the processed surface, it is necessary to adjust the power supply distribution of the cathode bottom surface, that is, to reduce the power supply from the middle area of ​​the cathode bottom surface to the middle area of ​​the processing groove, and relatively increase the power supply from the edge area of ​​the cathode bottom surface to the edge area of ​​the processing groove. In principle, at least two water outlets need to be provided to achieve this. Furthermore, because the aperture of the water outlet hole set in the center of the cathode bottom surface is too large, it is easy to cause a sudden drop in the electric field flow field, resulting in undulations and convexity on the processed surface. Therefore, it is better to set a variety of small-aperture water outlet holes in the middle area of ​​the cathode bottom surface than to set a whole large-aperture water outlet hole. In summary, the solution to achieve the best improvement in flatness effect at the lowest possible manufacturing cost requires three types of water outlet holes. Among them, two types of water outlet holes should be set in the middle area of ​​the cathode bottom surface. Only one water outlet hole with a small aperture can be set in the center of the cathode, and then a circle of water outlet holes with large apertures are set around it, so as to fully reduce the power supply from the middle area of ​​the cathode bottom surface to the middle area of ​​the processing tank. The edge area of ​​the cathode bottom surface should sacrifice as little metal conductive area as possible, while at the same time increasing the speed difference between the electrolyte flow rate in the processing gap below it and the flow rate below the middle area of ​​the cathode bottom surface, so as to significantly improve the conductivity below it. Therefore, the aperture of the water outlet holes set in the edge area of ​​the cathode bottom surface should be small and the number will be large. Based on this, simulation calculations were conducted and it was found that the ratio of the number of central water holes, large water holes, and small water holes was 1:5:10, which had the highest cost-effectiveness and the best versatility. At the same time, the radius should be r2>r1>r3. All water holes penetrate the upper and lower end faces of the cathode, and the axes are parallel to the cathode axis, so both the upper and lower end faces of the cathode can be used for fly-by electrolytic milling. The radius r1 of the central water hole satisfies If it is too small, it cannot fully reduce the power supply from the cathode center to the middle area of ​​the processing tank. If it is too large, the center of the processing tank will be wavy and convex due to the sudden drop of the electric field. This is also the reason why there are 5 large water holes surrounding the central water hole. A small amount of metal conductive material is retained between 1 central water hole and the 5 large water holes evenly distributed around the central water hole to serve as a transition of the electric field to avoid sudden changes in the electric field. The number of 5 large water holes is the result of comprehensive consideration after simulation calculation. It can fully reduce the power supply from the middle area of ​​the bottom surface of the cathode to the middle area of ​​the processing tank, and retain enough metal conductive material to transition the electric field. The radius r2 of the large water hole satisfies The purpose is to fully reduce the power supply from the middle area of ​​the cathode bottom surface to the middle area of ​​the processing tank, while not interfering with the power supply from the edge area of ​​the cathode bottom surface to the edge area of ​​the processing tank. The distance d1 between the center of the large water outlet and the center of the central water outlet satisfies This is for the convenience of manufacturing, and at the same time, the spacing is controlled to ensure that there is an appropriate amount of metal conductive material transition electric field. The radius of the small water outlet r3 = R / 9, which is small enough to avoid sacrificing too much metal conductive material in the edge area of ​​the bottom surface of the cathode. If it is smaller, the manufacturing cost and difficulty of manufacturing will be uncontrollable. In order to realize its function in flow field control on the basis of making the aperture of the small water outlet as small as possible, it is necessary to control it precisely. At least two small water outlets correspond to one large water outlet, so the number of small water outlets is set to 10. The 10 small water outlets are divided into five groups corresponding to 5 large water outlets respectively. The two small water outlets in each group are symmetrically distributed with the straight line corresponding to the center of the large water outlet and the center of the central water outlet as the symmetry axis, and the two straight lines corresponding to the center of the two small water outlets in each group and the center of the central water outlet are both at an angle of 20° to the symmetry axis. This angle and this arrangement enable the electrolyte columns ejected from the 10 small water outlets to effectively prevent the electrolyte ejected from the central water outlet and the 5 large water outlets from being discharged outside the processing gap, so that the electrolyte flow rate in the processing gap below the bottom surface of the cathode decreases from the edge to the center, and the electrolysis products also increase continuously from the edge to the center. In this way, the electrolysis products accumulated in the processing gap below the middle area of ​​the bottom surface of the cathode will greatly reduce the conductivity, further hindering the supply of electricity from the middle area of ​​the bottom surface of the cathode to the middle area of ​​the processing tank. At the same time, after the electrolysis products in the processing gap below the edge area of ​​the bottom surface of the cathode are smoothly discharged, the conductivity is improved, which relatively promotes the supply of electricity from the edge area of ​​the bottom surface of the cathode to the edge area of ​​the processing tank. The above layout is the most efficient and most universal layout scheme for achieving precise control of the flow field while sacrificing as little metal conductive material as possible through the 10 small water outlets. The distance d2 between the center of the circle of the 10 small water outlets and the center of the circle of the central water outlet satisfies On the one hand, it is to avoid the small water outlet hole being too close to the outer circular wall or the large water outlet hole wall, so as to avoid the tip effect that increases the manufacturing difficulty and interferes with the power supply distribution; on the other hand, it is to coordinate the distance between the small water outlet hole and the large water outlet hole to ensure flow field control and ensure that the layout can relatively increase the power supply from the edge area of ​​the cathode bottom surface to the edge area of ​​the processing groove.

[0013] The above-mentioned rotating cathode for improving the surface flatness of the fly-by electrolytic milling process is characterized in that the outer circle radius R of the above-mentioned cathode satisfies R≥3mm and the height H satisfies H≥4R.

[0014] The fly-by electrochemical milling process used in this invention is generally a macro-machining process. Surface flatness is less important at the meso- and micro-scales, so the cathode radius is no less than 3 mm. To ensure both the upper and lower cathode surfaces are usable for machining, the flow path length of all water outlets must be sufficient, and the cathode height must be no less than 4R.

[0015] The above-mentioned rotating cathode for improving the surface flatness of the fly-by electrolytic milling process is characterized in that the above-mentioned cathode material is an acid- and alkali-resistant conductor.

[0016] The above-mentioned method for improving the surface flatness of the fly-by electrochemical milling by using a rotating cathode is characterized by comprising the following steps:

[0017] The cathode is mounted on the machine tool spindle and connected to the negative pole of the power supply. The workpiece is mounted on the machine tool table and connected to the positive pole of the power supply. The bottom surface of the cathode is always higher than the upper surface of the workpiece. The electrolyte is injected into all the water outlet holes of the cathode from top to bottom through the spindle. It is then sprayed onto the surface of the workpiece and overflows and diffuses in all directions, filling the machining gap between the cathode and the workpiece, forming a conductive circuit. The spindle drives the cathode to rotate and feed according to a predetermined trajectory, performing electrochemical anodic dissolution on the workpiece surface.

[0018] During machining, the central water outlet and five large water outlets provided in the central area of ​​the cathode bottom surface significantly reduce the power supply to the corresponding area in the middle of the machining tank by reducing the amount of metal conductive material. The electrolyte columns ejected from the 10 small water outlets at the edge of the cathode bottom surface hinder the electrolyte ejected from the central water outlet and the five large water outlets from being discharged out of the machining gap, resulting in the continuous accumulation of electrolytic products in the machining gap below the central area of ​​the cathode bottom surface, a significant decrease in conductivity, and further hindering the power supply to the corresponding area in the middle of the machining tank. At the same time, the 10 small water outlets at the edge of the cathode bottom surface sacrifice as little metal conductive material as possible to ensure the smooth discharge of electrolyte and electrolytic products in the machining gap below them, thereby relatively improving the power supply to the corresponding edge area of ​​the machining tank. In this way, from the perspectives of the electric field and flow field, the power supply received by the machining tank from the cathode bottom surface in the vertical direction is consistent, resulting in a consistent amount of material removal at various locations in the machining tank in the vertical direction, thereby obtaining a machining surface with better flatness.

[0019] The present invention targets fly-by electrolytic milling machining, where the circular electric field distribution on the bottom surface of the rotating cathode, which is commonly used, is uneven. The cathode bottom surface is higher than the upper surface of the anode workpiece, which causes the electrolyte to overflow and disperse. Therefore, to improve surface flatness, the power supply distribution must be adjusted from the perspectives of both the electric field and the flow field. The total opening area of ​​the central water outlet and five large water outlets in the center of the cathode bottom surface is much larger than the total opening area of ​​the ten small water outlets at the edge of the cathode bottom surface. Therefore, the difference between the remaining conductive area in the center of the cathode bottom surface and the remaining conductive area at the edge of the cathode bottom surface is reduced, the degree of uneven electric field distribution is reduced, and the amount of power provided is more similar. Furthermore, because the electrolyte columns ejected from the 10 small outlet holes at the edge of the cathode bottom surface hinder the electrolyte ejected from the central outlet hole and the 5 large outlet holes from being discharged out of the machining gap, the electrolytic products accumulated at the bottom of the cathode gradually increase from the edge of the machining gap to the center of the machining gap, and the conductivity of the electrolyte at the bottom of the cathode gradually decreases from the edge of the machining gap to the center of the machining gap. This hinders the supply of electricity from the middle area of ​​the cathode bottom surface to the middle area of ​​the machining tank, while promoting the supply of electricity from the edge area of ​​the cathode bottom surface to the edge area of ​​the machining tank. Under the combined effect of the above, the power supply received by the machining tank from the bottom surface of the cathode in the vertical direction tends to be consistent, resulting in a consistent amount of material removal at various locations in the machining tank in the vertical direction, thereby improving the flatness of the machined surface.

[0020] The present invention has the following advantages:

[0021] 1. The present invention is simple, efficient and low-cost. It can significantly improve the surface flatness of fly-by electrolytic milling by simply adjusting the size, number and arrangement of the water outlet holes of the rotating cathode. It does not require a combined electrode or auxiliary process, has a short preparation cycle, and both end surfaces can be used for processing, with a high utilization rate. It is suitable for fly-by electrolytic milling using a rotating cathode under various conditions.

[0022] The rotating cathode water outlet design of this invention not only adjusts the electric field distribution by reducing the amount of conductive metal material on the circular bottom surface of the rotating cathode, but also adjusts the conductivity distribution within the flow field by varying the electrolyte velocity in various areas within the machining gap. The combined effects of the electric and flow fields ensure that the amount of power received by the machining tank vertically from the cathode bottom surface converges. This reduces the amount of anode material removed in the center of the machining tank and increases it relatively at the edges, making it easier to level the machined surface.

[0023] The flat surface achieved by this invention using a rotating cathode for fly-by electrochemical milling closely resembles the surface profile of a mechanically milled surface. Therefore, large, thin-walled aviation components with small thickness and minimal material removal depth can be machined in just one or two passes, significantly improving both efficiency and precision. This invention significantly advances the fly-by electrochemical milling process and the application and development of fly-by rotary cathode electrochemical milling. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A three-dimensional schematic diagram of fly-by electrochemical milling using a rotating cathode;

[0025] Figure 2 End view of a rotating cathode for improving surface flatness in electrochemical fly milling;

[0026] Figure 3 Schematic top view of fly-by electrochemical milling using a rotating cathode; (a) is a conventional cathode case, and (b) is a cathode machining case of the present invention;

[0027] Figure 4 A longitudinal cross-sectional view of a rotary cathode used to improve surface flatness in fly-by electrochemical milling.

[0028] Figure 5 Flow velocity distribution diagrams when using a rotating cathode for improving surface flatness in fly-by electrochemical milling and when using a conventional cathode for machining; wherein (a) is the conventional cathode case, and (b) is the cathode machining case of the present invention;

[0029] Figure 6 The figures are contour images after machining with a rotating cathode for improving surface flatness in fly-by electrochemical milling and machining with a conventional cathode; (a) corresponds to the case of Example 1, (b) corresponds to the case of Example 2, and (c) corresponds to the case of Example 3;

[0030] The numbers in the figure are: 1. workpiece; 2. cathode; 3. electrolyte; 4. central water outlet; 5. large water outlet; 6. small water outlet; 7. machining tank; 8. electrolysis product; 9. bubbles. DETAILED DESCRIPTION

[0031] The present invention will be described in further detail below with reference to the accompanying drawings:

[0032] The three-dimensional schematic diagram of fly-by electrochemical milling using a rotating cathode 2 is shown in FIG. Figure 1 As shown. The cathode 2 is installed on the machine tool spindle and connected to the negative pole of the power supply. The workpiece 1 is installed in the machine tool table and connected to the positive pole of the power supply. The bottom surface of the cathode 2 always moves above the surface of the anode workpiece 1, and the outer circle of the cathode 2 does not participate in the machining. The electrolyte 3 is injected into all the water outlets of the cathode 2 from top to bottom through the spindle, and then sprayed onto the surface of the workpiece 1, filling the machining gap between the cathode 2 and the workpiece 1, forming a conductive circuit. The spindle drives the cathode 2 to v xz The speed of rotation is v jjThe feed rate is set according to a predetermined trajectory to electrochemically dissolve the surface of the workpiece 1. Because the bottom surface of the cathode 2 is always higher than the upper surface of the workpiece 1, the depth of the processed groove 7 after electrochemical anodic dissolution is not deep, resulting in the electrolyte 3 in the processing gap freely overflowing and diffusing in all directions on the surface of the workpiece 1.

[0033] The end view of the rotating cathode 2 for improving the surface smoothness of the fly-by electrochemical milling process is shown in FIG. Figure 2 As shown, the cathode 2 is provided with a central water outlet 4 with a radius of r1, five large water outlet holes 5 with a radius of r2, and ten small water outlet holes 6 with a radius of r3. These water outlet holes penetrate the upper and lower end surfaces of the cathode 2, and their axes are parallel to the axis of the cathode 2. The axis of the central water outlet hole 4 coincides with the axis of the cathode 2. The five large water holes 5 are evenly distributed around the central water hole 4. Any two adjacent straight lines among the five straight lines that are collinear with the center of the five large water holes 5 and the center of the central water hole 4 form an angle of 72°, and the distance between the center of the five large water holes 5 and the center of the central water hole 4 is d1. The ten small water holes 6 are grouped in pairs, and the five groups of small water holes 6 correspond to the five large water holes 5 respectively. The two small water holes 6 in each group are symmetrically distributed with the straight line that is collinear with the center of the large water hole 5 and the center of the central water hole 4 as the axis of symmetry, and the two straight lines that are collinear with the center of the two small water holes 6 in each group and the center of the central water hole 4 form an angle of 20° with the axis of symmetry, and the distance between the center of the ten small water holes 6 and the center of the central water hole 4 is d2.

[0034] The schematic top view of the fly-by electrochemical milling process using the rotating cathode 2 is shown in FIG. Figure 3 On the surface of the processing groove 7 perpendicular to the feed direction, a dotted line is drawn to represent the cross section of the processing groove 7. When the rotating cathode 2 represented by the shadow flies from the right side of the dotted line to the left side of the dotted line, the processing of the cross section is completed. Figure 3 (a) shows the general case. The time for processing point O at the center of the processing groove 7 on the dotted line is equal to the length of the line segment O1O2 divided by the feed speed v jj The time for processing point P on the dotted line at the edge of the processing groove 7 is equal to the length of the line segment P1P2 divided by the feed speed v jj The feed rate is consistent, and line segment O1O2 is longer than line segment P1P2, so point O is machined for a longer period of time. This means that the central area of ​​the rotating cathode 2 supplies more power to the corresponding central area of ​​the machining groove 7. Consequently, more material is removed from this central area by the electrochemical anode, resulting in a deeper machining depth. Consequently, the machining depth of the machining groove 7 gradually decreases from the center to the sides, forming an arc-shaped profile. This explains the poor surface flatness after using the rotating cathode 2 for fly-by electrochemical milling. Figure 3(b) is a top view of a rotating cathode 2 used to improve surface smoothness in fly-by electrolytic milling. Because the central water outlet 4 and five large water outlets 5 reduce the amount of conductive metal, as the cathode 2 continues to rotate and fly over the dotted line, once the relative projections of these six holes overlap point O, no power is supplied, pausing electrochemical dissolution. As a result, the electrochemical dissolution time of the center region of the processing tank 7, represented by point O, is much shorter than normal, and the processing depth is much shallower than normal. The ten small water outlets 6 are very small, and their relative projections overlap point P for a short period of time, pausing power supply. Therefore, the electrochemical dissolution time of the edge region of the processing tank 7, represented by point P, is similar to normal, and the processing depth is also similar. The rotating cathode 2, which improves surface smoothness in fly-by electrolytic milling, significantly reduces the power supply from the center region of the cathode 2 bottom surface to the center region of the processing tank 7 through the design of the water outlets. This, in turn, reduces the difference in power supply between the center and edge regions of the processing tank 7, resulting in a more consistent amount of material removed (i.e., the processing depth) between the center and edge regions of the processing tank 7, thereby smoothing the processing surface.

[0035] Figure 4 The longitudinal cross-section of a rotating cathode 2 used to improve surface smoothness during fly-by electrolytic milling is shown. In the figure, the electrolyte 3 flowing from the central water outlet 4 and the large water outlet 5 is blocked by the jet of electrolyte 3 flowing from the small edge water outlet 6, making it difficult to smoothly discharge from the machining gap. Electrolysis products 8 and bubbles 9 resulting from electrochemical anode dissolution in the corresponding workpiece 1 area below will accumulate in the machining gap, causing the conductivity of the electrolyte 3 in the machining gap below the central water outlet 4 and the large water outlet 5 to continuously decrease, further hindering the supply of electricity from the middle area of ​​the bottom surface of the cathode 2 to the middle area of ​​the machining tank 7. In contrast, the electrolysis products 8 and bubbles 9 below the small edge water outlet 6 can be quickly discharged along with the electrolyte 3, maintaining a high conductivity in the machining gap below the edge area of ​​the bottom surface of the cathode 2 and promoting the supply of electricity from the edge area of ​​the bottom surface of the cathode 2 to the edge area of ​​the machining tank 7. In this way, on the basis of the electric field, the power supply distribution on the bottom surface of the cathode 2 is improved, and the power supply difference between the bottom surface of the cathode 2 and the middle area and the edge area of ​​the processing groove 7 is further reduced, so that the power supply received by the processing groove 7 in the vertical direction is made consistent.

[0036] The following is a comparison of the embodiments. The three types of rotating cathodes 2 selected in the embodiment of the present invention have an outer radius R of 9 mm and a height H of 60 mm. Figure 6 As shown on the left. The difference between the three cathodes 2 lies in the design of the water outlet hole on the end face. Example 1 uses a conventional cathode, such as Figure 6(a) As shown on the left, the seven water holes have a radius of 1mm and are dispersed. Conventional cathodes with small and dispersed openings are used in conventional electrochemical milling processes. The small opening area has almost no effect on the metal conductive material area and electric field distribution on the bottom surface of the conventional cathode, and the power supply distribution is also consistent with the conventional cathode. Figure 3 (a) is the same as in Example 2. A rotating cathode 2 is used to improve the surface smoothness of the electrolytic milling process. Figure 6 (b) As shown on the left. The center water hole has a radius of 4 Large water hole 5 radius The distance between the center of the 5 large water holes 5 and the center of the central water hole 4 Small water outlet 6 radius The distance between the center of 6 of the 10 small water holes and the center of 4 of the central water hole Example 3 uses another rotating cathode 2 to improve the surface smoothness of the electrolytic milling process. Figure 6 (c) As shown on the left. The center water hole has a radius of 4 Large water hole 5 radius The distance between the center of the 5 large water holes 5 and the center of the central water hole 4 Small water outlet 6 radius The distance between the center of 6 of the 10 small water holes and the center of 4 of the central water hole The actual results of the machined surface flatness can be clearly compared using three different cathode 2 test methods. The test parameters are as follows: electrolyte 3 is a 20% NaCl solution, temperature is 30°C, and electrolyte 3 pressure is 0.2 MPa. The cathode 2 material is 304 stainless steel, and the anode workpiece 1 material is 7075 aluminum alloy. The cathode 2 rotation speed is 500 rpm, the feed rate is 60 mm / min, the machining gap is 0.2 mm, and the machining voltage is 30 V.

[0037] Example 1:

[0038] This embodiment uses a conventional cathode. Figure 5 (a) is the flow velocity distribution diagram during processing. The overall flow velocity in the processing gap is very uniform and close to uniform, and the conductivity is also very uniform, so the flow field cannot affect the power supply distribution. Because the area of ​​the 7 water outlet holes is small, the electric field distribution on the bottom surface of the conventional cathode is still uneven. The power supply per unit area perpendicular to the feed direction decreases from the middle to both sides. The corresponding amount of material dissolved by the electrochemical anode is also more in the middle and less on both sides. The processing depth is naturally deep in the middle and shallow on both sides, showing an arc-shaped contour, as shown in the figure. Figure 6 (a) Cross-sectional profile. The machined surface has poor flatness, with a bottom height difference of 0.18 mm.

[0039] Example 2:

[0040] This embodiment uses a rotary cathode 2 for improving the surface smoothness of a fly-by electrolytic milling process. Figure 5 (b) is a flow velocity distribution diagram during processing. In the figure, the flow velocity of the electrolyte 3 in the central area of ​​the processing gap below the central water hole 4 and the 5 large water holes 5 is very low, while the flow velocity of the electrolyte 3 in the edge area of ​​the processing gap below the 10 small water holes 6 is very high, which makes the flow velocity in the processing gap continuously decrease from the edge to the center, the accumulated electrolysis products 8 continue to increase, and the conductivity naturally decreases gradually. In this way, the power supply from the middle area of ​​the bottom surface of the cathode 2 to the middle area of ​​the processing tank 7 is hindered, while the power supply from the edge area of ​​the bottom surface of the cathode 2 to the edge area of ​​the processing tank 7 is promoted. On the basis of the electric field, the power supply distribution of the bottom surface of the cathode 2 is assisted to improve, and finally a relatively flat processing surface is formed, such as Figure 6 As shown in the cross-sectional profile (b), the bottom surface height difference is only 0.033 mm, approximately one-sixth that of Example 1. This is very close to the surface profile produced by mechanical milling. Therefore, for large, thin-walled aviation components with small thickness and small material removal depth, machining can be completed in one or two passes, significantly improving machining efficiency and accuracy.

[0041] Example 3:

[0042] This embodiment also uses a rotary cathode 2 that improves the surface smoothness of the fly-by electrolytic milling process. Figure 6 (c) The cross-sectional profile shows that the bottom height difference is only 0.036 mm, which is about 1 / 5 of that in Example 1. The surface flatness is also significantly improved, demonstrating the rationality and versatility of the parameter range in the design of the present invention.

[0043] In summary, the present invention proposes a rotating cathode 2 for improving the surface flatness of fly-by electrolytic milling, which has a significant effect and greatly promotes the progress of fly-by electrolytic milling technology and the application development of fly-by rotating cathode 2 electrolytic milling.

[0044] The present invention proposes a rotating cathode 2 and a method for improving the surface smoothness of fly-by electrolytic milling. By designing the size, number and arrangement of the water holes, not only can the electric field distribution be adjusted by reducing the metal conductive material on the circular bottom surface of the rotating cathode 2, but also the conductivity distribution in the flow field can be adjusted by changing the speed of the electrolyte 3 in each area within the processing gap. In this way, from the perspective of the electric field and the flow field, the power supply received by the processing tank 7 from the bottom surface of the cathode 2 in the vertical direction is made to be consistent, resulting in the amount of material removed from the processing tank 7 in the vertical direction being consistent, thereby improving the smoothness of the processing surface. However, the above description cannot be understood as a limitation of the patent of the present invention. It should be noted that, without departing from the concept of the present invention, several improvements can be made, and these should all fall under the protection of the patent of the present invention.

Claims

1. A rotating cathode for improving surface flatness in electrolytic milling, characterized by: The cathode (2) is a cylindrical structure with a height of H and an outer radius of R; the cathode (2) is provided with a central water outlet (4) with a radius of r1, five large water outlet holes (5) with a radius of r2, and ten small water outlet holes (6) with a radius of r3, and these water outlet holes all penetrate the upper and lower end surfaces of the cathode (2), and their axes are all parallel to the axis of the cathode (2); The axis of the central water outlet (4) coincides with the axis of the cathode (2), and its radius r1 satisfies The radius r2 of the large outlet hole (5) satisfies The five large water outlet holes (5) are evenly distributed around the central water outlet hole (4). Any two adjacent straight lines among the five straight lines whose centers are collinear with the center of the central water outlet hole (4) form an angle of 72°. The distance between the centers of the five large water outlet holes (5) and the center of the central water outlet hole (4) is d1, and d1 satisfies The radius of the small water outlet (6) is r3=R / 9, and the 10 small water outlet holes (6) are arranged in groups of two. The five groups of small water outlet holes (6) correspond to the five large water outlet holes (5) respectively. The two small water outlet holes (6) in each group are symmetrically distributed with the straight line corresponding to the center of the large water outlet hole (5) and the center of the central water outlet hole (4) as the symmetry axis, and the two straight lines corresponding to the center of the two small water outlet holes (6) in each group and the center of the central water outlet hole (4) are both at an angle of 20° to the symmetry axis. The distances between the centers of the 10 small water outlet holes (6) and the center of the central water outlet hole (4) are all d2, and d2 satisfies 2. The rotary cathode for improving surface smoothness in electrolytic milling according to claim 1, characterized in that: The outer radius R of the cathode (2) satisfies R≥3mm, and the height H satisfies H≥4R.

3. The rotary cathode for improving surface smoothness in fly-by electrochemical milling according to claim 1, characterized in that: The cathode (2) material is an acid and alkali corrosion resistant conductor.

4. A process for improving surface smoothness of electrolytic milling by using a rotating cathode according to claim 1, characterized in that The following processes are included: The cathode (2) is mounted on the main spindle of the machine tool and connected to the negative pole of the power supply. The workpiece (1) is mounted on the worktable of the machine tool and connected to the positive pole of the power supply. The bottom surface of the cathode (2) is always higher than the upper surface of the workpiece (1). The electrolyte (3) is injected into all the water outlet holes of the cathode (2) from top to bottom through the main spindle, and then sprayed onto the surface of the workpiece (1) and overflows and diffuses in all directions, filling the processing gap between the cathode (2) and the workpiece (1) to form a conductive circuit. The main spindle drives the cathode (2) to rotate and feed according to a predetermined trajectory, and electrochemical anodic dissolution is performed on the surface of the workpiece (1). During processing, the central water outlet (4) and the five large water outlets (5) provided in the central area of ​​the bottom surface of the cathode (2) significantly reduce the power supply to the corresponding area in the middle of the processing tank (7) by reducing the metal conductive material; the electrolyte (3) liquid column ejected from the 10 small water outlet holes (6) at the edge of the bottom surface of the cathode (2) hinders the electrolyte (3) ejected from the central water outlet hole (4) and the five large water outlet holes (5) from being discharged out of the processing gap, resulting in the continuous accumulation of electrolysis products (8) in the processing gap below the central area of ​​the bottom surface of the cathode (2), which significantly reduces the conductivity and further hinders the power supply to the corresponding area in the middle of the processing tank (7); at the same time, the 10 small water outlet holes (6) at the edge of the bottom surface of the cathode (2) sacrifice as little metal conductive material as possible, thereby ensuring the smooth discharge of the electrolyte (3) and electrolysis products (8) in the processing gap below it, thereby relatively improving the power supply to the corresponding edge area of ​​the processing tank (7); In this way, from the perspectives of the electric field and the flow field, the amount of electricity received by the processing groove (7) from the bottom surface of the cathode (2) in the vertical direction is made uniform, resulting in the amount of material removed at various locations in the processing groove (7) in the vertical direction being made uniform, thereby obtaining a processing surface with better flatness.

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