Polishing method and polishing device using high-frequency alternating magnetic field to control liquid metal polishing disc

Abstract

The application belongs to the field of liquid metal polishing, and discloses a polishing method and polishing device for controlling a liquid metal polishing disc by using a high-frequency alternating magnetic field, which comprises the following steps: dividing the polishing process into four stages in sequence, i.e., a rough polishing stage, a middle polishing stage, an optimization stage and a fine polishing stage. After the liquid metal polishing disc is used for a long time, the abrasive grains on the surface of the disc will be passivated, and the polishing efficiency can be improved by using the application to make the abrasive grains turn over. By using the control means of the external high-frequency alternating magnetic field, the abrasive grains can be more uniformly distributed in the area in contact with the workpiece, and the polishing quality can be improved.

Description

Technical Field

[0001] The present invention relates to the field of liquid metal polishing, in particular to a polishing method and a polishing device for controlling a liquid metal polishing disc by using a high-frequency alternating magnetic field. Background Art

[0002] When using a polishing disc for polishing, the abrasive grains need to be fixed to the disc by coating or pressing, and the polishing effect is achieved by friction between the disc and the workpiece. There are various polishing discs on the market, some of which are made of liquid metal as the base material. After the abrasive grains are worn out and passivated, these liquid metal polishing discs need to be completely melted and remixed with new abrasive grains. They are then placed back into the mold to be formed into a new polishing disc. At the same time, a large amount of coolant needs to be injected during the processing to ensure a low temperature environment. This method has low processing efficiency, and the passivation of the abrasive grains cannot be effectively improved during the processing. Processing can only continue after the polishing disc is melted and mixed with new abrasive grains. In addition, the distribution of the abrasive grains in the processing area cannot be changed during the processing, and the processing quality cannot be further improved. Summary of the Invention

[0003] The object of the present invention is to provide a polishing method and a polishing device for controlling a liquid metal polishing disc by using a high-frequency alternating magnetic field, so as to solve the problems raised in the above-mentioned background technology.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] A polishing method for controlling a liquid metal polishing disc by using a high-frequency alternating magnetic field comprises: dividing the polishing process into four stages in sequence, namely a rough polishing stage, a medium polishing stage, an optimization stage, and a fine polishing stage;

[0006] Rough polishing stage: The electromagnetic coil does not intervene in the work. In the rough polishing stage, a higher working load and a lower liquid metal polishing disc speed are used according to the material of the workpiece;

[0007] Medium throwing stage: In the medium throwing stage, a medium working load and a medium liquid metal polishing disc speed are used, and a constant current is passed into the electromagnetic coil to generate a constant magnetic field;

[0008] Optimization stage: When entering the optimization stage, low workload and low liquid metal polishing disc speed are used for processing. During the optimization stage, high-frequency alternating current is passed into the electromagnetic coil, causing the electromagnetic coil to generate a high-frequency alternating magnetic field;

[0009] Fine polishing stage: add a coolant and further reduce the positive pressure on the workpiece, so that the temperature of the liquid metal polishing disc drops rapidly and solidifies, while increasing the rotation speed of the liquid metal polishing disc rotary table and further reducing the workload.

[0010] Furthermore, in the rough polishing stage, the upper working load range is 100N to 200N, and the lower liquid metal polishing disc speed range is 50rpm to 100rpm;

[0011] In the medium polishing stage, the medium working load range is 60N to 90N, and the medium liquid metal polishing disc speed range is 30rpm to 40rpm;

[0012] During the optimization stage, the low working load range is 20N to 50N, the low liquid metal polishing disc speed range is 15rpm to 25rpm; the high-frequency alternating current is a current with a frequency range of 10kHz to 100kHz, and the high-frequency alternating magnetic field is a magnetic field with a frequency range of 5kHz to 50kHz.

[0013] Furthermore, the rough polishing stage also includes: after a period of processing in the rough polishing stage, using a white light interferometer to check whether most of the rough marks on the surface of the workpiece have disappeared and using a roughness tester to check whether its surface roughness has been significantly reduced to determine whether it is possible to enter the medium polishing stage.

[0014] Furthermore, the intermediate polishing stage also includes: the liquid metal polishing disc rotates to cut the magnetic lines of force of the constant magnetic field generated by the electromagnetic coil, so that an induced current is generated inside the liquid metal. The liquid metal polishing disc thereby generates Joule heat and is affected by the Lorentz force during operation, causing relative movement between the abrasive and the liquid metal.

[0015] Furthermore, the intermediate polishing stage further includes: after a period of processing, detecting whether the surface roughness of the workpiece reaches a set threshold by using a white light interferometer and a roughness measuring instrument to determine whether it is possible to enter the optimization stage.

[0016] Furthermore, the optimization stage also includes: the liquid metal polishing disk not only generates induced current due to the cutting of magnetic flux lines, but also generates induced eddy currents due to the high-speed change of magnetic flux passing through it. Therefore, the superposition of the two parts of induced current causes the liquid metal polishing disk to generate more Joule heat, so that the area where the liquid metal polishing disk contacts the workpiece is semi-solid and liquid and solid phases coexist. At the same time, the liquid metal at this time has a larger induced current, so it will also be subject to a larger Lorentz force in the alternating magnetic field. The Lorentz force and the friction force exerted by the workpiece on the abrasive particles will further cause the liquid metal particles in the friction area where the polishing disk contacts the workpiece to flip and move. The flipping movement of the abrasive particles exposes its unpassivated side.

[0017] Further, the optimization stage further comprises: changing the direction of the high-frequency alternating magnetic field by controlling the direction of the current flowing into the electromagnetic coil, so that the direction of the Lorentz force acting on the liquid metal particles changes, and the abrasive particles are moved in different directions by the liquid metal particles, so that the abrasive particles in the contact area between the liquid metal lapping disc and the workpiece are more evenly distributed.

[0018] Further, the optimization stage further comprises: when the material hardness of the workpiece is low and the rotation speed and the working load of the liquid metal lapping disc are large, an alternating current with a lower frequency is selected, and otherwise an alternating current with a higher frequency is selected.

[0019] The application also provides a polishing device for controlling a liquid metal lapping disc by using a high-frequency alternating magnetic field, which is used to realize the polishing method as described above, and comprises a polishing machine body and a three-axis translation platform, the polishing machine body comprises a polishing machine base, an electromagnetic coil and a liquid metal lapping disc rotating table are arranged on the polishing machine base, the liquid metal lapping disc rotating table is located in the middle of the electromagnetic coil, a workpiece loading device is arranged on the three-axis translation platform, the three-axis translation platform drives the workpiece loading device to move in XYZ three-axis directions, and the workpiece loading device is used to press the workpiece towards the liquid metal lapping disc rotating table.

[0020] Compared with the prior art, the application has the following beneficial effects:

[0021] 1) When the surface abrasive particles of the liquid metal lapping disc are passivated after a long processing time, the abrasive particle turnover of the application can improve the polishing efficiency;

[0022] 2) The control means of the external high-frequency alternating magnetic field can make the abrasive particles more evenly distributed in the contact area with the workpiece, and can improve the polishing quality;

[0023] 3) The abrasive particle turnover can be controlled by the external electromagnetic field, so that the unpassivated side of the abrasive particle is exposed, and the service life of the lapping disc is increased;

[0024] 4) The current in the liquid metal lapping disc is an induced current, and an external electric field does not need to be applied to the liquid metal lapping disc, which saves the consumption of electric energy to a certain extent;

[0025] 5) The application can improve the surface morphology of the liquid metal lapping disc without completely melting the liquid metal lapping disc. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 FIG. 1 is a top view of a polishing device for controlling a liquid metal lapping disc by using a high-frequency alternating magnetic field according to the application.

[0027] Figure 2This is a schematic diagram of the main structure of a polishing device that uses a high-frequency alternating magnetic field to control a liquid metal polishing disc according to the present invention.

[0028] Figure 3 The diagram is a top view of the structure of a polishing device of the present invention that utilizes a high-frequency alternating magnetic field to control a liquid metal polishing disc.

[0029] Figure 4 The present invention is a flow chart of a polishing method for controlling a liquid metal polishing disc using a high-frequency alternating magnetic field.

[0030] Figure 5 This is a schematic diagram of the force exerted on abrasive particles in a high-frequency alternating magnetic field in a polishing method of the present invention that uses a high-frequency alternating magnetic field to control a liquid metal polishing disc. In the figure, the magnetic field passes from the lower surface of the liquid metal polishing disc through its upper surface.

[0031] Figure 6 The figure is a schematic diagram of the forced rotation of abrasive particles in a polishing method of the present invention using a high-frequency alternating magnetic field to control a liquid metal polishing disc.

[0032] Figure 7 This is a schematic diagram of the force exerted on abrasive particles in a high-frequency alternating magnetic field in a polishing method of the present invention that uses a high-frequency alternating magnetic field to control a liquid metal polishing disc. In the figure, the magnetic field passes from the upper surface of the liquid metal polishing disc through its lower surface.

[0033] Figure 8 This is a simulated flow velocity diagram of the optimization stage of the polishing method of the present invention using a high-frequency alternating magnetic field to control the liquid metal polishing disc, in which a high-frequency alternating current is used to cause the liquid metal particles to drive the abrasive particles to move.

[0034] Figure 9 This is a simulated streamline diagram of the optimization phase of a polishing method of the present invention that uses a high-frequency alternating magnetic field to control a liquid metal polishing disc, in which a high-frequency alternating current is used to cause liquid metal particles to drive the movement of abrasive particles. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0036] like Figures 1 to 3As shown, a polishing device that uses an alternating magnetic field to generate an electric field to control a liquid metal polishing disc includes a polishing machine body and a three-axis movable platform. The polishing machine body includes a polishing machine base 11, on which are disposed an electromagnetic coil 4, a liquid metal polishing disc rotating platform 6, and a polishing liquid inlet 13. The liquid metal polishing disc rotating platform 6 can secure the liquid metal polishing disc, driving the liquid metal polishing disc to rotate at high speed and produce a grinding effect on the workpiece. The liquid metal polishing disc rotating platform 6 is placed in the center of the electromagnetic coil 4, and the polishing liquid inlet 13 is connected to a conventional liquid supply mechanism, which supplies polishing liquid to the liquid metal polishing disc.

[0037] The three-axis mobile platform is a well-known technology and includes a first translation motor 3, a second translation motor 7, a first translation screw 2, a second translation screw 8, a traverse motor 1, a traverse screw 9, a vertical movement motor 5, a vertical screw 15, a first baffle 14, a second baffle 10, and a workpiece loading device 12. The first translation motor 3 forms the first translation screw 2, which forms the Y-axis electric slide. The second translation motor 7 and the second translation screw 8 also form the Y-axis electric slide. The traverse motor 1 and the traverse screw 9 form the X-axis electric slide. The vertical movement motor 5 and the vertical screw 15 form the Z-axis electric slide. The X-axis electric slide is mounted on the two Y-axis electric slides, and the Z-axis electric slide is mounted on the X-axis electric slide.

[0038] The workpiece loading device 12 can be driven up and down by a Z-axis electric slide, thereby applying varying loads to the workpiece. The aforementioned traverse motor 1, first translation motor 3, and second translation motor 7 can drive the workpiece loading device 12 in the xy directions, allowing the workpiece to be polished in different areas of the liquid metal polishing plate.

[0039] See also Figure 4-Figure 9 A polishing method that uses an alternating magnetic field to generate an electric field to control a liquid metal polishing disk includes: dividing the polishing process into four stages in sequence, namely, a rough polishing stage, a medium polishing stage, an optimization stage, and a fine polishing stage.

[0040] In the beginning of the process, and in the rough polishing stage, first fix the liquid metal polishing disc on the liquid metal polishing disc rotating table 6, then move the workpiece loading device 12 to the designated area of the liquid metal polishing disc through the three-axis translation platform, then give the workpiece a certain working load by moving the workpiece loading device 12 downward, then start the liquid metal polishing disc rotating table 6 drive motor to drive the liquid metal polishing disc to rotate and start the polishing operation. In the rough polishing stage, a larger working load and a smaller rotating speed are required to remove the rough layer on the surface of the material and quickly reduce the surface roughness. In the rough polishing stage, no current is applied to the electromagnetic coil 4, and the heat generated at this time is all from the heat generated by the friction between the workpiece and the liquid metal polishing disc. The change of the generated heat with time can be calculated by the following formula, and since no cooling liquid is added, the heat dissipation of the liquid metal polishing disc is not considered in this calculation formula.

[0041]

[0042] In the formula, Q1 is the heat generated during processing (excluding Joule heat), t is time, λ is the thermal conductivity of the liquid metal, S i is the effective force area between a single abrasive grain and the workpiece, P ω is the working load, μ is the friction coefficient, r i represents the distance from the center of the liquid metal polishing disc to the abrasive grain that produces friction effect with the workpiece, ω is the rotating speed of the liquid metal polishing disc rotating table 6, and n is the total number of abrasive grains in contact with the workpiece (related to the abrasive grain density on the surface of the liquid metal polishing disc and the surface area of the workpiece).

[0043] In the rough polishing stage, the main purpose is to remove most of the rough marks on the surface of the workpiece. Therefore, the liquid metal polishing disc needs to have a larger hardness and a larger working load in the rough polishing stage. According to the above calculation formula (1), the heat generated in this stage is related to the working load P ω and the rotating speed ω of the liquid metal polishing disc rotating table (6). In order to ensure that the polishing disc has a high hardness and can effectively remove most of the rough marks, it is necessary to use a smaller rotating speed ω and a larger working load P ω to polish.

[0044] After a period of time in the rough polishing stage, whether the workpiece can enter the medium polishing stage is judged by checking whether most of the rough marks on the surface of the workpiece disappear through the white light interferometer and whether the surface roughness is greatly reduced through the roughness detector.

[0045] By the time the intermediate polishing phase begins, most of the roughness on the workpiece surface has been removed during the rough polishing phase. The intermediate polishing phase primarily aims to further reduce the roughness to the threshold set for the optimization phase. Simultaneously, the intermediate polishing phase gathers heat for the optimization phase, reducing the hardness. Furthermore, the adhesion between the liquid metal particles is minimized, making it easier for the abrasive grains to loosen.

[0046] By controlling the vertical motion motor 5, the workpiece loading device 12 is slightly moved upward to reduce the workload, and the rotation speed of the liquid metal polishing disk rotary table 6 is increased. Simultaneously, a constant current is fed into the electromagnetic coil 4. This generates a constant magnetic field, and the liquid metal polishing disk rotary table 6 continuously moves the liquid metal polishing disk in a manner that cuts through the magnetic flux lines. Consequently, an induced current is generated within the liquid metal polishing disk, generating Joule heat in addition to the frictional heat.

[0047] The magnitude of the induced current can be expressed by the following formula.

[0048]

[0049] Where, e represents the base of the natural logarithm, which is approximately 2.718, μ0 represents the magnetic permeability in the atmosphere, and m is the number of turns of the solenoid coil. is the complex amplitude of the current passed into the electromagnetic coil 4, ω1 is the current change frequency, j is the imaginary unit, ω is the rotation speed of the liquid metal polishing disk turntable 6, L is the length of the solenoid, R represents the resistance value of the liquid metal polishing disk, r represents the radius of the liquid metal polishing disk, B represents the magnetic field strength generated after the electromagnetic coil 4 is energized, and I1 represents the magnitude of the induced current inside the liquid metal polishing disk.

[0050] According to the above formula (2), in order to reduce the surface roughness of the workpiece to a certain threshold range and accumulate heat for the optimization stage during the intermediate polishing stage, the workload of the liquid metal polishing disc should not be reduced too much, so its hardness should not be too low. The above formula (2) indicates that the magnitude of the induced current inside the liquid metal polishing disc is mainly related to the rotation speed ω and the magnetic field strength B of the liquid metal polishing disc rotating table 6. Therefore, according to the formula, the workload should be slightly reduced during the intermediate polishing stage, that is, a medium workload should be used. At the same time, the rotation speed ω should be slightly increased, and a medium rotation speed ω should be used for polishing. This stage is only for the purpose of gathering heat for the optimization stage, and the liquid metal polishing disc should be prevented from entering a solid-liquid coexistence state. At this time, a constant current should be passed through the electromagnetic coil, so the current frequency ω1 should be 0.

[0051] In the intermediate polishing stage, the heat generated by the liquid metal polishing disc during the processing can be divided into two parts. One part is the heat generated by friction, and the other part is the Joule heat generated by the induced current, which can be expressed by the following formula.

[0052]

[0053] Where Q2 is the total heat generated during processing, including Joule heat, λ is the thermal conductivity of liquid metal, S i is the effective force area between a single abrasive and the workpiece, P ω is the working load, μ is the friction coefficient, r i represents the distance from the center of the liquid metal polishing disk to the abrasive particles that generate friction with the workpiece, ω is the rotation speed of the liquid metal polishing disk rotating table 6, and n is the total number of abrasive particles in contact with the workpiece (related to the abrasive particle density on the liquid metal polishing disk surface and the surface area of ​​the workpiece). B represents the magnetic field strength generated by the electromagnetic coil 4 when energized, R represents the resistance of the liquid metal polishing disk, and r represents the radius of the liquid metal polishing disk.

[0054] According to the above formula (3), the heat generated in this stage is related to the rotation speed ω of the liquid metal polishing plate rotating table 6 and the workload P ω In order to ensure that the surface roughness of the workpiece can be reduced to the threshold range at this stage, sufficient heat can be accumulated and the viscosity of the liquid metal polishing disc abrasive particles can be reduced as much as possible, a medium working load P should be used at this stage. ω and a moderate rotational speed ω.

[0055] Although there is an induced current during the polishing stage, the temperature of the contact area between the liquid metal and the workpiece is not high enough to turn the liquid metal polishing disc into a semi-solid state. Therefore, even if the liquid metal particles are affected by the Lorentz force, they will not cause the abrasive particles to flip and move.

[0056] After a period of processing in the intermediate polishing stage, the surface roughness of the workpiece is further reduced to the specified threshold by using a white light interferometer and a roughness detector to determine whether it can enter the optimization stage.

[0057] During the optimization phase, a high-frequency alternating current is passed through the electromagnetic coil 4, which is used to improve the distribution of abrasive particles on the surface of the liquid metal polishing disc and enhance their quality. The electromagnetic coil, supplied with a high-frequency alternating current, generates a high-frequency alternating magnetic field at the same frequency as the current, with the magnetic field intensity being greatest in the center of the coil. The intensity of the generated high-frequency alternating magnetic field can be calculated using the following formula:

[0058]

[0059] Where μ0 represents the magnetic permeability in the atmosphere, m is the number of turns of the solenoid coil, is the complex amplitude of the current, ω1 is the frequency of the current change, L is the length of the solenoid, j is the imaginary unit, Re represents the real part, and t represents time. I(t) represents the change in the current in the electromagnetic coil 4 over time, and B(t) represents the change in the magnetic field strength in the electromagnetic coil 4 over time after the current is applied.

[0060] According to the above formula (4), in the optimization stage, the liquid metal polishing disc needs to have a high heat and be subjected to a large Lorentz force. Therefore, a high-frequency alternating current is used to pass through the electromagnetic coil. The above formula (4) shows that the frequency of change of the electromagnetic field is mainly related to the current change frequency ω1. Therefore, in this stage, different current change frequencies ω1 should be used for different types of liquid metal polishing discs. The specific analysis is as follows:

[0061] During the optimization phase, when using a liquid metal with a higher melting point as the base material to polish a hard workpiece, ω1 needs to be larger to increase the rate of change of the magnetic field generated by electromagnetic coil 4, thereby generating a greater Lorentz force and more heat. If the liquid metal used to make the liquid metal polishing disc has a lower melting point and the workpiece is also of lower hardness, ω1 needs to be smaller than that used in this polishing phase (greater than 0). This avoids unnecessary scratches on the workpiece surface during the optimization phase and prevents the semi-solid area of ​​the liquid metal polishing disc from becoming too large.

[0062] During the optimization phase, when the liquid metal polishing disc is placed in the alternating magnetic field generated by the electromagnetic coil 4, induced eddy currents are immediately generated inside the disc. During the optimization phase, not only induced eddy currents exist inside the liquid metal polishing disc, but also induced currents generated by the liquid metal polishing disc cutting the magnetic flux lines.

[0063] 1. Since the magnetic field is a high-frequency alternating magnetic field, the magnitude of the induced eddy current caused by the change in magnetic flux can be calculated by the following formula:

[0064]

[0065] Where r represents the radius of the liquid metal polishing disk, R represents the resistance of the liquid metal polishing disk, dΦ represents the change in magnetic flux during time dt, and I² represents the magnitude of the induced eddy current generated in the liquid metal polishing disk due to the change in magnetic flux.

[0066] 2. Since the liquid metal polishing disc is rotating at high speed and continuously cutting the magnetic flux lines, it will also generate induced current and superimpose with the induced eddy current. The magnitude of this part of the induced current can be calculated by the following formula:

[0067]

[0068] Where ω is the rotation speed of the liquid metal polishing disk rotating platform 6. I3 represents the magnitude of the induced current generated in the liquid metal polishing disk due to the liquid metal polishing disk cutting the magnetic flux lines.

[0069] Combining equations (1), (2), and (3), the total induced current inside the liquid metal polishing disc during processing can be calculated and expressed as follows:

[0070]

[0071] I total Indicates the magnitude of the total induced current in the liquid metal polishing plate.

[0072] Due to the induced current inside the liquid metal polishing plate, the entire liquid metal polishing plate will produce a Joule heating effect, which will increase the temperature of the polishing plate. The amount of Joule heat generated can be calculated by the following formula:

[0073]

[0074] Q3(t) represents the change of Joule heat generated inside the liquid metal polishing disk over time, and t represents the processing time.

[0075] At this time, the area in the liquid metal polishing plate that rubs against the workpiece will also generate heat due to friction, so the total heat in this area can be composed of two parts. It can be calculated by the following formula:

[0076]

[0077] Where Q4(t) represents the total heat generated inside the liquid metal polishing plate over time. λ is the thermal conductivity of the liquid metal, S i is the effective force area between a single abrasive and the workpiece, r is the radius of the polishing disc, P ω is the working load, μ is the friction coefficient, r i represents the distance from the center of the liquid metal polishing disc to the abrasive particles that produce friction effect with the workpiece, ω is the rotation speed of the liquid metal polishing disc rotating table (6), and n is the total number of abrasive particles in contact with the workpiece.

[0078] According to the above formulas (5), (6), (7), (8), and (9), the Joule heat generated inside the liquid metal polishing disc during the optimization stage of polishing has two parts working together, and there is still friction heat. The heat generated at this time is related to the liquid metal polishing disc speed, workload, and the current frequency of the electromagnetic coil 4. The magnitude of the current frequency ω1 is determined by formula (4) and the polishing conditions. The liquid metal polishing disc at this stage is in a solid-liquid coexistence state, so a larger workload P should not be used. ω. Combining the above five formulas, the following analysis is made on the rotation speed ω of the polishing disc rotary table in this stage: the selection of the rotation speed ω of the polishing disc rotary table is closely related to the current frequency ω1 passed through the electromagnetic coil used in the polishing process. When the material of the liquid metal polishing disc and the workpiece used supports the use of a larger current frequency ω1, a smaller rotation speed ω relative to the polishing stage can be used (but larger than the rotation speed ω in the intermediate polishing stage) to avoid excessive heat generated by the liquid metal polishing disc, which causes a large deformation of its surface. If a smaller current frequency ω1 is used after combining formula (4), then in order to ensure that the liquid metal polishing disc can reach a solid-liquid coexistence state, a larger rotation speed ω than the intermediate polishing stage needs to be used.

[0079] After a period of processing, the area of ​​the liquid metal polishing disc that is in contact with the workpiece will reach a semi-solid state, and the liquid metal particles within will begin to move slightly due to the Lorentz force. To ensure that the abrasive particles are fully turned and more evenly distributed in the area of ​​contact between the liquid metal polishing disc and the workpiece, the speed of the liquid metal polishing disc rotating table 6 is reduced.

[0080] The Lorentz force on the liquid metal particles will cause the abrasive particles to move at the same time. The abrasive particles are then subjected to the friction force given by the workpiece. At the same time, the Lorentz force on the liquid metal particles will also be indirectly transmitted to the abrasive particles to make them move. The loss of force is ignored in the analysis. The abrasive particles in the liquid metal polishing plate are subjected to the Lorentz force, centripetal force, and friction force transmitted by the liquid metal particles. The force they are subjected to can be expressed as follows: Figure 5 The net force F total The size of can be expressed by the following formula.

[0081]

[0082] M i Indicates the abrasive quality used in liquid metal polishing disc, P w represents the working load pressure, A represents the area of ​​the workpiece, μ represents the friction coefficient, B(t) represents the magnetic field intensity, ω represents the rotation speed of the liquid metal polishing disc rotary table (6), and D represents the abrasive particle size used in the liquid metal polishing disc.

[0083] During the optimization phase, high-frequency alternating current is used to make the liquid metal particles drive the abrasive particles to move. The simulated flow velocity diagram is shown in the figure below. Figure 8 As shown, the simulation streamline diagram is as follows Figure 9 shown.

[0084] This force will drive the abrasive particles to move in the semi-solid area of ​​the liquid metal polishing disc. During the movement, the friction force exerted by the workpiece on the abrasive particles and the Lorentz force exerted by the liquid metal particles on the abrasive particles are not in the same plane, so the abrasive particles will also rotate. The force diagram is shown as follows: Figure 6 As shown. The moment M that causes the abrasive to flip total It can be determined by the following formula:

[0085]

[0086] Where L2 represents the distance between the contact plane between the abrasive and the workpiece and the plane where the abrasive is embedded in the liquid metal, D is the abrasive particle size used in the liquid metal polishing disc, n is the total number of abrasive particles in contact with the workpiece (related to the abrasive particle density on the surface of the liquid metal polishing disc and the surface area of ​​the workpiece), A is the area of ​​the workpiece, μ is the friction coefficient, and P is the friction coefficient. w The working load pressure is ω, which is the rotation speed of the liquid metal polishing disc rotating table 6.

[0087] In the optimization stage, the Lorentz force plays a major role in the optimization effect of the liquid metal polishing disc. Combined with the above formulas (10)(11), the magnitude of the Lorentz force in this stage is closely related to the rotation speed ω and the current frequency ω1 of the liquid metal polishing disc rotating table 6. However, the effect it produces is obtained on the basis of formulas (4)(5)(6)(7)(8)(9). Therefore, the selection of the rotation speed ω and the current frequency ω1 needs to be made after making a selection according to formulas (4)(5)(6)(7)(8)(9), and then further adjusted according to this formula and the optimization situation of the liquid metal polishing disc. The specific analysis is as follows: When the passivated abrasive particles on the surface of the liquid metal polishing disc do not significantly flip over during the optimization stage, according to formulas (10)(11), it can be seen that the rotation speed ω and the current frequency ω1 need to be further increased. If it is found in the optimization stage that the abrasive particles on the surface of the liquid metal polishing disc sink deeper in some areas after flipping again, the rotation speed ω and the current frequency ω1 should be reduced at this time.

[0088] During the above process, the abrasive particles are turned over while moving, exposing the side that has not been blunted by friction to participate in the polishing operation in the fine polishing stage. At the same time, the abrasive particles in the liquid metal polishing disc can be more evenly distributed by changing the direction of the current passed into the electromagnetic coil 4.

[0089] After a period of processing in the optimization phase, the liquid metal polishing disc's surface morphology and roughness have significantly improved, as measured by white light interferometry and a roughness tester. This phase concludes when the current to the electromagnetic coil is cut off, eliminating Joule heating and the influence of Lorentz forces on the liquid metal polishing disc.

[0090] Then, during the fine polishing phase, coolant is rapidly added to rapidly cool the polishing disc, causing the semi-solid area of ​​the liquid metal polishing disc to solidify. Simultaneously, the rotational speed of the liquid metal polishing disc turntable 6 is increased, further reducing the workload. After solidification, the abrasive particles are now subject only to the friction required for polishing. Furthermore, since the liquid metal has solidified, the abrasive particles cannot move or flip. After a period of operation, the above steps can be repeated, if necessary, to flip the abrasive particles again.

[0091] This process improves polishing efficiency, quality, and the life of the polishing disc. Even if the abrasive becomes passivated, there's no need to melt the entire liquid metal polishing disc and remake it. Furthermore, electromagnetic fields control the movement of the liquid metal particles, driving the abrasive particles' motion and improving the uniformity of their distribution across the disc's surface.

[0092] The innovation of the present invention is:

[0093] 1) Regarding the electromagnetic field, the present invention utilizes a high-frequency alternating magnetic field with adjustable frequency and direction. This high frequency and adjustable direction simultaneously achieve a more uniform distribution of abrasive particles on the surface of the liquid metal polishing disc, thereby increasing the disc's lifespan. This differs from other patents that use fixed-frequency electromagnetic fields or permanent magnets.

[0094] 2. The present invention does not require the addition of an electric field in the liquid metal polishing plate. Since the present invention uses a high-frequency alternating magnetic field, induced eddy currents are generated on the liquid metal polishing plate according to Faraday's law of electromagnetic induction, saving energy consumption.

[0095] 3. The present invention divides the entire polishing process into four stages. Different types of electromagnetic fields are used or not used at different stages. This makes the use of electromagnetic fields more systematic and saves energy.

[0096] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A polishing method using a high-frequency alternating magnetic field to control a liquid metal polishing disc, characterized in that: include: The polishing process is divided into four stages in sequence, namely rough polishing stage, medium polishing stage, optimization stage and fine polishing stage; Rough polishing stage: The electromagnetic coil does not intervene in the work. In the rough polishing stage, a higher working load and a lower liquid metal polishing disc speed are used according to the material of the workpiece; Medium throwing stage: In the medium throwing stage, a medium working load and a medium liquid metal polishing disc speed are used, and a constant current is passed into the electromagnetic coil to generate a constant magnetic field; Optimization stage: When entering the optimization stage, low workload and low liquid metal polishing disc speed are used for processing. During the optimization stage, high-frequency alternating current is passed into the electromagnetic coil, causing the electromagnetic coil to generate a high-frequency alternating magnetic field; Fine polishing stage: add a coolant and further reduce the positive pressure on the workpiece, so that the temperature of the liquid metal polishing disc drops rapidly and solidifies, while increasing the rotation speed of the liquid metal polishing disc rotary table and further reducing the workload.

2. The polishing method of claim 1, wherein the polishing method comprises: In the rough polishing stage, the upper working load range is 100 N to 200 N, and the lower liquid metal polishing disc speed range is 50 rpm to 100 rpm; In the medium polishing stage, the medium working load range is 60 N to 90 N, and the medium liquid metal polishing disc speed range is 30 rpm to 40 rpm; During the optimization stage, the low working load range is 20 N to 50 N, the low liquid metal polishing disk speed range is 15 rpm to 25 rpm; the high-frequency alternating current is a current with a frequency range of 10 kHz to 100 kHz, and the high-frequency alternating magnetic field is a magnetic field with a frequency range of 5 kHz to 50 kHz.

3. The polishing method of claim 1, wherein the polishing method comprises: The rough polishing stage also includes: after a period of processing in the rough polishing stage, checking whether most of the rough marks on the surface of the workpiece have disappeared by using a white light interferometer and checking whether the surface roughness has been significantly reduced by using a roughness tester to determine whether it is possible to enter the medium polishing stage.

4. The polishing method of claim 1, wherein the polishing method comprises: The intermediate polishing stage also includes: the liquid metal polishing disc rotates to cut the magnetic lines of force of the constant magnetic field generated by the electromagnetic coil, so that an induced current is generated inside the liquid metal. The liquid metal polishing disc thus generates Joule heat and is affected by the Lorentz force during work, causing relative movement between the abrasive and the liquid metal.

5. The polishing method of claim 1, wherein the polishing method comprises: The intermediate polishing stage also includes: after a period of processing, using a white light interferometer and a roughness measuring instrument to detect whether the surface roughness of the workpiece reaches a set threshold to determine whether it is possible to enter the optimization stage.

6. The polishing method of claim 1, wherein the polishing method comprises: The optimization stage also includes: the liquid metal polishing disk not only generates induced current due to the cutting of magnetic flux lines, but also generates induced eddy currents due to the high-speed change of magnetic flux passing through it. Therefore, the superposition of the two parts of induced current causes the liquid metal polishing disk to generate more Joule heat, making the area where the liquid metal polishing disk contacts the workpiece semi-solid and the liquid and solid phases coexist. At the same time, the liquid metal at this time has a larger induced current, so it will also be subject to a larger Lorentz force in the alternating magnetic field. The Lorentz force and the friction force exerted by the workpiece on the abrasive particles will further cause the liquid metal particles in the friction area where the polishing disk contacts the workpiece to flip and move. The flipping movement of the abrasive particles exposes its unpassivated side.

7. The polishing method of claim 1, wherein the polishing method comprises: The optimization stage also includes: in the optimization stage, the direction of the high-frequency alternating magnetic field is changed by controlling the direction of the current passed into the electromagnetic coil, thereby changing the direction of the Lorentz force acting on the liquid metal particles. The liquid metal particles drive the abrasive particles to move in different directions, making the abrasive particles in the contact area between the liquid metal polishing disc and the workpiece more evenly distributed.

8. The polishing method of claim 1, wherein the polishing method utilizes a high-frequency alternating magnetic field to control a liquid metal polishing disc, The optimization stage also includes: when the hardness of the workpiece is low and the rotation speed and working load of the liquid metal polishing disc are large, a lower frequency alternating current is selected, otherwise a higher frequency alternating current is selected.

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