Polishing method and polishing device for controlling liquid metal grinding and polishing disc through high-frequency alternating magnetic field

Abstract

The invention belongs to the field of liquid metal polishing, and discloses a polishing method and device for controlling a liquid metal grinding and polishing disc through a high-frequency alternating magnetic field, and the polishing method comprises the step that the polishing process is divided into four stages including the rough polishing stage, the medium polishing stage, the optimization stage and the fine polishing stage in sequence. After the liquid metal grinding and polishing disc is machined for a long time, the abrasive particles on the surface can be passivated, and the polishing efficiency can be improved by turning over the abrasive particles through the grinding and polishing disc. Through the control means of externally adding the high-frequency alternating magnetic field, the abrasive particles can be distributed more evenly in the area making contact with the machined workpiece, and the polishing quality can be improved.

Description

Technical Field

[0001] The 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 on the polishing disc by coating or pressing, and the polishing effect is achieved by rubbing the polishing disc against the workpiece. There are various polishing discs on the market, some of which are polishing discs with 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 then remixed with new abrasive grains, and then put into the mold again 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. Only after the polishing disc is melted and mixed with new abrasive grains can the processing continue. In addition, the distribution of 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 a liquid metal polishing disc controlled by 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 using a high-frequency alternating magnetic field to control a liquid metal polishing disc 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 grinding disk 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 working load 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, so that the electromagnetic coil generates 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 higher working load ranges from 100N to 200N, and the lower liquid metal polishing disc speed ranges from 50rpm to 100rpm;

[0011] In the medium polishing stage, the medium working load ranges from 60N to 90N, and the medium liquid metal polishing disc speed ranges from 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 detector 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 flux lines 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 work, causing relative movement between the abrasive and the liquid metal.

[0015] Furthermore, the intermediate polishing stage also 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 current due to the high-speed change of magnetic flux passing through it. Therefore, the superposition of the two parts of the 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 coexisting with liquid and solid phases. 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 of 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] Furthermore, 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 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.

[0018] Furthermore, the optimization stage also includes: when the hardness of the material of the workpiece is low and the rotation speed and working load of the liquid metal polishing disc used are large, a lower frequency alternating current is selected, otherwise a higher frequency alternating current is used.

[0019] The present invention also provides a polishing device that utilizes a high-frequency alternating magnetic field to control a liquid metal polishing disk, which is used to implement the polishing method described above, and includes a polishing machine body and a three-axis translation platform. The polishing machine body includes a polishing machine base, and an electromagnetic coil and a liquid metal polishing disk rotating table are arranged on the polishing machine base. The liquid metal polishing disk 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 perform XYZ three-axis movement. The workpiece loading device is used to press the workpiece onto the liquid metal polishing disk rotating table.

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

[0021] 1) When the liquid metal polishing disc is processed for a long time, the surface abrasive particles will be passivated. The present invention can improve the polishing efficiency by turning the abrasive particles.

[0022] 2) By applying a high-frequency alternating magnetic field, the abrasive particles can be distributed more evenly in the area in contact with the workpiece, thus improving the polishing quality;

[0023] 3) The abrasive grain flipping can be controlled by an external electromagnetic field, so that the unpassivated side of the abrasive grain is exposed, which increases the life of the polishing disc;

[0024] 4) The current inside the liquid metal polishing plate is an induced current, and there is no need to apply an electric field to the liquid metal polishing plate, which saves energy consumption to a certain extent;

[0025] 5) The present invention can improve the surface morphology of the liquid metal polishing plate on the basis of incompletely melting the liquid metal polishing plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a schematic diagram of a top view of the structure of a polishing device that utilizes a high-frequency alternating magnetic field to control a liquid metal polishing disc.

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

[0028] Figure 3 The present invention is a schematic diagram of a top view of the structure of a polishing device 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 by using a high-frequency alternating magnetic field.

[0030] Figure 5 The present invention is a schematic diagram of the force exerted on abrasive particles in a high-frequency alternating magnetic field in a polishing method for controlling a liquid metal polishing disc using a high-frequency alternating magnetic field. 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 present invention is a schematic diagram of the abrasive particles being rotated under force in a polishing method of a liquid metal polishing disc controlled by a high-frequency alternating magnetic field.

[0032] Figure 7 The present invention is a schematic diagram of the force exerted on abrasive particles in a high-frequency alternating magnetic field in a polishing method for controlling a liquid metal polishing disc using a high-frequency alternating magnetic field. 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 a polishing method for controlling a liquid metal polishing disc using a high-frequency alternating magnetic field in the optimization stage of the present invention, in which a high-frequency alternating current is used to make liquid metal particles drive abrasive particles to move.

[0034] Fig. 9 The present invention is a method for controlling a liquid metal polishing disc by using a high-frequency alternating magnetic field, and in the optimization stage, a simulated streamline diagram of using a high-frequency alternating current to make liquid metal particles drive abrasive particles to move. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0036] like Figure 1 to Figure 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 moving platform. The polishing machine body includes a polishing machine base 11, and the polishing machine base 11 is provided with an electromagnetic coil 4, a liquid metal polishing disc rotating table 6, and a polishing liquid inlet 13, wherein the liquid metal polishing disc rotating table 6 can fix the liquid metal polishing disc, drive the liquid metal polishing disc to rotate at high speed and produce a grinding effect with the workpiece. At the same time, the liquid metal polishing disc rotating table 6 is placed in the middle of the electromagnetic coil 4, and the polishing liquid inlet 13 is connected to a conventional liquid supply mechanism, and the liquid supply mechanism delivers polishing liquid to the liquid metal polishing disc.

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

[0038] The workpiece loading device 12 can be driven to move up and down by the Z-axis electric slide, so as to apply different working loads to the workpiece. The above-mentioned traverse motor 1, the first translation motor 3, and the second translation motor 7 can drive the workpiece loading device 12 to move in the xy direction so that the workpiece can be polished in different areas of the liquid metal polishing disc.

[0039] See also Figure 4-Figure 9 A polishing method using an alternating magnetic field to generate an electric field to control a liquid metal polishing disc 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.

[0040] At the beginning of processing and in the rough polishing stage, the liquid metal polishing disc is first fixed on the liquid metal polishing disc rotating table 6, and then the workpiece loading device 12 is moved to the designated area of ​​the liquid metal polishing disc through the three-axis translation platform, and then the workpiece loading device 12 is moved downward to give the workpiece a certain working load, and then the liquid metal polishing disc rotating table 6 driving motor is started to drive the liquid metal polishing disc to rotate and start polishing. In the rough polishing stage, a larger working load and a smaller rotation speed need to be applied to remove the rough layer on the surface of the material and quickly reduce the surface roughness. In the rough polishing stage, there is no need to pass current to the electromagnetic coil 4. At this time, all the heat generated comes from the heat generated by the friction between the workpiece and the liquid metal polishing disc. The change in heat generation over time can be calculated by the following formula. Since no coolant is added, this calculation formula does not take into account the heat dissipated from the liquid metal polishing disc.

[0041]

[0042] In the formula, Q 1 is the heat generated during processing (excluding Joule heat), t is the time, λ is the thermal conductivity of the 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 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 (related to the abrasive particle density on the surface of the liquid metal polishing disc and the surface area of ​​the workpiece).

[0043] The main purpose of the rough polishing stage is to remove most of the rough marks on the surface of the workpiece. Therefore, the liquid metal polishing disc needs to have a greater hardness and a larger workload during the rough polishing stage. According to the above calculation formula (1), the heat generated in this stage is proportional to the workload P ω The rotation speed ω of the liquid metal polishing disc rotating table (6) is related to the rotation 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 rotation speed ω and a larger working load P at this stage. ω Polishing is performed.

[0044] After a period of processing in the rough polishing stage, a white light interferometer is used to check whether most of the rough marks on the surface of the workpiece have disappeared, and a roughness tester is used to check whether the surface roughness has been greatly reduced to determine whether it can enter the medium polishing stage.

[0045] When entering the intermediate polishing stage, most of the rough marks on the surface of the workpiece have been removed in the rough polishing stage. The intermediate polishing stage is mainly to further reduce the roughness to the threshold set for the optimization stage. At the same time, in the intermediate polishing stage, it is necessary to gather heat for the optimization stage and reduce its hardness. And the viscosity between the liquid metal particles is reduced as much as possible, so that the abrasive particles are more likely to loosen in it.

[0046] By controlling the vertical moving motor 5, the workpiece loading device 12 is slightly moved upward to reduce the working load, and the rotation speed of the liquid metal polishing disk rotating table 6 is increased. At the same time, a constant current begins to be passed into the electromagnetic coil 4. At this time, the electromagnetic coil 4 will generate a constant magnetic field, and the liquid metal polishing disk rotating table 6 will always carry the liquid metal polishing disk to cut the magnetic flux lines. Therefore, an induced current will be generated inside the liquid metal polishing disk and continue to generate Joule heat on the basis of the heat generated by friction.

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

[0048]

[0049] In the formula, e represents the base of natural logarithm, which is approximately 2.718, μ 0 represents the magnetic permeability in the atmosphere, m is the number of turns of the solenoid coil, is the complex amplitude of the current flowing into the electromagnetic coil 4, ω 1 is the frequency of current change, j is an imaginary unit, ω is the rotation speed of the liquid metal polishing disk rotating table 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 by the electromagnetic coil 4 after power is turned on, I 1 Represents the size of the induced current inside the liquid metal polishing plate.

[0050] According to the above formula (2), in order to reduce the surface roughness of the workpiece to a certain threshold range during the intermediate polishing stage and to gather heat for the optimization stage, the decrease in the workload of the liquid metal polishing disc should not be too large, 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 is slightly increased, and a medium rotation speed ω is used for polishing. This stage is only to gather 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 ω 1 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] In the formula, Q 2 is the total heat generated during processing, including Joule heat, λ is the thermal conductivity of the 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 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 (related to the abrasive particle density on the surface of the liquid metal polishing disc and the surface area of ​​the workpiece). B represents the magnetic field intensity generated after the electromagnetic coil 4 is energized, R represents the resistance value of the liquid metal polishing disc, and r represents the radius of the liquid metal polishing disc.

[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 roughness of the workpiece surface can be reduced to the threshold range at this stage, to gather enough heat and to reduce the viscosity of the liquid metal polishing disc abrasive as much as possible, a medium working load P should be used at this stage. ω and a medium rotation speed ω.

[0055] Although there is an induced current in the intermediate polishing stage, the temperature of the contact area between the liquid metal and the workpiece is not 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] In the optimization stage, a high-frequency alternating current is introduced into the electromagnetic coil 4, and the optimization stage of improving the distribution of abrasive particles on the surface of the liquid metal polishing disc and enhancing the quality of abrasive particles is entered. The electromagnetic coil with a high-frequency alternating current will generate a high-frequency alternating magnetic field with the same frequency as the current change, and the magnetic field strength is the largest in the middle area of ​​the coil. The high-frequency alternating magnetic field strength generated by it can be calculated by 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, ω 1 is the frequency of current change, L is the length of the solenoid, j is an imaginary unit, Re represents the real part, and t represents time. I(t) represents the change of the current in the electromagnetic coil 4 over time, and B(t) represents the change of the magnetic field strength in the electromagnetic coil 4 over time after power is applied.

[0060] According to the above formula (4), in the optimization stage, the liquid metal polishing plate needs to have a higher heat and be subjected to a larger Lorentz force, so 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 frequency of change of the current ω 1 Therefore, at this stage, different current change frequencies ω should be used for different types of liquid metal polishing discs. 1 , the specific analysis is as follows:

[0061] In the optimization stage, when using liquid metal with a higher melting point as the base material to polish a workpiece with a higher hardness, ω 1 A larger value is needed to increase the rate of change of the magnetic field generated by the electromagnetic coil 4, thereby generating a greater Lorentz force and more heat. If the melting point of the liquid metal used to make the liquid metal polishing disc is low and the hardness of the workpiece is also low, then ω 1 It is necessary to take a smaller value (greater than 0) relative to the polishing stage to avoid unnecessary scratches on the surface of the workpiece during the optimization stage and to prevent the semi-solid area of ​​the liquid metal polishing disc from being too large.

[0062] In the optimization stage, when the liquid metal polishing disc is placed in the alternating magnetic field generated by the electromagnetic coil 4, an induced eddy current is immediately generated inside the liquid metal polishing disc. In the optimization stage, there are not only induced eddy currents 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, and dΦ represents the change in magnetic flux in dt time. 2 It indicates the size of the induced eddy current generated in the liquid metal polishing plate due to the change of magnetic flux.

[0066] 2. Since the liquid metal polishing disc is rotating at high speed and constantly cutting the magnetic flux lines, an induced current will also be generated and superimposed 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 plate rotating platform 6. 3 It indicates 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, which can be expressed as follows:

[0070]

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

[0072] Since there is an induced current inside the liquid metal polishing plate, the entire liquid metal polishing plate will produce a Joule heating effect, causing the temperature of the polishing plate to rise. The amount of Joule heat generated can be calculated by the following formula:

[0073]

[0074] Q 3 (t) represents the change of Joule heat generated inside the liquid metal polishing disc 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] In the formula, Q 4 (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 in 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 speed of the liquid metal polishing disc, the workload, and the current frequency of the electromagnetic coil 4. The current frequency ω 1 The size of is determined by formula (4) and polishing conditions. At this stage, the liquid metal polishing disc is in a solid-liquid coexistence state, so a larger working load P should not be used. ω Combining the above five equations, the rotation speed ω of the polishing disc rotating table in this stage is analyzed as follows: The rotation speed ω of the polishing disc rotating table is selected in accordance with the current frequency ω of the electromagnetic coil used in the polishing process. 1 When the liquid metal polishing disc and the material of the workpiece support the use of a larger current frequency ω 1 At this time, a relatively small rotation speed ω can be used relative to the polishing stage (but larger than the rotation speed ω in the intermediate polishing stage) to avoid excessive heat generated by the liquid metal polishing disk, which may cause large deformation of its surface. If combined with formula (4), a smaller current frequency ω is used 1 In order to ensure that the liquid metal polishing disc can reach a solid-liquid coexistence state, it is necessary to adopt a rotation speed ω that is greater than that in the intermediate polishing stage.

[0079] After a period of processing, the area of ​​the liquid metal polishing disc that rubs against the workpiece will reach a semi-solid state, and the liquid metal particles inside it will begin to move slightly due to the Lorentz force. In order to allow the abrasive particles to fully flip and be more evenly distributed in the area where the liquid metal polishing disc contacts the workpiece, the rotation speed of the liquid metal polishing disc rotating table 6 is reduced at this time.

[0080] The Lorentz force on the liquid metal particles will cause the abrasive particles to move slightly, and the abrasive particles will be affected by 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 affected by the Lorentz force, centripetal force, and friction force transmitted by the liquid metal particles. The force they are subjected to can be expressed as Figure 5 The resultant 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 wrepresents 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 rotating table (6), and D represents the abrasive particle size used in the liquid metal polishing disc.

[0083] In the optimization stage, 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 Fig. 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 in the figure below. Figure 6 As shown. The moment M that causes the abrasive grain to flip total It can be determined by the following formula:

[0085]

[0086] Where L 2 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 by 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 surface area of ​​the workpiece. w The working load pressure, ω 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 equations (10) and (11), the magnitude of the Lorentz force in this stage is mainly related to the rotation speed ω of the liquid metal polishing disc rotating table 6 and the current frequency ω 1 However, the effect is based on formulas (4)(5)(6)(7)(8)(9), so the rotation speed ω and current frequency ω 1 The selection of needs to be made according to formulas (4)(5)(6)(7)(8)(9), and then further adjusted according to this formula and the optimization 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 flip significantly during the optimization stage, according to formulas (10)(11), it can be seen that the rotation speed ω and the current frequency ω need to be further increased. 1 If it is found during the optimization stage that the abrasive particles on the surface of the liquid metal polishing disc sink deeper in some areas after flipping, the rotation speed ω and current frequency ω should be reduced at this time. 1 .

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

[0089] After a period of processing in the optimization stage, the surface morphology and roughness of the liquid metal polishing disc are greatly improved by white light interferometer and roughness detector, and the optimization stage is ended. After the optimization stage is completed, the current of the electromagnetic coil is cut off, so that the liquid metal polishing disc no longer generates Joule heat and is no longer affected by the Lorentz force.

[0090] After entering the fine polishing stage, coolant is quickly added to rapidly reduce the temperature of the polishing disc, so that the semi-solid area of ​​the liquid metal polishing disc is rapidly solidified. At the same time, the rotation speed of the liquid metal polishing disc rotating table 6 is increased and the workload is further reduced. After solidification, the abrasive grains are only subjected to the friction required for the polishing operation. At the same time, since the liquid metal has solidified, the abrasive grains can no longer move or flip. After working for a period of time, if necessary, the above steps can be repeated to flip and move the abrasive grains again.

[0091] The above process improves polishing efficiency, polishing quality, and the life of the polishing disc. Even if the abrasive particles are passivated, there is no need to melt the entire liquid metal polishing disc and then remake it. At the same time, the electromagnetic field controls the movement of the liquid metal particles to drive the movement of the abrasive particles, thereby improving the uniformity of the distribution of the abrasive particles on the surface of the polishing disc.

[0092] The innovation of the present invention lies in:

[0093] 1) In terms of the use of electromagnetic fields, the present invention uses a high-frequency alternating magnetic field, the frequency and direction of which are adjustable. At the same time, the high frequency and adjustable direction characteristics are used to make the abrasive particles on the surface of the liquid metal polishing disc more evenly distributed and increase the life of the polishing disc. This is different from the fixed frequency electromagnetic field or permanent magnet used in other patents.

[0094] 2. The present invention does not need to add an additional electric field in the liquid metal polishing plate. Since the present invention uses a high-frequency alternating magnetic field, an induced eddy current will be 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 major stages. Different types of electromagnetic fields are used or not used in different stages. This makes the use of electromagnetic fields more systematic and saves energy consumption.

[0096] Although 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 the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A polishing method for controlling a liquid metal polishing disc by using a high-frequency alternating magnetic field, 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 grinding disk 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 working load 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, so that the electromagnetic coil generates 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 a liquid metal polishing disc controlled by a high-frequency alternating magnetic field according to claim 1, characterized in that: In the rough polishing stage, the higher working load ranges from 100N to 200N, and the lower liquid metal polishing disc speed ranges from 50rpm to 100rpm; In the medium polishing stage, the medium working load ranges from 60N to 90N, and the medium liquid metal polishing disc speed ranges from 30rpm to 40rpm; 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.

3. The polishing method of a liquid metal polishing disc controlled by a high-frequency alternating magnetic field according to claim 1, characterized in that: 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 using a roughness detector to check whether the surface roughness has been greatly reduced to determine whether it can enter the medium polishing stage.

4. The polishing method of a liquid metal polishing disc controlled by a high-frequency alternating magnetic field according to claim 1, characterized in that: The intermediate polishing stage also includes: the liquid metal polishing disc rotates to cut the magnetic flux lines 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, so that relative movement begins to occur between the abrasive and the liquid metal.

5. The polishing method of a liquid metal polishing disc controlled by a high-frequency alternating magnetic field according to claim 1, characterized in that: 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 processed workpiece reaches a set threshold to determine whether to enter the optimization stage.

6. The polishing method of a liquid metal polishing disc controlled by a high-frequency alternating magnetic field according to claim 1, characterized in that: 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 current due to the high-speed change of magnetic flux passing through it. Therefore, the superposition of the two parts of the 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 coexisting with liquid and solid phases. 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 of 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 a liquid metal polishing disc controlled by a high-frequency alternating magnetic field according to claim 1, characterized in that: 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, so that the direction of the Lorentz force on the liquid metal particles is changed, and the liquid metal particles drive the abrasive particles to move in different directions, so that the abrasive particles in the contact area between the liquid metal polishing disc and the workpiece are more evenly distributed.

8. The polishing method of a liquid metal polishing disc controlled by a high-frequency alternating magnetic field according to claim 1, characterized in that: The optimization stage also includes: when the hardness of the material 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 used.

9. A polishing device using a high-frequency alternating magnetic field to control a liquid metal polishing disc, used to implement the polishing method described in any one of claims 1 to 8, characterized in that: It includes a polishing machine body and a three-axis translation platform. The polishing machine body includes a polishing machine base. An electromagnetic coil and a liquid metal polishing disk rotating table are arranged on the polishing machine base. The liquid metal polishing disk 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 perform XYZ three-axis movement. The workpiece loading device is used to press the workpiece onto the liquid metal polishing disk rotating table.

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