Precise polishing method of ultrasonic-assisted electrolyte plasma

Abstract

The invention discloses an ultrasonic-assisted electrolyte plasma precise polishing method, and belongs to the technical field of metal material surface treatment. The method comprises the following steps: pretreating a to-be-polished metal material to obtain a metal sample; and the metal sample piece serves as an anode to be immersed in a polishing solution, a conductive material serves as a cathode to be immersed in the polishing solution, direct current is introduced into the anode and the cathode for electrolyte plasma treatment, meanwhile, ultrasonic vibration is applied for polishing, and precise polishing of the metal material to be polished is completed. A gas envelope layer is formed on the surface of a metal sample piece based on electrolyte plasma polishing, cavitation bubbles are formed in combination with ultrasonic vibration, under the synergistic effect of dynamic cavitation and ultrasonic cavitation of a polishing solution, hydroxyl is generated to the maximum extent, the plasma activity is enhanced, and the surface of the metal sample piece is polished. And the activated plasma is facilitated to strip the convex part on the surface of the metal sample piece, so that the surface roughness of the metal material is reduced, and the polishing effect is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material surface treatment, and in particular relates to an ultrasound-assisted electrolyte plasma precision polishing method. Background Art

[0002] The electrolyte plasma polishing method involves the interdisciplinary knowledge of plasma physics of gas breakdown and ionization and the electrode surface reaction process in the electrochemical system. The air gap film on the electrode surface is formed by the cation field characteristics regulated by the external circuit. The electrons pass through the air gap film to activate the plasma, and the surface of the sample is stripped and polished under the action of the plasma. The electrolyte plasma polishing method can effectively reduce the surface roughness of the sample and achieve the purpose of precision polishing. Due to its high efficiency and environmental friendliness in improving the performance of metal surfaces, it has attracted widespread attention from metal surface polishing researchers.

[0003] Existing patent CN113564683A discloses an electrolyte plasma polishing method for titanium alloy femoral stem prosthesis, which realizes low-cost, high-efficiency and environmentally friendly polishing of the surface of femoral stem prosthesis workpieces with complex shapes and structures, which is conducive to industrialization and commercial promotion. For example, patent CN113737268A discloses an electrolyte plasma polishing method for pure titanium denture brackets, wherein the polishing liquid of the denture bracket is a low-concentration inorganic salt aqueous solution, which reduces environmental pollution and realizes efficient polishing of complex structures. However, the above patent only adopts the electrolyte plasma polishing method. Although it can achieve efficient polishing of complex structures, it has the problems of poor surface uniformity and insufficient efficiency. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes an ultrasound-assisted electrolyte plasma precision polishing method.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides an ultrasound-assisted electrolyte plasma precision polishing method, comprising the following steps:

[0007] The metal material to be polished is pretreated to obtain a metal sample; the metal sample is immersed in the polishing liquid as an anode, and the conductive material is immersed in the polishing liquid as a cathode, direct current is passed through the anode and the cathode for electrolyte plasma treatment, and ultrasonic vibration is applied for polishing to complete the precision polishing of the metal material to be polished.

[0008] Technical principle: Based on the multi-field coordination of gas discharge, plasma electrochemistry, and ultrasonic cavitation, the negatively charged ions on the anode surface of the metal material precipitate gas to form an air gap film, and the electrons of the negatively charged ions break through the air gap film. The electrons collide with the gas atoms in the air gap film to form plasma. Under the action of plasma ultrasonic cavitation, the surface of the metal material is peeled off and polished, thereby reducing the surface roughness of the metal material and improving its surface quality.

[0009] Preferably, the pretreatment includes cutting, drilling, pre-grinding and step-by-step grinding.

[0010] Preferably, the arithmetic mean roughness of the metal sample is 0.4-0.5 μm.

[0011] Preferably, the metal material to be polished includes stainless steel or titanium alloy.

[0012] Preferably, when the metal material to be polished is stainless steel, the polishing liquid is an ammonium sulfate solution with a mass concentration of 3-5%; when the metal material to be polished is titanium alloy, the polishing liquid is a mixed aqueous solution of ammonium fluoride and potassium fluoride.

[0013] Preferably, the temperature of the polishing liquid is 70-90°C.

[0014] Preferably, the voltage of the direct current is 250-400V.

[0015] Preferably, the frequency of the ultrasonic vibration is 28-40 kHz.

[0016] Preferably, the conductive material includes stainless steel, platinum or copper.

[0017] Preferably, the timing starts from the generation of a stable gas layer on the surface of the metal sample, and the polishing time is 10-30 minutes.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects:

[0019] The present invention provides an ultrasound-assisted electrolyte plasma precision polishing method, which is based on the gas envelope layer formed on the surface of a metal sample by electrolyte plasma polishing, combined with ultrasonic vibration to form cavitation bubbles. Under the synergistic effect of dynamic cavitation of the polishing liquid and ultrasonic cavitation, the generation of hydroxyl groups is maximized, the plasma activity is enhanced, and the activated plasma is helpful to peel off the raised parts on the surface of the metal sample, thereby reducing the surface roughness of the metal material and improving the polishing effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0021] Figure 1 A schematic structural diagram of a device used in the ultrasonic-assisted electrolyte plasma precision polishing method provided by the present invention;

[0022] Figure 2 This is a graph showing the change of current over time after the polishing liquid current stabilizes in step (4) of Example 1;

[0023] Figure 3 This is the surface morphology of the 316 stainless steel sample in step (1) of Example 1;

[0024] Figure 4 This is a surface morphology image of the 316 stainless steel sample after polishing in step (4) of Example 1;

[0025] Figure 5 The three-dimensional surface morphology of the 316 stainless steel sample in step (1) of Example 1;

[0026] Figure 6 This is a three-dimensional surface morphology image of the bright surface 316 stainless steel sample obtained in Example 1. DETAILED DESCRIPTION

[0027] 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.

[0028] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] The embodiment of the present invention provides an ultrasound-assisted electrolyte plasma precision polishing method, comprising the following steps:

[0030] The metal material to be polished is pretreated to obtain a metal sample; the metal sample is immersed in the polishing liquid as an anode, and the conductive material is immersed in the polishing liquid as a cathode, direct current is passed through the anode and the cathode for electrolyte plasma treatment, and ultrasonic vibration is applied for polishing to complete the precision polishing of the metal material to be polished.

[0031] When ultrasonic waves propagate in a medium, there are positive and negative alternating cycles. In the positive phase, ultrasonic waves squeeze the medium molecules, increasing the density of the medium; in the negative phase, the medium molecules become sparse and then discrete, and the density decreases. When the intensity of ultrasonic waves is large enough, the average distance between the medium molecules in the liquid exceeds the critical molecular distance, the liquid medium breaks, and microbubbles are formed. When ultrasonic waves are introduced into the liquid medium, the molecules in the solution continue to oscillate under the alternating action of positive and negative pressures, causing periodic pressure changes in the liquid. When the amplitude of the alternating sound pressure is greater than the cavitation threshold, the cavitation nucleus in the liquid or on the liquid-solid interface will form, grow, and finally collapse. During the periodic oscillation of bubbles, especially during the collapse process, large transient high temperatures and high pressures will be generated, and the gas-liquid medium in the bubbles will rupture, which will help to further peel off the uneven parts of the metal sample surface and improve the polishing effect.

[0032] The present invention uses ultrasonic vibration in the electrolyte plasma polishing process, and realizes precise polishing of metal materials through electrolyte plasma activation and ultrasonic cavitation.

[0033] In a preferred embodiment, the pre-processing includes cutting, drilling, pre-grinding and step-by-step grinding.

[0034] In a preferred embodiment, the cutting device is a grinding wheel cutter; illustratively, the size of the metal material after cutting is 20×15×3 mm.

[0035] In a preferred embodiment, the drilling is: using a drilling machine to punch a through hole with a diameter of 2 mm just above the cut metal material at a distance of 1.5-2 cm from the edge; the drilling is for the convenience of hanging the metal sample.

[0036] In a preferred embodiment, the pre-grinding equipment is a metallographic pre-grinding machine; scratches and a passivation layer on the surface of the sample are removed by pre-grinding.

[0037] In a preferred embodiment, the step-by-step grinding is performed by using sandpapers with mesh sizes of 120, 240, and 600.

[0038] In a preferred embodiment, the arithmetic mean roughness of the metal sample is 0.4-0.5 μm.

[0039] In a preferred embodiment, the metal material to be polished includes stainless steel or titanium alloy.

[0040] In a preferred embodiment, when the metal material to be polished is stainless steel, the polishing liquid is an ammonium sulfate solution with a mass concentration of 3-5%. Using ammonium sulfate solution as a polishing liquid to polish stainless steel has the advantages of being environmentally friendly, having high surface quality, and being highly adjustable.

[0041] In a preferred embodiment, the ammonium sulfate solution is prepared by mixing ammonium sulfate powder and deionized water, and then placing the mixture on a magnetic stirrer for 5 minutes to obtain the ammonium sulfate solution.

[0042] In a preferred embodiment, when the metal material to be polished is a titanium alloy, the polishing liquid is a mixed aqueous solution of ammonium fluoride and potassium fluoride; the concentration of ammonium fluoride in the polishing liquid is 2.52-3.23%, and the concentration of potassium fluoride is 13.45-16.39%. The use of a mixed aqueous solution of ammonium fluoride and potassium fluoride as a polishing liquid to polish titanium alloy has the advantages of good chemical stability, strong pertinence, high polishing efficiency, good surface quality of titanium alloy, and relatively good environmental friendliness.

[0043] In a preferred embodiment, the temperature of the polishing liquid is 70-90° C. The present invention controls the temperature of the polishing liquid within the above range, which has the advantages of improving polishing efficiency, improving surface quality and enhancing polishing uniformity. If the temperature of the polishing liquid is too low, the polishing efficiency will be reduced, the polishing will be uneven, and the surface roughness will be increased. If the temperature of the polishing liquid is too high, the surface of the material will be damaged and the composition of the polishing liquid will be unstable.

[0044] In a preferred embodiment, the voltage of the direct current is 250-400 V. The present invention controls the voltage of the direct current within the above range, which is conducive to ensuring the polishing effect. Too low or too high a voltage will increase the roughness of the metal material surface.

[0045] In a preferred embodiment, the frequency of the ultrasonic vibration is 28-40kHz. The present invention controls the frequency of the ultrasonic vibration within the above range, which has the advantages of improving processing efficiency and processing quality. Too low a frequency will lead to insufficient energy density and it is difficult to achieve the ideal processing effect. Too high a frequency will increase the power consumption of the equipment and aggravate the vibration attenuation, affecting the processing stability.

[0046] In a preferred embodiment, the conductive material includes stainless steel, platinum or copper.

[0047] In a preferred embodiment, the time is counted from the time when a stable gas layer is generated on the surface of the metal sample, and the polishing time is 10-30 minutes. During the ultrasound-assisted electrolyte plasma process, a large number of bubbles will be generated on the surface of the metal sample, forming a very high density, and finally the bubbles will be connected to form a layer of gas film, forming a stable gas layer. At this time, the surface of the metal sample is surrounded by the gas film and is not in direct contact with the liquid.

[0048] In a preferred embodiment, a post-processing step is also included after polishing; the post-processing includes: first rinsing with deionized water, then ultrasonic cleaning with anhydrous ethanol, then absorbing the residual liquid on the surface of the sample with filter paper, and then quickly blowing it dry with compressed air.

[0049] The room temperature in the embodiments of the present invention refers to "25±2°C".

[0050] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources.

[0051] Example 1

[0052] A method for precision polishing of an ultrasonic-assisted electrolyte plasma, the structural schematic diagram of the device used is shown in Figure 1 :

[0053] (1) The 316 stainless steel plate to be polished was cut into a 20×15×3 mm sample using a grinding wheel cutter, and then a 2 mm through hole was drilled on the top of the sample using a drilling machine. The scratches and passivation layer on the surface of the sample were removed using a metallographic pre-grinding machine, and then 120 mesh, 240 mesh, and 600 mesh sandpaper were used for step-by-step grinding to obtain a 316 stainless steel sample with an arithmetic mean roughness of 0.4 μm;

[0054] (2) 33 g of ammonium sulfate solid powder was mixed with 1100 mL of deionized water, and then placed on a magnetic stirrer for 5 min to allow uniform dissolution, to obtain an ammonium sulfate solution with a concentration of 3 wt % as a polishing liquid;

[0055] (3) placing a polishing pool in a fume hood, then pouring the polishing liquid prepared in step (2) into the polishing pool, and using a temperature control sensor to keep the temperature of the polishing liquid constant at 85° C., then hanging the 316 stainless steel sample prepared in step (1) as an anode and immersing it in the polishing pool, and at the same time immersing another stainless steel in the polishing pool as a cathode, and installing an ultrasonic auxiliary device under the polishing pool;

[0056] (4) Passing a 300 V direct current into the cathode and anode in step (3), and applying ultrasonic vibration with a frequency of 40 kHz to the polishing liquid, and starting the timing when the current of the polishing liquid is stable, the current density at different positions on the surface of the 316 stainless steel sample is consistent, and a stable gas layer is generated on the surface of the 316 stainless steel sample, and polishing is performed for 15 minutes to obtain a polished 316 stainless steel sample;

[0057] (5) Turn off the power supply, use a fixture to take out the polished 316 stainless steel sample obtained in step (4), then rinse it with deionized water, ultrasonically clean it with anhydrous ethanol, then use filter paper to absorb the residual liquid on the surface of the sample, and then quickly blow it dry with compressed air to obtain a 316 stainless steel sample with a bright surface, which is then sealed in a vacuum packaging bag for storage.

[0058] Figure 2 The current changes with time after the polishing liquid current stabilizes in step (4) of Example 1. Figure 2It can be seen that the current value of the polishing liquid fluctuates around 1.576A. Based on this, it can be calculated that the current density on the sample surface is maintained at 0.533A / cm 2 Under this condition, the stainless steel samples can meet the basic conditions for electrolyte plasma polishing.

[0059] Figure 3 This is the surface morphology of the 316 stainless steel sample in step (1) of Example 1. Figure 4 This is the surface morphology of the 316 stainless steel sample after polishing in step (4) of Example 1. Figure 3 and Figure 4 It can be seen that the surface of the stainless steel sample before polishing is covered with scratches, while after polishing using the method in Example 1, the scratches on the surface of the stainless steel sample are basically removed, and the pitting is also removed, and the surface is basically smooth.

[0060] Figure 5 This is a three-dimensional surface morphology image of the 316 stainless steel sample in step (1) of Example 1. Figure 6 The three-dimensional surface morphology of the bright 316 stainless steel sample obtained in Example 1. Figure 5 and Figure 6 It can be seen that the average roughness of the 316 stainless steel sample before polishing is 0.396 μm, and the average surface roughness of the 316 stainless steel sample after polishing is 0.141 μm, indicating that the ultrasonic-assisted electrolyte plasma precision polishing method provided by the present invention can effectively reduce the surface roughness of the metal and improve the surface accuracy.

[0061] Example 2

[0062] A method for precision polishing of an ultrasonic-assisted electrolyte plasma, the structural schematic diagram of the device used is shown in Figure 1 :

[0063] (1) The 316 stainless steel plate to be polished was cut into a 20×15×3 mm sample using a grinding wheel cutter, and then a 2 mm through hole was drilled on the top of the sample using a drilling machine. The scratches and passivation layer on the surface of the sample were removed using a metallographic pre-grinding machine, and then 120 mesh, 240 mesh, and 600 mesh sandpaper were used for step-by-step grinding to obtain a 316 stainless steel sample with an arithmetic mean roughness of 0.5 μm;

[0064] (2) 35 g of ammonium sulfate solid powder and 1000 mL of deionized water were mixed, and then placed on a magnetic stirrer for 5 min to allow uniform dissolution, to obtain an ammonium sulfate solution with a concentration of 3.5 wt % as a polishing liquid;

[0065] (3) placing a polishing pool in a fume hood, then pouring the polishing liquid prepared in step (2) into the polishing pool, and using a temperature control sensor to keep the temperature of the polishing liquid constant at 85° C., then hanging the 316 stainless steel sample prepared in step (1) as an anode and immersing it in the polishing pool, and at the same time immersing another stainless steel in the polishing pool as a cathode, and installing an ultrasonic auxiliary device under the polishing pool;

[0066] (4) Passing a 280 V direct current into the cathode and anode in step (3), and applying ultrasonic vibration with a frequency of 40 kHz to the polishing liquid, and starting the timing when the current of the polishing liquid is stable, the current density at different positions on the surface of the 316 stainless steel sample is consistent, and a stable gas layer is generated on the surface of the 316 stainless steel sample, and polishing is performed for 15 minutes to obtain a polished 316 stainless steel sample;

[0067] (5) Turn off the power supply, use a fixture to take out the polished 316 stainless steel sample obtained in step (4), then rinse it with deionized water, ultrasonically clean it with anhydrous ethanol, then use filter paper to absorb the residual liquid on the surface of the sample, and then quickly blow it dry with compressed air to obtain a 316 stainless steel sample with a bright surface, which is then sealed in a vacuum packaging bag for storage.

[0068] Example 3

[0069] A method for precision polishing of an ultrasonic-assisted electrolyte plasma, the structural schematic diagram of the device used is shown in Figure 1 :

[0070] (1) The titanium alloy plate to be polished was cut into a 20×15×3 mm sample using a grinding wheel cutter, and then a 2 mm through hole was drilled on the top of the sample using a drilling machine. The scratches and passivation layer on the surface of the sample were removed using a metallographic pre-grinding machine, and then 120 mesh, 240 mesh, and 600 mesh sandpaper were used for step-by-step grinding to obtain a titanium alloy sample with an arithmetic mean roughness of 0.5 μm;

[0071] (2) 30 g of ammonium fluoride, 160 g of potassium fluoride and 1000 mL of deionized water were mixed and then placed on a magnetic stirrer for 5 min to allow uniform dissolution, thereby obtaining a mixed aqueous solution with an ammonium fluoride concentration of 2.52% and a potassium fluoride concentration of 13.45%, which was used as a polishing liquid;

[0072] (3) placing a polishing pool in a fume hood, then pouring the polishing liquid prepared in step (2) into the polishing pool, and using a temperature control sensor to keep the temperature of the polishing liquid constant at 78° C., then hanging the titanium alloy sample prepared in step (1) as an anode and immersing it in the polishing pool, while immersing platinum in the polishing pool as a cathode, and installing an ultrasonic auxiliary device under the polishing pool;

[0073] (4) Passing a 380 V direct current into the cathode and anode in step (3), and applying ultrasonic vibration with a frequency of 35 kHz to the polishing liquid, and starting the timing when the current of the polishing liquid is stable, the current density at different positions on the surface of the 316 stainless steel sample is consistent, and a stable gas layer is generated on the surface of the 316 stainless steel sample, and polishing is performed for 20 minutes to obtain a polished titanium alloy sample;

[0074] (5) Turn off the power supply, use a clamp to take out the polished titanium alloy sample obtained in step (4), then rinse it with deionized water, ultrasonically clean it with anhydrous ethanol, then use filter paper to absorb the residual liquid on the surface of the sample, and then quickly blow it dry with compressed air to obtain a titanium alloy sample with a bright surface, which is then sealed in a vacuum packaging bag for storage.

[0075] Comparative Example 1

[0076] The difference from Example 1 is that the step (4) of applying ultrasonic vibration with a frequency of 40 kHz to the polishing liquid is omitted, and the rest is the same as Example 1.

[0077] Comparative Example 2

[0078] The difference from Example 1 is that in step (4), ultrasonic vibration with a frequency of 50 kHz is applied to the polishing liquid, and the rest is the same as Example 1.

[0079] Comparative Example 3

[0080] The difference from Example 1 is that in step (4), ultrasonic vibration with a frequency of 25 kHz is applied to the polishing liquid, and the rest is the same as Example 1.

[0081] Surface roughness test:

[0082] Surface roughness refers to the distance between two peaks or two valleys on the surface of a material. It is a microscopic geometric error. The smaller the surface roughness, the smoother the surface. Surface roughness has a great influence on the use of parts. Generally speaking, the smaller the surface roughness value, the better the fit quality, the less wear, and the longer the service life of parts.

[0083] The surface roughness of the bright metal samples obtained in Examples 1 to 3 and the surface roughness of the metal samples obtained in Comparative Examples 1 to 3 were tested using a roughness tester. Three test points were tested on each sample, and the arithmetic average roughness Ra value was recorded. The results are shown in Table 1.

[0084] Table 1 Roughness of metal samples in Examples 1 to 3 and Comparative Examples 1 to 3

[0085]

[0086]

[0087] As can be seen from Table 1, after polishing using the ultrasonic-assisted electrolyte plasma precision polishing method provided by the present invention, the roughness values ​​at the three measuring points of the metal material decreased from 0.4-0.5 μm after step-by-step grinding to an average of 0.141-0.144 μm, meeting the requirements of precision polishing. However, in Comparative Examples 1 to 3, ultrasonic vibration was omitted and the frequency of ultrasonic vibration was changed, respectively, and the roughness values ​​at the three measuring points of the metal material after polishing decreased from 0.4-0.5 μm after step-by-step grinding to an average of 0.162-0.177 μm, failing to meet the requirements of precision polishing.

[0088] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for precision polishing of an ultrasonic-assisted electrolyte plasma, characterized in that: The following steps are involved: The metal material to be polished is pretreated to obtain a metal sample; the metal sample is immersed in the polishing liquid as an anode, and the conductive material is immersed in the polishing liquid as a cathode, direct current is passed through the anode and the cathode for electrolyte plasma treatment, and ultrasonic vibration is applied for polishing to complete the precision polishing of the metal material to be polished.

2. The method for precision polishing of ultrasonic-assisted electrolyte plasma according to claim 1, characterized in that: The pre-processing includes cutting, drilling, pre-grinding and step-by-step grinding.

3. The method for precision polishing of ultrasonic-assisted electrolyte plasma according to claim 1, characterized in that: The arithmetic mean roughness of the metal sample is 0.4-0.5 μm.

4. The method for precision polishing of ultrasonic-assisted electrolyte plasma according to claim 1, characterized in that: The metal material to be polished includes stainless steel or titanium alloy.

5. The method for precision polishing of ultrasonic-assisted electrolyte plasma according to claim 4, characterized in that: When the metal material to be polished is stainless steel, the polishing liquid is an ammonium sulfate solution with a mass concentration of 3-5%; when the metal material to be polished is titanium alloy, the polishing liquid is a mixed aqueous solution of ammonium fluoride and potassium fluoride.

6. The method for precision polishing of ultrasonic-assisted electrolyte plasma according to claim 1, characterized in that: The temperature of the polishing liquid is 70-90°C.

7. The method for precision polishing of ultrasonic-assisted electrolyte plasma according to claim 1, characterized in that: The voltage of the direct current is 250-400V.

8. The method for precision polishing of ultrasonic-assisted electrolyte plasma according to claim 1, characterized in that: The frequency of the ultrasonic vibration is 28-40 kHz.

9. The method for precision polishing of ultrasonic-assisted electrolyte plasma according to claim 1, characterized in that: The conductive material includes stainless steel, platinum or copper.

10. The method for precision polishing of ultrasonic-assisted electrolyte plasma according to claim 1, characterized in that: The timing starts when a stable gas layer is generated on the surface of the metal sample, and the polishing time is 10-30 minutes.

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