Polishing process for metal part with anodic oxide film

Abstract

The invention relates to the technical field of metal surface treatment, in particular to a polishing process for a metal part with an anodic oxide film. The polishing process for the metal part with the anodic oxide film is provided for solving the problems that in an existing anodic oxide film polishing process, the removal amount of an oxide layer is large, scratches are likely to be left on the surface, and glossiness is poor. The polishing jig fixed with the metal part is inversely arranged on a woolen blanket of a polishing disc, and a polishing solution containing 30-80 nm silicon dioxide particles and having the pH value of 9-11 is used for polishing; after polishing, pure water cleaning, neutral cleaning agent ultrasonic cleaning, pure water secondary cleaning and drying are carried out to complete machining, the removal amount of an oxide layer of the metal part can be only about 1 micron, the glossiness is improved to 400 from 300, scratches are reduced, the surface integrity and optical performance are improved, the metal part polishing process is suitable for high-end electronic components, the process is stable, and mass production is facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal surface treatment, in particular to a polishing process for metal parts with an anodic oxidation film. BACKGROUND

[0002] Anodic oxidation technology is widely used in the surface treatment of metal parts of mobile intelligent devices. For example, through an anodic oxidation process, a dense oxide film can be formed on the surface of an aluminum alloy, which can significantly improve the corrosion resistance, wear resistance and surface hardness of the aluminum alloy, and also provides a good substrate for subsequent coloring, sealing and other processing procedures. Therefore, it plays an important role in many industries such as aerospace, automobile manufacturing, electronic communication and building decoration.

[0003] However, the oxide film formed on the surface of the metal material after anodic oxidation often has defects such as micro concave-convex, burrs and oxidation residues, which need to be further improved by polishing treatment. At present, there are still many problems to be solved in the polishing process of the anodic oxidation film of metal materials: first, the existing polishing process generally has the problem of excessive removal of the anodic oxidation layer. In order to achieve the ideal surface flatness, it is often necessary to remove a thick oxide film, which will result in insufficient effective protective thickness of the oxide film and reduce the overall performance of the metal material; second, scratches are easily left on the surface of the metal material during polishing. Traditional polishing uses flat polishing liquid mainly composed of aluminum oxide and damping cloth polishing, which relies on the mechanical friction between the abrasive and the surface. If the abrasive particle size is not properly selected or the operation parameter control is not good, and because the aluminum oxide particles are hard, new scratches are easily produced on the surface of the oxide film, which destroys the surface integrity and affects the appearance quality and use performance of the product; third, the gloss of the product after polishing is poor. The traditional polishing process described above cannot form a uniform and bright mirror surface effect on the surface of the oxide film of the metal material, resulting in insufficient surface gloss of the product and failing to meet the requirements of high-end products for appearance decoration.

[0004] Therefore, in view of the problems of large removal of the oxide layer, easy scratches on the surface and poor gloss during the polishing process of the anodic oxidation film of the metal material, it is necessary to develop a polishing process that is efficient, precise and can significantly improve the surface quality of the anodic oxidation film of the metal material. SUMMARY

[0005] Based on this, it is necessary to aim at the above-mentioned shortcomings, provide a kind of polishing process for metal parts with anodic oxide film, the polishing liquid used includes: pure water, alkaline adjusting agent, dispersing agent and stabilizer, the polishing machine used includes: the polishing disc rotated by motor drive, woolen blanket is set on the polishing disc, polishing liquid tank is set above the woolen blanket and is equipped with valve, polishing fixture is opened with the recess matched with metal, the woolen blanket includes cashmere layer, EVA buffer layer and back adhesive layer from top to bottom, the Shore hardness of EVA buffer layer is 30±5 degrees, the woolen blanket is pasted on the polishing disc by back adhesive layer, the polishing liquid tank is used to contain polishing liquid, the polishing liquid also includes the silicon dioxide particles with 30% solid content, the particle size of the silicon dioxide particles is 30~80nm, the pH value of the polishing liquid is 9~11, specifically including the following steps: Step S100, the woolen blanket is fixed on the polishing disc of the polishing machine, and the woolen blanket rotates synchronously with the polishing disc; Step S200, the metal part with anodic oxide film on the surface after anodic oxidation is fixed in the recess of the polishing fixture; Step S300, the polishing fixture is inverted on the woolen blanket; Step S400, open all the valves of the polishing liquid tank, and the polishing liquid continuously drops on the woolen blanket. The motor of the polishing machine drives the polishing disc to rotate, and the polishing disc drives the woolen blanket on it to rotate to start polishing. Step S500, polishing is finished, the motor of the polishing machine and the valve of the polishing liquid tank are closed, the polishing fixture is removed from the woolen blanket, and the metal part is removed from the recess of the polishing fixture. Step S600, the polished metal part is washed with pure water, then placed in neutral cleaning agent for ultrasonic cleaning, and then washed with pure water 2~3 times, each time for 30s. Step S700, the cleaned metal part is placed in a drying oven. Step S800, after drying, enter the next process.

[0006] Preferably, in step S300, a stainless steel plate with the same shape as the fixture is used to press on the fixture, which is used to make the metal part closely adhere to the woolen blanket, and the pressing force provided by the stainless steel plate and the fixture is 0.2Mpa~0.25Mpa.

[0007] Preferably, the polishing machine further comprises a stopper arranged above the woolen blanket and adhered to the fixture, which is used to limit the movement of the fixture in horizontal direction.

[0008] Preferably, in step S400, the rotating speed of the woolen blanket is 18rpm, and the polishing time is 160s.

[0009] Preferably, in step S400, the woolen blanket rotates clockwise for 60s~100s and counterclockwise for the rest of the time when the polishing time is totally 160s.

[0010] Preferably, the particle size of the silica particles in the polishing liquid is 60nm.

[0011] Preferably, the alkaline regulator is sodium hydroxide or ammonia water.

[0012] Preferably, in step S600, the frequency of the ultrasonic cleaning is 40kHz and the cleaning time is 40s.

[0013] Preferably, in step S700, the drying oven is set to a drying temperature of 50±5℃ and a drying time of 10~15min.

[0014] The polishing process for metal parts with anodic oxide film described above, by using a polishing liquid containing 30~80nm silica particles (pH 9~11) in combination with woolen blanket polishing, combined with the fixing of the appropriate jig and the precise cleaning and drying process, realizes the reduction of rigid friction by nano-silica particles, in combination with the flexible contact of the woolen blanket, greatly reduces the removal amount of the oxide layer (only about 1μm), and guarantees the protection performance of the oxide film; the dispersant in the polishing liquid inhibits particle agglomeration, and small particle size particles and woolen blankets cooperatively reduce surface scratches, improving the integrity of the anodic oxide film; fine grinding reduces microscopic concave-convex and light scattering, significantly improves the surface gloss, and meets the appearance and gloss performance requirements of metal parts. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The flowchart of the polishing process for metal parts with anodic oxide film in an embodiment of the present application; Figure 2 The polishing process for metal parts with anodic oxide film in an embodiment of the present application is shown in the process flow diagram.

[0016] Reference signs: 100-woolen blanket, 200-limiter, 300-jig, 400-stainless steel plate. DETAILED DESCRIPTION

[0017] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the drawings. In the following description, a lot of specific details are set forth in order to fully understand the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the scope of the present application, so the present application is not limited to the specific embodiments disclosed below.

[0018] The application discloses a polishing process for metal parts with anodic oxidation film, as shown in Figure 1 、 Figure 2 In the embodiment, the metal part is an aluminum alloy part (such as commonly used aluminum alloy 6061, 6063, etc.), and after anodic oxidation, the aluminum alloy part forms an aluminum oxide film on the surface, the film thickness is 18-26 microns, the hardness of the aluminum oxide film is 450-500 HV, and the initial gloss is low. The polishing process specifically comprises the following steps: Step S100, fix the woolen blanket on the polishing disc of the polishing machine, and the woolen blanket rotates synchronously with the polishing disc; Step S200, fix the aluminum alloy part with an oxidation film on the surface after anodic oxidation on the polishing fixture, the polishing fixture has a groove matched with the aluminum alloy part, and the aluminum alloy part is fixed in the groove; Step S300, invert the polishing fixture on the woolen blanket; Step S400, open the polishing liquid valve and the polishing machine, the polishing liquid continuously drips on the woolen blanket of the polishing disc, the polishing disc drives the woolen blanket thereon to rotate and starts polishing, and the polishing liquid comprises pure water, silica particles with a solid content of 30%, an alkaline adjusting agent, a dispersing agent and a stabilizing agent. The particle size of the silica particles is 30-80 nm, the pH value of the polishing liquid in the particle size range is 9-11, the pure water can provide a stable liquid phase environment to avoid impurities affecting the polishing effect, and the silica particles with a particle size of 30-80 nm used in the embodiment can simultaneously reduce scratches and improve polishing efficiency. The alkaline environment with a pH value of 9-11, the dispersing agent and the stabilizing agent can improve the dispersibility of the silica particles in the polishing liquid, prevent the silica particles from agglomeration, and improve the stability of the polishing liquid; Step S500, after polishing, the polishing machine and the polishing liquid valve are closed, the polishing fixture is taken off from the polishing disc, and the metal part is taken off from the groove of the polishing fixture; Step S600, the polished metal part is cleaned with pure water, which can clean most of the residual polishing liquid on the surface of the aluminum alloy part, and then the aluminum alloy part is placed in a neutral cleaning agent for ultrasonic cleaning. The ultrasonic cleaning can clean the fine residues and impurities in the gap, and then the metal part is cleaned with pure water for 2-3 times, each time for 30 seconds. The pure water removes the cleaning agent residues, and subsequent drying will not leave water stains; Step S700, place the cleaned aluminum alloy part in a drying box for drying; Step S800, take out the aluminum alloy part after drying, and enter the next process.

[0019] The polishing process for metal parts with anodic oxidation film provided by the present application polishes the aluminum alloy parts by using a woolen blanket and a silica polishing liquid. In the present embodiment, in step S400, the rotating speed of the woolen blanket is 18 rpm, the polishing time is 160 s, the particle size of the silica particles is 60 nm, the alkaline adjusting agent for adjusting the polishing liquid is sodium hydroxide or ammonia water, the frequency of ultrasonic cleaning is 40 kHz, and the cleaning time is 40 s. The gloss of the anodic oxidation layer of the aluminum alloy part is increased from 300 to 400. The polishing removal amount is only about 1 μm, the anodic oxidation layer is not damaged, and the strict demand of high-end camera parts on surface brightness can be met. The polishing process of the present application can eliminate the slight roughness generated in the anodic oxidation process, reduce light scattering, improve the light transmission consistency of aluminum alloy or other metal products such as camera modules, and optimize the optical performance and appearance quality of the products. Compared with the traditional flat polishing liquid + damping cloth process, it is more suitable for high-end camera parts (such as smart phone lens ring, laser radar shell), solves the problem of insufficient gloss after hard anodization, and expands the application of metal anodization products in the high-end electronic field. Through precise control of the composition of the polishing liquid (such as the particle size of the silica, the pH value), the polishing parameters (rotating speed, time, pressure), the jig and the auxiliary components, and the cleaning and drying process, the polishing effect consistency and stability are ensured, which is beneficial to large-scale mass production application.

[0020] In one embodiment, as shown in Figure 2 In step S300, after the polishing jig is inverted on the woolen blanket, a stainless steel plate with the same shape as the jig is pressed on the jig. The stainless steel plate is used to make the metal part closely contact with the woolen blanket. The stainless steel plate and the jig together provide a downward pressure of 0.2 Mpa~0.25 Mpa. In this pressure range, the surface of the metal part can be fully contacted with the rotating woolen blanket (and the silica particles in the attached polishing liquid), the polishing efficiency is improved, and the polishing liquid is not damaged by excessive pressure. The silica particles (30~80 nm) in the polishing liquid can more uniformly act on the surface of the oxidation film. Through the synergistic effect of mechanical grinding and chemical corrosion (slight dissolution in alkaline environment), the polishing intensity of each area is consistent, the uniformity of the surface finish is significantly improved, and local polishing deficiency or excessive polishing is avoided.

[0021] In one embodiment, as shown in Figure 2As shown, the polishing machine used in the polishing process provided by the present application further comprises a limiting device arranged above the woolen blanket and matched with the jig, which is used to limit the movement of the jig in the horizontal direction. The limiting device and the jig are matched in shape and contacted to form a physical constraint. The limiting device provides a reverse constraint force in the horizontal direction for the jig through the matched surface, offsets the displacement force generated during polishing, firmly limits the jig in the preset polishing area, and ensures that the contact position and relative attitude of the metal part and the woolen blanket are always stable. The use of the limiting device can significantly improve the accuracy and uniformity of the surface finish; reduce the interference of factors such as jig placement deviation and rotational force fluctuation, reduce the polishing difference of the same batch or different batches of parts, and enhance the process stability and product consistency; at the same time, it can reduce the irregular friction between the jig edge and the woolen blanket, reduce the wear of the jig and the risk of local damage of the woolen blanket, prolong the service life of consumables; it can also ensure the uniform distribution of polishing liquid in the contact area, make the grinding action of nano silicon dioxide particles and the chemical action of alkaline environment more stable, and indirectly improve the polishing efficiency.

[0022] In an embodiment, the woolen blanket comprises, from top to bottom, a cashmere layer, an EVA buffer layer and a back adhesive layer. The Shore hardness of the EVA buffer layer is 30±5 degrees. The woolen blanket is pasted on the polishing disc through the back adhesive layer. In this embodiment, the back adhesive of the back adhesive layer is 3M adhesive. The back adhesive layer is used to paste and fix the woolen blanket on the polishing disc, to avoid displacement or slipping of the polishing disc during polishing due to high-speed rotation of the polishing disc, and to ensure synchronous and stable movement of the woolen blanket and the polishing disc; and the EVA buffer layer with a Shore hardness of 30±5 degrees has appropriate elasticity, can adapt to the fine concave-convex surface of the metal part through its own deformation, and can make the upper cashmere layer more closely and uniformly adhere to the surface of the part. At the same time, the EVA buffer layer can buffer the local impact force during polishing, avoid pressure concentration caused by rigid contact, and realize softer and more uniform polishing contact in cooperation with the grinding action of the cashmere layer. The stable fixation of the back adhesive layer improves the process stability and reduces the polishing deviation caused by displacement of the woolen blanket; the elastic adhesion of the EVA buffer layer enhances the uniformity of the contact between the surface of the part and the cashmere layer, effectively improves the problem of local insufficient or excessive polishing, and improves the consistency of the surface finish; the buffer layer can also reduce the risk of impact damage to the anodic oxide film during polishing, and protect the integrity of the oxide film.

[0023] In an embodiment, in step S400, the blanket is rotated clockwise for 60-100 seconds, and counterclockwise for the rest of the time. The alternating rotation changes the direction of the grinding force of the silica particles in the polishing liquid and the blanket on the surface of the oxide film of the metal part, avoids the accumulation of directional scratches or local stress concentration caused by continuous grinding in a single direction, and enables the uniform grinding of defects such as small protrusions and burrs at different angles and in different directions. At the same time, the direction switching balances the stress on the edges, corners, and grooves of the part, which are prone to excessive friction, and reduces the local oxide film wear deviation caused by long-term action in a single direction. The improved embodiment has the advantages that the alternating rotation can effectively eliminate the directional scratches caused by single-direction polishing, improve the fineness and uniformity of the surface finish of the part, balance the grinding intensity of different areas of the part, avoid excessive polishing or damage to the oxide film due to continuous one-way friction on the edge or protruding parts, and protect the integrity of the oxide film. At the same time, the grinding force in different directions can more comprehensively act on the surface of the oxide film, making the grinding action of the nano-silica particles more sufficient, indirectly improving the polishing efficiency, reducing rework caused by incomplete grinding in a single direction, and enhancing process stability and product quality consistency.

[0024] In an embodiment, the drying oven is set to a drying temperature of 50±5℃ and a drying time of 10-15 minutes. The drying stable interval belongs to low-temperature drying, which protects the integrity and performance stability of the anodic oxide film and avoids quality defects of the oxide film caused by high temperature. The appropriate time ensures that the water is completely evaporated, preventing problems such as rusting, surface water stains, or spots caused by residual moisture, and improving the surface cleanliness. The clear temperature and time parameters make the drying process more controllable, reduce the quality differences of different batches of parts caused by unstable drying conditions, and enhance process consistency. At the same time, the low-temperature setting reduces energy consumption, and the reasonable time control does not prolong the production cycle, balancing production efficiency and cost control while ensuring drying effect.

[0025] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, but as long as the combinations of the technical features do not contradict, they should be considered within the scope of the present disclosure.

[0026] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be construed as limiting the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the protection scope of the present patent should be subject to the appended claims.

Claims

1. A polishing process for metal parts with an anodized film, wherein the polishing solution used comprises: The invention comprises pure water, an alkaline regulator, a dispersant, and a stabilizer, characterized in that the polishing machine used includes: a polishing disc driven to rotate by a motor, a wool blanket disposed on the polishing disc, a polishing liquid tank with a valve disposed above the wool blanket, and a polishing fixture with grooves matching the metal. The wool blanket comprises, from top to bottom, a cashmere layer, an EVA buffer layer, and an adhesive backing layer. The Shore hardness of the EVA buffer layer is 30±5 degrees. The wool blanket is adhered to the polishing disc via the adhesive backing layer. The polishing liquid tank is used to contain the polishing liquid. The polishing liquid further includes silica particles with a solid content of 30%, the particle size of the silica particles being 30~80 nm, and the pH value of the polishing liquid being 9~11. The invention specifically includes the following steps: Step S100: Fix the wool blanket on the polishing disc of the polishing machine, and the wool blanket rotates synchronously with the polishing disc; Step S200: Fix the metal part with an oxide film on the anodized surface into the groove of the polishing fixture; Step S300: Invert the polishing fixture onto the wool blanket; Step S400: Open the valves of all polishing liquid tanks, and the polishing liquid will continuously drip onto the wool blanket. Start the motor of the polishing machine to drive the polishing disc to rotate, and the polishing disc will drive the wool blanket on it to rotate to start polishing. Step S500: Polishing is complete. Turn off the motor of the polishing machine and the valve of the polishing liquid tank. Remove the polishing fixture from the wool blanket and remove the metal parts from the groove of the polishing fixture. Step S600: Clean the polished metal parts with pure water, then place the metal parts in a neutral cleaning agent for ultrasonic cleaning, and then clean the metal parts with pure water 2-3 times, 30 seconds each time. Step S700: Place the cleaned metal parts into a drying oven to dry them; After step S800 and drying are completed, proceed to the next process.

2. The polishing process for metal parts with an anodic oxide film according to claim 1, characterized in that, In step S300, a stainless steel plate of the same shape as the fixture is pressed onto the fixture. The stainless steel plate is used to ensure that the metal parts are tightly attached to the wool blanket. The downward pressure provided by the stainless steel plate and the fixture is 0.2 MPa to 0.25 MPa.

3. The polishing process for metal parts with anodized films according to claim 1, characterized in that, The polishing machine also includes a limiter disposed above the wool blanket and in contact with the fixture, the limiter being used to restrict the movement of the fixture in the horizontal direction.

4. The polishing process for metal parts with an anodic oxide film according to claim 1, characterized in that, In step S400, the wool blanket rotates at 18 rpm and the polishing time is 160 s.

5. The polishing process for metal parts with an anodic oxide film according to claim 4, characterized in that, In step S400, when the total polishing time is 160s, the wool blanket rotates clockwise for 60s to 100s and then counterclockwise for the remaining time.

6. The polishing process for metal parts with an anodic oxide film according to claim 1, characterized in that, The silica particles in the polishing slurry have a particle size of 60 nm.

7. The polishing process for metal parts with an anodic oxide film according to claim 1, characterized in that, The alkalinity regulator is sodium hydroxide or ammonia.

8. The polishing process for metal parts with an anodic oxide film according to claim 1, characterized in that, In step S600, the ultrasonic cleaning frequency is 40kHz and the cleaning time is 40s.

9. The polishing process for metal parts with an anodic oxide film according to claim 1, characterized in that, In step S700, the drying chamber is set to a drying temperature of 50±5℃ and a drying time of 10~15min.

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