Method of preparing a self-lubricating coating for a stir-friction additive guide mechanism and guide mechanism

Abstract

This invention discloses a method for preparing a self-lubricating coating for a stirring friction additive manufacturing guide mechanism and a guide mechanism, comprising the following steps: Step 1, incoming part inspection; Step 2, preparation of silicon nitride powder; Step 3, spraying and assembly; Step 4, thermal spraying: silicon nitride powder is filled through the filler port 8, fed along the feed pipe 7 into the flame nozzle 6, heated to a molten state at high temperature, and then sprayed onto the inner surface; Step 5, device movement; Step 6, result inspection. The silicon nitride ceramic self-lubricating structure can improve the surface hardness of the cavity wall, solving the problem that the stirring head cannot fully soften the rod due to insufficient hardness; it also solves the problem of lubrication failure under additive manufacturing conditions where lubricants are not applicable. The silicon nitride ceramic self-lubricating coating has good self-lubricating stability; therefore, the stirring friction additive manufacturing guide lubrication device of this invention has good practical value and application potential.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing, and specifically relates to a method for preparing a self-lubricating coating for a friction stir additive guide mechanism and the guide mechanism itself. Background Technology

[0002] Additive Friction Stir Deposition (AFSD) is an advanced manufacturing method that combines friction stir welding and additive manufacturing technologies, and it is attracting increasing attention in the industrial manufacturing field. AFSD is a manufacturing method that utilizes the frictional heat generated between the additive material and the substrate to transform the additive material into a viscoplastic material. Lubrication is a critical aspect of AFSD, directly determining the overall performance of the additive components. In friction stir additive manufacturing without lubrication, the manufactured components have an uneven appearance, and the density varies even within a small range. Within the guiding device, prolonged friction between the additive rod and the cavity wall without lubrication can easily cause wear in the hollow cavity, reducing the service life of the additive manufacturing device. Existing thermal spraying equipment cannot complete the coating of silicon nitride ceramic coating in confined spaces, and most lubrication methods use graphite lubricating sprays or greases, which, when applied to the surface of the additive rod (wire), provide some lubrication. However, after experimental testing, the effect of using graphite directly as a lubricating material is not ideal; the additive appearance is poor, with flash and macroscopic cracks, and the mechanical properties are poor. Research has found that while graphite is introduced as a lubricant, graphite particles also infiltrate the additive deposition layer as impurities, distributing between crystal gaps and causing uneven changes in the overall component performance. Therefore, designing a material with self-lubricating properties can not only improve lubrication but also significantly optimize the overall performance of additive components. For example, Chinese patents CN219664943U and CN220242115U propose automatic lubrication to reduce mold wear, achieving automated lubrication. However, current lubrication technologies neglect the inherent self-lubricating properties of the material itself. Silicon nitride ceramics are engineering materials with excellent performance, exhibiting good stability and wear resistance under high temperature, high pressure, and extreme environments. The self-lubricating mechanism of silicon nitride ceramics is one of its unique properties. When silicon nitride ceramics are exposed to air, the surface silicon oxide film reacts with water vapor to form a hydrophilic silicon hydroxide layer, which, after adsorbing water molecules, forms a lubricating film on the surface of the silicon nitride ceramic. Meanwhile, the microstructure of silicon nitride ceramics itself is also conducive to its lubrication properties. The dense crystal structure and high hardness of silicon nitride ceramics make its surface relatively smooth, which greatly reduces frictional resistance, lowers the wear rate, and achieves a good self-lubricating effect. Summary of the Invention

[0003] The purpose of this invention is to provide a self-lubricating guide device for friction stir additive manufacturing and its preparation method, which solves the problems of poor lubrication and the inability of existing nozzles to process coatings in narrow spaces in the existing friction stir deposition additive manufacturing technology.

[0004] A method for preparing a self-lubricating coating for a friction stir additive guide mechanism includes the following steps:

[0005] Step 1, Incoming part inspection: Inspect the surface integrity of the processed part, grind the inner surface of the hollow guide device to obtain a smooth and regular surface, and use ultrasonic cleaning equipment or acetone to remove oil stains from the surface.

[0006] Step 2: Prepare silicon nitride powder;

[0007] Step 3, Spraying Assembly: Clamp the mixing head onto the thermal spraying device, extend the nozzle into the guide device, leaving a certain gap, and spray the exterior parts that do not need to be sprayed for protection.

[0008] Step 4, thermal spraying: Silicon nitride powder is filled into the filler port 8 and fed into the flame nozzle 6 through the feed pipe 7. After being heated to a molten state at high temperature, it is then sprayed onto the inner surface.

[0009] Step 5, device movement: The clamping fixture drives the stirring head to rotate at a constant speed of 4cm / s and pushes it forward at a speed of 3cm / s, forming a uniform and dense silicon nitride ceramic coating with a thickness of about 0.9mm on the inner surface.

[0010] Step 6, Result Inspection: After cooling, remove the stirring head and confirm that the coating is intact and has not been overheated or discolored. Sand the inner and outer surfaces.

[0011] The method, wherein step 2 involves preparing silicon nitride powder using a carbothermal reduction reaction, includes the following steps:

[0012] Step 21: Prepare water glass, silica, SiO2 sol, carbon black, nitrogen gas, and necessary reaction vessels;

[0013] Step 22: Prepare ammonium chloride solution and water glass solution for later use;

[0014] Step 23: Slowly pour the prepared ammonium chloride solution into the water glass solution while stirring with a magnetic heating stirrer until the solution completely forms a silica gel.

[0015] Step 24: Add a certain amount of water to dilute the silica gel, and control the amount of Na through filtration. + Percentage of mass;

[0016] Step 25: Mix silica gel and carbon black in a specific ratio. Then pour in distilled water, stir, and dry to obtain the silicon-carbon precursor.

[0017] Step 25: Weigh the prepared silicon-carbon precursor and place it in a crucible. Heat it by introducing nitrogen gas at different heating rates, and then keep it at the temperature to obtain silicon nitride powder.

[0018] Step 26, Purification: After the silicon nitride obtained from the high-temperature reaction is solidified and cooled, it is purified.

[0019] According to the method described in claim 2, the SiO2 sol selected in step 21 has an optimal particle size of 10 nm and the carbon black has an optimal particle size of 20-21 nm.

[0020] In the method described, the ammonium chloride solution in step 22 has a mass concentration of 40%, and the water glass solution has a mass concentration of 15%.

[0021] In the method described, the water glass solution in step 23 is 300 ml. When the amount added is 1 / 5 of the water glass solution, it completely transforms into silica gel. The reaction rate is optimal in the temperature range of 20℃-40℃.

[0022] The method described in step 24 involves selecting vacuum filtration as the filtration method and using slow-speed filter paper to reduce the loss of silica. + Quality percentage <1%.

[0023] In the method described, step 25 involves a silica gel to carbon black ratio of 2:1, a stirring time of 2 hours, and a drying temperature of 50℃-60℃. The carbon black is slowly poured in to ensure thorough mixing, and the addition of anhydrous ethanol can accelerate the mixing process.

[0024] In the method described above, step 26 involves weighing 5-6g of silicon precursor and heating it at two different heating rates: 5℃ / min to 300℃, 10℃ / min to 1195℃, and 5℃ / min to 1350℃. A drying temperature of 680℃ yields silicon nitride powder with higher purity.

[0025] In step 4 of the method, the mass of silicon nitride powder filled at one time is approximately 100g, the flame nozzle temperature range is 1000℃-2500℃, and the flame spraying speed is 30g-40g / min. The gas used for thermal spraying is 99% pure O2, which is used to heat and melt the silicon nitride powder.

[0026] A dedicated thermal spraying apparatus for implementing any of the methods described herein includes a flame nozzle (6), a feeding pipe (7), and a filling port (8); two flame nozzles (6) are installed at the tail end of the feeding pipe (7), and silicon nitride powder is filled from the filling port (8), fed into the flame nozzle (6) along the feeding pipe (7), heated to a molten state at high temperature, and then sprayed onto the inner surface.

[0027] The dedicated thermal spraying device has a unique dual-nozzle annular structure for the flame nozzle 6, which is embedded in a rigid base with a circular slide rail. Both nozzles can freely adjust the spraying angle, with a maximum angle of 360°, achieving 180° bidirectional linear spraying.

[0028] The thickness of the silicon nitride ceramic coating 4 in the friction additive guide mechanism with self-lubricating coating prepared according to any of the methods described is 0.8 to 1 mm.

[0029] Preferably, in the above-mentioned guide lubrication device for friction stir additive manufacturing, the guide device 3 is made of tungsten steel, which has the advantages of high hardness, wear resistance, heat resistance, and good strength and toughness. It still has high hardness even at 1000℃.

[0030] The beneficial effects of this invention compared to the prior art are as follows:

[0031] Compared to existing lubrication methods, this invention avoids the problem of uneven surface smoothness of the rod caused by manually applying graphite lubricant; it avoids the problem of flash caused by different lubrication effects on different surfaces of the rod due to the use of solid lubricants or greases; it solves the problem of inconsistent deposition layer width caused by the poor high-temperature resistance of manually applied lubricants leading to rod softening; the silicon nitride ceramic self-lubricating structure can improve the surface hardness of the cavity wall, solving the problem of insufficient hardness preventing the stirring head from fully softening the rod; and it solves the problem of inability to lubricate under additive manufacturing conditions where lubricants are not applicable. The silicon nitride ceramic self-lubricating coating has good self-lubricating stability; therefore, the stirring friction additive manufacturing guided lubrication device of this invention has great practical value and application potential. Attached Figure Description

[0032] Figure 1 A front sectional view of the stirring friction guide mechanism;

[0033] Figure 2 A schematic diagram of a thermal spraying device for silicon nitride ceramic coating;

[0034] Figure 3 The additively deposited layer, produced by using a self-lubricating structure, has a uniform thickness and a smooth surface.

[0035] Figure 4 Irregular appearance resulting from the use of traditional graphite lubricant;

[0036] 1. Annular stirring head; 2. Guide device; 3. Positioning hole; 4. Silicon nitride ceramic coating; 5. Hydraulic rod; 6. Annular flame nozzle; 7. Feeding pipe; 8. Filling port. Detailed Implementation

[0037] The present invention will be described in detail below with reference to specific embodiments.

[0038] Example 1

[0039] This embodiment relates to a guide lubrication device for 7075 aluminum alloy bars subjected to friction stirring. Its chemical composition is shown in Table 1.

[0040] Table 1. Composition of 7075 Aluminum Alloy

[0041]

[0042] Step 1, Incoming Inspection: Check the integrity of the stirring head. Sand the inner surface of the hollow guide device and remove oil stains with acetone.

[0043] Step 2: Prepare silicon nitride powder using a carbothermic reduction reaction:

[0044] Step 3: Prepare a 40% ammonium chloride solution and a 15% water glass solution for later use.

[0045] Step 4: Slowly pour the prepared ammonium chloride solution into 280 ml of water glass solution, while stirring with a magnetic stirrer at 30°C. When the amount poured in is 1 / 5 of the water glass solution, a silica gel is completely formed.

[0046] Step 5: Add a certain amount of water to dilute the silica gel to a paste state, and then use slow-speed filter paper to filter out the Na+. + (<1%)

[0047] Step 6: Mix silica gel and carbon black in a 2:1 mass ratio, dilute with distilled water until semi-transparent, stir with a magnetic stirrer for 2 hours, and dry in a 60°C drying oven to form a silicon-carbon precursor. Add 5 ml of anhydrous ethanol to accelerate mixing.

[0048] Step 7: Weigh 5g of silicon-carbon precursor and place it in a crucible. Pour in a high-temperature nitrogen stream and heat at 5℃ / min to 300℃, 10℃ / min to 1195℃, and 5℃ / min to 1350℃. Hold at this temperature for 3 hours to obtain high-temperature silicon nitride powder.

[0049] Step 8, Purification: After the silicon nitride obtained from the high-temperature reaction is solidified and cooled, it is purified.

[0050] Step 9, Spraying Assembly: Clamp the mixing head and insert the annular spray nozzle into the top of the hollow device.

[0051] Step 10, Thermal Spraying: Turn on the thermal spraying equipment and control the nozzle to spray at a distance of 51mm to avoid overheating. The spraying pressure is between 0.2Mpa and 0.6Mpa, and the spraying speed is 90mm / s until the coating is dense. The spraying temperature is controlled between 1000℃ and 2500℃. High-purity oxygen is introduced simultaneously to fill the solid powder into the feeding pipe.

[0052] Step 11, Device Movement: The clamp-driven stirring head rotates at a constant speed of 3-4 cm / s and pushes forward at a speed of 2-3 cm / s. The feeding speed is 32 g / min, until a dense and uniform silicon nitride ceramic coating with a thickness of approximately 0.9 mm is formed on the inner surface.

[0053] Step 12, result check: After it cools down, remove the stirring head and observe whether there is any burn damage on the coating surface. If there is no damage, polish it smooth.

[0054] Step thirteen: Cut and grind the aluminum alloy rod into a square cross-section, matching the size of the guide device. Smoothly push the aluminum alloy rod into the hollow guide device coated with a silicon nitride ceramic self-lubricating coating. The rod contacts the lubricating film on the silicon nitride ceramic surface, reducing friction and wear, resulting in better additive manufacturing. This is manifested in consistent deposition width, minimal flash, smooth and neat edges, uniform thickness of each layer, and stable additive manufacturing process. Figure 3 As shown, the additively deposited layer produced using a self-lubricating structure has a uniform thickness and a smooth surface. If traditional graphite lubrication is used, issues such as… Figure 4 The irregular shape shown.

[0055] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a self-lubricating coating for a friction stir additive guide mechanism, characterized in that, A thermal spraying device is used, which includes a flame nozzle (6), a feeding pipe (7), and a filling port (8). There are two flame nozzles (6), which are installed at the tail end of the feeding pipe (7). Silicon nitride powder is filled from the filling port (8) and fed into the flame nozzles (6) along the feeding pipe (7). The flame nozzles (6) have a double-nozzle annular structure, which is embedded in a rigid substrate with a circular slide rail. Both nozzles can freely adjust the spraying angle, and the maximum angle reaches 360°, realizing 180° bidirectional linear spraying. The method includes the following steps: Step 1, Incoming Inspection: Inspect the integrity of the stirring head surface, grind the inner surface of the hollow guide device to obtain a smooth and regular surface, and use ultrasonic cleaning equipment or acetone to remove oil stains from the cleaning surface. Step 2, Preparation of silicon nitride powder; Preparation of silicon nitride powder using a carbothermic reduction reaction includes the following steps: Step 21: Prepare water glass, silica, SiO2 sol, carbon black, nitrogen gas, and necessary reaction vessels; Step 22: Prepare ammonium chloride solution and water glass solution for later use; Step 23: Slowly pour the prepared ammonium chloride solution into the water glass solution while stirring with a magnetic heating stirrer until the solution completely forms a silica gel. Step 24: Add a certain amount of water to dilute the silica gel, and control the amount of Na through filtration. + Percentage of mass; Step 25: Mix silica gel and carbon black in a certain proportion, pour in distilled water, stir and dry to obtain silicon carbide precursor; Step 26: Weigh the prepared silicon-carbon precursor and place it in a crucible. Heat it by introducing nitrogen gas at different heating rates, and then keep it at the temperature to obtain silicon nitride powder. In step 26, 5g-6g of silicon carbide precursor is weighed and heated at two different heating rates: 5℃ / min to 300℃, 10℃ / min to 1195℃, and 5℃ / min to 1350℃. Step 27, Purification: After the silicon nitride obtained from the high-temperature reaction is solidified and cooled, it is purified. Step 3, Spraying Assembly: Clamp the mixing head onto the thermal spraying device, extend the nozzle into the guide device, leaving a certain gap, and spray the exterior parts that do not need to be sprayed for protection. Step 4, thermal spraying: Silicon nitride powder is filled in through the filler port and fed into the flame nozzle along the feed pipe. After being heated to a molten state at high temperature, it is sprayed onto the inner surface. Step 5, device movement: The clamping fixture drives the stirring head to rotate at a constant speed of 3-4 cm / s and pushes it forward at a speed of 2-3 cm / s, forming a uniform and dense silicon nitride ceramic coating with a thickness of 0.8~1 mm on the inner surface. Step 6, result inspection: After it cools down, remove the stirring head and confirm that the coating is intact and has not been overheated or discolored; polish the inner and outer surfaces.

2. The method according to claim 1, characterized in that, In step 21, the SiO2 sol has a particle size of 10 nm, and the carbon black has a particle size of 20-21 nm; in step 22, the ammonium chloride solution has a mass concentration of 40%, and the water glass solution has a mass concentration of 15%; in step 23, the water glass solution is 300 ml, and when the amount added is 1 / 5 of the water glass solution, it completely becomes a silica gel; the temperature range is 20℃-40℃.

3. The method according to claim 1, characterized in that, The filtration method in step 24 is vacuum filtration, using slow-speed filter paper to reduce the loss of silica and Na. + Quality percentage <1%.

4. The method according to claim 1, characterized in that, In step 25, the mass ratio of silica gel to carbon black is 2:1, the stirring time is 2 hours, and the drying temperature is 50℃-60℃. The carbon black is slowly poured in to ensure thorough mixing, and anhydrous ethanol is added dropwise to accelerate the mixing process.

5. The method according to claim 1, characterized in that, In step 4, the mass of silicon nitride powder filled at one time is 100g, the temperature range of the flame nozzle is 1000℃-2500℃, the flame spraying speed is 30g-40g / min, and the gas used for thermal spraying is 99% pure O2, which is used to heat and melt the silicon nitride powder.

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