Silicon nitride ceramic material and robot joint preparation method

Abstract

The invention relates to a silicon nitride ceramic material and a preparation method of a robot joint. The silicon nitride ceramic material is prepared from the following components in percentage by mass: a matrix phase: 90-95% of silicon nitride powder; the sintering aid is formed by mixing aluminum oxide and yttrium oxide according to the mass ratio of 1: (2-3); and 1%-3% of a reinforcing phase which is silicon carbide particles with the particle size of 50-100 nm. According to the preparation method of the robot joint, a silicon nitride ceramic material is adopted, and the robot joint is prepared through the steps of green body rough machining, sintering treatment, precision machining, quality detection, assembling and the like. By optimizing the sintering temperature and time and controlling the blank allowance and the accurate grinding precision, high compactness and high size consistency of the ceramic joint are achieved, the strength and abrasion resistance are remarkably improved, the service life is remarkably prolonged, the joint weight and energy consumption are reduced, and the method is suitable for preparing high-precision and high-frequency sports robot joints.

Description

Technical Field

[0001] This invention relates to the field of ceramic material preparation technology, specifically a silicon nitride ceramic material and a method for preparing robot joints. Background Technology

[0002] Robot joints are the core components of robot motion, needing to withstand high-frequency rotation, oscillation, and certain loads, thus requiring extremely high strength, toughness, wear resistance, and stability of the materials. Currently, robot joints are mostly made of metallic materials (such as alloy steel and titanium alloys), which, while meeting basic mechanical performance requirements, have inherent drawbacks: First, metallic materials have high density (stainless steel has a density of approximately 7.9 g / cm³), resulting in a high weight ratio of joint components and increasing robot drive energy consumption; second, metallic surfaces are prone to wear and have poor corrosion resistance, leading to increased joint clearance and significantly reduced precision after long-term use, requiring frequent maintenance and replacement, resulting in high maintenance costs; third, some metallic joints are prone to frictional heat under high-speed motion, affecting motion stability.

[0003] Silicon nitride ceramics possess characteristics such as low density (approximately 3.2 g / cm³), high strength, high hardness, and excellent wear and corrosion resistance, theoretically making them an ideal material to replace metals in the fabrication of robot joints. However, existing silicon nitride ceramic fabrication technologies face bottlenecks: on the one hand, traditional silicon nitride ceramic sintering requires extremely high temperatures (above 1800℃) and long holding times, making it difficult to achieve a density exceeding 95%, and the flexural strength is mostly below 700 MPa, failing to meet the mechanical requirements of robot joints; on the other hand, silicon nitride ceramics are highly hard and brittle, making post-sintering processing extremely difficult, and direct machining easily leads to cracks, making it difficult to guarantee the high-precision dimensions of the joints (error ≤ 0.01 mm); furthermore, existing processes do not have dedicated fabrication procedures designed for the structural characteristics of robot joints, resulting in low yield and high cost of ceramic joints, hindering large-scale application.

[0004] Therefore, those skilled in the art provide a silicon nitride ceramic material and a method for preparing robot joints to solve the problems mentioned in the background art. Summary of the Invention

[0005] The purpose of this invention is to provide a silicon nitride ceramic material and a method for preparing robot joints, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A silicon nitride ceramic material comprising the following components by weight percentage: Matrix phase: 90%–95% silicon nitride powder; sintering aid: 4%–8%; reinforcing phase: 1%–3%.

[0007] As a further technical solution of the present invention, the silicon nitride powder is selected from α-Si3N4 with a particle size of 1-3 μm.

[0008] As a further technical solution of the present invention, the sintering aid is a mixture of alumina and yttrium oxide, and the mass ratio of alumina to yttrium oxide is 1:(2-3).

[0009] As a further technical solution of the present invention, the reinforcing phase is silicon carbide particles with a particle size of 50-100 nm.

[0010] As a further technical solution of the present invention, the preparation method of the silicon nitride ceramic material includes the following steps: S1. Raw material mixing: Weigh silicon nitride powder, sintering aid, and reinforcing phase according to the formula, and mix them with anhydrous ethanol as dispersant at a solid-liquid ratio of 1:(1.2-1.5); use agate balls and ball milling at a ball-to-material ratio of 3:1, with a ball milling speed of 200-300 rpm and a ball milling time of 4-6 hours to obtain a uniformly dispersed mixed slurry. S2. Drying and granulation: The mixed slurry is vacuum dried at 80-100℃ for 4-6 hours, then pulverized and passed through an 80-100 mesh sieve to obtain ceramic particles with good flowability; S3. Dry pressing: The ceramic particles are loaded into a custom mold and dry pressed under a pressure of 15-20MPa for 30-60s to obtain a green body. S4. Cold isostatic pressing: Apply an isostatic pressure of 150-320 MPa to the green blank through a liquid medium and hold the pressure for 2-20 minutes to obtain the green blank. S5. Sintering and densification: The green body is sintered in a nitrogen protective atmosphere; nitrogen with a purity of not less than 99.99% is introduced as a protective atmosphere, and the gas flow rate is 50-100 mL / min. The sintering procedure is as follows: first, heat the temperature to 800-900℃ at a heating rate of 5℃ / min, and hold for 2 hours; Then raise the temperature to 1600-1700℃ at a heating rate of 3℃ / min and hold for 4-6 hours; Finally, the furnace was cooled to room temperature to obtain a silicon nitride ceramic preform.

[0011] As a further technical solution of the present invention, the diameter of the agate ball is 5-10 mm.

[0012] A method for manufacturing robot joints includes the following steps: Step 1: Rough machining of the blank: Based on the 3D model of the robot joint, the blank obtained in step S4 is rough machined using a CNC milling machine, with a machining allowance of 0.5 to 1 mm. Step 2, Sintering treatment: The rough-processed green body is placed in a nitrogen protective atmosphere for sintering; nitrogen with a purity of not less than 99.99% is introduced as the protective atmosphere, and the gas flow rate is 50-100 mL / min; The sintering procedure is as follows: first, heat the temperature to 800-900℃ at a heating rate of 5℃ / min, and hold for 2 hours; Then raise the temperature to 1600-1700℃ at a heating rate of 3℃ / min and hold for 4-6 hours; Finally, the ceramic joint blank was cooled to room temperature in the furnace to obtain the ceramic joint blank. Step 3, Precision Machining: The ceramic joint blank is precision ground using a diamond grinding wheel to control the dimensional accuracy error to no more than 0.01mm; then the joint mating surfaces are polished to make the surface roughness Ra value no more than 0.05μm, thus obtaining the ceramic joint; Step 4: Quality Inspection and Assembly: The ceramic joint is inspected for appearance defects, dimensional accuracy, and mechanical properties. After passing all inspections, it is assembled with the robot shaft and bearing components to complete the robot joint manufacturing.

[0013] As a further technical solution of the present invention, in step three, the particle size of the diamond grinding wheel is 800-1200 mesh.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention introduces composite sintering aids into silicon nitride ceramic powder and adopts hot isostatic pressing sintering process, which enables the ceramic material to achieve full densification at a lower temperature, significantly improving the high-temperature energy consumption and grain coarsening problems in the traditional silicon nitride ceramic sintering process; the ceramic joint material prepared by this method has low internal porosity, uniform structure, and significantly improved mechanical strength and crack resistance.

[0015] This invention combines the structural characteristics of robot joints and designs a pre-formed mold and a precision sintering fit structure. By controlling the shrinkage rate of the blank and the subsequent fine grinding allowance, the dimensional accuracy and fit stability of the ceramic joint are significantly improved, which can meet the requirements of high-precision assembly.

[0016] The composite surface treatment and polishing process used in this invention effectively reduces the joint friction coefficient, improves surface smoothness and wear resistance, thereby extending the service life of robot joints and reducing the accuracy decay caused by wear.

[0017] This invention achieves the reduction of joint mass and energy consumption while maintaining high strength and high stability, thereby improving overall motion efficiency and reliability, and has significant engineering application value. Attached Figure Description

[0018] Figure 1A flowchart of a method for preparing silicon nitride ceramic materials; Figure 2 A flowchart of a robot joint fabrication method. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 Please see Figure 1 A silicon nitride ceramic material comprising the following components by weight percentage: Matrix phase: 90%–95% silicon nitride powder, using α-Si3N4 powder with a particle size of 1–3 μm to ensure the strength of the material matrix; Sintering aid: 4% to 8%, which is a mixture of alumina and yttrium oxide with a mass ratio of alumina to yttrium oxide of 1:(2 to 3). It is used to lower the sintering temperature and promote densification. Reinforcing phase: 1% to 3%, consisting of silicon carbide (SiC) particles with a particle size of 50 to 100 nm, dispersed in the matrix to improve the bending strength and wear resistance of the material. α-Si3N4 is the α-phase crystal of silicon nitride (Si3N4), one of the two main crystalline phases of silicon nitride (the other being β-Si3N4). Its core characteristics include: a hexagonal crystal structure with dense and regular atomic arrangement; it is a low-temperature stable phase, typically forming at relatively low temperatures (approximately 1200-1400℃); the particles are mostly fine crystals or powders, exhibiting higher sintering activity and easy processing into dense ceramics. α-Si3N4 serves as a precursor powder for high-performance silicon nitride ceramics, used in the manufacture of high-temperature resistant, wear-resistant, and corrosion-resistant structural components; it is widely applied in machinery, aerospace, and electronics fields, such as engine parts, bearings, and ceramic cutting tools.

[0021] A method for preparing a silicon nitride ceramic material includes the following steps: S1, Raw material mixing Weigh each component according to the formula, add anhydrous ethanol as a dispersant to the raw materials, and mix them at a solid-liquid ratio of 1:(1.2-1.5); use agate balls for ball milling, with the diameter of the agate balls being 5-10 mm, the ball-to-material ratio being 3:1, the ball milling speed being 200-300 rpm, and the ball milling time being 4-6 h, to obtain a uniformly dispersed mixed slurry. S2, Drying and Granulation The mixed slurry was vacuum dried at 80-100°C for 4-6 hours, then pulverized and passed through an 80-100 mesh sieve to obtain ceramic particles with good flowability. S3, Dry pressing The ceramic particles are loaded into a custom mold (matching the shape of the robot joint blank), and dry-pressed under a pressure of 15-20 MPa for 30-60 seconds to obtain a green blank. S4, Cold Isostatic Pressing A green billet is obtained by applying an isostatic pressure of 150–320 MPa to the green billet through a liquid medium and holding the pressure for 2–20 minutes. S5, Sintering Densification The green body is sintered under a nitrogen protective atmosphere; nitrogen with a purity of not less than 99.99% is introduced as the protective atmosphere, and the gas flow rate is 50-100 mL / min. The sintering process is as follows: first, heat the temperature to 800-900℃ at a heating rate of 5℃ / min, hold for 2 hours, and remove residual ethanol and adsorbed water; Then, increase the temperature to 1600-1700℃ at a heating rate of 3℃ / min and hold for 4-6 hours to promote particle sintering and densification. Finally, the furnace is cooled to room temperature to obtain a silicon nitride ceramic preform, i.e., silicon nitride ceramic material.

[0022] Example 2 Please see Figure 2 The robot joint was fabricated using the silicon nitride ceramic material prepared in Example 1, including the following steps: Step 1: Rough machining of the green blank Based on the three-dimensional model of the robot joint (such as rotary joint and swing joint), the green blank obtained in step S4 of Example 1 is rough machined using CNC milling equipment, with a machining allowance of 0.5 to 1 mm reserved to avoid the problem of difficult processing of hard and brittle materials after sintering. Step 2, Sintering treatment: The rough-processed green body is placed in a nitrogen protective atmosphere for sintering; nitrogen with a purity of not less than 99.99% is introduced as the protective atmosphere, and the gas flow rate is 50-100 mL / min; The sintering procedure is as follows: first, heat the temperature to 800-900℃ at a heating rate of 5℃ / min, and hold for 2 hours; Then raise the temperature to 1600-1700℃ at a heating rate of 3℃ / min and hold for 4-6 hours; Finally, the ceramic joint blank was cooled to room temperature in the furnace to obtain the ceramic joint blank. Step 3: Precision Machining The ceramic joint blank is precision ground using a diamond grinding wheel (800-1200 mesh) to control the dimensional accuracy error to be no greater than 0.01 mm; then the joint mating surfaces are polished to make the surface roughness Ra value no greater than 0.05 μm, thus obtaining the ceramic joint. Step 4: Quality Inspection and Assembly The ceramic joints undergo visual defect inspection (no cracks, missing corners), dimensional accuracy inspection (using a coordinate measuring machine), and mechanical property sampling inspection (bending strength, hardness). After passing all inspections, they are assembled with robot shafts and bearing components to complete the robot joint manufacturing process.

[0023] The innovative material formulation in this application is achieved by controlling the ratio of Al2O3 to Y2O3 sintering aids (1:2~3) to densify silicon nitride ceramics (density ≥98%) at 1600~1700℃, while introducing nano-SiC particle reinforcement phase to synergistically improve the bending strength (≥800MPa) and wear resistance of the material. Process optimization: The process of "rough machining of green body → sintering → precision machining" is adopted to avoid the impact of ceramic sintering deformation on dimensional accuracy, solve the problem of hard and brittle ceramic processing, and ensure high precision of joints (error ≤ 0.01mm). Performance and cost balance: By reducing the sintering temperature (100-200℃ lower than the traditional process) and simplifying the processing steps, the yield of ceramic joints is increased (≥90%), the preparation cost is reduced, and the needs of large-scale application are met.

[0024] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A silicon nitride ceramic material, characterized in that, Includes the following components by mass percentage: Matrix phase: 90%–95% silicon nitride powder; sintering aid: 4%–8%; reinforcing phase: 1%–3%.

2. The silicon nitride ceramic material according to claim 1, characterized in that, The silicon nitride powder is selected from α-Si3N4 powder with a particle size of 1-3 μm.

3. The silicon nitride ceramic material according to claim 1, characterized in that, The sintering aid is a mixture of alumina and yttrium oxide, with a mass ratio of alumina to yttrium oxide of 1:(2-3).

4. The silicon nitride ceramic material according to claim 1, characterized in that, The reinforcing phase is silicon carbide particles with a particle size of 50-100 nm.

5. The silicon nitride ceramic material according to any one of claims 1-4, characterized in that, The preparation method of the silicon nitride ceramic material includes the following steps: S1. Raw material mixing: Weigh silicon nitride powder, sintering aid, and reinforcing phase according to the formula, and mix them with anhydrous ethanol as dispersant at a solid-liquid ratio of 1:(1.2-1.5); use agate balls and ball milling at a ball-to-material ratio of 3:1, with a ball milling speed of 200-300 rpm and a ball milling time of 4-6 hours to obtain a uniformly dispersed mixed slurry. S2. Drying and granulation: The mixed slurry is vacuum dried at 80-100℃ for 4-6 hours, then pulverized and passed through an 80-100 mesh sieve to obtain ceramic particles with good flowability; S3. Dry pressing: The ceramic particles are loaded into a custom mold and dry pressed under a pressure of 15-20MPa for 30-60s to obtain a green body. S4. Cold isostatic pressing: Apply an isostatic pressure of 150-320 MPa to the green blank through a liquid medium and hold the pressure for 2-20 minutes to obtain the green blank. S5. Sintering and densification: The green body is sintered in a nitrogen protective atmosphere; nitrogen with a purity of not less than 99.99% is introduced as a protective atmosphere, and the gas flow rate is 50-100 mL / min. The sintering procedure is as follows: first, heat the temperature to 800-900℃ at a heating rate of 5℃ / min, and hold for 2 hours; Then raise the temperature to 1600-1700℃ at a heating rate of 3℃ / min and hold for 4-6 hours; Finally, the furnace was cooled to room temperature to obtain a silicon nitride ceramic preform.

6. A silicon nitride ceramic material according to claim 6, characterized in that, The diameter of the agate ball is 5-10 mm.

7. A method for fabricating a robot joint, using the silicon nitride ceramic material as described in claim 5, characterized in that, Includes the following steps: Step 1: Rough machining of the blank: Based on the 3D model of the robot joint, the blank obtained in step S4 is rough machined using a CNC milling machine, with a machining allowance of 0.5 to 1 mm. Step 2, Sintering treatment: The rough-processed green body is placed in a nitrogen protective atmosphere for sintering; nitrogen with a purity of not less than 99.99% is introduced as the protective atmosphere, and the gas flow rate is 50-100 mL / min; The sintering procedure is as follows: first, heat the temperature to 800-900℃ at a heating rate of 5℃ / min, and hold for 2 hours; Then raise the temperature to 1600-1700℃ at a heating rate of 3℃ / min and hold for 4-6 hours; Finally, the ceramic joint blank was cooled to room temperature in the furnace to obtain the ceramic joint blank. Step 3, Precision Machining: The ceramic joint blank is precision ground using a diamond grinding wheel to control the dimensional accuracy error to no more than 0.01mm; then the joint mating surfaces are polished to make the surface roughness Ra value no more than 0.05μm, thus obtaining the ceramic joint; Step 4: Quality Inspection and Assembly: The ceramic joint is inspected for appearance defects, dimensional accuracy, and mechanical properties. After passing all inspections, it is assembled with the robot shaft and bearing components to complete the robot joint manufacturing.

8. A method for manufacturing a robot joint according to claim 7, characterized in that, In step three, the diamond grinding wheel has a grit size of 800-1200 mesh.

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