Method for inhibiting edge collapse during polishing of high-purity niobium metal plate

Abstract

The invention discloses a method for inhibiting edge collapse during polishing of a high-purity niobium metal plate, and belongs to the technical field of precise metal processing. Aiming at the problem of sanding edge collapse caused by softness and high viscoplasticity of a high-purity niobium plate (the purity is greater than or equal to 99.95%), the invention provides an innovative process based on homogeneous waste recycling and dynamic parameter collaboration. A self-locking tool is formed by precisely embedding a front-pass water cutting niobium offcut (the thickness tolerance is + / -0.2 mm) and a workpiece (the gap is smaller than or equal to 0.15 mm), parameter optimization of two stages of rough grinding (180-mesh abrasive paper / 10-30 mA / 1-5 m / min) and accurate grinding (320-mesh abrasive paper / 8-15 mA / 1-3 m / min) is combined, and the ratio of the abrasive belt speed to the current is regulated and controlled in real time based on the viscoplastic characteristic (the strain rate sensitive index m is 0.15-0.25) of niobium. And the grinding is in a quasi-static plastic flow area. According to the method, the edge collapse height is smaller than or equal to 0.02 mm, the surface roughness Ra is smaller than or equal to 0.8 micrometer, the yield is increased to 95% or above, the tool cost is zero, the production period is shortened by 30%, the niobium material utilization rate reaches 92%, and impurity pollution is thoroughly eliminated. The method is suitable for efficient precision machining of special-shaped parts and large-size niobium plates (2000 * 600mm at most) in the fields of national defense, nuclear energy and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of precision metal processing, and particularly relates to a method for suppressing the grinding edge collapse of high-purity niobium metal plates. Background Art

[0002] In the field of precision processing of metal plates, the edge collapse phenomenon commonly existing in the mechanical sanding process has become a core technical problem restricting the yield of high-end products. Especially for high-purity niobium metal (purity ≥ 99.95%) widely used in the national defense and military industry, its inherent soft characteristics, high viscoplasticity and high cost pose multiple challenges for edge collapse control: Complexity of defect types: During the sanding process, various defects are easily generated, such as longitudinal edge collapse (at the sanding belt cutting-in / cutting-out section), transverse edge collapse (parallel to the running direction of the sanding belt), peripheral edge collapse (rotary machining), eye socket type edge collapse (hole-like structure), and stepped edge collapse (special-shaped parts); Lack of process compatibility: Traditional methods (such as changing tooling, adjusting the grinding trajectory, and edge protection tooling) have problems such as local under-grinding and poor tooling adaptability for large special-shaped parts, and rely on the operator's experience, making it difficult to achieve standardized production; Contradiction between cost and quality: In the existing technology, although reducing the single-pass grinding depth can alleviate edge collapse, it leads to a long process (efficiency drops by 30% - 50%), a sharp increase in processing costs, and still cannot completely eliminate the risks of local deformation and tooling impurity contamination.

[0003] The current mainstream solutions in the industry and their technical bottlenecks can be summarized into the following three categories: 1. Process parameter optimization method The representative literature (DOI: 10.16371 / j.cnki.issn1009-962x.1997.04.020) proposes that by adjusting the hardness of the contact roller, the linear speed of the sanding belt (increased by 20% - 40%), the grinding depth (reduced to 50% - 70% of the original value), and using composite processes such as reverse grinding / oscillating grinding, the edge collapse amount can be reduced by 15% - 25%. However, this method requires structural transformation of the equipment (such as enhancing the rigidity of the machine tool and customizing the contact roller), resulting in an increase in the transformation cost of more than 80%, and the parameter optimization significantly prolongs the single-piece processing time, and the production efficiency drops by about 35%.

[0004] 2. Auxiliary tooling design method Chinese Patent CN211388289 uses the outer circle / inner hole support member limit design, which can theoretically inhibit the edge collapse of the workpiece. However, in actual applications, the contact surface between the tooling and the niobium plate is prone to generate metal debris due to high-frequency friction (pollution probability ≥ 12%), and the preparation cycle of the special-shaped part tooling is as long as 5 - 7 days, significantly increasing the production cost. More seriously, the accuracy attenuation caused by tooling wear (the flatness deviation expands to ±0.15 mm after 50 uses) forces frequent replacement, further reducing the economic benefits.

[0005] Chinese Patent CN109623628A adopts the grinding disc step morphology trimming technology, and controls the material removal rate by matching the width and depth of the edge collapse area. Although this scheme can achieve an edge accuracy of ±0.05 mm level, its complex three-stage disc trimming process (including edge collapse detection, morphology trimming, and removal rate calculation) results in an equipment utilization rate of less than 60%, and it is difficult to meet the production requirements of multi-variety and small-batch.

[0006] 3. Composite machining path method Chinese Patent CN101223006A compensates for the linear velocity difference in rotary grinding by differentially controlling the supply amount of the abrasive (the outer flow rate increases by 30% - 50%), effectively inhibiting the peripheral edge collapse. However, this technology is only applicable to axisymmetric rotary workpieces (such as wafers), and is completely ineffective for flat parts of sheet materials and special-shaped structures, and the process universality is severely limited.

[0007] The existing technology system has the following core contradictions: 1. Imbalance between accuracy and efficiency: Although the parameter optimization method can improve the edge collapse, it sacrifices efficiency, while the tooling method exchanges high costs for limited accuracy improvement; 2. Conflict between generality and specificity: The composite path method is limited by specific geometric features and cannot cover the diverse processing scenarios of high-purity niobium plates; 3. Paradox between cleanliness and cost: The risk of introducing impurities by traditional tooling and the adaptation cost of special-shaped parts form a double restriction.

[0008] Therefore, it is urgent to develop a short-process technology based on material property adaptation, which can simultaneously achieve three goals: edge collapse inhibition (defect rate ≤ 2%), processing efficiency improvement (process shortening ≥ 30%), and zero pollution risk through the closed-loop design of the process chain without the need for complex tooling and equipment transformation. Summary of the Invention

[0009] The present invention aims to solve the problem of edge collapse of high-purity niobium metal plates (purity ≥ 99.95%) during mechanical sanding due to the softness and high viscoplasticity of the material, especially for the core requirements of niobium plate processing in the fields of national defense and high-end target materials, including high precision (flatness ≤ 1.6 μm), pollution-free (impurity content ≤ 0.01%), low cost (tooling cost zero), and short process (production cycle ≤ 48 hours). By innovatively integrating waste recycling, process parameter collaborative optimization, and dynamic control technologies, it breaks through the technical bottlenecks such as tooling pollution, low efficiency, and poor adaptability of special-shaped parts in existing methods, and realizes the simultaneous improvement of niobium plate edge collapse suppression and processing efficiency.

[0010] The technical solution of the present invention is as follows: A method for suppressing the edge collapse of high-purity niobium metal plates during sanding, comprising the following steps: (1) Preparation of waste tooling: Using the niobium metal edge material generated in the previous water cutting process as the homogeneous tooling material, with the purity of the niobium metal edge material being the same as that of the niobium plate to be processed and the thickness tolerance being ±0.2 mm; (2) Inlay combination: Combining the niobium metal edge material and the edge of the niobium plate to be processed into a temporary reinforcement tooling through geometric fitting, with the gap of the fitting surface ≤ 0.15 mm; (3) Rough grinding: Using 180-mesh sandpaper, grinding under the conditions of a sand belt speed of 1 - 5 m / min and a pressing current of 10 - 30 mA until the surface roughness Ra ≤ 1.2 μm; (4) Fine grinding: After removing the temporary reinforcement tooling, using 320-mesh sandpaper, performing fine grinding under the conditions of a sand belt speed of 1 - 3 m / min and a pressing current of 8 - 15 mA, and finally the surface roughness Ra ≤ 0.8 μm; (5) Dynamic parameter matching: According to the viscoplastic characteristics of the niobium plate (strain rate sensitivity index m = 0.15 - 0.25), by real-time monitoring of the sand belt load current, dynamically adjusting the ratio of the sand belt speed to the pressing current to make the grinding process in the quasi-static plastic flow zone.

[0011] Preferably, in step (2), the geometric fitting method is a dovetail groove fitting structure or a vacuum adsorption structure, and the contact area ratio of the fitting surface ≥ 85%.

[0012] Preferably, in step (3), the pressing current for the rough grinding is 12 - 15 mA, and the sand belt speed is 2 - 4 m / min.

[0013] Preferably, in step (4), the pressing current for the fine grinding is 9 - 12 mA, and the sand belt speed is 1 - 2 m / min.

[0014] Preferably, in step (1), the surface roughness Ra of the water-jet cut offcuts is ≤ 6.3 μm, and the water pressure during cutting is 300 - 400 MPa, and the abrasive flow rate is 200 - 300 g / min.

[0015] Preferably, in step (5), the load current signal of the abrasive belt is collected in real time through a current sensor, and the ratio of the abrasive belt speed to the pressing current is dynamically adjusted based on a PID controller, so that the current fluctuation amplitude is controlled within the range of ±1 mA.

[0016] The core innovation of the present invention lies in constructing a "material - process - control" trinity technology system: At the material level: Utilizing the homogeneous characteristics of water-jet cut waste materials to break through the material limitations of traditional tooling, achieving zero pollution and resource recycling. At the process level: Through the hierarchical coordination of rough grinding / fine grinding parameters (three-dimensional matching of mesh number - current - speed), balancing the contradiction between efficiency and precision. At the control level: Introducing a dynamic feedback mechanism to quantify the viscoplastic characteristics of niobium into adjustable process parameters to ensure processing stability.

[0017] This solution fundamentally solves the industry problem that it is difficult to balance edge collapse control and economic benefits in the processing of high-purity niobium plates, providing a reusable technical paradigm for the precision processing of precious metals. Through the above technical solutions, the present invention achieves the following remarkable effects: (1) Quality improvement: The edge collapse defect rate is reduced from 15% - 20% of the traditional process to ≤ 2%, and the finished product rate is increased to over 95%; the surface roughness Ra ≤ 0.8 μm, and the flatness Ra ≤ 1.6 μm, meeting the precision processing standards of high-end target materials.

[0018] (2) Cost and efficiency optimization: The tooling material cost is zero, and the comprehensive production cost is reduced by 40%; the production process is shortened by 30%, and the energy consumption per piece is reduced by 37% (measured from 18.6 kWh / kg to 11.7 kWh / kg).

[0019] (3) Cleanliness guarantee: The homogeneous design of the tooling and the workpiece reduces the risk of impurity contamination to 0, meeting the cleanliness requirements of high-purity niobium plates (3N5 level) (the content of impurities such as Fe and Al ≤ 10 ppm).

[0020] (4) Process universality: It supports the processing of special-shaped parts, hole and groove structures, and large-sized plates (maximum size 2000 × 600 mm), adapting to the precision manufacturing requirements of complex components of national defense equipment. Specific embodiments

[0021] Example 1: Processing of special-shaped niobium plates 1. Preparation and embedding of homogeneous waste tooling Raw material preparation: Select niobium metal offcuts produced by water jet cutting in the previous process (purity 99.97%, thickness 8.2 ± 0.2 mm), with a surface roughness Ra = 5.8 μm (water jet cutting parameters: water pressure 380 MPa, abrasive flow rate 250 g / min, cutting speed 120 mm / min).

[0022] Chimney operation: Assemble the offcuts and the niobium plate to be processed (L325×B105×δ8mm) by dovetail groove fitting. Use a coordinate measuring machine to detect the fitting gap (the measured maximum gap is 0.12 mm), and the contact area ratio is 87.3% (measured by laser scanning method).

[0023] After the fixture and the workpiece are combined, the overall dimensions are L340×B120×δ8mm, forming a rigid reinforcement structure (the flexural rigidity is increased to 2.3 times that of a single body).

[0024] 2. Rough grinding - fine grinding Rough grinding stage: Use 180 - mesh ceramic alumina sandpaper, set the sanding belt speed at 3 m / min and the pressing current at 15 mA.

[0025] The material removal rate is stable at 1.05 mm³ / s. After metallographic inspection, the depth of the plastic deformation layer is 48 μm (the control group with traditional process is 105 μm).

[0026] After rough grinding, the surface roughness Ra = 1.1 μm, and the lateral collapse height is 0.08 mm (0.18 mm for the traditional process).

[0027] Fine grinding stage: After removing the fixture, replace it with 320 - mesh alumina sandpaper, set the sanding belt speed at 1.5 m / min and the pressing current at 10 mA.

[0028] The micro - force grinding pressure is 0.5 N / mm², and the final surface roughness Ra = 0.72 μm, with the collapse height ≤ 0.015 mm.

[0029] 3. Dynamic parameter matching control Install a Hall current sensor (accuracy ±0.2 mA) to monitor the load of the sanding belt motor in real - time, and dynamically adjust the ratio of the sanding belt speed to the pressing current through a PID controller (adjustment period 0.1 s).

[0030] During the processing, the current fluctuation is controlled within ±0.8 mA (target value ±1 mA), and the self - adaptive change range of the sanding belt speed is 2.8 - 3.2 m / min, ensuring that the grinding is in the quasi - static plastic flow zone (strain rate 1.2×10⁻³ s⁻¹).

[0031] 4. Short - process benefit verification Production cycle: The total time-consuming is 46 hours (72 hours for the traditional process control group), and the number of processes is reduced by 4 steps (from the original 12 steps to the current 8 steps). Material utilization rate: The consumption of niobium materials is reduced from 1.58 kg / piece in the traditional process to 1.02 kg / piece, and the utilization rate is 91.7%. Cleanliness detection: ICP-MS analysis shows that the Fe content ≤ 8 ppm and the Al content ≤ 5 ppm (35 ppm and 22 ppm respectively for the traditional tooling control group).

[0032] Example 2: Processing of large-size hole and groove niobium plates 1. Preparation and inlay of homogeneous waste tooling Raw material selection: Use water-cut circular niobium plate edge materials (outer diameter 600 mm, inner diameter 400 mm, thickness 6.2 ± 0.2 mm), cutting parameters: water pressure 350 MPa, abrasive flow rate 280 g / min, cutting speed 100 mm / min.

[0033] Vacuum adsorption design: Place a vacuum suction cup on the contact surface between the edge material and the workpiece. The negative pressure of the suction cup when pumping air ≤ -20 kPa, and the contact area ratio is 89.5%. The fitting gap ≤ 0.10 mm (measured by a laser interferometer), and the flatness error of the tooling-workpiece combination ≤ 0.05 mm / ㎡.

[0034] 2. Rough grinding - fine grinding processing Rough grinding stage: Use 180-mesh alumina sandpaper, sand belt speed 4 m / min, and pressing current 18 mA.

[0035] Material removal rate 1.18 mm³ / s, depth of the plastic deformation layer 52 μm (110 μm for the traditional process), and the depth of the socket-shaped collapse at the edge of the hole and groove is reduced from 0.25 mm to 0.07 mm.

[0036] Fine grinding stage: Replace with 320-mesh alumina sandpaper, sand belt speed 2 m / min, pressing current 12 mA, and micro-force grinding pressure 0.6 N / mm².

[0037] The final surface roughness Ra = 0.68 μm, and the collapse height ≤ 0.018 mm.

[0038] 3. Dynamic parameter matching control Adopt a multi-channel current acquisition system (sampling frequency 1 kHz), and adjust the parameters in real time through the fuzzy PID algorithm. The current fluctuation is ±0.7 mA, and the response time of the dynamic adjustment of the sand belt speed ≤ 0.05 s.

[0039] 4. Mass production data Processing efficiency: The man-hour per piece is 51 hours (78 hours for the traditional process), and the production capacity is increased by 34.6%; Cost analysis: The tooling cost is zero, and the comprehensive cost is reduced by 42.3% (the proportion of the tooling cost per piece in the traditional process is 18%); Batch consistency: When continuously processing 50 niobium plates, the standard deviation of the height of the collapsed edge σ = 0.003 mm (σ = 0.025 mm for the traditional process).

[0040] Comparison table of the effects of the embodiments Through the detailed implementation data of the above embodiments, the significant advantages of the present invention in suppressing the collapsed edge, improving efficiency, controlling costs, and ensuring cleanliness are fully verified. At the same time, the universality of the technical solution for special-shaped parts and large-sized parts is demonstrated.

Claims

1. A method for suppressing the grinding edge collapse of a high-purity niobium metal plate, characterized in that It includes the following steps: (1) Scrap tooling preparation: Using the niobium metal edge material generated in the previous water jet cutting process as the homogeneous tooling material, the purity of the niobium metal edge material is the same as that of the niobium plate to be processed, and the thickness tolerance is ±0.2 mm; (2) Inlay combination: Combining the niobium metal edge material with the edge of the niobium plate to be processed into a temporary reinforcement tooling through geometric fitting, and the gap of the fitting surface ≤ 0.15 mm; (3) Rough grinding: Using 180-mesh sandpaper, grinding under the conditions of a sand belt speed of 1 - 5 m / min and a pressing current of 10 - 30 mA until the surface roughness Ra ≤ 1.2 μm; (4) Fine grinding: After removing the temporary reinforcement tooling, using 320-mesh sandpaper, performing fine grinding under the conditions of a sand belt speed of 1 - 3 m / min and a pressing current of 8 - 15 mA, and finally the surface roughness Ra ≤ 0.8 μm; (5) Dynamic parameter matching: According to the viscoplastic characteristics of the niobium plate (the strain rate sensitivity index m = 0.15 - 0.25), by real-time monitoring of the sand belt load current, dynamically adjusting the ratio of the sand belt speed to the pressing current to make the grinding process in the quasi-static plastic flow zone.

2. The method for suppressing the grinding edge collapse of the high-purity niobium metal plate according to claim 1, wherein: The geometric fitting method in step (2) is a dovetail groove fitting structure or a vacuum adsorption structure, and the contact area ratio of the fitting surface ≥ 85%.

3. The method according to claim 1, wherein: The pressing current of the rough grinding in step (3) is 12 - 15 mA, and the sand belt speed is 2 - 4 m / min.

4. The method according to claim 1, wherein: The pressing current of the fine grinding in step (4) is 9 - 12 mA, and the sand belt speed is 1 - 2 m / min.

5. The method according to claim 1, wherein: The surface roughness Ra of the water jet cutting edge material in step (1) ≤ 6.3 μm, and the water pressure during cutting is 300 - 400 MPa, and the abrasive flow rate is 200 - 300 g / min.

6. The method according to claim 1, wherein: In step (5), the sand belt load current signal is collected in real time through a current sensor, and the ratio of the sand belt speed to the pressing current is dynamically adjusted based on a PID controller to control the current fluctuation amplitude within the range of ±1 mA.