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

Abstract

This invention discloses a method for suppressing edge collapse during grinding of high-purity niobium metal plates, belonging to the field of precision metal processing technology. Addressing the problem of edge collapse during grinding of high-purity niobium plates (purity ≥ 99.95%) due to their softness and high viscoplasticity, an innovative process based on the recycling of homogeneous waste materials and the synergy of dynamic parameters is proposed. By precisely fitting the previous water-cut niobium edge material (thickness tolerance ±0.2mm) with the workpiece (gap ≤ 0.15mm) to form a self-locking fixture, and combining two-stage parameter optimization of rough grinding (180-grit sandpaper / 10-30mA / 1-5m / min) and fine grinding (320-grit sandpaper / 8-15mA / 1-3m / min), and based on the viscoplastic characteristics of niobium (strain rate sensitivity index m = 0.15-0.25), the ratio of abrasive belt speed to current is adjusted in real time, keeping the grinding process in a quasi-static plastic flow zone. This method achieves a collapse height of ≤0.02mm, a surface roughness Ra of ≤0.8μm, a yield rate of over 95%, zero tooling costs, a 30% reduction in production cycle, a 92% utilization rate of niobium material, and completely eliminates impurity contamination. It is suitable for the efficient and precision machining of irregularly shaped parts and large-size niobium plates (maximum 2000×600mm) in fields such as national defense and nuclear energy.

Description

Technical Field

[0001] This invention belongs to the field of precision metal processing technology, and specifically relates to a method for suppressing edge collapse during grinding of high-purity niobium metal plates. Background Technology

[0002] In the field of precision machining of sheet metal, edge collapse, a common problem in mechanical sand grinding, has become a core technical challenge restricting the yield of high-end products. Especially for high-purity niobium metal (purity ≥99.95%) widely used in the defense industry, its inherent softness, high viscoplasticity, and high cost present multiple challenges to edge collapse control. The types of defects are becoming more complex: During the sanding process, a variety of defects are easily generated, such as longitudinal edge collapse (sand belt entry / exit section), transverse edge collapse (parallel to the sand belt running direction), peripheral edge collapse (rotary machining), eye socket-type edge collapse (hole-like structure), and stepped edge collapse (irregular parts); Insufficient process compatibility: Traditional methods (such as changing molds and dies, adjusting grinding paths, and edge protection fixtures) have problems such as localized missed grinding and poor tooling adaptability for large irregular parts, and they rely on operator experience, making it difficult to achieve standardized production. Cost versus quality dilemma: While reducing the amount of grinding pressure per pass can alleviate edge collapse in existing technologies, it leads to a lengthy process (efficiency down by 30%-50%) and a surge in processing costs. At the same time, it still cannot completely eliminate the risk of local deformation and tooling contamination.

[0003] Current mainstream industry solutions and their technological bottlenecks can be summarized into the following three categories: 1. Process parameter optimization method A representative paper (DOI:10.16371 / j.cnki.issn1009-962x.1997.04.020) proposes that by adjusting the contact roller hardness, the belt speed (increasing by 20%-40%), the grinding depth (reducing to 50%-70% of the original value), and using a combination of reverse grinding / oscillating grinding processes, the amount of edge collapse can be reduced by 15%-25%. However, this method requires structural modifications to the equipment (such as enhancing machine tool rigidity and customizing contact rollers), resulting in an increase in modification costs of over 80%, and parameter optimization significantly extends the processing time per piece, reducing production efficiency by approximately 35%.

[0004] 2. Auxiliary tooling design method Chinese patent CN211388289U, through its outer circle / inner hole support limit design, can theoretically suppress workpiece edge collapse. However, in practical applications, the contact surface between the tooling and the niobium plate is prone to generating metal debris due to high-frequency friction (contamination probability ≥12%), and the tooling preparation cycle for irregularly shaped parts is as long as 5-7 days, significantly increasing production costs. More seriously, the accuracy decay caused by tooling wear (flatness deviation expands to ±0.15mm after 50 uses) forces frequent replacements, further reducing economic efficiency.

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

[0006] 3. Composite processing path method Chinese patent CN101223006A effectively suppresses peripheral edge collapse by compensating for differences in linear velocity during rotary grinding through differentiated control of the abrasive supply (increasing the flow rate on the outer side by 30%-50%). However, this technology is only applicable to axisymmetric rotating workpieces (such as wafers) and is completely ineffective for planar parts such as sheet metal and irregularly shaped structures, severely limiting the universality of the process.

[0007] The existing technological system suffers from the following core contradictions: 1. Imbalance between accuracy and efficiency: While parameter optimization can improve edge collapse, it sacrifices efficiency, while tooling methods offer limited accuracy improvements at high costs. 2. Conflict between versatility 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. The paradox of cleanliness versus cost: Traditional tooling introduces the risk of impurities, while the cost of adapting to irregularly shaped parts creates a dual constraint.

[0008] Therefore, there is an urgent need to develop a short-process technology based on material properties that can simultaneously achieve three major goals—edge collapse suppression (defect rate ≤2%), improved processing efficiency (process shortening ≥30%), and zero pollution risk—through a closed-loop process chain design without requiring complex tooling and equipment modifications. Summary of the Invention

[0009] This invention aims to solve the problem of edge collapse caused by the softness and high viscoplasticity of high-purity niobium metal plates (purity ≥ 99.95%) during mechanical sand grinding. It specifically addresses the core requirements of the defense and high-end target material fields for niobium plate processing: high precision (flatness ≤ 1.6 μm), no pollution (impurity content ≤ 0.01%), low cost (zero tooling cost), and short process (production cycle ≤ 48 hours). By innovatively integrating waste recycling, process parameter synergistic optimization, and dynamic control technologies, it overcomes the technical bottlenecks of existing methods, such as tooling pollution, low efficiency, and poor adaptability to irregularly shaped parts, achieving simultaneous improvement in niobium plate edge collapse suppression and processing efficiency.

[0010] The technical solution of this invention is: A method for suppressing edge collapse during grinding of high-purity niobium metal plates includes the following steps: (1) Preparation of scrap tooling: The niobium metal scrap generated from the previous waterjet cutting process is used as the same tooling material. The purity of the niobium metal scrap is consistent with that of the niobium plate to be processed and the thickness tolerance is ±0.2mm. (2) Inlay assembly: The niobium metal edge material and the edge of the niobium plate to be processed are combined into a temporary reinforcing fixture by geometric inlay, with the gap between the inlay surfaces ≤0.15mm; (3) Rough grinding: Use 180-grit sandpaper and grind at a belt speed of 1-5 m / min and a current of 10-30 mA until the surface roughness Ra ≤ 1.2 μm; (4) Fine grinding: After removing the temporary reinforcement fixture, fine grinding is carried out using 320-grit sandpaper at a belt speed of 1-3 m / min and a current of 8-15 mA. The final surface roughness Ra ≤ 0.8 μm. (5) Dynamic parameter matching: Based on the viscoplastic characteristics of the niobium plate (strain rate sensitivity index m=0.15-0.25), the ratio of the sand belt speed to the pressing current is dynamically adjusted by real-time monitoring of the sand belt load current, so that the grinding process is in the quasi-static plastic flow zone.

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

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

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

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

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

[0016] The core innovation of this invention lies in the construction of a three-in-one technical system of "materials-process-control": From a materials perspective: by utilizing the homogeneous nature of waterjet cutting waste, we can overcome the material limitations of traditional tooling and achieve zero pollution and resource recycling. At the process level: By tiered coordination of roughing / fine grinding parameters (three-dimensional matching of mesh size, current, and speed), the contradiction between efficiency and precision is balanced; Control level: A dynamic feedback mechanism is introduced to quantify the viscoplastic characteristics of niobium into adjustable process parameters to ensure processing stability.

[0017] This solution fundamentally addresses the industry challenge of balancing edge collapse control and economic benefits in the processing of high-purity niobium plates, providing a reusable technological paradigm for precision machining of precious metals. The present invention achieves the following significant effects through the above technical solution: (1) Quality improvement: The edge collapse defect rate has been reduced from 15%-20% in traditional processes to ≤2%, and the yield has been increased to over 95%; the surface roughness Ra≤0.8μm and the flatness Ra≤1.6μm have reached the precision processing standards of high-end target materials.

[0018] (2) Cost and efficiency optimization: Tooling material costs are reduced to zero, and overall production costs are reduced by 40%; production process is shortened by 30%, and energy consumption per unit is reduced by 37% (actually measured from 18.6kWh / kg to 11.7kWh / kg).

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

[0020] (4) Process universality: It supports the processing of irregular parts, hole and groove structures and large-size plates (maximum size 2000×600mm), and is suitable for the precision manufacturing needs of complex components of national defense equipment. Detailed Implementation

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

[0022] Chimeration operation: The edge material and the niobium plate to be processed (L325×B105×δ8mm) were assembled by dovetail groove fitting. The fitting gap was detected by a coordinate measuring machine (the actual maximum gap was 0.12mm). The contact area ratio was 87.3% (measured by laser scanning method).

[0023] The overall dimensions of the tooling and workpiece after assembly are L340×B120×δ8mm, forming a rigid reinforced structure (the bending stiffness is increased to 2.3 times that of the single unit).

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

[0025] The material removal rate was stable at 1.05 mm³ / s, and the depth of the plastic deformation layer was 48 μm according to metallographic analysis (105 μm for the control group of the traditional process).

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

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

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

[0029] 3. Dynamic parameter matching control A Hall current sensor (accuracy ±0.2mA) is installed to monitor the load of the belt abrasive motor in real time, and the ratio of belt speed to pressing current is dynamically adjusted by a PID controller (adjustment cycle 0.1s).

[0030] During the processing, the current fluctuation is controlled within ±0.8mA (target value ±1mA), and the abrasive belt speed adapts within a range of 2.8-3.2m / min to ensure that the grinding is in the quasi-static plastic flow region (strain rate 1.2×10⁻³s⁻¹).

[0031] 4. Validation of the benefits of the short process Production cycle: Total time 46 hours (72 hours for traditional process control group), 4 steps reduced (original 12 steps → now 8 steps); Material utilization rate: Niobium consumption decreased from 1.58 kg / piece in the traditional process to 1.02 kg / piece, with a utilization rate of 91.7%; Cleanliness testing: ICP-MS analysis showed that Fe content was ≤8ppm and Al content was ≤5ppm (the traditional tooling control group had 35ppm and 22ppm respectively).

[0032] Example 2: Machining of Large-Size Hole-Groove Niobium Plate 1. Preparation and embedding of tooling for homogeneous waste materials Raw material selection: Water-cut ring-shaped niobium plate edge material (outer diameter 600mm, inner diameter 400mm, thickness 6.2±0.2mm) was used. Cutting parameters: water pressure 350MPa, abrasive flow rate 280g / min, cutting speed 100mm / min.

[0033] Vacuum adsorption design: The contact surface between the edge material and the workpiece is placed in a vacuum chuck, with a vacuum pressure of ≤-20kPa and a contact area ratio of 89.5%. The fitting gap is ≤0.10mm (measured by a laser interferometer), and the flatness error of the tooling-workpiece assembly is ≤0.05mm / ㎡.

[0034] 2. Coarse grinding - fine grinding process Coarse grinding stage: Use 180-grit alumina sandpaper, sanding belt speed 4m / min, and pressing current 18mA.

[0035] The material removal rate was 1.18 mm³ / s, the plastic deformation layer depth was 52 μm (110 μm in the traditional process), and the depth of the eye socket-type collapse at the edge of the hole and groove was reduced from 0.25 mm to 0.07 mm.

[0036] Fine grinding stage: Use 320-grit alumina sandpaper, sanding belt speed 2m / min, pressing current 12mA, and micro-grinding pressure 0.6N / mm².

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

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

[0039] 4. Large-scale production data Processing efficiency: 51 hours per piece (78 hours for traditional process), increasing capacity by 34.6%; Cost analysis: Tooling costs are reduced to zero, resulting in a 42.3% reduction in overall costs (tooling costs account for 18% of the cost per piece in traditional processes). Batch consistency: After processing 50 niobium plates continuously, the standard deviation of the edge collapse height σ = 0.003 mm (for traditional process, σ = 0.025 mm).

[0040] Comparison Table of Effects of Examples The detailed implementation data of the above embodiments fully verify the significant advantages of the present invention in terms of edge collapse suppression, efficiency improvement, cost control and cleanliness assurance, and also demonstrate the universality of the technical solution for irregular-shaped parts and large-sized parts.

Claims

1. A method for suppressing edge collapse during grinding of high-purity niobium metal plates, characterized in that, Includes the following steps: (1) Preparation of scrap tooling: The niobium metal scrap generated from the previous waterjet cutting process is used as the same tooling material. The purity of the niobium metal scrap is consistent with that of the niobium plate to be processed and the thickness tolerance is ±0.2mm. (2) Inlay assembly: The niobium metal edge material and the edge of the niobium plate to be processed are combined into a temporary reinforcing fixture by geometric inlay, with the gap between the inlay surfaces ≤0.15mm; (3) Rough grinding: Use 180-grit sandpaper and grind at a belt speed of 1-5 m / min and a current of 10-30 mA until the surface roughness Ra ≤ 1.2 μm; (4) Fine grinding: After removing the temporary reinforcement fixture, fine grinding is carried out using 320-grit sandpaper at a belt speed of 1-3 m / min and a current of 8-15 mA. The final surface roughness Ra ≤ 0.8 μm. (5) Dynamic parameter matching: Based on the strain rate sensitivity index m=0.15-0.25 of the high-purity niobium plate, the current signal of the sand belt load is collected in real time by the current sensor, and the ratio of the sand belt speed to the pressing current is dynamically adjusted based on the PID controller so that the current fluctuation amplitude is controlled within ±1mA.

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

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

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

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