A powder metallurgy rapid prototyping method

Abstract

The application discloses a powder metallurgy rapid forming method, aiming at solving the problems of low material utilization, high oxidation risk, poor size precision and insufficient adaptability of the existing titanium alloy forming process. The method comprises the steps of batching, compression molding, pre-sintering CNC, sintering and post-sintering CNC: in the batching stage, titanium alloy powder and PEG-PVA composite binder are mixed in an oxygen-controlled environment to form a uniform coating layer; after obtaining the green body through compression molding, the first CNC processing under dry low-oxygen protection obtains the enlarged blank body with a reserved shrinkage allowance; then vacuum sintering and the second CNC finishing are carried out, and optional laser shock peening post-processing is carried out. Through low-content binder coating, oxygen control throughout the process and intelligent linkage of CNC-sintering parameters, the material utilization is improved to more than 96%, the oxidation risk is reduced, and the size precision and mechanical properties of the finished product are guaranteed; without the need for precise molds, it is suitable for small-batch and multi-variety production, and can be widely applied to the fields of high-end titanium alloy products such as aerospace and medical implantation.

Description

Technical Field

[0001] This invention relates to the field of powder metallurgy technology, and more specifically to a rapid prototyping method for powder metallurgy. Background Technology

[0002] Titanium alloys, with their excellent specific strength, corrosion resistance, and biocompatibility, are increasingly widely used in high-end fields such as aerospace and medical implants. Powder metallurgy forming technology, due to its ability to achieve near-net-shape manufacturing and reduce material waste, has become one of the mainstream manufacturing methods for titanium alloy products. Currently, in the field of titanium alloy powder metallurgy forming, the mainstream process is injection molding combined with subsequent sintering and processing. However, this existing technology has many unavoidable defects in practical applications. From the perspective of the causes of defects, injection molding requires the addition of a high content of binder (15%-25%) to ensure the flowability of the powder material in the complex mold cavity. This high proportion of binder not only increases the complexity of the subsequent debinding process, but also easily generates internal stress due to uneven decomposition of organic matter during debinding, leading to deformation of the billet. At the same time, the introduction of high binder content increases the risk of titanium alloy oxidation. Because titanium alloys themselves are highly chemically reactive, the interaction between residual binder and oxygen in the debinding, subsequent transfer, and sintering stages can easily cause the oxygen content of the finished product to exceed the standard. Furthermore, injection molding demands extremely high mold precision. Custom-made precision molds are required for products of different specifications and shapes, resulting in long development cycles, high costs, and the need for mold redevelopment when switching product types. This makes it difficult to adapt to the needs of small-batch, multi-variety production. From the perspective of the consequences of these defects, the degreasing deformation and oxidation problems caused by high binder content directly affect the dimensional accuracy and mechanical properties of the finished product, leading to a high scrap rate. This is particularly problematic in applications such as high-precision connectors for aerospace and highly biocompatible products for medical implants, where stringent performance requirements are difficult to meet. The high cost and long lead time of the molds significantly increase production input, limiting rapid product iteration and market responsiveness. Simultaneously, the residual material generated during injection molding is difficult to recycle due to binder residue and oxidation pollution, resulting in a material utilization rate of only about 85%, causing a serious waste of high-value titanium alloy raw materials and further increasing production costs. Besides injection molding, some existing processes use direct compression molding combined with one-time processing after sintering. Although this method can reduce the amount of binder, it does not reserve sintering shrinkage allowance, resulting in large fluctuations in the size of the blank after sintering. This requires a lot of subsequent processing to remove the excess, which not only increases processing costs but also further reduces material utilization. Moreover, the hardness of titanium alloy increases after sintering, significantly increasing processing difficulty and tool wear. It is also difficult to balance production efficiency, cost and product performance.

[0003] For the reasons mentioned above, it is necessary to propose a rapid prototyping method for powder metallurgy to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects in the prior art and provide a rapid prototyping method for powder metallurgy.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: A rapid prototyping method for powder metallurgy includes the following process steps: S1: Ingredients, which are obtained by mixing titanium alloy powder raw materials with binders; S2: Press molding, the powder raw material is poured into the pressing mold and pressed at room temperature to obtain a green body of a specific shape; S3: Pre-sintering CNC machining, the green blank is machined for the first time to obtain an enlarged blank of the target shape; S4: Sintering and shaping: The enlarged blank is placed in a vacuum sintering furnace for vacuum sintering to obtain a sintered blank; S5: After sintering, CNC machining is performed on the sintered blank to obtain the target product.

[0006] Furthermore, the particle size of the titanium alloy powder raw material includes any one of the following particle size ranges or a mixture of multiple particle size ranges: 0.5-10μm, 10-20μm, 20-50μm, 50-100μm, 100-200μm, 200-300μm, and 300-500μm.

[0007] Furthermore, in step S1, the adhesive forms a coating layer on the surface of the titanium alloy powder particles. Step S1 is carried out in an oxygen-controlled environment, with the oxygen content controlled to ≤1000ppm, preferably ≤100ppm.

[0008] Furthermore, the raw materials used for the coating include: PEG-PVA composite adhesive (PEG-1000 / PVA-1788) in a ratio of 5:5, with a total addition of 3-5%, 0.5-1% zinc stearate release agent, 0.2-0.5% cerium oxide nanoparticles, and 99.999% high-purity argon / hydrogen. The step of forming the coating layer in step S1 includes: S11: After several argon gas purgings, titanium alloy powder is premixed with cerium oxide nanoparticles. S12: Add PEG-PVA composite adhesive aqueous solution, stir at medium speed for 1 hour under argon protection, then shear at high speed for 1 hour; S13: Atomize and add a small amount of adhesive, then perform gradient coating for 0.5 hours; S14: Switch to hydrogen activation and curing for 1 hour to enhance interface bonding; S15: Replace residual hydrogen with argon, cool and stir to room temperature to obtain coated powder raw material.

[0009] Furthermore, in step S3, the first CNC machining is a dry machining process, controlling the oxygen content to ≤1000ppm, preferably ≤100ppm. A protective atmosphere is formed by a mixture of argon and sulfur hexafluoride, wherein the volume ratio of argon to sulfur hexafluoride is 95:5.

[0010] Furthermore, in step S4, the sintering temperature is 1000-1400℃, preferably 1100-1300℃; the sintering time is 2-4 hours. The sintering process includes the following steps: S41: Gas replacement and preparation, argon gas is replaced in the glove box and vacuum furnace, and the oxygen content is controlled to be ≤1000ppm, preferably ≤100ppm. The billet is transferred to the sintering furnace through the glove box, the furnace door is closed, and the vacuum is drawn to within 100pa, preferably within 10pa. S42: Degas the billet, heat it in a vacuum furnace to 50-200℃, maintain it for more than half an hour, and reduce the vacuum degree to within 100pa, preferably within 10pa; S43: Secondary degassing of the billet, heating in an empty furnace to 450-900℃ and maintaining for more than half an hour, with a vacuum degree of less than 100pa, preferably less than 10pa; S44: Sintering of billets, heating in an empty furnace to 1000-1400℃, preferably 1100-1300℃, holding for more than half an hour, with a vacuum degree of less than 100pa, preferably less than 10pa; S45: Sintering is complete. Stop heating and wait until the temperature is below 700℃. Then introduce argon gas and start the circulating cooling system. Sintering is complete when the temperature is below 70℃.

[0011] Furthermore, it also includes a parameter linkage prediction module, which includes a ternary database consisting of the first CNC machining allowance, green body density, and sintering shrinkage rate. Based on the database prediction model, the enlarged allowance size parameters of the enlarged green body are calculated in reverse. The enlargement allowance of the enlarged blank = predicted sintering shrinkage + allowance for the second CNC finishing. The cutting parameters for the first CNC machining are guided by the enlarged allowance.

[0012] Furthermore, it also includes post-sintering laser shock peening treatment, which involves strengthening the target product with laser shock peening after the second CNC machining to improve the surface hardness and fatigue strength of the finished titanium alloy product.

[0013] Furthermore, the laser impact processing uses a fiber laser with a laser power of 2000-2500W, a scanning speed of 300-500mm / s, and a spot diameter of 3mm. The surface of the finished product is impacted under an argon protective atmosphere.

[0014] The advantages and beneficial effects of this invention are as follows: First, the material utilization rate is significantly improved. Through closed-loop recycling of CNC machining residue before sintering, the material utilization rate reaches over 96%, greatly reducing the waste of high-value titanium alloy raw materials. Second, the oxidation risk is controllable. The whole-process oxygen control design, combined with low-content adhesive coating, effectively avoids titanium alloy oxidation and ensures the stability of finished product performance. Third, the dimensional accuracy is high. Relying on the intelligent linkage of CNC and sintering parameters, the sintering shrinkage allowance is precisely reserved, and the dimensional tolerance of the finished product is controllable, meeting the requirements of high-end products. Fourth, the production adaptability is strong. There is no need to customize precision molds. CNC programming can adapt to multi-variety, small-batch production, shortening the development cycle and reducing production costs. Fifth, the performance can be optimized. Laser shock peening post-treatment can be selected to further improve the surface hardness and fatigue strength of the finished product and expand high-end application scenarios. Detailed Implementation

[0015] The specific embodiments of the present invention will be further described below with reference to examples. These examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0016] This invention provides a rapid prototyping method for powder metallurgy, which solves the pain points of traditional titanium alloy powder metallurgy materials such as low utilization rate, poor dimensional accuracy, and insufficient finished product performance through precise oxygen control, intelligent parameter linkage, and post-processing strengthening, while taking into account process flexibility and economy.

[0017] This invention discloses a rapid prototyping method for powder metallurgy, comprising the following steps: The S1 batching process uses precise coating to provide powder raw materials with sufficient strength and controllable oxygen content for subsequent molding and processing; S2 room temperature pressing molding quickly obtains preliminary green blanks, avoiding the impact of high temperature forming on the properties of titanium alloys; S3 pre-sintering CNC machining uses "dry low oxygen protection + intelligent allowance setting" to obtain an enlarged blank that is close to the target shape in advance, which reduces the subsequent machining allowance and reserves precise space for sintering shrinkage. S4 vacuum sintering achieves compaction of the green body through multi-stage degassing and precise temperature control, ensuring the mechanical properties of the material. After sintering, S5 is finished by CNC machining to ensure the dimensional accuracy of the finished product. The entire process breaks away from the traditional single-sequence logic of "forming-sintering-processing". Through pre-processing before sintering and intelligent parameter control, the "processing-sintering" process is coordinated and matched. At the same time, the whole-process oxygen control design solves the core problem of the high activity and easy oxidation of titanium alloys.

[0018] Specifically: Titanium alloy powder particle size selection: A variety of particle sizes and mixing ratios within the range of 0.5-500μm can be selected. The core design logic is to use a multi-particle-size gradient combination (such as combining nano-powder with micro-powder) to allow fine powder to fill the gaps between coarse powder, thereby improving the density of the green body. Different particle size ranges are suitable for different application scenarios. Fine-particle-size powder (0.5-20μm) can improve molding accuracy and is suitable for high-precision products such as medical implants; coarse-particle-size powder (20-500μm) can reduce raw material costs and improve flowability, making it suitable for mass production of large aerospace structural components.

[0019] Ingredient Coating Stage: This stage is crucial for ensuring the strength of the green body. It employs a multi-stage mechanism of physical dispersion, wetting, adsorption, and coating, using a PEG-PVA composite binder to form a uniform coating layer on the powder surface. The PEG-1000 / PVA-1788 ratio is 5:5 by mass. The key advantage of this ratio is achieving a balance between flowability and bond strength. PEG-1000 possesses excellent flowability, ensuring uniform dispersion and wetting of the powder surface, while PVA-1788 exhibits high bond strength, significantly enhancing the adhesion between powder particles. Together, they avoid the drawbacks of a single binder, such as poor flowability leading to uneven coating or insufficient strength causing cracking of the green body. The total addition amount of PEG-PVA composite binder is 3-5%, zinc stearate release agent is 0.5-1%, and cerium oxide nanoparticles are 0.2-0.5%. All these amounts are by mass and are precisely set based on the specific surface area of ​​the titanium alloy powder and molding requirements, ensuring both green body strength and avoiding excessive additive residues that could negatively impact sintering performance.

[0020] The segmented atmosphere design of the coating process is highly targeted: The S11 argon-replacement premixing is designed to isolate oxygen, prevent the titanium alloy powder from oxidizing in the early stages of mixing, and to premix the titanium alloy powder with cerium oxide nanoparticles at a low speed. S12 is added to an aqueous solution of PEG-PVA composite adhesive and combined with medium-speed stirring and high-speed shearing. Gradient shear force is used to achieve a tight bond between the adhesive and the powder, ensuring the uniformity of the coating layer. S13 atomized adhesive adds a gradient structure of "dense inner layer bonding + uniform outer layer wrapping", which further optimizes the coating effect; S14 hydrogen activation curing is carried out under the conditions of 0.1-0.12MPa and 80-100℃ for 1 hour. Hydrogen can reduce the trace amount of original oxide film on the surface of titanium powder, increase the active sites on the powder surface, and enable the binder to form a "pinning" chemical bond with the titanium powder. At the same time, it can improve the solid solubility of cerium oxide and strengthen the interfacial bonding. Argon purging cooling in S15 avoids the safety hazards posed by residual hydrogen in subsequent processes, while also ensuring the stability of the coated powder. The entire coating process is carried out in an oxygen-controlled environment with an oxygen content ≤1000ppm, controlling the increase in powder oxygen content from the source.

[0021] The pre-sintering CNC machining (S3) employs a dry machining mode (liquid-free and oil-free). The core purpose is to avoid oxygen contamination introduced by liquid media. Simultaneously, a protective atmosphere is created using a 95:5 volume ratio mixture of argon and sulfur hexafluoride. Argon acts as an inert gas to isolate oxygen, while sulfur hexafluoride forms a lubricating film on the tool surface, reducing localized high-temperature oxidation caused by cutting friction and minimizing tool wear. The design, controlling the oxygen content to ≤1000ppm, balances the cost and effectiveness of oxygen control while meeting the performance requirements of titanium alloy green blank machining.

[0022] The CNC machining residue before sintering can be reused without affecting the performance of the finished product. Since the residue has not undergone high-temperature sintering, its chemical composition, physical state, and interfacial bonding characteristics remain unchanged. From the perspective of the residue's inherent characteristics, the pre-sintering green blank only undergoes batching, coating, and room-temperature pressing. The titanium alloy powder particles retain their original chemical activity and particle size distribution, with physical bonding between particles achieved only through a low-content PEG-PVA composite binder, without forming the metallurgical bonding layer required after sintering. The first CNC machining is performed in a dry, low-oxygen environment, combined with a protective atmosphere of argon and sulfur hexafluoride, effectively preventing oxidation of the residue during processing. The oxygen content of the residue can be stably controlled below 0.2%, essentially consistent with the oxygen content level of the original titanium alloy powder, preventing the introduction of impurities or alteration of the titanium alloy matrix properties due to oxidation. In terms of reusability, the composition of the scrap material is completely consistent with the original coating powder, with only the physical form being different. When reusing it for the second time, a small amount of debris and impurities that may be generated during the processing can be removed by simple sieving. Then, it can be mixed with new titanium alloy powder in proportion, resulting in a high reuse rate of the scrap material, which can be re-entered into the batching and coating process. Since the low content of binder in the scrap material has not undergone high-temperature decomposition, its bonding characteristics can still meet the requirements of subsequent pressing and molding. The key indicators such as density and strength of the green body formed after mixing are basically the same as those of the green body prepared from virgin raw materials, realizing the efficient closed-loop recycling of the scrap material.

[0023] The vacuum sintering stage (S4): A multi-stage heating and exhaust design is crucial for ensuring sintering quality. It includes the following steps: Argon purging and vacuum pretreatment in S41 ensure a low-oxygen environment in the furnace and avoid oxidation during billet transfer and early sintering. Argon purging is performed in the glove box and vacuum furnace to control the oxygen content to ≤1000ppm, preferably ≤100ppm. The billet is transferred to the sintering furnace through the glove box, the furnace door is closed, and the vacuum is drawn to within 100pa, preferably within 10pa. S42 low-temperature exhaust (50-200℃) mainly removes free moisture and a small amount of volatile additives from the billet; the billet is exhausted by heating it in a vacuum furnace to 50-200℃ and maintaining it for more than half an hour, with the vacuum degree to within 100pa, preferably within 10pa. S43 medium-temperature exhaust (450-900℃) removes residual binder and organic matter to prevent rapid decomposition of organic matter during high-temperature sintering, which could lead to cracking of the green body; secondary exhaust, heating the empty furnace to 450-900℃ and maintaining it for more than half an hour, with a vacuum degree of less than 100pa, preferably less than 10pa. S44 high-temperature sintering (1000-1400℃, preferably 1100-1300℃) achieves diffusion bonding and densification of titanium alloy powder particles. This temperature range matches the phase transformation characteristics of titanium alloy, which can ensure the degree of sintering densification and avoid excessive grain growth that affects performance. The S45 segmented cooling design utilizes argon protection and circulating cooling to prevent internal stress caused by rapid cooling of the high-temperature billet, while also preventing oxidation during the cooling process. The vacuum level is controlled within 100 Pa (preferably within 10 Pa) throughout the process, further reducing oxygen contamination and impurity residue.

[0024] The parameter linkage prediction module, at its core, breaks through the limitations of traditional methods that rely on experience to set machining allowances by constructing a ternary database of "first CNC machining allowance - green compaction density - sintering shrinkage rate". Based on a prediction model trained with extensive experimental data, the module can accurately predict sintering shrinkage according to parameters such as the actual compaction density of the current batch of green compacts, and then reverse-calculate the enlargement allowance for the enlarged compact (enlargement allowance = predicted sintering shrinkage + second CNC finishing allowance), automatically matching the cutting parameters of the first CNC machining. This design achieves precise linkage between "machining" and "sintering", avoiding material waste and increased processing costs caused by excessive allowances, while solving the problem of out-of-tolerance finished product dimensions caused by insufficient allowances, significantly improving production consistency.

[0025] The laser shock peening post-treatment, as an optional performance enhancement step, is performed after the second CNC finishing. The core principle is to use a high-energy laser to vaporize a thin layer on the surface of the finished product, forming plasma. This plasma expands and generates a high-pressure shock wave exceeding 1 GPa, causing plastic deformation of the surface and forming a 200-500 μm thick strengthening layer. This process can refine the surface grains to the submicron level while introducing residual compressive stress, ultimately achieving an increase in surface hardness to HV1200-1400, a fatigue strength increase of over 22%, and a 3-fold extension of high-temperature oxidation resistance life. This effectively solves the traditional problem of balancing strength and toughness in titanium alloy finished products, expanding the application scenarios of the product under high-temperature and high-load conditions.

[0026] Example 1: Molding of titanium alloy connectors for aerospace applications 1. Application requirements: To prepare Ti-6Al-4V titanium alloy connectors, with surface hardness ≥ HV1200, fatigue strength ≥ 800MPa, material utilization rate ≥ 95%, and finished product dimensional tolerance ± 0.02mm.

[0027] 2. Process parameter settings: S1 Ingredients: Titanium alloy powder is selected from 10-20μm (70%) + 50-100μm (30%) by mass ratio, PEG-1000 / PVA-1788 composite binder (5:5 mass ratio) with a total addition of 4%, zinc stearate release agent 0.8%, cerium oxide nanoparticles 0.3%; oxygen content in the controlled oxygen environment is 800ppm; S11 was purged with argon gas 3 times (each time at 0.1 MPa for 10 min), and titanium alloy powder was premixed with cerium oxide at low speed (40 r / min) for 10 min. S12 was added to a PEG-PVA composite adhesive aqueous solution with a solid content of 20%, and stirred at medium speed (70 r / min) for 1 h under argon protection, followed by high speed (110 r / min) shearing for 1 h. S13 is atomized with an aqueous solution containing 10% of the total binder, and then gradient-coated at 80 r / min for 0.5 h. S14 is activated and cured with hydrogen (0.11MPa, 90℃) for 1 hour; The mixture was purged with argon gas three times using S15, stirred at 30 r / min and cooled to room temperature to obtain the coated powder.

[0028] S2 compression molding: The coated powder is injected into the mold and pressed at 350MPa at room temperature to obtain a green body (density 89%, transverse tensile strength 13MPa).

[0029] S3 CNC before sintering: Dry machining mode, argon and sulfur hexafluoride mixed protective atmosphere (volume ratio 95:5), oxygen content controlled at 850ppm; input data such as green compact density of 89% into the parameter linkage prediction module, predict sintering shrinkage of 0.7mm, set the enlargement allowance = 0.7mm + 0.3mm (finishing allowance) = 1.0mm; cutting parameters: cutting speed 200m / min, feed rate 0.08mm / r, depth of cut 0.2mm; completed in three steps: roughing (removing 75% of the allowance), semi-finishing (removing 20% ​​of the allowance), and finishing, to obtain an enlarged green body (dimensional tolerance ±0.01mm).

[0030] S4 sintering: S41 argon-purified glove box and sintering furnace, oxygen content controlled at 80ppm, billet transferred to furnace through glove box and vacuumed to 8pa; S42 is heated to 150℃ and held for 1 hour, while maintaining a vacuum of 8 Pa. S43 is heated to 600℃ and held for 1 hour, while maintaining a vacuum of 8 Pa. S44 is heated to 1200℃ and held for 3 hours, while maintaining a vacuum of 8 Pa. S45 heating is stopped. When the temperature drops to 650℃, argon gas is introduced and the circulating cooling system is turned on. Sintering ends when the temperature drops to 65℃, and a sintered green body (density 98.5%) is obtained.

[0031] S5 sintered CNC: conventional wet machining, cutting parameters: cutting speed 300m / min, feed rate 0.1mm / r, depth of cut 0.1mm, finishing to target size.

[0032] Laser shock peening: A 2.5kW fiber laser with a laser power of 2200W, a scanning speed of 400mm / s, and a spot diameter of 3mm is used for processing under an argon protective atmosphere.

[0033] Finished product performance testing: surface hardness HV1320, fatigue strength 850MPa, high temperature oxidation resistance life (600℃) 1200h, material utilization rate 96.2%, dimensional tolerance ±0.015mm, fully meeting the application requirements of aerospace connectors.

[0034] Example 2: Molding of Titanium Alloy Artificial Joints for Medical Implantation Application requirements: To prepare pure titanium artificial joints, with excellent biocompatibility (low impurity residue), surface hardness ≥ HV1200, fatigue strength ≥ 750 MPa, material utilization rate ≥ 95%, and finished product surface roughness Ra ≤ 0.8 μm.

[0035] Process parameter settings: S1 Ingredients: Titanium alloy powder of 0.5-10μm (pure titanium powder), PEG-1000 / PVA-1788 composite binder (5:5 mass ratio) total addition of 3.5%, zinc stearate release agent 0.6%, cerium oxide nanoparticles 0.2%; oxygen-controlled environment with oxygen content of 600ppm; S11 Argon purging 3 times, titanium alloy powder and cerium oxide premixed at low speed (35r / min) for 10min; S12 Add 20% solid content PEG-PVA composite adhesive aqueous solution, stir at medium speed (65r / min) for 1h under argon protection + shear at high speed (100r / min) for 1h. S13 is atomized with an aqueous solution containing 10% of the total binder, and then gradient-coated at 80 r / min for 0.5 h. S14 is activated and cured with hydrogen (0.1MPa, 85℃) for 1 hour; The material was purged with argon gas three times using S15, stirred at 25 r / min and cooled to room temperature to obtain the coated powder.

[0036] S2 compression molding: The coated powder is injected into the mold and pressed at 320MPa at room temperature to obtain a green body (density 88%, transverse tensile strength 12.5MPa).

[0037] S3 CNC before sintering: Dry machining mode, argon and sulfur hexafluoride mixed protective atmosphere (volume ratio 95:5), oxygen content controlled at 700ppm; input data such as green compact density of 88% into the parameter linkage prediction module, predict sintering shrinkage of 0.6mm, set the enlargement allowance = 0.6mm + 0.25mm (finishing allowance) = 0.85mm; cutting parameters: cutting speed 150m / min, feed rate 0.06mm / r, depth of cut 0.15mm; three-step machining to obtain the enlarged green body (dimensional tolerance ±0.01mm).

[0038] S4 sintering: S41 argon-purified glove box and sintering furnace, oxygen content controlled at 50ppm, billet transferred to furnace through glove box and vacuumed to 5pa; S42 is heated to 120℃ and held for 1 hour, while maintaining a vacuum of 5 Pa. S43 is heated to 550℃ and held for 1 hour, while maintaining a vacuum of 5 Pa. S44 is heated to 1150℃ and held for 2.5 hours, with the vacuum level maintained at 5 Pa. S45 heating is stopped. When the temperature drops to 600℃, argon gas is introduced and the circulating cooling system is turned on. Sintering ends when the temperature drops to 60℃, and a sintered green body (density 98.2%) is obtained.

[0039] S5 sintered CNC: conventional wet machining, cutting parameters: cutting speed 250m / min, feed rate 0.08mm / r, depth of cut 0.08mm, finishing to target size (surface roughness Ra≤0.6μm).

[0040] Laser shock peening: A 2.5kW fiber laser with a laser power of 2000W, a scanning speed of 350mm / s, and a spot diameter of 3mm is used for processing under an argon protective atmosphere.

[0041] Finished product performance testing: surface hardness HV1280, fatigue strength 780MPa, high temperature oxidation resistance life (37℃ human body simulation environment) no decay, material utilization rate 96.5%, impurity residue ≤0.01%, surface roughness Ra=0.5μm, biocompatibility meets GB / T13810-2017 standard, and meets the application requirements of artificial joints for medical implantation.

[0042] In summary, compared to traditional injection molding, the "compression molding + pre-sintering CNC machining" process combination is not a simple process replacement, but a precise adaptation to the pain points of high-end titanium alloy product manufacturing. Its core advantages are highly tied to applicable scenarios, which can be summarized as follows: In terms of applicable scenarios, this process is more suitable for the production of small-batch customized titanium alloy products with complex structures and high-performance requirements, especially meeting the needs of high-end fields such as aerospace and medical implants. These scenarios often have stringent standards for product dimensional accuracy, mechanical properties, biocompatibility, or high-temperature oxidation resistance, while also having small batch sizes and rapid product iteration, making it difficult to bear the high precision mold development costs and long cycles of injection molding. For example, Ti-6Al-4V titanium alloy connectors used in aerospace applications need to meet high mechanical performance requirements such as surface hardness ≥ HV1200 and fatigue strength ≥ 800MPa, and dimensional tolerances need to be controlled within ±0.02mm; pure titanium artificial joints for medical implants have mandatory requirements for biocompatibility and low impurity residues, while ensuring a surface roughness Ra≤0.8μm. In these scenarios, injection molding is difficult to balance precision, performance and cost, while CNC process before sintering can achieve precise matching.

[0043] From the perspective of core advantages, firstly, it offers superior cost and flexibility. Injection molding requires customized precision molds, resulting in high mold development costs and long lead times. Furthermore, mold iteration costs are extremely high when switching product types. In contrast, the pre-sintering CNC process utilizes cold isostatic pressing flexible molds combined with programming processing, eliminating the need for complex mold investment. Modifications only require adjustments to the CNC program, making it particularly suitable for small-batch, multi-variety production. As in the two embodiments mentioned above, whether it's the small-batch production of aerospace connectors or artificial joints, there is no need to bear mold development costs, significantly reducing upfront investment. Secondly, it offers superior material utilization and performance. Injection molding requires the addition of 15-25% high-content binder to ensure mold filling fluidity. This not only easily leads to deformation and introduces oxidative contamination during the degreasing process, but also makes it difficult to reuse the leftover material due to binder residue and oxidation, resulting in a material utilization rate of only about 85%. In contrast, this process uses 3-5% low-content PEG-PVA composite binder, combined with a closed-loop recycling design for CNC machining residue before sintering, increasing material utilization to over 96%. For example, the material utilization rate in the aerospace connector example reaches 96.2%, and in the artificial joint example, it reaches 96.5%. Simultaneously, the low binder content reduces the risk of degreasing residue and oxidation. Combined with a full-process oxygen control design, it ensures high product performance—the finished aerospace connector has a fatigue strength of 850MPa and a high-temperature oxidation resistance life of 1200h, while the artificial joint has an impurity residue of ≤0.01%, all superior to injection molding. Thirdly, it has a stronger capability for processing complex structures. Injection molding presents significant challenges in filling and demolding parts with deep holes, complex internal cavities, and large wall thickness differences, easily leading to issues such as uneven density and dimensional deviations. In contrast, CNC machining before sintering allows for precise processing of complex features through accurate programming, while a parameter-linked prediction module reserves precise sintering shrinkage allowance, ensuring the dimensional accuracy of the finished product. For example, in both embodiments, the enlarged blank dimensional tolerance is controlled within ±0.01mm, and the final finished product dimensional tolerance is ≤±0.015mm with a surface roughness Ra≤0.6μm, fully meeting the precision requirements of high-end products.

[0044] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A rapid prototyping method for powder metallurgy, characterized in that, The process includes the following steps: S1: Ingredients, which are obtained by mixing titanium alloy powder raw materials with binders; S2: Compression molding, the powder raw material is poured into the compression mold and compressed at room temperature to obtain a green body of a specific shape; S3: Pre-sintering CNC machining, the green blank is machined for the first time to obtain an enlarged blank of the target shape; S4: Sintering and shaping: The enlarged blank is placed in a vacuum sintering furnace for vacuum sintering to obtain a sintered blank; S5: After sintering, CNC machining is performed on the sintered blank to obtain the target product.

2. The rapid prototyping method for powder metallurgy according to claim 1, characterized in that, The particle size of the titanium alloy powder raw material includes any one of the following particle size ranges or a mixture of multiple particle size ranges: 0.5-10μm, 10-20μm, 20-50μm, 50-100μm, 100-200μm, 200-300μm, and 300-500μm.

3. The rapid prototyping method for powder metallurgy according to claim 1, characterized in that, In step S1, the adhesive forms a coating layer on the surface of the titanium alloy powder particles. Step S1 is carried out in an oxygen-controlled environment with an oxygen content ≤1000ppm.

4. The rapid prototyping method for powder metallurgy according to claim 3, characterized in that, The raw materials used for the coating include: PEG-PVA composite adhesive, with a mass ratio of 5:5, and a total addition of 3-5%, 0.5-1% zinc stearate release agent, 0.2-0.5% cerium oxide nanoparticles, and 99.999% high-purity argon / hydrogen. The step of forming the coating layer in step S1 includes: S11: After several argon gas purgings, titanium alloy powder is premixed with cerium oxide nanoparticles. S12: Add PEG-PVA composite adhesive aqueous solution, stir at medium speed for 1 hour under argon protection, then shear at high speed for 1 hour; S13: Atomize and add a small amount of adhesive, then coat in a gradient manner for 0.5 hours; S14: Switch to hydrogen activation and curing for 1 hour to enhance interface bonding; S15: Argon gas is used to replace the residual hydrogen gas, and the mixture is cooled and stirred to room temperature to obtain the coated powder raw material.

5. The rapid prototyping method for powder metallurgy according to claim 1, characterized in that, In step S3, the first CNC machining is a dry machining process, with the oxygen content controlled to be ≤1000ppm. A protective atmosphere is created using a mixture of argon and sulfur hexafluoride.

6. The rapid prototyping method for powder metallurgy according to claim 1, characterized in that, In step S4, the sintering temperature is 1000-1400℃; the sintering time is 2-4 hours. The sintering process includes the following steps: S41: Gas replacement and preparation, argon gas is replaced in the glove box and vacuum furnace, and the oxygen content is controlled to be ≤1000ppm, preferably ≤100ppm. The billet is transferred to the sintering furnace through the glove box, the furnace door is closed, and the vacuum is drawn to within 100pa, preferably within 10pa. S42: Degas the billet, heat it in a vacuum furnace to 50-200℃, maintain it for more than half an hour, and reduce the vacuum degree to within 100pa, preferably within 10pa; S43: Secondary degassing of the billet, heating in an empty furnace to 450-900℃ and maintaining for more than half an hour, with a vacuum degree of less than 100pa, preferably less than 10pa; S44: Sintering of billets, heating in an empty furnace to 1000-1400℃, preferably 1100-1300℃, and holding for more than half an hour, with a vacuum degree of less than 100pa, preferably less than 10pa; S45: Sintering is complete. Stop heating and wait until the temperature is below 700℃. Then introduce argon gas and start the circulating cooling system. Sintering is complete when the temperature is below 70℃.

7. The rapid prototyping method for powder metallurgy according to claim 1, characterized in that, It also includes a parameter linkage prediction module, which includes a ternary database consisting of the first CNC machining allowance, green body density and sintering shrinkage rate, and calculates the enlarged allowance size parameters of the enlarged green body in reverse according to the database prediction model. The enlargement allowance of the enlarged blank = predicted sintering shrinkage + allowance for the second CNC finishing. The enlarged allowance guides the cutting parameters for the first CNC machining.

8. The rapid prototyping method for powder metallurgy according to claim 1, characterized in that, It also includes post-sintering laser shock peening treatment, which strengthens the target product with laser shock after the second CNC machining, thereby improving the surface hardness and fatigue strength of the finished titanium alloy product.

9. The rapid prototyping method for powder metallurgy according to claim 8, characterized in that, The laser impact processing uses a fiber laser with a laser power of 2000-2500W, a scanning speed of 300-500mm / s, and a spot diameter of 3mm. The surface of the finished product is impacted under an argon protective atmosphere.