A method for rheo-pressing of powder metallurgical large components

Abstract

The application discloses a kind of powder metallurgy large components rheological pressure injection preparation method, raw material powder and organic binder are mixed to obtain material group, material group is shaped to obtain rheological pressure injection material, rheological pressure injection material is preheated to 10-50 ℃ higher than material softening point temperature, then under the pressure of 20 ~ 200MPa, rheological pressure injection material is injected into the mold that has been preheated to 10-50 ℃ higher than material softening point temperature through flow channel, then carries out pressure maintaining 1-60min, stop mold heating, after mold cooling, blank solidification is released to obtain large component blank, large component blank is carried out and is released, sintered to obtain large component, the powder metallurgy large component product obtained by the preparation method has the following effects, wherein the shape complexity of the component product can be higher;The dimensional accuracy control of sintered product is excellent, and the wall thickness of large component can be ≥15mm, weight ≥1kg.

Description

Technical Field

[0001] This invention relates to a rheological injection molding method for preparing large powder metallurgy components, belonging to the fields of powder metallurgy and powder engineering technology. Background Technology

[0002] Powder metallurgy products are widely used in automotive parts, high-speed rail equipment, and electronic information devices, making them a crucial product category in Industry 4.0 manufacturing. As high-end equipment and devices place higher demands on lightweight components, high service performance, and form-fit integration, powder metallurgy products are showing a trend towards more complex shapes, larger sizes, more diverse compositions, and integrated functions. This presents significant challenges to traditional powder metallurgy manufacturing technologies. Besides the high costs of hot isostatic pressing (HIP) and additive manufacturing (AM), traditional powder metallurgy pressing-sintering, cold isostatic pressing, and powder injection molding are insufficient for near-net-shape manufacturing of complex, large powder metallurgy products. While HIP involves placing powder within a complex encapsulation structure and sintering it under high temperature and pressure to achieve near-net-shape forming of large-sized powder metallurgy products with complex structures, this technology suffers from low production efficiency and extremely high manufacturing costs, making it suitable only for manufacturing special, difficult-to-process, and difficult-to-sinter high-value-added products. In recent years, additive manufacturing technology has developed rapidly, but it still suffers from problems such as a limited variety of printable materials, insufficient uniformity of structure, and large differences in mechanical properties, making it difficult to meet the needs of my country's powder metallurgy manufacturing industry. Summary of the Invention

[0003] To address the problems of high manufacturing costs, limited applicable material types, and poor material dimensional stability in the preparation of large-size complex products using existing powder metallurgy methods, the present invention aims to provide a rheological injection molding method for preparing large powder metallurgy components. This method utilizes the good flowability of the forming material above the binder softening point temperature to achieve injection molding of a high-uniformity density preform. Combined with the matching design of the powder material and the multi-component binder, a two-step debinding process is employed to achieve non-destructive and efficient removal of the binder from large products. Finally, after sintering and densification, the rapid manufacturing of large-size complex powder metallurgy products can be achieved.

[0004] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0005] This invention provides a method for preparing large powder metallurgy components by rheological injection molding. The method involves mixing raw material powder and an organic binder to obtain a material agglomerate, shaping the agglomerate to obtain a rheological injection molding material, preheating the rheological injection molding material to a temperature 10-50°C above its softening point, and then injecting the rheological injection molding material through a flow channel into a mold preheated to a temperature 10-50°C above its softening point under a pressure of 20-200 MPa, preferably 20-50 MPa. The pressure is then maintained for 1-60 minutes, mold heating is stopped, and the mold is allowed to cool and solidify. After demolding, a large component blank is obtained. The large component blank is then degreased and sintered to obtain the large component. The raw material powder is selected from at least one of metal powder, ceramic powder, metal-ceramic composite powder, and metal-coated ceramic composite powder. The organic binder, by volume percentage, comprises: 65-90 vol% filler binder, 5-35 vol% backbone binder, and 2-8 vol% additives.

[0006] This invention provides an innovative method for preparing large powder metallurgy components by rheological injection molding. The method involves preheating the rheological injection material to a temperature above its softening point, causing it to exhibit shear-thinning and easy-flowing properties. Then, under a certain pressure, the rheological injection material is injected through a flow channel into a mold that has been preheated to a temperature 10-50°C above its softening point. After cooling, solidification, and demolding, a blank with high surface quality, complex shape and structure, and high uniformity of density is obtained. Finally, through debinding and sintering, a highly uniform and dense precision part blank is obtained.

[0007] The binder for powder metallurgy rheological injection molding materials of the present invention adopts a high filler binder content, provides the strength of the blank with a small amount of suitable backbone binder, and forms a large amount of filler binder to form interconnected channels, thereby achieving efficient and complete debinding of large parts. Furthermore, based on the use of smaller binders, the binder components are easier and faster to remove. At the same time, the powder solid phase content is increased, which reduces the linear shrinkage of sintering and better controls dimensional accuracy.

[0008] In a preferred embodiment, when the raw material powder is metal powder, the particle size of the metal powder is 5-100 μm, preferably 10-50 μm. Because the raw material powder accounts for a high proportion and has a higher powder loading in the material of this invention, the sintering shrinkage rate is relatively low, and the requirements for the sintering activity of the powder are lower. Therefore, raw material powder with a larger particle size than that used in injection molding can be used, resulting in lower oxygen content, higher fluidity, and, in conjunction with rheological injection molding, higher precision, better performance, and lower cost.

[0009] In a further preferred embodiment, the metal powder is spherical. This spherical gold powder is prepared by methods such as water atomization, gas atomization, and plasma spheroidization.

[0010] In a further preferred embodiment, the metal powder is composed of fine particles with a particle size of 5-20 μm and coarse particles with a particle size of 30-50 μm, wherein the mass ratio of coarse particles to fine particles is 5-9:1-5. By combining coarse and fine particles, the powder volume content can be further increased, thereby improving the dimensional control accuracy of the rheological injection molded products.

[0011] In a preferred embodiment, when the raw material powder is selected from ceramic powder or metal-ceramic composite powder, the particle size of the ceramic powder or metal-ceramic composite powder is 20-500 μm, preferably spherical powder of 50-200 μm; the ceramic powder is obtained by spheroidizing ceramic fine powder with a particle size of 0.05-10 μm, preferably 0.5-5 μm, and the metal-ceramic composite powder is obtained by spheroidizing ceramic fine powder and metal fine powder with a particle size of 0.05-10 μm, preferably 0.5-5 μm.

[0012] In a further preferred embodiment, the ceramic powder is obtained by mixing ceramic fine powder NO with binder A, followed by spheroidizing, granulation, and pre-sintering. The ratio of the pre-sintering temperature T1 to the sintering temperature T0 of the green body obtained after pressing and molding the powder metallurgy rheological injection material into the finished product is 0.6-0.9, preferably 0.7-0.8.

[0013] More preferably, the amount of binder A added is 0.5-3.0 wt% of the ceramic fine powder, and binder A is selected from at least one of paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, polyethylene glycol, polyvinyl alcohol, methylcellulose, and rubber.

[0014] In actual operation, ceramic fine powder NO is mixed with binder A by wet ball milling or stirring, and the spheroidizing granulation process is spray granulation, ultrasonic spray drying, or other types of drying spheroidizing treatment processes.

[0015] In a further preferred embodiment, the metal-ceramic composite powder is obtained by mixing ceramic fine powder N1, metal fine powder M1 and binder B, followed by spheroidization, granulation and pre-sintering. The ratio of the pre-sintering temperature T1 to the sintering temperature T0 of the green body obtained after pressing and molding with powder metallurgy rheological injection material is 0.6-0.9, preferably 0.7-0.8.

[0016] The metal-ceramic composite powder obtained through the above spheroidization treatment not only has high fluidity but also a certain strength, which allows it to maintain the spherical shape of the powder during the mixing process with the binder and prevent it from being sheared and broken. By controlling the pre-firing temperature within the above ratio range, the powder can have both high sintering activity and good strength.

[0017] More preferably, the particle size of both the ceramic fine powder N1 and the metal fine powder M1 is 0.05-10μm, preferably 0.5-5μm, and the amount of binder B added is 0.5-3.0wt% of the total mass of the ceramic fine powder N1 and the metal fine powder M1. The binder B is selected from at least one of paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, polyethylene glycol, polyvinyl alcohol, methylcellulose, and rubber.

[0018] More preferably, the ceramic in the ceramic fine powder N1 is selected from at least one of tungsten carbide, molybdenum carbide, titanium carbide, silicon carbide, titanium nitride, titanium boride, boron nitride, iron oxide, nickel oxide, aluminum oxide, magnesium oxide, zirconium oxide, nickel ferrite, manganese ferrite, cobalt ferrite, zinc ferrite, copper ferrite, chromium ferrite, and iron ferrite.

[0019] In a further preferred embodiment, the metal in the fine metal phase powder M1 is selected from at least one of W, Mo, Zr, Ti, Co, Ni, Fe, Cu, Al, Zn, Sn, Ag, Au, and Pb.

[0020] In actual operation, ceramic fine powder N1 and metal fine powder M1 are mixed with binder B by wet ball milling or stirring. The spheroidizing granulation process includes spray granulation, ultrasonic spray drying, and other types of drying spheroidizing treatment processes.

[0021] In a preferred embodiment, when the raw material powder is a metal-coated ceramic composite powder, the average particle size of the metal-coated ceramic composite powder is 150–350 μm. The inventors have discovered that metal-coated ceramic composite powder has higher flowability, and by controlling the particle size within the aforementioned range, the final large-scale component exhibits optimal performance.

[0022] A further preferred embodiment is that the metal-coated ceramic composite powder is obtained as follows: first, ceramic phase fine powder N2, metal core fine powder M2, and binder C are mixed to obtain a mixed powder; the mixed powder is pressed into blocks, sieved, and granulated to obtain composite particle powder; the composite particle powder is then self-ground and spheroidized with metal binder phase fine powder M3 to obtain a core-shell structured porous spherical composite powder; finally, the porous spherical composite powder is pre-sintered to obtain spherical metal-ceramic composite powder. The ceramic in the ceramic fine powder N2 is selected from tungsten carbide. The metal in the metal core fine powder M2 is selected from at least one of the following: molybdenum carbide, titanium carbide, silicon carbide, titanium nitride, titanium boride, boron nitride, iron oxide, nickel oxide, aluminum oxide, magnesium oxide, zirconium oxide, nickel ferrite, manganese ferrite, cobalt ferrite, zinc ferrite, copper ferrite, chromium ferrite, and iron ferrite; the metal in the metal core fine powder M2 is selected from at least one of W, Mo, Zr, Ti, Co, Ni, and Fe; and the metal in the metal binder fine powder M3 is selected from at least one of Cu, Al, Zn, Sn, Ag, Au, and Pb.

[0023] The spherical powder obtained by the above method has a core-shell structure, high density, uniform particle size, good flowability, and is easy to sinter.

[0024] More preferably, the volume ratio of the ceramic phase fine powder N2 to the metal core fine powder M2 is 1 to 8:1. Controlling the volume ratio of the ceramic phase fine powder to the metal core fine powder M2 within the above range can ensure a uniform dispersion distribution between the ceramic phase and metal phase powders with large density differences.

[0025] More preferably, the binder C is selected from at least one of paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, polyethylene glycol, polyvinyl alcohol, methylcellulose, and rubber. Adding a small amount of binder C to the mixed powder can ensure particle bonding strength while increasing surface viscosity, thereby promoting the coating of the metal binder phase during self-grinding.

[0026] More preferably, the amount of binder C added is 1 to 5% of the mass of the mixed powder.

[0027] In a further preferred embodiment, ceramic phase fine powder N2, metal core fine powder M2, and binder C are mixed and then dried to obtain a mixed powder, wherein the drying temperature is 100-120°C.

[0028] More preferably, the mixing method is wet ball milling, the medium for wet ball milling is deionized water, the rotation speed of wet ball milling is 60-200 rpm, and the wet ball milling time is 15-60 min. Wet ball milling ensures that the mixed powder is fully and uniformly dispersed.

[0029] In actual operation, wet ball milling can be carried out in a drum ball mill, and drying can be carried out in a blower drying oven.

[0030] In a preferred embodiment, the pressure for pressing into blocks is 30–50 MPa. By controlling the pressing pressure within this range, it is possible to press into briquettes while also effectively crushing them to obtain composite granular powder through sieving.

[0031] In a preferred embodiment, the granules obtained by sieving (-40 mesh + 100 mesh) are the composite particle powder. The inventors have discovered that the composite particle powder with the above particle size has optimal flowability, which is beneficial for ensuring the smooth progress of self-grinding and balling.

[0032] In a preferred embodiment, the volume ratio of the composite particle powder to the metal binder phase fine powder M3 is 5–8:1. Controlling the volume ratio of the composite particle powder to the metal binder phase fine powder M3 within this range ensures that the metal binder phase fine powder M3 coats the composite particles without agglomerating itself.

[0033] In a preferred embodiment, the self-grinding spheroidization is carried out in a drum ball mill, the rotational speed of the self-grinding spheroidization is 100-400 r / min, preferably 150-250 r / min, and the self-grinding spheroidization time is 10-40 h, preferably 20-30 h.

[0034] The self-grinding spheroidization process in this invention involves feeding composite particle powder and fine metal binder powder M3 into a drum ball mill. Under conditions of no grinding balls and no media, the particles are self-grinded for an extended period. During the high-speed rotation of the drum, the surface tension and inter-particle attraction of the powder particles cause them to spontaneously aggregate into near-spherical shapes. In this process, due to the high surface viscosity of the large-diameter composite particles containing the organic binder, a layer of binder C initially adheres, forming an initial coating structure. Further rotation causes the surface tension between the fine powder particles to continuously thicken the coating layer. Simultaneously, collisions between the particles prevent the fine powder from agglomerating and gradually increase the sphericity of the coated particles, ultimately forming near-spherical particles with a certain regular shape.

[0035] In a preferred embodiment, the pre-sintering is carried out in a protective atmosphere, the pre-sintering temperature is 600-1000℃, and the holding time is 30-180min.

[0036] Pre-firing further densifies the spherical powder, eliminating internal defects, and also improves the strength of the composite powder.

[0037] In a further preferred embodiment, the protective atmosphere is selected from at least one of nitrogen, argon, helium, and carbon monoxide.

[0038] In a preferred embodiment, the volume fraction of the raw material powder in the powder metallurgy rheological injection material is 50%–62%; preferably 55–62%.

[0039] In a preferred embodiment, the organic binder, by volume percentage, comprises: 70-80 vol% filler binder, 12-27 vol% backbone binder, and 3-5 vol% additives. Using this preferred organic binder formulation, the resulting powder metallurgy rheostat casting material, after rheostat casting sintering, yields products with optimal performance.

[0040] More preferably, the filler binder is selected from at least one of paraffin wax, carnauba wax, microcrystalline wax, beeswax, polyethylene wax, polyoxymethylene, and polyethylene glycol.

[0041] The backbone binder is selected from at least one of polypropylene, polyethylene, polystyrene, polymethyl methacrylate, and ethylene-vinyl acetate copolymer.

[0042] The additive is selected from at least one of stearic acid, zinc stearate, glycerol, castor oil, peanut oil, dibutyl phthalate, dioctyl phthalate, isooctyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol 4-[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 4,4'-methylenebis(2,6-di-tert-butylphenol), and n-octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

[0043] In a preferred embodiment, the mixing process is as follows: first, the raw material powder and organic binder are placed in a mixer for preheating and dehydration; then, the backbone binder is added, and the first mixing is carried out above the melting point of the backbone binder; then, filler binder and additives are added, and the second mixing is carried out above the blending melting point of the filler binder and additives to obtain the final product.

[0044] In a further preferred embodiment, the preheating and dehydration temperature is 80-150℃, preferably 100-120℃, the preheating and dehydration time is 15-120min, preferably 30-60min, and the rotor speed during preheating and dehydration is 1-30r / min, preferably 5-10r / min.

[0045] In a further preferred embodiment, the first mixing time is 15-120 min, preferably 20-60 min, and the rotor speed for the first mixing is 1-30 r / min, preferably 5-15 r / min.

[0046] In a further preferred embodiment, the second mixing time is 30-120 min, preferably 45-60 min, and the rotor speed for the second mixing is 20-60 r / min, preferably 30-45 r / min.

[0047] The above mixing method can ensure that the raw material powder and organic binder are fully mixed.

[0048] In a preferred embodiment, the morphology of the material used for powder metallurgy rheological injection is one of powder, particles, or blocks, wherein the blocks are selected from at least one of discs with round holes, cubes, or honeycomb-shaped blocks.

[0049] The inventors discovered that the powder metallurgy rheological injection molding materials with the above three morphologies all have good filling effects. When the material is a honeycomb-shaped block, a heating rod can be inserted into the pores of the honeycomb-shaped block to achieve rapid and uniform heating of large-volume materials. The material preheating process time is ≤30min, which can prevent the loss of binder in the material due to excessive time and reduce the process stability of rheological injection molding.

[0050] In a further preferred embodiment, when the rheological injection material is a powder, the particle size of the rheological injection material is 10-500 μm, preferably 50-200 μm.

[0051] In a further preferred embodiment, when the rheological injection material is a powder, the particle size of the rheological injection material is 10-500 μm, preferably 50-200 μm.

[0052] In a further preferred embodiment, when the powder metallurgy rheological injection material is a particle, the particle size is 2-8 mm, preferably 3-5 mm.

[0053] When the material used for rheological pressure injection is powder, it is obtained by crushing with a crusher. When the material used for rheological pressure injection is particles, it is obtained by granulation with a screw granulator. When the material used for rheological pressure injection is block, it is obtained by pressing the block into tablets.

[0054] In a preferred embodiment, the rheological injection material is heated to 10-50°C above its softening point, and the shear rate is 100 s. -1 When feeding, the viscosity of the feed is 200-1000 Pa·S, preferably 50-400 Pa·S.

[0055] The rheological injection molding material of the present invention exhibits high density uniformity in all parts of the formed blank, with a density difference of ≤1.5wt% in each part, and ≤0.8wt% in the preferred embodiment. The material also has good thermal stability; when held at a temperature 10-50°C above the softening point of the binder for 60 minutes, the mass loss of the material is ≤1.0wt%, and ≤0.6wt% in the preferred embodiment.

[0056] When the viscosity of the rheological injection material is too high (>1000Pa) at 10-50℃ above the softening point, its fluidity is poor, which will reduce the density uniformity of the formed blank. The density difference between different parts is >1.5wt%, and the blank is prone to deformation and poor dimensional stability after sintering. When the viscosity of the powder metallurgy rheological injection material is too low (<20Pa), its fluidity is too high, the binder content in the formed blank is too high, which will reduce the forming pressure of the formed blank. Pores are easy to remain in the formed blank, and the binder is difficult to remove in the later stage after sintering. Large blanks are prone to cracking during the sintering process.

[0057] In a preferred embodiment, when the rheological pressure injection material is preheated, a pressure of 5-200 MPa, preferably 30-100 MPa, is applied to the rheological pressure injection material.

[0058] After obtaining the rheology injection material, preheat the material to a temperature 10-50°C above its softening point. In actual operation, if the material is in powder or particle form, it can be directly placed in an oven or the heating chamber of the injection molding machine for preheating. The preheating temperature should be ≥ the mixing temperature of the material. More preferably, the material is placed in the heating chamber of the injection molding machine for preheating, and a pressure of 5-200 MPa, preferably 30-100 MPa, is applied to the material to accelerate the homogenization heating of the powder or particles. If the material is in block form, it is placed in a specific heating device or the heating chamber of the injection molding machine, more preferably a specific heating device. The heating method is oil heating, microwave heating, etc., to enable the block material to quickly reach the preheating temperature.

[0059] In a preferred embodiment, the degreasing process involves first placing the large component blank in an organic solvent and performing solvent degreasing at 20-60°C, preferably 30-50°C, or first subjecting the large component blank to catalytic degreasing at 100-140°C in an environment of nitric acid vapor or oxalic acid vapor, followed by thermal degreasing.

[0060] The degreasing method of this invention employs a two-step process. The first step involves solvent degreasing and / or catalytic degreasing to create interconnected pores. The second step involves thermal degreasing to remove the remaining binder through thermal decomposition. After degreasing, the green body undergoes final high-temperature sintering for densification, resulting in a large-sized complex powder metallurgy product. Solvent degreasing involves placing the green body in a solvent corresponding to polymer filler component A and slowly dissolving and removing it at a low temperature of 20-60°C, preferably 30-50°C. Catalytic degreasing, when polymer filler component A is polyoxymethylene (POM) binder, involves placing the green body in a nitric acid or oxalic acid-type catalytic degreasing furnace, introducing nitric acid or oxalic acid vapor, and rapidly removing POM at a temperature of 100-140°C.

[0061] Principles and advantages

[0062] This invention provides a rheological injection molding method for preparing large powder metallurgy components. Compared with conventional powder metallurgy manufacturing methods, this invention uses a special material composed of powder and binder, which exhibits shear-thinning and easy-flowing characteristics above its softening point temperature. Then, under a certain pressing pressure, the powder is rapidly injected into the mold cavity through a runner. After cooling, solidification, and demolding, a green body with high surface quality, complex shape and structure, and high uniformity of density is obtained. The green body then undergoes a two-step debinding process: the first step uses solvent debinding and / or catalytic debinding and / or siphon debinding to remove most of the polymer filler component A and / or unbound component C; the second step uses thermal debinding to remove the polymer backbone component B, as well as the remaining component A and / or unbound component C. Finally, the debinded large powder metallurgy product is sintered to obtain the final large-size complex powder metallurgy product.

[0063] The advantages of the method of the present invention are as follows: (1) The density uniformity of the complex forming blank is high, and the density difference of each region is ≤0.5%; the reason is that the binder in the special material can effectively improve the flowability of the powder in the forming process and fully and uniformly fill the mold cavity. (2) It can realize the near-net-shape manufacturing of large-size products, the weight of the product can be ≥1kg, and the maximum wall thickness of the product can be ≥15mm; the reason is the matching design of the binder components and powder in the material, combined with two-step efficient degreasing, which improves the non-destructive removal efficiency of the binder in the large-size blank. (3) The powder metallurgy products prepared by this method have uniform structure and good dimensional stability, and the dimensional difference of each batch of products is ≤0.5%; the reason is the good control of the density uniformity of the forming blank and the good quality stability of the forming product. (4) The method has wide material applicability and can theoretically meet all powder metallurgy material systems that can be sintered and densified, such as metal ceramic materials, non-ferrous metals, metal matrix composites, and high-temperature resistant ceramic materials. Attached Figure Description

[0064] Figure 1 The image shows the morphology of a Fe-8Ni alloy preform manufactured by rheo-injection and the sintered product. (a) is a product model manufactured by rheo-injection, (b) is the appearance of the preform, and (c) is an image of the preform after solvent degreasing and after sintering.

[0065] The figure shows the sample morphology of the corresponding implementation 1, in which the sintered green body has good dimensional stability.

[0066] Figure 2 : A complex cemented carbide billet manufactured by rheo-pressure injection and the density values ​​of various parts thereof.

[0067] (a) shows the appearance of the cemented carbide billet manufactured by rheo-injection, and (b) shows the density values ​​of each part of the formed billet after dissection.

[0068] The figure shows the microstructure of the sample corresponding to Example 2, in which the formed blank has high density uniformity.

[0069] Figure 3 This is a SEM image of the Cu-coated Ni / NiO / NiFe2O4 powder particles obtained in Example 3. Detailed Implementation

[0070] Example 1

[0071] The material composition used in this embodiment includes 62 parts by volume of Fe-8Ni alloy powder and 38 parts by volume of polymer binder. The polymer binder comprises the following components by volume fraction: polymer filler A is 70 parts of ordinary paraffin wax; polymer backbone component B is 20 parts of high-density polyethylene and 5 parts of ethylene-vinyl acetate copolymer; and polymer additive component C is 5% stearic acid. The average particle size of the Fe-8Ni alloy powder is 10 μm, and the material has a particle size of 3-5 mm. The preparation method of this embodiment is as follows:

[0072] (1) Material preparation: Fe-8Ni alloy powder and binder components were added to a mixer in sequence for homogenization and mixing. The mixing steps were as follows: First, Fe-8Ni alloy powder was placed in the mixer for preheating and dehydration. The drying temperature was 120℃, the preheating time was 45min, and the rotor speed was 5r / min. Next, high-density polyethylene and ethylene-vinyl acetate copolymer were added. The mixing temperature was 190℃, the mixing time was 30min, and the rotor speed was 10r / min. Then, ordinary paraffin wax and stearic acid were added. The mixing temperature was 160℃, the mixing time was 60min, and the rotor speed was 45r / min. Finally, the mixed materials were placed into a crusher and a screw granulator for preparation to obtain the final required granular material.

[0073] (2) Preheating of materials: The above materials are placed in the heating chamber of the injection molding machine for preheating, and a pressure of 50MPa is applied to the materials. The preheating temperature is 160℃.

[0074] (3) Blank forming: After the material is preheated and softened, the material is directly injected into the mold cavity of the T-shaped structure through the flow channel to complete the densification of the blank; the temperature of the injection mold is 160℃ and the injection pressure is 30MPa; then, after cooling until the blank is solidified, the blank can be demolded and taken out.

[0075] (4) Two-step degreasing and sintering densification: First, the Fe-8Ni green body is placed in n-heptane solvent and degreased at 40°C for 48 hours; then the Fe-8Ni green body is degreased at 600°C for 2 hours; then the Fe-8Ni green body is sintered at 1280°C for 2 hours.

[0076] The Fe-8Ni alloy obtained in this example weighed 2.3 kg, with a maximum wall thickness of 16 mm. Its complex structure included a hollow core, high aspect ratio, and a complex curved bottom surface. The alloy exhibited good dimensional stability after sintering, with dimensional differences between products exceeding 0.3%. The resulting finished product had a density of 97.5%, a tensile strength of 650 MPa, and a dimensional accuracy of ±0.5 mm / 100 mm.

[0077] Example 2

[0078] The material composition used in this embodiment includes 56 parts by volume of WC-Co cemented carbide powder and 44 parts by volume of polymer binder. The polymer binder comprises the following components by volume fraction: polymer filler A is 80 parts of polyoxymethylene, polymer backbone component B is 12 parts of polypropylene, and polymer additive component C is 3% stearic acid and 2% dioctyl phthalate. The cemented carbide powder undergoes spherical pretreatment, resulting in an average particle size of 120 μm. The material is in the form of discs with a diameter of 90 mm and a thickness of 20 mm. The preparation method steps of this embodiment are as follows:

[0079] (5) Material preparation: The cemented carbide powder and binder components are added to the internal mixer in sequence for homogenization and mixing. The mixing steps are as follows: First, the cemented carbide powder is placed in the mixer for preheating and dehydration. The drying temperature is 150℃, the preheating time is 30min, and the rotor speed is 5r / min. Next, polypropylene is added. The mixing temperature is 200℃, the mixing time is 60min, and the rotor speed is 5r / min. Then, polyoxymethylene, stearic acid, and dioctyl phthalate are added in sequence. The mixing temperature is 180℃, the mixing time is 45min, and the rotor speed is 40r / min. Finally, the mixed materials are placed into the block tablet press for preparation to obtain the final round tablet material blocks.

[0080] (6) Preheating of materials: The above materials are placed in a specific heating device, which is heated by oil and the preheating temperature is 180°C.

[0081] (7) Blank forming: After the material is preheated and softened, the material is directly injected into the mold cavity of the T-shaped structure through the flow channel to complete the densification of the blank; the temperature of the injection mold is 180℃ and the injection pressure is 80MPa; then, after cooling until the blank is solidified, the blank can be demolded and taken out.

[0082] (8) Two-step degreasing and sintering densification: First, the cemented carbide billet is placed in an oxalic acid catalytic degreasing furnace and catalytically degreased at 120°C for 24 hours; then the cemented carbide billet is hot degreased at 500°C for 2 hours; then the cemented carbide billet after degreasing is sintered at 1380°C for 2 hours.

[0083] The cemented carbide obtained in this example weighs 9.0 kg, with a maximum wall thickness of 20 mm. Its complex shape features a high aspect ratio and a complex curved bottom surface. The alloy exhibits good dimensional stability after sintering, with dimensional differences between products exceeding 0.5%. The resulting product has a density of 98.5%, a bending strength of 1760 MPa, and a dimensional accuracy of ±1.0 mm / 100 mm.

[0084] Example 3

[0085] Preparation of metal-coated ceramic composite powder:

[0086] A method for preparing Cu-coated Ni / NiO / NiFe2O4 cermet composite powder for rheological forming includes the following steps:

[0087] Step S1: Using nano-grinding and air classifying technology, each of the 100kg samples of NiO, NiFe2O4, Cu, and Ni with an average particle size of 5μm is crushed and classified to obtain ultrafine raw material powder with an average particle size of 0.4μm. The operating parameters of the nano-grinding mill are: rotation speed 600rpm, flow rate 50L / H, zirconium bead loading ratio 70%; the operating parameters of the spray air classifier are: feed rate 50kg / h, working pressure 15MPa, and cyclone collector air pressure 10KPa.

[0088] Step S2: Add 60 kg of ultrafine NiFe2O4 ceramic phase powder, 10 kg of ultrafine NiO powder, 20 kg of ultrafine Ni powder and 5 kg of PVA to 150 L of water, mix thoroughly by roller ball milling at 100 rpm, and then dry the moisture at 120 °C to obtain mixed powder.

[0089] Step S3: The mixed powder is pressed into blocks at 30MPa and then granulated by sieving to obtain composite granular powder of -40 mesh and +100 mesh.

[0090] Step S4: Using a drum ball mill, the composite particle powder is mixed with 10 kg of ultrafine Cu powder and self-milled for 10 h at a self-milling speed of 200 r / min to obtain a porous spherical composite powder with a core-shell structure.

[0091] Step S5: Under a protective atmosphere, the porous spherical powder is pre-sintered to remove the organic binder. Specific parameters are: sintering temperature 900℃, sintering time 45 min, to obtain a preliminary dense spherical metal-ceramic composite powder. SEM images of the preliminary dense spherical powder are shown below. Figure 3 The main properties of the obtained powder are shown in Appendix Table 1.

[0092] Table 1

[0093] Porosity (%) D50(μm) D90(μm) Flowability (s / 50g) 19.8 245 335 39

[0094] Organic binder composition: Polymer filler component A is paraffin wax, polymer backbone component B is polypropylene and polystyrene, and surfactant component C is stearic acid. Volume percentage: Paraffin wax: Polypropylene: Polystyrene: Stearic acid = 70%: 20%: 7%: 3%.

[0095] During the mixing process, 56 vol% of metal-ceramic powder and 44 vol% of polymer binder are added.

[0096] 2. Material preparation:

[0097] Mixing of powder and binder: Pour the metal ceramic powder obtained in step (1) into a preheated internal mixer and continue to dry for 1 hour. Add the binder component and metal powder according to the feeding ratio and mix them. The mixing temperature is 160℃ and the mixing time is 45 minutes.

[0098] Material preparation: The mixed material agglomerates are placed in a screw extruder for granulation. The extruder head cuts the material into short cylindrical particles with a diameter of 2 mm and a length of 4 mm.

[0099] At 160°C (approximately 40°C above the softening point), the material... (The sentence is incomplete and requires more context to translate accurately.) -1 At a shear rate of 50 Pa, its viscosity is 50 Pa; after forming, the density uniformity of the blank is high, and the density difference between different parts is ≤0.8 wt%; the material also has good thermal stability. Under conditions 40°C higher than the softening point of the binder, after holding at the temperature for 60 min, the mass loss of the material is ≤0.5 wt%.

[0100] 3. Application effects of materials

[0101] First, the material is preheated to 20°C above its softening point. Then, under a pressure of 50 MPa, the material is injected through a runner into a mold preheated to 40°C above its softening point, and held under pressure for 10 minutes. After rheological injection molding, the above-mentioned cermet material yields a dense and uniform preform with good surface quality. After degreasing, all components are removed. Sintering at 1200°C results in a product that does not crack, exhibits high dimensional accuracy, and has a uniform microstructure. The resulting finished product has a relative density of 97.5%, a flexural strength of 450 MPa, and a dimensional accuracy of ±0.8 mm / 100 mm.

[0102] Comparative Example 1

[0103] The material composition used in this embodiment includes 62 parts by volume of Fe-8Ni alloy powder and 38 parts by volume of polymer binder. The polymer binder comprises the following components by volume fraction: polymer filler A is 60 parts of ordinary paraffin wax; polymer backbone component B is 35 parts of high-density polyethylene and 5 parts of ethylene-vinyl acetate copolymer; and polymer additive component C is 5% stearic acid. The Fe-8Ni alloy powder has an average particle size of 10 μm, and the material has a particle size of 3-5 mm. The preparation method of this embodiment is as follows:

[0104] (9) Material preparation: Fe-8Ni alloy powder and binder components are added to a mixer in sequence for homogenization and mixing. The mixing steps are as follows: First, Fe-8Ni alloy powder is placed in the mixer for preheating and dehydration. The drying temperature is 120℃, the preheating time is 45min, and the rotor speed is 5r / min. Next, high-density polyethylene and ethylene-vinyl acetate copolymer are added. The mixing temperature is 190℃, the mixing time is 30min, and the rotor speed is 10r / min. Then, ordinary paraffin wax and stearic acid are added. The mixing temperature is 160℃, the mixing time is 60min, and the rotor speed is 45r / min. Finally, the mixed materials are placed into a crusher, screw granulator, or block tablet press for preparation to obtain the final required granular material.

[0105] (10) Preheating of materials: The above materials are placed in the heating chamber of the injection molding machine for preheating, and a pressure of 50MPa is applied to the materials. The preheating temperature is 160℃.

[0106] (11) Blank forming: After the material is preheated and softened, the material is directly injected into the mold cavity of the T-shaped structure through the flow channel to complete the densification of the blank; the temperature of the injection mold is 160℃ and the injection pressure is 30MPa; then, after cooling until the blank is solidified, the blank can be demolded and taken out.

[0107] (12) Two-step degreasing and sintering densification: First, the Fe-8Ni blank is placed in n-heptane solvent and degreased at 40°C for 48 hours; then the Fe-8Ni blank is degreased at 600°C for 2 hours; then the Fe-8Ni blank after degreasing is sintered at 1280°C for 2 hours.

[0108] The Fe-8Ni alloy obtained in this example weighed 2.3 kg, and the maximum wall thickness of the product was 16 mm. Its shape and structure were complex, with a hollow structure, high aspect ratio and complex bottom curved surface. The alloy had poor dimensional stability after sintering, and the dimensional difference stability of each product was less than 1.0%.

[0109] Comparative Example 2

[0110] The material composition used in this embodiment includes 56 parts by volume of WC-Co cemented carbide powder and 44 parts by volume of polymer binder. The polymer binder comprises the following components by volume: polymer filler A is 80 parts of polyoxymethylene, polymer backbone component B is 12 parts of polypropylene, and polymer additive component C is 3% stearic acid and 2% dioctyl phthalate. The cemented carbide powder is not pre-treated to resemble spheres and has an average particle size of 3 μm. The material is in the form of discs with a diameter of 90 mm and a thickness of 20 mm. The preparation method steps of this embodiment are as follows:

[0111] (13) Material preparation: The cemented carbide powder and binder components are added to the internal mixer in sequence for homogenization and mixing. The mixing steps are as follows: First, the cemented carbide powder is placed in the mixer for preheating and dehydration. The drying temperature is 150℃, the preheating time is 30min, and the rotor speed is 5r / min. Then, polypropylene is added. The mixing temperature is 200℃, the mixing time is 60min, and the rotor speed is 5r / min. Subsequently, polyoxymethylene, stearic acid, and dioctyl phthalate are added in sequence. The mixing temperature is 180℃, the mixing time is 45min, and the rotor speed is 40r / min. Finally, the mixed materials are placed into the block tablet press for preparation to obtain the final round tablet material blocks.

[0112] (14) Preheating of materials: The above materials are placed in a specific heating device, which is heated by oil and the preheating temperature is 180°C.

[0113] (15) Blank forming: After the material is preheated and softened, the material is directly injected into the mold cavity of the T-shaped structure through the flow channel to complete the densification of the blank; the temperature of the injection mold is 180℃ and the injection pressure is 80MPa; then, after cooling until the blank is solidified, the blank can be demolded and taken out.

[0114] (16) Two-step degreasing and sintering densification: First, the cemented carbide billet is placed in an oxalic acid catalytic degreasing furnace and catalytically degreased at 120°C for 24 hours; then the cemented carbide billet is hot degreased at 500°C for 2 hours; then the cemented carbide billet after degreasing is sintered at 1380°C for 2 hours.

[0115] The cemented carbide obtained in this example weighs 9.0 kg and has a maximum wall thickness of 20 mm. Its shape and structure are complex, with a high aspect ratio and a complex bottom curved surface. The dimensional stability of the alloy after sintering is poor, and the dimensional difference stability of each product is less than 1.5%.

Claims

1. A method for preparing large powder metallurgy components by rheological pressure casting, characterized in that: The raw material powder and organic binder are mixed to obtain a material agglomerate. The material agglomerate is shaped to obtain a rheology injection molding material. The rheology injection material is preheated to a temperature 10-50°C above the material's softening point. Then, under a pressure of 20-50 MPa, the rheology injection material is injected through a flow channel into a mold that has been preheated to a temperature 10-50°C above the material's softening point. The pressure is then maintained for 1-60 minutes. The mold heating is stopped, and after the mold cools and the blank solidifies, it is demolded to obtain a large component blank. The large component blank is degreased and sintered to obtain a large component. The raw material powder is selected from at least one of metal powder, ceramic powder, and metal-coated ceramic composite powder. The organic binder, by volume percentage, has the following composition: 65-90 vol% filler binder, 5-35 vol% backbone binder, and 2-8 vol% additives. When the raw material powder is metal powder, the particle size of the metal powder is 5-100 μm. When the raw material powder is selected from ceramic powder, the particle size of the ceramic powder is 20-500 μm. When the raw material powder is metal-coated ceramic composite powder, the average particle size of the metal-coated ceramic composite powder is 150~350μm; The method for obtaining the metal-coated ceramic composite powder is as follows: First, ceramic phase fine powder N2, metal core fine powder M2, and binder C are mixed to obtain a mixed powder. The mixed powder is pressed into blocks, sieved, and granulated to obtain composite particle powder. The composite particle powder is then self-ground and spheroidized with metal binder phase fine powder M3 to obtain a porous spherical composite powder with a core-shell structure. The porous spherical composite powder is then pre-sintered to obtain spherical metal-coated ceramic composite powder. The ceramic phase fine powder N2 is selected from at least one of tungsten carbide, molybdenum carbide, titanium carbide, silicon carbide, titanium nitride, titanium boride, boron nitride, iron oxide, nickel oxide, aluminum oxide, magnesium oxide, zirconium oxide, nickel ferrite, manganese ferrite, cobalt ferrite, zinc ferrite, copper ferrite, chromium ferrite, and iron ferrite. The metal in the metal core fine powder M2 is selected from at least one of W, Mo, Zr, Ti, Co, Ni, and Fe. The metal in the metal binder phase fine powder M3 is selected from at least one of Cu, Al, Zn, Sn, Ag, Au, and Pb. The self-grinding spheroidization is carried out in a drum-type ball mill without grinding balls or media, and the rotation speed of the self-grinding spheroidization is 100~400 r / min, and the self-grinding spheroidization time is 10~40 h.

2. The method for preparing large powder metallurgy components by rheological injection molding according to claim 1, characterized in that: The volume ratio of the ceramic phase fine powder N2 to the metal core fine powder M2 is 1~8:1; The binder C is selected from at least one of paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, polyethylene glycol, polyvinyl alcohol, methylcellulose, and rubber; The amount of binder C added is 1-5% of the mass of the mixed powder; After mixing ceramic phase fine powder N2, metal core fine powder M2 and binder C, the mixture is dried to obtain a mixed powder. The drying temperature is 100~120℃. The mixing method is wet ball milling, the medium for wet ball milling is deionized water, the rotation speed of wet ball milling is 60~200 rpm, and the wet ball milling time is 15~60 min; The pressure for pressing the blocks is 30~50MPa; The granules obtained by sieving and screening to obtain -40 mesh and +100 mesh are composite particle powders; the volume ratio of the composite particle powder to the fine powder M3 of the metal binder phase is 5~8:

1. The pre-sintering is carried out in a protective atmosphere at a temperature of 600-1000℃ and a holding time of 30-180 minutes.

3. The method for preparing large powder metallurgy components by rheological injection molding according to claim 1 or 2, characterized in that: In the rheological injection material, the volume fraction of the raw material powder is 50%~62%; The organic binder, by volume percentage, comprises: 70-80 vol% filler binder, 12-27 vol% backbone binder, and 3-5 vol% additives.

4. The method for preparing large powder metallurgy components by rheological injection molding according to claim 3, characterized in that: The filler binder is selected from at least one of paraffin wax, carnauba wax, microcrystalline wax, beeswax, polyethylene wax, polyoxymethylene, and polyethylene glycol. The backbone binder is selected from at least one of polypropylene, polyethylene, polystyrene, polymethyl methacrylate, and ethylene-vinyl acetate copolymer. The additive is selected from at least one of stearic acid, zinc stearate, glycerol, castor oil, peanut oil, dibutyl phthalate, dioctyl phthalate, isooctyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol 4-[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 4,4'-methylenebis(2,6-di-tert-butylphenol), and n-octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

5. A method for preparing large powder metallurgy components by rheological injection molding according to claim 1 or 2, characterized in that: The mixing process is as follows: first, the raw material powder and organic binder are placed in a mixer for preheating and dehydration, then the backbone binder is added, and the first mixing is carried out above the melting point of the backbone binder. Then, filler binder and additives are added, and the second mixing is carried out above the blending melting point of the filler binder and additives. The preheating and dehydration temperature is 80-150℃, the preheating and dehydration time is 15-120 min, and the rotor speed during preheating and dehydration is 1-30 r / min. The first mixing time is 15-120 minutes, and the rotor speed for the first mixing is 1-30 r / min. The second mixing time is 30-120 min, and the rotor speed for the second mixing is 20-60 r / min.

6. A method for preparing large powder metallurgy components by rheological injection molding according to claim 1 or 2, characterized in that: The morphology of the rheological injection material is one of powder, particles, and blocks, and the blocks are selected from at least one of discs with round holes, cubes, and honeycomb-shaped blocks. When the rheological injection material is a powder, the particle size of the rheological injection material is 10-500 μm. When the rheological injection material is in the form of particles, the particle size is 2-8 mm. When the rheological injection material is at a temperature 10-50°C above its softening point, and the shear rate is 100 s, -1 At that time, the viscosity of the feed was 200-1000 Pa·S.

7. A method for preparing large powder metallurgy components by rheological injection molding according to claim 1 or 2, characterized in that: When the rheological pressure injection material is preheated, a pressure of 5-200 MPa is applied to the rheological pressure injection material.

8. A method for preparing large powder metallurgy components by rheological injection molding according to claim 1 or 2, characterized in that: The degreasing process involves first placing the large component blank in an organic solvent and performing solvent degreasing at 20-60°C, or first placing the large component blank in an environment of nitric acid vapor or oxalic acid vapor and performing catalytic degreasing at 100-140°C, followed by thermal degreasing.

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