Method for producing large parts using the metal powder injection molding process

Abstract

The application discloses a method for preparing large parts by using a metal powder injection molding process, belongs to the technical field of large part processing, and aims at solving the technical problem that the strength of large parts prepared by the metal powder injection molding process in the prior art needs to be further improved; the method comprises the following steps: stirring a reinforcing agent, paraffin and acetone in a reaction kettle, increasing the temperature of the reaction kettle to 40-50 DEG C, and stirring until the system is dissolved to obtain a reinforcing modification liquid; and adding metal powder into a high-speed mixer and heating until the temperature of the metal powder reaches 100-110 DEG C, and then slowly adding the reinforcing modification liquid into the high-speed mixer; the application effectively improves the ultimate tensile strength, yield strength, elongation and hardness performance of the injection part by preparing modified metal powder with high flow performance, combining the modified metal powder with a binding aid, and optimizing injection conditions and debinding and roasting conditions.

Description

Technical Field

[0001] This invention relates to the field of large component processing technology, and specifically to a method for preparing large components using metal powder injection molding. Background Technology

[0002] With the rapid development of modern industrial technology, the requirements for the size, precision and complexity of parts are increasing. Traditional metal processing methods, such as casting, forging and machining, often face challenges such as low production efficiency, large material waste and high cost when preparing large and complex parts. Metal powder injection molding technology is to uniformly mix metal powder with organic binder, and then use an injection molding machine to inject the mixture into a mold under high temperature and high pressure to solidify and form the part. Subsequently, the binder is removed through debinding and sintering steps, and finally a dense metal part is obtained.

[0003] In the prior art, Chinese invention patent with publication number CN105290392A discloses a method for injection molding of 304L stainless steel metal powder, which includes steps such as mixing and granulating 304L stainless steel powder with a binder to form feedstock, injection molding to prepare blanks, catalytic degreasing and negative pressure degreasing, vacuum internal firing and forced cooling three-stage atmosphere process sintering, so as to obtain 304L stainless steel parts with high dimensional accuracy, high surface accuracy and no burr phenomenon, and avoid the complex processes of solvent degreasing and thermal degreasing, resulting in high production efficiency and low production cost.

[0004] However, traditional metal powder injection molding technology mainly relies on the high precision, uniform structure, excellent performance, and low production cost of the metal powder injection molding process. It is often used to produce small, complex parts with special requirements. For large parts, due to their greater thickness, although small-particle-size powder can help improve the density and microstructure uniformity of the material, the large specific surface area and high surface energy of small-particle-size metal powder make it prone to agglomeration during the preparation of large parts. This leads to a decrease in the uniformity of feeding and mixing, affecting the stability and quality of injection molding. Furthermore, the debinding process of small-particle-size metal powder is more complex, requiring longer debinding time and higher debinding temperature. This not only increases production costs but may also lead to incomplete debinding, affecting the performance of the final product. The strength of large parts prepared by metal powder injection molding needs to be further improved.

[0005] To address this technical deficiency, a solution is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing large parts using metal powder injection molding, thereby solving the technical problem that the strength of large parts prepared by metal powder injection molding in the prior art needs to be further improved.

[0007] The objective of this invention can be achieved through the following technical solution: a method for preparing large parts using metal powder injection molding, comprising the following steps:

[0008] S1. Add the reinforcing agent, paraffin and acetone to the reaction vessel and stir. Raise the temperature of the reaction vessel to 40-50℃ and stir until the system is dissolved to obtain the reinforcing and modified liquid.

[0009] S2. Add the metal powder to a high-speed mixer and heat it until the temperature of the metal powder reaches 100-110℃. Slowly add the reinforcing and modifying liquid to the high-speed mixer. After the addition is complete, keep it warm and mix for 60-80 minutes to obtain the modified metal powder.

[0010] S3. After mixing the modified metal powder and binder, add the mixture into the injection molding machine and injection mold to obtain an injection preform with a thickness of 30mm.

[0011] S4. Place the injection preform into an atmosphere furnace for hot degreasing and sintering to obtain the injection part.

[0012] Furthermore, in step S1, the ratio of the reinforcing agent, paraffin, and acetone is 2-3g:1g:20mL.

[0013] Furthermore, in step S2, the ratio of the metal powder to the reinforcing and modifying liquid is 100g:7-12mL, the high-speed mixer speed is 800-900r / min, and the metal powder is composed of stainless steel powder, titanium nitride, niobium carbide, lanthanum oxide and cerium oxide in a weight ratio of 100:0.05:0.02:0.01:0.01. The stainless steel powder is 17-4PH stainless steel powder with a particle size of 70-90μm.

[0014] Furthermore, in step S3, the weight ratio of the modified metal powder to the binder is 100:8-12, the binder is composed of polyoxymethylene and agar in a weight ratio of 10:3, the feeding temperature of the injection molding machine is 180-190℃, the injection pressure is 95-105MPa, the holding pressure is 95-105MPa, and the holding time is 10-15s.

[0015] Further, in step S4, the hot degreasing sintering method is as follows: the vacuum degree of the atmosphere furnace is reduced to 0.1 MPa, the temperature of the atmosphere furnace is increased to 180-200℃ at a heating rate of 1℃ / min, and held for 60-80 min; the temperature of the atmosphere furnace is increased to 450-500℃ at a heating rate of 2℃ / min, and held for 30-50 min; the temperature of the atmosphere furnace is increased to 780-820℃ at a heating rate of 2℃ / min, and held for 60-80 min; the temperature of the atmosphere furnace is increased to 1350-1400℃ at a heating rate of 4℃ / min, and held for 90-120 min; the temperature of the atmosphere furnace is reduced to room temperature, and the material is discharged to obtain the injection molded part.

[0016] Furthermore, the reinforcing agent is obtained by the following steps:

[0017] A1. Add acrylic acid, methyl methacrylate, butyl acrylate and toluene to a reaction vessel and stir. Add an initiator to the reaction vessel, raise the temperature of the reaction vessel to 80-90℃, keep the reaction at this temperature for 4-6 hours, and then process to obtain polyolefin.

[0018] The synthesis reaction mechanism of polyolefins is as follows:

[0019] Under the action of an initiator, the olefin double bonds on acrylic acid, methyl methacrylate, and butyl acrylate molecules are opened to form free radical intermediates, and free radical polymerization reaction occurs, causing the chain to grow continuously and form a high molecular weight polymer chain. Polyolefin segments with carboxyl groups are prepared, and polyolefins are obtained.

[0020] A2. Polyolefin, bisphenol A epoxy resin and N,N-dimethylformamide are added to a nitrogen-protected reactor and stirred. A catalyst is added to the reactor, the temperature of the reactor is raised to 90-100℃, and the reaction is maintained for 4-5 hours. The reinforcing agent is obtained after post-treatment.

[0021] The synthesis reaction mechanism of the reinforcing agent is as follows:

[0022] Under the action of a catalyst, the epoxy groups of bisphenol A epoxy resin react with the carboxyl groups on polyolefin molecules to form covalent bonds, thus preparing a reinforcing agent.

[0023] Further, in step A1, the ratio of acrylic acid, methyl methacrylate, and butyl acrylate is 3 mol: 1 mol: 2 mol, and the ratio of butyl acrylate, toluene, and initiator is 1 g: 8 mL: 0.1 g. The initiator is azobisisobutyronitrile. The post-treatment includes: after the reaction is complete, maintaining the temperature of the reaction vessel at 80-90°C, removing the solvent under reduced pressure, and obtaining polyolefin.

[0024] Further, in step A2, the ratio of the polyolefin, bisphenol A epoxy resin, N,N-dimethylformamide, and catalyst is 8-10g:4-5g:50mL:0.5g, and the catalyst is diisopropylamine. The post-treatment includes: after the reaction is complete, the temperature of the reaction vessel is lowered to room temperature, 3wt% sodium dodecyl sulfate aqueous solution is slowly added to the reaction vessel, stirred and dispersed for 30-50min, filtered, the filter cake is washed three times with ethanol and then dried, the filter cake is transferred to a drying oven at 60-70℃ and dried to constant weight to obtain the reinforcing agent.

[0025] The present invention has the following beneficial effects:

[0026] 1. The method for preparing large parts using metal powder injection molding provided by the present invention involves reinforcing and modifying metal powder with a reinforcing and modifying liquid composed of a reinforcing agent prepared by reacting polyolefin with bisphenol A type epoxy resin, paraffin wax, and acetone, and depositing an organic coating on the surface of the metal powder to obtain modified metal powder. In the preparation of modified metal powder, paraffin wax is used as an auxiliary agent to promote the dissolution of the reinforcing agent in acetone, so that the reinforcing agent can be uniformly dispersed in the solvent. Paraffin wax is a natural lubricant and also has a certain film-forming property. The long-chain hydrocarbon groups in its molecular structure can reduce the friction and resistance between powder particles. After adding paraffin wax to the modifying liquid, when the reinforcing and modifying liquid is added to the metal powder, a lubricating film can be formed on the outside of the metal powder. The combined effect of paraffin wax and reinforcing agent improves the flowability of the metal powder.

[0027] 2. The method for preparing large parts using metal powder injection molding provided by this invention involves the interaction of polyoxymethylene (POM) and agar. Agar is a natural polysaccharide colloid with good water solubility and gelling properties, which can promote the gelation of the binder and improve its lubrication performance. When POM and agar are mixed, the binder softens rapidly under high temperature and pressure, allowing it to penetrate into the tiny gaps between powder particles and form a strong bond. Modified metal powder fills every corner of the mold, and the binder solidifies rapidly under the cooling effect of the mold, forming a blank with a certain strength and density. In this process, POM provides the main strength and rigidity support, while agar optimizes the bonding effect through thickening, gelation, and lubrication, making the blank more uniform and dense. During the heat treatment process in the atmosphere furnace, residual stress and defects in the blank are eliminated by controlling the temperature and time, promoting the densification of the material and grain growth. Higher temperatures and longer holding times help to form a more uniform and dense microstructure, thereby improving the tensile strength, yield strength, and hardness of the material.

[0028] 3. The method for preparing large parts using metal powder injection molding provided by this invention involves mixing 17-4PH stainless steel powder, titanium nitride, niobium carbide, lanthanum oxide, and cerium oxide to form a metal powder. 17-4PH stainless steel powder is a martensitic precipitation-hardening stainless steel with high strength, high hardness, and good corrosion resistance. Titanium nitride and niobium carbide act as second-phase strengthening phases, improving the tensile strength and yield strength of the material by hindering dislocation movement and crack propagation. Lanthanum oxide and cerium oxide act as heterogeneous nucleation sites in the metal powder, promoting grain refinement and improving the microstructure, thereby enhancing the strength and toughness of the material. Grain size can cause materials to become brittle and reduce elongation. This invention selects larger-sized stainless steel powder, which utilizes the relative melting and flowability of larger powder particles to reduce the injection pressure and temperature requirements for large parts. Furthermore, larger-sized powder particles can further promote grain growth during sintering, reduce the number of grain boundaries, and mitigate the adverse effects of grain boundaries on material properties. During heat treatment, recrystallization occurs, which promotes the accumulation of distortion energy within the material, leading to the formation and growth of new distortion-free grains, eliminating work hardening and residual stress, and further improving the plasticity and toughness of the material. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is an SEM image of the cross-section of the injection part in this invention;

[0031] Figure 2 This is an SEM image of the cross-section of the injection part in this invention;

[0032] Figure 3 This is the infrared spectrum of the modified metal powder used in this invention. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] The bisphenol A type epoxy resin used in this application is model E-51, with an epoxy value of 0.48-0.54 eq / 100g;

[0035] The polyoxymethylene (POM) was selected from Dongguan Xingxiang New Materials Co., Ltd., brand name F25-03H.

[0036] The agar was selected from Shaanxi Rankang Biotechnology Co., Ltd., with product number 0-11-78.

[0037] Example 1

[0038] The method for manufacturing large parts using metal powder injection molding provided in this embodiment includes the following steps:

[0039] S1. Preparation of reinforcing agent

[0040] Weigh out 21.6g of acrylic acid, 10.0g of methyl methacrylate, 25.6g of butyl acrylate, and 204.8mL of toluene and add them to the reaction vessel and stir. Add 2.56g of azobisisobutyronitrile to the reaction vessel, raise the temperature of the reaction vessel to 80℃, keep the reaction at this temperature for 4 hours, keep the temperature of the reaction vessel at 80℃, and remove the solvent by vacuum evaporation to obtain polyolefin.

[0041] Weigh 80-100g of polyolefin, 40g of bisphenol A epoxy resin, and 500mL of N,N-dimethylformamide and add them to a nitrogen-protected reactor and stir. Add 5g of diisopropylamine to the reactor, raise the reactor temperature to 90℃, and keep the reaction at that temperature for 4 hours. Lower the reactor temperature to room temperature, slowly add 1000mL of 3wt% sodium dodecyl sulfate aqueous solution to the reactor, stir and disperse for 30 minutes, filter, wash the filter cake three times with ethanol and dry it under vacuum. Transfer the filter cake to a drying oven at 60℃ and dry it to constant weight to obtain the reinforcing agent.

[0042] S2, Preparation of modified metal powder

[0043] Add the reinforcing agent, paraffin and acetone to the reaction vessel at a ratio of 2g:1g:20mL and stir. Raise the temperature of the reaction vessel to 40℃ and stir until the system is dissolved to obtain the reinforcing and modified liquid.

[0044] 17-4PH stainless steel powder with a particle size of 70-90μm, titanium nitride, niobium carbide, lanthanum oxide and cerium oxide are mixed evenly in a weight ratio of 100:0.05:0.02:0.01:0.01 to obtain metal powder;

[0045] Weigh 500g of metal powder and add it to a high-speed mixer and heat it. When the temperature of the metal powder reaches 100℃, slowly add 200mL of the reinforcing and modifying liquid to the high-speed mixer. After the addition is complete, keep it warm and mix for 60min to obtain the modified metal powder.

[0046] S3. Preparation of injection-molded preforms

[0047] Polyoxymethylene and agar were mixed evenly at a weight ratio of 10:3 to obtain an adhesive additive;

[0048] After mixing the modified metal powder and binder at a weight ratio of 100:8, the feeding temperature of the injection molding machine was increased to 180℃ and the injection pressure was increased to 95MPa. Injection molding was performed, and the holding pressure was set to 95MPa and the holding time was 10s to obtain an injection preform with a thickness of 30mm.

[0049] S4. Preparation of injection mold

[0050] The injection preform is placed in an atmosphere furnace, the vacuum degree of the atmosphere furnace is reduced to 0.1 MPa, the temperature of the atmosphere furnace is increased to 180℃ at a heating rate of 1℃ / min and held for 60 min, the temperature of the atmosphere furnace is increased to 450℃ at a heating rate of 2℃ / min and held for 30 min, the temperature of the atmosphere furnace is increased to 780℃ at a heating rate of 2℃ / min and held for 60 min, the temperature of the atmosphere furnace is increased to 1350℃ at a heating rate of 4℃ / min and held for 90 min, the temperature of the atmosphere furnace is reduced to room temperature, and the material is discharged to obtain the injection part.

[0051] Example 2

[0052] The method for manufacturing large parts using metal powder injection molding provided in this embodiment includes the following steps:

[0053] S1. Preparation of reinforcing agent

[0054] Weigh out 21.6g of acrylic acid, 10.0g of methyl methacrylate, 25.6g of butyl acrylate, and 204.8mL of toluene and add them to a reaction vessel and stir. Add 2.56g of azobisisobutyronitrile to the reaction vessel, raise the temperature of the reaction vessel to 85℃, and keep the reaction at this temperature for 5 hours. Keep the temperature of the reaction vessel at 85℃ and remove the solvent under reduced pressure to obtain polyolefin.

[0055] Weigh out 90g of polyolefin, 45g of bisphenol A epoxy resin and 500mL of N,N-dimethylformamide and add them to a nitrogen-protected reactor and stir. Add 5g of diisopropylamine to the reactor and raise the temperature of the reactor to 95℃. Maintain the temperature for 4.5h and lower the temperature of the reactor to room temperature. Slowly add 1000mL of 3wt% sodium dodecyl sulfate aqueous solution to the reactor and stir to disperse for 30-50min. Filter the mixture and wash the filter cake three times with ethanol. Dry the filter cake and transfer it to a drying oven at 65℃. Dry the mixture to constant weight to obtain the reinforcing agent.

[0056] S2, Preparation of modified metal powder

[0057] The reinforcing agent, paraffin, and acetone were added to the reaction vessel in a ratio of 2.5g:1g:20mL and stirred. The temperature of the reaction vessel was raised to 45℃ and stirred until the system was dissolved to obtain the reinforcing and modified liquid.

[0058] 17-4PH stainless steel powder with a particle size of 70-90μm, titanium nitride, niobium carbide, lanthanum oxide and cerium oxide are mixed evenly in a weight ratio of 100:0.05:0.02:0.01:0.01 to obtain metal powder;

[0059] Weigh 500g of metal powder and add it to a high-speed mixer and heat it. When the temperature of the metal powder reaches 105℃, slowly add 250mL of the reinforcing modification liquid to the high-speed mixer. After the addition is complete, keep it warm and mix for 70min to obtain the modified metal powder.

[0060] S3. Preparation of injection-molded preforms

[0061] Polyoxymethylene and agar were mixed evenly at a weight ratio of 10:3 to obtain an adhesive additive;

[0062] After mixing the modified metal powder and binder at a weight ratio of 100:10, the feeding temperature of the injection molding machine was increased to 185℃ and the injection pressure was increased to 100MPa. Injection molding was performed, and the holding pressure was set to 100MPa and the holding time was 13s to obtain an injection preform with a thickness of 30mm.

[0063] S4. Preparation of injection mold

[0064] The injection preform is placed in an atmosphere furnace, the vacuum degree of the atmosphere furnace is reduced to 0.1 MPa, the temperature of the atmosphere furnace is increased to 190℃ at a heating rate of 1℃ / min and held for 70 min, the temperature of the atmosphere furnace is increased to 475℃ at a heating rate of 2℃ / min and held for 40 min, the temperature of the atmosphere furnace is increased to 800℃ at a heating rate of 2℃ / min and held for 70 min, the temperature of the atmosphere furnace is increased to 1375℃ at a heating rate of 4℃ / min and held for 105 min, the temperature of the atmosphere furnace is reduced to room temperature, and the material is discharged to obtain the injection part.

[0065] Example 3

[0066] The method for manufacturing large parts using metal powder injection molding provided in this embodiment includes the following steps:

[0067] S1. Preparation of reinforcing agent

[0068] Weigh out 21.6g of acrylic acid, 10.0g of methyl methacrylate, 25.6g of butyl acrylate, and 204.8mL of toluene and add them to a reaction vessel and stir. Add 2.56g of azobisisobutyronitrile to the reaction vessel, raise the temperature of the reaction vessel to 90℃, and keep the reaction at this temperature for 6 hours. Keep the temperature of the reaction vessel at 90℃ and remove the solvent under reduced pressure to obtain polyolefin.

[0069] Weigh 100g of polyolefin, 50g of bisphenol A epoxy resin, and 500mL of N,N-dimethylformamide and add them to a nitrogen-protected reactor and stir. Add 5g of diisopropylamine to the reactor, raise the temperature of the reactor to 100℃, and keep the reaction at this temperature for 5 hours. Lower the temperature of the reactor to room temperature, slowly add 1000mL of 3wt% sodium dodecyl sulfate aqueous solution to the reactor, stir and disperse for 50 minutes, filter, wash the filter cake three times with ethanol and dry it under vacuum. Transfer the filter cake to a drying oven at 70℃ and dry it to constant weight to obtain the reinforcing agent.

[0070] S2, Preparation of modified metal powder

[0071] Add the reinforcing agent, paraffin and acetone to the reaction vessel at a ratio of 3g:1g:20mL and stir. Raise the temperature of the reaction vessel to 50℃ and stir until the system is dissolved to obtain the reinforcing and modified liquid.

[0072] 17-4PH stainless steel powder with a particle size of 70-90μm, titanium nitride, niobium carbide, lanthanum oxide and cerium oxide are mixed evenly in a weight ratio of 100:0.05:0.02:0.01:0.01 to obtain metal powder;

[0073] Weigh 500g of metal powder and add it to a high-speed mixer and heat it. When the temperature of the metal powder reaches 110℃, slowly add 300mL of the reinforcing modification liquid to the high-speed mixer. After the addition is complete, keep it warm and mix for 80min to obtain the modified metal powder.

[0074] S3. Preparation of injection-molded preforms

[0075] Polyoxymethylene and agar were mixed evenly at a weight ratio of 10:3 to obtain an adhesive additive;

[0076] After mixing the modified metal powder and binder at a weight ratio of 100:12, the feeding temperature of the injection molding machine was increased to 190℃ and the injection pressure was increased to 105MPa. Injection molding was performed, and the holding pressure was set to 105MPa and the holding time was 15s to obtain an injection preform with a thickness of 30mm.

[0077] S4. Preparation of injection mold

[0078] The injection preform is placed in an atmosphere furnace, the vacuum degree of the atmosphere furnace is reduced to 0.1 MPa, the temperature of the atmosphere furnace is increased to 200℃ at a heating rate of 1℃ / min and held for 80 min, the temperature of the atmosphere furnace is increased to 500℃ at a heating rate of 2℃ / min and held for 50 min, the temperature of the atmosphere furnace is increased to 820℃ at a heating rate of 2℃ / min and held for 80 min, the temperature of the atmosphere furnace is increased to 1400℃ at a heating rate of 4℃ / min and held for 120 min, the temperature of the atmosphere furnace is reduced to room temperature, and the material is discharged to obtain the injection part.

[0079] Comparative Example 1

[0080] The difference between this comparative example and Example 3 is that the polyolefin in step S1 is used instead of the reinforcing agent in step S2.

[0081] Comparative Example 2

[0082] The difference between this comparative example and Example 3 is that no paraffin was added to the reinforcing and modifying liquid in step S2.

[0083] Comparative Example 3

[0084] The difference between this comparative example and Example 3 is that the 17-4PH stainless steel powder used in step S2 has a particle size of 10-20 μm.

[0085] Comparative Example 4

[0086] The difference between this comparative example and Example 3 is that titanium nitride and niobium carbide were not added to the metal powder in step S2.

[0087] Performance testing:

[0088] The flowability of the modified metal powders used in Examples 1-3 and Comparative Examples 1-4 was tested in accordance with the standard GB / T 41329-2022 "Determination of Flowability of Metal Powders - Standard Funnel Method (Gustavsen Flowmeter)".

[0089] The ultimate tensile strength, yield strength (0.2%), elongation and hardness of the injection molded parts prepared in Examples 1-3 and Comparative Examples 1-4 were tested in accordance with the standard JB / T 13067.1-2017 "Metal Injection Molding Materials Part 1: Technical Conditions for Sintered Low Alloy Steel and Stainless Steel". The specific test results are shown in Table 1 below.

[0090] Table 1 - Performance Test Data of Samples

[0091]

[0092]

[0093] Data Analysis:

[0094] Comparative analysis of the data in the table above shows that the modified metal powder prepared by this invention has a flowability of 23s / 50g, the injection molded part has an ultimate tensile strength of 1671MPa, a yield strength of 1258MPa, an elongation of 4.5%, and a hardness of 60.3HRB. All of these properties are superior to those of the comparative example.

[0095] This invention describes a process that optimizes the size and composition of stainless steel powder, uses a prepared reinforcing agent and paraffin to modify the metal powder, prepares modified metal powder, improves the flowability of the metal powder, combines the modified metal powder with a binder composed of polyoxymethylene and agar, and optimizes injection and debinding / calcination conditions, effectively improving the ultimate tensile strength, yield strength, elongation, and hardness of the injection-molded parts.

[0096] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

[0097] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0098] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for manufacturing large parts using metal powder injection molding, characterized in that, Includes the following steps: S1. Add the reinforcing agent, paraffin and acetone to the reaction vessel and stir. Raise the temperature of the reaction vessel to 40-50℃ and stir until the system is dissolved to obtain the reinforcing and modified liquid. S2. Add the metal powder to a high-speed mixer and heat it until the temperature of the metal powder reaches 100-110℃. Slowly add the reinforcing modification liquid to the high-speed mixer. After the addition is complete, keep it at the temperature and mix for 60-80 minutes to obtain modified metal powder. The metal powder is composed of stainless steel powder, titanium nitride, niobium carbide, lanthanum oxide and cerium oxide in a weight ratio of 100:0.05:0.02:0.01:0.

01. The stainless steel powder is 17-4PH stainless steel powder with a particle size of 70-90μm. S3. The modified metal powder and the binder are mixed and added to the injection molding machine for injection molding to obtain an injection preform with a thickness of 30mm. The binder is composed of polyoxymethylene and agar in a weight ratio of 10:

3. S4. Place the injection preform in an atmosphere furnace, perform hot degreasing and sintering to obtain the injection part; The reinforcing agent is obtained by the following steps: A1. Add acrylic acid, methyl methacrylate, butyl acrylate and toluene to a reaction vessel and stir. Add an initiator to the reaction vessel, raise the temperature of the reaction vessel to 80-90℃, keep the reaction at this temperature for 4-6 hours, and then process to obtain polyolefin. A2. Polyolefin, bisphenol A epoxy resin and N,N-dimethylformamide are added to a nitrogen-protected reactor and stirred. A catalyst is added to the reactor, the temperature of the reactor is raised to 90-100℃, and the reaction is maintained for 4-5 hours. The reinforcing agent is obtained after post-treatment.

2. The method for preparing large parts using metal powder injection molding according to claim 1, characterized in that, In step S1, the ratio of the reinforcing agent, paraffin and acetone is 2-3g:1g:20mL.

3. The method for preparing large parts using metal powder injection molding according to claim 1, characterized in that, In step S2, the ratio of the metal powder to the reinforcing and modifying liquid is 100g:7-12mL, and the speed of the high-speed mixer is 800-900r / min.

4. The method for preparing large parts using metal powder injection molding according to claim 1, characterized in that, In step S3, the weight ratio of the modified metal powder to the binder is 100:8-12, the feeding temperature of the injection molding machine is 180-190℃, the injection pressure is 95-105MPa, the holding pressure is 95-105MPa, and the holding time is 10-15s.

5. The method for preparing large parts using metal powder injection molding according to claim 1, characterized in that, In step S4, the hot debinding and sintering method is as follows: the vacuum degree of the atmosphere furnace is reduced to 0.1 MPa, the temperature of the atmosphere furnace is increased to 180-200℃ at a heating rate of 1℃ / min, and held for 60-80 min; the temperature of the atmosphere furnace is increased to 450-500℃ at a heating rate of 2℃ / min, and held for 30-50 min; the temperature of the atmosphere furnace is increased to 780-820℃ at a heating rate of 2℃ / min, and held for 60-80 min; the temperature of the atmosphere furnace is increased to 1350-1400℃ at a heating rate of 4℃ / min, and held for 90-120 min; the temperature of the atmosphere furnace is reduced to room temperature, and the material is discharged to obtain the injection molded part.

6. The method for preparing large parts using metal powder injection molding according to claim 1, characterized in that, In step A1, the ratio of acrylic acid, methyl methacrylate, and butyl acrylate is 3 mol: 1 mol: 2 mol, and the ratio of butyl acrylate, toluene, and initiator is 1 g: 8 mL: 0.1 g. The initiator is azobisisobutyronitrile. The post-treatment includes: after the reaction is complete, maintaining the temperature of the reaction vessel at 80-90°C, removing the solvent under reduced pressure, and obtaining polyolefin.

7. The method for preparing large parts using metal powder injection molding according to claim 1, characterized in that, In step A2, the ratio of the polyolefin, bisphenol A epoxy resin, N,N-dimethylformamide, and catalyst is 8-10g:4-5g:50mL:0.5g. The catalyst is diisopropylamine. The post-treatment includes: after the reaction is complete, the temperature of the reaction vessel is lowered to room temperature, 3wt% sodium dodecyl sulfate aqueous solution is slowly added to the reaction vessel, stirred and dispersed for 30-50min, filtered, the filter cake is washed three times with ethanol and dried, and the filter cake is transferred to a drying oven at 60-70℃ and dried to constant weight to obtain the reinforcing agent.

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