Method for preparing large part by using metal powder injection molding process

Abstract

The invention discloses a method for preparing a large part by using a metal powder injection molding process, belongs to the technical field of large part processing, and aims to solve the technical problem that the strength of the large part prepared by metal powder injection molding in the prior art needs to be further improved. The method comprises the following steps that a reinforcing agent, paraffin and acetone are added into a reaction kettle to be stirred, the temperature of the reaction kettle is increased to 40-50 DEG C, stirring is conducted till a system is dissolved, reinforced modified liquid is obtained, metal powder is added into a high-speed mixer to be heated, and when the temperature of the metal powder reaches 100-110 DEG C, the reinforced modified liquid is slowly added into the high-speed mixer; according to the method, the ultimate tensile strength, the yield strength, the ductility and the hardness performance of an injection part are effectively improved by preparing the modified metal powder with the high flowing property and combining the modified metal powder with the bonding auxiliary agent and optimizing the injection condition and the degreasing roasting condition.

Description

Technical Field

[0001] The invention relates to the technical field of large-scale parts processing, and in particular to a method for preparing large-scale parts by utilizing a metal powder injection molding process. Background Art

[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 mix metal powder with organic binder evenly, and then use an injection molding machine to inject the mixture into the mold under high temperature and high pressure to solidify and form it. The binder is then removed through steps such as degreasing and sintering to finally obtain dense metal parts.

[0003] In the prior art, a Chinese invention patent with publication number CN105290392A discloses a 304L stainless steel metal powder injection molding method, including the steps of mixing 304L stainless steel powder with a binder to form a granulated feed, injection molding to prepare a blank, catalytic degreasing, and three-stage atmosphere process sintering including negative pressure degreasing, vacuum sintering and forced cooling, so as to obtain 304L stainless steel parts with high dimensional accuracy, high surface accuracy, and no burrs, and avoid the complex processes of solvent degreasing and thermal degreasing, with high production efficiency and low production cost.

[0004] However, traditional metal powder injection molding technology is mainly used to produce small, complex and special parts due to the high precision, uniform structure, excellent performance and low production cost of the metal powder injection molding process. For large parts, due to their large thickness, small-particle powder can help improve the density and microstructure uniformity of the material. However, in the preparation process of large parts, small-particle metal powder has a large specific surface area and high surface energy, which is prone to agglomeration, resulting in a decrease in the uniformity of feed mixing, affecting the stability and quality of injection molding. In addition, the degreasing process of small-particle metal powder is more complicated, requiring longer degreasing time and higher degreasing temperature, which not only increases production costs, but may also lead to incomplete degreasing, affecting the performance of the final product. The strength of large parts prepared by metal powder injection molding needs to be further improved.

[0005] In view of the technical defects in this aspect, a solution is now proposed. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing large parts by using a metal powder injection molding process, so as to solve 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 object of the present invention can be achieved by the following technical solution: A method for preparing large parts by using a metal powder injection molding process comprises the following steps:

[0008] S1. Add the enhancer, paraffin and acetone into a reactor and stir. Raise the temperature of the reactor to 40-50°C and stir until the system is dissolved to obtain an enhanced modified liquid.

[0009] S2, adding the metal powder to a high-speed mixer and heating it, and when the temperature of the metal powder reaches 100-110°C, slowly adding the enhanced modification liquid to the high-speed mixer, and after the addition is completed, heat-insulating and mixing for 60-80 minutes to obtain modified metal powder;

[0010] S3, mixing the modified metal powder and the bonding aid, adding the mixture into an injection molding machine, and performing injection molding to obtain an injection blank with a thickness of 30 mm;

[0011] S4. Place the injection blank into an atmosphere furnace, perform thermal debinding and sintering, and obtain an injection part.

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

[0013] Furthermore, in step S2, the amount ratio of the metal powder to the enhanced modification liquid is 100g:7-12mL, the speed of the high-speed mixer is 800-900r / min, 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, and 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 bonding aid is 100:8-12, the bonding aid is composed of polyformaldehyde and agar in a weight ratio of 10:3, the feeding temperature of the injection machine is 180-190°C, the injection pressure is 95-105MPa, the holding pressure is 95-105MPa, and the holding time is 10-15s.

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

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

[0017] A1. Add acrylic acid, methyl methacrylate, butyl acrylate and toluene into a reactor and stir. Add an initiator into the reactor. Raise the temperature of the reactor to 80-90° C. and keep the temperature for 4-6 hours. Post-treat to obtain polyolefin.

[0018] The synthesis reaction mechanism of polyolefins is:

[0019] Under the action of the initiator, the olefin double bonds on the acrylic acid, methyl methacrylate, and butyl acrylate molecules are opened to form free radical intermediates, and free radical polymerization occurs, causing the chain to continue to grow to form a high molecular weight polymer chain, thereby preparing a carboxyl-modified polyolefin segment to obtain a polyolefin.

[0020] A2. Add polyolefin, bisphenol A epoxy resin and N,N-dimethylformamide into a nitrogen-protected reactor and stir. Add a catalyst into the reactor, increase the temperature of the reactor to 90-100°C, keep the temperature for 4-5 hours, and perform post-treatment to obtain an enhancer.

[0021] The synthetic reaction mechanism of the enhancer is:

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

[0023] Furthermore, in step A1, the usage ratio of acrylic acid, methyl methacrylate and butyl acrylate is 3 mol:1 mol:2 mol, the usage ratio of butyl acrylate, toluene and initiator is 1 g:8 mL:0.1 g, the initiator is azobisisobutyronitrile, and the post-treatment includes: after the reaction is completed, the temperature of the reactor is kept at 80-90° C., and the solvent is evaporated under reduced pressure to obtain polyolefin.

[0024] Furthermore, in step A2, the amount 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, and the post-treatment includes: after the reaction is completed, the temperature of the reactor is lowered to room temperature, 3wt% sodium dodecyl sulfate aqueous solution is slowly added to the reactor, stirred and dispersed for 30-50min, filtered, the filter cake is washed three times with ethanol and then dried, and the filter cake is transferred to a drying oven at a temperature of 60-70°C and dried to constant weight to obtain an enhancer.

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

[0026] 1. The method for preparing large parts by using a metal powder injection molding process provided by the present invention comprises: reinforcing and modifying metal powder by using a reinforcing and modifying liquid composed of a reinforcing agent prepared by reacting polyolefin and bisphenol A epoxy resin, paraffin and acetone, and coating a layer of organic coating on the surface of the metal powder to prepare modified metal powder; when preparing the modified metal powder, paraffin is used as an auxiliary agent to promote the dissolution of the reinforcing agent in acetone so that the reinforcing agent can be evenly dispersed in the solvent; paraffin is a natural lubricant and has certain film-forming properties; the long-chain hydrocarbon groups in its molecular structure can reduce the friction and resistance between powder particles; after paraffin is added 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 paraffin and the reinforcing agent can jointly improve the fluidity of the metal powder.

[0027] 2. The method for preparing large parts by using metal powder injection molding process provided by the present invention, through the cooperation of polyformaldehyde and agar, agar is a natural polysaccharide colloid with good water solubility and gelling property, can promote the gelling of bonding agent, improve the lubricating property of bonding agent, polyformaldehyde and agar are mixed, the bonding agent is rapidly softened in a high temperature and high pressure environment, the bonding agent is penetrated into the tiny gaps between powder particles, and a firm bond is formed, the modified metal powder is filled into every corner of the mold, and the cooling effect of the mold makes the bonding agent rapidly solidify to form a blank with certain strength and density. In this process, polyformaldehyde provides the main strength and rigid support, while agar optimizes the bonding effect through thickening, gelling and lubricating effects, making the blank more uniform and dense. In the heat treatment process in the atmosphere furnace, the residual stress and defects in the blank are eliminated by controlling the temperature and time, and the densification and grain growth of the material are promoted. The higher temperature and longer insulation time 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 by using metal powder injection molding process provided by the present invention comprises mixing 17-4PH stainless steel powder, titanium nitride, niobium carbide, lanthanum oxide and cerium oxide to form 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 are used as second phase strengthening phases to improve the tensile strength and yield strength of the material by hindering dislocation movement and crack propagation. Lanthanum oxide and cerium oxide are used as heterogeneous nucleation points in the metal powder to promote grain refinement and improve the organizational structure, thereby improving the strength and toughness of the material. Grains can cause materials to become brittle and reduce elongation. The present invention selects larger-sized stainless steel metal powders and utilizes the relative melting and fluidity of larger-sized powder particles to reduce the requirements of large parts for injection pressure and temperature. In addition, larger-sized powder particles can further promote grain growth during the sintering process, reduce the number of grain boundaries, and reduce the adverse effects of grain boundaries on material properties. During the heat treatment process, recrystallization occurs, and the distortion energy inside the material is promoted through recrystallization to accumulate until the formation and growth of new distortion-free grains in the material occurs, eliminating work hardening and residual stress, and further improving the plasticity and toughness of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 This is a SEM photo of the cross section of the injection molded part of the present invention;

[0031] Figure 2 This is a SEM photo of the cross section of the injection molded part of the present invention;

[0032] Figure 3 It is the infrared spectrum of the modified metal powder in the present invention. DETAILED DESCRIPTION

[0033] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

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

[0035] Polyoxymethylene was selected from Dongguan Xingxiang New Materials Co., Ltd., brand F25-03H;

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

[0037] Example 1

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

[0039] S1. Preparation of enhancer

[0040] Weigh: 21.6 g of acrylic acid, 10.0 g of methyl methacrylate, 25.6 g of butyl acrylate, and 204.8 mL of toluene, add them into a reactor and stir, add 2.56 g of azobisisobutyronitrile into the reactor, raise the temperature of the reactor to 80° C., keep the temperature for 4 hours, keep the temperature of the reactor at 80° C., and evaporate the solvent under reduced pressure to obtain polyolefin;

[0041] Weigh: 80-100g of polyolefin, 40g of bisphenol A epoxy resin and 500mL of N,N-dimethylformamide, add them into a nitrogen-protected reactor and stir, add 5g of diisopropylamine into the reactor, raise the temperature of the reactor to 90°C, keep the reaction for 4h, lower the temperature of the reactor to room temperature, slowly add 1000mL of 3wt% sodium dodecyl sulfate aqueous solution into the reactor, stir and disperse for 30min, filter, wash the filter cake three times with ethanol and then drain, transfer the filter cake to a drying oven at 60°C, dry to constant weight, and obtain an enhancer.

[0042] S2. Preparation of modified metal powder

[0043] The enhancer, paraffin and acetone were added into the reactor in a ratio of 2g:1g:20mL and stirred. The temperature of the reactor was raised to 40°C and stirred until the system was dissolved to obtain an enhanced modified liquid.

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

[0045] Weigh: 500 g of metal powder is added to a high-speed mixer and heated. When the temperature of the metal powder reaches 100° C., 200 mL of the enhanced modification liquid is slowly added to the high-speed mixer. After the addition is completed, the mixture is kept warm and mixed for 60 minutes to obtain a modified metal powder.

[0046] S3. Preparation of injection blanks

[0047] The polyoxymethylene and agar are mixed uniformly in a weight ratio of 10:3 to obtain a bonding aid;

[0048] After the modified metal powder and the bonding aid were mixed in a weight ratio of 100:8, the feeding temperature of the injection molding machine was increased to 180°C, the injection pressure of the injection molding machine was increased to 95 MPa, and injection molding was performed. The holding pressure was set to 95 MPa and the holding time was 10 s to obtain an injection blank with a thickness of 30 mm.

[0049] S4. Preparation of injection parts

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

[0051] Example 2

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

[0053] S1. Preparation of enhancer

[0054] Weigh: 21.6 g of acrylic acid, 10.0 g of methyl methacrylate, 25.6 g of butyl acrylate, and 204.8 mL of toluene, add them into a reactor and stir, add 2.56 g of azobisisobutyronitrile into the reactor, raise the temperature of the reactor to 85° C., keep the temperature for 5 hours, keep the temperature of the reactor at 85° C., and evaporate the solvent under reduced pressure to obtain polyolefin;

[0055] Weigh: 90g of polyolefin, 45g of bisphenol A epoxy resin and 500mL of N,N-dimethylformamide, add them into a nitrogen-protected reactor and stir, add 5g of diisopropylamine into the reactor, raise the temperature of the reactor to 95°C, keep the reaction for 4.5h, lower the temperature of the reactor to room temperature, slowly add 1000mL of 3wt% sodium dodecyl sulfate aqueous solution into the reactor, stir and disperse for 30-50min, filter, wash the filter cake three times with ethanol and then drain, transfer the filter cake to a drying oven at a temperature of 65°C, dry to constant weight, and obtain an enhancer.

[0056] S2. Preparation of modified metal powder

[0057] The enhancer, paraffin and acetone were added into the reactor in a ratio of 2.5 g:1 g:20 mL and stirred. The temperature of the reactor was raised to 45°C and stirred until the system was dissolved to obtain an enhanced modified liquid.

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

[0059] Weigh: 500 g of metal powder is added to a high-speed mixer and heated. When the temperature of the metal powder reaches 105° C., 250 mL of the enhanced modification liquid is slowly added to the high-speed mixer. After the addition is completed, heat and mix for 70 minutes to obtain modified metal powder.

[0060] S3. Preparation of injection blanks

[0061] The polyoxymethylene and agar are mixed uniformly in a weight ratio of 10:3 to obtain a bonding aid;

[0062] After the modified metal powder and the bonding aid were mixed in a weight ratio of 100:10, the feeding temperature of the injection molding machine was increased to 185°C, the injection pressure of the injection molding machine was increased to 100 MPa, and injection molding was performed. The holding pressure was set to 100 MPa and the holding time was 13 s to obtain an injection blank with a thickness of 30 mm.

[0063] S4. Preparation of injection parts

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

[0065] Example 3

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

[0067] S1. Preparation of enhancer

[0068] Weigh: 21.6 g of acrylic acid, 10.0 g of methyl methacrylate, 25.6 g of butyl acrylate, and 204.8 mL of toluene, add them into a reactor and stir, add 2.56 g of azobisisobutyronitrile into the reactor, raise the temperature of the reactor to 90° C., keep the temperature for 6 hours, keep the temperature of the reactor at 90° C., and evaporate the solvent under reduced pressure to obtain polyolefin;

[0069] Weigh: 100 g of polyolefin, 50 g of bisphenol A epoxy resin and 500 mL of N,N-dimethylformamide, add them into a nitrogen-protected reactor and stir, add 5 g of diisopropylamine into the reactor, raise the temperature of the reactor to 100° C., keep the reaction warm for 5 hours, lower the temperature of the reactor to room temperature, slowly add 1000 mL of 3 wt% sodium dodecyl sulfate aqueous solution into the reactor, stir and disperse for 50 minutes, filter, wash the filter cake three times with ethanol and then dry it, transfer the filter cake to a drying oven at 70° C., dry to constant weight, and obtain an enhancer.

[0070] S2. Preparation of modified metal powder

[0071] The enhancer, paraffin and acetone were added into the reactor in a ratio of 3g:1g:20mL and stirred. The temperature of the reactor was raised to 50°C and stirred until the system was dissolved to obtain an enhanced modified liquid.

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

[0073] Weigh: 500 g of metal powder is added to a high-speed mixer and heated. When the temperature of the metal powder reaches 110° C., 300 mL of the enhanced modification liquid is slowly added to the high-speed mixer. After the addition is completed, the mixture is kept warm and mixed for 80 minutes to obtain a modified metal powder.

[0074] S3. Preparation of injection blanks

[0075] The polyoxymethylene and agar are mixed uniformly in a weight ratio of 10:3 to obtain a bonding aid;

[0076] After the modified metal powder and the bonding aid were mixed in a weight ratio of 100:12, the feeding temperature of the injection molding machine was increased to 190°C, the injection pressure of the injection molding machine was increased to 105 MPa, and injection molding was performed. The holding pressure was set to 105 MPa and the holding time was 15 s to obtain an injection blank with a thickness of 30 mm.

[0077] S4. Preparation of injection parts

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

[0079] Comparative Example 1

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

[0081] Comparative Example 2

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

[0083] Comparative Example 3

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

[0085] Comparative Example 4

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

[0087] Performance Test:

[0088] The fluidity of the modified metal powders used in Examples 1-3 and Comparative Examples 1-4 was tested with reference to the standard GB / T 41329-2022 "Standard funnel method for determination of the fluidity of metal powders (Gustafson rheometer)";

[0089] With reference to the standard JB / T 13067.1-2017 "Metal Injection Molding Materials Part 1: Technical Conditions for Sintered Low Alloy Steel and Stainless Steel", the ultimate tensile strength, yield strength (0.2%), elongation and hardness of the injection parts prepared in Examples 1-3 and Comparative Examples 1-4 were tested. 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 above table shows that the fluidity of the modified metal powder prepared by the present invention reaches 23s / 50g, the ultimate tensile strength of the prepared injection part reaches 1671MPa, the yield strength reaches 1258MPa, the elongation reaches 4.5%, and the hardness reaches 60.3HRB, and all performance references are better than the comparative examples;

[0095] It is explained that the present invention optimizes the size of stainless steel powder and the composition of metal powder, strengthens and modifies the metal powder with prepared reinforcing agent and paraffin, prepares modified metal powder, improves the fluidity of the metal powder, combines the modified metal powder with a bonding agent composed of polyformaldehyde and agar, optimizes the injection conditions and degreasing and roasting conditions, and effectively improves the ultimate tensile strength, yield strength, elongation and hardness performance of the injection part.

[0096] The above contents are merely examples and explanations of the structure of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

[0097] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0098] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing large parts using a metal powder injection molding process, characterized in that: The following steps are involved: S1. Add the enhancer, paraffin and acetone into a reactor and stir. Raise the temperature of the reactor to 40-50°C and stir until the system is dissolved to obtain an enhanced modified liquid. S2, adding the metal powder to a high-speed mixer and heating it, and when the temperature of the metal powder reaches 100-110°C, slowly adding the enhanced modification liquid to the high-speed mixer, and after the addition is completed, heat-insulating and mixing for 60-80 minutes to obtain modified metal powder; S3, mixing the modified metal powder and the bonding aid, adding the mixture into an injection molding machine, and performing injection molding to obtain an injection blank with a thickness of 30 mm; S4. Place the injection blank into an atmosphere furnace, perform thermal debinding and sintering, and obtain an injection part.

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

3. The method for preparing large parts by metal powder injection molding process according to claim 1, characterized in that: In step S2, the amount ratio of the metal powder to the enhanced modification liquid is 100g:7-12mL, the speed of the high-speed mixer is 800-900r / min, 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, and the particle size is 70-90μm.

4. The method for preparing large parts by metal powder injection molding process according to claim 1, characterized in that: In step S3, the weight ratio of the modified metal powder to the bonding aid is 100:8-12, the bonding aid is composed of polyformaldehyde and agar in a weight ratio of 10:3, the feeding temperature of the injection machine is 180-190°C, 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 by metal powder injection molding process according to claim 1, characterized in that: In step S4, the method of thermal degreasing and sintering is as follows: the vacuum degree of the atmosphere furnace is reduced to 0.1MPa, the temperature of the atmosphere furnace is increased to 180-200°C at a heating rate of 1°C / min, and kept warm for 60-80min, the temperature of the atmosphere furnace is increased to 450-500°C at a heating rate of 2°C / min, and kept warm for 30-50min, the temperature of the atmosphere furnace is increased to 780-820°C at 2°C / min, and kept warm for 60-80min, the temperature of the atmosphere furnace is increased to 1350-1400°C at a heating rate of 4°C / min, and kept warm for 90-120min, the temperature of the atmosphere furnace is reduced to room temperature, the material is discharged, and the injection molded part is obtained.

6. The method for preparing large parts by metal powder injection molding process according to claim 1, characterized in that: The reinforcing agent is obtained by processing the following steps: A1. Add acrylic acid, methyl methacrylate, butyl acrylate and toluene into a reactor and stir. Add an initiator into the reactor. Raise the temperature of the reactor to 80-90° C. and keep the temperature for 4-6 hours. Post-treat to obtain polyolefin. A2. Add polyolefin, bisphenol A epoxy resin and N,N-dimethylformamide into a nitrogen-protected reactor and stir. Add a catalyst into the reactor, increase the temperature of the reactor to 90-100°C, keep the temperature for 4-5 hours, and perform post-treatment to obtain an enhancer.

7. The method for preparing large parts by using metal powder injection molding process according to claim 6, characterized in that: In step A1, the usage ratio of acrylic acid, methyl methacrylate and butyl acrylate is 3 mol:1 mol:2 mol, the usage ratio of butyl acrylate, toluene and initiator is 1 g:8 mL:0.1 g, the initiator is azobisisobutyronitrile, and the post-treatment comprises: after the reaction is completed, the temperature of the reactor is kept at 80-90° C., and the solvent is evaporated under reduced pressure to obtain polyolefin.

8. The method for preparing large parts by using metal powder injection molding process according to claim 6, characterized in that: In step A2, the amount ratio of the polyolefin, bisphenol A type epoxy resin, N,N-dimethylformamide and catalyst is 8-10g:4-5g:50mL:0.5g, the catalyst is diisopropylamine, and the post-treatment includes: after the reaction is completed, the temperature of the reactor is lowered to room temperature, 3wt% sodium dodecyl sulfate aqueous solution is slowly added to the reactor, stirred and dispersed for 30-50min, filtered, the filter cake is washed three times with ethanol and then dried, and the filter cake is transferred to a drying oven at a temperature of 60-70°C and dried to constant weight to obtain an enhancer.

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