Polyformaldehyde-based metal injection molding feed as well as preparation method and application thereof

Abstract

The invention provides a polyformaldehyde-based metal injection molding feed as well as a preparation method and application thereof, and the polyformaldehyde-based metal injection molding feed comprises the following components in percentage by mass: 87-97% of metal powder and 3-13% of a binder, the metal powder comprises tungsten powder; the tungsten powder comprises first tungsten powder and second tungsten powder; the average particle size of the first tungsten powder is larger than that of the second tungsten powder; the binder comprises polyformaldehyde, a skeleton unit and a formaldehyde inhibitor. In the invention, the polyformaldehyde-based metal injection molding feed has good fluidity, stability and sintering performance, can be recycled for multiple times, is beneficial to improving the strength and degreasing efficiency of an injection blank, can reduce the production cost and energy consumption, and can obtain a product with better performance.

Description

Technical Field

[0001] The invention belongs to the technical field of injection molding feed materials, and in particular relates to a polyoxymethylene-based metal injection molding feed material and a preparation method and application thereof. Background Art

[0002] Tungsten alloy has the characteristics of high density, high tensile strength, good radiation shielding ability, good thermal conductivity, low linear expansion coefficient and good corrosion resistance. It is widely used in aerospace, national defense and military industry, consumer electronics, medical equipment, sports and nuclear energy and nuclear power.

[0003] Metal Injection Molding (MIM) is a novel near-net-shape powder metallurgy technology developed by integrating modern plastic injection molding techniques into the powder metallurgy field. MIM technology offers advantages such as high dimensional accuracy, the ability to form complex structural parts, high production efficiency, and low production costs. The application of MIM technology in the production of tungsten alloys has promoted the further application of tungsten alloy materials.

[0004] Tungsten powder is a reduced powder. Commercially available tungsten powder for MIM has disadvantages such as fine particle size, severe powder agglomeration, irregular morphology, and poor fluidity. Therefore, the polyformaldehyde-based tungsten alloy feedstock produced by traditional methods is prone to frictional heat generation due to the poor fluidity of the tungsten powder, which causes polyformaldehyde volatilization, resulting in poor feedstock stability and a limited number of cycles. To improve the fluidity of the tungsten alloy feedstock, the most commonly used tungsten alloy feedstock is wax-based feedstock, with paraffin as the main component of the molding agent. However, although wax-based feedstock has better fluidity, it also has problems such as low injection strength of the blank, low degreasing efficiency, high degreasing cost, and difficulty in producing products with large wall thickness (wall thickness greater than 8mm).

[0005] Therefore, developing a tungsten alloy injection molding feed with good fluidity, high injection embryo strength, high degreasing efficiency, good sintering performance, good stability, and the ability to be recycled multiple times to obtain products with good performance and low cost is an urgent problem to be solved in this field. Summary of the Invention

[0006] In response to the shortcomings of the prior art, the present invention provides a polyoxymethylene (POM)-based metal injection molding (MIM) feedstock, its preparation method, and its application. The POM-based MIM feedstock exhibits excellent fluidity, stability, and sintering properties, can be recycled multiple times, and is beneficial for increasing the strength of injection molded parts, reducing deformation of injection molded parts, and improving the degreasing efficiency of finished parts. Furthermore, the feedstock can reduce production costs and energy consumption, resulting in products with superior performance.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a polyformaldehyde-based metal injection molding feed, which comprises, by mass percentage, 87-97% metal powder and 3-13% binder; the metal powder comprises tungsten powder; the tungsten powder comprises a first tungsten powder and a second tungsten powder; the average particle size of the first tungsten powder is greater than the average particle size of the second tungsten powder; the binder comprises polyformaldehyde, a skeleton unit and a formaldehyde inhibitor.

[0009] In the present invention, tungsten powders of different particle sizes are compounded, wherein fine-grained tungsten powder (second tungsten powder) is filled in the gaps between coarse-grained tungsten powder (first tungsten powder), which can significantly improve the tap density of the powder, increase the feed loading capacity, improve the degreasing efficiency, reduce the degreasing cost, and improve the stability of the finished product's dimensional shrinkage. At the same time, the coarse-grained tungsten powder has good fluidity, which is beneficial for improving the rheological properties of the feed and reducing the volatilization of polyformaldehyde; the fine-grained tungsten powder can reduce the sintering temperature, increase the sintering density, and improve the mechanical properties of the product; at the same time, the addition of formaldehyde inhibitors can inhibit the production of formaldehyde, reduce the thermal decomposition of polyformaldehyde, and improve the thermal stability of polyformaldehyde, thereby greatly improving the batch stability of the feed and increasing the number of times the feed is reused, reducing production costs and obtaining products with better performance.

[0010] In the present invention, the 87-97% metal powder may be, for example, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, etc.

[0011] In the present invention, 3% to 13% of the binder may be, for example, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, etc.

[0012] Preferably, the mass ratio of the first tungsten powder to the second tungsten powder is (2-30):1, wherein the specific values of (2-30) can be, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, etc.

[0013] Preferably, the average particle size of the first tungsten powder is 1 to 25 μm, for example, it can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, etc.

[0014] Preferably, the average particle size of the second tungsten powder is 0.1-10 μm, for example, it can be 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc.

[0015] Preferably, the metal powder further comprises a second metal.

[0016] Preferably, the second metal comprises at least one of nickel, iron, copper, cobalt, manganese, chromium, yttrium, lanthanum or rhenium.

[0017] In the present invention, the metal powder is preferably tungsten alloy powder, and the tungsten alloy powder includes at least one of tungsten-nickel-iron alloy, tungsten-nickel-copper alloy, tungsten-nickel-cobalt alloy, tungsten-nickel-iron-cobalt alloy, tungsten-nickel-copper-cobalt alloy, tungsten-copper alloy, tungsten-yttrium alloy, tungsten-lanthanum alloy or tungsten-rhenium alloy.

[0018] Preferably, the average particle size of the second metal is 0.1 to 50 μm, for example, it can be 0.1 μm, 0.5 μm, 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm, 32 μm, 35 μm, 38 μm, 40 μm, 42 μm, 45 μm, 48 μm, 50 μm, etc.

[0019] In the present invention, the average particle sizes of the first tungsten powder, the second tungsten powder and the second metal can be obtained by testing with a Fisher particle size analyzer.

[0020] Preferably, the mass percentage of the second metal in the metal powder is 0.03-20%, for example, it can be 0.03%, 0.07%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc.

[0021] Preferably, the binder comprises, by mass percentage, 70-90% polyoxymethylene (for example, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, etc.), 2-25% backbone units (for example, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 25%, etc.) and 0.3-2% formaldehyde inhibitor (for example, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, etc.).

[0022] Preferably, the backbone unit includes at least one of polypropylene (PP), polyethylene (PE), ethylene-vinyl acetate copolymer (EVA) or olefin thermoplastic elastomer.

[0023] Preferably, the formaldehyde inhibitor comprises melamine and / or urea.

[0024] Preferably, the binder further comprises at least one of an antioxidant, a lubricant or a surfactant.

[0025] Preferably, the binder further comprises, by weight percentage, 0.2-2% antioxidant (for example, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, etc.), 0.3-2.5% lubricant (for example, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, %. The present invention relates to a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant and a surfactant agent; ... comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant comprising: a surfactant

[0026] Preferably, the antioxidant includes at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1010), β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1076), triethylene glycol bis[β-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate] (antioxidant 245), tris[2,4-di-tert-butylphenyl]phosphite (antioxidant 168) or N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexanediamine (antioxidant 1098).

[0027] Preferably, the lubricant comprises at least one of paraffin wax, microcrystalline wax, palm wax, beeswax, polyethylene wax, ethylene bisstearamide or oleamide.

[0028] Preferably, the surfactant includes at least one of stearic acid, calcium stearate, zinc stearate or pentaerythritol stearate.

[0029] In a second aspect, the present invention provides a method for preparing the polyoxymethylene-based metal injection molding feedstock according to the first aspect, the preparation method comprising the following steps:

[0030] The metal powder is mixed with a binder to obtain the polyoxymethylene-based metal injection molding feedstock.

[0031] Preferably, the step of grinding the metal powder is further included before mixing the metal powder with the binder.

[0032] Preferably, the grinding method comprises ball milling.

[0033] Preferably, the ball-to-material ratio of the ball mill is (0.3-3):1, wherein the specific value of (0.3-3) can be, for example, 0.3, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, etc.

[0034] Preferably, the ball milling time is 4 to 30 h, for example, 4 h, 6 h, 8 h, 10 h, 12 h, 16 h, 18 h, 20 h, 22 h, 24 h, 26 h, 28 h, 30 h, etc.

[0035] Preferably, the mixing temperature is 150-200°C, for example, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, 200°C, etc.

[0036] In the present invention, the mixing is carried out in an internal mixer.

[0037] Preferably, the preparation method comprises: first mixing the ground metal powder with a formaldehyde inhibitor, then adding a backbone unit and optional antioxidants, lubricants and surfactants thereto for a second mixing, and then adding polyformaldehyde thereto and mixing evenly to obtain the polyformaldehyde-based metal injection molding feed.

[0038] Preferably, the first mixing time is 5 to 30 min, for example, it can be 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 18 min, 20 min, 25 min, 30 min, etc.; the second mixing time is 15 to 60 min, for example, it can be 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, etc.

[0039] In a third aspect, the present invention provides a metal part, wherein the raw materials for preparing the metal part include the polyoxymethylene-based metal injection molding feed described in the first aspect.

[0040] The numerical range described in the present invention includes not only the point values listed above, but also any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values included in the range.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The polyoxymethylene-based metal injection molding feed provided by the present invention is compounded with tungsten powders of different particle sizes and added with a formaldehyde inhibitor, so that the feed has good fluidity, stability and sintering performance, can be recycled multiple times, and is beneficial to improving the strength of the injection blank and the degreasing efficiency of the product. It can also reduce production costs and energy consumption, thereby obtaining products with better performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a graph showing the change trend of the melt index of the polyoxymethylene-based metal injection molding feed provided in Example 1 and Comparative Examples 1 and 2 of the present invention as the number of recycling times increases.

[0044] Figure 2 This is a graph showing the change trend of the melt index of the polyoxymethylene-based metal injection molding feed provided in Example 2 and Comparative Example 3 of the present invention as the number of recycling times increases. DETAILED DESCRIPTION

[0045] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0046] The materials used in the present invention can be obtained from commercial sources or prepared by conventional methods. Unless otherwise specified, the materials used in the present invention are as follows:

[0047] Copolymer polyoxymethylene: Brand: 7520, Manufacturer: Asahi Kasei, Japan.

[0048] PP: Brand: 3204, Manufacturer: Formosa Plastics Corporation of Taiwan, China.

[0049] PE: Brand: 2100J, Manufacturer: Yanshan Petrochemical.

[0050] EVA: Brand: EV210, Manufacturer: Mitsui Chemicals.

[0051] Tungsten powder of different particle sizes: Manufacturer: Xiamen Jinlu.

[0052] Example 1

[0053] This embodiment provides a polyoxymethylene-based metal injection molding feed, which includes, by mass percentage, 94.21% metal powder and 5.79% binder; by mass percentage, the metal powder includes 95% tungsten powder, 3.5% nickel powder and 1.5% iron powder; the tungsten powder includes a first tungsten powder (with an average particle size of 5 μm) and a second tungsten powder (with an average particle size of 0.5 μm) in a mass ratio of 10:1; by mass percentage, the binder includes 84% copolymerized polyoxymethylene, 12.3% backbone units (8.5% PP and 3.8% PE), 1.2% antioxidant (0.8% antioxidant 1010 and 0.4% antioxidant 168), 1% melamine, 1% paraffin and 0.5% stearic acid.

[0054] This embodiment provides a method for preparing a polyoxymethylene-based metal injection molding feedstock, which specifically includes the following steps:

[0055] Tungsten powder, nickel powder and iron powder are added to a ball mill with a ball-to-material ratio of 2:1, and ball milling is performed for 12 hours to obtain metal powder; the metal powder and melamine are added to an internal mixer, and after keeping the temperature at 180°C for 15 minutes, PP, PE, antioxidant 1010, antioxidant 168, paraffin and stearic acid are added thereto, and the mixture is mixed for 35 minutes, and then polyoxymethylene is added and mixed for 25 minutes to obtain the polyoxymethylene-based metal injection molding feed.

[0056] Example 2

[0057] This embodiment provides a polyoxymethylene-based metal injection molding feed, which includes, by mass percentage, 91.06% metal powder and 8.94% binder; by mass percentage, the metal powder includes 80% tungsten powder and 20% copper powder; the tungsten powder includes a first tungsten powder (average particle size of 1.5 μm) and a second tungsten powder (average particle size of 0.5 μm) in a mass ratio of 5:1; by mass percentage, the binder includes 83% copolymerized polyoxymethylene, 12.4% backbone units (10.2% PP and 2.2% EVA), 1.35% antioxidant (0.9% antioxidant 1076 and 0.45% antioxidant 245), 1.2% melamine, 1.5% ethylene bisstearamide and 0.55% stearic acid.

[0058] This embodiment provides a method for preparing a polyoxymethylene-based metal injection molding feedstock, which specifically includes the following steps:

[0059] Tungsten powder and copper powder were added to a ball mill with a ball-to-material ratio of 2:1, and ball milled for 10 hours to obtain metal powder; the metal powder and melamine were added to an internal mixer, kept warm at 175°C for 10 minutes, and then PP, EVA, antioxidant 1076, antioxidant 245, ethylene bisstearamide and stearic acid were added thereto and mixed for 30 minutes, and then polyoxymethylene was added and mixed for 30 minutes to obtain the polyoxymethylene-based metal injection molding feed.

[0060] Example 3

[0061] This embodiment provides a polyoxymethylene-based metal injection molding feed, which includes 90.07% metal powder and 9.93% binder, calculated by mass percentage; the metal powder includes 90% tungsten powder, 6% nickel powder and 4% iron powder, calculated by mass percentage; the tungsten powder includes a first tungsten powder (average particle size of 7 μm) and a second tungsten powder (average particle size of 1 μm) with a mass ratio of 20:1; the binder includes 74% copolymerized polyoxymethylene, 20.3% backbone units (11.5% PP and 8.8% PE), 1% antioxidant (0.6% antioxidant 1010 and 0.4% antioxidant 168), 2% urea, 1.7% paraffin and 1% stearic acid.

[0062] This embodiment provides a method for preparing a polyoxymethylene-based metal injection molding feedstock, and the specific steps are the same as those in Example 1.

[0063] Example 4

[0064] This embodiment provides a polyformaldehyde-based metal injection molding feedstock, which differs from Example 1 only in that the total mass of the tungsten powder remains unchanged, the mass ratio of the first tungsten powder to the second tungsten powder is 40:1, and the other components, amounts, and preparation methods are the same as those in Example 1.

[0065] Example 5

[0066] This embodiment provides a polyoxymethylene-based metal injection molding feedstock, which differs from Example 1 only in that the total mass of the tungsten powder remains unchanged, the mass ratio of the first tungsten powder to the second tungsten powder is 1:1, and the other components, amounts, and preparation methods are the same as those in Example 1.

[0067] Example 6

[0068] This embodiment provides a polyoxymethylene-based metal injection molding feedstock, which differs from Example 1 only in that the mass percentage of melamine in the binder is 0.1%, the mass ratio of PP to PE remains unchanged, and the total mass is 13.2%. The other components, amounts, and preparation methods are the same as those in Example 1.

[0069] Example 7

[0070] This embodiment provides a polyoxymethylene-based metal injection molding feedstock, which differs from Example 1 only in that the mass percentage of melamine in the binder is 3%, the mass ratio of PP to PE remains unchanged, and the total mass is 10.3%. The other components, amounts, and preparation methods are the same as those in Example 1.

[0071] Comparative Example 1

[0072] This comparative example provides a polyoxymethylene-based metal injection molding feedstock, which differs from Example 1 only in that the total mass of the tungsten powder remains unchanged, there is no second tungsten powder, and the other components, amounts, and preparation methods are the same as those in Example 1.

[0073] Comparative Example 2

[0074] This comparative example provides a polyoxymethylene-based metal injection molding feedstock. This feedstock differs from Example 1 in that the total mass of the tungsten powder remains unchanged, and the first tungsten powder is omitted. Furthermore, due to the poor flowability and low tap density of fine tungsten powder, a high loading rate is not possible, so the feedstock loading is reduced. Specifically, by weight percentage, the feedstock comprises 92.75% metal powder and 7.25% binder. Other components, amounts, and preparation methods are the same as in Example 1.

[0075] Comparative Example 3

[0076] This comparative example provides a polyformaldehyde-based metal injection molding feed, which differs from Example 2 only in that the binder does not contain melamine, the PP content is 11.2%, and the EVA content is 2.4%. The other components, amounts, and preparation methods are the same as those in Example 2.

[0077] Performance Testing

[0078] (1) The original feed (i.e., the polyoxymethylene-based metal injection molding feed provided in the examples and comparative examples) is marked as R0; R0 is injection molded, and the resulting injection blank and nozzle material are recycled and crushed, and the resulting feed is reused and marked as R1. This is repeated 20 times (i.e., the recycling times are 20 times, marked as R20); the melt index of the feed obtained each time is tested according to the standard ISO 1133 (175°C / 5500g), and the stability and number of reuses of the feed are characterized by the melt index (MFI) after multiple uses. Injection molding is performed using a German Arburg Allrounder 270S injection molding machine, and the injection process is as follows: injection pressure 95-105MPa, holding pressure 80MPa, holding time 0.2s, injection speed 22ccm / s, injection mold temperature 95°C, and injection material temperature 175°C.

[0079] Among them, the polyoxymethylene-based metal injection molding feed provided in Example 1, Comparative Examples 1 and 2 increases with the number of recycling times, and the feed melt index change trend diagram is as follows: Figure 1 shown by Figure 1 It can be seen that coarse-grained tungsten powder has better fluidity, while fine-grained tungsten powder has poor fluidity. By compounding tungsten powders of different particle sizes, compared with tungsten powder of a single particle size, it is beneficial to further improve the fluidity of the feed; moreover, the obtained feed has better stability and can be reused more times.

[0080] The polyoxymethylene-based metal injection molding feed provided in Example 2 and Comparative Example 3 has a feed melt index change trend as the number of recycling times increases. Figure 2 shown by Figure 2 It can be seen that adding formaldehyde inhibitors can improve the stability of the feed and increase the number of times the feed can be reused.

[0081] (2) The polyoxymethylene-based metal injection molding feed provided in the examples and comparative examples was injection molded, catalytically degreased, and thermally desintered. The density of the sintered samples was tested using the drainage method, with reference to GB / T3850-2015. The relative density was obtained based on the sintered density: relative density = sintered density / theoretical density × 100%. The catalytic degreasing was performed using a Shenzhen Xingtesuo STZ-800K oxalic acid catalytic degreasing furnace, with solid oxalic acid as the degreasing catalyst, a degreasing temperature of 125°C, and a degreasing time of 8 hours. The polyoxymethylene removal rate was above 95%. Thermal desintering is carried out in a molybdenum heating element batch furnace in a hydrogen atmosphere. The heating process is as follows: from room temperature to 500°C at a rate of 1.5°C / min, and kept at 500°C for 1 hour; then heated to 1200°C at a rate of 5°C / min, and kept at 1200°C for 1 hour; then heated to the maximum temperature at a rate of 1°C / min (the maximum sintering temperature is adjusted according to the composition and particle size design, as shown in Table 1), and kept at the maximum temperature for 30 minutes, and finally cooled naturally to room temperature with the furnace. (3) The tap density of the metal powders in the examples and comparative examples was tested using a tap density meter. The test method refers to GB / T 21354-2008.

[0082] The specific test results are shown in Table 1:

[0083] Table 1

[0084]

[0085] As can be seen from Table 1, the polyoxymethylene-based metal injection molding feed provided by the present invention is compounded with tungsten powders of different particle sizes and a formaldehyde inhibitor is added, so that the feed has good fluidity, stability, and sintering performance, and can be recycled multiple times, which is beneficial to improving the strength of the injection molded product and improving the degreasing efficiency of the product. It can also reduce production costs and energy consumption, and obtain products with better performance. The polyoxymethylene-based metal injection molding feed still has a high melt index after being recycled 20 times, and the sintered relative density of the feed is ≥99%.

[0086] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A polyoxymethylene-based metal injection molding feed, characterized in that: The polyoxymethylene-based metal injection molding feed comprises, in percentage by mass, 87-97% of metal powder and 3-13% of a binder; The metal powder includes tungsten powder; the tungsten powder includes first tungsten powder and second tungsten powder; the average particle size of the first tungsten powder is greater than the average particle size of the second tungsten powder; The binder includes polyoxymethylene, a backbone unit and a formaldehyde inhibitor.

2. The polyoxymethylene-based metal injection molding feed according to claim 1, characterized in that The mass ratio of the first tungsten powder to the second tungsten powder is (2-30):1; Preferably, the average particle size of the first tungsten powder is 1 to 25 μm; Preferably, the average particle size of the second tungsten powder is 0.1-10 μm.

3. The polyoxymethylene-based metal injection molding feed according to claim 1 or 2, characterized in that: The metal powder further includes a second metal; Preferably, the second metal comprises at least one of nickel, iron, copper, cobalt, manganese, chromium, yttrium, lanthanum or rhenium; Preferably, the average particle size of the second metal is 0.1 to 50 μm; Preferably, the mass percentage of the second metal in the metal powder is 0.03-20%.

4. The polyoxymethylene-based metal injection molding feed according to any one of claims 1 to 3, characterized in that: Calculated by mass percentage, the binder includes 70-90% polyoxymethylene, 2-25% backbone units and 0.3-2% formaldehyde inhibitor; Preferably, the backbone unit comprises at least one of polypropylene, polyethylene, ethylene-vinyl acetate copolymer or olefin thermoplastic elastomer; Preferably, the formaldehyde inhibitor comprises melamine and / or urea.

5. The polyoxymethylene-based metal injection molding feed according to any one of claims 1 to 4, characterized in that: The binder further comprises at least one of an antioxidant, a lubricant or a surfactant; Preferably, the binder further comprises, by weight percentage, 0.2-2% antioxidant, 0.3-2.5% lubricant and 0.3-1.5% surfactant; Preferably, the antioxidant includes at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, n-octadecylβ-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, triethylene glycol bis[β-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate], tris[2,4-di-tert-butylphenyl]phosphite or N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexanediamine; Preferably, the lubricant comprises at least one of paraffin wax, microcrystalline wax, palm wax, beeswax, polyethylene wax, ethylene bisstearamide or oleamide; Preferably, the surfactant includes at least one of stearic acid, calcium stearate, zinc stearate or pentaerythritol stearate.

6. A method for preparing a polyoxymethylene-based metal injection molding feedstock according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: The metal powder is mixed with a binder to obtain the polyoxymethylene-based metal injection molding feedstock.

7. The preparation method according to claim 6, characterized in that The metal powder is further ground before being mixed with the binder; Preferably, the grinding method comprises ball milling; Preferably, the ball-to-material ratio of the ball mill is (0.3-3):1; Preferably, the ball milling time is 4 to 30 hours.

8. The preparation method according to claim 6 or 7, characterized in that The mixing temperature is 150-200°C.

9. The preparation method according to any one of claims 6 to 8, characterized in that The preparation method comprises: first mixing the ground metal powder with a formaldehyde inhibitor, then adding a backbone unit and an optional antioxidant, a lubricant and a surfactant thereto, performing a second mixing, and then adding polyoxymethylene thereto, mixing uniformly, to obtain the polyoxymethylene-based metal injection molding feed; Preferably, the first mixing time is 5 to 30 minutes, and the second mixing time is 15 to 60 minutes.

10. A metal part, characterized in that: The raw materials for preparing the metal parts include the polyoxymethylene-based metal injection molding feed according to any one of claims 1 to 5.

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