Novel MIM feed based on plastic-based binder and preparation method

Abstract

The invention discloses a novel MIM feed based on a plastic-based binder and a preparation method. The novel MIM feed comprises the following components in parts by mass: 90-120 parts of metal powder; 8 to 10 parts of a plastic-based binder; the plastic-based binder comprises a filler, a skeleton agent, a lubricant and a surfactant. According to the invention, the MIM feed adopts the plastic-based binder, and by adjusting the feed formula, the green body is high in strength (not easy to deform) and good in dimensional stability, and the relative density after sintering can reach 98.3%, so that the requirements of high-precision parts are met; meanwhile, the dosage of a binder is reduced by optimizing the powder loading capacity, the degreasing time is shortened, the degreasing cost is reduced, and the method is suitable for batch production; the process adaptability is good, the feeding rheological property is excellent (the shear thinning characteristic is obvious, and the temperature sensitivity is low), the injection temperature of 180-210 DEG C can be matched, and the defects of flash, under-injection and the like are reduced; the bonding agent is good in compatibility, the bonding agent has good compatibility with 316L stainless steel powder, powder-glue separation is avoided, feeding uniformity is high, and a stable basis is provided for subsequent degreasing and sintering.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal injection molding, and more particularly, to a new MIM feedstock based on plastic-based binder and a preparation method thereof. BACKGROUND

[0002] Metal injection molding (MIM) is a new powder metallurgy near-net shaping technology derived from the plastic injection molding industry. Specifically, it is a process in which metal powder and binder are mixed under certain conditions to form a feedstock, which is then injected into a mold to form a shaped product.

[0003] The process generally consists of four steps: granulation, injection, debinding, and sintering. First, the metal powder is mixed with the binder through the granulation step, and the metal powder is evenly coated with the binder. Then, the injection step is used to form a shaped green body, which is then debound to form a brown body by removing most of the binder, and the brown body is sintered to obtain a metal product.

[0004] MIM feedstock is formed by uniformly mixing metal powder and binder, and its quality directly affects the stability of subsequent injection, debinding, and sintering processes and the performance of the final product, such as density, mechanical properties, and dimensional accuracy. In the preparation of the feedstock, the design of the binder system is particularly important. The selection of appropriate binder components and their ratio, the determination of appropriate powder loading, and the development of reasonable mixing processes, including mixing time and the order of binder addition, are important factors for obtaining high-quality feedstock.

[0005] Currently, the commonly used binders for MIM feedstock are mainly divided into three categories: wax-based, plastic-based, and water-based. Among them, wax-based binders are widely used due to their low cost and good flowability, but they have low green strength (<12 MPa), high shrinkage after debinding (>37%), and poor dimensional accuracy. Water-based binders are environmentally friendly, but their stability and flowability are greatly affected by the environment (flowability changes by >20% when humidity fluctuates by ±5%). Plastic-based binders have high strength and good dimensional stability, but their formulation and preparation process are not yet mature, and they cannot meet the needs of high-precision parts.

[0006] Based on the above defects and deficiencies, there is an urgent need in the art to develop a new MIM feedstock and its preparation method to improve process adaptability and part precision, and reduce production costs. SUMMARY

[0007] In view of the above defects or improvement needs of the prior art, the present application provides a new MIM feed based on plastic-based binder and a preparation method, which adopts plastic-based binder, adjusts the feed formula, so that the green strength is high (not easy to deform), the dimensional stability is good, and the high-precision part demand is met; meanwhile, the binder amount is reduced by optimizing the powder loading amount, the debinding time and cost are reduced, and batch production is suitable.

[0008] To achieve the above effects, according to one aspect of the present application, the present application provides a new MIM feed based on plastic-based binder, characterized in that it comprises the following components in mass fraction: 90-120 parts of metal powder; 8-10 parts of plastic-based binder; The plastic-based binder comprises a filler, a framework agent, a lubricant and a surfactant.

[0009] Further, in an optional embodiment of the present application, the plastic-based binder comprises a filler, a framework agent, a first lubricant, a second lubricant, a first surfactant and a second surfactant.

[0010] Further, in an optional embodiment of the present application, the mass ratio of the filler, the framework agent, the first lubricant, the second lubricant, the first surfactant and the second surfactant is: 85:5~10:3~5:0.5~4.5:0.1~0.5.

[0011] Further, in an optional embodiment of the present application, the mass ratio of the filler, the framework agent, the first lubricant, the second lubricant, the first surfactant and the second surfactant is: 85:5:5:4.5:0.5.

[0012] Further, in an optional embodiment of the present application, the filler is polyformaldehyde.

[0013] Further, in an optional embodiment of the present application, the framework agent is high-density polyethylene.

[0014] Further, in an optional embodiment of the present application, the first lubricant is N,N'-ethylene bis-stearamide; and the second lubricant is pentaerythritol stearate.

[0015] Further, in an optional embodiment of the present application, the first surfactant is stearic acid; and the second surfactant is paraffin wax.

[0016] According to another aspect of the present application, the present application provides a preparation method of a new MIM feed based on plastic-based binder, comprising the following steps: weighing metal powder and plastic-based binder; The plastic-based binder comprises a filler, a framework agent, a first lubricant, a second lubricant, a first surfactant and a second surfactant. The temperature and rotating speed of the internal mixer are adjusted, and the metal powder and the plastic-based binder are added into the internal mixer for mixing to obtain the MIM feedstock.

[0017] Further, in an optional embodiment of the present application, the rotating speed of the internal mixer is 10-15 r / min when the metal powder is added, the rotating speed of the internal mixer is 30-35 r / min when the plastic-based binder is added, and the temperature of the internal mixer is 100-180℃.

[0018] Overall, compared with the prior art, the above technical scheme conceived by the present application can achieve the following beneficial effects: 1. The MIM feedstock of the present application adopts a plastic-based binder, and by adjusting the feedstock formula, the green strength is high (not easy to deform), the dimensional stability is good, the relative density after sintering can reach 98.3%, and the demand for high-precision parts is met; at the same time, by optimizing the powder loading amount, the amount of binder is reduced, the debinding time and cost are reduced, and it is suitable for batch production.

[0019] 2. The MIM feedstock process of the present application has good adaptability, and the rheological properties of the feedstock are excellent (the shear thinning property is obvious, and the temperature sensitivity is low), which can match the injection temperature of 180-210℃, and reduce defects such as flash and underfilling; 3. The MIM feedstock of the present application has good compatibility, the binder has good compatibility with 316L stainless steel powder, there is no "powder-glue separation", the uniformity of the feedstock is high, which provides a stable foundation for subsequent debinding and sintering; the dimensional stability of the sintered parts is good, the relative density is high, and the demand for high-precision parts is met.

[0020] 4. In the MIM feedstock of the present application, POM polyoxymethylene is used as a filler, which is the main component to provide the flowability of the feedstock; HDPE high-density polyethylene is used as a framework agent to form a three-dimensional network to maintain the shape of the green body during the debinding process; EBS and PETS are N,N'-ethylene bis-stearamide and pentaerythritol stearate used as lubricants, which mainly play the roles of external lubrication and internal lubrication respectively, and together reduce the friction between particles and equipment, and improve the processing flowability; SA and PW stearic acid and straight-chain alkanes (C20-C40) are used as surfactants to effectively reduce the interfacial tension between the metal powder and the binder, and enhance the compatibility and dispersion uniformity of the two. By adjusting the feedstock formula, high green strength, high dimensional stability and excellent sintering densification are realized. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The figure is a green body morphology graph (the scale is 50 microns) under a scanning electron microscope (SEM) of an embodiment of the present application; Figure 2 Green body morphology under scanning electron microscope (SEM) (scale bar: 10 microns) of the embodiment of the present application. DETAILED DESCRIPTION

[0022] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in details below in combination with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0023] In the embodiment of the present application, metal injection molding (MIM) is a new type of powder metallurgy near-net forming technology derived from the plastic injection molding industry. Specifically, it is to mix metal powder and binder under certain conditions, then extrude and granulate into feed, and then inject the feed into the mold to form the required shape product. The process is roughly divided into four steps of granulation, injection, debinding and sintering.

[0024] The proportions used in the following examples are mass ratios unless otherwise specified.

[0025] The experimental methods used in the following examples are conventional methods unless otherwise specified.

[0026] The materials, reagents, etc. used in the following examples are commercially available unless otherwise specified.

[0027] In the embodiment of the present application, the used internal mixer is KY-3220A-1.5L type open-closed internal mixer (rotating speed 0-60r / min, heating power 13KW, effective volume 1.5L, heating temperature room temperature -280℃); the used injection machine is Norit NEX130 type (mold clamping force 1300kN, nozzle temperature range 150-250℃); the used debinding furnace is Star Special STZ-2400K oxalic acid catalytic debinding furnace (temperature range room temperature - 200℃, acid gas flow 0-10cm³ / min); and the used sintering furnace is HP-SF480S vacuum sintering furnace (vacuum degree ≤1×10⁻³Pa, temperature range room temperature - 1600℃).

[0028] In the embodiment of the present application, the composition of the binder in the MIM feedstock includes: POM polyoxymethylene as a filler, which is the main component to provide the flowability of the feedstock; HDPE high-density polyethylene as a skeleton agent, which forms a three-dimensional network to maintain the shape of the green body during the debinding process; EBS and PETS are N,N'-ethylene bis-stearamide and pentaerythritol stearate as lubricants, which mainly play the roles of external lubrication and internal lubrication respectively, and together reduce the friction between the particles and the equipment, and improve the processing flowability; SA and PW are stearic acid and linear alkanes (C20-C40) as surfactants, which effectively reduce the interfacial tension between the metal powder and the binder, and enhance the compatibility and dispersion uniformity of the two. This specific combination, especially the optimized mass ratio thereof, is the key to achieving high strength, high dimensional stability and excellent sintering densification of the green body. Among them, the role of the filler POM is to provide flowability and assist in shape retention; the role of the skeleton agent HDPE is to maintain the stability of the green body after debinding; the role of the lubricant EBS is external lubrication to reduce particle friction; the role of the lubricant PETS is internal lubrication to improve flowability; the role of the surfactant SA is to reduce the interfacial tension between the powder and the glue; the role of the surfactant PW is to assist dispersion and prevent agglomeration. The physical properties and solubility parameters of each binder component are shown in Table 1: Table 1 Physical properties and solubility parameters of binder components , When preparing the MIM feedstock, the compatibility of the binder needs to be considered. The metal powder and the binder with good compatibility will not cause "powder-glue separation", the feedstock has high uniformity, and the compatibility of the binder can be calculated as follows: the low molecular and high molecular components of the binder need to have certain compatibility. The compatibility can be measured by the closeness of the solubility parameter δ value. The smaller the difference between the two components, the less the heat absorption during dissolution, and the more favorable the dissolution process. The δ of the polymer can be estimated from the molar attraction constant of each group or atom in the structural unit F i : , In the formula, F i is the molar attraction constant, with the unit of (J / cm 3 ) 1 / 2 ·mol -1 ; ρ is the density of the polymer, with the unit of g·cm -3 ; M0 is the molecular weight of the structural unit.

[0029] In the embodiment of the present application, the calculation results of the compatibility of the binder components are as follows: According to the above method, the solubility parameters of each binder component selected in the present application are calculated as shown in the following table: Table 2 Solubility parameters of binder components , As can be seen from the table, the solubility parameters of each main component (polyformaldehyde POM, high-density polyethylene HDPE, N,N'-ethylene bis-stearamide EBS, pentaerythritol stearate PETS) are very close (the difference in δ value is less than 0.5), indicating that they have good thermodynamic compatibility in the molten state and can form a uniform and stable mixture, which is the basis for preparing high-performance feedstock. The δ values of the surfactant SA and the lubricant PW are similar, and there is a certain difference from other main components, but the small amount of addition is mainly used to improve the powder-glue interface properties or as an auxiliary lubricant, and will not destroy the overall compatibility of the binder system.

[0030] POM polyformaldehyde as a filler is the main component to provide the flowability of the feedstock; HDPE high-density polyethylene as a skeleton agent forms a three-dimensional network to maintain the shape of the green body during the debinding process; EBS and PETS are N,N'-ethylene bis-stearamide and pentaerythritol stearate as lubricants, which mainly play the roles of external lubrication and internal lubrication respectively, and together reduce the friction between particles and equipment to improve the processing fluidity; SA and PW stearic acid and straight-chain alkanes (C20-C40) as surfactants effectively reduce the interfacial tension between metal powder and binder, and enhance the compatibility and dispersion uniformity of the two. This specific combination, especially its optimized mass ratio, is the key to achieving high strength, high dimensional stability and excellent sintering densification of the green body.

[0031] Example 1 To prepare the MIM feedstock, the mass of 316L powder required for each mixing is first determined. The capacity of the internal mixer is currently in the appropriate range of 3-5 kg, and in an embodiment of the present application, the intermediate value is adopted, i.e. the mass of 316L powder is 4 kg, and the total mass of the feedstock is calculated by the following formula: , The mass of the binder is the total mass of the feedstock minus the mass of 316L powder; In Example 1 of the present application, the mass ratio of the filler POM, the skeleton agent HDPE, the lubricant EBS, the lubricant PETS, the surfactant SA, and the surfactant PW in the binder is 85:5:5:5:4.5:0.5, and according to the mass of the binder, the mass of the filler POM, the skeleton agent HDPE, the lubricant EBS, the lubricant PETS, the surfactant SA, and the surfactant PW in the binder is 293.5 g, 17.3 g, 17.3 g, 17.3 g, 15.5 g, and 1.7 g, respectively.

[0032] The method for preparing the MIM feedstock comprises the following steps: 1) Set the machine temperature of the internal mixer to 180℃, turn on the machine and heat it to about 100℃, add all the 316L powder, and adjust the speed to 10-15 r / min; 2) The machine is warmed up to 150℃, and all the HDPE is added; 3) The machine is warmed up to 180℃, all the POM is added, the rotating speed is adjusted to 30-35 r / min, and is kept for 10-15 min, 4) All the EBS is added, the rotating speed is kept unchanged, and is kept for 5-10 min; 5) All the PW is added, the rotating speed is kept unchanged, and is kept for 5-10 min; 6) All the SA is added, the rotating speed is kept unchanged, and is kept for 5-10 min; 7) All the PETS is added, the rotating speed is kept unchanged, and is kept for 30 min before discharging; 8) The rotating speed is first adjusted to 0, then cooling water is passed, the temperature is set to 160℃, and when the temperature is reduced to 170℃, the discharging can be started, and the MIM feedstock is obtained.

[0033] It should be noted that the machine used in the above steps in the embodiment of the application is a banbury mixer.

[0034] Embodiment 2 In order to prepare the MIM feedstock, the mass of 316L powder required for each mixing is first determined, and the capacity of the banbury mixer is currently suitable in the range of 3-5 kg, and in an embodiment of the application, the middle value is adopted, that is, the mass of 316L powder is 4 kg, and the total mass of the feedstock is calculated by the following formula: , The mass of the binder is the total mass of the feedstock minus the mass of the 316L powder; In the embodiment 2 of the application, the mass ratio of the filler POM, the framework agent HDPE, the lubricant EBS, the lubricant PETS, the surfactant SA and the surfactant PW in the binder is 85:5:3:2:4.5:0.5; According to the mass of the binder, the mass of the filler POM, the framework agent HDPE, the lubricant EBS, the lubricant PETS, the surfactant SA and the surfactant PW in the binder is 308.9 g, 18.2 g, 10.9 g, 7.3 g, 18.2 g and 1.8 g.

[0035] The preparation method of the MIM feedstock comprises the following steps: 1) The machine temperature of the banbury mixer is set to 180℃, the machine is started and warmed up to about 100℃, all the 316L powder is added, and the rotating speed is adjusted to 10-15 r / min; 2) The machine is warmed up to 150℃, and all the HDPE is added; 3) Machine temperature is raised to 180℃, all POM is added, and the rotating speed is adjusted to 30-35 r / min, and maintained for 10-15 min, 4) All EBS is added, and the rotating speed is maintained, for 5-10 min; 5) All PW is added, and the rotating speed is maintained, for 5-10 min; 6) All SA is added, and the rotating speed is maintained, for 5-10 min; 7) All PETS is added, and the rotating speed is maintained, for 30 min, and then the material is discharged; 8) The rotating speed is first adjusted to 0, then cooling water is passed, and the temperature is set to 160℃, and when the temperature is reduced to 170℃, the material can be discharged, and MIM feedstock is obtained.

[0036] It should be noted that the machine used in the above steps in the embodiments of the present application is a banbury mixer.

[0037] Embodiment 3 In order to prepare MIM feedstock, the mass of 316L powder required for each mixing is first determined, and the capacity of the banbury mixer is currently in the range of 3-5 kg, and in an embodiment of the present application, the intermediate value is adopted, that is, the mass of 316L powder is 4 kg, and the total mass of the feedstock is calculated by the following formula: , The mass of the binder is the total mass of the feedstock minus the mass of the 316L powder; In the embodiment 2 of the present application, the mass ratio of the filler POM, the framework agent HDPE, the lubricant EBS, the lubricant PETS, the surfactant SA and the surfactant PW in the binder is 85:10:3:1:0.5:0.5; According to the mass of the binder, the mass of the filler POM, the framework agent HDPE, the lubricant EBS, the lubricant PETS, the surfactant SA and the surfactant PW in the binder is 294.2 g, 34.6 g, 10.4 g, 3.5 g, 1.7 g and 1.7 g.

[0038] The preparation method of the MIM feedstock comprises the following steps: 1) The machine temperature of the banbury mixer is set to 180℃, the machine is started and the temperature is raised to about 100℃, all 316L powder is added, and the rotating speed is adjusted to 10-15 r / min; 2) The machine temperature is raised to 150℃, and all HDPE is added; 3) The machine temperature is raised to 180℃, all POM is added, and the rotating speed is adjusted to 30-35 r / min, and maintained for 10-15 min, 4) All EBS is added, and the rotating speed is maintained, for 5-10 min; 5) Add all PW, keep the rotation speed unchanged, and maintain for 5-10 min; 6) Add all SA, keep the rotation speed unchanged, and maintain for 5-10 min; 7) Add all PETS, keep the rotation speed unchanged, and maintain for 30 min before discharging; 8) First, adjust the rotation speed to 0, then pass cooling water, set the temperature to 160℃, and wait until the temperature decreases to 170℃, and then start discharging to obtain the MIM feedstock.

[0039] It should be noted that the machines used in the above steps in the embodiments of the present application are all internal mixers.

[0040] Comparative Example 1 To prepare the MIM feedstock, the mass of 316L powder required for each mixing is first determined. At present, the capacity of the internal mixer is suitable in the range of 3-5 kg, and in an embodiment of the present application, the intermediate value is adopted, that is, the mass of 316L powder is 4 kg, and the total mass of the feedstock is calculated by the following formula: , The mass of the binder is the total mass of the feedstock minus the mass of the 316L powder; In the embodiment 2 of the present application, the mass ratio of the filler POM, the framework agent HDPE, the lubricant EBS, the lubricant PETS, the surfactant SA and the surfactant PW in the binder is 80:5:5:5:0:5; According to the mass of the binder, the mass of the filler POM, the framework agent HDPE, the lubricant EBS, the lubricant PETS, the surfactant SA and the surfactant PW in the binder is 290.8 g, 18.2 g, 18.2 g, 18.2 g, 0 g and 18.2 g respectively.

[0041] The preparation method of the MIM feedstock comprises the following steps: 1) Set the machine temperature of the internal mixer to 180℃, start the machine and heat it to about 100℃, add all the 316L powder, and adjust the rotation speed to 10-15 r / min; 2) Heat the machine to 150℃, and add all the HDPE; 3) Heat the machine to 180℃, add all the POM, adjust the rotation speed to 30-35 r / min, and maintain for 10-15 min, 4) Add all the EBS, keep the rotation speed unchanged, and maintain for 5-10 min; 5) Add all the PW, keep the rotation speed unchanged, and maintain for 5-10 min; 6) Add all the SA, keep the rotation speed unchanged, and maintain for 5-10 min; 7) Add all PETS, keep the speed unchanged, and discharge after 30 min; 8) First, adjust the speed to 0, then pass the cooling water, set the temperature to 160℃, and wait until the temperature decreases to 170℃, then start discharging to obtain the MIM feedstock.

[0042] It should be noted that the machines used in the above steps in the embodiments of the present application are all internal mixers.

[0043] Comparative Example 2 To prepare the MIM feedstock, the mass of 316L powder required for each mixing is first determined. The capacity of the internal mixer is currently in the range of 3-5 kg, and in an embodiment of the present application, the intermediate value is adopted, i.e. the mass of 316L powder is 4 kg, and the total mass of the feedstock is calculated by the following formula: , The mass of the binder is the total mass of the feedstock minus the mass of the 316L powder; In the embodiment 2 of the present application, the mass ratio of the filler POM, the framework agent HDPE, the lubricant EBS, the lubricant PETS, the surfactant SA, and the surfactant PW in the binder is 80:5:5:5:0:5; According to the mass of the binder, the mass of the filler POM, the framework agent HDPE, the lubricant EBS, the lubricant PETS, the surfactant SA, and the surfactant PW in the binder is 290.8g, 18.2g, 18.2g, 18.2g, 0g, and 18.2g, respectively.

[0044] The preparation method of the MIM feedstock comprises the following steps: 1) Set the machine temperature of the internal mixer to 180℃, turn on the machine and heat it to about 100℃, add all the 316L powder, and adjust the speed to 10-15 r / min; 2) Heat the machine to 150℃, and add all the HDPE; 3) Heat the machine to 180℃, add all the POM, adjust the speed to 30-35 r / min, and keep for 10-15 min, 4) Add all the EBS, keep the speed unchanged, and keep for 5-10 min; 5) Add all the PW, keep the speed unchanged, and keep for 5-10 min; 6) Add all the SA, keep the speed unchanged, and keep for 5-10 min; 7) Add all the PETS, keep the speed unchanged, and discharge after 30 min; 8) First, adjust the speed to 0, then pass the cooling water, set the temperature to 160℃, and wait until the temperature decreases to 170℃, then start discharging to obtain the MIM feedstock.

[0045] It should be noted that the machines used in the above steps in the embodiments of the present application are all internal mixers.

[0046] Example 4: Green part morphology characterization In the embodiments of the present application, the samples prepared according to the feeding ratio in Example 1 were selected for green part morphology characterization under a scanning electron microscope, and the results are shown in Figs. Figure 1 and Figure 2 Figure 1 and Figure 2 are pictures of the same sample characterized by scanning electron microscopy at different microscales): Under the specific binder system and preparation process of the present application, the metal powder particles (bright spherical particles in the figure) are completely and uniformly wrapped by the binder (the gray base in the figure). The powder particles are densely filled, and no obvious binder enrichment area, pore or powder agglomeration area is observed.

[0047] This indicates that the binder components described in the present application have good compatibility and binding state between each other and between the binder and the metal powder, effectively preventing the "powder-glue separation" phenomenon, ensuring the high uniformity of the feeding, and laying a solid foundation for subsequent debinding and sintering to prepare high-performance products.

[0048] Example 5: Feeding performance test In the embodiments of the present application, the green strength, dimensional stability and relative density of the samples with different feeding ratios were tested according to GB / T 23561-2009 "Metal Powder Injection Molding Product Performance Test Method", and the specific method is as follows: Green strength test: three-point bending method was used, the sample size was 50mm×10mm×5mm, the span was 30mm, the loading rate was 2mm / min, 5 samples were tested for each group, and the average value was taken.

[0049] Dimensional stability test: a three-coordinate measuring instrument with a precision of 0.001mm was used to measure the key dimensions (length, width, height) of the green part and the sintered sample, and the volume shrinkage rate was calculated, the formula was: , Relative density: Archimedes drainage method was used to measure the mass of the sample in air and water, calculate the actual density, and then compare it with the theoretical density of 316L stainless steel (7.98g / cm³) to obtain the relative density, the formula was: , The results of Examples 1-3, Comparative Examples 1 and 2 are shown in Table 3: Table 3: Feeding performance test , ​From Table 3, it can be seen that the green strength of Example 1 is the highest (15.8 MPa), which is significantly higher than that of Comparative Example 1 (13.2 MPa) and Comparative Example 2 (12.5 MPa), indicating that when the binder ratio is 85:5:5:4.5:0.5, the binding force between the binder and the 316L powder is stronger, and the green body deformation resistance is better; the volume shrinkage rate of Example 1 is the lowest (36.4%), which is lower than that of the comparative examples and other examples, indicating that the size stability of the feed under this ratio is better, which is conducive to controlling the size accuracy of the final product; the relative density of Example 1 reaches 98.3%, which is higher than that of other groups, indicating that the feed under this ratio can better densify during sintering, reducing pore defects; without adding surfactants SA and PW, the green strength, volume shrinkage rate and size stability are worse than when both surfactants are added.

[0050] In the method of the present application, POM polyoxymethylene as a filler is the main component to provide the flowability of the feed; HDPE high-density polyethylene as a skeleton agent forms a three-dimensional network to maintain the shape of the green body during debinding; EBS and PETS are N,N'-ethylene bis-stearamide and pentaerythritol stearate as lubricants, which mainly play the roles of external and internal lubrication respectively, and together reduce the friction between particles and equipment, and improve the processing flowability; SA and PW stearic acid and linear alkanes (C20-C40) as surfactants effectively reduce the interfacial tension between metal powder and binder, and enhance the compatibility and dispersion uniformity of the two. This specific combination, especially its optimized mass ratio, is the key to achieving high green strength, high dimensional stability and excellent sintering densification.

[0051] In summary, the MIM feed of the present application uses a plastic machine binder, and by adjusting the feed formula, the green strength is high (not easy to deform), the dimensional stability is good, and the relative density after sintering can reach 98.3%, meeting the demand for high-precision parts; at the same time, by optimizing the powder loading amount, the amount of binder is reduced, the debinding time and cost are reduced, and it is suitable for mass production; the MIM feed process of the present application has good adaptability, excellent rheological properties (obvious shear thinning characteristics, low temperature sensitivity), can match the injection temperature of 180-210°C, and reduce defects such as flash and underfill; the feed of the present application has good compatibility, the binder and 316L stainless steel powder have good compatibility, there is no "powder and glue separation", the feed uniformity is high, providing a stable basis for subsequent debinding and sintering; the sintered part has good dimensional stability and high relative density, meeting the demand for high-precision parts.

[0052] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting; thus the use of any

[0053] Each of the embodiments in the present specification is described in a related manner, and the same or similar parts among the embodiments can be referred to each other. Each of the embodiments focuses on the difference from other embodiments.

[0054] It should be noted that the above-mentioned embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the implementation modes of the present application. For those skilled in the art, various obvious changes, re-adjustments and substitutions can be made without departing from the protection scope of the present application. It is not necessary and impossible to enumerate all the implementation modes.

[0055] Those skilled in the art can easily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A novel MIM feedstock based on a plastic-based binder, characterized in that, The components include the following parts by mass: 90-120 parts metal powder; 8-10 parts plastic binder; The plastic-based binder includes fillers, skeletonizing agents, lubricants, and surfactants.

2. The novel MIM feeder based on a plastic-based binder according to claim 1, characterized in that, The plastic-based binder includes a filler, a skeletonizing agent, a first lubricant, a second lubricant, a first surfactant, and a second surfactant.

3. A novel MIM feeder based on a plastic-based binder according to claim 2, characterized in that, The mass ratio of the filler, skeleton agent, first lubricant, second lubricant, first surfactant, and second surfactant is 85:5~10:3~5:0.5~4.5:0.1~0.

5.

4. A novel MIM feeder based on a plastic-based binder according to claim 3, characterized in that, The mass ratio of the filler, skeleton agent, first lubricant, second lubricant, first surfactant, and second surfactant is 85:5:5:4.5:0.

5.

5. A novel MIM feed based on a plastic-based binder according to any one of claims 1-4, characterized in that, The filler is polyoxymethylene.

6. A novel MIM feed based on a plastic-based binder according to any one of claims 1-4, characterized in that, The skeleton agent is high-density polyethylene.

7. A novel MIM feed based on a plastic-based binder according to any one of claims 2-4, characterized in that, The first lubricant is N,N'-ethylene bis-stearamide; the second lubricant is pentaerythritol stearate.

8. A novel MIM feed based on a plastic-based binder according to any one of claims 2-4, characterized in that, The first surfactant is stearic acid; the second surfactant is paraffin.

9. A method for preparing a novel MIM feedstock based on a plastic-based binder according to any one of claims 1-8, characterized in that, Includes the following steps: Weigh out the metal powder and plastic binder; The plastic-based binder includes: a filler, a skeletonizing agent, a first lubricant, a second lubricant, a first surfactant, and a second surfactant; Adjust the temperature and speed of the internal mixer, and add the metal powder and plastic binder into the internal mixer to mix and obtain MIM feed.

10. A method for preparing a novel MIM feedstock based on a plastic-based binder according to claim 9, characterized in that: When metal powder is added, the speed of the internal mixer is 10-15 r / min; when plastic binder is added, the speed of the internal mixer is 30-35 r / min; and the temperature of the internal mixer is 100-180℃.

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