MIM manufacturing method for special-shaped cutting tools

Abstract

The present invention discloses a MIM manufacturing method for special-shaped cutting tools, which relates to MIM injection molding technology. A MIM manufacturing method for special-shaped cutting tools, including multiple steps such as mixing and granulation, injection molding, calcination and degreasing, sintering and shaping, and sharpening. Specifically, the metal powder and the binder are first mixed and granulated in a certain proportion, and then the binder is removed and the metal powder is diffused and rearranged through the steps of calcination and degreasing, sintering and shaping to obtain an unsharpened semi-finished tool, and finally the semi-finished tool is sharpened to complete the manufacturing. The above method is used to produce special-shaped cutting tools, which is beneficial to improving the dimensional accuracy of the special-shaped cutting tools and reducing shape errors; and the blades and stirring blades of the tool are uniform in the longitudinal or transverse structure, and the internal stress generated is small, which is beneficial to improving the comprehensive strength of the special-shaped cutting tools; the manufacturing method is simple, the production efficiency is high, and it is suitable for large-scale and large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of preparing special-shaped cutting tools, and in particular to a MIM manufacturing method of special-shaped cutting tools. Background Art

[0002] There are two main conventional preparation methods for special-shaped cutting tools. The first is to first produce the parts of the special-shaped cutting tools by casting, and then weld the parts together. The special-shaped cutting tools produced by this method have disadvantages such as poor strength, high cost, and low production efficiency. Improper welding during use can easily cause the tools to break. The second method is to produce through precision casting. Compared with the first preparation method of welding, although this process has higher strength, it has higher production requirements. Improper operation will also cause certain precision problems in the product. Since most special-shaped cutting tools are used in high-speed rotating cutting devices, the low precision can easily cause the special-shaped cutting tools to shake violently when rotating at high speeds.

[0003] A special-shaped cutting tool 1, referring to Figure 1 , similar to the fan blades, including a hub 11 and blades 12 and stirring blades 13 arranged on the circumference of the hub 11. A mounting hole 111 is provided on the back side of the hub 11, and a number of clips 112 are spirally arranged in the mounting hole 111 of the hub 11. The clips 112 are used to interlock with other products to achieve the installation of the special-shaped cutting tool 1. The blades 12 and stirring blades 13 both have a certain curvature and inclination, and the blades 12 and stirring blades 13 are spaced apart along the circumference of the hub 11, so that the entire special-shaped cutting tool 1 forms a "cross" shape. A blade 121 is provided on one side of the blade 12, and the cutting edge of the blade 121 is located at the bottom end of the entire special-shaped cutting tool 1, so that when the special-shaped cutting tool 1 rotates at high speed, the blade 121 can first contact the object to be cut and achieve cutting.

[0004] Most factories use precision casting to manufacture this type of fan-shaped special-shaped cutting tool 1. However, the products currently produced by precision casting have the following problems: First, the dimensional stability of the clip 112 in the mounting hole 111 is poor. Not only will there be a large gap when it is fastened to other products, causing the tool to shake when it rotates, but it may even be impossible to install and fasten it with other products. Second, due to the large shape error of precision casting, the blade 12 and the stirring blade 13 may be severely deformed, which is inconsistent with the designed curvature and inclination, thus affecting not only the appearance of the entire product, but also the subsequent sharpening step or cutting function of the blade 12, making it impossible to use the special-shaped cutting tool 1 normally and the yield rate low. Summary of the Invention

[0005] In order to improve the dimensional accuracy of special-shaped cutting tools, reduce the shape error of special-shaped cutting tools, and improve the yield of special-shaped cutting tools, this application provides a MIM manufacturing method for a special-shaped cutting tool mentioned in the background technology.

[0006] The MIM manufacturing method of a special-shaped cutting tool provided in this application adopts the following technical solution:

[0007] A MIM manufacturing method for a special-shaped cutting tool includes the following preparation methods:

[0008] S1. Mixing and granulating: The metal powder to be formed and the binder are fully mixed to form a mixed powder, wherein the amount of metal powder added accounts for 88%-90% of the weight of the mixed powder, and the amount of binder added accounts for 10%-12% of the mixed powder. The mixed powder is then granulated to obtain feed;

[0009] S2, injection molding: heating and melting the feed obtained in step S1 and injecting it into a mold under high temperature and high pressure, taking it out and cooling it to obtain a green body;

[0010] S3, calcination and degreasing: placing the green body obtained in step S2 on a sintering support plate, then sending the sintering support plate together with the green body into a degreasing furnace for calcination and degreasing, taking it out and cooling it to obtain a brown body;

[0011] S4, sintering and shaping: the brown blank obtained in step S3 together with the sintering support plate is transferred into a vacuum sintering furnace for vacuum sintering and shaping, and then taken out and cooled to obtain an unsharpened semi-finished tool;

[0012] S5, sharpening: The semi-finished tool obtained in step S4 is mounted in a machining fixture, and the blade is sharpened by machining and grinding to obtain a special-shaped cutting tool.

[0013] By adopting the above technical solution, the resulting special-shaped cutting tools have low average dimensional deviation, which helps improve the dimensional accuracy of the special-shaped cutting tools and reduce their shape errors. Furthermore, the average dimensional deviations of the blades and stirring blades in the length and width directions of the produced special-shaped cutting tools are similar, indicating that the shrinkage rates of the blades and stirring blades in the longitudinal and transverse directions are similar, resulting in a uniform structure of the blades and stirring blades in the longitudinal and transverse directions, reducing the internal stress generated, and improving the overall strength of the special-shaped cutting tools. The production method is simple, highly efficient, and suitable for large-scale production.

[0014] Optionally, the binder includes the following raw materials in parts by weight:

[0015] Polyoxymethylene: 78-84 parts;

[0016] High-density polyethylene: 3.5-4.5 parts;

[0017] Polystyrene: 4.4-6 parts;

[0018] Ethylene vinyl acetate: 1.8-2.5 parts;

[0019] Polyacrylamide: 0.8-2 parts;

[0020] Stearic acid: 0.5-1.5 parts;

[0021] Wax: 4-5 parts;

[0022] The wax material comprises a mixture of one or more of paraffin wax, palm wax and beeswax.

[0023] By adopting the above technical solution, using polyoxymethylene as the main binder, the feed material can be provided with stable viscosity and thermal stability during the injection molding process. Combined with the bonding and lubricating effects of other auxiliary agents such as high-density polyethylene, polystyrene, ethylene-vinyl acetate, polyacrylamide, stearic acid, and wax, the plasticity of the mixed powder can be maintained during the injection molding process, which is conducive to forming a uniform and strong green body and ensuring the dimensional accuracy of the green body. Secondly, all components of the binder can be fully removed by calcination in an acidic environment, which helps to reduce the impact of binder residues on special-shaped cutting tools, and ultimately obtain highly dense, surface-sounding, and dimensionally accurate special-shaped cutting tools.

[0024] Optionally, the wax material is a mixture of paraffin wax, palm wax and beeswax, and the mixing weight ratio of the paraffin wax, palm wax and beeswax is 1:(1.2-1.4):(0.1-0.3).

[0025] By adopting the above technical solution, the average size deviation of the produced special-shaped cutting tool is low, and it is conducive to uniform longitudinal and transverse contraction of the blade and the stirring blade, thereby improving the comprehensive strength of the special-shaped cutting tool.

[0026] Optionally, in the calcination and degreasing in step S3, an inert gas is first circulated into the degreasing furnace. After the degreasing furnace is filled with inert gas, the sintering support plate and the green body are placed in the degreasing furnace, and then the temperature is slowly raised to 95-135°C at a heating rate of 2-3°C / min. At the same time, an acidic substance is introduced to maintain the temperature and acidic environment to continuously calcine the green body for 14-16 hours.

[0027] By adopting the above technical solution, the circulating inert gas can fully remove the formaldehyde and other waste gases generated by the binder during the calcination process, which is beneficial to stabilize the calcination and degreasing environment in the degreasing furnace, reduce the occurrence of side reactions, and enable the green body to fully and evenly remove the binder.

[0028] Optionally, the inert gas is nitrogen, and is introduced into the degreasing furnace at a flow rate of 70-95 L / min.

[0029] By adopting the above technical solution, the cost of nitrogen is low, which is not only beneficial to reducing the preparation cost, but also nitrogen can promote the nitriding effect, which is beneficial to grain refinement and improving the surface hardness and wear resistance of special-shaped cutting tools.

[0030] Optionally, the acidic substance is oxalic acid, and is introduced into the degreasing furnace at a flow rate of 3-5 g / min.

[0031] By adopting the above technical solution, oxalic acid as an acidic catalyst is not only conducive to promoting the decomposition and volatilization of the binder, accelerating the degreasing speed of the binder, and shortening the entire degreasing cycle, but also compared with other acidic substances, the degreasing catalytic conditions of oxalic acid are relatively mild. It can create a suitable acidic environment at 80-180°C, which can reduce the thermal stress caused by temperature changes in the green body during the calcination and degreasing process, and is conducive to reducing the risk of cracks or deformation of special-shaped cutting tools after forming.

[0032] Optionally, the sintering support plate includes a square bottom plate and a plurality of support steps, wherein the support steps are evenly distributed at the four corners of the bottom plate and respectively support the blades and stirring blades of the green body.

[0033] By adopting the above technical solution, the blades and stirring parts around the green wheel hub are supported by supporting steps respectively, which not only helps to improve the stability when supporting the green wheel hub, but also can support the middle wheel hub, reduce the impact on the wheel hub during support, and ensure the dimensional accuracy of the wheel hub.

[0034] Optionally, the upper surface of the supporting step is provided with a curved surface, and the supporting step is in contact with the blade and the stirring blade through the curved surface.

[0035] By adopting the above technical solution, the upper surface of the support step is rationally designed so that the blade and the stirring blade can maintain their own curvature and inclination to fit with the support step, and the contact area between the support step and the blade and the stirring blade is increased, thereby reducing the pressure per unit area of ​​the support step on the blade and the stirring blade at the support, which is beneficial to reducing the possibility of the support step affecting the shape or size of the blade and the stirring blade, and ensuring the dimensional accuracy of the special-shaped cutting tool.

[0036] Optionally, during the sintering and shaping in step S4, the vacuum sintering furnace maintains a vacuum degree less than or equal to 15 KPa and is heated to 1280-1350° C. for sintering and shaping for 24-30 hours.

[0037] By adopting this technical solution, a vacuum environment helps prevent oxidation reactions between oxygen and metal powder, thereby maintaining the purity and performance of the metal powder. Furthermore, sintering in a vacuum effectively reduces the obstruction of the brown blank interior by gases or volatiles generated by the combustion of residual binder, facilitating the diffusion and rearrangement of metal powder particles, resulting in higher density and better overall strength for special-shaped cutting tools.

[0038] Optionally, the machining fixture includes a machining template, which is provided with a limiting groove matching the semi-finished tool. The machining template is also provided with a pneumatic chuck, which is located in the limiting groove and corresponds to the hub of the semi-finished tool. The pneumatic chuck is used to extend into the mounting hole of the hub and expand and clamp the hub.

[0039] By adopting the above technical solution, the pneumatic chuck is used to penetrate into the mounting hole of the wheel hub for expansion and support, so that the wheel hub can be evenly stressed. The limit groove opened in the machining fixture is not only conducive to fully fixing the semi-finished tool, making the semi-finished tool less likely to deviate during the cutting process, reducing vibration, and ensuring the appearance of the special-shaped cutting tool, but also helps to prevent the semi-finished tool from being deformed due to excessive force for supporting or fixing the semi-finished tool, thereby causing the curvature or inclination of the blade and stirring blade to be incorrect, affecting the normal use of the special-shaped cutting tool.

[0040] In summary, the technical solution of this application has at least one of the following beneficial effects:

[0041] 1. The use of MIM manufacturing methods to produce special-shaped cutting tools is beneficial to improving the dimensional accuracy of special-shaped cutting tools and reducing the shape error of special-shaped cutting tools. It also makes the blades and stirring blades uniform in the vertical or horizontal structure, which generates less internal stress and helps to improve the comprehensive strength of special-shaped cutting tools. The manufacturing method is simple and the production efficiency is high, which is suitable for large-scale production.

[0042] 2. By rationally designing the sintering support plate and increasing the contact area between the sintering support plate and the green body, it is beneficial to reduce the pressure per unit area of ​​the sintering support plate on the green body surface and reduce the possibility of the sintering support plate step affecting the shape or size of the green body, thereby preventing the problem of sintering deformation.

[0043] 3. By rationally designing the machining fixture and using the limit groove and pneumatic chuck to cooperate with each other, the semi-finished tool can be fully fixed during the machining and sharpening process. This can not only reduce the vibration of the semi-finished tool during the machining and sharpening process, prevent the semi-finished tool from offset, and ensure the appearance of the special-shaped cutting tool, but also prevent the plastic deformation caused by excessive force to fix the semi-finished tool, thereby causing the curvature or inclination of the blade and stirring blade to be incorrect, affecting the normal use of the special-shaped cutting tool. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a structural schematic diagram of a special-shaped cutting tool in the background technology of this application.

[0045] Figure 2 This is a structural schematic diagram of a special-shaped cutting tool green body placed on a sintering support plate in the MIM manufacturing method of a special-shaped cutting tool in Example 1 of the present application.

[0046] Figure 3 This is a structural schematic diagram of a semi-finished tool installed in a machining fixture in the MIM manufacturing method of a special-shaped cutting tool in Example 1 of the present application.

[0047] Figure 4 This is a structural schematic diagram of a machining fixture used in the MIM manufacturing method of a special-shaped cutting tool in Example 1 of the present application.

[0048] Description of reference numerals:

[0049] 1. Special-shaped cutting tool; 11. Wheel hub; 111. Mounting hole; 112. Fastener; 12. Blade; 121. Blade; 13. Stirring blade; 2. Sintering support plate; 21. Bottom plate; 22. Support step; 221. Arc surface; 3. Machining fixture; 31. Machining template; 32. Limiting groove; 33. Pneumatic chuck. DETAILED DESCRIPTION

[0050] The stainless steel powder used is 17-4PH stainless steel powder with a particle size of 50 μm.

[0051] The following is combined with Figure 1-4 , preparation examples, embodiments and comparative examples are provided to further illustrate this application in detail.

[0052] Preparation Example

[0053] [Preparation Example 1]

[0054] A binder comprising the following raw materials:

[0055] 8.4kg polyoxymethylene, 0.35kg high-density polyethylene, 0.44kg polystyrene, 0.18kg ethylene vinyl acetate, 0.08kg polyacrylamide, 0.15kg stearic acid, and 0.4kg paraffin.

[0056] [Preparation Example 2]

[0057] A binder comprising the following raw materials:

[0058] 7.8kg polyoxymethylene, 0.48kg high-density polyethylene, 0.64kg polystyrene, 0.3kg ethylene vinyl acetate, 0.2kg polyacrylamide, 0.08kg stearic acid, and 0.5kg wax.

[0059] In this preparation example, the wax material is a mixture of palm wax and beeswax, and the specific weight ratio of palm wax to beeswax is 1.2:0.1, that is, the added amount of palm wax is 0.462 kg and the added amount of beeswax is 0.038 kg.

[0060] [Preparation Example 3]

[0061] A binder, which differs from [Preparation Example 1] in that different wax materials are used.

[0062] In this preparation example, paraffin wax is replaced by a mixture of paraffin wax and palm wax in equal amounts, and the specific weight ratio of the paraffin wax to palm wax is 1:1.5, that is, the added amount of paraffin wax is 0.16 kg and the added amount of palm wax is 0.24 kg.

[0063] [Preparation Example 4]

[0064] A binder, which differs from [Preparation Example 1] in that different wax materials are used.

[0065] In this preparation example, paraffin is replaced by a mixture of paraffin wax, palm wax and beeswax in equal amounts. The specific weight ratio of the mixture of paraffin wax, palm wax and beeswax is 1:1.4:0.1, that is, the amount of paraffin added is 0.16 kg, the amount of palm wax added is 0.224 kg, and the amount of beeswax added is 0.016 kg.

[0066] Preparation Example 5

[0067] A binder, which differs from [Preparation Example 1] in that different wax materials are used.

[0068] In this preparation example, paraffin is replaced by a mixture of paraffin wax, palm wax and beeswax in equal amounts. The specific weight ratio of the mixture of paraffin wax, palm wax and beeswax is 1:1.2:0.3, that is, the amount of paraffin added is 0.16 kg, the amount of palm wax added is 0.192 kg, and the amount of beeswax added is 0.384 kg.

[0069] Example

[0070] [Example 1]

[0071] A MIM manufacturing method for a special-shaped cutting tool comprises the following steps:

[0072] S1. Mixing and granulating: 45 kg of metal powder and 5 kg of binder are fully mixed to form a mixed powder, and then the mixed powder is granulated to obtain feed;

[0073] The metal powder is stainless steel powder, and the binder is a binder prepared in [Preparation Example 1].

[0074] S2, injection molding: adding the feed obtained in step S1 into a powder injection molding machine, and injection molding, taking it out and cooling it to obtain a green body of the special-shaped cutting tool 1;

[0075] The injection temperature of the barrel is set to 205℃ in zone 1, 195℃ in zone 2, 190℃ in zone 3 and 4, and 195℃ in zone 5. The injection pressure is maintained at 95MPa and the injection speed is 25cm 3 / s.

[0076] S3, calcination and degreasing: Place the green body obtained in step S2 on the sintering support plate 2, then send the sintering support plate 2 and the green body into the degreasing furnace for calcination and degreasing, take out and cool to obtain a brown body;

[0077] Among them, nitrogen is first circulated into the degreasing furnace at a flow rate of 95L / min. After the degreasing furnace is filled with nitrogen, the sintering support plate 2 and the green body are placed in the degreasing furnace, and then slowly heated to 135°C at a heating rate of 3°C / min. At the same time, oxalic acid is introduced at a flow rate of 3g / min, and then the green body is continuously calcined for 14h while maintaining 135°C and an acidic atmosphere.

[0078] Among them, reference Figure 2 The sintering support plate 2 includes a square base plate 21 and a plurality of support steps 22. The support steps 22 are evenly distributed at the four corners of the base plate 21 and respectively support the blade 12 and stirring blade 13 of the green body. Specifically, in this embodiment, the upper surface of the support steps 22 is provided with a curved surface 221. The curved surface 221 corresponds to the curvature and inclination of the blade 12 and stirring blade 13. The support steps 22 achieve support by the curved surface 221 and the blade 12 and stirring blade 13 being in contact with each other.

[0079] S4, sintering and shaping: the brown blank obtained in step S3 together with the sintering support plate 2 is transferred into a vacuum sintering furnace for vacuum sintering and shaping, and then taken out and cooled to obtain an unsharpened semi-finished tool;

[0080] The vacuum sintering furnace maintains a vacuum degree of 15KPa and is heated to 1350°C for sintering and shaping for 24 hours.

[0081] S5, sharpening: placing the semi-finished tool obtained in step S4 in a machining fixture 3, and sharpening the blade 12 by machining and grinding, to finally obtain the special-shaped cutting tool 1.

[0082] Among them, reference Figure 3 and Figure 4The machining fixture 3 includes a machining template 31. The upper surface of the machining template 31 is provided with a retaining groove 32 that matches the special-shaped cutting tool 1. The machining template 31 is also provided with a pneumatic chuck 33. The pneumatic chuck 33 is located in the retaining groove 32 and corresponds to the mounting hole 111 of the hub 11 of the semi-finished tool. When installing the semi-finished tool, the pneumatic chuck 33 extends into the mounting hole 111 of the hub 11 of the semi-finished tool and expands and clamps the hub 11 there. Furthermore, the upper surface of the machining template 31 is lower than the cutting edge 121 of the semi-finished tool, facilitating sharpening of the cutting edge 121.

[0083] [Example 2]

[0084] A MIM manufacturing method for a special-shaped cutting tool 1 comprises the following steps:

[0085] S1. Mixing and granulating: 43 kg of metal powder and 7 kg of binder are fully mixed to form a mixed powder, and then the mixed powder is granulated to obtain feed;

[0086] The metal powder is stainless steel powder, and the binder is a binder prepared in [Preparation Example 2].

[0087] S2, injection molding: adding the feed obtained in step S1 into a powder injection molding machine, and injection molding, taking it out and cooling it to obtain a green body of the special-shaped cutting tool 1;

[0088] The injection temperature of the barrel is set to 205℃ in zone 1, 195℃ in zone 2, 190℃ in zone 3 and 4, and 195℃ in zone 5. The injection pressure is maintained at 95MPa and the injection speed is 25cm 3 / s.

[0089] S3, calcination and degreasing: Place the green body obtained in step S2 on the sintering support plate 2, then send the sintering support plate 2 and the green body into the degreasing furnace for calcination and degreasing, take out and cool to obtain a brown body;

[0090] Among them, nitrogen is first circulated into the degreasing furnace at a flow rate of 70L / min. After the degreasing furnace is filled with nitrogen, the sintering support plate 2 and the green body are placed in the degreasing furnace, and then slowly heated to 95°C at a heating rate of 2°C / min. At the same time, oxalic acid is introduced at a flow rate of 5g / min, and then the green body is calcined for 16 hours while maintaining 95°C and an acidic atmosphere.

[0091] Among them, the sintering support plate 2 is the same as the sintering support plate 2 used in [Example 1], and the placement method is the same as [Example 1].

[0092] S4, sintering and shaping: the brown blank obtained in step S3 together with the sintering support plate 2 is transferred into a vacuum sintering furnace for vacuum sintering and shaping, and then taken out and cooled to obtain an unsharpened semi-finished tool;

[0093] The vacuum sintering furnace maintains a vacuum degree of 15KPa and is heated to 1280°C for sintering and shaping for 30 hours.

[0094] S5, sharpening: placing the semi-finished tool obtained in step S4 in a machining fixture 3, and sharpening the blade 12 by machining and grinding, to finally obtain the special-shaped cutting tool 1.

[0095] Among them, the machining fixture 3 is the same as the machining fixture 3 used in [Example 1], and the placement method is the same as [Example 1].

[0096] [Example 3]

[0097] A MIM manufacturing method for a special-shaped cutting tool, which differs from [Example 1] in that a different adhesive is used.

[0098] In this embodiment, the adhesive is an adhesive prepared in [Preparation Example 3].

[0099] [Example 4]

[0100] A MIM manufacturing method for a special-shaped cutting tool, which differs from [Example 1] in that a different adhesive is used.

[0101] In this embodiment, the adhesive is an adhesive prepared in [Preparation Example 4].

[0102] [Example 5]

[0103] A MIM manufacturing method for a special-shaped cutting tool, which differs from [Example 1] in that a different adhesive is used.

[0104] In this embodiment, the adhesive is an adhesive prepared in [Preparation Example 5].

[0105] Comparative Example

[0106] [Comparative Example 1]

[0107] The invention discloses a method for manufacturing a special-shaped cutting tool, which adopts a conventional precision casting process for casting.

[0108] [Comparative Example 2]

[0109] A method for manufacturing a special-shaped cutting tool, which differs from [Example 1] in that the ratio of metal powder and binder is different.

[0110] In this comparative example, the metal powder accounts for 70% of the mixed powder, and the binder accounts for 30% of the mixed powder, that is, the added amount of metal powder is 35 kg, and the added amount of binder is 15 kg.

[0111] [Comparative Example 3]

[0112] A method for manufacturing a special-shaped cutting tool, which differs from [Example 1] in step S3.

[0113] In this comparative example, no acidic substance was introduced into the degreasing furnace during the calcination and degreasing.

[0114] Performance test data

[0115] Preparation of samples to be tested: According to the manufacturing methods disclosed in each embodiment and comparative example and in accordance with the same standard design drawings, corresponding special-shaped cutting tools are prepared as samples to be tested, wherein no less than 10 are produced according to the manufacturing methods of each embodiment and comparative example.

[0116] 1. Surface Condition: Observe the surface of the special-shaped cutting tools produced in each embodiment and comparative example, and record the surface condition.

[0117] 2. Dimensional Accuracy Testing: Use a measuring tool to measure the dimensions of the specific parts of any ten special-shaped cutting tools produced in each embodiment and comparative example. Then, calculate the deviations between the specific dimensions of the ten special-shaped cutting tools and the standard dimensions in the design drawings. Finally, calculate the average deviation of the specific dimensions of the special-shaped cutting tools produced in each embodiment and comparative example. Wherein, deviation = |measured dimension - standard dimension|, average deviation = (deviation 1 + ... + deviation 10) / 10. The specific dimensions to be measured are the blade length, blade width, stirring blade length, stirring blade width, and the inner diameter of the roller mounting hole.

[0118] Table 1 Special-shaped cutting tool performance test data

[0119]

[0120] Combining Example 1 and Comparative Example 1 and the data in Table 1, it can be seen that the special-shaped cutting tool 1 produced by the MIM injection molding method has a significantly smaller average dimensional deviation of a specific part of the special-shaped cutting tool 1 than that produced by the precision casting method, which means that the dimensional accuracy of the product is higher, and the average dimensional deviations of the length and width of the blade 12 and the stirring blade 13 are relatively close, which means that when the special-shaped cutting tool 1 is produced, the longitudinal and lateral shrinkage rates of the blade 12 and the stirring blade 13 are close, so that the longitudinal or lateral structure of the blade 12 and the stirring blade 13 is uniform, and the internal stress generated is small, which is beneficial to improving the comprehensive strength of the special-shaped cutting tool 1.

[0121] Combining Examples 1-2 and Comparative Example 2 and the data in Table 1, it can be seen that when the metal powder accounts for 86%-90% of the mixed powder and the binder accounts for 10%-14% of the mixed powder, the special-shaped cutting tool 1 produced by the MIM injection molding method not only has better appearance performance, but also has a lower average dimensional deviation of specific parts of the tool and higher dimensional accuracy, which is conducive to ensuring that the tool has higher comprehensive strength. When the proportion of the binder in the mixed powder reaches 30%, the surface of the special-shaped cutting tool 1 produced has a large number of pores, and the average deviation value of each specific part of the tool is relatively large. This may be because when the binder accounts for 30% of the mixed powder, the binder has been added in excess, and the binder needs to be removed in the calcination and degreasing in step S3. The higher the binder content, the greater the shrinkage of the material after calcination and degreasing, which will directly affect the dimensional accuracy of the product. In addition, after the excess binder is removed, a large number of voids will be left in the product structure. If the metal powder fails to shrink and fill these voids in time, this will easily lead to pores on the surface of the special-shaped cutting tool 1 after final sintering and shaping.

[0122] Combining Example 1 and Comparative Example 3 with the data in Table 1, it can be seen that calcining and degreasing the green body in an acidic environment ultimately produces a dense and smooth surface of the special-shaped cutting tool 1, with low average dimensional deviation in specific areas and no obvious black spot defects on the surface. This may be because in an acidic environment, the acid can act as a catalyst in the decomposition of the binder, thereby promoting the decomposition and volatilization of the binder, which is conducive to the complete sintering and removal of the binder within the green body, preventing the residual binder from affecting the diffusion and rearrangement of the metal powder particles during the sintering process, ensuring the sintering and shaping effect of the special-shaped cutting tool 1, and facilitating the improvement of dimensional accuracy and overall strength.

[0123] Combining Examples 1 and 3-5 with the data in Table 1, it can be seen that when the wax material in the binder is paraffin wax, palm wax, and beeswax mixed in a weight ratio of 1: (1.2-1.4): (0.1-0.3), the average dimensional deviation of the produced special-shaped cutting tool 1 at a specific location is low, and the average dimensional deviation of the blade 12 and the stirring blade 13 in the longitudinal or transverse direction is close, which means that the longitudinal and transverse shrinkage rates of the blade 12 and the stirring blade 13 are close, and the overall strength performance is better. This may be because palm wax has a high melting point and good thermal stability. When palm wax and paraffin wax are mixed, palm wax can provide certain high-temperature performance for the binder, which is beneficial for maintaining the shape and size of the green body at high temperatures. In addition, palm wax is removed slowly during calcination and degreasing, which may be beneficial for more uniform degreasing of the green body and reducing the shrinkage rate of the green body during sintering. Secondly, beeswax has good plasticity and adhesion, which can improve the rheological properties and forming properties of the feed. Moreover, beeswax can gradually soften and then be completely removed during the calcination and degreasing process, thereby reducing the stress and deformation of the green body during the degreasing process, which is conducive to ensuring the shape and dimensional accuracy of the green body.

[0124] This specific implementation manner is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the specific implementation manner as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A MIM manufacturing method for a special-shaped cutting tool, characterized in that: The following steps are involved: S1. Mixing and granulating: The metal powder to be formed and the binder are fully mixed to form a mixed powder, wherein the amount of metal powder added accounts for 86%-90% of the weight of the mixed powder, and the amount of binder added accounts for 10%-14% of the mixed powder. The mixed powder is then granulated to obtain feed; S2, injection molding: heating and melting the feed obtained in step S1 and injecting it into a mold, taking it out and cooling it to obtain a green body; S3, calcination and degreasing: placing the green body obtained in step S2 on a sintering support plate (2), and then sending the sintering support plate (2) together with the green body into a degreasing furnace for calcination and degreasing, taking it out and cooling it to obtain a brown body; wherein, the degreasing furnace needs to be circulated with inert gas first, and after the degreasing furnace is filled with inert gas, the sintering support plate (2) and the green body are placed in the degreasing furnace, and then slowly heated to 95-135°C at a heating rate of 2-3°C / min, and acidic substances are introduced at the same time, and the temperature and acidic environment are maintained to continuously calcine the green body for 14-16h; S4, sintering and shaping: the brown blank obtained in step S3 together with the sintering support plate (2) are transferred into a vacuum sintering furnace for vacuum sintering and shaping, and then taken out and cooled to obtain an unsharpened semi-finished tool; S5, sharpening: installing the semi-finished tool obtained in step S4 in a machining fixture (3), and sharpening the blade (12) by machining and grinding, thereby finally obtaining a special-shaped cutting tool (1); Wherein, the binder comprises the following raw materials in parts by weight: Polyoxymethylene: 78-84 parts; High-density polyethylene: 3.5-4.5 parts; Polystyrene: 4.4-6 parts; Ethylene vinyl acetate: 1.8-2.5 parts; Polyacrylamide: 0.8-2 parts; Stearic acid: 0.5-1.5 parts; Wax: 4-5 parts; The wax material is a mixture of paraffin wax, palm wax and beeswax, and the weight ratio of the paraffin wax, palm wax and beeswax is 1: (1.2-1.4): (0.1-0.3); The sintering support plate (2) comprises a square bottom plate (21) and a plurality of support steps (22), wherein the support steps (22) are evenly distributed at the four corner positions of the bottom plate (21), and the upper surface of the support steps (22) is provided with an arc surface (221), and the support steps (22) are in surface contact with the blade (12) and the stirring blade (13) through the arc surface (221); The machining fixture (3) includes a machining template (31), the machining template (31) is provided with a limiting groove (32) matching the semi-finished tool, and the machining template (31) is also provided with a pneumatic chuck (33), the pneumatic chuck (33) is located in the limiting groove (32) and corresponds to the hub (11) of the semi-finished tool, and the pneumatic chuck (33) is used to extend into the mounting hole (111) of the hub (11) and expand and clamp the hub (11).

2. The MIM manufacturing method of a special-shaped cutting tool according to claim 1, characterized in that: The inert gas is nitrogen, and is circulated into the degreasing furnace at a rate of 70-95 L / min.

3. The MIM manufacturing method of a special-shaped cutting tool according to claim 1, characterized in that: The acidic substance is oxalic acid, and is introduced into the degreasing furnace at a flow rate of 3-5 g / min.

4. The MIM manufacturing method of a special-shaped cutting tool according to claim 1, characterized in that: In the sintering and shaping of step S4, the vacuum sintering furnace is maintained at a vacuum degree less than or equal to 15 KPa, and is heated to 1280-1350° C. for sintering and shaping for 24-30 hours.

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