A production process of a high-pressure fit performance mesopore press-fitting type powder metallurgy part

Abstract

The application discloses a high-pressure assembly performance middle-hole press-fit type powder metallurgy part production process and belongs to the technical field of powder metallurgy, and comprises the following steps: S1, mixing; S2, forming; S3, sintering; and S4, deburring; the mesh belt sintering furnace in the step S3 comprises a dewaxing area, a heating area, a carbon recovery area and a cooling area, the mesh belt width of the mesh belt sintering furnace is 450-600 mm, and the mesh belt advancing speed in the mesh belt sintering furnace is 100-125 mm / min; the application omits the 'processing' procedure, avoids the internal diameter wall gap from being extruded and reduced, omits 'grinding' and 'oil immersion', retains the original gap state of the powder metallurgy product, and monitors the open loop strength and open loop displacement after sampling and detection after sintering, so that the high-pressure assembly requirement of a large interference amount is met, the cracking problem in the part press-fit process is avoided, and the comprehensive production cost is reduced by more than 10% after the multiple steps are omitted.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy technology, specifically relating to a production process for high-pressure assembly performance medium-hole press-fit powder metallurgy parts. Background Technology

[0002] Powder metallurgy parts have advantages such as low manufacturing cost, high processing efficiency, one-time molding, no need for secondary processing after molding, no other metal waste generated during the molding process, and high resource utilization. Hole-type press-fit powder metallurgy parts refer to powder metallurgy parts with through holes for press-fit connections. Some existing hole-type press-fit powder metallurgy parts require press-fit connection with connecting shafts (usually splined shafts for high-pressure press-fit performance). The connecting shaft is press-fitted into the through hole of the powder metallurgy part. However, due to the larger outer diameter of some connecting shafts, the required interference fit for high-pressure press-fit performance is between 0.18 and 0.35 mm. The larger outer diameter results in an interference fit of around 0.3 mm. Under normal circumstances, the toughness and strength of some powder metallurgy parts produced cannot adapt to the interference fit of around 0.3 mm, leading to a certain proportion of powder metallurgy parts cracking outwards from the hole, causing damage. Summary of the Invention

[0003] Technical Problem: In view of the above-mentioned problems existing in the prior art, the technical problem to be solved by the present invention is to provide a high-pressure press-fitting performance medium-hole press-fitting powder metallurgy parts manufacturing process to meet the use requirements of interference fit, and avoid cracking of medium-hole press-fitting powder metallurgy parts during press-fitting.

[0004] Technical Solution: To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] A manufacturing process for high-pressure press-fit type powder metallurgy parts includes the following steps:

[0006] S1. Mixing: Mix the powdered raw materials evenly according to the mass percentage;

[0007] S2. Forming: The mixed powder raw materials are molded to obtain powder metallurgy parts.

[0008] S3. Sintering: The powder metallurgy part blank is placed in a mesh belt sintering furnace for sintering;

[0009] S4. Deburring: Powder metallurgy parts are deburred by tumbling and collision in a closed cylinder or by sandblasting.

[0010] The mesh belt sintering furnace in step S3 includes a dewaxing zone, a heating zone, a carbon recovery zone, and a cooling zone. The width of the mesh belt in the mesh belt sintering furnace is 450-600 mm, and the forward speed of the mesh belt in the mesh belt sintering furnace is 100-125 mm / min.

[0011] The length of the dewaxing zone is 210-250cm, and the temperature range of the dewaxing zone is 500℃-700℃.

[0012] The heating zone is 580-700cm long and has a temperature range of 1110℃-1150℃.

[0013] The carbon recovery zone is 210-250cm in length and has a temperature range of 800℃-900℃.

[0014] The cooling zone is 580-700cm long and has a temperature range of 30℃-50℃.

[0015] Furthermore, in step S1, the following raw materials are mixed uniformly by mass percentage: C: 0.72%–0.88%, Cu: 2.25%–2.75%, Mn: 0.26%–0.34%, powder lubricant: 0.54%–0.66%, Fe: balance.

[0016] Furthermore, in step S2, the molding pressure is 13-16 MPa and the molding density is 6.8-6.9 g / cm3.

[0017] Furthermore, step S3 involves sintering in a protective atmosphere, which is AX gas.

[0018] Furthermore, in step S3, when the width of the mesh belt in the mesh belt sintering furnace is 450mm, the temperature range of the heating zone is 1110℃-1130℃, and the mesh belt forward speed is 110mm / min; when the width of the mesh belt in the mesh belt sintering furnace is 600mm, the temperature range of the heating zone is 1120℃-1140℃, and the mesh belt forward speed is 115mm / min.

[0019] Furthermore, the powder metallurgy part has a through hole with a diameter of D1 and a diameter of D2, wherein D1 ≤ 0.8D2, and 5 mm ≤ D1 ≤ 30 mm, 20 mm ≤ D2 ≤ 60 mm.

[0020] Furthermore, the step S3 is followed by the following steps:

[0021] Step S3.2, Sampling and testing: Sampling of sintered powder metallurgy parts, with a sampling frequency of 2-20 parts per batch, testing the open-loop strength and open-loop displacement of the powder metallurgy parts samples, and comparing them with the preset values ​​of the open-loop strength and open-loop displacement of the powder metallurgy parts. If the sample is greater than the preset value, it is qualified; if it is less than the preset value, it is unqualified.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0023] 1. By changing the sintering conditions of powder metallurgy parts, the strength of the parts is improved. The conveyor belt speed is controlled and the temperature of each area in the sintering furnace is controlled at the same time. After sintering, sampling and testing are carried out to monitor the open-loop strength and open-loop displacement, so as to meet the high pressure fitting requirements of large interference and avoid cracking problems in the pressing process of parts.

[0024] 2. Compared with existing processes, the "processing" step is omitted, which avoids the inner diameter wall voids being squeezed and reduced, maintains a high degree of plastic deformation, and improves the high pressure fitting performance of the parts;

[0025] 3. Compared with the existing process, the "grinding" and "oil immersion" are omitted to preserve the original porosity of the powder metallurgy product, avoid the influence of oil pressure in the pore cavity during press fitting, and further improve the high-pressure fitting performance of the parts; at the same time, since the "processing, grinding" and "oil immersion" steps are omitted, the "washing" step is also eliminated, and the overall production cost is reduced by more than 10% after omitting multiple steps. Attached Figure Description

[0026] Figure 1 This is a structural diagram of the pore-pressed powder metallurgy part in this invention;

[0027] Figure 2 This is a cross-sectional structural diagram of a medium-hole press-fit powder metallurgy part;

[0028] Figure 3 This is a schematic diagram of the push rod structure of the testing tool;

[0029] Figure 4 This is a schematic diagram of the measuring base structure of the testing tool. Detailed Implementation

[0030] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0031] Example 1:

[0032] This embodiment discloses a high-pressure performance powder metallurgy part manufacturing process for fabricating insert 1 (such as...). Figure 1 and Figure 2 As shown), insert 1 is an injection-molded insert for a windshield wiper. Insert 1 has a through hole 2 in the middle for interference fit with the corresponding spline shaft. The diameter of the through hole 2 is D1, which equals 10.1mm (+0.02 / -0.01). The outer diameter of insert 1 is D2, which equals 21mm (±0.1). The outer diameter of the corresponding spline shaft is 10.37mm±0.07mm, and the interference fit is 0.18mm~0.35mm—median 0.26mm. The manufacturing process of insert 1 includes the following steps:

[0033] S1. Mixing: Mix the following raw materials evenly according to the following mass percentages: C: 0.74%, Cu: 2.6%, Mn: 0.3%, powdered lubricant: 0.6%, Fe: balance. The mixed product can be purchased directly from external suppliers.

[0034] S2. Forming: The mixed powder raw materials are molded to obtain powder metallurgy part blanks. The molding pressure is 14.5MPa and the forming density is about 6.85g / cm3.

[0035] S3. Sintering: The formed powder metallurgy part blanks are placed in a continuous mesh belt sintering furnace for sintering. The mesh belt of the mesh belt sintering furnace is 450mm wide. The mesh belt sintering furnace includes a dewaxing zone, a heating zone, a carbon recovery zone and a cooling zone from front to back. The powder metallurgy part blanks pass through the four zones in sequence under the drive of the mesh belt. The mesh belt forward speed is 110mm / min.

[0036] The dewaxing zone is 250cm long and 700℃. The part blank gradually heats up during the process, and the lubricant contained in the raw material is burned off between 250℃ and 700℃.

[0037] The heating zone is 700cm long and has a temperature of 1120℃, where the parts are sintered.

[0038] The carbon recovery zone is 250cm long and 850℃. The decarburized parts on the surface of the parts are recarburized at 800-900℃.

[0039] The cooling zone is 700cm long and 50℃. The sintered part is rapidly cooled to 150℃ before being exposed to air.

[0040] S3.2 Sampling Inspection: Sample the sintered parts at a rate of 5 per batch. Test the open-loop strength and open-loop displacement of the sample parts and compare them with the preset values ​​for the open-loop strength and open-loop displacement of powder metallurgy parts. The preset value for open-loop strength is 1250 kgf and the preset value for open-loop displacement is 6.4 mm. If the sample is greater than the preset value, it is qualified; if it is less than the preset value, it is unqualified. If any sample is unqualified, the batch of products is unqualified. If all samples are qualified, the batch of products proceeds to the next step.

[0041] The open-loop strength and open-loop displacement are tested using existing methods, with the testing tool being a pull rod (such as...). Figure 3 (as shown) and the hollow measuring base (such as Figure 4As shown), the push rod is 120mm long, with a bottom diameter of 9.5mm and a top diameter of 16mm. The push rod angle is 3° to 5°. During testing, the insert is placed in the middle of the measuring base, and the push rod is inserted through the insert from above. The open-loop strength (the maximum pressure that the insert can withstand before cracking during the pressure test) and the open-loop displacement (the displacement generated by the push rod when the insert cracks during the pressure test) are measured.

[0042] The preset values ​​for open-loop strength and open-loop displacement are determined based on the sintering furnace and different sintering conditions (different sintering temperatures and speeds under a constant sintering atmosphere). A reasonable number of sintering samples are set and produced in small batches. For powder metallurgy parts sintered in multiple batches (more than 50) under different sintering furnaces and conditions, while ensuring the size and hardness of the parts after sintering, the open-loop strength and open-loop displacement of the parts are tested and the values ​​are recorded. The preset values ​​for open-loop strength and open-loop displacement are set at 95% of the lowest value among the three best samples. (In the production process of other products, when the press fit interference is small, the preset values ​​for open-loop strength and open-loop displacement can be reduced. The normal press fit of the product can be met according to the actual situation.)

[0043] S4. Deburring: Place multiple parts into a sealed cylinder, filling it to less than 1 / 2 full. The parts tumble and collide with each other to remove burrs.

[0044] S5. Quality Inspection and Packaging: The parts are inspected for quality. After the size, density and hardness of the parts are confirmed to be qualified by quality inspection sampling, they are sent to the packaging department for packaging.

[0045] Example 2:

[0046] This embodiment discloses a high-pressure performance powder metallurgy part manufacturing process for producing insert 1 identical to that in Embodiment 1. The manufacturing process of insert 1 includes the following steps:

[0047] S1. Mixing: Mix the following raw materials evenly according to the following mass percentages: C: 0.74%, Cu: 2.6%, Mn: 0.3%, powder lubricant: 0.6%, Fe: balance.

[0048] S2. Forming: The mixed powder raw materials are molded to obtain powder metallurgy part blanks. The molding pressure is 14.5MPa and the forming density is about 6.85g / cm3.

[0049] S3. Sintering: The formed powder metallurgy part blanks are placed in a continuous mesh belt sintering furnace for sintering. The mesh belt of the mesh belt sintering furnace is 600mm wide. The mesh belt sintering furnace includes a dewaxing zone, a heating zone, a carbon recovery zone and a cooling zone from front to back. The powder metallurgy part blanks pass through the four zones in sequence under the drive of the mesh belt. The mesh belt forward speed is 115mm / min.

[0050] The dewaxing zone is 210cm long and 700℃, where the lubricant in the raw material of the part is burned off between 250℃ and 700℃.

[0051] The heating zone is 580cm long and 1140℃, where the parts are sintered.

[0052] The carbon recovery zone is 210cm long and 800℃. The decarburized parts on the surface of the parts are recarburized at 800-900℃.

[0053] The cooling zone is 580cm long and 30℃. The sintered part is rapidly cooled to 150℃ before being exposed to air.

[0054] S3.2 Sampling Inspection: Sample the sintered parts at a rate of 10 parts per batch. Test the open-loop strength and open-loop displacement of the sample parts and compare them with the preset values ​​for the open-loop strength and open-loop displacement of powder metallurgy parts. The preset value for open-loop strength is 1250 kgf and the preset value for open-loop displacement is 6.4 mm. If the sample is greater than the preset value, it is qualified; if it is less than the preset value, it is unqualified. If any sample is unqualified, the batch of products is unqualified. If all samples are qualified, the batch of products proceeds to the next step.

[0055] S4. Deburring: Place multiple parts into a sealed cylinder, filling it to less than 1 / 2 full. The parts tumble and collide with each other to remove burrs.

[0056] S5. Quality Inspection and Packaging: The parts are inspected for quality. After the size, density and hardness of the parts are confirmed to be qualified by quality inspection sampling, they are sent to the packaging department for packaging.

[0057] Comparative Example 1

[0058] Using the existing production process, mixing → forming → sintering → grinding → processing → quality inspection → washing → oil immersion → packaging, about 10% of the pressing cracks occur after pressing.

[0059] The existing production process includes the following steps:

[0060] S1. Mixing: Mix the following raw materials evenly according to the following mass percentages: C: 0.74%, Cu: 2.6%, Mn: 0.3%, powder lubricant: 0.6%, Fe: balance.

[0061] S2. Forming: The mixed powder raw materials are molded to obtain powder metallurgy part blanks. The molding pressure is 14.5MPa and the forming density is 6.85g / cm3.

[0062] S3. Sintering: The formed powder metallurgy part blanks are placed in a continuous mesh belt sintering furnace for sintering. The mesh belt of the mesh belt sintering furnace is 450mm wide and includes a dewaxing zone, a heating zone, a carbon recovery zone and a cooling zone. The powder metallurgy part blanks pass through the four zones in sequence under the drive of the mesh belt. The mesh belt forward speed is 135mm / min.

[0063] The dewaxing zone is 250cm long and 700℃, where the lubricant contained in the raw material of the part is burned off between 250℃ and 700℃.

[0064] The heating zone is 700cm long and the temperature is 1100℃, where the parts are sintered.

[0065] The carbon recovery zone is 250cm long and 800℃. The decarburized parts on the surface of the parts are recarburized at 800-900℃.

[0066] The cooling zone is 700cm long and 30℃. The sintered parts are rapidly cooled to 250℃~150℃ before being exposed to air.

[0067] S4. Grinding: Place the parts and millstones in a grinding pot at a ratio of 1:2, while simultaneously immersing them in dripping rust-preventive oil. Under the action of a rotating motor and a swirl bar, the millstones and sintered parts are tumbled and rotated, removing burrs from the sintered parts through vibration and friction.

[0068] S5. Processing: The sintered powder metallurgy parts are pressed again in the mold to cause plastic deformation, so as to ensure the overall length, inner diameter, outer diameter and other geometric tolerances of the sintered parts.

[0069] S6. Quality Inspection: Conduct quality inspection on sintered parts, mainly by sampling and confirming the size, density, hardness, and appearance of the parts.

[0070] S7. Cleaning: Place the powder metallurgy parts in a water washing machine for cleaning: add cleaning agent and rust inhibitor to the washing solution, and the parts are cleaned by ultrasonic cleaning, rinsing, and drying to finally remove oil stains from the surface of the parts.

[0071] S8. Oil immersion: After cleaning, the parts are immersed in rust-preventive oil in an oil immersion tank to achieve a certain rust prevention effect.

[0072] S9. Packaging: Pack into a packaging bag.

[0073] Comparative Example 2

[0074] The difference between Comparative Example 2 and Comparative Example 1 is that the processing step S5 and the oil immersion step S8 are both omitted.

[0075] Comparative Example 3

[0076] The difference between Comparative Example 3 and Comparative Example 1 is that the heating zone of the sintering furnace used is 730cm long, the heating zone temperature is 1120℃, the carbon recovery zone temperature is 850℃, and the processing in step S5 and the oil immersion in step S8 are omitted.

[0077] Comparative Example 4

[0078] The difference between Comparative Example 4 and Comparative Example 1 is that the mesh belt width of the mesh belt sintering furnace is 600mm, the mesh belt forward speed is 125mm / min, the length of the dewaxing zone is 210cm, the temperature of the dewaxing zone is 600℃, the length of the heating zone is 580cm, the temperature of the heating zone is 1140℃, the length of the carbon recovery zone is 210cm, the temperature of the carbon recovery zone is 850℃, the length of the cooling zone is 580cm, and the temperature is 30℃. In addition, the processing in step S5 and the oil immersion in step S8 are omitted.

[0079] The insert products manufactured using the original process in Comparative Examples 1-4 were compared with those manufactured using the processes in Examples 1 and 2. The open-loop strength and open-loop displacement were tested using a pull rod (e.g., a push rod). Figure 3 (as shown) and the hollow measuring base (such as Figure 4 As shown in the figure, the length of the push rod is 120mm, the bottom diameter is 9.5mm, the top diameter is 16mm, and the push rod angle is 3°~5°. During the test, the insert is placed in the middle of the measuring base, and the push rod is inserted through the insert from the top. The open-loop strength (the maximum pressure that the insert can withstand before cracking during the pressure test of the compression test) and the open-loop displacement (the displacement generated by the push rod when the insert cracks during the pressure test of the compression test) are measured. The test results of multiple batches are shown in Table 1.

[0080] In Table 1, sintering furnace number J represents a continuous mesh belt sintering furnace with a mesh belt width of 450mm, and sintering furnace number W represents a continuous mesh belt sintering furnace with a mesh belt width of 600mm.

[0081] The unit for open-loop strength is kgf, and the unit for open-loop displacement is mm;

[0082] Table 1

[0083]

[0084]

[0085] As can be seen from Table 1, in Comparative Example 1, after the "processing" and "oil immersion" steps, the average open-loop strength and open-loop displacement of the insert (row X in the table) were the smallest. In Comparative Example 2, omitting the "processing" and "oil immersion" steps resulted in a significant improvement in open-loop strength and open-loop displacement. In Comparative Examples 3 and 4, after changing some sintering conditions in the sintering furnace, the open-loop strength and open-loop displacement were improved. In Examples 1 and 2 of the present invention, compared with the comparative examples, the open-loop strength and open-loop displacement were further improved. During the manufacturing process of insert 1, the open-loop strength and open-loop displacement of insert 1 were tested. When the open-loop strength of 1250 kgf and the open-loop displacement of 6.4 mm were met, insert 1 did not crack. As can be seen from Table 1, some parts in Comparative Examples 1 to 3 did not meet the requirements, while Examples 1 and 2 of the present invention all met the requirements. After sintering, the open-loop strength and open-loop displacement all met the control specifications, and the actual use was 100% OK, with no cracking.

[0086] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A manufacturing process for high-pressure press-fit type powder metallurgy parts, characterized in that, Includes the following steps: S1. Mixing: Mix the powdered raw materials evenly according to the mass percentage; S2. Forming: The mixed powder raw materials are molded to obtain powder metallurgy parts. S3. Sintering: The powder metallurgy parts blanks are placed in a mesh belt sintering furnace for sintering. S4. Deburring: Powder metallurgy parts are deburred by tumbling and collision in a closed cylinder or by sandblasting. In step S1, the following raw materials are mixed evenly according to the following mass percentages: C: 0.72%–0.88%, Cu: 2.25%–2.75%, Mn: 0.26%–0.34%, powdered lubricant: 0.54%–0.66%, Fe: balance; In step S2, the molding pressure is 13–16 MPa, and the molding density is 6.8–6.9 g / cm³. 3 ; The mesh belt sintering furnace in step S3 includes a dewaxing zone, a heating zone, a carbon recovery zone, and a cooling zone. Sintering is carried out in a protective atmosphere, which is AX gas. The width of the mesh belt in the mesh belt sintering furnace is 450-600 mm, and the forward speed of the mesh belt in the mesh belt sintering furnace is 100-125 mm / min. The length of the dewaxing zone is 210-250cm, and the temperature range of the dewaxing zone is 500℃-700℃. The heating zone is 580-700cm long and has a temperature range of 1110℃-1150℃. The carbon recovery zone is 210-250cm in length and has a temperature range of 800℃-900℃. The cooling zone is 580-700cm long and has a temperature range of 30℃-50℃.

2. The manufacturing process for high-pressure press-fit type powder metallurgy parts according to claim 1, characterized in that, In step S3, when the width of the mesh belt in the mesh belt sintering furnace is 450mm, the temperature range of the heating zone is 1110℃-1130℃, and the mesh belt forward speed is 110mm / min; when the width of the mesh belt in the mesh belt sintering furnace is 600mm, the temperature range of the heating zone is 1120℃-1140℃, and the mesh belt forward speed is 115mm / min.

3. The manufacturing process for high-pressure press-fit type powder metallurgy parts according to claim 1, characterized in that, The powder metallurgy part has a through hole (2) with a diameter of D1 and a diameter of D2. D1 ≤ 0.8D2, and 5 mm ≤ D1 ≤ 30 mm, 20 mm ≤ D2 ≤ 60 mm.

4. The manufacturing process for high-pressure ductile powder metallurgy parts with medium-hole pressure-fitting properties according to claim 1, characterized in that, The following steps are included after step S3: Step S3.2, Sampling and testing: Sampling of sintered powder metallurgy parts, with a sampling frequency of 2-20 parts per batch, testing the open-loop strength and open-loop displacement of the powder metallurgy parts samples, and comparing them with the preset values ​​of the open-loop strength and open-loop displacement of the powder metallurgy parts. If the sample is greater than the preset value, it is qualified; if it is less than the preset value, it is unqualified.

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