Manufacturing method of powder metallurgy small folding mobile phone hinge

Abstract

The invention provides a manufacturing method of a powder metallurgy small folding mobile phone hinge, and relates to the technical field of powder metallurgy, and the method comprises the steps of material preparation, injection molding, ornament positioning, degreasing treatment, sintering densification, magnetic polishing and drying, full detection and finished product packaging: firstly, preparing a mixed raw material of 17-4PH stainless steel powder and a binder; performing injection molding to obtain a hinge green body; the green body is fixed to the ceramic plate in a specific decoration mode; the binder is removed through 1 # program degreasing, and densification is achieved through 2 # program high-temperature sintering; and the surface quality is optimized through magnetic polishing and drying, and finally the size precision and performance are ensured through full inspection. By optimizing the material formula and the process parameters, high-precision and high-strength manufacturing of the small folding hinge is achieved, the production efficiency is improved by 30% or above, the comprehensive cost is reduced by 10%, and the requirements for light weight and miniaturization of folding mobile phones are met.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of powder metallurgy, in particular to a manufacturing method of a small folding mobile phone hinge. BACKGROUND

[0002] Folding smart phones have become one of the mainstream development directions in the smart phone market due to their dual advantages of large screen display and portable storage. The hinge, as the core transmission component of the folding phone, directly determines the folding experience and service life of the phone in terms of precision, strength and durability. The structure of the small folding phone hinge is complex (usually including multiple rotating arms, shaft sleeves and limiting structures), the dimensional accuracy requirement is very high (the key dimensional tolerance needs to be controlled within ±0.03mm), and at the same time, it needs to have excellent fatigue strength and wear resistance. The traditional manufacturing process faces significant challenges.

[0003] Currently, the mainstream manufacturing methods of folding phone hinges include cutting processing, forging + precision grinding, etc. Although cutting processing can ensure a certain precision, it is difficult to form complex cavities and microstructures (such as shaft holes with a diameter of <1mm) in one step, which requires multiple clamping, resulting in low production efficiency, high processing cost, and a material utilization rate of less than 50%. Although the forging process can improve the material density and mechanical properties, a large amount of grinding is required to correct the size afterwards, and complex thin-walled structures (thickness <0.5mm) cannot be formed, making it difficult to meet the lightweight requirements of small folding hinges.

[0004] Metal injection molding (MIM) is an advanced process in the field of powder metallurgy, which has the advantage of "near net shape" and can realize high-precision and large-batch manufacturing of complex structural parts, and the material utilization rate can reach more than 95%, which has been gradually applied to the manufacturing of mobile phone parts. However, for the MIM manufacturing of small folding phone hinges, the existing technology still has the following shortcomings:

[0005] Poor material flowability: The microstructure of the hinge (such as narrow gaps and small holes) requires high flowability of the feed material. The binder ratio of the existing 17-4PH stainless steel feed material is not reasonable, which easily leads to defects such as "material deficiency" and "air bubbles" during injection;

[0006] Incomplete debinding: The hinge wall thickness is uneven (0.3-2mm), and the traditional debinding process (such as single temperature debinding) easily leads to residual binder in the thick wall area, which produces cracking or bubbling during subsequent sintering;

[0007] Large sintering deformation: The slender structure of the small hinge (aspect ratio >5) is prone to bending deformation during high-temperature sintering. The existing sintering parameters (such as heating rate and holding time) are not optimized for the hinge structure, resulting in a size out-of-tolerance rate of >8%;

[0008] Short mold life: the mold cavity precision requirement of the hinge mold is up to ±0.005mm, the existing mold material (such as Cr12MoV) is insufficient in wear resistance, the mold cavity is easy to wear, and the service life is less than 50,000 mold times.

[0009] Therefore, developing a high-precision and high-stability powder metallurgy manufacturing method for small folding mobile phone hinges, optimizing the material formula and process parameters, and solving the above forming defects and performance problems have become a technical direction that needs to be broken through in the field. SUMMARY

[0010] The purpose of the present application is to overcome the low manufacturing precision, difficult forming of complex structure, and defects such as incomplete debinding and sintering deformation in the existing MIM process of folding mobile phone hinges, and to provide a powder metallurgy small folding mobile phone hinge manufacturing method, which realizes high-precision, high-strength and low-cost manufacturing of small folding hinges by optimizing the material formula, injection parameters, debinding-sintering process and mold design.

[0011] In order to achieve the above purpose, the present application is realized by the following technical scheme: a powder metallurgy small folding mobile phone hinge manufacturing method, comprising the following steps:

[0012] S1, material preparation: mixing stainless steel powder and binder according to a predetermined proportion to prepare MIM feedstock with a predetermined fluidity;

[0013] S2, injection molding: injecting the MIM feedstock into a mold with a predetermined structure under predetermined injection parameters to obtain a folding mobile phone hinge green body;

[0014] S3, hinge positioning: placing the hinge green body on a ceramic plate at a predetermined interval and direction to form a debinding assembly;

[0015] S4, debinding treatment: placing the debinding assembly in a debinding furnace, removing the binder in the green body by using a predetermined debinding program to obtain a debound body;

[0016] S5, sintering densification: transferring the debound body to a sintering furnace, and performing high-temperature sintering by using a predetermined sintering program to obtain a densified hinge semi-finished product;

[0017] S6, magnetic polishing and drying: performing magnetic polishing treatment on the densified hinge semi-finished product, and then placing it in an oven for drying to obtain a polished semi-finished product;

[0018] S7, full inspection test: performing size precision, appearance quality and mechanical property detection on the polished semi-finished product to select qualified hinge finished products;

[0019] S8, finished product packaging: packaging the qualified hinge finished products according to a predetermined packaging method to complete the manufacturing.

[0020] Further as the improvement of the technical scheme of the present application, in step S1, the stainless steel powder is 17-4PH stainless steel powder with a particle size of 5-20 μm; the binder is a paraffin-polyvinyl alcohol blend, wherein paraffin accounts for 55-65% of the total mass of the binder, and polyvinyl alcohol accounts for 35-45%; the mixing mass ratio of the stainless steel powder and the binder is 90:10-95:5, the mixing temperature is 60-80℃, the stirring speed is 400-600 rpm, and the mixing time is 25-35 minutes.

[0021] Further as the improvement of the technical scheme of the present application, in step S2, the number of cavities of the mold is 12-14, the mold material is H13 hot work die steel, and the mold is manufactured by electric spark machining and precision grinding process; the preset injection parameters include: machine tonnage 80-120T, front mold temperature 130-140℃, rear mold temperature 100-110℃, injection cycle 18-22s, injection pressure 80-100Bar, and injection speed 30-50mm / s; the green density of the hinge green body is ≥5.3g / cm³.

[0022] Further as the improvement of the technical scheme of the present application, in step S3, the specification of the ceramic plate is , and the ceramic plate is cleaned by a brush before use to remove dirt and dust on the surface; the preset spacing includes a row spacing of 1-3mm and a column spacing of 1-3mm, each ceramic plate is placed with 77-117 hinge green bodies, and the placing directions of all the green bodies are consistent; the red plane of the hinge green body faces downward and is attached to the surface of the ceramic plate.

[0023] Further as the improvement of the technical scheme of the present application, in step S4, the preset debinding program includes: debinding temperature 300-400℃, acid passing time 470-530 minutes, acid passing amount 2.5-3.5g / min, and cleaning time 85-95 minutes; after the debinding treatment, the debinding rate is >7.2%, and the green body without debinding is verified by a destructive experiment, wherein the destructive experiment is to extract 1-2 green bodies in the middle layer of the innermost side of the debinding furnace, and to observe the internal state by manually and slowly kneading and crushing.

[0024] Further as the improvement of the technical scheme of the present application, in step S5, the preset sintering program includes: sintering temperature 1300-1350℃, heating rate 4-6℃ / min, holding time 1.5-2.5 hours, and vacuum degree in the sintering furnace The sintered density of the densified hinge semi-finished product is greater than or equal to 7.6 g / cm3, the single weight is 0.24-1.75 g, and the appearance is free of defects such as sintering, ash, material shortage, cracking and material sticking.

[0025] Further as the improvement of the technical scheme of the application, in step S6, the parameters of the magnetic force polishing treatment include: the polishing needle specification is , the polishing liquid addition amount is 450-550 mL, the polishing rotation speed is 100-120 rpm, and the total polishing time is 14-16 minutes, wherein the left rotation time is 6-8 minutes and the right rotation time is 8-10 minutes; the drying parameters include: the drying temperature is 115-135 DEG C, the drying time is 4-6 minutes, and the surface of the semi-finished product after drying is free of dirt, water stains, rust and damage.

[0026] Further as the improvement of the technical scheme of the application, in step S7, the size precision detection adopts a caliper, a two-dimensional measuring instrument and a needle gauge, and the detection items include the ball gauge size, wherein the ball gauge diameter tolerance is ±0.02-±0.03 mm, the length size tolerance is ±0.03-±0.07 mm, and the angle tolerance is ±1°; the appearance quality detection is full inspection, and the semi-finished product free of scratches, scratches, material shortage, bulges and sintering cracks is screened; the mechanical property detection includes hardness detection, and the hardness is greater than or equal to 30 HRC.

[0027] Further as the improvement of the technical scheme of the application, in step S2, the mold is also provided with an independent cooling system, the front mold cooling waterway and the rear mold cooling waterway are designed separately, the cooling waterway diameter is 6-8 mm, and the cooling water flow rate is 1.5-2.5 L / min; the residual material in the screw needs to be discharged before starting, the first 10 products are discarded after starting, and sampling is performed after the product is stable for the first inspection.

[0028] Further as the improvement of the technical scheme of the application, in step S1, the 17-4PH stainless steel powder is subjected to vacuum drying treatment before mixing, the drying temperature is 80-100 DEG C, and the drying time is 1-2 hours; the binder is preheated to 50-70 DEG C before mixing, so as to reduce the mixing resistance and improve the uniformity of the raw materials.

[0029] The powder metallurgy small folding mobile phone hinge manufacturing method has the following beneficial effects compared with the prior art:

[0030] High forming precision: by optimizing the mold material (H13 steel) and the injection parameters (mold temperature and pressure), the key size tolerance of the hinge is controlled within ±0.03 mm, the size tolerance rate is less than 2%, and the assembly requirements of the folding mobile phone are met.

[0031] Excellent mechanical properties: after sintering at 1300-1350℃, the density of 17-4PH stainless steel is ≥7.6g / cm³, the hardness is ≥30HRC, and the fatigue life is >100000 times, which is better than that of traditional machining parts (<80000 times);

[0032] High production efficiency: MIM process realizes near-net forming, the subsequent machining amount is reduced by 80%, the number of mold cavities is 12-14, and the single-shift output can reach 5000-10000 pieces, and the production efficiency is improved by more than 30% compared with traditional machining;

[0033] Cost reduction: the material utilization rate is more than 95% (traditional machining <50%), and through the optimization of debinding-sintering process, the waste rate is reduced from 8% to 2%, and the comprehensive manufacturing cost is reduced by 10%;

[0034] Strong process stability: through gradient debinding, vacuum sintering and full inspection process, the defect rate caused by process fluctuation is <1%, which is suitable for large-scale stable production. BRIEF DESCRIPTION OF DRAWINGS

[0035] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments, made with reference to the accompanying drawings:

[0036] Figure 1 An exemplary flowchart of a powder metallurgy small folding mobile phone hinge manufacturing method of the present application;

[0037] Figure 2 One of the physical drawings of the GMMP0480 type folding mobile phone hinge manufactured in Example 1 of the present application;

[0038] Figure 3 The second physical drawing of the GMMP0480 type folding mobile phone hinge manufactured in Example 1 of the present application;

[0039] Figure 4 One of the physical drawings of the GMMP0481 type folding mobile phone hinge manufactured in Example 2 of the present application;

[0040] Figure 5 The second physical drawing of the GMMP0481 type folding mobile phone hinge manufactured in Example 2 of the present application;

[0041] Figure 6 One of the physical drawings of the GMMP0490 type folding mobile phone hinge manufactured in Example 3 of the present application;

[0042] Figure 7 The second physical drawing of the GMMP0490 type folding mobile phone hinge manufactured in Example 3 of the present application. DETAILED DESCRIPTION

[0043] The application will be described in detail below with reference to specific embodiments. The embodiments are illustrative of the application and are not intended to limit the scope of the application.

[0044] With reference to Figure 1 A powder metallurgy small folding mobile phone hinge manufacturing method, comprising the following steps:

[0045] S1, material preparation: mixing stainless steel powder and binder according to a preset ratio to prepare MIM feedstock with a preset fluidity;

[0046] S2, injection molding: injecting the MIM feedstock into a mold with a preset structure, molding under preset injection parameters to obtain a folding mobile phone hinge green body;

[0047] S3, hinge positioning: placing the hinge green body on a ceramic plate at a preset interval and direction to form a component to be debound;

[0048] S4, debinding treatment: placing the component to be debound in a debinding furnace, removing the binder in the green body using a preset debinding program to obtain a debound body;

[0049] S5, sintering densification: transferring the debound body to a sintering furnace, performing high-temperature sintering using a preset sintering program to obtain a densified hinge semi-finished product;

[0050] S6, magnetic polishing and drying: performing magnetic polishing treatment on the densified hinge semi-finished product, placing it in an oven for drying after removing surface defects to obtain a polished semi-finished product;

[0051] S7, full inspection test: detecting the size accuracy, appearance quality and mechanical properties of the polished semi-finished product to screen out qualified hinge finished products;

[0052] S8, finished product packaging: packaging the qualified hinge finished products according to a preset packaging method to complete the manufacturing.

[0053] In a specific implementation, the core of the present application is based on the near-net forming characteristics of the metal injection molding (MIM) process, and is implemented in the following steps: first, the stainless steel powder and the binder are mixed in a predetermined proportion through the material preparation link to form a MIM feedstock with good fluidity, laying a foundation for subsequent forming; then the MIM feedstock is injected into a customized mold to form a hinge green body under specific injection parameters, realizing the preliminary forming of the complex structure of the hinge; then the green body is fixed in order on the ceramic plate through the positioning of the swing piece, ensuring uniform stress on the blank body during subsequent hot working; then the binder in the green body is removed through the debinding process to avoid defects caused by residual binder during subsequent sintering; then the debound blank body is densified through sintering to achieve the target density in a high-temperature vacuum environment, improving the mechanical properties; then the surface quality is optimized through magnetic polishing and drying to remove machining burrs and prevent rust; finally, the qualified products are selected through full inspection testing, and the entire manufacturing process is completed through finished product packaging. The entire process organically connects the various links of the MIM process around the needs of precision, strength and lightweight of the folding mobile phone hinge, forming a standardized manufacturing system. The present application effectively solves the problems of low precision, difficulty in forming complex structures and high cost in the manufacturing of existing folding mobile phone hinges. Through the near-net forming advantage of the MIM process, the subsequent processing amount is reduced, and the production efficiency is improved by more than 30% compared with traditional cutting machining, meeting the target of improving production efficiency; at the same time, the material utilization rate is more than 95%, combined with the optimization of debinding and sintering processes, the comprehensive manufacturing cost is reduced by 10%, meeting the requirement of cost control; the entire process forms a complete quality control system to ensure that the hinge size precision, structural strength and surface quality meet the standards, improving the technical level and market competitiveness of the enterprise in the field of folding smart phone parts manufacturing, and promoting the large-scale application of the MIM process in folding smart phone manufacturing.

[0054] In some embodiments, in step S1, the stainless steel powder is 17-4PH stainless steel powder with a particle size of 5-20 μm; the binder is a paraffin-polyvinyl alcohol blend, in which paraffin accounts for 55-65% of the total mass of the binder, and polyvinyl alcohol accounts for 35-45%; the mixing mass ratio of the stainless steel powder and the binder is 90:10-95:5, the mixing temperature is 60-80°C, the stirring speed is 400-600 rpm, and the mixing time is 25-35 minutes.

[0055] In specific implementation, the forming performance of the MIM feedstock is ensured by optimizing the selection of raw materials and the mixing process. In the selection of raw materials, 17-4PH stainless steel powder is selected, and the particle size is controlled in the range of 5-20 microns. This particle size range can ensure the bulk density of the powder and improve the mixing uniformity of the binder. The binder is a blend of paraffin and polyvinyl alcohol, with paraffin accounting for 55-65%. The main function of paraffin is to provide the flowability of the feedstock, ensuring that the feedstock can fill the complex structure of the mold cavity during injection. Polyvinyl alcohol accounts for 35-45%, which can improve the green strength of the feedstock and avoid damage to the green body during subsequent handling and placement. In the mixing process, the stainless steel powder and the binder are mixed in a mass ratio of 90:10-95:5, and the mixing temperature is controlled in the range of 60-80℃. This temperature range can make the binder in a molten state, reduce the mixing resistance, and avoid the decomposition of the binder caused by high temperature. The stirring speed is set to 400-600rpm, and the mixing time is 25-35 minutes, which ensures that the powder and the binder are fully mixed to form a MIM feedstock with uniform composition, avoiding defects such as material shortage and bubbles caused by uneven mixing during injection. By precisely controlling the material composition and mixing process, the present application solves the problems of poor flowability of the feedstock and insufficient green strength in the existing MIM process. The selection of 17-4PH stainless steel powder provides a basis for the subsequent excellent mechanical properties of the hinge. The specific ratio of the binder system makes the feedstock have good flowability and green strength, and the injection molding can completely fill the complex mold cavity of the mold. The breakage rate during green body handling is reduced to less than 1%. Uniform MIM feedstock can avoid defects such as cracking and bulging caused by composition segregation during subsequent debinding and sintering, providing protection for the quality of the finished hinge, improving material utilization, and further reducing manufacturing costs.

[0056] In some embodiments, in step S2, the number of mold cavities of the mold is 12-14, the mold material is H13 hot work die steel, and the mold is manufactured by electric spark machining and precision grinding process; the preset injection parameters include: machine tonnage 80-120T, front mold temperature 130-140℃, rear mold temperature 100-110℃, injection cycle 18-22s, injection pressure 80-100Bar, and injection speed 30-50mm / s; the green density of the hinge green body is ≥5.3g / cm³.

[0057] In a specific implementation, for the injection molding link, the hinge green part quality is guaranteed from two aspects of mold design and injection parameters. In the mold design, the number of mold cavities is set to 12-14, which is suitable for the batch production demand of small folding mobile phone hinges and improves the unit time output; the mold material is selected from H13 hot work die steel, which has excellent high temperature hardness and wear resistance, can withstand temperature changes and mechanical wear during long-term injection process, and prolongs the service life of the mold; the mold manufacturing adopts electric spark machining and precision grinding process to ensure the size accuracy and surface finish of the mold cavity, laying a foundation for the accuracy of the hinge green part. In the injection parameters, the tonnage of the machine is selected as 80-120T, which matches the molding demand of the hinge green part, avoids damage to the mold due to excessive tonnage, or incomplete molding due to insufficient tonnage; the temperature of the front mold is controlled at 130-140℃, and the temperature of the rear mold is controlled at 100-110℃, which ensures the uniform flow and rapid solidification of the feed material in the mold through temperature difference control, and prevents the green part from sticking to the mold; the injection cycle is 18-22s, the injection pressure is 80-100Bar, and the injection speed is 30-50mm / s, which makes the feed material fill the mold cavity with stable pressure and speed within the specified time, ensures that the green part density is greater than or equal to 5.3g / cm³, and avoids the existence of pores in the green part. Through the optimization of mold design and injection parameters, the accuracy and production efficiency of the hinge green part are effectively improved. The application of H13 hot work die steel makes the mold life increase to 80-100 thousand times, reduces the mold replacement frequency and cost, and meets the technical demand for mold design optimization; the multi-cavity design combined with reasonable injection parameters can produce 5000-10000 pieces per shift, and the production efficiency is significantly improved; the green part density is greater than or equal to 5.3g / cm³, which ensures that the blank body is not easy to deform during subsequent debinding and sintering process, provides guarantee for the size accuracy and mechanical properties of the hinge finished product, reduces the scrap rate caused by green part quality problems, further reduces the comprehensive manufacturing cost, and improves the market competitiveness of enterprise products.

[0058] In some embodiments, in step S3, the size of the ceramic plate is The ceramic plate is cleaned with a brush before use to remove dirt and dust from the surface; the preset distance includes a row distance of 1-3mm and a column distance of 1-3mm, each ceramic plate is placed with 77-117 hinge green parts, and the directions of all the green parts are consistent; the red plane of the hinge green part faces downward and is attached to the surface of the ceramic plate.

[0059] In a specific implementation, for the positioning of the swing piece, the stability of the subsequent debinding and sintering process is ensured through carrier selection and swing specification. In carrier selection, a ceramic plate with specifications of 115*100*3mm is selected. This ceramic plate has the characteristics of low thermal expansion coefficient and is not easy to deform in the high-temperature environment of debinding and sintering, which can avoid the position deviation of the green body caused by carrier deformation. Before use, the ceramic plate is cleaned with a brush to remove dirt and dust from the surface, preventing impurities from adhering to the surface of the green body and affecting the surface quality and performance of the hinge product. In the placement specification, the placement interval is set to 1-3mm in row and 1-3mm in column. This interval can ensure that each ceramic plate is placed with 77-117 green bodies, improving space utilization, and also ensures that there is enough space between the green bodies to allow the decomposition products of the binder to be discharged smoothly during the debinding process and the heat to be evenly transmitted during the sintering process. At the same time, all green bodies are required to be placed in the same direction, with the red plane of the green body facing down and adhering to the surface of the ceramic plate, ensuring that each green body is subjected to uniform stress and heat during the hot working process, and avoiding uneven forming caused by different placements. Through reasonable swing positioning design, the problem of green body deformation and uneven heating during debinding and sintering is solved. The application of low-expansion ceramic plates effectively controls the deformation of the carrier, and the position deviation rate of the green body is reduced to below 0.5%. The surface cleaning step avoids the introduction of impurities, and the surface defect rate of the hinge product is significantly reduced. The standard placement interval and direction ensure that the green body is thoroughly debound and evenly sintered, reducing sintering cracking caused by incomplete debinding and size out-of-tolerance caused by uneven heating, meeting the target of part size precision meeting the use requirements. At the same time, the space utilization of the ceramic plate is improved, the energy consumption and cost of the hot working link are reduced, and the requirements of process optimization and cost control are realized.

[0060] In some embodiments, in step S4, the preset debinding program includes: debinding temperature 300-400℃, acid passing time 470-530 minutes, acid passing amount 2.5-3.5g / min, and cleaning time 85-95 minutes; after the debinding treatment, the debinding rate is >7.2%, and the green body is verified to be not debound by destructive experiment, which is to extract 1-2 green bodies from the middle layer of the innermost side of the debinding furnace, and observe the internal state by slowly kneading manually.

[0061] In a specific implementation, for the debinding process, a custom debinding program and detection means are used to ensure debinding effect. In the debinding program design, the debinding temperature is set to 300-400℃, which can make the binder fully decompose and avoid the deformation of the blank due to overheating; the pickling time is 470-530 minutes, and the pickling amount is 2.5-3.5 g / min, which can accelerate the discharge of the binder decomposition products through the auxiliary action of organic acid and improve the debinding efficiency; the cleaning time is 85-95 minutes, which can remove the residual acid and binder fragments on the surface of the blank to prevent impurity defects during subsequent sintering. In the debinding effect detection, the debinding rate is set to be greater than 7.2%, which can ensure that most of the binder in the blank is removed; at the same time, destructive testing is used for verification, 1-2 blanks are extracted from the middle layer of the inner side of the debinding furnace, and the internal state is observed after being slowly kneaded by hand, if there is no un-debinding green body (un-debinding green body has a loose structure), it is determined that the debinding is qualified, which can effectively check the debinding uniformity of the blanks at different positions in the furnace, and avoid incomplete local debinding due to temperature and airflow differences in the furnace. Through optimization of the debinding program and strict detection, the present application solves the problems of incomplete debinding and poor debinding uniformity in the existing MIM process. The customized debinding parameters make the debinding rate stable at more than 7.2%, and the residual amount of the binder is greatly reduced, which effectively avoids the defects such as cracking and bulging of the blank caused by the expansion of the residual binder during the subsequent sintering process, and improves the qualified rate of the hinge product; the application of destructive testing ensures that the debinding quality of all blanks in the furnace is consistent, reduces the batch waste caused by local debinding problems, and at the same time, the reasonable pickling and cleaning time design avoids energy waste and blank damage under the premise of ensuring debinding effect, so that the research and development goals of process optimization and cost control are realized, and a good foundation is laid for subsequent sintering densification.

[0062] In some embodiments, in step S5, the preset sintering program includes: a sintering temperature of 1300-1350℃, a heating rate of 4-6℃ / min, a holding time of 1.5-2.5 hours, and a vacuum degree in the sintering furnace of ; the sintered density of the densified hinge semi-finished product is ≥7.6 g / cm³, the single weight is 0.24-1.75 g, and the appearance has no sintering, gray, material shortage, cracking and material sticking defects.

[0063] In a specific implementation, for the sintering densification link, the performance of the hinge blank is improved through precise sintering parameter control and quality control. In the sintering parameter design, the sintering temperature is set to 1300-1350℃, which can make the stainless steel powder particles fully diffuse and combine to achieve a high degree of densification, while avoiding overheating of the blank, deformation; the heating rate is 4-6℃ / min, slow heating can reduce the thermal stress generated inside the blank due to temperature difference, preventing cracking; the holding time is 1.5-2.5 hours to ensure that the powder particles fully combine and improve the mechanical properties of the blank; the vacuum degree in the sintering furnace , the vacuum environment can avoid oxidation of the blank at high temperature, ensuring the surface quality and corrosion resistance of the hinge. In terms of quality control, the density after sintering is set to ≥7.6g / cm³ to ensure that the blank has excellent mechanical properties; the single weight control is 0.24-1.75g to meet the lightweight requirements of foldable mobile phones; at the same time, strict requirements are placed on the appearance, without burning, gray, material shortage, cracking and sticking defects, to ensure that the finished product appearance meets the standards. The present application significantly improves the mechanical properties and appearance quality of the hinge product by optimizing the sintering parameters and quality control. The density after sintering is ≥7.6g / cm³, which makes the hinge have high strength and hardness, the fatigue life is >100,000 times of folding, the vacuum environment sintering effectively avoids oxidation, the hinge surface does not need additional rust removal treatment, reducing the subsequent processing cost; strict appearance control makes the finished product appearance defect rate <1%, improving the product market competitiveness; at the same time, the lightweight single weight design meets the requirements of foldable mobile phones for part weight, helping enterprises to launch more market-attractive products, and promoting the technical progress of the MIM process in the field of foldable smart phone manufacturing.

[0064] In some embodiments, in step S6, the parameters of the magnetic force polishing process include: the polishing needle specification is , the polishing liquid addition amount is 450-550mL, the polishing rotation speed is 100-120rpm, and the total polishing time is 14-16 minutes, wherein the left rotation time is 6-8 minutes and the right rotation time is 8-10 minutes; the drying parameters include: the drying temperature is 115-135℃, the drying time is 4-6 minutes, and the surface of the semi-finished product after drying is free of dirt, water stains, rust and damage.

[0065] In a specific implementation, for the magnetic force polishing and drying link, the surface quality of the hinge is optimized and rust is prevented through customized polishing process and drying parameters. In the magnetic force polishing process, the The polishing needle of the specification can penetrate into the tiny gap and complex structure of the hinge, remove the burrs and scale after sintering, the polishing liquid is added in an amount of 450-550 mL, which provides lubrication and cleaning effect for the polishing process, and improves the polishing effect, the polishing rotation speed is 100-120 rpm, which ensures that the polishing needle has enough grinding force and avoids deformation of the hinge due to too high rotation speed, and the total polishing time is 14-16 minutes, including left rotation for 6-8 minutes and right rotation for 8-10 minutes, bidirectional polishing can make the force on each surface of the hinge uniform, and avoid local over-grinding or insufficient grinding caused by unidirectional polishing. In the drying process, the drying temperature is set to 115-135 DEG C, which can quickly evaporate the moisture on the surface of the hinge, and avoid oxidation of the hinge surface caused by too high temperature; the drying time is 4-6 minutes, which ensures that the moisture is completely evaporated and the structure of the hinge is not damaged; finally, the surface of the semi-finished product after drying is free of dirt, water stains, rust and damage, and meets the appearance quality requirements. The surface quality and corrosion resistance of the finished hinge are effectively improved through the optimization of the magnetic polishing and drying process. The customized polishing parameters can completely remove the sintering burrs and scale, the surface roughness of the hinge is reduced, the hand feeling and appearance are significantly improved, and the surface quality of the parts meets the use requirements; the bidirectional polishing design ensures that each part of the hinge is polished uniformly, avoids local defects, and improves product consistency; the drying treatment at a specific temperature and time can completely remove the surface moisture, prevent rust in the subsequent storage and transportation process, and prolong the shelf life of the product; the whole process does not need complex manual operation, can realize automatic processing, improves production efficiency, reduces labor cost, and meets the requirements of production efficiency improvement and cost control.

[0066] In some embodiments, in step S7, the size precision detection adopts a caliper, a two-dimensional measuring instrument and a needle gauge, and the detection items include ball size, wherein the ball diameter tolerance is ±0.02-±0.03 mm, the length size tolerance is ±0.03-±0.07 mm, and the angle tolerance is ±1°; the appearance quality detection is full inspection, which screens the semi-finished products without scratches, scratches, material defects, bulges and sintering cracks; the mechanical property detection includes hardness detection, and the hardness is greater than or equal to 30HRC.

[0067] In specific implementation, for the full inspection test link, qualified products are screened through multi-dimensional detection means and clear indicators to ensure the quality of products leaving the factory. In size precision detection, professional detection tools such as calipers, two-dimensional measuring instruments and needle gauges are used, among which calipers are used for preliminary measurement of conventional sizes, two-dimensional measuring instruments are used for accurate detection of complex sizes (such as ball size), and needle gauges are used for detection of small apertures; the ball diameter tolerance is set to ±0.02-±0.03mm, the length size tolerance is set to ±0.03-±0.07mm, and the angle tolerance is set to ±1°, so as to ensure that the hinge size meets the assembly requirements. In appearance quality detection, a full inspection method is adopted, and professional detection personnel are arranged to visually inspect each semi-finished product to screen out products without scratches, scratches, material defects, bulges and sintering cracks, so as to avoid appearance defect products flowing into the market. In mechanical property detection, hardness detection is mainly performed, and the hardness is set to ≥30HRC, which is detected by a Vickers hardness tester to ensure that the hinge has sufficient wear resistance and deformation resistance to meet the long-term use requirements of folding mobile phones. The present application builds a perfect quality control system through multi-dimensional full inspection test, effectively guaranteeing the quality of hinge finished products. The size precision detection adopts professional tools and clear tolerances to ensure the assembly compatibility of the hinge and other components of the folding mobile phone, reduce the assembly failure rate, and meet the target of satisfying the use requirements of the size precision of the parts; the appearance full inspection can prevent appearance defect products from leaving the factory, improve user satisfaction and brand reputation; the hardness detection ensures that the hinge has excellent mechanical properties, prolongs the service life of the product, and meets the research and development requirements of the strength of the parts; at the same time, the full inspection test can timely find the abnormalities in the production process, facilitate the rapid adjustment of process parameters, reduce the generation of batch waste, reduce production cost, and improve the quality control level and market competitiveness of enterprises.

[0068] In some embodiments, in step S2, the mold is also provided with an independent cooling system, the front mold cooling waterway and the rear mold cooling waterway are designed separately, the cooling waterway diameter is 6-8mm, the cooling water flow rate is 1.5-2.5L / min; the residual material in the screw needs to be discharged before starting, the first 10 products are discarded after starting, and sampling is performed for first inspection after the product is stable.

[0069] In specific implementation, the mold cooling system design and the start-up process specification further guarantee the stability of injection molding and the quality of green body. In the design of mold cooling system, an independent cooling system is adopted, and the cooling water paths of the front mold and the rear mold are designed separately, so that the temperature of the front mold and the rear mold can be precisely controlled respectively, and the quality difference of green body caused by uneven mold temperature can be avoided. The diameter of the cooling water path is set to 6-8mm, which can not only ensure the stability of the cooling water flow rate (1.5-2.5L / min), but also avoid the risk of blockage caused by too thin water path, so as to ensure uniform and continuous cooling effect and stable mold temperature. In the specification of start-up process, the residual material in the screw needs to be discharged before starting, so as to prevent the mixing of different batches of feeding material and affect the quality of green body. The first 10 products are discarded after starting, because the mold temperature and injection parameters are not completely stable at the beginning of starting, and the green body of the first 10 products is prone to size deviation or appearance defect, and the discarded treatment can avoid the unqualified green body flowing into the subsequent link. After the product is stable, sampling is carried out for first inspection, and whether the indexes such as size, density and appearance of green body meet the standards is confirmed through the first inspection, so that the green body can enter batch production only after meeting the standards, and the consistency of the quality of subsequent green body is ensured. Through the optimization of mold cooling system and the specification of start-up process, the stability of injection molding process and the consistency of green body quality are significantly improved. The independent cooling system improves the temperature control precision of the front mold and the rear mold, and reduces the size fluctuation range of green body, which meets the target of stable size precision of parts. The reasonable design of cooling water path avoids water path blockage, reduces the frequency and cost of mold maintenance, prolongs the service life of mold, and meets the requirements of mold design optimization. The specification of start-up process effectively avoids the influence of residual material pollution and unstable green body at the beginning, improves the qualified rate of green body to more than 98%, reduces the waste rate of subsequent processes, and reduces the production cost. At the same time, the stable production process facilitates the realization of automatic batch production, improves the production efficiency, and helps enterprises to meet the large-scale supply demand of folding intelligent mobile phone market.

[0070] In some embodiments, in step S1, the 17-4PH stainless steel powder is subjected to vacuum drying treatment before mixing, the drying temperature is 80-100℃, and the drying time is 1-2 hours; and the binder is preheated to 50-70℃ before mixing, so as to reduce the mixing resistance and improve the uniformity of raw materials.

[0071] In a specific implementation, for the pretreatment link before material preparation, the mixing effect and feeding performance are improved by pretreating the stainless steel powder and the binder. In the pretreatment of the stainless steel powder, vacuum drying treatment is adopted, the drying temperature is set to 80-100 DEG C, the drying time is 1-2 hours, and the vacuum environment can quickly remove the adsorbed moisture in the powder, so that the moisture in the mixing process is avoided to form bubbles, resulting in the appearance of pores in the feeding; at the same time, the drying treatment can prevent the powder from caking, ensure the uniform dispersion of the powder particles, and improve the mixing efficiency with the binder. In the pretreatment of the binder, the binder is preheated to 50-70 DEG C, which can soften the binder, reduce the viscosity resistance during mixing, and facilitate the full fusion with the stainless steel powder; at the same time, the flowability of the preheated binder is improved, which can more uniformly wrap the powder particles, avoid the segregation of components during mixing, and ensure the uniformity of the feeding composition. The pretreatment of the powder and the binder effectively improves the quality and stability of the MIM feeding. The vacuum drying treatment of the stainless steel powder removes moisture and prevents caking, avoids the generation of bubbles in the feeding, reduces defects such as material shortage and pores during injection molding, improves the stability of green density, and meets the goal of uniform green body quality; the preheating treatment of the binder reduces the mixing resistance, improves the mixing uniformity, reduces the flowability fluctuation range of the feeding, ensures the consistency of the feeding in the injection process, reduces the green body quality difference caused by the fluctuation of the feeding performance, meets the research and development requirements of material formula optimization and improved molding performance; at the same time, the pretreatment link improves the mixing efficiency, shortens the mixing time, reduces the energy consumption cost, helps enterprises to improve production efficiency and product competitiveness, and lays a solid foundation for the stable operation of subsequent processes.

[0072] In order to more clearly understand the present application, the present application is further described as follows:

[0073] The present application provides a powder metallurgy small folding mobile phone hinge manufacturing method, and the specific technical solutions are as follows:

[0074] In the material preparation stage, 17-4PH stainless steel powder (particle size 5-20 μm) is selected as the base material, which has high strength and corrosion resistance, and is suitable for the long-term rotation requirement of the folding hinge; the binder adopts a paraffin-polyvinyl alcohol blending system, in which paraffin provides flowability and polyvinyl alcohol improves the feeding strength, and the mass ratio of the two is 55-65:35-45; the stainless steel powder and the binder are mixed in a mass ratio of 90:10-95:5, the mixing temperature is controlled at 60-80 DEG C, the stirring speed is 400-600 rpm, and the mixing time is 25-35 minutes, so as to ensure the uniformity of the raw materials and avoid the segregation of components in the subsequent injection.

[0075] Injection molding stage: the mold is made of H13 hot work die steel, which has excellent high-temperature hardness (hardness ≥45HRC at 600℃) and wear resistance, and the mold life can reach 80-100 thousand times; the number of mold cavities is designed to be 12-14 to match the batch production demand of small hinges; the injection machine is selected to be 80-120T tons, the front mold temperature is 130-140℃ (to ensure the flowability of the feed), the back mold temperature is 100-110℃ (to prevent the green body from sticking to the mold), the injection cycle is 18-22s, the injection pressure is 80-100Bar, and the injection speed is 30-50mm / s; the green density of the molded hinge green body is ≥5.3g / cm³, which ensures the stability of subsequent debinding and sintering.

[0076] Pendulum piece positioning stage: a high-purity alumina ceramic plate (low thermal expansion coefficient, small deformation during debinding and sintering) is selected , the surface is cleaned with a brush before use to avoid impurities affecting the quality of the green body; the hinge green body is placed at a row distance of 1-3mm and a column distance of 1-3mm, 77-117 pieces are placed on each ceramic plate, and the green body red plane is downward to ensure uniform heating during sintering; after the pendulum piece is placed, the ceramic plate is placed in a debinding special vehicle to avoid displacement of the green body during transportation.

[0077] Debinding treatment stage: adopt "gradient heating + acid auxiliary" debinding process (1# program), the debinding temperature gradually rises from room temperature to 300-400℃, the heating rate is 5℃ / min, to avoid cracking of the green body due to large temperature difference; the acid time is 470-530 minutes, the acid amount is 2.5-3.5g / min (organic acid solution, such as citric acid solution), to accelerate the decomposition of the binder; after debinding, wash with deionized water for 85-95 minutes to remove residual acid and binder fragments; the debinding rate needs to be >7.2%, and the destructive experiment is verified: 1-2 pieces of green body are taken from the middle layer of the debinding furnace, and are slowly kneaded by hand, and the cross section is observed without undetached green body (undetached green body is "white flocculent", and the cross section of qualified green body is uniform).

[0078] Sintering densification stage: adopt vacuum sintering furnace (vacuum degree ), to avoid oxidation of the hinge surface; the sintering program (2# program) is set as follows: the heating rate is 4-6℃ / min, the temperature rises to 1300-1350℃, and then the temperature is kept for 1.5-2.5 hours, and then the furnace is cooled to room temperature; this parameter is optimized for the slender structure of the hinge, which can reduce the bending deformation caused by thermal stress, and the density of the sintered hinge is ≥7.6g / cm³ (close to the theoretical density of 17-4PH stainless steel 7.75g / cm³), and the single weight is controlled within 0.24-1.75g, which meets the lightweight demand of small folding mobile phones.

[0079] magnetic force polishing drying stage: using a stainless steel polishing needle of , adding 450-550 mL of polishing solution (neutral surfactant solution), polishing rotation speed 100-120 rpm, total time 14-16 minutes (left rotation 6-8 minutes, right rotation 8-10 minutes), removing sintering burrs and oxide scale on the hinge surface by bidirectional polishing; after polishing, the hinge is placed in a mesh basket and placed in a 115-135°C oven for drying for 4-6 minutes to avoid rust caused by residual moisture.

[0080] full inspection test stage: size accuracy detection uses digital calipers (accuracy ±0.01 mm), two-dimensional measuring instrument (accuracy ±0.001 mm), and needle gauge to detect key ball size, such as ball diameter tolerance ±0.02-±0.03 mm, length size tolerance ±0.03-±0.07 mm, and angle tolerance ±1°; visual inspection is used for appearance quality to screen out products without scratches, scratches, material defects, bulges, and sintering cracks; Vickers hardness tester is used for mechanical property detection, with hardness ≥30HRC to ensure the hinge's wear resistance; unqualified products are classified and processed: slight appearance defects (such as small scratches) can be re-polished, and size out-of-tolerance or cracked products are directly scrapped.

[0081] finished product packaging stage: using colorless PE sealed bags (250×200×0.07mm) for packaging, 2500 pieces per bag, to prevent scratches on the hinge surface; then packed into brown KC3CA paper boxes (255×220×130mm), 5000 pieces per box, with foam cushioning layer inside the paper box; packaging labels indicate customer name, material number (such as GMMP0480 / 0481 / 0490 series), packaging date, and total number, and the stack height of the pallet during logistics is <8 layers, and the stack height is <7 layers when less than one stack, and it needs to be oil and water resistant to avoid damage during transportation.

[0082] To make the technical solutions of the present application clearer and easier to understand, the powder metallurgy small folding mobile phone hinge manufacturing method of the present application is described in detail below in conjunction with specific examples.

[0083] Example 1: GMMP0480 type folding mobile phone hinge manufacturing, as shown in Figure 2 and Figure 3 ;

[0084] Material preparation: 17-4PH stainless steel powder (particle size 10 μm, purity 99.9%) was selected, and the binder was a blend of paraffin (60wt%) and polyvinyl alcohol (40wt%); the stainless steel powder and the binder were mixed at a mass ratio of 92:8, the mixing temperature was 70°C, the stirring speed was 500 rpm, and the mixing time was 30 minutes, to prepare a uniform MIM feedstock. The feedstock fluidity test (melt flow indexer, 190°C / 2.16kg) showed that the melt flow index was 15g / 10min, meeting the injection requirements.

[0085] Injection molding: the mold was made of H13 hot work die steel, the number of mold cavities was 1-4, and the mold cavity precision was ±0.005mm; the injection machine was 80T, the front mold temperature was 135°C, the rear mold temperature was 105°C, the injection molding cycle was 20s, the injection pressure was 90Bar, and the injection speed was 40mm / s; the green density of the hinge green body after molding was 5.4g / cm³, and there were no missing material and bubble defects in the appearance.

[0086] Arrangement of the pendulum: the ceramic plate specifications , and the surface was cleaned with a nylon brush before use; the hinge green body was arranged at a row distance of 2mm and a column distance of 2mm, 117 pieces were placed on each ceramic plate, and the green red plane faced downward; after the pendulum was arranged, the ceramic plate was placed into a special debinding vehicle and pushed to the front of the debinding furnace to check that the green body was not displaced.

[0087] Debinding treatment: the debinding furnace used 1# program, the heating rate was 5°C / min, the final debinding temperature was 350°C, the pickling time was 500 minutes, the pickling amount was 3g / min (citric acid solution concentration 5wt%), and the cleaning time was 90 minutes; after debinding, the debinding rate was 7.5%, and 2 green bodies were taken out for destructive testing, and the cross section was uniform without un-debonded green body.

[0088] Sintering densification: the sintering furnace was a vacuum sintering furnace, the vacuum degree , and 2# program was used: the heating rate was 5°C / min, the holding temperature was 1320°C for 2 hours, and the furnace was cooled down; after sintering, the hinge single weight was 0.24±0.05g, the density was 7.7g / cm³, and there were no burning, cracking and other defects in the appearance.

[0089] Magnetic polishing and drying: the polishing needle specifications , the polishing liquid addition amount was 500mL, the rotation speed was 110rpm, the left rotation was 7 minutes, and the right rotation was 8 minutes; after polishing, it was placed into a 125°C oven for drying for 5 minutes, and the surface was bright without burrs.

[0090] Full inspection test: use the two-dimensional measuring instrument to detect the ball size, ball 5 (0.81±0.03mm), ball 10 (φ1.22±0.03mm) meet the requirements; appearance full inspection no scratch; hardness test is 32HRC; the qualified product rate is 98.5%.

[0091] Finished product packaging: use 250x200x0.07mm PE sealing bag packaging, 2500 pieces per bag, and then put into 255x220x130mm paper box, 5000 pieces per box, label "GMMP0480 rotating shaft" "packaging date 2025.8.9", stack 6 layers, cover with rain cloth when transportation.

[0092] Example 2: GMMP0481 type folding mobile phone hinge manufacturing, as shown in Figure 4 and Figure 5 ;

[0093] Material preparation: 17-4PH stainless steel powder particle size 15μm, binder is paraffin (55wt%) and polyvinyl alcohol (45wt%), mixing ratio 95:5, mixing temperature 65℃, stirring speed 450rpm, mixing time 28 minutes; feed melt index 14g / 10min.

[0094] Injection molding: mold cavity number 1-2, injection machine 100T, front mold temperature 130℃, back mold temperature 100℃, injection cycle 19s, injection pressure 85Bar; green density 5.3g / cm³.

[0095] Jewelry positioning: 77 pieces of ceramic plate are placed on each plate, row distance 1mm, column distance 1mm.

[0096] Degreasing treatment: degreasing temperature 380℃, acid passing time 480 minutes, acid passing amount 3.2g / min; degreasing rate 7.3%.

[0097] Sintering densification: sintering temperature 1340℃, holding time 1.8 hours; sintering density 7.65g / cm³, single weight 1.75±0.05g.

[0098] Subsequent process: polishing parameters are the same as example 1, the qualified product rate after full inspection is 97.8%, and the packaging method is the same as example 1.

[0099] Example 3: GMMP0490 type folding mobile phone hinge manufacturing, as shown in Figure 6 and Figure 7 ;

[0100] Material preparation: 17-4PH stainless steel powder particle size 8 μm, binder is paraffin (65wt%) and polyvinyl alcohol (35wt%), mixing ratio 90:10, mixing temperature 75℃, stirring speed 550rpm, mixing time 32 minutes; feeding melt index 16g / 10min.

[0101] Injection molding: mold cavity number 1-3, injection machine 120T, front mold temperature 140℃, back mold temperature 110℃, injection cycle 21s, injection pressure 95Bar; green density 5.5g / cm³.

[0102] Pendulum positioning: 104 pieces of ceramic plate are placed on each block, row distance 3mm, column distance 3mm.

[0103] Degreasing treatment: degreasing temperature 320℃, acid passing time 520 minutes, acid passing amount 2.8g / min; degreasing rate 7.4%.

[0104] Sintering densification: sintering temperature 1310℃, holding time 2.2 hours; sintering density 7.72g / cm³, single weight 0.44±0.03g.

[0105] Subsequent process: polishing parameters are the same as example 1, qualified product rate after full inspection 99.1%, packaging method is the same as example 1.

[0106] The above examples show that the manufacturing method of the present application can stably produce different models of small folding mobile phone hinges, and the product precision, strength and qualified rate meet the industry requirements, and is suitable for industrial batch application.

[0107] The above describes the technical solutions provided by the embodiments of the present application in detail. The principles and implementation manners of the embodiments of the present application are described by applying specific examples. The above example description is only applicable to help understand the principles of the embodiments of the present application; at the same time, for those skilled in the art, according to the embodiments of the present application, the specific implementation manners and application ranges will be changed; in summary, the content of the specification should not be understood as a limitation of the present application.

Claims

1. A method for manufacturing a powder metallurgy small folding mobile phone hinge, characterized in that, Includes the following steps: S1. Material preparation: Stainless steel powder and binder are mixed in a preset ratio to prepare MIM feed with preset flowability; S2, Injection Molding: The MIM feedstock is injected into a mold with a preset structure and molded under preset injection parameters to obtain a folding mobile phone hinge blank; S3. Ornament positioning: The hinge blanks are placed on the ceramic plate at a preset spacing and direction to form the assembly to be degreased; S4. Degreasing treatment: The component to be degreased is placed in a degreasing furnace, and the binder in the green body is removed by a preset degreasing program to obtain a degreased green body. S5. Sintering densification: The degreased green body is transferred to a sintering furnace and sintered at high temperature using a preset sintering program to obtain a densified hinge semi-finished product. S6. Magnetic polishing and drying: The densified hinge semi-finished product is subjected to magnetic polishing to remove surface defects, and then placed in an oven to dry, thereby obtaining the polished semi-finished product. S7. Full inspection test: The polished semi-finished products are tested for dimensional accuracy, appearance quality and mechanical properties, and qualified hinge products are selected. S8. Finished Product Packaging: The qualified hinge finished products are packaged according to the preset packaging method to complete the manufacturing process.

2. The method for manufacturing a powder metallurgy small folding mobile phone hinge according to claim 1, characterized in that: In step S1, the stainless steel powder is 17-4PH stainless steel powder with a particle size of 5-20μm; the binder is a paraffin-polyvinyl alcohol blend, wherein paraffin accounts for 55-65% of the total mass of the binder and polyvinyl alcohol accounts for 35-45%; the mixing mass ratio of the stainless steel powder to the binder is 90:10-95:5, the mixing temperature is 60-80℃, the stirring speed is 400-600rpm, and the mixing time is 25-35 minutes.

3. The method for manufacturing a powder metallurgy small folding mobile phone hinge according to claim 1, characterized in that: In step S2, the number of cavities in the mold is 12-14, the mold material is H13 hot work die steel, and the mold is manufactured using electrical discharge machining and precision grinding processes. The preset injection parameters include: machine tonnage 80-120T, front mold temperature 130-140℃, rear mold temperature 100-110℃, injection cycle 18-22s, injection pressure 80-100Bar, and injection speed 30-50mm / s. The green density of the hinge preform is ≥5.3g / cm³.

4. The method for manufacturing a powder metallurgy small folding mobile phone hinge according to claim 1, characterized in that: In step S3, the specifications of the ceramic plate are as follows: Before use, the ceramic plate is cleaned of dirt and dust by brushing; the preset spacing includes row spacing of 1-3mm and column spacing of 1-3mm, and each ceramic plate holds 77-117 hinge blanks, and all blanks are placed in the same direction; the red flat side of the hinge blank is attached to the surface of the ceramic plate.

5. The method for manufacturing a powder metallurgy small folding mobile phone hinge according to claim 1, characterized in that: In step S4, the preset degreasing program includes: degreasing temperature 300-400℃, acid passage time 470-530 minutes, acid passage rate 2.5-3.5g / min, and washing time 85-95 minutes; after the degreasing treatment, the degreasing rate is >7.2%, and the destructive test verifies that there are no undegreased green blanks. The destructive test involves extracting 1-2 green blanks from the innermost middle layer of the degreasing furnace and manually crushing them slowly to observe their internal state.

6. The method for manufacturing a powder metallurgy small folding mobile phone hinge according to claim 1, characterized in that: In step S5, the preset sintering program includes: sintering temperature 1300-1350℃, heating rate 4-6℃ / min, holding time 1.5-2.5 hours, and vacuum degree inside the sintering furnace. The sintered density of the densified hinge semi-finished product is ≥7.6g / cm³, the single weight is 0.24-1.75g, and the appearance is free from defects such as melting, graying, material shortage, cracking and sticking.

7. The method for manufacturing a powder metallurgy small folding mobile phone hinge according to claim 1, characterized in that: In step S6, the parameters of the magnetic polishing process include: the polishing needle specifications are... The polishing liquid addition is 450-550mL, the polishing speed is 100-120rpm, and the total polishing time is 14-16 minutes, including 6-8 minutes of left-hand rotation and 8-10 minutes of right-hand rotation. The drying parameters include: drying temperature 115-135℃, drying time 4-6 minutes, and the surface of the semi-finished product after drying is free of dirt, water stains, rust, and damage.

8. The method for manufacturing a powder metallurgy small folding mobile phone hinge according to claim 1, characterized in that: In step S7, the dimensional accuracy inspection uses calipers, a two-dimensional measuring instrument, and a pin gauge. The inspection items include the ball scale dimensions, where the diameter tolerance is ±0.02 - ±0.03 mm, the length tolerance is ±0.03 - ±0.07 mm, and the angle tolerance is ±1°. The appearance quality inspection is a full inspection, screening out semi-finished products without dents, scratches, missing materials, bulges, or sintering cracks. The mechanical property inspection includes hardness testing, with a hardness ≥30 HRC.

9. The method for manufacturing a powder metallurgy small folding mobile phone hinge according to claim 1, characterized in that: In step S2, the mold is also equipped with an independent cooling system. The cooling water channels of the front mold and the rear mold are designed separately. The diameter of the cooling water channel is 6-8mm and the cooling water flow rate is 1.5-2.5L / min. Before starting the machine, the residual material in the screw needs to be drained. After starting the machine, the first 10 mold products are discarded. After the products are stabilized, samples are taken for the first inspection.

10. The method for manufacturing a powder metallurgy small folding mobile phone hinge according to claim 2, characterized in that: In step S1, the 17-4PH stainless steel powder is vacuum dried before mixing at a temperature of 80-100℃ for 1-2 hours. The adhesive is preheated to 50-70°C before mixing.

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