Method for manufacturing an internal gear ring and internal gear ring

Abstract

The application discloses a kind of inner gear ring preparation method and inner gear ring, preparation method includes the following steps: S1, metal powder is mixed with polymer binder and is densified, granulation;S2, the inner gear ring green body of mould forming is relative to the structure basis top of inner gear ring finished product and is additionally provided with glue inlet end portion, bottom annular flange portion is additionally provided;Glue is injected from glue inlet end portion using top center glue inlet mode, and inner gear ring green body is obtained;S3, after forming, inner gear ring green body is placed in defatting furnace, and the binder inside inner gear ring green body is removed, and defatting blank is obtained;S4, defatting blank is placed in vacuum sintering furnace and is sintered, and sintered blank is obtained;S5, sintered blank is machined, and the glue inlet end portion of top and the annular flange portion of bottom are cut off;S6, finishing machining is carried out, and tooth profile, tooth pitch, roundness and hardness are detected.The application has the effects of improving inner gear ring production precision and reducing product oval deformation.

Description

Technical Field

[0001] This application relates to the field of powder metallurgy technology, and in particular to a method for preparing an internal gear ring and the internal gear ring itself. Background Technology

[0002] Internal gear rings are widely used in precision reducers, power tools, intelligent transmission mechanisms, and other fields. These products require high tooth profile accuracy, good roundness, dense microstructure, and uniform mechanical properties. Currently, small and medium-sized precision internal gear rings are often manufactured using metal powder injection molding (MIM) technology. MIM technology offers advantages such as high material utilization, strong ability to mold complex structures, and low cost for mass production.

[0003] Existing traditional MIM (Metal Injection Molding) internal gear ring designs typically employ a through-hole green body structure, which presents significant technical drawbacks in the manufacturing process: The glue injection method is limited; traditional internal gear rings use single-point side injection, resulting in an asymmetrical feed flow path and noticeable filling timing discrepancies. Filling is faster and at higher pressure near the gate, while filling is delayed and pressure decay is severe in the internal gear areas further away from the gate, leading to defects such as insufficient material at the tooth tip, burrs at the tooth root, and large tooth pitch deviations. During the sintering stage, the cylindrical green body is suspended at the bottom without stable support, making it prone to elliptical deformation due to its own weight and shrinkage stress under high temperatures, further reducing the accuracy of the internal gear ring and product yield.

[0004] In summary, existing traditional manufacturing processes have technical shortcomings such as uneven glue application, poor tooth profile accuracy, and large deformation, making it difficult to meet the requirements for stable mass production of high-precision internal gear rings. Summary of the Invention

[0005] To improve the manufacturing accuracy of internal gear rings and reduce elliptical deformation of the products, this application provides a method for manufacturing internal gear rings and an internal gear ring itself.

[0006] Firstly, this application provides a method for preparing an internal gear ring, which adopts the following scheme:

[0007] A method for manufacturing an internal gear ring includes the following steps:

[0008] S1. Feed preparation: Metal powder and polymer binder are mixed and granulated to prepare MIM feed;

[0009] S2, Injection Molding: Based on the structure of the molded internal gear ring preform, an injection end is added to the top and an annular flange is added to the bottom; injection is performed from the injection end using a top center injection method to obtain the internal gear ring preform; the mold includes a sealing system for sealing the mold cavity, a vacuum pump, and an active exhaust vacuum valve, and S2 includes the following steps:

[0010] S21. The mold closes, and the sealing system takes effect;

[0011] S22. The control system issues a command to drive the active exhaust vacuum valve to open, connecting the vacuum pump and the mold cavity;

[0012] S23. The vacuum pump operates to extract the gas in the mold cavity to the set value.

[0013] S24, The control system commands the active exhaust vacuum valve to close, and then the molten MIM is fed into the mold cavity;

[0014] S25. Open the mold and remove the inner gear ring blank.

[0015] S3. Homogenized degreasing: The formed internal gear ring blank is placed in a degreasing furnace to remove the binder inside the internal gear ring blank and obtain a degreased blank with pores.

[0016] S4. High-temperature sintering: The degreased blank is placed in a vacuum sintering furnace for sintering, and the sintering shrinkage rate is controlled to obtain a high-density sintered blank.

[0017] S5. Post-processing removal: Machining the sintered blank to remove the top glue inlet end and the bottom annular flange part;

[0018] S6. Precision shaping and inspection: Perform finishing processes, inspect tooth profile, tooth pitch, roundness and hardness to obtain qualified high-precision internal gear ring finished products.

[0019] Optionally, in S2,

[0020] Optionally, in S24, a multi-stage injection process is adopted: first, filling is carried out at a first injection speed to prevent jetting; then, the cylinder wall area is filled at a second injection speed higher than the first injection speed; and finally, the tooth-shaped cavity is filled at a third injection speed higher than the second injection speed.

[0021] Optionally, in S2, the thickness of the annular flange portion is greater than the wall thickness of the internal gear ring.

[0022] Optionally, in S2, the mold has an exhaust groove on the annular flange, the exhaust groove has a depth of 0.05mm, and the gas in the mold cavity is discharged through the exhaust groove.

[0023] Optionally, in S3, the degreasing furnace has a rack for placing the inner gear ring blank, and the inner gear ring blank rotates uniformly inside the degreasing furnace with the rack, so that the catalyst gas contacts the inner gear ring blank in a uniform circumferential direction.

[0024] Optionally, in step S4, the degreased blank is placed in the vacuum sintering furnace with its top end face as the horizontal support reference.

[0025] Optionally, after step S25, compressed air is used to backflush out any residue in the flow channel.

[0026] Optionally, after removing the glue inlet face and the annular flange, the cumulative pitch deviation of the finished internal gear ring is ≤0.03mm, the roundness is ≤0.02mm, and the sintering density is ≥97% of the theoretical density.

[0027] By adopting the above solution

[0028] Secondly, this application provides an internal gear ring, which adopts the following technical solution:

[0029] An internal gear ring is manufactured using the aforementioned method for preparing internal gear rings.

[0030] In summary, this application includes at least one of the following beneficial technical effects:

[0031] 1. By introducing process-aiding structures into the mold design—namely, adding a glue inlet end to the top of the internal gear ring preform and adopting a top-center glue inlet method, and adding an annular flange at the bottom—the filling path of injection molding is optimized, and stable support is provided for the sintering process. This method also includes internal mixing and granulation to prepare MIM feedstock, degreasing to remove binders, vacuum sintering to obtain a high-density sintered preform, machining to remove auxiliary structures, and finishing and inspection. This effectively solves the technical shortcomings of traditional processes, such as uneven glue flow, poor tooth profile accuracy, and large deformation, resulting in high-precision finished internal gear rings.

[0032] 2. By pre-vacuuming the mold cavity before injection molding, the air resistance within the cavity is significantly reduced. This allows the molten MIM feedstock to flow more smoothly and evenly as it fills the mold cavity, effectively preventing gas from being trapped inside the product and forming voids or bubbles. The reduced pressure within the mold cavity helps the feedstock better fill complex structures such as the internal gear area, reducing material shortages. Simultaneously, the lower air resistance within the mold cavity improves the flowability of the feedstock, facilitating the formation of a denser and more uniform green body structure. Ultimately, this pre-vacuum injection molding process significantly improves the density and uniformity of the internal gear ring green body, thereby reducing uneven shrinkage and deformation caused by internal defects during subsequent sintering, ensuring the acquisition of high-precision, high-quality internal gear ring finished products.

[0033] 3. Through the multi-stage injection process described above, this phased and differentiated speed control strategy, combined with the cavity vacuum technology, enables the molten feed to fill the entire cavity more smoothly and evenly, especially in complex tooth profile areas. This significantly improves the molding accuracy and density uniformity of the internal gear ring blank, providing high-quality semi-finished products for subsequent sintering and machining, and ultimately helps to obtain high-precision, high-performance internal gear ring finished products. Attached Figure Description

[0034] Figure 1This is a schematic flowchart of the internal gear ring manufacturing method in an embodiment of this application;

[0035] Figure 2 This is a schematic diagram of the injection-molded internal gear ring green structure in an embodiment of this application;

[0036] Figure 3 This is a schematic diagram of the finished internal gear ring structure after removing the process auxiliary structures in the embodiments of this application.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1. Cylindrical body; 2. Internal tooth profile; 3. Glue inlet end; 4. Annular flange. Detailed Implementation

[0039] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0040] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0041] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0042] The present application will be further described in detail below with reference to the accompanying drawings.

[0043] Reference Figure 1 This application discloses a method for manufacturing an internal gear ring, comprising the following steps:

[0044] S1. Feed preparation: Metal powder and polymer binder are mixed and granulated to prepare MIM feed;

[0045] S2. Injection molding: The molded internal gear ring blank is structurally based on the finished internal gear ring, with an additional injection end at the top and an annular flange at the bottom; the internal gear ring blank is obtained by injection from the injection end using a top center injection method.

[0046] S3. Homogenized degreasing: The formed internal gear ring blank is placed in a degreasing furnace to remove the binder inside the internal gear ring blank and obtain a degreased blank with pores.

[0047] S4. High-temperature sintering: The degreased blank is placed in a vacuum sintering furnace for sintering, and the sintering shrinkage rate is controlled to obtain a high-density sintered blank.

[0048] S5. Post-processing removal: Machining the sintered blank to remove the top glue inlet end and the bottom annular flange part;

[0049] S6. Precision shaping and inspection: Perform finishing processes, inspect tooth profile, tooth pitch, roundness and hardness to obtain qualified high-precision internal gear ring finished products.

[0050] In step S1, the internal mixing of the metal powder and the polymer binder is carried out using a twin-screw extruder. The shearing and mixing action of the screws ensures that the powder and binder are uniformly mixed. Subsequently, the extrudate is cut into uniform particles by a pelletizer to prepare the MIM feedstock. In other embodiments, internal mixing can also be carried out using a kneader, where mixing is achieved through stirring and kneading, followed by crushing and sieving to obtain the feedstock of the desired particle size. The metal powder is stainless steel powder, and the polymer binder is polyoxymethylene (POM).

[0051] Reference Figure 2 and Figure 3 In step S2, the mold design adopts a traditional parting surface structure, and the mold cavity is precisely formed by CNC machining equipment. It is worth mentioning that the internal gear ring product in this embodiment includes a cylindrical body 1, with openings at both ends along the axial direction. The radial inner wall of the cylindrical body 1 has an internal gear profile 2 for transmission, which meshes with the external gear profile of the external spline shaft to achieve torque transmission. For ease of understanding, the two ends along the axial direction of the cylindrical body 1 are defined as the top and bottom, respectively. In this embodiment, during injection molding, the molten MIM feedstock is injected into the rubber from the top.

[0052] Reference Figure 2 and Figure 3Because the cylindrical body 1 has an opening in the central region at the top, without the addition of the injection end 3, top injection would only allow injection from both radial sides, resulting in poor injection flow. In this embodiment, the mold cavity is designed such that, relative to the finished internal gear ring, the injection-molded green internal gear ring has an additional injection end 3 at the top of the cylindrical body 1. The shape and size of the injection end 3 match the top opening of the cylindrical body 1, completely closing the top opening, and the injection end 3 corresponds to the gate position of the mold. During injection, a single-point injection method is used, injecting molten MIM material from the center point of the injection end 3 into the mold cavity until the cavity is completely filled, thus obtaining the green internal gear ring.

[0053] In step S3, the green internal gear ring is placed in a degreasing furnace. Under a nitrogen protective atmosphere, catalyst gas heated to 100–140°C is introduced into the degreasing furnace. The catalyst undergoes a depolymerization reaction with the POM molecular chains, decomposing them into gaseous formaldehyde. This reaction acts only on the POM binder and does not corrode the metal, thus ensuring the integrity of the green structure and obtaining a degreased green with uniform porosity.

[0054] In step S4, the degreased blank is placed stably on a sintering plate inside a vacuum sintering furnace. The furnace is evacuated and filled with an inert gas, such as argon, to provide a protective atmosphere. The sintering temperature is set to a single, constant temperature, such as 1200°C, and held for a period of time to promote the densification of the metal powder particles. By precisely controlling the sintering temperature and holding time, the sintering shrinkage rate can be controlled, ultimately obtaining a high-density sintered blank.

[0055] In step S5, the sintered blank is machined by turning. Using a lathe and cutting tool, the glue inlet end 3 at the top and the annular flange portion 4 at the bottom of the sintered blank are precisely removed. After removal, the size and shape of the sintered blank closely approximate the requirements of the final internal gear ring product.

[0056] In step S6, finishing processes are performed, including deburring the finished internal gear ring to eliminate minor burrs generated during machining. Subsequently, a gear measuring instrument is used to inspect the tooth profile and pitch of the internal gear ring, a roundness tester is used to check its roundness, and a Rockwell hardness tester is used to test its hardness. These tests ensure that the finished internal gear ring meets the required high precision.

[0057] The internal gear ring manufacturing method of this application optimizes the material flow path by adding a glue inlet end 3 at the top and using top center glue inlet during the molding of the internal gear ring blank, effectively avoiding material shortage and uneven filling problems in the internal gear area. At the same time, the addition of an annular flange part 4 at the bottom provides a stable support reference for the sintering process, significantly suppressing elliptical deformation caused by high-temperature sintering, thereby improving the tooth profile accuracy, roundness and product yield of the internal gear ring, and meeting the requirements for stable mass production of high-precision internal gear rings.

[0058] During injection molding, due to the rapid filling of the molten MIM feedstock, air in the mold cavity cannot be completely expelled in a very short time. This can easily lead to some gas being trapped inside the green body, forming voids or bubbles. These defects can cause uneven shrinkage, deformation, or even cracks in the product during subsequent sintering, seriously affecting the quality and precision of the finished internal gear ring.

[0059] Therefore, this application further proposes a method for manufacturing an internal gear ring, wherein in step S2, the mold includes a sealing system for sealing the mold cavity, a vacuum pump, and an active exhaust vacuum valve, and step S2 includes the following steps:

[0060] S21. The mold closes, and the sealing system takes effect;

[0061] S22. The control system issues a command to drive the active exhaust vacuum valve to open, connecting the vacuum pump and the mold cavity;

[0062] S23. The vacuum pump operates to extract the gas in the mold cavity to the set value.

[0063] S24, The control system commands the active exhaust vacuum valve to close, and then the molten MIM is fed into the mold cavity;

[0064] S25. Open the mold and remove the inner gear ring blank.

[0065] Specifically, step S2 includes the following operations: First, the mold closes, at which point the sealing system activates, ensuring isolation between the mold cavity and the external environment. The sealing system is made of silicone sealing rings, which are precisely installed on the parting surface of the mold or at the interface between the mold cavity and the outside. When the mold closes, these silicone sealing rings are compressed, creating a highly airtight environment around the mold cavity, effectively preventing external air from entering the mold cavity during injection. Then, the control system issues a command to open the active exhaust vacuum valve, thereby connecting the vacuum pump to the mold cavity. The active exhaust vacuum valve is a valve that can respond quickly and seal reliably, such as a solenoid valve or pneumatic valve. Its function is to establish or disconnect the air path connection between the mold cavity and the vacuum pump according to the command of the control system. Next, the vacuum pump starts working, extracting gas from the mold cavity to a set value. Its pumping rate and ultimate vacuum ensure that the pressure inside the mold cavity is reduced to the preset vacuum level before injection, minimizing the air content inside the mold cavity. Once the vacuum level inside the mold cavity reaches the preset value, the control system commands the active exhaust vacuum valve to close, disconnecting the mold cavity from the vacuum pump to maintain the vacuum state inside the mold cavity. Next, the molten MIM feedstock is injected into the mold cavity for injection molding. Finally, after the injection, holding pressure, and cooling processes are completed, the mold is opened, and the molded internal gear ring blank is removed.

[0066] By pre-vacuuming the mold cavity before injection molding, air resistance within the cavity is significantly reduced. This allows the molten MIM feedstock to flow more smoothly and evenly as it fills the cavity, effectively preventing gas from being trapped inside the product and forming voids or bubbles. The reduced pressure within the mold cavity helps the feedstock better fill complex structures such as the internal gear area, reducing material shortages. Simultaneously, the lower air resistance within the cavity improves the feedstock's flowability, facilitating the formation of a denser and more uniform green body structure. Ultimately, this pre-vacuum injection molding process significantly improves the density and uniformity of the internal gear ring green body, thereby reducing uneven shrinkage and deformation caused by internal defects during subsequent sintering, ensuring the production of high-precision, high-quality internal gear rings.

[0067] However, in metal injection molding, even if the mold cavity is evacuated, when the molten feed fills the complex cavity at high speed, especially the internal toothed ring with fine teeth, a single injection speed is difficult to meet the requirements of preventing jetting, efficiently filling large volume areas, and ensuring complete filling of the toothed cavity. This may lead to defects such as uneven flow, inconsistent density, or local underfilling inside the green blank, which in turn affects the accuracy and performance of the final product.

[0068] Therefore, this application further proposes that in S24, a multi-stage injection process is adopted: first, filling is carried out at a first injection speed to prevent jetting; then, the cylinder wall area is filled at a second injection speed higher than the first injection speed; and finally, the tooth-shaped cavity is filled at a third injection speed higher than the second injection speed.

[0069] Specifically, multi-stage injection molding refers to a control strategy that dynamically adjusts the injection speed during injection molding based on the flow characteristics of the molten material at different stages within the mold cavity and the cavity structure. Its core lies in dividing the entire filling process into multiple stages, each using a different injection speed to achieve the optimal filling effect. In the initial stage of injection molding, when the molten MIM feed first enters the mold cavity, if the injection speed is too high, the feed may rush into the cavity like a jet, forming a jet stream. This jet stream can easily lead to material folding, air bubble formation, or surface defects during subsequent filling. Therefore, using a relatively low initial injection speed for initial filling allows the feed to enter the mold cavity smoothly, in a piston-like flow manner, avoiding the generation of jet streams and ensuring the uniformity of the product's surface quality and internal structure. After the initial filling stage, when the feed smoothly enters the mold cavity and begins to fill the cylindrical body 1 area of ​​the internal gear ring preform, the injection speed is appropriately increased to improve filling efficiency and shorten the molding cycle. The second injection speed is higher than the first, thus quickly and effectively filling the larger volume areas of the internal gear ring preform while maintaining a stable flow front and preventing premature cooling and solidification of the material due to excessively low speed. The tooth cavities of internal gear rings typically have complex geometries and small cross-sectional dimensions, causing significant flow resistance to the molten feedstock when filling these areas. To ensure complete and uniform filling of the tooth cavities and avoid underfilling or porosity defects, a higher injection speed is used at the end of the filling process. The third injection speed, higher than the second, provides sufficient pressure and velocity to allow the feedstock to overcome flow resistance and rapidly fill all the fine tooth features, resulting in a high-precision, defect-free tooth profile.

[0070] Through the multi-stage injection process described above, this phased and differentiated speed control strategy, combined with the aforementioned cavity vacuum technology, enables the molten feed to fill the entire cavity more smoothly and evenly, especially in complex tooth profile areas. This significantly improves the molding accuracy and density uniformity of the internal gear ring blank, providing high-quality semi-finished products for subsequent sintering and machining, and ultimately helps to obtain high-precision, high-performance internal gear ring finished products.

[0071] In actual operation, when using injection molding, the molten MIM feedstock often experiences temperature drops in the initial feedstock or feedstock at the end of the filling process due to factors such as the mold cavity temperature being lower than the melt temperature and the long flow path. This results in poor flowability and may even lead to the formation of cold material. If this low-pressure, low-temperature, and poorly flowing low-density feedstock directly enters the cylinder wall area of ​​the internal gear ring, it may cause uneven product density, internal defects, or poor molding, affecting the quality and performance of the final internal gear ring product.

[0072] Therefore, this application further proposes that, in step S2, the thickness of the annular flange portion 4 is greater than the wall thickness of the internal gear ring.

[0073] The annular flange 4 is a process auxiliary structure added to the bottom of the internal gear ring preform. During injection molding, it is located at the end of the molten feed path. Its design considers its function as a cold slug trap and venting channel. The wall thickness of the internal gear ring refers to the thickness of the internal gear ring body structure, while the thickness of the annular flange 4 refers to its radial thickness. The thickness of the annular flange 4 is greater than the wall thickness of the internal gear ring, meaning that the radial dimension of this auxiliary structure is designed to be larger than the actual functional wall thickness of the internal gear ring. In this embodiment, the thickness of the annular flange 4 is 1.5-2 times the wall thickness. Its specific value can be optimized and adjusted according to the flow characteristics of the MIM feed, mold design, and the size requirements of the internal gear ring, so that the annular flange 4 forms a relatively large volume space that can effectively accommodate the low-quality feed generated during injection.

[0074] Specifically, the annular flange 4 is located at the end of the injection path. During injection, the feed material flows a long way from the top gate to the bottom annular flange 4. Overcoming frictional resistance, the pressure decreases from 100 MPa at the gate to only 30-50 MPa at the end. At the end of the filling stage, the feed material experiences the lowest pressure, and the gaps between powder particles are not yet compacted, resulting in a lower initial density than near the gate. The feed temperature (approximately 210°C) is much higher than the mold temperature (approximately 100°C). The longer the runner, the longer the contact time with the cold mold wall, the greater the temperature drop and the sharp increase in viscosity. By the time it reaches the end, the feed material has become very viscous, making further compaction between particles difficult. At the very end of the filling stage, the holding pressure has not yet begun, and the screw has not yet added material to the cavity. At this point, the feed material at the end has begun to cool and shrink, but without additional feed material, the green density of the inner gear ring at the end of the mold cavity is low. Since the annular flange 4 serves as the filling end of the mold cavity, these low-pressure, low-temperature, and poorly flowing feed materials will flow into the annular flange 4. After the holding pressure stage begins, the high-pressure feed material near the gate will continue to supply material to the cylinder wall and toothed area of ​​the cylindrical body 1, compressing the density of the critical areas to a sufficiently high level. The low-density feed material in the annular flange 4 will not flow back, thus avoiding contamination of the main product. As a process auxiliary structure, the annular flange 4 will be removed by CNC machining later, so that these low-density, defective feed materials will not affect the density of the cylinder wall and internal teeth of the cylindrical body 1, which are critical areas.

[0075] However, during the injection process, the gas in the mold cavity may not be fully expelled due to rapid filling, especially in complex tooth profile areas, which can easily lead to trapped air defects, affecting the quality of the green internal gear ring and the performance of the final product.

[0076] Therefore, this application further proposes that, in the above-mentioned S2 step, the mold has an exhaust groove in the annular flange portion 4, the exhaust groove depth is 0.05mm, and the gas in the mold cavity is discharged through the exhaust groove.

[0077] Specifically, the mold has an venting groove in the annular flange 4. The venting groove is a small channel in the mold used to expel air or volatile gases from the mold cavity. In this embodiment, the venting groove depth is 0.05 mm. Too shallow a depth may lead to poor venting, while too deep a depth may cause MIM feed material to overflow, forming flash. The 0.05 mm depth is an optimized value, ensuring effective gas expulsion while effectively preventing the overflow of high-viscosity MIM feed material. During injection molding, as the MIM feed material continuously fills the mold cavity, the gas inside is compressed and pushed towards the venting groove. It is worth noting that, compared to traditional molds that do not require pre-vacuuming of the mold cavity, the venting groove in this application is connected to a vacuum storage tank, which is also connected to a vacuum pump. The actual workflow is as follows: after mold closing, the active venting vacuum valve opens, and the vacuum pump operates at full speed to extract air from the mold cavity and the vacuum storage tank, establishing a negative pressure environment. At the start of injection, the active venting vacuum valve closes, cutting off the direct connection between the mold cavity and the vacuum pump. During injection molding, the vacuum gas reservoir acts like a water tank. During the short filling time, it maintains a low pressure. Residual gas compressed by the feed front is drawn into the vacuum gas reservoir through the venting channels, thus depressurizing the mold cavity. This allows the gas to escape smoothly from the mold cavity, preventing it from becoming trapped inside the green gear ring.

[0078] Through the above technical solution, a venting groove with a depth of 0.05mm is opened in the annular flange portion 4 of the mold, allowing gas in the mold cavity to be discharged through this venting groove, effectively solving the problem of trapped gas caused by insufficient gas discharge in the mold cavity during injection molding. Given that the annular flange portion 4 is a process auxiliary structure with relatively large height and thickness, it provides favorable conditions for opening a wider and more efficient venting channel. Compared to the smaller 0.01mm venting gap in traditional molds, the 0.05mm deep venting groove can significantly improve venting efficiency, ensuring that gas can be quickly and completely discharged when the molten MIM feed fills complex toothed cavities, thereby avoiding defects such as bubbles and voids. Combined with pre-vacuuming technology, the venting effect will be further enhanced, completely eliminating the risk of trapped gas.

[0079] In the traditional debinding process, if the green internal gear ring is placed statically in the debinding furnace, the catalyst gas is usually blown towards the green internal gear ring from a fixed direction, resulting in uneven contact between the catalyst gas and the green ring. This may lead to incomplete decomposition of the binder or inconsistent decomposition rates in different parts, which in turn causes uneven internal stress in the debinded green ring, and may even cause deformation or defects in the subsequent sintering process, affecting the quality and precision of the final finished internal gear ring.

[0080] Therefore, this application further proposes that, in step S3, the degreasing furnace has a rack for placing the inner gear ring blank, and the inner gear ring blank rotates uniformly inside the degreasing furnace with the rack, so that the catalyst gas contacts the inner gear ring blank in a uniform circumferential direction.

[0081] Specifically, the material rack inside the degreasing furnace primarily functions to support and position the internal gear ring green billet, ensuring it remains stably positioned within the catalyst gas environment during degreasing. During degreasing, the material rack moves circumferentially within the furnace at a constant angular velocity, synchronously rotating the internal gear ring green billet it carries. This uniform rotation ensures that all surfaces of the green billet come into even contact with the incoming catalyst gas during degreasing, effectively promoting uniform circumferential contact between the catalyst gas and the green billet surface. The rotational motion breaks up this inhomogeneity, ensuring that every part of the green billet receives sufficient catalyst gas within a similar timeframe.

[0082] Through the above technical solution, uniform contact between the green body and the catalyst gas is crucial for the synchronous decomposition of the binder. This helps ensure that the binder removal rate inside the green body remains consistent in the circumferential direction, thereby avoiding stress concentration and subsequent sintering deformation caused by uneven local debinding. Therefore, during the binder decomposition process, the residual injection stress inside the green body can be released more evenly, significantly reducing the risk of elliptical deformation, bending, or cracking of the debinded green body during subsequent sintering. Ultimately, this contributes to obtaining a high-density internal gear ring with high dimensional accuracy and stable geometry.

[0083] In the above-mentioned method for preparing internal gear rings, step S4 involves placing the degreased blank in a vacuum sintering furnace for sintering. However, as a thin-walled cylindrical structure, the internal gear ring is prone to shape deviations such as ellipticity and bending during high-temperature sintering due to its own weight and the plastic deformation of the material at high temperatures, thereby affecting the dimensional accuracy and performance of the final product.

[0084] In response, this application further proposes that, in step S4, the degreased blank is placed in the vacuum sintering furnace with its top end face as the horizontal support reference. Specifically, because the degreased blank has a certain porosity and relatively low structural strength, it is prone to deformation during high-temperature sintering. During the sintering process, the inside of the sintering furnace is not in an absolute vacuum environment, and there is a slight airflow disturbance inside the furnace; at the same time, the friction coefficient of the contact surface of the material rack used to support the degreased blank is uneven, and there are slight friction differences on the material rack plane. If the bottom annular flange 4 is placed flat, since the inner side of the bottom annular flange 4 is a hollow through-hole structure, the inner ring of the annular flange 4 has no solid support. During the high-temperature sintering softening stage, the shrinkage stress of the blank itself combined with the uneven friction of the material rack will cause the annular flange 4 to be pulled inward and shifted during the shrinkage process. The annular flange 4 is subjected to uneven force and shrinks and deforms towards the center, which can easily induce elliptical deformation of the entire blank, thereby destroying the roundness of the inner tooth ring and causing an increase in the deviation of tooth shape and tooth pitch.

[0085] Therefore, by inverting the degreased blank and using the closed end face of the glue-inlet side at the top of the blank as a horizontal support reference, the top end face is sealed by the glue-inlet end 3 into a complete solid closed end face. The overall stress is uniform and the structural rigidity is stronger. Compared with the hollow annular flange part 4, it can stably fit the material rack plane and weaken the local pulling effect caused by the inconsistent friction coefficient of the material rack. At the same time, after the blank is inverted, the bottom annular flange part 4 and the cylindrical body 1 are in a suspended state with no rigid support contact surface, avoiding the inward shrinkage elliptical defect caused by the inner suspension and uneven stress of the annular flange part 4. In addition, the inverted support method makes the gravity distribution of the blank uniform during the high-temperature shrinkage process. The axial shrinkage is not rigidly constrained, which can uniformly release the sintering shrinkage stress, further suppressing the undesirable deformation such as cylinder skewing and tooth offset. Ultimately, it significantly improves the roundness and tooth pitch accuracy of the internal gear ring after sintering, ensuring the dimensional stability of batch products.

[0086] In injection molding step S2, molten MIM feedstock is injected into the mold cavity to prepare the internal gear ring preform, and the preform is removed from the mold in step S25. In actual injection molding, to completely eliminate the risk of cavitation, the mold's venting valve may maintain a small gap for continuous evacuation, even during injection. However, although this small gap is much smaller than the diameter of the MIM feedstock powder particles, high-viscosity melt and solid powder can still form residues or cause localized blockages in the runners, especially near these small gaps, thus affecting the normal operation of the mold and the quality of subsequent products.

[0087] Therefore, this application further proposes that, after step S25, compressed air be used to backflush and remove the residue in the flow channel.

[0088] Specifically, compressed air backflushing refers to using high-pressure gas, such as compressed air, to blow into the mold runner from the outlet end or a pre-designed backflushing port in the opposite direction to the normal injection direction. This effectively peels off and removes MIM feed residue adhering to the runner walls. The backflushing pressure and duration can be precisely controlled according to the mold runner structure, the viscosity of the MIM feed, and the amount of residue to ensure thorough cleaning without damaging the mold. Residue in the runner mainly includes MIM feed that was not completely discharged during injection, cooled and solidified on the inner wall of the runner, and localized blockages that may form in the tiny gaps of the mold venting. If these residues are not removed in time, they will gradually accumulate, reducing the cross-sectional area of ​​the runner, affecting the flow rate and pressure stability of subsequent injections, and even completely blocking the runner, causing production interruptions. Compressed air backflushing can effectively remove these residues and keep the runner unobstructed.

[0089] Through the above technical solution, after the internal gear ring preform is removed from the mold in step S25, compressed air is immediately used to backflush and remove residues from the runner. This backflush operation can completely remove high-viscosity MIM feed residues containing solid powder from the runner, preventing them from solidifying and accumulating, thereby avoiding runner blockage. This ensures the smooth progress of subsequent injection molding processes and effectively avoids contamination or defects in the new product caused by residues.

[0090] This application further proposes that the top glue inlet end 3 and the bottom annular flange part 4 removed by machining in step S5 are both process auxiliary structures and do not belong to the functional structure of the finished product. The cumulative deviation of the tooth pitch of the finished internal gear ring after removal is ≤0.03mm, the roundness is ≤0.02mm, and the sintering density of the product is ≥97% of the theoretical density.

[0091] Specifically, the top injection end 3 and the bottom annular flange 4, which are removed by machining in step S5, are temporary structures specially designed to facilitate the smooth forming and sintering of the internal gear ring preform. The top injection end 3 is mainly used to optimize the injection path of the molten MIM feed, ensuring sufficient filling of the mold cavity, especially the internal gear area, and avoiding material shortage defects. The bottom annular flange 4 serves as a support surface during sintering, effectively preventing the internal gear ring from undergoing elliptical or bending deformation at high temperatures, and providing a stable positioning reference for subsequent machining. These structures do not play any functional role in the finished internal gear ring; their existence is solely to assist the manufacturing process, and therefore they are completely removed in step S5.

[0092] After removing the auxiliary structures, the finished internal gear ring must meet stringent quality standards. Among these, the cumulative pitch deviation refers to the cumulative difference between the actual and theoretical pitch between any two teeth on the entire gear ring. This parameter is a key indicator for measuring the accuracy and stability of gear transmission. A smaller cumulative pitch deviation means smoother gear meshing, higher transmission accuracy, and can effectively reduce transmission noise and wear, extending service life.

[0093] Roundness is a geometric tolerance that measures how close a part's cross-sectional shape is to an ideal circle. For internal gear rings, roundness directly affects their concentricity with mating parts and the uniformity of meshing. Excessive roundness can lead to unstable gear transmission, uneven stress, and even vibration and premature failure. Controlling roundness within 0.02mm ensures precise alignment and stable performance during assembly and operation.

[0094] The sintered density of a product is the ratio of the actual density of the material after sintering to its theoretical density. High sintered density indicates low internal porosity and tight grain bonding, thus endowing the internal gear ring with excellent mechanical properties such as high strength, high hardness, good wear resistance, and fatigue life. A density of 97% or higher than the theoretical density indicates that the sintering process has achieved high densification, effectively eliminating porosity in the green and degreased blanks, ensuring that the finished internal gear ring can withstand harsh operating conditions under high loads and long operating times.

[0095] This application also discloses an internal gear ring, which is manufactured using the aforementioned internal gear ring preparation method. This method involves mixing and granulating fine metal powder with a polymer binder to prepare an MIM feedstock, which is then injection molded using a mold with process-aided structures. The mold has an additional injection end 3 at the top and an annular flange 4 at the bottom, with injection from the injection end 3 via a top-center injection method. During injection molding, the mold can be equipped with a sealing system, a vacuum pump, and an active exhaust vacuum valve. The MIM feedstock is injected after the mold closes, the sealing system activates, the vacuum pump evacuates to a set value, and the active exhaust vacuum valve closes, thereby reducing mold cavity pressure and minimizing gas retention. The injection molding process can employ a multi-stage injection process: first, filling at a first injection speed to prevent jetting; then, filling the cylinder wall area at a second injection speed higher than the first; and finally, filling the toothed cavity at a third injection speed higher than the second, to optimize the filling effect. The thickness of the annular flange 4 can be designed to be greater than the cylinder wall thickness of the internal gear ring, serving as a cold slug trap at the filling end. A venting groove with a depth of 0.05 mm can be opened in the annular flange portion 4 of the mold to further discharge the gas in the mold cavity. The formed internal gear ring blank is placed in a debinding furnace to remove the internal binder and obtain a debinding blank with uniform porosity. The material rack inside the debinding furnace allows the internal gear ring blank to rotate at a uniform speed, ensuring uniform circumferential contact of the catalyst gas. Subsequently, the debinding blank is placed in a vacuum sintering furnace for sintering, controlling the sintering shrinkage rate to obtain a high-density sintered blank. During sintering, the debinding blank is placed with the bottom annular flange portion 4 as a horizontal support reference to suppress elliptical deformation caused by high-temperature sintering. After removing the internal gear ring blank, compressed air is used to backflush to remove the residue in the flow channel. Finally, the sintered blank is machined, the top glue inlet end 3 and the bottom annular flange portion 4 are removed, and finishing is performed. The tooth shape, tooth pitch, roundness and hardness are inspected to obtain a qualified high-precision internal gear ring finished product.

[0096] By employing the aforementioned method for preparing internal gear rings, the resulting finished internal gear rings effectively overcome defects caused by uneven filling, gas retention, and sintering deformation in traditional processes. Specifically, the design and application of the mold auxiliary structure, combined with vacuum-assisted injection and multi-stage injection processes, significantly improves the uniformity and density of MIM feeding, avoiding material shortages and porosity in the internal gear area. Simultaneously, the annular flange 4 serves as a sintering support reference, effectively suppressing elliptical deformation and bending during high-temperature sintering, ensuring the geometric stability of the product. Finally, through precise machining and finishing, the finished internal gear ring achieves high density and high precision, such as a cumulative pitch deviation ≤0.03mm, roundness ≤0.02mm, and a sintering density ≥97% of the theoretical density, thereby significantly improving the overall performance and service life of the internal gear ring.

[0097] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Identical components are represented by the same reference numerals. Therefore, all equivalent changes made to the structure, shape, and principle of this application should be included within the scope of protection of this application.

Claims

1. A method for manufacturing an internal gear ring, characterized in that, Includes the following steps: S1. Feed preparation: Metal powder and polymer binder are mixed and granulated to prepare MIM feed; S2, Injection Molding: Based on the structure of the molded internal gear ring preform, an injection end is added to the top and an annular flange is added to the bottom; injection is performed from the injection end using a top center injection method to obtain the internal gear ring preform; the mold includes a sealing system for sealing the mold cavity, a vacuum pump, and an active exhaust vacuum valve, and S2 includes the following steps: S21. The mold closes, and the sealing system takes effect; S22. The control system issues a command to drive the active exhaust vacuum valve to open, connecting the vacuum pump and the mold cavity; S23. The vacuum pump operates to extract the gas in the mold cavity to the set value. S24, The control system commands the active exhaust vacuum valve to close, and then the molten MIM is fed into the mold cavity; S25. Open the mold and remove the inner gear ring blank; S3. Homogenized degreasing: The formed internal gear ring blank is placed in a degreasing furnace to remove the binder inside the internal gear ring blank and obtain a degreased blank with pores. S4. High-temperature sintering: The degreased blank is placed in a vacuum sintering furnace for sintering, and the sintering shrinkage rate is controlled to obtain a high-density sintered blank. S5. Post-processing removal: Machining the sintered blank to remove the top glue inlet end and the bottom annular flange part; S6. Precision shaping and inspection: Perform finishing processes, inspect tooth profile, tooth pitch, roundness and hardness to obtain qualified high-precision internal gear ring finished products.

2. The method for manufacturing an internal gear ring according to claim 1, characterized in that, In S24, a multi-stage injection process is adopted: first, the cylinder wall area is filled at a first injection speed to prevent jetting; then, the cylinder wall area is filled at a second injection speed higher than the first injection speed; and finally, the tooth-shaped cavity is filled at a third injection speed higher than the second injection speed.

3. The method for manufacturing an internal gear ring according to claim 1, characterized in that, In S2, the thickness of the annular flange portion is greater than the thickness of the cylinder wall of the internal gear ring.

4. The method for manufacturing an internal gear ring according to claim 1, characterized in that, In S2, the mold has an exhaust groove on the annular flange, the depth of which is 0.05mm, and the gas in the mold cavity is discharged through the exhaust groove.

5. The method for manufacturing an internal gear ring according to claim 1, characterized in that, In S3, the degreasing furnace has a rack for placing the inner gear ring blank. The inner gear ring blank rotates at a constant speed inside the degreasing furnace with the rack, so that the catalyst gas contacts the inner gear ring blank in a uniform circumferential direction.

6. The method for manufacturing an internal gear ring according to claim 1, characterized in that, In step S4, the degreased blank is placed in the vacuum sintering furnace with its top end face as the horizontal support reference.

7. The method for manufacturing an internal gear ring according to claim 1, characterized in that, After step S25, compressed air is used to backflush out any residue in the flow channel.

8. The method for manufacturing an internal gear ring according to claim 1, characterized in that, After removing the glue inlet face and the annular flange, the cumulative deviation of the tooth pitch of the finished internal gear ring is ≤0.03mm, the roundness is ≤0.02mm, and the sintering density of the product is ≥97% of the theoretical density.

9. An internal gear ring, characterized in that: The internal gear ring is manufactured using the internal gear ring preparation method according to any one of claims 1-8.

Images