Multi-field linkage injection molding method of a magnet

Abstract

The application discloses a kind of multi-field linkage injection molding methods of magnet, it is related to injection molding technical field, the injection molding method of magnet is applied to the mold with adjustable magnetic field, the injection molding method of magnet includes: step S1: to the mold cavity injection powder material to form forming embryo;Wherein, injection pressure is between 50MPa to 100MPa, the temperature in the mold cavity is between 95 DEG C to 140 DEG C, while applying magnetic field to the mold cavity, and control magnetic field intensity gradually rises from initial setting intensity to target intensity;Step S2: the forming embryo is cooled;Step S3: the forming embryo after cooling is sequentially subjected to debinding treatment and sintering treatment, to obtain magnet.The injection molding method of the present application can prepare magnet with high magnetic performance, excellent mechanical strength and high dimensional stability, to improve the qualified rate of magnet after forming.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of injection molding, in particular to a multi-field linkage injection molding method of a magnet. BACKGROUND

[0002] In the magnet injection molding process adopted in the related art, the problem of coordinated control of multiple physical fields has not been effectively solved. Specifically, the magnet injection molding process is essentially a complex multiphase flow and solidification process of a magnet powder-binder melt under the action of a magnetic field, involving strong coupling of temperature field, flow field (injection force field) and magnetic field. However, the existing technology often lacks systematic coordinated control of the above multiple physical fields: on the one hand, mismatched process parameters will interfere with the preset orientation magnetic field, destroying the ordered arrangement of the magnetic powder; on the other hand, a static or single magnetic field cannot adapt to the dynamic flow of the material in the complex cavity during the injection process, resulting in significant differences in the orientation effect of the magnetic powder in different regions. The direct consequence of this lack of multiple physical field coordination is uneven filling and different orientation degrees in the magnet, which makes the green body prone to problems such as poor consistency of magnetic properties, dimensional deformation, etc. in subsequent forming and sintering, resulting in a low product qualification rate. SUMMARY

[0003] The main purpose of the present application is to provide a multi-field linkage injection molding method of a magnet, aiming to improve the qualification rate of the magnet after molding through the coordinated control between the temperature field, the injection force field and the magnetic field.

[0004] To achieve the above-mentioned purpose, the present application provides a multi-field linkage injection molding method of a magnet, applied to a mold with an adjustable magnetic field, the injection molding method of the magnet comprising:

[0005] Step S1: injecting a magnetic powder material into a mold cavity to form a molded embryo; wherein the injection pressure is between 50 MPa and 100 MPa, the temperature in the mold cavity is between 95℃ and 140℃, a magnetic field is applied to the mold cavity at the same time, and the magnetic field strength is gradually increased from an initial set strength to a target strength;

[0006] Step S2: cooling the molded embryo;

[0007] Step S3: sequentially performing a debinding treatment and a sintering treatment on the cooled molded embryo to obtain a magnet.

[0008] In an embodiment, before the step S1, the method further comprises:

[0009] Step S0: maintaining the magnetic field strength in the mold cavity at an initial set strength for a first set period of time, the initial set strength being 55% to 75% of the target strength.

[0010] In an embodiment, the step S1 comprises a first sub-step of injecting the magnetic powder material into the mold cavity for a second set period of time until filling to 30% of the volume of the mold cavity;

[0011] In the first sub-step, the magnetic powder material is injected into the mold cavity at a speed of 6 mm / s to 9 mm / s, and the magnetic field strength is gradually increased from the initial set strength to 75% to 82% of the target strength at a first rate.

[0012] In an embodiment, in the first sub-step, the first rate is set to be between 0.015 T / s to 0.035 T / s.

[0013] In an embodiment, the step S1 further comprises a second sub-step of continuing to inject the magnetic powder material into the mold cavity for a third set period of time until filling to 70% of the volume of the mold cavity;

[0014] In the second sub-step, the magnetic powder material is injected into the mold cavity at a speed of 9 mm / s to 12 mm / s, and the magnetic field strength is gradually increased from 75% to 82% of the target strength to the target strength at a second rate, which is smaller than the first rate.

[0015] In an embodiment, in the second sub-step, the second rate is set to be between 0.012 T / s to 0.025 T / s.

[0016] In an embodiment, the step S1 further comprises a third sub-step of continuing to inject the magnetic powder material into the mold cavity for a fourth preset period of time until the mold cavity is completely filled;

[0017] In the third sub-step, the magnetic powder material is injected into the mold cavity at a speed of 6 mm / s to 9 mm / s, and the magnetic field strength is maintained at the target strength.

[0018] In an embodiment, the step S1 further comprises a pressure maintaining step:

[0019] In a fifth preset period of time, the magnetic field strength is maintained at the target strength, and the mold cavity filled with the magnetic powder material is subjected to pressure maintaining.

[0020] In an embodiment, the step S2 comprises:

[0021] In the process of reducing the temperature of the shaped body from the first temperature value to the second temperature value, the magnetic field strength is gradually reduced from the target strength to the first set strength at a third rate;

[0022] during the process of reducing the temperature of the shaped body from the second temperature value to a third temperature value, the magnetic field strength is gradually reduced from the first set strength to a second set strength at a fourth rate;

[0023] wherein the fourth rate is less than the third rate.

[0024] In an embodiment, the mold cavity has a plurality of regions capable of independent temperature control, the plurality of regions comprising a first region, a second region, a third region and a fourth region, the first region corresponding to a main body portion of the shaped body, the second region corresponding to a thin-walled portion of the shaped body, the third region corresponding to a thin-rib portion of the shaped body, and the fourth region corresponding to a gate of the mold cavity.

[0025] In step S1, the temperature of the first region is controlled to maintain between 95℃ and 105℃, the temperature of the second region is controlled to maintain between 115℃ and 135℃, the temperature of the third region is controlled to maintain between 125℃ and 140℃, and the temperature of the fourth region is controlled to maintain between 105℃ and 120℃.

[0026] In the technical solution of the present application, the embryo is formed by injection under specific parameters through synergistic regulation of injection force field, temperature field and magnetic field. Specifically, under an injection pressure of 50MPa to 100MPa, the magnetic powder material is injected into a mold cavity at a temperature of 95℃ to 140℃ to form a shaped body, and a magnetic field with an initial strength gradually increasing to a target strength is applied synchronously to ensure the consistency of the orientation of the magnetic powder; then the shape and size precision of the embryo are fixed through a cooling process; finally, through a debinding and sintering process, the binder in the magnetic powder material is completely removed and the magnetic powder is densified, and finally a magnet with high magnetic performance, excellent mechanical strength and high dimensional stability is successfully prepared, thereby improving the qualified rate of the magnet after forming. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only show some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of the drawings shown.

[0028] Figure 1 a structural schematic diagram of an embodiment of the mold provided by the present application;

[0029] Figure 2 a structural schematic diagram of an embodiment of the Halbach array assembled in the mold provided by the present application; Figure 1

[0030] ​Figure 3 Fig. 1 is a schematic diagram of a cross-sectional structure of a Halbach array; Figure 2 Fig. 1 is a schematic diagram of a cross-sectional structure of a Halbach array;

[0031] Figure 4 Fig. 1 is a schematic diagram of a cross-sectional structure of a Halbach array;

[0032] Figure 5 Fig. 1 is a schematic diagram of a cross-sectional structure of a Halbach array; Figure 2 Fig. 1 is a schematic diagram of a cross-sectional structure of a Halbach array;

[0033] Figure 6 Fig. 1 is a schematic diagram of a cross-sectional structure of a Halbach array;

[0034] BRIEF DESCRIPTION OF THE DRAWINGS

[0035] 100, mold; 1, fixed mold; 2, movable mold; 3, coil; 200, Halbach array.

[0036] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0038] It should be noted that if the embodiments of the present application involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement condition, etc. between the components in a certain posture, and if the certain posture changes, the directional indications will also change accordingly.

[0039] In addition, if the description of "first", "second" and the like is involved in the embodiments of the present application, the description of "first", "second" and the like is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can be explicitly or implicitly included at least one of the features. In addition, if "and / or" or "and / or" appears throughout the text, it means that the three parallel schemes are included, for example, "A and / or B" includes A scheme, or B scheme, or A and B scheme. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the realization of ordinary skilled in the art, when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, and is not within the protection scope required by the present application.

[0040] In the magnet injection molding process adopted in the related art, the problem of coordinated control of multiple physical fields has not been effectively solved. Specifically, the magnet injection molding process is essentially a complex multiphase flow and solidification process of a magnetic powder-binder melt under the action of a magnetic field, involving strong coupling of temperature field, flow field (injection force field) and magnetic field. However, the existing technology often lacks systematic coordination of the above-mentioned multiple physical fields: on the one hand, mismatched process parameters will interfere with the preset orientation magnetic field, destroying the ordered arrangement of the magnetic powder; on the other hand, a static or single magnetic field cannot adapt to the dynamic flow of the material in the complex cavity during the injection process, resulting in significant differences in the orientation effect of the magnetic powder in different regions. The direct consequence of this lack of multiple physical field coordination is that the magnet is not uniformly filled and the orientation degree is not uniform, which makes the green body prone to problems such as poor consistency of magnetic properties, dimensional deformation, etc. in subsequent forming and sintering, resulting in a low product qualification rate.

[0041] First, the injection molding device applied by the injection molding method of the magnet proposed in the embodiments of the present application is described.

[0042] In some embodiments of the present application, the injection molding device includes a rack, an injection system, a mold system, a multi-field regulation system, a monitoring system, a control system and an automatic auxiliary system, which cooperate with each other to realize precise forming of complex structure magnets.

[0043] In some embodiments of the present application, the rack adopts a high-strength steel structure, including a base, a column, a beam and a workbench, for supporting various functional modules in the injection molding device. The base is internally provided with a damping device to reduce the influence of vibration on the forming precision of the magnet during injection; the workbench can be driven by a servo motor to move in three degrees of freedom, such as movement on X-axis, Y-axis and Z-axis, to facilitate the installation and positioning of the mold 100.

[0044] In some embodiments of the present application, the injection system comprises a barrel, a screw, a driving device and a feeding device, and is used for injecting the mixture of the rare earth iron-based alloy magnetic powder and the binder after being heated and plasticized into a mold cavity.

[0045] In some embodiments of the present application, the barrel adopts a bimetal bushing structure, the inner layer is a wear-resistant alloy, and the outer layer is provided with a partition heating device, so that the gradient temperature control of the barrel in the axial direction can be realized. The inner wall of the barrel is provided with a special spiral groove, which enhances the mixing and plasticizing effect of the mixture.

[0046] Specifically, the temperature control range of the partition heating device is between 60° and 300°, and the temperature fluctuation is stably controlled within ±1°C.

[0047] In some embodiments of the present application, the screw is a barrier type screw, the length-diameter ratio of which is between 18:1 and 25:1, and the compression ratio is between 2.5:1 and 4:1, so that the uniform plasticization and stable conveying of the mixture can be effectively realized. The screw is driven by a servo motor through a reduction box, the rotating speed of which can be adjusted within the range of 0 to 300 r / min, and the control precision is controlled within ±1 r / min.

[0048] In some embodiments of the present application, the driving device adopts an electro-hydraulic servo driving mode, the injection pressure can be adjusted within the range of 0 to 150 MPa, the injection speed can be adjusted within the range of 0.1 mm / s to 50 mm / s, and the holding pressure can be adjusted within the range of 0 to 120 MPa, so that the feeding of the mold cavity can be ensured to be stable.

[0049] In some embodiments of the present application, the feeding device is a loss-in-weight feeder, so that the feeding amount can be accurately controlled, and the control precision of the feeding device is controlled within ±0.2%.

[0050] In some embodiments of the present application, the mold system comprises a mold 100, a guide mechanism, an ejection mechanism and a cooling system, the mold 100 comprises a fixed mold 1 and a movable mold 2, and the fixed mold 1 and the movable mold 2 can form a molding cavity with a complex structure.

[0051] Please refer to Figure 1 In some embodiments of the present application, the mold 100 comprises the fixed mold 1 and the movable mold 2, the fixed mold 1 and the movable mold 2 are made of P20 mold steel, the fixed mold 1 and the movable mold 2 are combined to form a mold cavity, and the surface of the mold cavity is subjected to nitriding treatment to improve the hardness, wear resistance and service life. According to the processing requirements of the magnet product with a complex structure, the mold cavity can be designed as a multi-cavity and a special-shaped structure, and an optimized runner and gate system is provided to reduce the feeding flow resistance.

[0052] In some embodiments of the present application, the guide mechanism adopts a guide pillar and guide sleeve structure, and the cooperation precision is H7 / g6, so as to ensure the accurate clamping of the fixed mold 1 and the movable mold 2.

[0053] In some embodiments of the present application, the ejection mechanism adopts a hydraulic ejection mode, the ejection speed can be adjusted in the range of 0.5 mm / s to 20 mm / s, and the ejection stroke can be adjusted to ensure smooth removal of the molded embryo.

[0054] In some embodiments of the present application, the cooling system is integrated inside the mold 100 and adopts a spiral cooling water channel design. The cooling system adjusts the cooling water in a closed loop through a temperature control unit, and the water temperature is controlled in the range of 5℃ to 50℃, so as to realize precise control of the temperature of the mold 100, and the control accuracy can reach ±1℃.

[0055] In some embodiments of the present application, the multi-field regulation system includes a magnetic field generation system, a gradient temperature control system, and a precise force field control system to realize the coordinated regulation of the magnetic field, temperature field, and force field during the magnet injection molding process.

[0056] In some embodiments of the present application, the magnetic field generation system has two setting modes.

[0057] In an embodiment, the magnetic field generation system includes a Halbach array 200 assembled with the mold 100 to adjust the magnetic field strength in the mold cavity through the Halbach array 200.

[0058] In another embodiment, the magnetic field generation system includes a coil 3 arranged in the mold 100 to adjust the magnetic field strength in the mold cavity through the coil 3.

[0059] As shown in FIG. 1, the magnetic field generation system includes a Halbach array 200 and a coil 3. Figures 2-3 As shown in FIG. 1, the magnetic field generation system includes a Halbach array 200 and a coil 3.

[0060] As shown in FIG. 1, the magnetic field generation system includes a Halbach array 200 and a coil 3. Figure 4

[0061] In some embodiments of the present application, the gradient temperature control system includes a mold partition heating device, a barrel partition heating device, and a temperature monitoring unit.

[0062] As shown in FIG. 1, the magnetic field generation system includes a Halbach array 200 and a coil 3.

[0063] The barrel partition heating device adopts an aluminum casting heater and is divided into three regions of a feeding section, a compression section, and a metering section to realize gradient temperature control.

[0064] The feeding section refers to the starting region of the barrel and is mainly responsible for receiving and conveying materials.​

[0065] Compression section refers to the middle part of the barrel, mainly responsible for compaction, melting and compression of the material, realizing the phase change from solid to liquid.

[0066] Metering section refers to the last section of the material before leaving the barrel, mainly responsible for uniformization, pressurization and quantitative delivery of the material to the mold 100, and ensuring the accuracy of the injection amount.

[0067] The temperature monitoring unit adopts a thermocouple sensor with an accuracy of ±0.5℃, which collects the temperature data of the mold 100 and the barrel in real time and feeds back to the control system.

[0068] In some embodiments of the present application, the precise force field control system is linked with the driving device of the injection system, integrating three control modules of injection pressure control module, holding pressure control module and clamping force control module. Among them, the injection pressure control module realizes continuous and precise adjustment of pressure through an electro-hydraulic proportional valve; the holding pressure control module adopts a segmented strategy that can be adjusted in real time to adapt to the filling process; the clamping force control module relies on a servo motor driven elbow mechanism to ensure stable mold closing and prevent material overflow.

[0069] In some embodiments of the present application, the monitoring system includes a process parameter monitoring module and a product quality online monitoring module for real-time collection of key parameters and product quality information during the forming process.

[0070] The process parameter monitoring module includes pressure sensors, temperature sensors, displacement sensors, magnetic field sensors, etc., which can collect process parameters such as injection pressure, barrel temperature, mold temperature, screw displacement and magnetic field strength in real time, with a sampling frequency greater than or equal to 1000Hz.

[0071] Specifically, the measurement range of the pressure sensor is between 0 and 200MPa, with an accuracy of ±0.5%FS.

[0072] The temperature sensor includes thermocouples, infrared thermometers, etc., with a measurement accuracy of ±0.5℃.

[0073] The displacement sensor includes a grating ruler, with a measurement accuracy of ±0.001mm.

[0074] The magnetic field sensor includes a Hall sensor, with a measurement accuracy of ±0.005T.

[0075] The product quality detection module integrates an industrial camera and an image recognition system, which can detect the appearance size and surface quality of the formed blank in real time, with a detection accuracy of ±0.01mm, and can identify common defects such as material shortage, flash and cracks. At the same time, the product quality detection module also includes an online magnetic property detector, which can quickly detect the preliminary magnetic properties of the blank, with a detection time of less than or equal to 10s / piece.

[0076] In some embodiments of the present application, the automation auxiliary system comprises an automatic picking device, an automatic detection and sorting device, and a waste recycling device.

[0077] The automatic picking device adopts a multi-axis robot equipped with a visual positioning system, which can accurately identify the position of the molded blank, realize the automatic picking and placing of the molded blank, and the picking efficiency is greater than or equal to 10 pieces / min.

[0078] The automatic detection and sorting device cooperates with the online product quality monitoring module to automatically sort and stack the molded blanks that pass the detection, and mark and isolate the unqualified products.

[0079] The waste recycling device automatically collects, crushes and recycles the waste such as sprue and runner generated during the injection process. The incorporation ratio of recycled materials can be set through the control system to realize the recycling of resources.

[0080] Based on the above injection molding device, the present application also proposes a multi-field linkage injection molding method of a magnet. The multi-field linkage injection molding method of a magnet is applied to an adjustable magnetic field mold 100. The adjustable magnetic field mold 100 is as described above, and will not be repeated here.

[0081] Please refer to Figure 6 In some embodiments of the present application, the injection molding method comprises:

[0082] Step S1: injecting a magnetic powder material into a mold cavity to form a molded embryo; wherein the injection pressure is between 50 MPa and 100 MPa, the temperature in the mold cavity is between 95°C and 140°C, a magnetic field is applied to the mold cavity at the same time, and the magnetic field strength is gradually increased from an initial set strength to a target strength.

[0083] In step S1, the molded embryo is formed by injecting the magnetic powder material into the mold cavity at a temperature of 95°C to 140°C with an injection pressure of 50 MPa to 100 MPa, and a magnetic field with an initial strength gradually increasing to a target strength is applied at the same time. Therefore, the synergistic regulation among the injection force field, the temperature field and the magnetic field can be realized, the balance between the magnetic powder orientation effect and the solubility flow stability can be effectively achieved, the disturbance of high-speed magnetic field change to the solubility flow front can be avoided, the vortex can be prevented from destroying the magnetic powder arrangement, so that the magnetic powder can be ordered arranged along the easy axis direction of the product, and the magnetic powder orientation deviation can be reduced.

[0084] In some embodiments of the present application, the injection molding method further comprises:

[0085] Step S2: cooling treatment is performed on the molded embryo.

[0086] In step S2, the cooling treatment of the injection-molded molded body can fix the shape of the magnet, prevent defects, and ensure dimensional accuracy.

[0087] In the injection molding process, the magnet and the plastic magnetic powder material are in a molten state. If left to cool naturally, warping, deformation, or internal shrinkage may occur due to uneven shrinkage of different parts, which not only affects the appearance and assembly accuracy, but also leads to uneven distribution of magnetic properties. By controlling the cooling process, the molded body can be uniformly solidified, locking its final shape and internal structure, and achieving a higher mold cavity filling rate.

[0088] At the same time, the cooling treatment can also enable the magnet to achieve higher magnetic properties during secondary magnetization.

[0089] It should be noted that the secondary magnetization step is set after the sintering process step.

[0090] In some embodiments of the present application, the injection molding method further comprises:

[0091] Step S3: sequentially performing debinding and sintering treatment on the cooled molded body to obtain a magnet.

[0092] In step S3, debinding and sintering treatment of the cooled molded body can convert the mixed billet of plastic and metal powder into a dense and strong pure metal magnet. Deb integration is achieved by removing the plastic binder added during molding through heating or other methods, which clears the space for subsequent steps; then sintering is performed in a protective atmosphere much higher than the melting point of the metal, allowing the loose metal powder particles to diffuse and fuse at high temperatures, thus eliminating internal pores and forming a high-density microstructure to ensure excellent magnetic properties and mechanical strength of the magnet.

[0093] In summary, in the technical solution of the present application, the injection force field, temperature field, and magnetic field are synergistically regulated to form a body under specific parameters. Specifically, under an injection pressure of 50MPa to 100MPa, the magnetic powder material is injected into a mold cavity at a temperature of 95℃ to 140℃ to form a molded body, and a magnetic field with an initial strength gradually increasing to a target strength is applied simultaneously to ensure the consistency of the magnetic powder orientation; then the shape and dimensional accuracy of the body are fixed through a cooling process; finally, through debinding and sintering processes, the binder in the magnetic powder material is completely removed and the magnetic powder is densified, successfully preparing a magnet with high magnetic performance, excellent mechanical strength, and high dimensional stability to improve the yield of the molded magnet.

[0094] In some embodiments of the present application, the target strength is not greater than 1.6T.

[0095] Please refer to Figure 5 For example, Figure 5The magnetic induction intensity table of the Halbach array 200 is shown, and the curve shown can represent the surface magnetic induction intensity distribution of the permanent magnet. The magnetic induction intensity represented by the Y axis can be 1.6T, which is the target intensity in the present application.

[0096] In some embodiments of the present application, step S1 further includes:

[0097] Step S0: maintaining the magnetic field intensity in the mold cavity at an initial set intensity for a first set period of time, the initial set intensity being 55% to 75% of the target intensity.

[0098] In step S0, a stable magnetic field environment can be established in the mold cavity in advance before injecting the magnetic powder, to uniformly form a preliminary magnetic field atmosphere inside the mold cavity, reduce the hysteresis of the magnetic powder in response to the magnetic field in the subsequent injection filling process, and especially for the areas such as fine ribs of the product after forming, which are prone to insufficient orientation, the orientation willingness of the magnetic powder can be activated in advance to avoid the orientation disorder of the magnetic powder due to the delayed response during filling.

[0099] The initial set intensity is 55% to 75% of the target intensity of the adjustable magnetic field, i.e., the initial set intensity can be 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, or 75% of the target intensity of the adjustable magnetic field. The value of the initial set intensity is not limited to the listed proportion values, and other unlisted proportion values in this range are also applicable.

[0100] Specifically, taking the target intensity of the adjustable magnetic field as 1.5T as an example, the initial set intensity is controlled to be 65% of the target intensity, and the initial set intensity is 0.975T. In the first preset period of time, the intensity of the adjustable magnetic field is kept stable at 0.975T, and no magnetic field intensity adjustment is performed, to stabilize the magnetic field environment inside the mold cavity and uniformly form a preliminary magnetic field atmosphere inside the mold cavity, reduce the hysteresis of the magnetic powder in response to the magnetic field in the subsequent injection filling process, and especially for the areas such as fine ribs of the product after forming, which are prone to insufficient orientation, the orientation willingness of the magnetic powder can be activated in advance to avoid the orientation disorder of the magnetic powder due to the delayed response during filling.

[0101] In some embodiments of the present application, the first preset period of time is between 5S and 10S, to form a stable magnetic field environment inside the mold cavity and provide a uniform magnetic field basis for subsequent material filling.

[0102] The value of the first preset time period can be 5S, 5.5S, 6S, 6.5S, 7S, 7.5S, 8S, 8.5S, 9S, 9.5S, 10S. The value of the first preset time period is not limited to the listed ratio values, and other non-listed ratio values in this range are also applicable.

[0103] Specifically, the first preset time period is 8S.

[0104] In some embodiments of the present application, step S1 includes a first sub-step:

[0105] In the second set time period, the magnetic powder material is injected into the mold cavity until it is filled to 30% of the volume of the mold cavity.

[0106] In the first sub-step, the speed of injecting the magnetic powder material into the mold cavity is 6mm / s to 9mm / s, and the magnetic field strength is gradually increased from the initial set strength to 75% to 82% of the target strength of the adjustable magnetic field at a first rate.

[0107] In the first sub-step, since the magnetic field strength is gradually increased from the initial set strength to 75% to 82% of the target strength of the adjustable magnetic field, the change in the magnetic field strength is relatively slow, and since the injection speed is maintained at 6mm / s to 9mm / s, the speed of the magnetic powder material injected into the mold cavity is also relatively slow; wherein the slow rate of change of the magnetic field strength is suitable for the low-speed flow of the magnetic powder material solution, guiding the synchronous and smooth flow of the magnetic powder with the front of the magnetic powder material solution, avoiding the agglomeration of the magnetic powder due to the sudden increase in the magnetic field strength, and at the same time, the gradual increase in the magnetic field strength at this rate can ensure the preliminary ordered arrangement of the magnetic powder in the inlet and runner regions of the mold cavity, laying a good foundation for the orientation of the magnetic powder in the subsequent filling stage.

[0108] In the gradual increase of the initial set strength to 75% to 82% of the target strength of the adjustable magnetic field at a first rate, the initial set strength can be increased to 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82% of the target strength. Other non-listed ratio values in this range are also applicable.

[0109] It should be noted that the above injection speed is the speed of the screw of the injection system advancing in the barrel, which is positively correlated with the filling speed of the magnetic powder material into the mold cavity.

[0110] In some embodiments of the present application, the first rate is set to be between 0.015T / s and 0.035T / s; in this way, a slow change in the magnetic field strength is provided, avoiding the agglomeration of the magnetic powder due to the sudden increase in the magnetic field strength, and at the same time, the gradual increase in the magnetic field strength at this rate can ensure the preliminary ordered arrangement of the magnetic powder in the inlet and runner regions of the mold cavity, laying a good foundation for the orientation of the magnetic powder in the subsequent filling stage.

[0111] If the first rate is lower than 0.015T / s, the magnetic field strength changes too slowly, and the magnetic powder cannot be arranged along the magnetic field arrangement direction in time in the first sub-step, the magnetic field orientation efficiency is low, and the magnetic performance of the final obtained magnet product cannot meet the standard requirements.

[0112] If the first rate is greater than 0.035T / s, the magnetic field strength changes too fast, and the magnetic field mutation can make the magnetic powder agglomerate, destroy the material flowability, cause the mold cavity to be not filled fully, and the magnetic powder orientation is chaotic, so that the consistency of the magnetic performance of the final obtained magnet product is poor.

[0113] The first rate can be 0.015T / s, 0.016T / s, 0.017T / s, 0.018T / s, 0.019T / s, 0.020T / s, 0.021T / s, 0.022T / s, 0.023T / s, 0.024T / s, 0.025T / s, 0.026T / s, 0.027T / s, 0.028T / s, 0.029T / s, 0.030T / s, 0.031T / s, 0.032T / s, 0.033T / s, 0.034T / s, 0.035T / s; the value of the first rate is not limited to the listed ratio values, and other unlisted ratio values in the range are also applicable.

[0114] The length of the above-mentioned second set time period is flexibly adjusted according to the volume size of the mold cavity and the injection speed, so as to ensure that the magnetic powder material flows at low speed in the mold cavity.

[0115] Specifically, the length of the second set time period is 10s, the injection system advances the magnetic powder material solution to fill the mold cavity at a speed of between 6mm / s and 9mm / s, and the magnetic field strength gradually increases from 0.975T to between 81% and 82% of the target strength, that is, the magnetic field strength increases to 1.225T after the second set time period, and the adjustment rate is controlled at 0.025T / s; wherein the magnetic field strength change rate is matched with the low-speed flowing magnetic powder material solution, guides the magnetic powder to flow smoothly with the front edge of the magnetic powder material solution, avoids the agglomeration of the magnetic powder due to the sudden increase of the magnetic field strength, and at the same time, the gradual increase of the magnetic field strength at this rate can ensure the preliminary ordered arrangement of the magnetic powder at the inlet and flow channel area of the mold cavity, and lay a good foundation for the orientation of the magnetic powder in the subsequent filling stage.

[0116] It needs to be supplemented that the front edge of the magnetic powder material solution refers to the boundary of the solution at the forefront when the solution advances in the mold cavity.

[0117] In some embodiments of the present application, step S1 further comprises a second sub-step:

[0118] continuing to inject the magnetic powder material into the mold cavity until 70% of the volume of the mold cavity is filled;

[0119] In the second sub-step, the speed of injecting the magnetic powder material into the mold cavity is 9mm / s to 12mm / s, and the magnetic field strength is gradually increased from 75% to 82% of the target strength to the target strength at a second rate, which is less than the first rate.

[0120] In the second sub-step, the adjustment rate of the magnetic field needs to be reduced, that is, the rate of change of the magnetic field strength is adjusted from the first rate to the second rate in this stage, so as to balance the magnetic powder orientation effect and the melt flow stability of the magnetic powder material, avoid the high-speed magnetic field change interfering with the melt flow front of the magnetic powder material, and prevent the vortex phenomenon from destroying the arrangement of the magnetic powder. At this rate, the magnetic field strength can be continuously increased to strengthen the orientation of the magnetic powder, and the melt flow at a medium speed can be adapted to ensure that the magnetic powder in the key areas such as complex cavities and thin walls fully responds to the magnetic field and is orderly arranged along the easy axis direction of the product, thereby reducing the orientation deviation.

[0121] The length of the third set time period is flexibly adjusted according to the volume of the mold cavity and the injection speed, so as to ensure that the magnetic powder material flows at a medium speed in the mold cavity.

[0122] Specifically, the length of the third set time period is between 11S and 12S, the injection system advances the magnetic powder material solution to fill the mold cavity at a speed of 9mm / s to 12mm / s, the magnetic field strength is continuously increased from 1.225T to the target strength 1.5T, and the second rate is 0.023T / s. In this way, the magnetic powder orientation effect and the melt flow stability of the magnetic powder material are balanced, the high-speed magnetic field change is avoided to interfere with the melt flow front of the magnetic powder material, and the vortex phenomenon is prevented from destroying the arrangement of the magnetic powder. At this rate, the magnetic field strength can be continuously increased to strengthen the orientation of the magnetic powder, and the melt flow at a medium speed can be adapted to ensure that the magnetic powder in the key areas such as complex cavities and thin walls fully responds to the magnetic field and is orderly arranged along the easy axis direction of the product, thereby reducing the orientation deviation.

[0123] In some embodiments of the present application, the second rate is set to be between 0.012T / s and 0.025T / s, so as to continuously strengthen the orientation of the magnetic powder without interfering with the flow front of the solution due to the too fast change of the magnetic field.

[0124] If the second rate is less than 0.012T / s, the magnetic field strength is increased too slowly, so that the magnetic powder orientation driving force is insufficient, the magnetic powder cannot be fully arranged along the easy axis in the complex areas of the mold cavity, the pre-magnetization effect is poor, and the secondary magnetization and the product magnetic performance are affected.

[0125] If the second rate is higher than 0.025T / s, the magnetic field will change suddenly, which will interfere with the melt flow front, cause the magnetic powder to agglomerate, the filling to be unsaturated, and finally the magnetic performance consistency to be poor.

[0126] The second rate can be 0.012T / s, 0.013T / s, 0.014T / s, 0.015T / s, 0.016T / s, 0.017T / s, 0.018T / s, 0.019T / s, 0.020T / s, 0.021T / s, 0.022T / s, 0.023T / s, 0.024T / s, 0.025T / s. The value of the second rate is not limited to the listed ratio values, and other unlisted ratio values in this range are also applicable.

[0127] In some embodiments of the present application, step S1 further comprises a third sub-step:

[0128] In the fourth preset time period, the magnetic powder material is continuously injected into the mold cavity until the mold cavity is completely filled;

[0129] In the third sub-step, the speed of injecting the magnetic powder material into the mold cavity is 6mm / s to 9mm / s, and the magnetic field strength is maintained at the target strength.

[0130] In the third sub-step, by reducing the flow speed of the magnetic powder flow melt, the impact caused by the too fast speed of the magnetic powder flow melt when filling the end of the cavity is avoided, the constant strong magnetic field can keep the magnetic powder in the filled area in a stable orientation state, and at the same time ensure that the magnetic powder in the last filling area is fully oriented, avoid the different orientations of the magnetic powder in different areas caused by the fluctuation of the magnetic field strength, and ensure the uniformity of the magnetic performance of the entire product.

[0131] Specifically, the magnetic field strength is maintained at 1.5T.

[0132] It should be noted that the speed of injecting the magnetic powder material in the above is positively correlated with the injection pressure, so the control of the injection speed can realize the regulation and control of the injection pressure.

[0133] In some embodiments of the present application, step S1 further comprises a pressure maintaining step:

[0134] In the fifth preset time period, the magnetic field strength is maintained at the target strength, and the mold cavity filled with the magnetic powder material is pressure maintained.

[0135] In the pressure maintaining step, shrinkage and porosity defects of the green body can be prevented by feeding, while maintaining the magnetic powder orientation effect. The magnetic field strength is maintained at the target strength, constant and without adjustment. The constant high magnetic field can ensure that the magnetic powder does not deviate from the optimal orientation direction due to the change of melt pressure during the pressure maintaining process, and the orientation results of the early stage are stable, which lays a foundation for the orientation of the subsequent cooling and setting stage, and avoids the rebound of the magnetic powder orientation due to the decrease of the magnetic field strength, which affects the magnetic performance of the product.

[0136] In some embodiments of the present application, the fifth preset time period is between 5S and 12S.

[0137] If the length of the fifth preset time period is less than 5S, the risk of shrinkage and porosity of the formed green body increases, the magnetic field pressure maintaining time is short, the magnetic powder orientation effect is insufficient, and the product magnetic performance standard rate decreases.

[0138] If the length of the fifth preset time period is greater than 12S, the time consumption of the whole process increases, the production efficiency decreases, the internal stress of the formed green body concentrates, the deformation rate increases after cooling, and the size precision and magnetic performance consistency of the complex structure magnet are poor.

[0139] The value of the fifth preset time period can be 5S, 5.5S, 6S, 6.5S, 7S, 7.5S, 8S, 8.5S, 9S, 9.5S, 10S, 10.5S, 11S, 11.5S, 12S. The value of the fifth preset time period is not limited to the listed proportion values, and other unlisted proportion values in this range are also applicable.

[0140] In some embodiments of the present application, step S2 comprises:

[0141] During the process of reducing the temperature of the formed body from the first temperature value to the second temperature value, the magnetic field strength is gradually reduced from the target strength to the first set strength at a third rate;

[0142] During the process of reducing the temperature of the formed body from the second temperature value to the third temperature value, the magnetic field strength is gradually reduced from the first set strength to the second set strength at a fourth rate;

[0143] Wherein, the fourth rate is less than the third rate.

[0144] In step S2, the magnetic field strength is gradually reduced to avoid the deformation of the formed green body caused by the magnetic stress generated by the sudden change of the magnetic field, especially for complex and special structures. Slow and segmented change of the magnetic field can keep the structure of the formed green body stable during the cooling and shrinkage process, and the residual low strength magnetic field can prevent the orientation disorder of the magnetic powder caused by thermal motion during the cooling process, and ensure the stable magnetic performance of the final product.

[0145] In some embodiments of the present application, the second set strength is 10% of the target strength.

[0146] Specifically, the step S2 starts after the pressure maintaining ends, and is specifically divided into a temperature decreasing initial stage and a temperature decreasing middle-late stage.

[0147] In some embodiments of the present application, the first temperature value is between 130°C and 140°C.

[0148] In some embodiments of the present application, the third temperature value is between 50°C and 80°C.

[0149] The following is an example.

[0150] In the temperature decreasing initial stage, the temperature of the shaped body is decreased from the first temperature value 130°C to the second temperature value 90°C, and the magnetic field strength is decreased from the target strength 1.5T to the first set strength 0.6T at the third rate 0.078T / s.

[0151] In the temperature decreasing middle-late stage, the temperature of the shaped body is decreased from the second temperature value 90°C to the third temperature value 60°C, and the magnetic field strength is decreased from the first set strength 0.6T to the second set strength 0.15T at the fourth rate 0.072T / s.

[0152] In some embodiments of the present application, before the step of gradually decreasing the magnetic field strength from the target strength to the first set strength at the third rate in the process of decreasing the temperature of the shaped body from the first temperature value to the second temperature value, the method further comprises:

[0153] In the sixth preset time period, the magnetic field strength is maintained at the target strength.

[0154] In this way, the orientation structure of the magnetic powder can be further consolidated after the pressure maintaining step completely ends.

[0155] Specifically, the value of the sixth preset time period can be between 3S and 5S.

[0156] In some embodiments of the present application, during the process of reducing the temperature of the shaped body from the first temperature value to the second temperature value, the magnetic field strength is gradually reduced from the target strength to a first set strength at a third rate; during the process of reducing the temperature of the shaped body from the second temperature value to the third temperature value, the magnetic field strength is gradually reduced from the first set strength to a second set strength at a fourth rate, and the process time is between 10S and 15S, and the third rate and the fourth rate are both between 0.07T / s and 0.08T / s. This is because the presence of the magnetic field will produce a "magnetic viscosity" effect on the oriented magnetic powder, hindering its relaxation due to shrinkage caused by cooling. By gradually reducing the magnetic field strength and the increasing rigidity of the material, the magnetic stress can be gradually released, avoiding the rebound or deformation of the magnetic powder arrangement caused by the sudden disappearance of the external field, while continuing to guide the magnetic powder to complete the final orientation when there is still fine adjustment capability.

[0157] In some embodiments of the present application, after the step of gradually reducing the magnetic field strength from the first set strength to the second set strength during the process of reducing the temperature of the shaped body from the second temperature value to the third temperature value, the method further comprises:

[0158] gradually attenuating the magnetic field strength to zero within a seventh preset time period.

[0159] wherein the time of the seventh preset time period is between 5S and 10S, and the speed of the magnetic field attenuation is between 0.02T / s and 0.04T / s, so as to eliminate any residual magnetization force and ensure that the blank completes the final cooling in a state completely free of external field interference, preventing the generation of small anisotropic stress.

[0160] In some embodiments of the present application, the mold cavity has a plurality of regions capable of independent temperature control, and the plurality of regions include a first region, a second region, a third region, and a fourth region. The first region corresponds to the main body part of the shaped body, the second region corresponds to the thin-walled part of the shaped body, the third region corresponds to the fine rib part of the shaped body, and the fourth region corresponds to the gate of the mold cavity.

[0161] wherein the main body part refers to a structural part with a thickness not less than 3mm and a total volume accounting for more than 50% of the volume of the mold cavity;

[0162] The thin-walled part refers to a structural part with a thickness not greater than 2mm and a total volume accounting for less than 20% of the volume of the mold cavity;

[0163] The fine rib refers to a structure with a thickness not greater than 1.5mm and a height-depth ratio (i.e. the ratio of height to width) greater than 3, and the total volume of the structure satisfying this condition accounts for less than 25% of the volume of the mold cavity.

[0164] In some embodiments of the present application, in step S1, the temperature of the first region is controlled to be between 95℃ and 105℃, the temperature of the second region is controlled to be between 115℃ and 135℃, the temperature of the third region is controlled to be between 125℃ and 140℃, and the temperature of the fourth region is controlled to be between 105℃ and 120℃.

[0165] In this way, the temperature in the complex region of the mold cavity is properly increased to reduce the viscosity of the melt, and the injection force field control and the magnetic field control ensure that the melt is filled sufficiently everywhere in the mold cavity.

[0166] For example, the thin-walled part of the product, the thin rib, and the high-depth-ratio region structure are relatively complex, and the melt is not easy to flow in these places. Therefore, the temperature of these parts is increased, that is, the temperature of the second region and the third region is greater than that of the first region, so that the viscosity of the melt corresponding to the second region and the third region is reduced to ensure that the melt is filled sufficiently in the second region and the third region.

[0167] In addition, by controlling the temperature of the fourth region to be between 105℃ and 120℃, the melt in the region of the mold cavity is prevented from being cooled too early to cause the gate to be blocked.

[0168] The temperature value of the first region can be 95℃, 96℃, 97℃, 98℃, 99℃, 100℃, 101℃, 102℃, 103℃, 104℃, or 105℃. The temperature value of the first region is not limited to the listed proportion values, and other proportion values not listed in this range are also applicable.

[0169] The temperature value of the second region can be 115℃, 116℃, 117℃, 118℃, 119℃, 120℃, 121℃, 122℃, 123℃, 124℃, 125℃, 126℃, 127℃, 128℃, 129℃, 130℃, 131℃, 132℃, 133℃, 134℃, or 135℃. The temperature value of the second region is not limited to the listed proportion values, and other proportion values not listed in this range are also applicable.

[0170] The temperature value of the third region can be 125℃, 126℃, 127℃, 128℃, 129℃, 130℃, 131℃, 132℃, 133℃, 134℃, 135℃, 136℃, 137℃, 138℃, 139℃, or 140℃. The temperature value of the third region is not limited to the listed proportion values, and other proportion values not listed in this range are also applicable.

[0171] The temperature value of the fourth region can be 105°C, 106°C, 107°C, 108°C, 109°C, 110°C, 111°C, 112°C, 113°C, 114°C, 115°C, 116°C, 117°C, 118°C, 119°C, 120°C. The temperature value of the fourth region is not limited to the listed proportion values, and other unlisted proportion values in this range are also applicable.

[0172] In some embodiments of the present application, step S3 comprises the following steps:

[0173] Blank taking out: start the movable mold moving mechanism, open the mold 100, take the formed blank from the mold cavity through the automatic taking device, and place it on the conveying belt.

[0174] Debinding treatment: place the formed blank in a debinding furnace, use a multi-effect composite debinding process, first perform catalytic debinding to remove part of the binder; then perform thermal debinding under heating in the sintering furnace stage to remove the remaining binder and greatly improve the product performance; finally, perform catalytic debinding at 300-400°C to reduce the harmful element residue.

[0175] In the thermal debinding stage, the heating rate is controlled to be 10-15°C / min, and the holding time is 2-3h, so as to adapt to the heating rhythm of the sintering furnace, quickly remove the remaining binder, and at the same time improve the product density and magnetic performance through high temperature.

[0176] In the catalytic debinding stage, the heating rate is controlled to be 3-8°C / min, and the holding time is 0.5-1h; wherein, the low-temperature slow rise can accurately remove harmful element residues.

[0177] Combining the above steps, the carbon content of the blank after debinding can be guaranteed to be ≤500ppm.

[0178] Sintering treatment: place the debound blank in a vacuum sintering furnace, sinter at 1050-1150°C for 2-4h, and the vacuum degree is ≤1×10 -3 Pa. During the sintering process, a segmented heating strategy is adopted, the heating rate is 5-10°C / min, and the holding time is 1-2h at 600-800°C to eliminate internal stress. After sintering, the furnace is cooled to room temperature, and a complex structure sintered rare earth iron-based alloy blank is obtained.

[0179] Subsequent processing and detection: according to the product requirements, a small amount of machining (machining weight reduction ratio ≤10%) is performed on the sintered blank to correct the size accuracy. Subsequently, the magnetic properties (remanence, coercive force, etc.), size accuracy, and surface quality of the product are comprehensively detected, and the qualified products are put into storage for use.

[0180] In some embodiments of the present application, the injection molding of the magnet further comprises a preparation step of the magnetic powder material, which comprises three steps of magnetic powder pretreatment, adhesive preparation and feed mixing.

[0181] Magnetic powder pretreatment: Nd-Fe-B rare earth iron-based alloy magnetic powder is selected, and the powder with a particle size D50 < 5 μm is prepared by airflow milling process. The magnetic powder is placed in a vacuum drying oven and dried at 80-120°C for 4-6h to remove the surface adsorbed moisture. Subsequently, a metal modified layer (such as Zn, Al, etc.) is coated on the surface of the magnetic powder by rotary diffusion method, with a coating thickness of 0.1-0.5 μm, to improve the oxidation resistance and flowability of the magnetic powder.

[0182] Adhesive preparation: a paraffin-polyethylene-polypropylene composite adhesive system is used, in which paraffin accounts for 50%-60%, polyethylene accounts for 20%-30%, and polypropylene accounts for 10%-20%. After mixing the components in proportion, melt at 150-180°C, and stir uniformly to prepare the adhesive.

[0183] Feed mixing: the pretreated rare earth iron-based alloy magnetic powder is mixed with the adhesive, and then extruded and granulated by a double screw extruder to prepare feed particles with a diameter of 3-5 mm, which are placed in a sealed bag for use.

[0184] The injection molding method of the present application is applied to the preparation of a 12-pole radially oriented magnetic ring blank with an outer diameter of 25 mm, a height of 6.5 mm, and a thinnest wall thickness of only 0.8 mm. The temperature of the mold 100 corresponding to the thin wall and thin rib part is set to 130°C, and the temperature of the main part is set to 95-105°C; at the same time, the dynamic magnetic field generating system generates and maintains a tangential magnetic field of 1.2T at the cavity. Compared with the traditional constant temperature mold 100 and static magnetic field process, the filling rate of this complex blank is increased from 85% to more than 99.9%, the magnetic powder orientation degree is increased by 35%, the sintered blank deformation is less than 0.05 mm, and the good product rate is increased from less than 50% to more than 90%, fully proving the effectiveness and advancement of the present application.

[0185] The above only describes exemplary embodiments of the present application, and does not limit the patent scope of the present application. Any equivalent structural transformation made by using the content of the present application specification and drawings, or direct / indirect application in other related technical fields is included in the patent protection scope of the present application.

Claims

1. A multi-field linkage injection molding method for a magnet, applied to a mold with an adjustable magnetic field, characterized in that, include: Step S1: Inject magnetic powder material into the mold cavity to form a molded preform; wherein, the injection pressure is between 50MPa and 100MPa, the temperature inside the mold cavity is between 95℃ and 140℃, and at the same time, a magnetic field is applied to the mold cavity, and the magnetic field strength is controlled to gradually increase from the initial set strength to the target strength. Step S2: Cool the molded preform. Step S3: The cooled molded blank is subjected to degreasing and sintering treatment in sequence to obtain a magnet; Before step S1, the procedure also includes: Step S0: During a first set time period, the magnetic field strength inside the mold cavity is maintained at an initial set strength, wherein the initial set strength is 55% to 75% of the target strength; Step S1 includes a first sub-step: during a second set time period, injecting the magnetic powder material into the mold cavity until it fills 30% of the volume of the mold cavity; In the first sub-step, the magnetic powder material is injected into the mold cavity at a rate of 6 mm / s to 9 mm / s, and the magnetic field strength is gradually increased from the initial set strength to 75% to 82% of the target strength at a first rate.

2. The injection molding method as described in claim 1, characterized in that, In the first sub-step, the first rate is set between 0.015T / s and 0.035T / s.

3. The injection molding method as described in claim 1, characterized in that, Step S1 further includes a second sub-step: during a third set time period, continuing to inject the magnetic powder material into the mold cavity until it fills 70% of the volume of the mold cavity; In the second sub-step, the magnetic powder material is injected into the mold cavity at a rate of 9 mm / s to 12 mm / s, and the magnetic field strength is gradually increased from 75% to 82% of the target strength to the target strength at a second rate, wherein the second rate is less than the first rate.

4. The injection molding method as described in claim 3, characterized in that, In the second sub-step, the second rate is set between 0.012T / s and 0.025T / s.

5. The injection molding method as described in claim 3, characterized in that, Step S1 further includes a third sub-step: during a fourth preset time period, continue to inject the magnetic powder material into the mold cavity until the mold cavity is completely filled; In the third sub-step, the magnetic powder material is injected into the mold cavity at a rate of 6 mm / s to 9 mm / s, and the magnetic field strength is maintained at the target strength.

6. The injection molding method as described in claim 5, characterized in that, Step S1 further includes a pressure holding step: During the fifth preset time period, the magnetic field strength is maintained at the target strength, and the mold cavity filled with the magnetic powder material is pressurized.

7. The injection molding method as described in claim 1, characterized in that, Step S2 includes: During the process of reducing the temperature of the molded preform from a first temperature value to a second temperature value, the magnetic field strength is gradually reduced from the target strength to a first set strength at a third rate. During the process of reducing the temperature of the molded preform from the second temperature value to the third temperature value, the magnetic field strength is gradually reduced from the first set strength to the second set strength at a fourth rate. The fourth rate is less than the third rate.

8. The injection molding method as described in claim 1, characterized in that, The mold cavity has multiple independently temperature-controlled areas, including a first area, a second area, a third area, and a fourth area. The first area corresponds to the main body of the molded blank, the second area corresponds to the thin-walled part of the molded blank, the third area corresponds to the fine rib part of the molded blank, and the fourth area corresponds to the gate of the mold cavity. In step S1, the temperature of the first region is controlled to be maintained between 95°C and 105°C, the temperature of the second region is controlled to be maintained between 115°C and 135°C, the temperature of the third region is controlled to be maintained between 125°C and 140°C, and the temperature of the fourth region is controlled to be maintained between 105°C and 120°C.

Images