An injection mold for forming external threads

Abstract

This invention provides an injection mold for forming external threads, including an upper fixed mold assembly, a lower moving mold assembly, a screw forming assembly, and a drive assembly. The upper fixed mold assembly has a rectangular head forming groove; the screw forming assembly includes an integrally formed forming shaft, which has a screw forming part, a rotating gear part, and a moving thread part; the drive assembly drives a spur rack through a single drive cylinder, which in turn drives the rotating gear part to rotate, causing the forming shaft to move axially while rotating, thus achieving thread demolding. This mold adopts a single-drive structure, avoiding the synchronization problem of dual drives, reducing debugging difficulty and cost, improving thread forming accuracy and demolding reliability, and is suitable for the mass production of high-precision plastic screws.

Description

Technical Field

[0001] This utility model relates to the field of injection mold technology, and more specifically, to an injection mold for forming external threads. Background Technology

[0002] Injection molding is a widely used molding method in industrial product manufacturing, especially in the fields of automotive parts, electronic components, and home appliances. Plastic injection molding has become a mainstream process because it enables the mass production of products with complex structures. As the core technological foundation of plastic injection molding, the mold's structural design and transmission stability directly determine the product molding accuracy, production efficiency, and the mold's own lifespan.

[0003] As my country's mold industry accelerates its alignment with international standards, downstream industries are continuously raising their requirements for product precision and production cycle time. Market competition has shifted from simple cost competition to comprehensive strength competition based on "quality and efficiency," and traditional molds are gradually becoming unable to meet high-end demands.

[0004] In the injection molding production of plastic screws with external threads, the thread ejection mold is a key piece of equipment for achieving thread forming and demolding. Chinese patent (CN216267369U) discloses a rack-and-pinion thread ejection mold that employs a dual-drive structure for demolding, adapting to the molding requirements of threaded products. However, this rack-and-pinion thread ejection mold relies on two independent drive components (such as a drive motor and a drive cylinder) to collaboratively control the rack transmission, thereby achieving the rotational ejection of the threaded core and axial demolding. This dual-drive collaborative mode places extremely high demands on the synchronization of the rotational speeds and the accuracy of the stroke of the two components: during the debugging phase, the drive parameters need to be repeatedly calibrated, which not only increases the time cost and technical threshold of mold installation and debugging but also easily leads to jamming or excessive friction between the threaded core and the product thread due to synchronization deviation. Improper debugging and matching can cause damage to the product thread profile and an increased scrap rate, or even more serious damage to the threaded core, shortening the mold's service life and making it difficult to meet the stable production needs of large-volume, high-precision plastic parts. Utility Model Content

[0005] The main technical problem this application addresses is the poor synchronization of existing dual-drive structures, complex debugging, and easy damage to products. To overcome the above-mentioned defects of the prior art, this application provides an injection mold for forming external threads.

[0006] This application provides an injection mold for molding external threads, comprising:

[0007] The upper mold assembly includes a mold base plate and a mold plate mounted on the bottom surface of the mold base plate. The bottom surface of the mold plate is recessed with a head forming groove for forming the screw head. The head forming groove has a rectangular structure and is used to restrict the circumferential rotation of the injection screw during demolding.

[0008] The lower moving mold assembly includes a moving mold base plate and a moving template mounted on the top surface of the moving mold base plate, wherein the top surface of the moving template and the bottom surface of the fixed template are matched for mold closing.

[0009] A screw forming assembly includes a forming shaft and a screw sleeve. The forming shaft is rotatably disposed inside a moving template and extends vertically. The forming shaft has a screw forming part, a rotating gear part, and a movable threaded part integrally formed coaxially from top to bottom. The screw forming part is located directly below the head forming groove and matches the head forming groove to form a screw forming cavity. The screw sleeve is fixedly installed on the moving template and threadedly connected to the movable threaded part. When the rotating gear part drives the forming shaft to rotate, the screw sleeve cooperates with the movable threaded part to drive the forming shaft to move vertically up and down.

[0010] A drive assembly includes a rack and a drive cylinder. The drive cylinder is fixedly mounted on the outer wall of the moving template. The rack passes through the moving template and is fixed to the telescopic end of the drive cylinder. The rack meshes with a rotating gear. The rack drives the rotating gear to rotate through the drive cylinder.

[0011] The screw forming part includes an internal threaded hole, and the pitch and direction of the internal threaded hole are the same as the pitch and direction of the movable threaded part.

[0012] Compared with existing technologies, the injection mold for forming external threads disclosed in this application has the following advantages: It replaces the dual-drive collaborative mode of existing technologies with a transmission structure of "single-drive cylinder, rack and pinion, and rotating gear," eliminating the need for repeated calibration of the speed synchronization and stroke accuracy of the two independent drive components, significantly reducing the time cost and technical threshold of mold installation and debugging. Simultaneously, it avoids the problems of jamming and excessive friction between the forming shaft and the product thread caused by dual-drive synchronization deviation, reducing product thread profile damage, lowering the scrap rate, extending the service life of the forming shaft, and adapting to the stable production needs of large-volume, high-precision plastic screws. The pitch and direction of the internal thread hole and the moving thread part are completely consistent. When the rotating gear part drives the forming shaft to rotate, the cooperation between the thread sleeve and the moving thread part can drive the forming shaft to move precisely vertically, and the rotation and movement are completely synchronized, ensuring the reliability of screw demolding, improving the thread dimensional tolerance accuracy, and meeting the precision requirements of downstream industries for high-end products. The head forming groove is designed as a rectangular structure, which can restrict the circumferential rotation of the screw during mold demolding, preventing the screw from deforming due to rotation during demolding, ensuring the forming accuracy of the screw shank, and improving the overall product quality.

[0013] In one possible implementation, there are multiple sets of screw molding assemblies, with the rotating gear on each molding shaft meshing with the rack and pinion drive. Compared to the prior art, multiple sets of screw molding assemblies can simultaneously perform injection molding of multiple plastic screws, significantly increasing product output per unit time compared to a single set, thus meeting the needs of mass production. There is no need to configure an independent drive component for each set of screw molding assemblies; multiple sets can work synchronously through a single drive and multiple meshing, simplifying the overall mold structure, reducing the number of drive components, and lowering mold manufacturing and maintenance costs.

[0014] In one possible implementation, the drive assembly further includes a gear transmission mechanism, through which the rack is connected to the rotating gear section of all forming shafts. Compared to existing technologies, the gear transmission mechanism serves as an intermediate adjustment unit between the rack and the rotating gear section, capable of changing the direction of power transmission and adjusting the transmission ratio. This allows the rack's movement speed to be flexibly adapted to the required rotational speed of the forming shaft, meeting the molding process requirements of different specifications of plastic screws. Gear transmission features smooth transmission and high precision, reducing potential transmission errors from direct meshing between the rack and the rotating gear section, ensuring the accuracy of the forming shaft's rotation angle and movement distance, and further improving the quality of thread forming.

[0015] In one possible implementation, the gear transmission mechanism includes at least one double gear rotatably connected inside the moving mold plate. Compared with the prior art, the double gear has a fixed number of teeth on both gears, and the transmission ratio is precisely controllable. This ensures a strict power transmission ratio between the rack and the rotating gear section, preventing instability in the forming shaft speed and movement speed due to transmission ratio fluctuations. This, in turn, ensures the accuracy of dimensions such as thread pitch and depth, reducing product dimensional deviations. The structural stability of the double gear is superior to that of a single gear. It is less prone to uneven tooth wear and gear misalignment during power transmission, ensuring long-term transmission stability and reducing mold downtime and product scrap due to gear transmission failures, thus improving mold operational reliability.

[0016] In one possible implementation, the axial length of the rotating gear is greater than the vertical travel of the forming shaft. Compared to the prior art, during the entire vertical travel of the forming shaft (from mold closing and forming to mold opening and demolding), the rotating gear maintains a constant meshing with the rack, preventing disengagement due to shaft movement. This ensures continuous power transmission to the forming shaft, avoiding sudden stops due to meshing interruptions and preventing damage to product threads or shaft jamming. The continuous meshing ensures smooth operation of the forming shaft's "rotary unwinding and vertical withdrawal" actions during demolding, eliminating the need for mid-process adjustments or re-meshing. This avoids product residue and mold damage caused by interruptions during demolding, improving demolding efficiency and stability, and reducing downtime during production.

[0017] In one possible implementation, the moving template has a horizontally extending rack guide hole, through which the straight rack passes. Compared to existing technologies, the rack guide hole strictly restricts the movement direction of the straight rack, ensuring that it moves stably only in the horizontal direction. This prevents the rack from deviating or wobbling during movement, thus ensuring stable meshing between the rack and the rotating gear, reducing transmission errors caused by poor meshing, and improving the accuracy of the forming shaft's rotation and movement. The guide hole also supports the rack, reducing deformation caused by its own weight or impact forces during movement. Simultaneously, it prevents friction between the rack and other parts of the moving template, reducing the wear rate of the rack, extending its service life, and lowering mold maintenance costs. The stable movement of the rack prevents internal mold vibration or noise caused by component misalignment, reducing abnormal wear during mold operation, improving overall mold stability, and further ensuring consistent product quality throughout long-term production.

[0018] In one possible implementation, a bushing is provided inside the moving template, and the bushing is fitted onto the outside of the screw forming part to support the rotation and vertical sliding of the forming shaft. Compared with the prior art, the bushing fitted onto the outside of the screw forming part can provide precise guidance for the rotation and vertical sliding of the forming shaft, ensuring that the forming shaft maintains coaxiality with its own axis throughout the entire operation, avoiding misalignment of the forming shaft that would cause thread forming eccentricity, significantly improving thread forming accuracy, and meeting the dimensional tolerance requirements of high-end products.

[0019] In one possible implementation, a stroke sensor is provided on the drive cylinder, which is electrically connected to an external control system to detect the travel distance of the extension / retraction end of the drive cylinder. Compared with the prior art, the stroke sensor can detect the travel distance of the extension / retraction end of the drive cylinder in real time and feed the data back to the external control system. The control system can accurately control the extension / retraction stroke of the drive cylinder according to preset process parameters, thereby precisely controlling the "rotation and movement" of the forming shaft, avoiding over- or under-molding due to inaccurate stroke control, and significantly reducing the product scrap rate. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of this application. Figure 1 ;

[0021] Figure 2 This is a schematic diagram of the overall structure of this application. Figure 2 ;

[0022] Figure 3 This is a cross-sectional view of this application;

[0023] Figure 4 This is a partial structural diagram of this application;

[0024] Figure 5 This is a schematic diagram of the forming shaft.

[0025] Explanation of reference numerals in the attached figures:

[0026] 1. Upper fixed mold assembly; 11. Fixed mold base plate; 12. Fixed template; 121. Head forming groove; 2. Lower moving mold assembly; 21. Moving mold base plate; 22. Moving template; 221. Rack guide hole; 3. Screw forming assembly; 31. Forming shaft; 311. Screw forming part; 3111. Internal threaded hole; 312. Rotating gear part; 313. Moving threaded part; 32. Screw sleeve; 4. Drive assembly; 41. Straight rack; 42. Drive cylinder; 43. Gear transmission mechanism; 431. Double gear; 5. Bushing. Detailed Implementation

[0027] First, those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the embodiments of this application and are not intended to limit the scope of protection of the embodiments of this application. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0028] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; 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. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application based on the specific circumstances.

[0029] In the embodiments of this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0030] The present application will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0031] See Figures 1 to 5 This application discloses an injection mold for forming external threads, including: an upper fixed mold assembly 1, a lower moving mold assembly 2, a screw forming assembly 3, and a drive assembly 4.

[0032] The upper mold assembly 1 includes a mold base plate 11 and a mold plate 12 mounted on the bottom surface of the mold base plate 11. A rectangular head forming groove 121 is recessed on the bottom surface of the mold plate 12. The size of the head forming groove 121 matches the head of the screw to be formed, and is used to form the screw head. Its rectangular structure can effectively prevent circumferential rotation during demolding by holding the injection-molded screw head in place after mold opening.

[0033] The lower moving mold assembly 2 includes a moving mold base plate 21 and a moving mold plate 22 mounted on the top surface of the moving mold base plate 21. The top surface of the moving mold plate 22 and the bottom surface of the fixed mold plate 12 can fit tightly together when the mold is closed to form a closed injection cavity.

[0034] The screw forming assembly 3 includes a forming shaft 31 and a screw sleeve 32. The forming shaft 31 is rotatably supported in a vertical hole inside the moving template 22 by the sleeve 5. The forming shaft 31 is machined from the same alloy steel bar from top to bottom, forming three coaxial integral parts: a screw forming section 311, a rotating gear section 312, and a moving thread section 313. The screw forming section 311 is located at the uppermost end of the forming shaft 31 and includes an internal threaded hole 3111, which is used to form the external thread of the plastic screw. The rotating gear section 312 is located in the middle of the forming shaft 31 and is a spur gear. The moving thread section 313 is located at the lowermost end of the forming shaft 31 and is an external threaded section, whose pitch and direction of rotation are exactly the same as the internal threaded hole 3111 at the upper end. The screw sleeve 32 is an insert that is pressed into a fixed hole in the moving template 22 by locking. The screw sleeve 32 has an internal thread that matches the moving threaded part 313. When the rotating gear part 312 drives the forming shaft 31 to rotate, the moving threaded part 313 engages with the internal thread of the screw sleeve 32, converting the rotational motion into axial linear motion, so as to realize the vertical movement of the forming shaft 31.

[0035] The drive assembly 4 includes a rack 41 and a drive cylinder 42. The drive cylinder 42 is preferably a servo electric cylinder, which is fixedly mounted on the outer wall of the moving template 22 via a mounting bracket. The extension and retraction end of the servo electric cylinder allows for precise stroke control. The rack 41 is a hardened steel rack, horizontally positioned, with one end fixed to the extension and retraction end of the servo electric cylinder. The rack passes through the moving template 22 and engages with the rotating gear 312 on the forming shaft 31.

[0036] During demolding, the drive cylinder 42 pushes the rack 41 horizontally, which in turn drives the rotating gear 312, which in turn rotates the entire forming shaft 31. Due to the interaction between the movable threaded part 313 and the fixed threaded sleeve 32, the rotating forming shaft 31 moves downwards while rotating, thus achieving the "screw-out" action from the formed plastic screw, completing the thread demolding and avoiding damage to the threads caused by forceful demolding. Because the pitch and direction of the screw forming part 311 and the movable threaded part 313 are matched, the axial movement distance generated by the movable threaded part 313 during one rotation of the forming shaft 31 is exactly equal to one pitch of the plastic screw thread. This ensures that the axial movement of the forming shaft 31 during "screw-out" is completely synchronized with the helix of the thread, resulting in a smooth and seamless demolding action without shearing or scraping forces on the product threads, guaranteeing the forming quality of the threads and the service life of the mold.

[0037] In this embodiment, to accommodate efficient production of multi-cavity molds, the mold can be equipped with multiple sets of screw forming components 3. The rotating gear portion 312 (with the same number of teeth and module) on each forming shaft 31 is engaged with the same common rack 41. In this way, a single drive cylinder 42 can drive all forming shafts 31 to rotate and retract synchronously by driving a rack 41, realizing the simultaneous demolding of multiple plastic screws, which greatly improves production efficiency.

[0038] In this embodiment, the drive assembly 4 further includes a gear transmission mechanism 43, through which the rack 41 is connected to the rotating gear section 312 of all forming shafts 31. The gear transmission mechanism 43 includes at least one double gear 431, which is rotatably connected inside the moving template 22 via bearings. The horizontal movement of the rack 41 is transmitted to the rotating gear section 312 after the transmission direction is changed by the double gear 431, thereby solving the transmission problem caused by space layout constraints; at the same time, the gear transmission mechanism 43 can adjust the speed ratio and increase the torque.

[0039] In this embodiment, to ensure that the rack 41 and the rotating gear 312 never disengage during the entire vertical movement of the forming shaft 31, the axial length of the rotating gear 312 is designed to be greater than the maximum vertical movement of the forming shaft 31, thereby ensuring the continuity and stability of the transmission.

[0040] In this embodiment, in order to accurately guide the rack 41 and prevent it from shaking or tilting during transmission, a through hole is horizontally machined inside the moving template 22 as a rack guide hole 221. The rack 41 is precisely inserted into this hole, and the guide hole and the rack 41 slide together, ensuring that the rack 41 can slide freely horizontally while avoiding movement or deviation.

[0041] In this embodiment, the bushing 5 is fitted on the shaft segment outside the screw forming part 311, providing additional radial support and sliding bearing surface for the forming shaft 31, which greatly improves the motion accuracy and mold life.

[0042] In this embodiment, to achieve precise automated control of the demolding process, a stroke sensor is integrated into the servo electric cylinder. This sensor detects the position of the cylinder's extension and retraction end in real time and transmits the signal to an external PLC control system. The system controls the servo electric cylinder according to a preset program, precisely controlling the number of rotations and stopping position of the forming shaft 31, thereby achieving fully automated production.

[0043] In other embodiments, the drive cylinder 42 can be selected according to different production needs and power sources. In workshops where pneumatic sources are readily available, a pneumatic cylinder can be used; in situations requiring greater demolding force, a hydraulic cylinder can be used.

[0044] The beneficial effects of this application include:

[0045] 1. Single drive replaces dual drive, eliminating the need to calibrate drive synchronization, significantly reducing mold debugging costs and technical barriers, avoiding problems such as jamming and excessive friction between the forming shaft 31 and the product threads caused by dual drive synchronization deviation, reducing product scrap, and extending the life of the forming shaft 31.

[0046] Second, the pitch and direction of the internal threaded hole 3111 of the screw forming part 313 are consistent with those of the moving threaded part 313, ensuring that the rotation of the forming shaft 31 and the vertical movement are completely synchronized, improving the reliability of demolding, ensuring the thread size tolerance accuracy, and meeting quality requirements.

[0047] 3. The rectangular head forming groove 121 restricts the circumferential rotation of the screw to avoid thread deformation during demolding; multiple sets of screw forming components 3 rely on single drive to work synchronously, improving production efficiency, and eliminating the need for multiple drives, simplifying the structure and reducing manufacturing and maintenance costs.

[0048] IV. The gear transmission mechanism 43 (including the double gear 431), rack guide hole 221, bushing 5 and stroke sensor respectively improve the smoothness of transmission, structural stability and control accuracy, and are suitable for mass production with high precision.

[0049] In the description of the embodiments of this application, it should be noted that the terms "inner" and "outer" and other terms indicating direction or positional relationship are based on the direction or positional relationship shown in the drawings. This is only for the convenience of description and does not indicate or imply that the device or component must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this application.

[0050] In the description of this application, the references to terms such as "an embodiment," "some embodiments," "in this embodiment," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0051] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An injection mold for forming external threads, characterized in that, include: The upper mold assembly includes a mold base plate and a mold plate mounted on the bottom surface of the mold base plate. The bottom surface of the mold plate is recessed with a head forming groove for forming the screw head. The head forming groove has a rectangular structure and is used to restrict the circumferential rotation of the injection screw during demolding. The lower moving mold assembly includes a moving mold base plate and a moving template mounted on the top surface of the moving mold base plate, wherein the top surface of the moving template and the bottom surface of the fixed template are matched for mold closing. A screw forming assembly includes a forming shaft and a screw sleeve. The forming shaft is rotatably disposed inside a moving template and extends vertically. The forming shaft has a screw forming part, a rotating gear part, and a movable threaded part integrally formed coaxially from top to bottom. The screw forming part is located directly below the head forming groove and matches the head forming groove to form a screw forming cavity. The screw sleeve is fixedly installed on the moving template and threadedly connected to the movable threaded part. When the rotating gear part drives the forming shaft to rotate, the screw sleeve cooperates with the movable threaded part to drive the forming shaft to move vertically up and down. A drive assembly includes a rack and a drive cylinder. The drive cylinder is fixedly mounted on the outer wall of the moving template. The rack passes through the moving template and is fixed to the telescopic end of the drive cylinder. The rack meshes with a rotating gear. The rack drives the rotating gear to rotate through the drive cylinder. The screw forming part includes an internal threaded hole, and the pitch and direction of the internal threaded hole are the same as the pitch and direction of the movable threaded part.

2. The injection mold for forming external threads according to claim 1, characterized in that, The screw forming assembly comprises multiple sets, and the rotating gear on each forming shaft meshes with the rack and pinion drive.

3. The injection mold for forming external threads according to claim 2, characterized in that, The drive assembly also includes a gear transmission mechanism, through which the spur rack is connected to the rotating gear section of all forming shafts.

4. The injection mold for forming external threads according to claim 3, characterized in that, The gear transmission mechanism includes at least one double gear, which is rotatably connected inside the moving template.

5. The injection mold for forming external threads according to claim 1, characterized in that, The axial length of the rotating gear is greater than the vertical travel of the forming shaft.

6. The injection mold for forming external threads according to claim 1, characterized in that, The moving template has a rack guide hole extending horizontally inside, and the straight rack passes through the rack guide hole.

7. The injection mold for forming external threads according to claim 1, characterized in that, The moving template has a bushing inside, which is sleeved on the outside of the screw forming part to support the rotation and vertical sliding of the forming shaft.

8. The injection mold for forming external threads according to claim 1, characterized in that, The drive cylinder is equipped with a stroke sensor, which is electrically connected to an external control system and is used to detect the travel of the extension and retraction end of the drive cylinder.

9. The injection mold for forming external threads according to claim 1, characterized in that, The drive cylinder can be any one of a pneumatic cylinder, a hydraulic cylinder, or a servo electric cylinder.

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