Local shrinkage prevention mechanism for mold and control method

Abstract

The invention belongs to the technical field of mold forming. The mold local shrink-proof mechanism comprises at least one shrink-proof insert, a preset gap is reserved between the shrink-proof insert and the end face of a product thickness area in a mold closing state, and the shrink-proof insert and the end face of the product thickness area are used for forming compensation allowance in the forming process; the driving unit is arranged outside or inside the mold, one end of the transmission mechanism is connected with the driving unit, and the other end of the transmission mechanism is in driving fit with the shrink-proof insert. After the cavity is filled with the molten material, the drive unit drives the shrink-proof insert to move towards the product through the transmission mechanism, and volume loss of the product caused by cooling shrinkage in the area is dynamically compensated. Through dynamic following feeding of the shrink-proof insert, the defects of shrinkage cavities, shrinkage marks and the like in a local thick area of a product are effectively eliminated, the forming quality and the size precision of the product are remarkably improved, meanwhile, the forming period can be shortened, the manufacturing cost is reduced, and the shrink-proof insert has the advantages of being simple in structure, accurate in control and high in adaptability.

Description

Technical Field

[0001] This invention relates to the field of mold forming technology, and more specifically, to a mold local shrinkage prevention mechanism and its control method for solving the shrinkage defect in local thick areas of a product, applicable to injection molding, die casting and other processes. Background Technology

[0002] In die casting and injection molding processes, product structural design often results in uneven wall thickness in certain areas due to functional or assembly requirements. For example, some products require structures such as bosses, reinforcing ribs, and mounting bosses, where the wall thickness in these areas is much greater than the base wall thickness of the product. Figure 1 Taking a disc-shaped die-cast part as an example, the average wall thickness of the main body of the product is 3mm, but there is a cylindrical structure with a diameter of 15mm in the central part, and the local wall thickness of this area is significantly greater than that of the surrounding area.

[0003] During the molding process, molten metal or plastic material fills the mold cavity and enters the cooling and solidification stage. Because thicker areas have a larger heat capacity than thinner areas, they cool more slowly, shrinkage occurs later, and the amount of shrinkage is greater. Even after the surrounding thin-walled areas have solidified, the thicker internal areas continue to shrink. If material cannot be replenished in time, shrinkage cavities will form within these areas, or defects such as shrinkage marks and depressions will appear on the surface. In severe cases, pinholes may form, directly affecting the product's mechanical properties, airtightness, and appearance quality, leading to an increased product scrap rate.

[0004] To address the issue of shrinkage defects easily occurring in the aforementioned areas of thicker wall material, the industry typically employs the following methods:

[0005] One approach is to communicate with product designers to modify the product structure, thinning out areas with excessive thickness to eliminate the risk of shrinkage at the source. However, in actual engineering applications, product structures often need to meet specific functional requirements or appearance designs, making it difficult for designers to easily modify drawings, thus significantly limiting the implementation of this method.

[0006] Secondly, the cooling capacity of this area can be enhanced during mold design by optimizing the cooling water channel layout and increasing the cooling flow rate to accelerate heat dissipation in the thicker areas and reduce the difference in cooling rate between them and the thinner areas. While this method has some improvement effect, it cannot fundamentally solve the problem of shrinkage volume loss, and excessive cooling may lead to increased internal stress in the product.

[0007] Third, improve the venting capacity of this area by adding venting channels or venting inserts in the thicker areas to prevent gas stagnation from affecting material filling. This method mainly solves the problem of trapped gas, but has limited effect on improving shrinkage defects.

[0008] Fourth, by improving the runner design and optimizing the gate position and size, the molding pressure in this area can be increased as much as possible, allowing more material to enter the thicker area during the holding pressure stage. However, once the gate or runner solidifies first, the feeding channel is blocked, and even if the pressure is increased, the material cannot be delivered to the interior, so the improvement effect is also limited.

[0009] In summary, while the aforementioned traditional treatment methods offer some optimization when the product structure cannot be altered, they often fail to fundamentally resolve the shrinkage defects in areas of localized wall thickness. Therefore, providing a mold localized shrinkage prevention mechanism and its control method that can effectively compensate for shrinkage in localized wall thickness areas and eliminate shrinkage cavities and marks from a mechanistic perspective has become a pressing technical problem for those skilled in the art. Summary of the Invention

[0010] The present invention aims to provide a mold local anti-shrinkage mechanism and its control method to solve the problem of defects such as shrinkage cavities and depressions caused by cooling shrinkage in local thick areas of the product in existing molds, thereby improving the product molding quality and dimensional accuracy.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] In a first aspect, the present invention provides a mold local anti-shrinkage mechanism, comprising: at least one anti-shrinkage insert disposed in the mold cavity corresponding to a local thick area of ​​the product; a preset gap is reserved between the anti-shrinkage insert and the end face of the thick area of ​​the product in the mold-closed state, so as to form a compensation allowance in the area during the molding process; a driving unit disposed outside or inside the mold; a transmission mechanism, one end of which is connected to the driving unit and the other end of which drives and cooperates with the anti-shrinkage insert; wherein, after the molten material has filled the cavity, the driving unit drives the anti-shrinkage insert to move towards the product through the transmission mechanism, so as to dynamically compensate for the volume loss of the product in this area due to cooling and shrinkage.

[0013] In addition to the above-mentioned technical features, the present invention has also made optimizations and improvements in the following aspects:

[0014] As a preferred embodiment of the present invention, the transmission mechanism includes an inclined shovel block, the inclined shovel block having an inclined driving surface, and the anti-shrink insert having an inclined surface that slides in cooperation with the inclined driving surface; the inclined shovel block moves horizontally under the drive of the drive unit, and drives the anti-shrink insert to vertically push the product upward through the inclined surface cooperation.

[0015] As a preferred embodiment of the present invention, the driving unit is any one of a hydraulic cylinder, a pneumatic cylinder, or an electric push rod, and the output end of the driving unit is fixedly connected or transmitted to the inclined shovel block.

[0016] As a preferred embodiment of the present invention, the anti-shrinkage insert is a detachable insert structure, and a guide structure is provided between it and the mold frame to restrict its movement only in a direction perpendicular to the product surface.

[0017] As a preferred technical solution of the present invention, the numerical range of the preset gap is 1mm to 5mm, and the numerical range is determined by simulation or calculation based on the volume of the thick area of ​​the product or the amount of thermal shrinkage.

[0018] As a preferred embodiment of the present invention, the anti-shrinkage insert is made of an alloy material with higher thermal conductivity than the mold substrate, or has a cooling medium channel inside it to enhance local cooling capacity.

[0019] Secondly, the present invention provides a method for local shrinkage prevention in molds, applied to any of the mechanisms described above, comprising the following steps:

[0020] Step S1: Install anti-shrinkage inserts in the thicker areas of the mold and reserve compensation gaps on their end faces;

[0021] Step S2: Close the mold and inject molten material to fill the cavity, so that the thick area forms a blank structure with compensation allowance;

[0022] Step S3: After filling is completed, during the pressure holding stage or the initial cooling stage, the anti-shrinkage insert is driven by the drive unit to move towards the product and press against the product surface.

[0023] Step S4: As the product cools and shrinks, the anti-shrinkage insert moves under the continuous action of the driving force to dynamically compensate for the shrinkage.

[0024] Step S5: After mold opening, remove the product and remove the compensation allowance through subsequent machining to obtain the final size.

[0025] As a preferred technical solution of the present invention, in step S3, the clamping force of the anti-shrink insert is adjusted by the drive unit through pressure control or position control to ensure that it always fits the product surface without causing indentation or deformation.

[0026] Thirdly, the present invention provides an application method of a mold local anti-shrinkage mechanism, wherein multiple anti-shrinkage inserts are provided, each corresponding to multiple areas of different wall thicknesses of the product, and each anti-shrinkage insert is controlled by the same driving unit or an independent driving unit; the end face of the anti-shrinkage insert that contacts the product is provided with a surface texture or coating to improve the surface quality of the product or facilitate subsequent demolding.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention provides a mold local shrinkage prevention mechanism and its control method, which combines structural innovation and control method optimization to solve the shrinkage defect in local thick areas, while achieving multiple optimizations in molding quality, production efficiency and manufacturing cost, resulting in significant comprehensive technical effects.

[0029] 1. Regarding molding quality, this invention uses dynamically movable anti-shrinkage inserts in the mold cavity corresponding to the thicker areas of the product, and reserves a compensation gap in the mold-closed state. This allows the area to form a blank structure with compensation allowance in the early stages of molding. After filling, the drive unit drives the anti-shrinkage inserts towards the product via a transmission mechanism, and continuously follows and compensates for shrinkage during cooling, dynamically compensating for material loss caused by volume shrinkage. This mechanism fundamentally eliminates defects such as shrinkage cavities and depressions caused by uneven cooling and insufficient shrinkage in traditional molds, significantly improving the internal density and appearance quality of the product. Simultaneously, precise control of the clamping force by the drive unit ensures that the inserts always adhere to the product surface without causing indentations or deformation, further improving the surface quality and dimensional accuracy of the product, making it particularly suitable for the production needs of precision plastic parts or die-cast parts.

[0030] 2. In terms of production efficiency, the anti-shrinkage inserts are made of alloy materials with higher thermal conductivity than the mold base material or have built-in cooling medium channels, which can accelerate heat dissipation in areas with thick walls. Combined with the dynamic shrinkage compensation effect of the inserts, this effectively shortens the holding and cooling times, thereby reducing the molding cycle and improving production efficiency. Multiple anti-shrinkage inserts can be controlled by the same drive unit or independent drive units to achieve synchronous shrinkage compensation in multiple thick areas of the product, further optimizing the molding process and adapting to the high-efficiency production needs of complex structure products.

[0031] 3. Regarding manufacturing costs and process adaptability, this invention achieves precise compensation for locally thick areas without requiring large-scale modifications to the overall mold structure. Its simple structural design facilitates installation and debugging, significantly reducing mold manufacturing costs and time. The anti-shrinkage insert features a detachable structure with a guiding mechanism, facilitating replacement and maintenance and enhancing the mold's versatility and lifespan. The preset gap range can be determined through simulation or calculation based on the volume of the thick area or the amount of thermal shrinkage, enabling the invention to flexibly adapt to the molding requirements of products with different materials and structures, thus possessing wide applicability.

[0032] 4. In terms of demolding performance and surface quality, the end face of the anti-shrinkage insert that contacts the product can be textured or coated. This can improve the surface smoothness or functional texture molding effect of the product during the molding process, reduce the adhesion between the product and the insert, facilitate demolding, reduce the risk of product damage, and further improve the product yield.

[0033] In summary, this invention, through the organic combination of structural innovation and control methods, has achieved significant progress in eliminating local shrinkage defects, improving product molding quality, shortening molding cycle, reducing manufacturing costs, and enhancing process adaptability. It has produced a synergistic and effective comprehensive technical result, demonstrating outstanding practical value and broad application prospects. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall structure of the mold local anti-shrinkage mechanism of the present invention;

[0035] Figure 2 This is a top view of the mold local anti-shrinkage mechanism of the present invention;

[0036] Figure 3 This is a partial cross-sectional view along line AA of the mold local anti-shrinkage mechanism of the present invention.

[0037] The components in the attached diagram are labeled as follows:

[0038] 1-Anti-shrinkage insert; 11-Chamfered surface; 2-Drive unit; 3-Transmission mechanism; 31-Chamfered shovel block; 311-Chamfered drive surface; 4-Cavity; 5-Product; 6-Preset gap; 7-Mold frame; 8-Guide structure. Detailed Implementation

[0039] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0040] I. Explanation of descriptive terms used in this invention

[0041] The embodiments provided in conjunction with the technical solutions of this invention are intended to make the invention more thorough and complete, and to fully express the scope of the invention to those skilled in the art. It should be noted that unless otherwise specifically stated in this invention, the relative arrangements of components described in these embodiments should be interpreted as merely exemplary and not as a limitation on the technical solutions of this invention.

[0042] In this invention, when directional terms such as "up," "down," "left," "right," "bottom," and "top" are used, they are defined relative to the directions shown in the accompanying drawings and are used only to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly. These or other directional terms should not be construed as restrictive terms.

[0043] In this invention, the terms "a," "an," "an," "the," and similar words used do not indicate quantity limitations and can represent singular or plural. The terms "comprising," "including," "having," and any variations thereof used in this invention are intended to cover non-exclusive inclusion; the terms "first," "second," "third," etc., used in this invention are merely to distinguish similar objects and do not represent a specific ordering of objects.

[0044] In this invention, when a specific device is described as being located between a first device and a second device, an intermediary device may or may not be present between the specific device and the first or second device. When a specific device is described as being connected to other devices, the specific device may be directly connected to the other devices without an intermediary device, or it may be not directly connected to the other devices but have an intermediary device.

[0045] Furthermore, this invention does not discuss in detail the technologies and equipment known to those skilled in the art, but where appropriate, such technologies and equipment should be considered part of the specification.

[0046] II. The core technical problem to be solved by the technical solution of this application

[0047] In die casting and injection molding processes, products often exhibit uneven wall thickness in certain areas due to functional requirements (such as bosses and reinforcing ribs). Because thick-walled areas have a large heat capacity and cool later than thin-walled areas, when the surrounding area has already solidified, the subsequent shrinkage of the thick-walled area cannot be compensated for by the melt in time, which easily leads to shrinkage cavities inside or shrinkage marks on the surface. This seriously affects the mechanical properties, airtightness, and appearance of the product, resulting in a high scrap rate.

[0048] To address this challenge, existing technologies have the following limitations: First, while structural thinning at the design level can fundamentally solve the problem, it is often limited by the product's functional or aesthetic requirements and cannot be modified. Second, mold-side optimization measures, such as enhanced local cooling, can reduce temperature differences but cannot compensate for the volume loss due to solidification shrinkage; adding vents only improves trapped air and has little effect on the shrinkage defects themselves. Furthermore, while improving runner design aims to enhance pressure holding and shrinkage compensation, the thin walls surrounding thick-walled areas or the gate often solidify first, cutting off the shrinkage compensation channel and preventing subsequent high pressure from effectively reaching the internal defect area.

[0049] In summary, given that the structure cannot be altered, existing technologies are insufficient to fundamentally compensate for the volume shrinkage caused by delayed cooling in thicker areas, and thus cannot effectively eliminate shrinkage cavities and marks.

[0050] III. Based on the above problems, the present invention specifically provides a technical solution to solve these problems. The following describes specific embodiments and references the appendix. Figures 1-3As shown, the technical solution, working principle, and technical effects of the present invention will be explained in detail.

[0051] Example 1

[0052] like Figure 1 , Figure 3 As shown, this embodiment provides a mold local shrinkage prevention mechanism, which is suitable for shrinkage compensation in local thick areas of products during injection molding or die casting processes.

[0053] The mechanism in this embodiment mainly consists of an anti-shrinkage insert 1, a drive unit 2, and a transmission mechanism 3. The anti-shrinkage insert 1 is positioned within the mold cavity 4 corresponding to the thicker area of ​​the product 5. The anti-shrinkage insert 1 is a detachable insert structure, made of beryllium bronze alloy material with higher thermal conductivity than the mold base material. A preset gap 6, 2.5 mm, is provided between the insert and the end face of the thicker area of ​​the product 5 when the mold is closed. This gap is calculated using mold flow analysis software based on the volume and thermal shrinkage of the thicker area of ​​the product.

[0054] The drive unit 2 is located outside the mold; in this embodiment, a hydraulic cylinder is used. The output end of the drive unit 2 is connected to the transmission mechanism 3.

[0055] The transmission mechanism 3 includes an inclined shovel block 31, which has an inclined driving surface 311 with an inclination angle of 15°. The bottom of the anti-shrink insert 1 is provided with an inclined surface 11 that slides in cooperation with the inclined driving surface 311. The inclined shovel block 31 moves horizontally under the drive of the drive unit 2, and drives the anti-shrink insert 1 to move vertically through the inclined surface cooperation. A guide structure 8, including a guide post and a guide sleeve, is provided between the anti-shrink insert 1 and the mold base 7 to restrict the anti-shrink insert 1 to move only in a direction perpendicular to the surface of the product 5.

[0056] The anti-shrinkage insert 1 has a cooling medium channel inside, through which cooling water or compressed air can be introduced for cooling. In this embodiment, compressed air cooling is preferred to reduce carbon buildup and extend the service life of the insert.

[0057] The working principle and process of this embodiment are as follows:

[0058] In the mold-closed state, a pre-set gap 6 of 2.5mm is reserved between the anti-shrinkage insert 1 and the end face of the thick area of ​​the product 5, so that the area forms a blank structure with compensation allowance in the early stage of molding. After the molten material fills the cavity 4, the pressure holding stage is entered. At this time, the control system receives the injection completion signal from the die casting machine or injection molding machine, and starts the drive unit 2 after a 0.5-second delay.

[0059] The drive unit 2 pushes the inclined shovel block 31 to move horizontally forward. The inclined drive surface 311 of the inclined shovel block 31 slides relative to the inclined surface 11 of the anti-shrink insert 1, converting the horizontal movement into vertical movement. This drives the anti-shrink insert 1 to move towards the product 5 and press against the product surface. The pressing force is adjusted by the drive unit 2 through pressure control to ensure that the anti-shrink insert always fits against the product surface without causing indentations or deformation.

[0060] As product 5 cools and shrinks, the anti-shrinkage insert 1 moves under the continuous driving force to dynamically compensate for the shrinkage. The holding time is set to 8 seconds until the product is completely solidified. Before mold opening, the drive unit 2 moves in the opposite direction, causing the inclined spade block 31 to retract, and the anti-shrinkage insert 1 returns to its original position under the action of the return spring 9. After mold opening, product 5 is removed, and the compensation allowance is removed through subsequent machining to obtain the final dimensions.

[0061] Through the aforementioned structure and working principle, this embodiment effectively eliminates shrinkage cavities and depressions in areas of localized thick material on the product, reducing the surface depression rate to below 0.1% and achieving dimensional accuracy at IT8 level. Due to the use of beryllium bronze alloy inserts and built-in cooling channels, localized cooling time is reduced by 30%, and the molding cycle is shortened from 45 seconds to 35 seconds. The detachable insert structure facilitates replacement and maintenance, the guiding structure ensures smooth insert movement, and the overall mechanism operates stably and reliably, significantly improving production efficiency and product yield.

[0062] Example 2

[0063] The difference between this embodiment and Embodiment 1 is that the number of anti-shrinkage inserts is set to multiple, each corresponding to a different wall thickness area of ​​the product. Each anti-shrinkage insert is controlled by an independent drive unit to achieve independent shrinkage compensation in each area. In this embodiment, three anti-shrinkage inserts a, b, and c are provided, each corresponding to a different wall thickness area of ​​product 5.

[0064] Each anti-shrinkage insert (a, b, c) is equipped with an independent drive unit (a, b, c) and a transmission mechanism (a, b, c). Each drive unit is an independently controlled hydraulic cylinder, and its pressure parameters can be set according to the actual shrinkage requirements of the corresponding area.

[0065] In addition, in this embodiment, the end faces of the anti-shrinkage inserts a, b, and c that contact the product 5 are provided with a surface texture coating. In this embodiment, a diamond-like coating is preferred. This coating can not only improve the surface finish of the product, but also reduce the adhesion between the product and the insert, making it easier to demold.

[0066] The working process of this embodiment is basically the same as that of Embodiment 1, except that the timing and pressure parameters of each anti-shrinkage insert can be adjusted according to the solidification characteristics of the corresponding area. An independent time-delay relay is set in the control system, and different extrusion start times are set for areas with different wall thicknesses: the central thick-walled area solidifies more slowly, so the extrusion start time is set to 0.8 seconds; the thinner areas on both sides solidify more quickly, so the extrusion start time is set to 0.4 seconds, ensuring that each area receives compensation at the optimal time.

[0067] Thanks to its multi-point independent control structure, this embodiment offers greater adaptability to complex product structures. Compared to Embodiment 1, this embodiment improves dimensional accuracy consistency by approximately 30% and further reduces the scrap rate to below 0.8% for complex products with multiple thick areas. Simultaneously, the coating design on the anti-shrinkage insert end face reduces demolding force by 25%, effectively minimizing demolding damage.

[0068] Example 3

[0069] The difference between this embodiment and Embodiment 1 is that the drive unit uses an electric push rod instead of a hydraulic cylinder, and the structure of the transmission mechanism is adjusted accordingly. This embodiment is suitable for injection molding environments with high cleanliness requirements.

[0070] The electric linear actuator is a ball screw type driven by a servo motor, which has the advantage of high position control accuracy. The drive unit and the inclined shovel block are fixedly connected by a connecting block. The control method is changed from pressure control in Example 1 to position control. The position of the anti-shrinkage insert is fed back in real time by the encoder of the servo motor, so as to achieve precise displacement control.

[0071] In this embodiment, the preset gap value is set to 1.5mm, which is determined based on the precise calculation of the product's heat shrinkage. During the molding process, the control system controls the electric push rod to drive the anti-shrinkage insert to shrink along with the product at a specific speed according to the preset displacement curve, with a displacement control accuracy of ±0.02mm.

[0072] Due to the adoption of servo electric actuators and position control, this embodiment has significant advantages in molding high-precision optical products. Compared to Embodiment 1, the dimensional tolerance range of this embodiment is reduced from ±0.1mm to ±0.03mm, significantly improving product consistency. Furthermore, it eliminates the need for a hydraulic system, avoiding the risk of oil leakage, and is suitable for cleanroom production environments.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0074] Furthermore, the technical solutions of the various embodiments can be combined with each other, but only if they are feasible for those skilled in the art. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

Claims

1. A mold local shrinkage prevention mechanism, characterized in that, include: At least one anti-shrinkage insert (1) is disposed in the cavity (4) of the mold corresponding to the local thick area of ​​the product (5); A preset gap (6) is reserved between the anti-shrinkage insert (1) and the end face of the thick area of ​​the product (5) in the mold closing state, so as to form a compensation allowance in the area during the molding process; The drive unit (2) is located outside or inside the mold; The transmission mechanism (3) has one end connected to the drive unit (2) and the other end driven by the anti-shrink insert (1); After the molten material fills the cavity (4), the drive unit (2) drives the anti-shrinkage insert (1) to move toward the product (5) through the transmission mechanism (3) to dynamically compensate for the volume loss of the product (5) in this area due to cooling and shrinkage.

2. The mold local anti-shrinkage mechanism according to claim 1, characterized in that, The transmission mechanism (3) includes an inclined shovel block (31), which has an inclined driving surface (311). The anti-shrink insert (1) is provided with an inclined surface (11) that slides with the inclined driving surface (311). The inclined shovel block (31) moves horizontally under the drive of the drive unit (2) and drives the anti-shrink insert (1) to vertically push the product (5) upward through the inclined surface.

3. The mold local anti-shrinkage mechanism according to claim 2, characterized in that, The drive unit (2) is any one of a hydraulic cylinder, a pneumatic cylinder, or an electric push rod, and the output end of the drive unit (2) is fixedly connected or transmitted to the inclined shovel block (31).

4. The mold local anti-shrinkage mechanism according to claim 1, characterized in that, The anti-shrinkage insert (1) is a detachable insert structure, and a guide structure (8) is provided between it and the mold frame (7) to restrict it to move only in a direction perpendicular to the surface of the product (5).

5. A mold local anti-shrinkage mechanism according to claim 1, characterized in that, The preset gap (6) has a numerical range of 1 mm to 5 mm, and the numerical range is determined by simulation or calculation based on the volume of the thick area of ​​the product (5) or the amount of thermal shrinkage.

6. A mold local shrinkage prevention mechanism according to claim 1, characterized in that, The anti-shrinkage insert (1) is made of an alloy material with higher thermal conductivity than the mold substrate, or has a cooling medium channel inside it to enhance local cooling capacity.

7. A mold local shrinkage prevention mechanism according to claim 1, characterized in that, The anti-shrinkage insert (1) is provided in multiple parts, each corresponding to a different thickness area of ​​the product (5). Each anti-shrinkage insert (1) is controlled by the same drive unit (2) or an independent drive unit.

8. A mold local shrinkage prevention mechanism according to claim 1, characterized in that, The anti-shrinkage insert (1) has a surface texture or coating on the end face that contacts the product (5) to improve the surface quality of the product or facilitate subsequent demolding.

9. A method for controlling local shrinkage of a mold, applied to the local shrinkage prevention mechanism of the mold as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Step S1: Set anti-shrinkage inserts (1) in the local thick area of ​​the mold and reserve a compensation gap (6) on its end face; Step S2: Close the mold and inject molten material to fill the cavity (4), so that the thick area forms a blank structure with compensation allowance; Step S3: After filling is completed, during the pressure holding stage or the initial cooling stage, the anti-shrink insert (1) is driven by the drive unit (2) to move towards the product (5) and press against the surface of the product (5); Step S4: As the product (5) cools and shrinks, the anti-shrinkage insert (1) moves under the continuous action of the driving force to dynamically compensate for the shrinkage amount; Step S5: After mold opening, take out the product (5) and remove the compensation allowance through subsequent machining to obtain the final size.

10. A method for preventing local shrinkage of a mold according to claim 9, characterized in that, In step S3, the clamping force of the anti-shrink insert (1) is adjusted by the drive unit (2) through pressure control or position control to ensure that it always fits the surface of the product (5) without causing indentation or deformation.

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