Mold structure based on secondary mold opening micro-foaming and injection molding foaming forming method

Abstract

The invention relates to a mold structure based on secondary mold opening micro-foaming and a forming method. The mold structure comprises a fixed mold assembly, a movable mold assembly, a bearing plate and a servo control system. The fixed mold assembly comprises a fixed mold bottom plate and a fixed mold plate, and the movable mold assembly comprises a movable mold plate and a movable mold base plate; the bearing plate is arranged between the movable mold plate and the movable mold base plate, a replaceable cavity insert is installed on the bearing plate, a plastic part forming cavity is formed among the upper surface of the cavity insert, the lower surface of the fixed mold plate and the bearing plate, and the bearing plate can move relative to the movable mold plate in the mold opening direction under driving of a servo control system. Dynamic expansion of the volume of the molding cavity of the plastic part is realized; an initial cavity is formed after the fixed mold plate and the movable mold plate are closed, and after melt injection and pressure maintaining in the initial cavity are completed, the servo control system drives the bearing plate to move in the mold opening direction, so that the size of a plastic part forming cavity is enlarged; the problems that a traditional injection molding foaming mold is single in structure, unstable in forming quality, poor in process adaptability and the like are solved.

Description

Technical Field

[0001] This invention relates to a mold structure and injection molding process, and particularly to a mold structure and injection molding foaming method based on secondary mold opening and micro-foaming. Background Technology

[0002] Traditional injection foaming molds face many technical bottlenecks in the molding process, making it difficult to meet the requirements for fine control of cell structure. Because the cavity structure of traditional injection foaming molds is fixed and cannot be dynamically adjusted in the key stages of foaming, the coupling effect of physical and chemical behaviors such as melt flow, bubble nucleus formation and gas diffusion during the foaming process is difficult to control effectively, which can easily lead to typical defects such as uneven cell distribution, surface collapse and silver streaks.

[0003] In addition, traditional molds usually rely on a single adjustment of holding pressure or cooling parameters to affect foaming behavior. The adjustment means are limited and cannot adapt to the complex matching relationship between different material systems and foaming agent properties. This results in large fluctuations in the mechanical properties of the products and prominent stress concentration problems, which seriously restricts the application of foamed products in the fields of lightweighting and high strength.

[0004] In existing similar technologies, such as the two-stage mold-opening injection molding apparatus disclosed in Chinese patent document CN110142911A, the apparatus uses a holding pressure process to redissolve the formed bubbles into the melt during the filling process, restoring the melt to an unfoamed state and obtaining a uniform and stable high holding pressure environment. Subsequently, in the first mold opening stage of the two-stage mold opening process, the melt undergoes a uniformly distributed high holding pressure drop, thereby providing sufficient space for volume expansion and achieving effective foaming. Simultaneously, by utilizing variable mold temperature control technology, a high mold temperature is maintained during melt filling and holding pressure, slowing down the melt cooling rate and ensuring that the melt still has sufficient temperature conditions to complete the subsequent foaming process at the end of holding pressure and the first mold opening. This process effectively suppresses the interference of foaming during the filling stage on product quality and achieves control over the foaming process.

[0005] For example, the foaming mold disclosed in Chinese patent document CN109177025A has a mold structure in which the punch and the die are closed to form a product cavity, and the product is formed in the cavity. The punch is provided with an edge forming part for forming the edge area of ​​the product. The edge forming part is provided with a protruding structure protruding into the cavity, so that the edge of the product forms a thinning groove. The depth of the thinning groove along the mold opening direction is not less than the moving distance during the first stage of mold opening. By setting a protruding structure on the edge of the punch, the thinning of the product edge is effectively achieved, so that it can cool and solidify first and freeze quickly after injection, thereby forming a stable sealing area during the foaming expansion process, preventing the melt from overflowing or bulging at the edge, and ensuring that the product edge is clean and has excellent appearance quality.

[0006] However, the existing technologies described above have the following drawbacks:

[0007] 1. Limited process control: Most are closed structures, injection molding is completed in one mold opening, there is no space for mold cavity expansion, and it is difficult to achieve the dynamic adjustment required for foam volume expansion.

[0008] 2. Poor product molding quality: It is prone to defects such as surface bubbles, weld lines, and warping, and cannot effectively vent air and relieve internal stress, making it difficult to balance weight reduction and mechanical properties.

[0009] 3. Simple molding structure: The mold cavity and mold core are mostly machined as a whole, lacking modular design, resulting in long product development cycle, poor flexibility in structural adjustment, and insufficient mold versatility.

[0010] 4. Limited application scope: It is mainly suitable for general plastic products, and has poor process adaptability to high-performance and functional materials, making it difficult to meet the molding requirements of complex structural parts such as interior parts of new energy vehicles and shells of home appliances. Summary of the Invention

[0011] In view of the above-mentioned shortcomings of the prior art, the present invention aims to overcome the problems of traditional injection foaming molds having a simple structure, unstable molding quality and poor process adaptability, and proposes a secondary mold opening injection foaming mold and molding method with foaming control capability.

[0012] The technical solution of the present invention is as follows:

[0013] A mold structure based on secondary mold opening and micro-foaming is characterized by comprising a fixed mold assembly, a moving mold assembly, a support plate, and a servo control system. The fixed mold assembly includes a fixed mold base plate and a fixed mold plate, and the moving mold assembly includes a moving mold plate and a moving mold pad. The support plate is disposed between the moving mold plate and the moving mold pad, and a replaceable cavity insert is installed on the support plate. The upper surface of the cavity insert, the lower surface of the fixed mold plate, and the support plate form a plastic part molding cavity. The support plate can move relative to the moving mold plate in the mold opening direction under the drive of the servo control system, realizing the dynamic expansion of the plastic part molding cavity volume. After the fixed mold plate and the moving mold plate are closed, an initial cavity is formed. After the melt is injected into the initial cavity and pressure is maintained, the servo control system drives the support plate to move in the mold opening direction, thereby expanding the plastic part molding cavity volume and providing space for secondary expansion of the bubbles.

[0014] Furthermore, it also includes a flow-stopping valve control system, which is installed on the secondary flow channel of the moving template. The secondary flow channel includes at least one flow-stopping valve, which can realize the cutting off and opening of the flow channel to control the flow path and time of the melt.

[0015] Furthermore, the aforementioned shut-off valve is precisely positioned on the secondary diversion channel using an M4 hex socket screw, and the opening and closing of the shut-off valve is synchronously controlled by a servo control system.

[0016] Furthermore, the aforementioned cavity insert is fixed in the groove of the bearing plate by screws.

[0017] Furthermore, the distance the aforementioned support plate moves relative to the moving template is 1-5mm, and the servo control system precisely controls the speed, displacement, and time of the support plate's movement.

[0018] Furthermore, an ejection mechanism is provided between the aforementioned moving mold plate and the moving mold pad. The ejection mechanism includes an ejector pin, an ejector pin fixing plate, and an ejector pin push plate. The ejector pin passes through the support plate and the cavity insert to eject the plastic part after the mold is fully opened.

[0019] The injection foaming molding method of the present invention using the above-described mold structure is characterized by comprising the following steps:

[0020] (1) Mold closing: The fixed mold plate and the moving mold plate close together to form the initial cavity;

[0021] (2) Injection and holding pressure: The molten polymer is injected into the initial cavity and held under pressure;

[0022] (3) Secondary mold opening and cavity expansion: After the injection and holding pressure is completed, after a set delay time, the servo control system drives the bearing plate to move along the mold opening direction to expand the cavity volume, release the cavity pressure, and promote the secondary expansion of the bubble.

[0023] (4) Cooling and shaping: Cooling is performed while maintaining the expanded cavity state to stabilize the bubble structure;

[0024] (5) Full mold opening and ejection: The mold is fully opened and the ejection mechanism ejects the plastic part to complete the molding process.

[0025] Furthermore, in step (3) above, the speed, displacement and time of the plate movement are adjusted according to the product material and structural requirements.

[0026] Furthermore, the above-mentioned molten polymer is TPU, PP or PA, and the foaming gas is N2 or CO2.

[0027] Furthermore, the molten polymer is thermoplastic polyurethane, the foaming gas is nitrogen, and the process parameters are set as follows: injection pressure 70 MPa, injection speed 30 mm / s, melt temperature 195℃, mold temperature 45℃, cooling time 6 s, and gas content 0.6 wt.%. The mold opening distance for the secondary mold opening is 1-5 mm. By adjusting the mold opening distance, the cell structure and product properties can be precisely controlled: when the mold opening distance is 1-2 mm, a dense and uniform cell structure is formed, and the cell density can reach 6.9 × 10⁻⁶. 6 -9.0×10 6 cells / cm³; when the mold opening distance is 3mm, cell nucleation and growth reach dynamic equilibrium, and the peak cell density is 1.0×10⁻⁶. 7cells / cm³; when the mold opening distance is 3-5mm, the product density decreases to 0.418g / cm³, and the foaming ratio increases to 2.655, which is suitable for preparing TPU microporous foamed products with lightweight, high strength and excellent surface quality.

[0028] This invention introduces a controllable mold opening structure and a dynamic mold cavity expansion design. After melt injection and pressure holding, the support plate moves along a set path to expand the cavity volume, release gas, promote uniform expansion of the bubbles, and significantly improve the foaming uniformity and molding quality of the product.

[0029] The modular cavity structure, composed of replaceable inserts, enables rapid switching between different sizes or structural requirements, enhancing the versatility of the mold and the flexibility of structural adjustment, making it suitable for multi-specification, small-batch, or customized production scenarios.

[0030] By arranging a controllable flow-stopping mechanism in the runner system, precise control of the melt flow path and rhythm can be achieved, which can assist in the expansion and regulation of the foaming pressure of the mold cavity, optimize the cell structure, and improve the mechanical properties and weight reduction of the product.

[0031] It simplifies system composition, reduces energy consumption and equipment investment, and improves industrial adaptability. It is suitable for injection molding of foamed products of different scales, and is especially suitable for the preparation of thick-walled, irregularly shaped or functional foamed products.

[0032] In summary, this application, by introducing a controllable mold opening structure and a dynamic cavity expansion design, allows the mold platen to move along a set path to expand the cavity volume after melt injection and holding pressure, releasing gas and promoting uniform bubble expansion, significantly improving the foaming uniformity and molding quality of the product. To enhance mold versatility and structural adjustment capabilities, key areas of the mold cavity employ a replaceable insert design, enabling rapid switching between different sizes or structural requirements, suitable for multi-specification, small-batch, or customized production scenarios. Furthermore, a controllable flow-stopping mechanism is arranged in the runner system to achieve precise control of the melt flow path and rhythm, assisting in cavity expansion to regulate foaming pressure and optimize bubble structure. The synergistic effect of these three elements effectively solves the defects of uneven bubble formation and structural collapse in traditional molds during the foaming process, improving process adaptability and product performance. Attached Figure Description

[0033] Figure 1 This is a left view of the mold of the present invention;

[0034] Figure 2 This is a front view of the mold of the present invention;

[0035] Figure 3 This is a schematic diagram of the mold opening process of the present invention.

[0036] Figure 4 This is a schematic diagram of the secondary mold opening of the mold of the present invention;

[0037] Figure 5 This is a schematic diagram of the flow channel closure state;

[0038] Figure 6 This is a schematic diagram of the flow path. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] like Figure 1 As shown, the main structure of the mold includes a fixed mold assembly (fixed part) and a moving mold assembly (movable part). The fixed mold assembly includes a fixed mold base plate 1 and a fixed mold plate 2, while the moving mold assembly includes a moving mold plate 3 and a moving mold pad 6. The cooperation between the fixed mold plate 2 and the moving mold plate 3 directly affects the molding quality and production efficiency of the plastic part. During the plastic melt filling process, the moving mold plate 3 needs to withstand high pressure. If the structural support is insufficient, it is easy to cause mold plate deformation, affecting product accuracy. Therefore, this application sets a load-bearing support plate 4 between the moving mold plate 3 and the moving mold pad 6, which not only enhances the structural support but also adjusts the assembly gap and improves the overall stability of the mold.

[0041] A replaceable cavity insert 9 is installed on the support plate 4. The cavity insert 9 is fixed in the groove of the support plate 4 by screws. The upper surface of the cavity insert 9, the lower surface of the fixed template 2 and the support plate 4 work together to form the cavity outline of the final plastic part (or the initial cavity, which is called the plastic part molding cavity 8 after dynamic expansion). The support plate 4 can move relative to the moving template 3 in the mold opening direction under the drive of the servo control system in the injection molding machine to realize the dynamic expansion of the volume of the plastic part molding cavity 8. The mold opening distance is 1-5 mm. The mold opening sequence is accurate and the process is stable, which makes it easy to observe or control the foaming behavior in the cavity at a specific stage and improve the molding accuracy.

[0042] The mold structure also includes a flow control system (including a first flow control valve 16, a second flow control valve 17, and a third flow control valve 18). These flow control valves are installed on the secondary flow channel 15 and are precisely installed and positioned by M4 hexagonal screws. The flow channel can be cut off and opened by the action of the flow control valves, thereby controlling the flow path and time of the melt.

[0043] This application's mold structure, combined with an injection molding machine servo system, achieves secondary mold opening control: after the injection and holding time is 2 seconds, a 4-second delay is set for mold opening. The servo system precisely drives the support plate 4 to move along a predetermined path, achieving dynamic cavity expansion (i.e., secondary mold opening). This action allows for controllable changes in cavity volume, releases gas pressure within the cavity, reduces the risk of bubble collapse, and provides space for secondary bubble expansion, contributing to obtaining uniformly distributed and structurally stable foamed products. The speed, displacement, and timing accuracy of the support plate 4's movement affect the primary mold opening, thus significantly impacting the quality and performance of the foamed product. After mold opening and cooling, the mold performs a full mold opening action, and the ejection mechanism smoothly pushes out the plastic part, completing the entire injection molding foaming process.

[0044] Specifically, during the mold opening process, the support plate 4 first partially opens under the drive of the control system, that is, the template moves along the mold opening direction, such as... Figure 3 As shown. At this point, the mold is completely closed, with only a portion of the mold plate moving. The molding cavity 8 of the plastic part gradually expands, providing space for the release of gas inside the melt and the secondary expansion of the bubbles. This process usually begins after the injection holding pressure is completed, with a preset delay. The mold opening delay time and speed directly affect the bubble development morphology and uniformity. After partial mold opening, the cavity volume expands rapidly, and the melt further foams in the reduced pressure environment, allowing the bubbles to grow fully and improving the lightweight and structural uniformity of the product. After the bubbles expand and initially solidify, the mold remains in an expanded cavity state and enters cooling, allowing the product to gradually solidify within the expanded cavity. Subsequently, the mold opening continues until it is fully open, as shown. Figure 4 As shown, the moving mold and the fixed mold are completely separated, and the ejection mechanism starts synchronously to smoothly push out the shaped foamed product, completing the molding process. The time control between partial mold opening and full mold opening, the cavity expansion stroke, and the cooling time need to be precisely coordinated to ensure stable product dimensions, uniform cell size, and excellent surface quality, effectively improving the problems of poor foaming uniformity, mechanical properties, and surface quality caused by traditional one-time full mold opening.

[0045] An ejection mechanism is provided between the moving mold plate 3 and the moving mold pad 6. The ejection mechanism includes an ejector pin 10, an ejector pin fixing plate 11 and an ejector pin push plate 12. The ejector pin 10 passes through the support plate 4 and the cavity insert 9 to eject the plastic part 13 after the mold is fully opened.

[0046] In the specific embodiments of this application, compared with the traditional micro-foaming injection molding process, the biggest advantage of the secondary mold opening micro-foaming injection molding process is that it can achieve precise control of the foaming ratio of the product by adjusting the mold opening distance (increasing the cavity and increasing the foaming space), thereby producing foam with better surface quality, higher foaming ratio, lighter weight and better cell uniformity.

[0047] This example experiment used BASF TP (Elastollan® 1180A) as the research material, with N2 as the foaming gas. The injection molding process conditions were as follows: injection speed 70 MPa, injection pressure 30 mm / s, melt temperature 195°C, mold temperature 45°C, cooling time 6 s, and gas content 0.6 wt.%. Under these process conditions, the average cell diameter of the product was 66.4 μm, and the cell density was 6.9 × 10⁻⁶. 5 This application investigated the effect of increasing the mold opening distance and changing the cavity volume (1-5 mm) on the cell structure using a conventional microfoaming injection molding process (without cavity expansion). Experimental results show that, specifically, when the mold opening distance is 1 mm and 2 mm, the overall cell structure is compact and small in size; when the mold opening distance increases from 1 mm to 2 mm, the average cell diameter decreases from 48.7 μm to 44.2 μm, and the cell density increases from 6.9 × 10⁻⁶ cells / cm³. 6 The number of cells / cm³ increased to 9.0×10⁻⁶. 6 The cell density decreased from 13.09 μm to 9.15 μm, indicating that an appropriate die-opening distance contributes to uniform cell nucleation, resulting in a denser cell structure. When the die-opening distance was further increased to 3 mm, the cell density reached a peak of 1.0 × 10⁻⁶ cells / cm³. 7 The cell / cm³ density decreased to 7.09 μm, but the cell diameter slightly increased to 51.9 μm. At this stage, cell nucleation and growth reached a relative equilibrium, and the overall structure remained relatively uniform. When the mold opening distance continued to increase (3-5 mm), the cell diameter increased significantly, and the cell density decreased rapidly. The cell diameter reached its maximum value of 82.9 μm, and the cell density decreased to its minimum of 2.4 × 10⁻⁶. 6 The foam density increased by 1 mm / cm³, and the shape of the cells showed significant stretching along the mold opening direction, with the cells appearing as elongated or irregular ovals. As the mold opening distance increased from 1 mm to 5 mm, the skin thickness increased from 0.330 mm to 0.521 mm, the cell wall thickness decreased from 13.09 μm to 5.05 μm, the part density gradually decreased from 0.660 g / cm³ to 0.418 g / cm³, and the foaming ratio increased from 1.681 to 2.655, showing an overall trend of decreasing density and increasing foaming ratio. By comparing conventional microfoaming injection molding with cavity expansion molding, it can be found that the secondary mold opening microfoaming process can optimize the cell diameter and cell density, improve surface quality and cell uniformity, and enhance the macroscopic properties of the product, such as foaming ratio, compression performance, and thermal insulation performance. Ultimately, it can produce TPU microporous foamed products with excellent comprehensive properties. This patent application helps to provide a theoretical basis for the process optimization of polymer foamed products and promote their practical application in the fields of lightweight parts and high-end packaging materials.

[0048] This invention achieves structural cavity expansion after injection and holding pressure by setting a controllable support plate and modular inserts. It does not rely on complex variable mold temperature systems and high-pressure gas environments, simplifying system configuration, reducing energy consumption and equipment investment, and possessing higher industrial adaptability, making it suitable for injection molding of foamed products of different scales. By precisely controlling the mold opening distance and timing, precise control of the mold opening action is achieved, ensuring stable bubble expansion space and improving molding stability and yield. The structure design of the support plate and replaceable cavity inserts allows for quick replacement of key mold cavity components to meet different product structures or bubble requirements, significantly reducing mold modification and maintenance costs and extending mold life. It is particularly suitable for injection molding of thick-walled, irregularly shaped, or functional foamed products.

[0049] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A mold structure based on secondary mold opening and micro-foaming, characterized in that, The system includes a fixed mold assembly, a moving mold assembly, a support plate (4), and a servo control system. The fixed mold assembly includes a fixed mold base plate (1) and a fixed mold plate (2). The moving mold assembly includes a moving mold plate (3) and a moving mold pad (6). The support plate (4) is disposed between the moving mold plate (3) and the moving mold pad (6). A replaceable cavity insert (9) is installed on the support plate (4). The upper surface of the cavity insert (9), the lower surface of the fixed mold plate (2), and the support plate (4) form a plastic part molding cavity (8). The support plate (4) can move relative to the moving mold plate (3) in the mold opening direction under the drive of the servo control system to realize the dynamic expansion of the volume of the plastic part molding cavity (8). After the fixed mold plate (2) and the moving mold plate (3) are closed, an initial cavity is formed. After the melt is injected into the initial cavity and the pressure is maintained, the servo control system drives the support plate (4) to move in the mold opening direction, so that the volume of the plastic part molding cavity (8) is expanded, providing space for the secondary expansion of the bubble.

2. The mold structure based on secondary mold opening and micro-foaming according to claim 1, characterized in that, It also includes a flow control system, which is set on the secondary flow channel (15) of the moving template (3). The secondary flow channel includes at least one flow control valve, which can cut off and open the flow channel to control the flow path and time of the melt.

3. The mold structure based on secondary mold opening and micro-foaming according to claim 2, characterized in that, The shut-off valve is precisely positioned on the secondary diversion channel using an M4 hex socket screw, and the opening and closing of the shut-off valve is synchronously controlled by a servo control system.

4. The mold structure based on secondary mold opening and micro-foaming according to claim 3, characterized in that, The cavity insert (9) is fixed in the groove of the support plate (4) by screws.

5. The mold structure based on secondary mold opening and micro-foaming according to claim 1, characterized in that, The distance the bearing plate moves relative to the moving template (3) is 1-5mm, and the servo control system precisely controls the speed, displacement and time of the bearing plate movement.

6. The mold structure based on secondary mold opening and micro-foaming according to claim 1, characterized in that, An ejection mechanism is provided between the moving template (3) and the moving mold pad (6). The ejection mechanism includes an ejector pin (10), an ejector pin fixing plate (11), and an ejector pin push plate (12). The ejector pin (10) passes through the support plate (4) and the cavity insert (9) to eject the plastic part (13) after the mold is fully opened.

7. A method for injection foaming molding based on the mold structure described in any one of claims 1-6, characterized in that, Includes the following steps: (1) Mold closing: The fixed mold plate and the moving mold plate close together to form the initial cavity; (2) Injection and holding pressure: The molten polymer is injected into the initial cavity and held under pressure; (3) Secondary mold opening and cavity expansion: After the injection and holding pressure is completed, after a set delay time, the servo control system drives the bearing plate to move along the mold opening direction to expand the cavity volume, release the cavity pressure, and promote the secondary expansion of the bubble. (4) Cooling and shaping: Cooling is performed while maintaining the expanded cavity state to stabilize the bubble structure; (5) Full mold opening and ejection: The mold is fully opened and the ejection mechanism ejects the plastic part to complete the molding process.

8. The molding method according to claim 7, characterized in that, In step (3), the speed, displacement and time of the plate movement are adjusted according to the product material and structural requirements.

9. The molding method according to claim 7, characterized in that, The molten polymer is TPU, PP or PA, and the foaming gas is N2 or CO2.

10. The molding method according to claim 7, characterized in that, The molten polymer is thermoplastic polyurethane, and the foaming gas is nitrogen. The process parameters are set as follows: injection pressure 70 MPa, injection speed 30 mm / s, melt temperature 195℃, mold temperature 45℃, cooling time 6 s, and gas content 0.6 wt.%. The mold opening distance for the secondary mold opening is 1-5 mm. By adjusting the mold opening distance, the cell structure and product properties can be precisely controlled: when the mold opening distance is 1-2 mm, a dense and uniform cell structure is formed, and the cell density can reach 6.9 × 10⁻⁶. 6 -9.0×10 6 cells / cm³; when the mold opening distance is 3mm, cell nucleation and growth reach dynamic equilibrium, and the peak cell density is 1.0×10⁻⁶. 7 cells / cm³; when the mold opening distance is 3-5mm, the product density decreases to 0.418g / cm³, and the foaming ratio increases to 2.655, which is suitable for preparing TPU microporous foamed products with lightweight, high strength and excellent surface quality.

Images