Three-stage air flotation auxiliary demolding method and structure for injection mold

Abstract

The invention discloses a three-stage air flotation auxiliary demolding method and structure for an injection mold, and belongs to the technical field of injection molding. The invention aims to solve the problems of top white, top marks, buckling deformation and other defects caused by stress concentration and non-uniform demolding force due to traditional mechanical ejection during demolding of thin-wall and large-curved-surface parts. The method comprises the steps that S1, in the pressure maintaining and cooling stage, low-pressure gas is introduced through a porous gas permeation insert integrated with the ejector pin to form a gas floating layer so as to share stress; s2, at the moment of opening the mold, introducing pulse type medium-high pressure gas to integrally release the workpiece; and S3, the separated workpiece is ejected out in a stress-free mode through the ejector pin. Through a cooperative working mode of pre-separation, impact release and unstressed ejection, the demolding resistance is reduced from the source, uniform and instantaneous integral release is realized, demolding defects are eradicated, and the yield and the surface quality of precise workpieces are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of injection molding technology, specifically relating to a demolding method and demolding structure for injection molds, and in particular a method and structure for achieving low-stress, high-quality demolding using gas assistance, which is especially suitable for the production of thin-walled, large-curved or high-precision optical components. Background Technology

[0002] Injection molding is one of the most widely used processing methods in modern plastic product manufacturing. With the development of the automotive industry, consumer electronics, and optical instruments, the demand for plastic parts with complex structures, precise dimensions, and high surface quality requirements is increasing, such as curved reflective lenses and precision optical lenses in automotive head-up displays (HUDs). These parts typically have thin walls, large projected areas, complex surface curvatures, and require zero surface defects.

[0003] In traditional injection molding processes, the demolding process is one of the key bottlenecks determining the final product quality and production efficiency. Conventional demolding methods primarily rely on mechanical ejection mechanisms, where multiple ejector pins or blocks apply mechanical force after the mold opens to forcibly eject the cooled and solidified part from the mold core. However, when applied to the aforementioned thin-walled, large-curvature optical parts, this purely mechanical ejection method reveals several insurmountable drawbacks: 1. During the cooling process, the workpiece shrinks, generating a significant clamping force on the mold core, resulting in a tight fit between the workpiece and the core surface. When the ejector pin ejects, its force is highly concentrated in the tiny area of ​​contact with the workpiece. For plastics that are not yet fully rigidified (especially optical materials such as polycarbonate PC), this concentrated stress can easily exceed the material's yield strength, leading to permanent plastic deformation or damage in the ejector pin's area of ​​action. Macroscopically, this manifests as ejector whitening or ejector marks (i.e., stress whitening). The microscopic mechanism of this phenomenon is that under stress, microcracks and microvoids are generated within the polymer. These microstructures scatter light, causing transparent or translucent materials to appear white or opaque, severely affecting optical performance and product aesthetics.

[0004] 2. Although the ejection actions of multiple ejector pins are theoretically synchronized, it is difficult to guarantee a completely uniform force distribution in practice. Uneven demolding forces can cause uneven peeling of the part during the process of detaching from the mold core. Combined with the inherent residual stress inside the part, this can easily lead to overall warping or local twisting deformation, damaging its precise optical surface contours and causing the product to be scrapped.

[0005] 3. For parts with large surface areas and small draft angles, the total contact force between the part and the mold core (composed of clamping force and possible vacuum adsorption) is very large, requiring a very large ejection force to complete demolding. This not only places higher demands on the strength and precision of the ejection mechanism, but also increases the risk of the part being torn or damaged during demolding.

[0006] To address these issues, the industry has explored various approaches. For example, gas-assisted demolding technology has been employed. Current gas-assisted demolding methods typically involve blowing high-pressure gas instantaneously between the part and the mold using nozzles on the mold after mold opening, using air pressure to blow the part away from the mold. However, this simple and direct blowing method presents new problems: first, the instantaneous high-pressure airflow may create air streaks or scorch marks on the part's surface, which is unacceptable for optical components; second, uneven airflow can also lead to part deformation or being blown away, making the process difficult to control precisely.

[0007] In addition, there is gas-assisted injection molding technology, which mainly involves injecting high-pressure gas into the melt during the injection and holding pressure stages to form a hollow structure, eliminate shrinkage marks, and assist in filling. The mechanism of action and application stages of this technology are different from those for solving demolding problems, as the gas acts inside the melt rather than on the contact surface between the part and the mold.

[0008] Therefore, existing technologies still lack a mild demolding solution that can effectively solve the demolding difficulties of thin-walled, large-curvature optical components and fundamentally avoid defects such as whitening, marks, and deformation, and has a controllable process. Summary of the Invention

[0009] To address the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a three-stage air-float assisted demolding method and structure for injection molds. This aims to solve the problems of stress concentration, uneven demolding force, and surface and structural defects such as whitening, ejection marks, and warping caused by the prior art's reliance on mechanical ejection when demolding thin-walled, large-curved, and high-precision optical parts.

[0010] To achieve the above objectives, the present invention provides a three-stage air-float assisted demolding method for injection molds, comprising the following steps: S1. During the pressure holding and cooling stages of the injection molding cycle, at least one porous gas permeation insert is provided at the ejector pin position to introduce low-pressure gas with a first preset pressure between the molded part and the mold core provided in the moving mold, forming a uniform air floating layer on the contact surface between the part and the mold core. This layer is used to actively share and balance the internal stress generated by the part during the cooling and shrinkage process, and to suppress excessive adhesion between the part and the mold core. S2. At the initial moment of mold opening, a pulsed medium-high pressure gas with a duration of a preset pulse width and a second preset pressure is introduced into the air flotation layer through the porous air-permeable insert. The instantaneous impact force generated by the pulsed medium-high pressure gas is used to make the part detach from the mold core surface as a whole and synchronously. S3. After the part is separated from the mold core surface by the pulsed high-pressure gas, the ejector pin is driven to perform an ejection motion to complete the final ejection and demolding of the part that is already in the separated state.

[0011] Preferably, the pressure range of the low-pressure gas at the first preset pressure is 0.05 MPa to 0.2 MPa.

[0012] Preferably, the pressure range of the medium-high pressure gas at the second preset pressure is 0.4 MPa to 1 MPa.

[0013] Preferably, the preset pulse width of the pulsed medium-high pressure gas is 0.1s to 0.5s.

[0014] Preferably, the part is a thin-walled optical curved surface part.

[0015] The present invention also provides a three-stage air-float assisted demolding structure for injection molds, comprising: A fixed mold and a moving mold, wherein the moving mold is provided with a mold core for forming the back side of the part and an ejection mechanism, the ejection mechanism including a plurality of ejector pins; At least one porous venting insert is integrated with the ejector pin and disposed within the moving mold, wherein the venting surface of the porous venting insert is configured to face the part. A gas supply and control system is provided, which is connected to the porous gas-permeable insert through a gas passage provided inside the mold. The gas supply and control system is configured to supply low-pressure gas at a first preset pressure to the porous gas-permeable insert during the holding and cooling stages according to the timing of the injection molding cycle, and to supply pulsed medium-high pressure gas at a second preset pressure to the porous gas-permeable insert at the initial moment of mold opening.

[0016] Preferably, the porous permeable insert is made of sintered porous metal material.

[0017] Preferably, the sintered porous metal material has an interconnected internal microporous structure with pore sizes configured to allow gas molecules to pass through while preventing molten plastic from entering its interior, and the porosity of the sintered porous metal material accounts for 20% to 30% of its total volume.

[0018] Preferably, the porous air-permeable insert is coaxially arranged with the ejector pin and is configured as a top cover structure covering the top surface of the ejector pin or a sleeve structure surrounding the top of the ejector pin.

[0019] Preferably, the gas supply and control system includes: Gas source; Low-pressure regulator and high-pressure regulator connected to the gas source; A first electromagnetic control valve and a second electromagnetic control valve are respectively connected to the downstream gas path of the low-pressure regulator and the high-pressure regulator. The outlets of the first electromagnetic control valve and the second electromagnetic control valve are combined and connected to the gas path channel. The PLC controls both the first and second electromagnetic control valves. The PLC is synchronized with the injection molding machine's control system and is used to independently and precisely control the timing and duration of the supply of the low-pressure gas and the pulsed medium-high pressure gas.

[0020] One or more technical solutions provided in this invention have at least the following technical effects or advantages: This invention introduces a first air-float stress-sharing stage. During the critical period when the workpiece is still under pressure and cooling, and internal stress is forming, a uniform air-float layer is pre-formed between the workpiece and the mold core by introducing low-pressure gas. This air-float layer not only actively shares and balances the internal stress generated by uneven shrinkage of the workpiece, but more importantly, it effectively prevents excessive adhesion and vacuum adsorption between the workpiece and the mold core due to cooling shrinkage. This fundamentally reduces the basic resistance that needs to be overcome for subsequent demolding, realizing a shift from passive, forceful demolding to active, gentle pre-separation.

[0021] In the second pulse release stage of this invention, a uniform, instantaneous impact force covering the entire back of the part is generated at the moment the mold opens using pulsed medium-high pressure gas. This impact force enables the part to detach synchronously and perpendicularly to the mold core surface, avoiding the peeling-type demolding caused by uneven force application at multiple points in traditional ejector pins. This effectively suppresses warping and twisting deformation of the part, ensuring the dimensional and surface accuracy of the part.

[0022] In the third mechanical ejection stage of this invention, the timing of the ejector pin's action is fundamentally changed. At this point, the workpiece has been completely separated from the mold core by the gas pulse of the second stage and is in a floating or slightly contacting state. The role of the ejector pin is no longer to forcefully break apart the workpiece by overcoming huge viscous forces, but to smoothly push a freed object. Because the force applied by the ejector pin is extremely small, far below the yield limit of the material, surface quality defects such as ejector whitening, ejector marks, and stress whitening caused by ejector pin stress concentration are completely eliminated, greatly improving the product yield, especially for optical-grade products with stringent requirements for appearance and performance.

[0023] Furthermore, this invention cleverly integrates a porous gas-permeable insert with an ejector pin structure, ensuring a high degree of alignment between the gas action area and the mechanical ejection point, resulting in a compact structure and high efficiency. The timing and pressure control of the entire three-stage process can be precisely synchronized with the injection molding machine control system, achieving seamless coordination between pneumatic and mechanical actions. This method is not only applicable to high-requirement thin-walled optical components such as HUD lenses, but also provides a highly reliable and high-quality solution for the production of other precision, complex, or large thin-walled parts prone to mold release defects. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the injection mold in a closed state in the first embodiment of the present invention.

[0025] Figure 2 This is a partially enlarged schematic diagram of the working state in the first stage (S1) of the demolding method according to the first embodiment of the present invention.

[0026] Figure 3 This is a partially enlarged schematic diagram of the working state in the second stage (S2) of the demolding method according to the first embodiment of the present invention.

[0027] Figure 4 This is a partially enlarged schematic diagram of the working state in the third stage (S3) of the demolding method according to the first embodiment of the present invention.

[0028] Figure 5 This is a schematic diagram of the injection mold in the first embodiment of the present invention, in the open and ejected state.

[0029] Figure 6 This is a schematic diagram of the injection mold in a closed state in the second embodiment of the present invention.

[0030] Figure 7 This is a block diagram of the gas supply and control system in an embodiment of the present invention.

[0031] Figure 8 A flowchart of a three-stage air flotation-assisted demolding method provided in an embodiment of the present invention. Explanation of reference numerals in the attached drawings: 1. Ejector pin; 2. Porous air-permeable insert; 3. Part; 3a. Air flotation layer; 3b. Gap; 4. Air passage; 5. Gas source; 6. Low-pressure regulator; 7. High-pressure regulator; 8a. First electromagnetic control valve; 8b. Second electromagnetic control valve; 9. PLC; 10. Mold core; 11. Fixed mold; 12. Moving mold; 13. Mold cavity. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0033] This invention provides a three-stage air-float assisted demolding structure and method for injection molds, which is particularly suitable for producing thin-walled optical curved surface parts such as automotive HUD curved reflective lenses. Example 1

[0034] Please see Figures 1 to 5 ,as well as Figure 7 and Figure 8 .

[0035] The demolding structure of this embodiment is applied in an injection mold. The injection mold includes a fixed mold 11 and a moving mold 12. The fixed mold 11 has a mold cavity 13 for forming the front side (typically an optical functional surface) of the part 3. The moving mold 12 has a mold core 10 for forming the back side of the part 3, and an ejection mechanism for ejecting the part 3. The ejection mechanism includes at least one ejector pin 1. During injection molding, as... Figure 1 As shown, the fixed mold 11 and the moving mold 12 are closed, and the mold cavity 13 and the mold core 10 together form a cavity space for filling the plastic melt.

[0036] The core structure of this embodiment lies in the integration of a gas-assisted device and a mechanical ejection mechanism within the moving mold 12. Specifically, this structure includes a porous gas-permeable insert 2 and a gas supply and control system.

[0037] like Figure 1 and Figure 2 As shown, a porous venting insert 2 is integrated at the ejection position of at least one ejector pin 1. In this embodiment, the porous venting insert 2 is constructed as a top cover structure and is reliably fixed to the top surface of the ejector pin 1 via a threaded connection or other means. The ejector pin 1 has a communicating air passage 4 machined inside. In this structure, the porous venting insert 2 and the ejector pin 1 are integrated as a whole and move synchronously with the ejection mechanism. The venting surface of the porous venting insert 2 is flush with the surface of the mold core 10, together forming the molding surface of the part 3.

[0038] Preferably, the porous gas-permeable insert 2 is made of a sintered porous metal material with a large number of interconnected micropores. A key characteristic of this material is that it is permeable to air but not to material. The pore size of its micropores is precisely controlled, allowing gas molecules to pass freely while effectively preventing molten plastic with larger molecular chains from penetrating into its interior, thus avoiding blockage of the porous gas-permeable insert 2. This structure ensures that gas can act uniformly and stably on the surface of the part 3 without contaminating the part 3 or causing the porous gas-permeable insert 2 to fail. More preferably, the porosity of the sintered porous metal material accounts for 20% to 30% of its total volume, so as to ensure sufficient air permeability while possessing the mechanical strength required to withstand the high pressure of injection molding.

[0039] like Figure 7 As shown, the gas supply and control system supplies gas to the porous gas-permeable insert 2 according to a preset timing and pressure. This gas supply and control system includes a gas source 5, whose output gas path is split into two: one branch connects to a low-pressure regulator 6 and a first solenoid control valve 8a controlled by a PLC 9; the other branch connects to a high-pressure regulator 7 and a second solenoid control valve 8b controlled by a PLC 9. The outlets of the first solenoid control valve 8a and the second solenoid control valve 8b merge through pipelines, connecting to a gas passage 4 located inside the mold, and ultimately delivering the gas to the porous gas-permeable insert 2. The PLC 9 is synchronized with the central control system of the injection molding machine, enabling it to independently and precisely control the opening and closing of the first solenoid control valve 8a and the second solenoid control valve 8b according to different stages of the injection molding cycle, thereby achieving time-sharing supply of low-pressure gas and pulsed medium- and high-pressure gas.

[0040] Based on the above structure, the three-stage air flotation-assisted demolding method of the present invention is carried out according to the following steps, as follows: Figure 8 As shown: S1: First stage of air buoyancy stress sharing See Figure 2 When the injection molding machine completes injection filling and enters the holding and cooling stage, PLC9 controls the opening of the first electromagnetic control valve 8a. At this time, low-pressure gas (preferably within the pressure range of 0.05 MPa to 0.2 MPa) regulated by the low-pressure regulator 6 enters the porous gas-permeable insert 2 through the gas passage 4 and permeates evenly from the surface of the porous gas-permeable insert 2. Since the part 3 is still in a high-temperature molten or semi-solid state at this time, this uniform low-pressure gas will form an extremely thin air-floating layer 3a between the part 3 and the mold core 10. The innovation of this stage lies in proactive prevention: this air-floating layer can not only actively share and balance the internal stress generated by the part 3 during cooling and shrinkage, but also prevent excessive adhesion and vacuum adsorption between the part 3 and the mold core 10 due to cooling and shrinkage from the source. This greatly reduces the basic resistance that needs to be overcome for subsequent demolding, laying a crucial foundation for achieving low-stress demolding.

[0041] S2: Second Pulse Demolding Stage See Figure 3 At the initial moment when cooling is complete and the injection molding machine performs the mold opening action, PLC9 immediately closes the first electromagnetic control valve 8a and simultaneously opens the second electromagnetic control valve 8b in a pulse manner (preferably with a pulse width of 0.1s to 0.5s). At this time, the medium-high pressure gas (preferably with a pressure range of 0.4Mpa to 1Mpa) regulated by the high pressure regulator 7 instantly impacts the existing air flotation layer 3a. This instantaneous high-pressure pulse generates a uniform and powerful impact force on the entire back side of the part 3, enabling the part 3 to detach from the mold core 10 surface as a whole and synchronously, forming a uniform gap 3b. This impact-type release method avoids the peeling process caused by uneven force application at multiple points by the traditional ejector pins 1, thereby effectively suppressing the warping and twisting deformation of the part 3, which is crucial for ensuring the precision surface shape of optical components such as HUD lenses.

[0042] S3: Third Mechanical Ejection Stage See Figure 4 and Figure 5 After part 3 is completely separated from mold core 10 by gas pulse, the ejection mechanism of the injection molding machine is activated, driving ejector pin 1 to move forward. Figure 4 Enlarged view of the part and Figure 5 As shown in the overall state diagram, at this point, ejector pin 1 and the porous air-permeable insert 2 fixed to it move forward together. Their function is no longer to forcefully break apart the object by overcoming huge viscous forces, but to smoothly push the object, which is already in a separated state, out of the mold. Since the force applied by ejector pin 1 at this stage is extremely small, far below the yield limit of the material, the surface defects such as ejector whitening, ejector marks, and stress whitening caused by stress concentration of ejector pin 1 are completely eliminated, greatly improving the product qualification rate and appearance quality. Example 2

[0043] Please see Figure 6 This embodiment is largely the same in structure and method as Embodiment 1, with the main difference being the integration method of the porous gas-permeable insert 2 and the ejector pin 1.

[0044] In this embodiment, the porous venting insert 2 is constructed as a sleeve structure. Specifically, the porous venting insert 2 is machined into an annular sleeve. Its installation method involves directly machining an annular groove on the mold core 10 to mate with the annular sleeve, and then precisely embedding the annular porous venting insert 2 into the groove, ensuring its end face is flush with the surface of the mold core 10. The ejector pin 1 is independently disposed within the central hole of the annular sleeve-shaped porous venting insert 2 and can slide freely driven by the ejection mechanism. In this structure, the porous venting insert 2 remains stationary during demolding; only the ejector pin 1 performs the ejection movement in the third stage. The air passage 4 is directly connected to the fixed porous venting insert 2 without passing through the interior of the ejector pin 1.

[0045] This embodiment also adopts Figure 7 The gas supply and control system shown follows... Figure 8 The three-stage demolding method shown is the same as that in Example 1, in terms of its working principle and the beneficial effects it can achieve.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A three-stage air-flood assisted demolding method for injection molds, characterized in that, Includes the following steps: S1. During the pressure holding and cooling stages of the injection molding cycle, at least one porous gas-permeable insert (2) located at the ejector pin (1) position introduces low-pressure gas with a first preset pressure between the molded part (3) and the mold core (10) located in the moving mold (12), forming a uniform air-floating layer on the contact surface between the part (3) and the mold core (10), which is used to actively share and balance the internal stress generated by the part (3) during the cooling and shrinkage process, and suppress the excessive adhesion force between the part (3) and the mold core (10). S2. At the initial moment of mold opening, a pulsed medium-high pressure gas with a duration of a preset pulse width and a second preset pressure is introduced into the air flotation layer through the porous gas permeation insert (2). The instantaneous impact force generated by the pulsed medium-high pressure gas is used to make the part (3) detach from the surface of the mold core (10) as a whole and synchronously. S3. After the part (3) is separated from the mold core (10) surface by the pulsed high-pressure gas, the ejector pin (1) is driven to make an ejection movement to complete the final ejection and demolding of the part (3) which is already in the separated state.

2. The method according to claim 1, characterized in that, The pressure range of the low-pressure gas at the first preset pressure is 0.05 MPa to 0.2 MPa.

3. The method according to claim 1, characterized in that, The pressure range of the medium-high pressure gas at the second preset pressure is 0.4 MPa to 1 MPa.

4. The method according to claim 1, characterized in that, The preset pulse width of the pulsed medium-high pressure gas is 0.1s to 0.5s.

5. The method according to claim 1, characterized in that, The component (3) is a thin-walled optical curved surface component.

6. A three-stage air-flood assisted demolding structure for injection molds, characterized in that, include: A fixed mold (11) and a moving mold (12), wherein the moving mold (12) is provided with a mold core (10) for forming the back of the part (3) and an ejection mechanism, wherein the ejection mechanism includes a plurality of ejector pins (1). At least one porous venting insert (2) is integrated with the ejector pin (1) within the moving mold (12), and the venting surface of the porous venting insert (2) is configured to face the part (3). A gas supply and control system is provided, which is connected to the porous gas infiltration insert (2) through a gas passage (4) set inside the mold. The gas supply and control system is configured to supply low-pressure gas with a first preset pressure to the porous gas infiltration insert (2) during the pressure holding and cooling stages according to the timing of the injection molding cycle, and to supply pulsed medium-high pressure gas with a second preset pressure to the porous gas infiltration insert (2) at the initial moment of mold opening.

7. The demolding structure according to claim 6, characterized in that, The porous permeable insert (2) is made of sintered porous metal material.

8. The demolding structure according to claim 7, characterized in that, The sintered porous metal material has an interconnected internal microporous structure with pore sizes configured to allow gas molecules to pass through while preventing molten plastic from entering its interior. The porosity of the sintered porous metal material accounts for 20% to 30% of its total volume.

9. The demolding structure according to claim 6, characterized in that, The porous permeable insert (2) is coaxially arranged with the ejector pin (1) and is configured as a top cover structure covering the top surface of the ejector pin (1) or a sleeve structure surrounding the top of the ejector pin (1).

10. The demolding structure according to claim 6, characterized in that, The gas supply and control system includes: Gas source (5); A low-pressure regulator (6) and a high-pressure regulator (7) are connected to the gas source (5). A first electromagnetic control valve (8a) and a second electromagnetic control valve (8b) are respectively connected to the downstream gas path of the low-pressure regulator (6) and the high-pressure regulator (7). The outlets of the first electromagnetic control valve (8a) and the second electromagnetic control valve (8b) merge and are connected to the gas path channel (4). The PLC (9) controls both the first electromagnetic control valve (8a) and the second electromagnetic control valve (8b). The PLC (9) is synchronized with the control system of the injection molding machine and is used to independently and accurately control the timing and duration of the supply of the low-pressure gas and the pulsed medium-high pressure gas.

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