Injection molding process for improving gas lines and weld lines

Abstract

The application proposes an injection molding process for improving gas marks and welding lines, which systematically optimizes injection molding process parameters by precisely controlling melt temperature, front and back mold temperature and injection holding period, maintains high temperature and high pressure state of the melt in the filling and holding stage, enhances the flow intersection pressure, realizes sufficient fusion and strength improvement of the split melt interface; at the same time, cooperates with the main exhaust structure and / or the ejector pin exhaust structure, uses the main exhaust structure and / or the ejector pin exhaust structure to efficiently guide and exhaust the gas in the molding cavity to realize the first-stage exhaust in the filling stage, uses the ejector pin exhaust structure to cooperate with the ejection action to break the vacuum negative pressure to realize the second-stage exhaust in the demolding stage, forms the multi-stage collaborative exhaust effect; thereby effectively eliminates the surface gas marks, obvious welding lines and local scorching defects caused by poor exhaust of the traditional mold, and significantly improves the appearance quality and overall forming yield of the injection molding product.

Description

[Technical Field] This invention relates to the field of injection mold technology, and in particular to an injection molding process that improves air bubbles and weld lines. [Background Technology] In injection molding, molding defects such as weld lines and air trapping often appear on the surface or inside the product. Specifically, on the one hand, when the melt flows in the cavity, it may split due to encountering the core, multiple gates, or sudden changes in wall thickness, forming two or more streams. When these streams re-merge, they cannot fully fuse due to the drop in temperature at the front end of the melt, interface oxidation, and pressure decay, thus leaving obvious linear marks on the surface of the product, i.e., forming weld lines. This not only seriously affects the appearance of the product but also weakens its mechanical strength. On the other hand, during the melt filling process, the original air in the cavity and the gases generated by the thermal decomposition of the plastic cannot be discharged in time. They are compressed by the high-pressure melt and trapped at the end of the cavity or in flow dead corners, which leads to air trapping defects such as air marks, localized scorching, and insufficient filling on the surface of the product. [Summary of the Invention] The purpose of this invention is to provide an injection molding process that improves air lines and weld lines, aiming to solve the problem of weld lines or air lines appearing on the surface or inside of products due to untimely venting.

[0004] This invention is achieved by the following technical solution: An injection molding process for improving air bubbles and weld lines, applied to an injection mold, the injection mold including at least a molding cavity, an ejector pin assembly, a main venting structure, and an ejector pin venting structure, comprising the following steps: S1. Injection molding: The plastic melt is injected into the molding cavity. During the flow and diversion process, the plastic melt pushes the gas in the molding cavity to be discharged to the outside through the main exhaust structure and / or the ejector pin exhaust structure, so as to achieve primary exhaust. S2, Pressure Holding and Cooling: After filling is completed, the plastic melt in the molding cavity is pressurized and held to promote the fusion of the melt interface under pressure, and then cooled and shaped. S3. Demolding: The mold is opened and the molded product is ejected through the ejector pin assembly. During the ejection process, the ejector pin venting structure works in conjunction with the ejection action to break the vacuum negative pressure in the molding cavity and achieve secondary venting.

[0005] As described above, in the injection molding process for improving air bubbles and weld lines, in step S1, the plastic melt is polycarbonate (PC) and acrylonitrile-butadiene-styrene copolymer (ABS); the hopper temperature is 90℃±10℃, the upper mold temperature of the injection mold is 95℃±10℃, and the lower mold temperature is 90℃±10℃.

[0006] As described above, in the injection molding process to improve air marks and weld lines, in step S2, the injection time is 6±2s, the cooling time is 31±5s, and the molding cycle is 62±5s.

[0007] As described above, the injection molding process improves air bubbles and weld lines. The injection mold includes an outer molding assembly disposed between the upper mold and the lower mold, an inner molding block disposed within the outer molding assembly, a molding cavity formed by the inner molding block and the outer molding assembly, and an ejector assembly passing through the inner molding block. The inner molding block is provided with a main venting structure for guiding the gas in the molding cavity to be discharged, and an ejector venting structure that cooperates with the ejector assembly.

[0008] As described above, to improve the injection molding process of air bubbles and weld lines, the inner molding block includes an upper molding part that cooperates with the outer molding component to form the molding cavity, and a lower supporting part.

[0009] As described above, to improve the injection molding process of air marks and weld lines, the main venting structure includes at least one main venting insert that penetrates the inner molding block along the direction from the upper mold to the lower mold, and the end face of the main venting insert is flush with the molding surface of the inner molding block.

[0010] As described above, to improve the injection molding process of air marks and weld lines, the main venting insert is provided with a first venting channel located at the lower part of the support.

[0011] As described above, to improve the injection molding process of air marks and weld lines, the ejector pin venting structure is embedded between the upper molding part and the lower support part, and the end face of the ejector pin venting structure is flush with the molding surface of the inner molding block.

[0012] As described above, to improve the injection molding process of air marks and weld lines, the ejector assembly includes a plurality of ejector pins that can slide relative to the inner molding block. The inner molding block is provided with a plurality of ejector pin through holes that cooperate with the ejector pins, and at least one mounting groove for accommodating the ejector pin venting structure. The mounting groove communicates with the ejector pin through holes.

[0013] As described above, to improve the injection molding process of air marks and weld lines, the ejector pin venting structure is provided with a relief groove that mates with the ejector pin through hole, and a second venting channel located at the lower part of the support.

[0014] Compared with the prior art, the present invention has the following advantages: This invention proposes an injection molding process to improve air marks and weld lines. By precisely controlling the melt temperature, front and rear mold temperatures, and injection holding pressure cycle, the injection process parameters are systematically optimized. During the mold filling and holding pressure stages, the high temperature and high pressure of the melt are maintained, enhancing the material flow convergence pressure and achieving full fusion and strength improvement at the interface of the split melt. Simultaneously, in conjunction with the main venting structure and / or ejector pin venting structure, the main venting structure and / or ejector pin venting structure are used to efficiently guide and discharge the gas in the molding cavity during the mold filling stage to achieve primary venting. During the demolding stage, the ejector pin venting structure, in conjunction with the ejection action, breaks the vacuum negative pressure to achieve secondary venting, forming a multi-stage synergistic venting effect. This effectively eliminates surface air marks, obvious weld lines, and local scorching defects caused by poor venting in traditional molds, significantly improving the appearance quality and overall molding yield of injection molded products. [Attached Image Description] Figure 1 This is a perspective view of the present invention; Figure 2 This is a partial three-dimensional view of the structure of the present invention; Figure 3 This is a top view of the outer molding component and the inner molding block of the present invention; Figure 4 This is a schematic diagram of a partial structure of the outer molding component and the inner molding block of the present invention. Figure 1 ; Figure 5 This is a schematic diagram of a partial structure of the outer molding component and the inner molding block of the present invention. Figure 2 ; Figure 6 Disassembly of the outer molding component and inner molding block of the present invention Figure 1 ; Figure 7 Disassembly of the outer molding component and inner molding block of the present invention Figure 2 ; Figure 8 Decomposition of the internal molding block of the present invention Figure 1 ; Figure 9 for Figure 8 Enlarged view of the structure at point -a; Figure 10 Decomposition of the internal molding block of the present invention Figure 2 .

Detailed Implementation Methods

[0017] In this implementation, by precisely controlling the melt temperature, front and rear mold temperatures, and injection holding pressure cycle, the injection molding process parameters are systematically optimized. During the mold filling and holding pressure stages, the high temperature and high pressure state of the melt is maintained, enhancing the material flow convergence pressure and achieving full fusion and strength improvement at the interface of the split melt. Simultaneously, in conjunction with the main venting structure and / or ejector pin venting structure, the main venting structure and / or ejector pin venting structure are used to efficiently guide and discharge the gas in the molding cavity during the mold filling stage to achieve primary venting. During the demolding stage, the ejector pin venting structure is used in conjunction with the ejection action to break the vacuum negative pressure to achieve secondary venting, forming a multi-stage synergistic venting effect. This effectively eliminates surface air marks, obvious weld lines, and local scorching defects caused by poor venting in traditional molds, significantly improving the appearance quality and overall molding yield of injection molded products.

[0018] Further, in step S1, the plastic melt is polycarbonate (PC) and acrylonitrile-butadiene-styrene copolymer (ABS).

[0019] In this embodiment, the plastic melt material combines high fluidity and high mechanical strength, providing a material basis for improving product appearance defects.

[0020] Further, in step S1, the hopper temperature is 90℃±10℃, the upper mold temperature of the injection mold is 95℃±10℃, and the lower mold temperature is 90℃±10℃.

[0021] In this implementation, controlling the hopper temperature during the injection molding stage effectively prevents plastic particles from softening and sticking prematurely at the discharge port, thus preventing bridging and ensuring uniform and stable material discharge. It also avoids localized overheating and degradation of the material, reducing gas defects at the source. Furthermore, precise control of the upper and lower mold temperatures, achieved through higher mold temperatures, effectively slows the cooling rate of the melt within the cavity, maintaining sufficient temperature and fluidity at the interface of the split melt flow. This promotes deep entanglement of molecular chains, significantly weakening weld lines and eliminating surface gas defects. The slightly higher upper mold temperature allows the product to more tightly adhere to the lower mold side during cooling and shrinkage, ensuring smooth demolding with the moving mold upon mold opening. Combined with the ejector pin assembly, this enables smooth demolding and secondary venting, effectively preventing product sticking or deformation during ejection.

[0022] Furthermore, in step S2, the injection time is 6±2s, the cooling time is 31±5s, and the molding cycle is 62±5s.

[0023] In this implementation, precise control of injection time to increase injection speed avoids both excessively fast injection causing blockage of the main venting structure's micro-grooves and resulting in trapped air and scorching, and excessively slow injection causing heat loss from the melt. This ensures that the split melts maintain high temperature and pressure when converging, effectively weakening weld lines. By setting a cooling time, the product is fully shaped to resist ejection stress, preventing warping and residual internal stress. Simultaneously, the product shrinks and appropriately tightens around the mold, ensuring smooth demolding and providing stable physical conditions for the ejector pin venting structure to achieve secondary venting. Finally, a stable molding cycle ensures mold thermal balance during continuous production, guaranteeing efficient coordination between injection process parameters and the venting system. This achieves high-quality requirements of ≥95% air mark elimination rate and visually invisible weld lines while also considering mass production efficiency and yield.

[0024] Figure 1-10 The injection mold shown includes an outer molding component 1 disposed between an upper mold 100 and a lower mold 200, an inner molding block 2 disposed within the outer molding component 1, a molding cavity 3 formed by the inner molding block 2 and the outer molding component 1, and an ejector pin assembly 4 passing through the inner molding block 2. The inner molding block 2 is provided with a main venting structure 5 for guiding the gas in the molding cavity 3 to be discharged, and an ejector pin venting structure 6 that cooperates with the ejector pin assembly 4.

[0025] Specifically, the injection mold also includes a gating assembly 300, and both the main venting structure 5 and the ejector pin venting structure 6 are made of breathable steel.

[0026] In this implementation, the inner molding block and the outer molding assembly are joined together in the cavity. A main venting structure and an ejector pin venting structure are integrated on the inner molding block. The main venting structure serves as a guide channel for the main airflow, achieving efficient discharge of the main airflow within the molding cavity and effective weakening of weld lines. The ejector pin assembly performs the demolding ejection action, and in conjunction with the ejector pin venting structure, precise extraction and smooth discharge of gas from dead corners and weld line areas of the product are achieved. Furthermore, utilizing the microporous permeability of the breathable steel material, while ensuring smooth venting, it effectively prevents melt overflow and the formation of flash, significantly improving the appearance quality of the injection molded product and the overall molding yield.

[0027] Furthermore, the inner molding block 2 includes a molding upper part 21 that cooperates with the outer molding component 1 to form the molding cavity 3, and a supporting lower part 22.

[0028] Furthermore, the main venting structure 5 includes at least one main venting insert 51 that penetrates the inner forming block 2 along the direction from the upper mold 100 to the lower mold 200, and the end face of the main venting insert 51 is flush with the forming surface of the inner forming block 2.

[0029] In this implementation, the main venting insert is vertically penetrating along the upper and lower mold directions, serving as a straight flow channel for the main airflow, thereby achieving efficient discharge of trapped air in the molding cavity and a significant reduction in venting resistance. By flushing the end face of the main venting insert with the molding surface of the inner molding block, the seamless splicing of the flush end faces allows it to directly participate in product molding while achieving a complete and smooth product molding surface and effectively eliminating venting marks.

[0030] Furthermore, there are two main exhaust inserts 51, and the two main exhaust inserts 51 are symmetrically arranged along the center line of the inner forming block 2.

[0031] Furthermore, the main exhaust insert 51 is provided with a first exhaust channel 511 located in the lower part 22 of the support.

[0032] In this embodiment, by setting a first exhaust channel along its width on the main exhaust insert, the first exhaust channel serves as the lateral outlet path for the gas, thereby achieving smooth exhaust of the collected gas and effective elimination of exhaust back pressure; by placing the first exhaust channel at the lower part of the support, drilling or slotting in the upper part of the molding is avoided, thus achieving a concealed arrangement of the exhaust circuit.

[0033] Furthermore, the ejector pin venting structure 6 is embedded between the upper molding part 21 and the lower support part 22, and the end face of the ejector pin venting structure 6 is flush with the molding surface of the inner molding block 2.

[0034] In this embodiment, by embedding the ejector pin venting structure between the upper part of the molding and the lower part of the support, and using the interface between the two as the installation reference, large-area hollowing or deep hole processing is avoided in the upper part of the molding. By setting the end face of the ejector pin venting structure flush with the molding surface of the inner molding block, the seamless transition of the flush end face allows it to directly participate in the product molding while achieving a complete and smooth inner wall of the product molding and effectively eliminating the risk of demolding scratches.

[0035] Furthermore, the ejector pin assembly 4 includes a plurality of ejector pins that can slide relative to the inner molding block 2. The inner molding block 2 is provided with a plurality of ejector pin through holes 23 that cooperate with the ejector pins, and at least one mounting groove 24 for accommodating the ejector pin venting structure 6. The mounting groove 24 communicates with the ejector pin through holes 23.

[0036] In this implementation, by sliding the ejector pins with the ejector pin through holes on the inner molding block, the ejector pin through holes are used as the guiding reference for the ejector pin movement, so as to achieve smooth and stable product demolding and ejection and effectively eliminate the risk of ejector pin deflection and jamming; by connecting the mounting groove for accommodating the ejector pin venting structure with the ejector pin through holes, the combined air guiding cavity formed by the groove and hole connection is used to achieve efficient collection and smooth discharge of trapped air around the ejector pin and in local dead corners.

[0037] Furthermore, the ejector pin venting structure 6 is provided with a relief groove 61 that mates with the ejector pin through hole 23.

[0038] In this embodiment, by setting a clearance groove on the ejector exhaust structure that matches the ejector through hole, the clearance groove serves as a physical clearance space for the ejector sliding, thereby achieving smooth and interference-free reciprocating motion of the ejector assembly and effectively eliminating the risk of mechanical jamming. Through the annular air collection cavity formed by the clearance groove around the ejector through hole, the expansion and guiding effect of the annular air collection cavity achieves efficient collection of trapped air in local dead corners around the ejector and further improves exhaust efficiency.

[0039] Furthermore, the ejector pin exhaust structure 6 is provided with a second exhaust channel 62 located in the lower part 22 of the support.

[0040] In this embodiment, by setting a second exhaust channel along its width on the ejector pin exhaust structure, the second exhaust channel serves as a rapid outlet path for local dead zone gas, thereby achieving smooth exhaust of collected gas and effective elimination of local exhaust back pressure; by placing the second exhaust channel in the lower part of the support, the non-forming area of ​​the lower part of the support can accommodate the gas, avoiding drilling or slotting in the upper part of the forming, thus achieving a concealed arrangement of the exhaust circuit.

[0041] Furthermore, the outer molding component 1 includes an upper molding block 11 connected to the upper mold 100, a lower molding block 12 connected to the lower mold 200, and a first side molding block 13, a second side molding block 14, a third side molding block 15 and a fourth side molding block 16 disposed between the upper molding block 11 and the lower molding block 12. The upper molding block 11, the lower molding block 12, the first side molding block 13, the second side molding block 14, the third side molding block 15, and the fourth side molding block 16 cooperate with the upper molding part 21 to form the molding cavity 3.

[0042] The above descriptions are specific implementation methods and do not imply that the specific implementation of this invention is limited to these descriptions. Furthermore, due to differences in industry naming conventions, the invention is not limited to the names mentioned above, nor is it limited to English names. Any methods or structures that are similar to or identical to those of this invention, or any technical deductions or substitutions made based on the concept of this invention, should be considered within the scope of protection of this invention.

Claims

1. An injection molding process for improving air bubbles and weld lines, applied to an injection mold, said injection mold comprising at least a molding cavity (3), an ejector pin assembly (4), a main venting structure (5), and an ejector pin venting structure (6), characterized in that: Includes the following steps: S1, Injection molding: The plastic melt is injected into the molding cavity (3). During the flow and diversion process, the plastic melt pushes the gas in the molding cavity (3) to be discharged to the outside through the main exhaust structure (5) and / or the ejector pin exhaust structure (6) to achieve primary exhaust. S2, Pressure Holding and Cooling: After filling is completed, the plastic melt in the molding cavity (3) is pressurized and held to promote the fusion of the melt interface under pressure, and then cooled and shaped. S3, Demolding: The mold is opened and the molded product is ejected through the ejector assembly (4). During the ejection process, the ejector venting structure (6) works in conjunction with the ejection action to break the vacuum negative pressure in the molding cavity (3) and achieve secondary venting.

2. The injection molding process for improving air bubbles and weld lines according to claim 1, characterized in that: In step S1, the plastic melt is polycarbonate (PC) and acrylonitrile-butadiene-styrene copolymer (ABS); the hopper temperature is 90℃±10℃, the upper mold temperature of the injection mold is 95℃±10℃, and the lower mold temperature is 90℃±10℃.

3. The injection molding process for improving air bubbles and weld lines according to claim 1, characterized in that: In step S2, the injection time is 6±2s, the cooling time is 31±5s, and the molding cycle is 62±5s.

4. The injection molding process for improving air bubbles and weld lines according to claim 1, characterized in that: The injection mold includes an outer molding component (1) disposed between the upper mold (100) and the lower mold (200), an inner molding block (2) disposed within the outer molding component (1), a molding cavity (3) formed by the inner molding block (2) and the outer molding component (1), and an ejector assembly (4) passing through the inner molding block (2). The inner molding block (2) is provided with a main exhaust structure (5) for guiding the gas in the molding cavity (3) to be discharged, and an ejector exhaust structure (6) that cooperates with the ejector assembly (4).

5. The injection molding process for improving air bubbles and weld lines according to claim 4, characterized in that: The inner molding block (2) includes a molding upper part (21) that cooperates with the outer molding component (1) to form the molding cavity (3), and a supporting lower part (22).

6. The injection molding process for improving air bubbles and weld lines according to claim 5, characterized in that: The main exhaust structure (5) includes at least one main exhaust insert (51) that penetrates the inner forming block (2) along the direction from the upper mold (100) to the lower mold (200), and the end face of the main exhaust insert (51) is flush with the forming surface of the inner forming block (2).

7. The injection molding process for improving air bubbles and weld lines according to claim 6, characterized in that: The main exhaust insert (51) is provided with a first exhaust channel (511) located at the lower part (22) of the support.

8. The injection molding process for improving air bubbles and weld lines according to claim 5, characterized in that: The ejector venting structure (6) is embedded between the upper forming part (21) and the lower supporting part (22), and the end face of the ejector venting structure (6) is flush with the forming surface of the inner forming block (2).

9. The injection molding process for improving air bubbles and weld lines according to claim 8, characterized in that: The ejector assembly (4) includes a plurality of ejector pins that can slide relative to the inner molding block (2). The inner molding block (2) is provided with a plurality of ejector pin through holes (23) that cooperate with the ejector pins, and at least one mounting groove (24) for accommodating the ejector pin venting structure (6). The mounting groove (24) communicates with the ejector pin through holes (23).

10. The injection molding process for improving air bubbles and weld lines according to claim 9, characterized in that: The ejector pin exhaust structure (6) is provided with a relief groove (61) that mates with the ejector pin through hole (23), and a second exhaust channel (62) located in the lower part (22) of the support.

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