Mold for reducing sink marks in injection molded product

Abstract

The present invention relates to a mold for reducing sink marks in an injection molded product. The mold for reducing sink marks in an injection molded product according to the present invention comprises a fixed-side mold (100) and a movable-side mold (200), wherein the movable-side mold includes: external gas injection (EGI) core pins (220) installed on a movable-side core (210) to inject compressed air toward ribs of a resin molded product; and air supply pipes (240) installed on the movable-side core to transfer the compressed air to the EGI core pins.

Description

Mold for reducing sink marks in injection molded products

[0001] The present invention relates to a mold for reducing sink marks in an injection-molded product, and more specifically, to a mold for reducing sink marks in an injection-molded product by installing an EGI (External Gas Injection) core pin on a movable core and injecting compressed air into the skin layer of the resin filled into the mold cavity.

[0002]

[0003] Generally, sink marks refer to a phenomenon where localized depressions occur due to significant shrinkage in areas of a molded product with large thickness differences. While this can generally be reduced to some extent by changing the thickness and shape of ribs and adjusting injection molding conditions, it remains a major cause of surface quality defects.

[0004] In Non-patent Literature 1, research was conducted to solve the sink mark problem using low-pressure air by utilizing Partial Frame Process (PFP) molding technology to prevent sink marks. PFP molding technology is a technique in which, after completely filling the mold with resin during the injection molding process, bubbles are generated using low-pressure air, and the volume shrinkage of the resin is compensated for by the growth of the bubbles. This method has the advantage of being able to reduce sink marks or warping deformation, which mainly occur in general injection molding, to some extent, and does not require high pressure. However, Non-patent Literature 1 is still lacking in research on the dynamics of bubble growth to aid in understanding the air pressure affecting bubble generation and growth, as well as the generation of bubble nuclei and the initial growth process.

[0005] Non-patent literature 2 experimentally investigated the effects of various process variables on the quality of plastic parts in external gas injection and reported that mold and resin temperatures, gas delay time, gas holding pressure, and time are major factors affecting shrinkage of molded products. However, a mold design method for applying the external gas injection molding process to general injection molding molds was not specifically presented.

[0006]

[0007] [Prior Art Literature]

[0008] [Non-patent literature]

[0009] (Non-patent Document 1) An, KH, "Analysis of the void growth mechanism in partial frame process," The Korean Society of Rheology, Vol. 9, No. 2, pp. 60-65, 1997.

[0010] (Non-patent Document 2) Jiang, S., Zheng, W., Zhang J. and Li, J., "Experimental study on the influence of parameters on the plastic parts quality of external gas-assisted injection molding", Appl. Math. Inf. Sci., Vol. 6, pp. 665-671, 2012.

[0011]

[0012] Accordingly, the present invention has been made to solve the above-mentioned problems, and the objective of the present invention is to provide a mold for reducing sink marks of an injection-molded product, which can improve the appearance quality of the molded product by using compressed air to reduce sink marks on an injection-molded product having ribs.

[0013]

[0014] To achieve the above objective, a mold for reducing sink marks of an injection molded product according to an embodiment of the present invention comprises a fixed-side mold and a movable-side mold, wherein the movable-side mold is characterized by including: an EGI (External Gas Injection) core pin installed in the movable-side core for injecting compressed air toward the rib of the resin molded product; and an air supply pipe installed in the movable-side core for delivering compressed air to the EGI core pin.

[0015] In a mold for reducing sink marks of an injection molded product according to the above embodiment, the resin molded product has a curvature of a set length at the left and right corners, and at least one rib may be formed symmetrically on both sides with respect to the center at the bottom.

[0016] In a mold for reducing sink marks of an injection molded product according to the above embodiment, the EGI core pin is formed such that compressed air is injected toward a portion spaced apart by a distance symmetrically set on both the left and right sides centered on the rib, the upper portion is formed by planar machining in the longitudinal direction to a depth set on the outer four sides of the circular pin, the body groove is formed by planar machining in the longitudinal direction to a depth set on two sides of the body, and the lower portion may be connected to the air supply pipe through an O-ring.

[0017] In a mold for reducing sink marks of an injection molded product according to the above embodiment, a sealing groove is formed on the outer portion of the movable core, which generally has a square rim shape and a portion of the rim is curved inward, and a portion of the sealing groove is designed with a trapezoidal cross-sectional shape, and a sealing material can be inserted into the sealing groove.

[0018] The mold for reducing sink marks of an injection molded product according to the above embodiment further includes a plurality of ejector pins configured to be installed in the edge groove of the movable core surface and to push out the injection molded product after it is manufactured, and a seal plug is coupled around the ejector pin, and an O-ring may be inserted into the seal plug.

[0019]

[0020] According to a mold for reducing sink marks of an injection molded product according to an embodiment of the present invention, the mold for reducing sink marks of an injection molded product comprises a fixed-side mold and a movable-side mold, wherein the movable-side mold is configured to include an EGI (External Gas Injection) core pin installed in the movable-side core for injecting compressed air toward the ribs of the resin molded product; and an air supply pipe installed in the movable-side core for delivering compressed air to the EGI core pin. By using compressed air to reduce sink marks on an injection molded product having ribs, the appearance quality of the molded product can be improved, which is an excellent effect.

[0021]

[0022] FIG. 1 is a schematic diagram of a mold for reducing sink marks of an injection-molded product according to an embodiment of the present invention.

[0023] Figure 2 is a drawing showing an injection-molded product with ribs formed on the movable side core of Figure 1.

[0024] Figure 3 is a detailed view showing the detailed dimensions of the rib portion in the injection-molded product of Figure 2.

[0025] Figure 4 is a drawing showing an EGI core pin installed on the movable side core of Figure 1, an air supply pipe, and a distributor that distributes compressed air to the air supply pipe.

[0026] Figure 5 is a detailed view of the EGI core pin of Figure 4.

[0027] Figure 6 is a diagram showing the installation location of the EGI core pin in the movable side core of Figure 1.

[0028] Figure 7 is a drawing showing that a sealing groove is formed in the outer part of the movable side core of Figure 1.

[0029] Figure 8 is a drawing showing a sealing material inserted into the sealing groove of Figure 7.

[0030] Figure 9 is a drawing showing a compressed air injection device that supplies compressed air to the distributor of Figure 4.

[0031] Figure 10 is a drawing showing that a push pin is installed on the movable side core of Figure 1.

[0032] FIG. 11 is a drawing showing a push pin and a seal plug installed on a movable core.

[0033] Figure 12 is a diagram showing the depth measurement location of the sink mark.

[0034] Figure 13a is a graph showing the surface depth measurement according to position.

[0035] Figure 13b is a diagram showing PV values ​​according to position.

[0036] Figure 14 is a diagram showing the sink mark depth according to the delay time.

[0037] Figure 15 is a diagram showing the depth of the sink mark according to the discharge pressure and supply time.

[0038] Figure 16 is a diagram showing the depth of the sink mark according to the supply time.

[0039] FIG. 17 is a drawing showing the case where a mold for reducing sink marks in an injection molded product according to an embodiment of the present invention is not used and the case where it is used.

[0040]

[0041] In describing the embodiments of the present invention, if it is determined that a detailed description of known technology related to the present invention may unnecessarily obscure the essence of the present invention, such detailed description will be omitted. Furthermore, the terms described below are defined considering their functions in the present invention, and these may vary depending on the intentions or practices of the user or operator. Therefore, such definitions should be based on the content throughout this specification. Terms used in the detailed description are intended merely to describe the embodiments of the present invention and should not be interpreted restrictively. Unless explicitly stated otherwise, expressions in the singular form include the meaning of the plural form. In this description, expressions such as "include" or "comprise" are intended to refer to certain characteristics, numbers, steps, actions, elements, parts thereof, or combinations thereof, and should not be interpreted as excluding the existence or possibility of one or more other characteristics, numbers, steps, actions, elements, parts thereof, or combinations thereof other than those described.

[0042] In each system illustrated in the drawings, elements in some cases may have the same or different reference numbers, suggesting that the represented elements may be different or similar. However, elements may have different implementations and may operate with some or all of the systems shown or described herein. The various elements illustrated in the drawings may be the same or different. It is optional which is referred to as the first element and which is referred to as the second element.

[0043] In this specification, the phrase “transmits,” “delives,” or “provides” data or signals from one component to another component includes not only the direct transmission of data or signals from one component to another component, but also the transmission of data or signals to another component through at least one other component.

[0044]

[0045] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0046] FIG. 1 is a schematic diagram of a mold for reducing sink marks of an injection-molded product according to an embodiment of the present invention; FIG. 2 is a diagram showing an injection-molded product with ribs formed on the movable core of FIG. 1 arranged thereon; FIG. 3 is a detailed diagram including the rib dimensions of the injection-molded product of FIG. 2; FIG. 4 is a diagram showing an EGI core pin and an air supply pipe installed on the movable core of FIG. 1, and a distributor that distributes compressed air to the air supply pipe; FIG. 5 is a detailed diagram of the EGI core pin of FIG. 4; FIG. 6 is a diagram showing the installation position of the EGI core pin in the movable core of FIG. 1; FIG. 7 is a diagram showing a sealing groove formed on the outer part of the movable core of FIG. 1; FIG. 8 is a diagram showing a sealing material inserted into the sealing groove of FIG. 7; FIG. 9 is a diagram showing a compressed air injection device that provides compressed air to the distributor of FIG. 4; FIG. 10 shows an ejector pin on the movable core of FIG. 1 This is a drawing showing the installed structure, and FIG. 11 is a drawing showing the ejector pin and seal plug installed on the movable core.

[0047]

[0048] A mold for reducing sink marks of an injection molded product according to an embodiment of the present invention includes a fixed mold (100) and a movable mold (200), as shown in FIGS. 1 to 11.

[0049] A plurality of EGI (External Gas Injection) core pins (220), a plurality of air supply pipes (240), a sealing material (S), and a plurality of ejector pins (P) are installed in the movable side mold (200).

[0050]

[0051] A plurality of EGI core pins (220) are installed in the movable core (210) of the movable mold (200) and serve to inject compressed air toward the ribs (R) of the resin molded product. As shown in FIGS. 2 and 3, the resin molded product has a curvature of a set length at the left and right corners, and two ribs (R) are formed symmetrically on both sides with respect to the center at the bottom. As shown in FIGS. 4 to 6, the EGI core pin (220) is formed by planar machining in the longitudinal direction to a depth set on the outer four sides of the circular pin in order to spray compressed air toward a portion spaced symmetrically on both the left and right sides centered on the rib (R), and by planar machining in the longitudinal direction to a depth set on two sides of the body (222), and the lower part (226) is connected to an air supply pipe (240) and an O-ring (230).

[0052]

[0053] As shown in FIG. 4, the air supply pipe (240) is installed horizontally on the movable core (210) and serves to deliver compressed air to the EGI core pin (220). The distributor (260) serves to distribute compressed air to the air supply pipe (240). FIG. 9 is a drawing showing a compressed air injection device that provides compressed air to the distributor (260). It uses a booster to compress air up to 110 bar, and the compressed air is stored in a tank with a capacity of 10 liters. It can be supplied to up to three supply lines while controlling the supply pressure, supply time, etc., using a solenoid valve. The distributor (260) and the air supply pipe (240) are connected by a connecting part (250).

[0054]

[0055] As shown in FIGS. 7 and 8, the sealing material (S) is inserted into a sealing groove (212) formed on the outer part of the movable core (210) to prevent compressed air injected into the mold from leaking out when the mold is closed. The sealing groove (212) forms a square rim shape on the outer part of the movable core (210), and the four rim parts are curved inward. A portion of the sealing groove (212) (the four corner parts) is designed with a trapezoidal cross-sectional shape to increase the fastening force of the sealing material (S). The remaining portion of the sealing groove (212) has a rectangular cross-sectional shape.

[0056]

[0057] As shown in FIG. 10 and FIG. 11, a plurality of ejector pins (P) are configured to be installed in the edge grooves of the movable side core (210) surface and to push out after the injection molded product is manufactured. A seal plug (270) is attached to the circumference of the ejector pin (P), and an O-ring (230a) is inserted into the seal plug (270). The seal plug (270) is manufactured to match the diameter of the ejector pin (P) and prevents air leakage by means of the O-ring (230a) installed inside. As shown in FIG. 10, the seal plug core may be designed with a groove having a diameter of approximately Ø12mm and a height of 12mm at the bottom of the core at the gate ejector pin position, and a groove having a diameter of approximately Ø14mm and a height of 16mm at the bottom of the core at the molded product ejector pin position. Furthermore, a seal plug with a negative tolerance can be fitted into the groove to which the seal plug (270) is fitted, with a tolerance of +0.03.

[0058]

[0059] The operation of a mold for reducing sink marks of an injection-molded product according to an embodiment of the present invention configured as above will be explained.

[0060]

[0061] Figure 12 is a drawing showing the depth measurement locations of sink marks. The depth of the sink marks was measured in 10mm increments over a 10 to 40mm section from the end where the rib (R) was installed, and the measurement area at each point was set to 4mm.

[0062]

[0063] Figure 13a is a graph showing the surface depth measurement according to location, and Figure 13b is a graph showing the PV values ​​according to location. The PV value was defined as the depth of the sink mark, and it was found that the sink mark depth was greatest at 10.078 μm at a point 10 mm from the end where the rib (R) was installed.

[0064]

[0065] Figure 14 is a diagram showing the sink mark depth according to the delay time. When the delay time is 2.2 seconds, the depth of the sink mark is 1.465 μm, which is the smallest, and it was found that the depth increases when the delay time is too short or too long.

[0066]

[0067] Figure 15 is a diagram showing the depth of the sink mark according to discharge pressure and supply time. It was found that when the discharge pressure was low at 30 bar and 50 bar, the change in the depth of the sink mark was not significant. On the other hand, at a discharge pressure of 70 bar, the depth of the sink mark decreased significantly, and at a supply time of 5 seconds, the depth of the sink mark was found to be 1.089 μm.

[0068]

[0069] Figure 16 is a diagram showing the depth of the sink mark according to the supply time. It was found that the depth of the sink mark was smallest at 0.594 μm at a supply time of 6 to 7 seconds, which is about 94% lower than the depth of 10.078 μm in general injection molding.

[0070]

[0071] FIG. 17 is a drawing showing the case where a mold for reducing sink marks in an injection-molded product according to an embodiment of the present invention is not used and the case where it is used. In the case of a product molded by general injection molding, sink marks occur significantly enough to be easily identified with the naked eye, but when the mold according to an embodiment of the present invention is applied, sink marks hardly occur.

[0072]

[0073] According to an embodiment of the present invention, a mold for reducing sink marks of an injection molded product comprises a fixed mold and a movable mold, wherein the movable mold is configured to include an EGI (External Gas Injection) core pin installed in the movable core for injecting compressed air toward the ribs of the resin molded product; and an air supply pipe installed in the movable core for delivering compressed air to the EGI core pin. By using compressed air to reduce sink marks on an injection molded product having ribs, the appearance quality of the molded product can be improved.

[0074]

[0075] Optimal embodiments have been disclosed in the drawings and specification, and specific terms have been used, but these are used only for the purpose of describing embodiments of the invention and are not intended to limit the meaning or the scope of the invention as described in the claims. Therefore, those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible therefrom. Accordingly, the true technical scope of protection of the invention should be determined by the technical spirit of the appended claims.

Claims

1. A mold for reducing sink marks of an injection molded product, comprising a fixed side mold (100) and a movable side mold (200), In the above-mentioned movable mold An EGI (External Gas Injection) core pin (220) installed on the movable side core (210) for injecting compressed air toward the ribs of the resin molded product; and A mold for reducing sink marks in an injection molded product, comprising: an air supply pipe (240) installed in the above-mentioned movable core to deliver compressed air to the above-mentioned EGI core pin.

2. In Paragraph 1, A mold for reducing sink marks of an injection molded product, wherein the above resin molded product has curvature of a set length at the left and right corners, and at least one rib is formed symmetrically on both sides with respect to the center at the bottom.

3. In Paragraph 2, A mold for reducing sink marks in an injection molded product, wherein the EGI core pin (220) is formed such that compressed air is injected toward a portion spaced apart from the left and right sides symmetrically centered on the rib, the upper portion (224) has an upper groove (224a) formed by planar machining in the longitudinal direction to a depth set on the outer four sides of the circular pin, the body groove (222a) is formed by planar machining in the longitudinal direction to a depth set on two sides of the body (222), and the lower portion (226) is connected to the air supply pipe (240) through an O-ring (230).

4. In Paragraph 1, On the outer part of the above-mentioned movable core (210), a sealing groove (212) is formed that forms a square border shape overall and has a portion of the border curved inward. A portion of the above sealing groove is designed with a trapezoidal cross-sectional shape, and A mold for reducing sink marks of an injection molded product, wherein a sealing material (S) is inserted into the sealing groove above.

5. In Paragraph 1, It further includes a plurality of ejector pins (P) configured to be installed in the edge grooves of the surface of the movable core (210) and to push out the injection molded product after it is manufactured. A seal plug (270) is attached around the above-mentioned ejector pin, and A mold for reducing sink marks of an injection molded product, into which an O-ring (230a) is inserted in the seal plug above.

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