Injection molding die

Abstract

To provide an injection molding die capable of effectively venting gas within a cavity that molds an irregular cylindrical molded article having one end open and the other end, being on the injection side of a molten resin, closed by using a columnar core die and a pair of split dies disposed to surround an entire periphery of the core die.SOLUTION: A laminated piece plate body J formed by laminating a plurality of degassing piece plates P1 to P4 is integrally incorporated in a portion that forms a box-shaped second cavity portion C2 of a cavity C in a pair of split dies B1 and B2. A number of degassing holes H are formed inside the laminated piece plate body J by covering degassing grooves G1 to G4 formed on the respective degassing piece plates P1 to P4 with the respective degassing piece plates P2 to P4 directly above them. A gas remaining in the cavity C is discharged to the outside of the molding die through the degassing holes H.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to an injection molding mold in which a cavity for molding an irregular cylindrical molded product is formed by a cylindrical core mold and a pair of split molds arranged around the entire circumference of the core mold, with one end open and the other end, which is the injection side of molten resin, closed. [Background technology]

[0002] Molten thermoplastic elastomer (molten resin) is injected into a cavity formed between a cylindrical core mold and multiple outer molds arranged around the core mold to form an irregular cylindrical molded product. The cavity has only one open end in the removal direction, and the open end has a large-dimension portion that is larger than the portion molded by the core mold. The molten resin is injected from the portion of the cavity that forms the closed portion of the irregular cylindrical molded product, opposite the large-dimension portion. The box-shaped cavity portion that forms the large-dimension portion is farthest from the cavity portion that forms the closed portion of the molded product and is curved relative to the cavity portion that forms the cylindrical portion. As a result, sinks and underfill due to insufficient molten resin reach the large-dimension portion of the irregular cylindrical molded product, causing molding defects.

[0003] The core mold is formed in a block shape at the portion that forms the box-shaped large portion, which is the opening side of the molded product, to correspond to the shape of the molded product. The applicant of the present patent attempted to discharge gas from the portion of the cavity that forms the large portion by embedding multiple vents with tiny discharge holes in the block-shaped portion of the core mold, thereby generating vent formation marks on the inner surface of the molded product where each vent is located, rather than on the outer surface of the molded product. With this gas discharge method, gas is effectively discharged from the portions where each vent is located, but gas accumulates in other portions of the cavity where no vents are located, causing sinks, underfill, etc. on the outer surface of the molded product, and this method was not put to practical use.

[0004] Generally, as shown in Patent Document 1, in resin injection molding, when a cavity is formed on each mating surface of a split mold, it is possible to discharge gas from the cavity by placing an extremely thin shim on each mating surface. However, in order to discharge gas from the large-dimension portion of the cavity of an irregular cylindrical molded product having a large-dimension portion on the opening side, which is formed between a core mold and a pair of split molds arranged to surround the entire periphery of the core mold, it is necessary to provide a gas discharge hole inside the core mold or the pair of split molds that make up the mold, making it extremely difficult to discharge the gas. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2017-213692 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention aims to provide an injection molding mold that can effectively vent gas from a cavity that molds an irregular cylindrical molded product, which has one end open and the other end, which is the injection side of molten resin, closed, using a cylindrical core mold and a pair of split molds arranged around the entire circumference of the core mold. [Means for solving the problem]

[0007] The invention of claim 1 to solve the above problem is as follows: an injection molding die comprising a columnar core die and a pair of split dies arranged around the core die to form a cavity, wherein molten resin is injected into the cavity, only one end in the removal direction is open, and the other end, which is the injection side of the molten resin, is closed, and an irregular cylindrical molded product having a large-dimension portion in the open portion that is shaped like a square box and larger in dimensions than the other portions is molded, and then the split dies are separated from the core die to remove the molded product from the core die; A plurality of flat gas venting piece plates, each having a gas vent groove formed on at least one surface, are stacked along the direction of removal of the molded product to form an integrated laminated piece plate in a laminated piece plate placement recess provided in the portion of each split mold where the large dimension portion is molded, and the gas vent grooves form a number of gas vent holes in the portion of each split mold where the large dimension portion of the molded product is molded, which communicate the portion of the cavity where the large dimension portion is molded with the outside of the mold, Each of the gas vent grooves forming the gas vent holes is characterized in that it is formed to a depth that can prevent the molten resin injected into the cavity from penetrating into the gas vent hole.

[0008] According to the invention of claim 1, a stack of flat venting plates, each having a vent groove on at least one side, is stacked along the direction of removal of the molded product in a stacking plate placement recess provided in the portion of each split mold where the rectangular box-shaped large portion of the molded product is molded, and a plurality of vent holes are formed inside the stack of plates, connecting the portion of the cavity where the large portion is molded with the outside of the mold. This allows a plurality of vent holes to be formed directly in the portion of the cavity where the large portion is molded in the pair of split molds. Furthermore, each of the vent holes is formed to a depth sufficient to prevent molten resin injected into the cavity from penetrating the vent holes, allowing gas that tends to accumulate in the portion of the cavity where the large portion is molded to be effectively discharged from the vent holes to the outside of the mold. This allows the molding of large portions according to design without sinks, underfill, etc., which are prone to occur in conventional molding.

[0009] Furthermore, according to the invention of claim 1, each of the gas vent grooves forming the numerous gas vent holes formed inside the laminated piece board must be formed to a depth that can prevent the molten resin injected into the cavity from penetrating into the gas vent hole, but there is no limit to the width of the gas vent groove, so by making the gas vent groove wider, the cross-sectional area of ​​the gas vent hole can be increased, and the total cross-sectional area of ​​the numerous gas vent holes can be made considerably large.From this perspective, too, gas remaining in the large dimension parts of the cavity can be reliably and effectively discharged to the outside of the molding die.

[0010] A second aspect of the present invention is characterized in that, in the first aspect of the present invention, the depth of the gas release groove is 0.02 to 0.03 mm.

[0011] The invention of claim 2 specifies the depth of the gas vent groove formed on the surface of the gas venting block plate to be 0.02 to 0.03 mm, which is the limit of the resin that can penetrate into the gas vent hole due to the resin injection pressure. A groove of this depth can be formed by polishing the metal plate.

[0012] The invention of claim 3 is characterized in that, in the invention of claim 1 or 2, the gas venting piece plates have the largest plate thickness in the outermost gas venting piece plate, and the gas venting piece plate located in the middle has a thinner plate thickness than each of the gas venting piece plates located on both sides along the stacking direction, and the stacking piece plates incorporated into the stacking piece plate placement recesses of each split mold are fixed to each split mold by a plurality of fixing bolts.

[0013] According to the invention of claim 3, it is possible to provide a recess in the gas venting piece plate with the greatest plate thickness, which is located on the outermost side, into which the head of the fixing bolt is inserted and positioned, so that the fixing bolt does not protrude from the stacked piece plate incorporated into the stacked piece plate positioning recess of each split mold, making it easier to design the mold for each split mold, which is a movable mold.

[0014] Claim 4 is characterized in that, in the invention of claim 1 or 2, a gas exhaust gap is formed between the outer surface of the stacked piece plate incorporated into the stacked piece plate placement recess on the side opposite the cavity and the inner surface of the stacked piece plate placement recess, allowing gas to be exhausted to the outside of the molding die through a number of gas vent holes formed inside the stacked piece plate.

[0015] According to the invention of claim 4, gas discharged through the numerous gas vent holes formed inside the stacked piece plate can be effectively discharged to the outside of the forming mold through the gas discharge gap.

[0016] The invention of claim 5 is characterized in that, in the invention of claim 1 or 2, the injection molding mold is configured to be able to mold two molded products simultaneously, and each cavity for molding each molded product is connected by a separate gas vent hole formed inside the stacked piece plate.

[0017] According to the invention of claim 5, in an injection molding mold capable of simultaneously forming two molded products, the portions of each cavity that mold the large dimension portions are connected by separate gas vent holes formed inside the stacked piece plate. Therefore, if a pressure difference occurs between the two cavities due to a difference in the total amount of gas retained, the gas moves from one cavity to the other, making the gas retention state in each cavity equal, and making it possible to effectively discharge the gas from both cavities.

[0018] The invention of claim 6 is as follows: An injection molding die comprising a columnar core die and a pair of split dies arranged around the core die to form a cavity, wherein molten resin is injected into the cavity to form an irregular cylindrical molded product having only one end in the removal direction open and the other end, which is the injection side of the molten resin, closed, and then the split dies are separated from the core die to remove the molded product from the core die, A plurality of flat gas venting blocks, each having a gas vent groove formed on at least one surface, are stacked along the direction of removal of the molded product to form an integrated laminated block plate in a laminated block plate placement recess provided in the portion of each split mold that will mold the open side of the molded product, and the gas venting grooves form a number of gas vent holes that communicate with the outside of the mold in the portion of each split mold that will mold the open side of the molded product, Each of the gas vent grooves forming the gas vent holes is characterized in that it is formed to a depth that can prevent the molten resin injected into the cavity from penetrating into the gas vent hole.

[0019] The molded product of the invention of claim 1 is an irregular cylindrical product in which only one end in the removal direction is open and the other end, which is the injection side of the molten resin, is closed, and the open part has a large dimension part that is larger than the other parts, whereas the molded product of the invention of claim 6 is an irregular cylindrical product in which only one end in the removal direction is open and the other end, which is the injection side of the molten resin, is closed, and does not have a large dimension part. Even if the open side of the molded product does not have a large dimension portion, the molten resin is injected from the closed side of the molded product, and therefore the open side of the molded product is the slowest to receive the molten resin and is prone to gas stagnation.Therefore, a laminated piece plate arrangement recess is provided in the part of each split mold that molds the open side of the molded product, and multiple flat gas venting piece plates with gas vent grooves formed on at least one side are stacked along the removal direction of the molded product to form an integrated laminated piece plate.By incorporating this laminated piece plate, each gas vent groove forms a large number of gas vent holes that communicate with the outside of the mold in the part that molds the open side of each split mold, thereby preventing the occurrence of sink marks, underfill, etc., and enabling the molding of the molded product. [Effects of the Invention]

[0020] According to the present invention, a stack of flat venting plates, each with a vent groove on at least one side, is stacked along the direction of removal of the molded product in a stacking plate placement recess provided in the portion of each split mold cavity that will form the open side of the molded product. This makes it possible to form multiple vent holes directly in the portion of the split mold that will form the large portion, connecting the portion of the cavity that will form the open side of the molded product with the outside of the mold. As a result, gas that tends to accumulate in the portion of the cavity that will form the open side of the molded product can be effectively released to the outside of the mold through the multiple vent holes, making it possible to mold the molded product without generating sinks or underfill on the open side of the molded product.

[0021] In particular, when a large-dimension portion larger than other portions is provided on the open side of the molded product, the path of the cavity in the portion of the cavity that molds the large-dimension portion of the molded product is bent, making it difficult for the molten resin injected from the closed side of the molded product to reach one side, and gas is likely to stagnate, so the effect of the present invention is great. [Brief explanation of the drawings]

[0022] [Figure 1] 7 is a front view of the movable mold M of the injection molding mold K (a view taken along the line UU in FIG. 6 when the pair of split molds B1, B2 are closed). [Figure 2] 1 is a plan cross-sectional view (cross-sectional view along line XX in FIG. 1) of a pair of split molds B1, B2 closed together to form a cavity C between the pair of split molds B1, B2 and the core mold A. FIG. [Figure 3] 3(a) is an enlarged view of the main part of FIG. 2, and FIG. 3(b) is an enlarged cross-sectional view taken along line ZZ in FIG. [Figure 4] FIG. 3 is a cross-sectional view taken along line YY in FIG. 2. [Figure 5] FIG. 5 is an enlarged view of the main part of FIG. [Figure 6] This is a plan cross-sectional view of an injection molding mold K in a state in which compressed air is supplied between the inner surface of the molded product F and the outer surface of the core mold A to slightly inflate the molded product F, and the molded product F is removed from the core mold A by pushing out the ejector pin E. [Figure 7] FIG. 2 is a perspective view of a molded product F with a portion broken away. [Figure 8] 10 is a perspective view of a split mold B1 (B2) in which a stacked piece board J is incorporated into a stacked piece board placement recess 9. FIG. [Figure 9] 1 is an exploded perspective view of one split mold B1 (B2), a pair of core molds A, and a stacked piece plate J. FIG. [Figure 10] (a) and (b) are oblique views of the separated state of multiple gas venting piece plates P1 to P4 that form the stacked piece plate body J, and an oblique view of the stacked piece plate body J, and (c) is a partially enlarged cross-sectional view of the gas venting piece plates P1 to P4. [Figure 11] FIG. 10 is a perspective view of one split mold B1 (B2) as seen from obliquely below. [Figure 12] This is a vertical cross-sectional view of the gas vent groove G4 of the stacked piece plate J integrally incorporated into the stacked piece plate placement recess 9 of each split mold B1, B2, showing that a large number of gas vent holes H have been formed in the stacked piece plate J. [Figure 13] 10 is a partially enlarged cross-sectional view showing a state in which a stacked piece plate J is inserted into a stacked piece plate placement recess 9 of a split mold B1 (B2) and fixed via a fixing bolt 31. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be described in more detail below with reference to the best embodiment. First, the general structure of the injection molding die K for carrying out the present invention will be described, followed by the stacked piece plate J, which is made up of multiple gas venting piece plates P1 to P4 stacked together to form the gas vent hole H, which is a characteristic feature of the present invention, and the assembly structure of the split molds B1 and B2 into the stacked piece plate placement recess 9.

[0024] The injection molding die K consists of a fixed die S and a movable die M. As shown in Figures 1 to 6, the movable die M is a "two-cavity" die capable of simultaneously molding two molded products, and has a rigid structure that is rectangular in front view. A pair of core dies A are integrally formed at the horizontal center of the front part of a vertically arranged base 1, spaced a predetermined distance apart in the vertical direction and perpendicular to the base 1, so that the pair of core dies A are arranged horizontally in absolute space. The core die A consists of a columnar core main body A1 for molding the cylindrical portion F1 of the irregular cylindrical molded product F, and a rectangular parallelepiped portion A2 that is integrally formed at the base end of the core main body A1 and molds the rectangular box portion F2 of the molded product F (see Figure 9). A pair of left and right split dies B1, B2 are arranged on both sides of a pair of core dies A integrally mounted in the horizontal center of base 1, and are slidable in the horizontal direction indicated by arrow Q so that they can move toward and away from each other. When the pair of split dies B1, B2 are closed and their mating surfaces 12 are in close contact, a cavity C for molding a molded product F is formed by the inner peripheral surfaces of two molding recesses 2 formed on each mating surface 12 of the die main bodies 11 of the pair of split dies B1, B2 and the outer peripheral surfaces of the two (pair of) core dies A integrally mounted on base 1. Cavity C is made up of a hollow columnar first cavity portion C1 formed between the core main body portion A1 of core die A and the pair of split dies B1, B2, and a box-shaped second cavity portion C2 formed between the rectangular parallelepiped portion A2 of core die A and a stacked piece plate J incorporated into the pair of split dies B1, B2.

[0025] A back plate 4 is arranged on the back surface of the base 1 via a plurality of horizontal support columns 3, and the space formed by the back surface of the base 1, the back plate 4, and the left and right horizontal support columns 3 serves as a plate arrangement space 6 for arranging an ejector plate 5. The base end of an ejector pin E, which is used to remove a molded product F from the core mold A after injection molding, is integrally connected to the ejector plate 5.

[0026] In the movable mold M, a pair of split molds B1, B2 supported by a base stand 1 slide toward and away from each other between a close end position (combined position) and a separate end position. A hollow truncated pyramidal mold fitting recess 22 is formed in the mold body 21 of the fixed mold S, opening toward the movable mold M. The hollow truncated pyramidal mold fitting recess 22 fits onto the outside of the truncated pyramidal mold body 11 of each split mold B1, B2 combined at the close end position of the pair of split molds B1, B2. Two sets of inclined angular pins 23, a total of four, are provided on both sides of the mold fitting recess 22 in a plan view, protruding toward the movable mold M. The two inclined angular pins 23 in each set are arranged in the same horizontal plane, and about half of their entire lengths are embedded in the mold body 21 of the fixed mold S, protruding significantly to the side at an angle such that the spacing between them becomes wider from the base end to the tip. The two sets of inclined angular pins 23 of the fixed mold S are configured to be inserted into two sets of inclined guide holes 8 formed in a pair through the thick flange portion 7 on the outer periphery of the pair of split molds B1 and B2.

[0027] 2 and 6, when the two sets of inclined angular pins 23 of the fixed mold S are inserted into the inclined guide holes 8 of the pair of split molds B1 and B2, and the entire movable mold M is slid horizontally relative to the fixed mold S in the direction indicated by arrow R, the movable mold M moves toward and away from the fixed mold S. A sprue bushing 24 for injecting molten thermoplastic elastomer (molten resin) is embedded in the fixed mold S. Note that, in order to ensure space for removing the molded product F, as shown in FIG. 6, when the pair of split molds B1 and B2 are separated, the pair of inclined angular pins 23 of the fixed mold S are completely removed from the inclined guide holes 8 formed in the thick flange portions 7 of each of the split molds B1 and B2, and the movable mold M is separated from the fixed mold S.

[0028] As shown in Fig. 7, the molded product F has an irregular cylindrical shape, with one end of a cylindrical portion F1 closed and the other end open, forming a rectangular box portion F2 whose dimension along the direction of separation of the pair of split molds B1 and B2 is larger than the dimension along the same direction of the cylindrical portion F1. The portion of the cavity C that forms the rectangular box portion F2 is the last to reach the molten resin, and is bent at two right angles relative to the straight cavity portion that forms the cylindrical portion F1, making it easy for gas within the cavity C to accumulate. The peripheral wall portion F2a that forms the rectangular box portion F2 is slightly bent relative to the top wall portion F2b, so that the peripheral wall portion F2a and the top wall portion F2b form an acute angle that is close to a right angle. For this reason, in the present invention, as shown in Figures 9 to 12, in order to form a large number of gas vent holes H in the portion of the pair of split dies B1 and B2 that constitute the movable die M where the rectangular box section F2 is molded, a stacked piece plate arrangement recess 9 is formed in the portion of each split die B1 and B2 where the rectangular box section F2 is molded, in which a stacked piece plate J is placed, which is made of a plurality of (four in this embodiment) gas venting piece plates P1 to P4 stacked together, each having different plate thicknesses and slightly different overall shapes, and the stacked piece plate J is fitted into the stacked piece plate arrangement recess 9 and integrated with each split die B1 and B2 via a plurality of fixing bolts 31, and a large number of gas vent holes H leading to the outside of each split die B1 and B2 are formed inside the stacked piece plate J, thereby creating a structure where gas in the portion of the cavity C where the rectangular box section F2 of the molded product F is molded can be discharged outside the mold.

[0029] 1 and 2, when the pair of split dies B1, B2 are closest to each other and the portion where each die body 11 is joined together in a truncated pyramidal shape is fitted into the die fitting recess 22 of the fixed die S, the space formed by the outer circumferential surface of the core die A and the inner circumferential surfaces of the molding recesses 2 formed in the die mating surfaces 12 of each split die B1, B2 becomes a cavity (molding space) C. The opposing U-shaped recesses Ja (see FIG. 9) of a pair of stacked piece plates J fitted into each split die B1, B2 are joined together, and the inner circumferential surfaces of the joined opposing U-shaped recesses Ja and the outer circumferential surface of the rectangular parallelepiped portion A2 of the core die A form a box-shaped second cavity portion C2 that forms the rectangular box portion F2 of the molded product F in the cavity C. The second cavity portion C2 is connected to the outside of each split die B1, B2 by a number of gas vent holes H formed inside the stacked piece plate J. In addition, in the state where the cavity C is formed, the mold mating surfaces 12 of the split molds B1 and B2 are in close contact with each other, thereby forming a short runner 13 that communicates with the first cavity portion C1.

[0030] Next, the stacked piece board J will be described in more detail with reference to Figures 8 to 12. The stacked piece board J is fitted into the stacked piece board placement recess 9 of each split mold B1, B2 and is integrated with each split mold B1, B2 via multiple fixing bolts 31. Since the injection molding mold K of this embodiment is a "two-cavity" mold, two U-shaped recesses Ja are formed in one stacked piece board J, and each U-shaped recess Ja is positioned in a portion corresponding to the rectangular box section F2 of the molded product F of each of the two cavities C formed in the pair of split molds B1, B2. In Figures 5, 8, and 9, reference numeral 33 denotes an assembly block having the same planar shape as the stacked piece board J and positioned below the stacked piece board J in the pair of split molds B1, B2. 9 and 11, reference numeral 10 denotes a female screw portion formed on the ceiling surface 14 of the stacked piece plate arrangement recess 9 of each split mold B1, B2 for threading the fixing bolt 31.

[0031] The laminated piece plate J is formed by stacking multiple (four in this embodiment) metal venting pieces P1-P4 (with respect to thickness, the relationship is (P1>P2=P3>P4)) that are different in thickness and only slightly different in the shape of the portion that forms the second cavity C2 for molding the rectangular box section F2 of the molded product F. That is, the peripheral wall F2a that forms the rectangular box section F2 of the molded product F is bent inward at a slightly acute angle relative to the top wall F2b, so that the multiple venting pieces P1-P4 that make up the laminated piece plate J have U-shaped recesses Ja whose widths gradually increase from the bottom to the top, and the end faces (the continuous inner surfaces of the U-shaped recesses Ja) are formed as continuous inclined surfaces.

[0032] As shown in Fig. 10, each gas venting piece P1-P4 has a rectangular overall shape, and one surface (the upper surface when stacked) of each gas venting piece P1-P4 has multiple very shallow gas venting grooves G1-G5 formed across the entire width of that portion. That is, the gas venting grooves G1 and G2 are formed between the remaining long sides of the rectangular gas venting piece P1-P4 and the U-shaped recess Ja, perpendicular to the long sides, across the entire length. The gas venting grooves G3 and G4 are formed in the longitudinal center of the remaining rectangular portion outside each U-shaped recess Ja, across the entire width of the rectangular portion (the longitudinal direction when viewed from the entire gas venting piece P1-P4). Furthermore, in the remaining approximately square portion between each U-shaped recess Ja, a gas venting groove G5 is formed along the extension of each gas venting groove G3 and G4, across the entire length. By stacking the gas vent grooves G1-G5, each gas vent groove G1-G5 covers the corresponding gas vent groove G1-G5, and together with the ceiling surface 14 (see Figure 11) of the stacked piece plate arrangement recess 9 of the split molds B1, B2 to which another gas venting piece plate P2-P4 stacked above or the top gas venting piece plate P4 is in close contact, multiple gas vent holes H are formed inside the stacked piece plate J. The depth D (see Figure 10(c)) of each gas vent groove G1-G5 formed in each gas venting piece plate P1-P4 is 0.02-0.03 mm, and this dimension prevents the molten resin from seeping into the cavity C due to the injection pressure when the molten resin is injection molded. The extremely shallow gas vent grooves G1-G5 are formed by grinding specific positions of the metal gas venting blocks P1-P4 with a grinding machine, and can also be formed by etching, which dissolves the surface of the metal plate. However, since each gas vent groove G1-G5 has a simple rectangular shape with the same width over its entire length, grinding with a grinding machine is the preferred method of formation. In Figures 9 and 10, the gas vent grooves G1-G5 are extremely shallow and cannot be displayed in three dimensions, so the parts of the gas vent grooves G1-G5 are displayed as "dots."

[0033] Furthermore, in the areas of each of the gas venting piece plates P1-P4 away from the gas venting grooves G1, G2, a plurality of bolt insertion holes 32 are formed through which a number of fixing bolts 31 are inserted to fix the stacked piece plate J, which is made by stacking the gas venting piece plates P1-P4, to the ceiling surface 14 of the stacked piece plate arrangement recess 9 of each of the split molds B1, B2 when the stacked piece plate J is installed in the stacked piece plate arrangement recess 9 of each of the split molds B1, B2. The gas venting piece plate P1, which is the thickest and located at the bottom, is provided with head insertion holes 32a connected to the bolt insertion holes 32, into which the entire heads 31a of the headed fixing bolts 31 can be inserted.

[0034] Therefore, when the stacked piece plate J is assembled into the stacked piece plate arrangement recess 9 of each split mold B1, B2 and integrated with each split mold B1, B2 via a number of fixing bolts 31, the cross section of the stacked piece plate J becomes as shown in Figure 13. Note that in Figure 12(c), the depth D of the gas vent groove G4 is extremely shallow and cannot be shown in the figure, so the depth D of the gas vent groove G4 is shown much deeper than it actually is, and the ratio between the depth D of the gas vent groove G4 and the plate thickness of the gas venting piece plates P1 to P4 is ignored. The upper surfaces of the gas vent grooves G1-G5 of the stacked piece plate J, which is integrally incorporated into the stacked piece plate placement recess 9 of each split mold B1, B2, are closed to form multiple gas vent holes H. At the opposite end of the gas vent holes H opposite the end communicating with the second cavity C2, a gas discharge gap 42 is formed between the first outer end surface 41 of the stacked piece plate J and the opposing inner surface 15 of the stacked piece plate placement recess 9 of each split mold B1, B2 (see Figures 9 and 11).Furthermore, the gas discharge gap 42 has an external communication hole 43 that communicates with the outside of each split mold B1, B2.The cross-sectional view of the gas vent hole H formed by the gas vent groove G3 inside the stacked piece plate J is a diagram obtained by flipping Figure 12. Furthermore, the gas vent holes H formed by the gas vent grooves G1, G2 inside the stacked piece board J form another gas discharge gap 42 similar to the gas discharge gap 42 between the second outer end face 44 of the stacked piece board J and the rear inner surface 20 (see Figure 11) perpendicular to both of the opposing inner surfaces 15 of the stacked piece board placement recess 9 of each split mold B1, B2, allowing the gas in the cavity C to be discharged to the outside of each split mold B1, B2. In this embodiment, the total number of gas vent holes H formed inside the stacked piece board J is (4 x 4 = 16) formed in the stacked piece board J incorporated into one split mold B2, and the same number is also formed in another stacked piece board J incorporated into the other split mold B1. Therefore, a total of 32 gas vent holes H are formed in the part of the cavity C that forms the rectangular box section F2. Furthermore, the numerous gas vent holes H are arranged almost evenly along both the circumferential and vertical directions of the peripheral wall portion F2a of the rectangular box portion F2 of the molded product F in the second cavity portion C2, so that the enclosed gas does not stagnate and is effectively discharged to the outside.In addition, since the gas vent groove G5 connects the second cavity portions C2 of the two-cavity split molds B1 and B2, it is a "gas communication hole" rather than a "gas vent hole." Therefore, for example, if a pressure difference occurs between the cavities, gas will move from one cavity to the other, and the gas retention state in each cavity will become equal, making it possible to effectively discharge the gas in each cavity.

[0035] Therefore, when molten resin is injected into cavity C, the portion forming the rectangular box section F2 of molded product F is the last place where the molten resin arrives, and because it arrives accompanied by gas, the gas tends to accumulate there. However, this gas is reliably discharged to the outside of each split mold B1, B2 through the numerous gas vent holes H, gas discharge gaps 42, and external communication holes 43 formed in the stacked piece board J. Therefore, sinks and underfills do not occur on the rectangular box section F2 of molded product F, particularly on its outer surface, as occurs with conventional molding methods, and molding can be performed with a high yield.

[0036] 3, 5, and 9, a wide block fitting groove 17 is formed at the tip of the core body A1 of the core die A, into which an ejector block 16 integrally connected to the tip of the ejector pin E is fitted, and an ejector pin hole 18 through which the ejector pin E is inserted is formed in the core die A. The portion of the ejector pin E that is inserted into the core die A is formed with a smaller diameter than the other portions, so that a compressed air flow gap 19 is formed between the portion and the inner peripheral surface of the ejector pin hole 18 (see FIG. 3(b)).

[0037] When the ejector block 16 connected to the tip of the ejector pin E is fitted into the block fitting groove 17 at the tip of the core main body portion A1 of the core die A, the ejector block 16 forms the tip of the core main body portion A1 of the core die A. 6, the width of the block fitting groove 17 gradually increases from the portion connected to the ejector pin hole 18 toward the tip, and when the ejector pin E projects from the block fitting groove 17, compressed air supplied to the compressed air passage gap 19 passes through an air passage gap (not shown) formed between the opposing inner surface of the block fitting groove 17 and the outer surface of the ejector block 16, and is forced into the gap between the inner peripheral surface of the molded product F and the outer peripheral surface of the core die A, slightly expanding the molded product F so that the inner peripheral surface of the molded product F is slightly spaced from the outer peripheral surface of the core die A. In this state, the ejector pin E projects, thereby removing the molded product F from the core die A. In FIGS. 2 and 3, a compressed air hole 51 communicating with the compressed air passage gap 19 is formed between the base 1 of the movable die M and one of the split dies B2. 2, 3 and 5, reference numeral 25 denotes a bushing incorporated into the base 1 of the movable mold M so that a part of the ejector pin E is inserted therein to close the lower end side of the compressed air flow gap 19.

[0038] The shape of the rectangular box portion (large dimension portion) F2 of the actual molded product F varies, provided that the overall shape is a square box, but the overall shape of the gas venting piece plate and the number of stacked gas venting piece plates are determined in various ways depending on the shape of the large dimension portion.

[0039] In addition, in order to increase the total number of vent holes H formed in the laminated piece plate body J, it is also possible to form vent grooves on both the front and back surfaces of the vent piece plate.

[0040] Furthermore, in the above example, the present invention was applied to a "two-cavity" injection molding mold, but it can also be applied to "multiple-cavity" and "single-cavity" injection molding molds with more than two cavities by changing the overall shape of the gas venting plate.

[0041] Furthermore, in the above embodiment, an injection molding mold for molding an irregular cylindrical molded product in which only one end in the removal direction is open and the other end, which is the injection side of the molten resin, is closed, and the open side has a large dimension portion in the shape of a square box that is larger than the other parts, has been described. However, the present invention can also be applied to an injection molding mold for molding an irregular cylindrical molded product in which only one end in the removal direction is open and the other end, which is the injection side of the molten resin, is closed, and does not have the large dimension portion on the open side. [Explanation of symbols]

[0042] A: Core type A1: Core body part A2: Rectangular part of the core mold B1,B2: split mold C: Cavity C1: First cavity C2: Second cavity D: Depth of gas vent groove F: Molded product F1: Cylindrical part F2: Rectangular box section (large dimension section) F2a: Peripheral wall of rectangular box F2b: Top wall of rectangular box G1 to G5: Gas release groove H: Gas vent hole J: Laminated piece board Ja: U-shaped recess of laminated piece plate K: Injection mold M: Movable type P1~P4: Gas release plate Q: Slide direction of split mold R: Slide direction of movable type W: Width of gas vent groove 9: Laminated piece board placement recess 31: Fixing bolt 32: Bolt insertion hole 32a: Head insertion hole

Claims

1. an injection molding die comprising a columnar core die and a pair of split dies arranged around the core die to form a cavity, wherein molten resin is injected into the cavity, only one end in the removal direction is open, and the other end, which is the injection side of the molten resin, is closed, and an irregular cylindrical molded product having a large-dimension portion in the open portion that is shaped like a square box and larger in dimensions than the other portions is molded, and then the split dies are separated from the core die to remove the molded product from the core die; A plurality of flat gas venting piece plates, each having a gas vent groove formed on at least one surface, are stacked along the direction of removal of the molded product to form an integrated laminated piece plate in a laminated piece plate placement recess provided in the portion of each split mold where the large dimension portion is molded, and the gas vent grooves form a number of gas vent holes in the portion of each split mold where the large dimension portion of the molded product is molded, which communicate the portion of the cavity where the large dimension portion is molded with the outside of the mold, an injection molding die characterized in that each of the vent grooves forming each of the vent holes is formed to a depth sufficient to prevent molten resin injected into the cavity from penetrating into the vent hole.

2. 2. The injection molding die according to claim 1, wherein the depth of the gas release groove is 0.02 to 0.03 mm.

3. An injection molding mold as described in claim 1 or 2, characterized in that the gas venting plate arranged on the outermost side has the largest plate thickness, and the gas venting plate arranged in the middle has a thinner plate thickness than the gas venting plate arranged on both sides along the stacking direction, and the stacking plate incorporated into the stacking plate arrangement recess of each split mold is fixed to each split mold by a plurality of fixing bolts.

4. An injection molding die as described in claim 1 or 2, characterized in that a gas exhaust gap is formed between the outer surface of the stacked piece plate incorporated into the stacked piece plate placement recess on the side opposite the cavity and the inner surface of the stacked piece plate placement recess, allowing gas to be exhausted to the outside of the molding die through a number of gas vent holes formed inside the stacked piece plate.

5. The injection molding die according to claim 1 or 2, characterized in that the injection molding die is configured to be capable of molding two molded products simultaneously, and each cavity for molding each molded product is connected by a separate gas vent hole formed inside the stacked block plate.

6. An injection molding die comprising a columnar core die and a pair of split dies arranged around the core die to form a cavity, wherein molten resin is injected into the cavity to form an irregular cylindrical molded product having only one end in the removal direction open and the other end, which is the injection side of the molten resin, closed, and then the split dies are separated from the core die to remove the molded product from the core die, A plurality of flat gas venting blocks, each having a gas vent groove formed on at least one surface, are stacked along the direction of removal of the molded product to form an integrated laminated block plate in a laminated block plate placement recess provided in the portion of each split mold that will mold the open side of the molded product, and the gas venting grooves form a number of gas vent holes that communicate with the outside of the mold in the portion of each split mold that will mold the open side of the molded product, an injection molding die characterized in that each of the vent grooves forming each of the vent holes is formed to a depth sufficient to prevent molten resin injected into the cavity from penetrating into the vent hole.

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