JP2011101967A - Method for manufacturing mold for injection molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an advantageous method for manufacturing a mold for injection molding, which enables stable injection molding of a resin molded article without a weld line. <P>SOLUTION: After a mold for preliminary molding in which at a position where a heating means 54 is roughly embedded determined from a forecasting position of a weld line producing a cavity part 58, although a storing part 60 formable region is ensured, but the storing part 60 is not formed yet, is prepared, a preliminary molding is performed using this mold for the preliminary molding, to find out the accurate position of the weld line producing a cavity part 58 from the weld line generating position of a preliminary molded article, and then, in the storing part 60 formable region, the storing part 60 is formed at the nearest position to the accurate position of the weld line producing cavity part 58, and in addition, the heating means 54 is stored in this storing part 60. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method of manufacturing an injection mold, and more particularly to an advantageous method of manufacturing an injection mold having a heating means for preventing the occurrence of weld lines.

  As is well known, there is a weld line as one type of molding failure that occurs during injection molding of a resin molded product. This weld line is a flow of molten resin in a molding cavity formed inside an injection mold, and when the molten resin is once divided and then rejoined, or from a plurality of flow paths. This occurs due to incomplete fusion of the joining surfaces at the flow fronts of the molten resin to be merged when the flows merge.

  In a resin molded product in which a coating film or plating film is formed on the design surface, even if a weld line occurs on the design surface, by increasing the film thickness of the coating film or plating film, It can be hidden to some extent. However, in a resin molded product in which no coating film, plating film, or the like is formed on the design surface, the appearance is significantly impaired due to the generation of weld lines.

  As a resin molded product in which a coating film or a plating film is not provided on the design surface, for example, a colored resin pre-colored with a pigment, a dye, or the like, or a bright material such as aluminum flake is further added to such a colored resin There is a resin molded product that is injection-molded by using a so-called material resin such as a glitter resin. In such an injection-molded product of a resin-coated resin, since the coating and plating after molding are not performed, the production work can be advantageously simplified and the cost can be reduced. There exists an advantage that the fall of the external appearance by peeling can be eliminated effectively. However, on the other hand, if a weld line or the like is generated on the design surface, it is exposed to the outside and a serious appearance defect is caused.

  In view of this, for example, Japanese Patent Application Laid-Open No. 2009-248423 (Patent Document 1) describes a so-called weld that includes welded portions of molten resin in a molding cavity and generates a weld line in the resin molded product by the molten resin. There has been proposed an injection mold in which a heater is embedded in a portion corresponding to a line generating cavity portion. In such an injection mold, the molten resin introduced into the weld line generating cavity is heated by a heater, so that the joining surfaces at the flow fronts of the molten resin to join together are surely and completely. As a result, the occurrence of weld lines in the resin molded product to be injection-molded can be advantageously prevented or suppressed.

  When manufacturing such an injection mold with a built-in heater for preventing the generation of weld lines, conventionally, first, in the mold, from the occurrence of the weld line of the resin molded product to be injection molded after the mold is completed. The target injection molding die is manufactured by finding the position of the weld line generation cavity portion of the wafer and performing additional processing to embed a heater in a portion corresponding to the found weld line generation cavity portion. Method is adopted.

  However, with such a conventional technique, it may be difficult to embed a weld line generation preventing heater at a desired position in the vicinity of the weld line generation cavity.

  That is, usually, in the injection mold, a cooling flow path in which a cooling medium (for example, cooling water) for cooling the molten resin injected and filled in the molding cavity flows is formed in the vicinity of the molding cavity. Has been. Therefore, when a heater is embedded in a portion corresponding to a weld line generation cavity portion which is a part of the molding cavity, a part of the cooling channel already exists or the heater should be embedded therein. In some cases, a cooling flow path may be provided in the immediate vicinity of the location. In this case, the cooling flow path is an obstacle, and the heater can be embedded at a desired position in the immediate vicinity of the weld line generation cavity. It will disappear.

  In such a case, the heater is buried at a position distant from the weld line generation cavity portion, so that the molten resin introduced into the weld line generation cavity portion is not sufficiently heated by the heater. Therefore, it is difficult to prevent the generation of the weld line, or it becomes impossible to perform the heating and the generation of the weld line cannot be prevented even though the heater for preventing the generation of the weld line is embedded. Even there was.

JP 2009-248423 A

  Here, the present invention has been made in the background as described above, and the problem to be solved is to heat a heater or the like for preventing the generation of a weld line when manufacturing an injection mold. The method can be securely embedded in an appropriate position inside the mold, sufficiently close to the cavity where the weld line is generated, so that stable injection molding of resin molded products with excellent appearance performance without weld lines is possible. It is an object of the present invention to provide an advantageous manufacturing method of an injection mold that enables the above-described process.

  In the present invention, in order to solve such a problem, a molding cavity having a shape corresponding to a resin molded product to be injection molded is formed inside, and a weld line is formed on the resin molded product. Injection in which heating means for heating the molten resin introduced into the weld line generating cavity portion is embedded in a portion corresponding to the weld line generating cavity portion formed of a part of the molding cavity. A method for producing a molding die, wherein (a) a position of the weld line generation cavity portion is predicted from an assumed flow behavior of the molten resin in the molding cavity, and based on the predicted position, A step of determining an approximate position for embedding the heating means; and (b) an area where a housing portion for accommodating the heating means can be formed is embedded in the heating means. A step of producing a preforming mold that is secured in a location including a position but in which the accommodating portion is not yet formed; and (c) the resin molded product by injection molding using the preforming mold. And (d) securing to the preforming mold, the step of finding the exact position of the weld line generating cavity portion from the weld line generating position in the preformed resin molded product. After forming the accommodating portion at a position closest to the exact position of the weld line generating cavity portion found by preforming the resin molded product, in the formable region of the accommodating portion, the accommodating portion Including the step of embedding the heating means in a portion corresponding to the weld line generating cavity portion by accommodating the heating means in the section. The manufacturing method of exiting mold, it is an gist thereof.

  In addition, according to one of the advantageous aspects of the method for manufacturing an injection mold according to the present invention, in the molding cavity obtained by performing a flow analysis of the molten resin injected into the molding cavity. From the analysis result of the flow behavior of the molten resin, the position of the weld line generating cavity is predicted.

  Moreover, according to one of the preferable aspects of the manufacturing method of the injection mold according to the present invention, the cooling flow path in which the cooling medium for cooling the molten resin injected and filled in the molding cavity flows. However, the preforming of the resin molded product is performed using the preforming mold formed in a portion excluding the region where the housing portion can be formed.

  That is, in the method for manufacturing an injection mold according to the present invention, the approximate position where the heating means is embedded is determined in advance based on the predicted position of the weld line generating cavity portion before the preparation of the preform mold. The Thereafter, a preforming mold is manufactured in a state where an area where the accommodating portion of the heating means can be formed is secured at a location including the approximate position of the heating means embedding. For this reason, it can be reliably avoided that the cooling flow path or the like is disposed in the formable region of the accommodating portion located corresponding to the weld line generating cavity portion of the manufactured preforming mold. Therefore, when forming the accommodating part of the heating means in such a preforming mold or when accommodating the heating means in the formed accommodating part, the cooling flow path or the like becomes an obstacle and the It can be effectively solved that it is difficult to form and further accommodate the heating means in the formed accommodating portion. And thereby, the heating means can be surely embedded in a desired position corresponding to the weld line generating cavity portion in the preforming mold, and the target injection molding mold can be manufactured.

  In addition, in the method for manufacturing an injection mold according to the present invention, the heating means is embedded at a position closest to the exact position of the weld line generating cavity portion found by the preliminary molding. Therefore, at the time of injection molding using the produced injection mold, the cavity surface of the weld line generation cavity part, and further, the molten resin introduced into the weld line generation cavity part is more sufficiently heated by the heating means. It becomes possible to heat to.

  Therefore, according to the method for manufacturing an injection mold according to the present invention as described above, the heating means can be reliably embedded in an appropriate position inside the mold, sufficiently close to the weld line generating cavity part, As a result, it is possible to extremely advantageously manufacture an injection mold capable of stably injection-molding a resin molded product having excellent appearance performance without a weld line. Then, if the injection mold manufactured by the method of the present invention is used, for example, a resin molded product using a material resin can be molded extremely stably and easily with high appearance quality. It can be done.

It is a perspective explanatory view showing an example of a resin molded product formed by injection molding using an injection mold manufactured according to the method of the present invention. It is longitudinal cross-sectional explanatory drawing which shows an example of the injection mold manufactured according to this invention method, Comprising: It is a figure equivalent to the II-II cross section of FIG. FIG. 3 is an explanatory plan view of a movable mold in the injection mold shown in FIG. 2. It is IV-IV sectional explanatory drawing in FIG. It is explanatory drawing which shows one process example implemented in order to manufacture the injection mold according to this invention method, Comprising: A cavity formation recessed part and an injection gate formation recessed part are provided in the movable mold of a preforming mold. And the state which formed the runner formation recess and the insertion hole for cooling pipes is shown. It is VI-VI cross-section explanatory drawing in FIG. FIG. 6 is an explanatory view showing a process performed subsequent to the process shown in FIG. 5, corresponding to a section taken along the line VII-VII in FIG. 6, showing a state in which a cooling pipe is arranged on the movable mold of the preforming mold. FIG. It is explanatory drawing which shows the process implemented following the process shown by FIG. 7, Comprising: The state which implemented preforming using the produced preforming mold is shown.

  Hereinafter, in order to clarify the present invention more specifically, embodiments of the present invention will be described in detail with reference to the drawings.

  First, FIG. 1 shows a perspective view of an example of a resin molded product that is injection-molded using an injection mold manufactured according to the method of the present invention. As is clear from FIG. 1, the resin molded product 10 as a whole is an injection molded product having a longitudinal rectangular frame shape.

  More specifically, the resin molded product 10 includes two long side portions 12a and 12b having a rectangular cross section extending in parallel in the longitudinal direction at a predetermined distance from each other, and perpendicular to the longitudinal direction at a predetermined distance from each other. And two short sides 14a and 14b having a rectangular cross section extending in parallel in each direction. And both the length direction both ends of the two long side parts 12a and 12b are integrally connected by the two short side parts 14a and 14b, respectively. Thereby, the resin molded product 10 is configured with a longitudinal rectangular frame shape.

  Moreover, in this resin molded product 10, the outer peripheral surface which consists of each outer side of each long side part 12a, 12b and each short side part 14a, 14b, the inner peripheral surface which consists of those inner surfaces, and each long side part 12a , 12b and the upper surface formed by the surface on one side in the height direction of each of the short side portions 14a, 14b are design surfaces. And the gate mark 15 is formed in the connection part with one short side part 14a in one long side part 12a.

  Here, a polymer alloy of polycarbonate and ABS resin that exhibits sufficient strength is used as the resin material for forming the resin molded product 10. In addition, an appropriate pigment is added to such a resin material, and the resin material 10 is colored in a predetermined color, so that the resin molded product 10 can be obtained without forming a coating film or the like on the surface. The color is colored. Of course, the forming material of the resin molded product 10 is not particularly limited to the illustrated material.

  By the way, generally, when a resin molded product having an annular shape or a frame shape is injection-molded by using an injection mold having a conventional structure, a molten resin in a molding cavity formed inside the mold. In this flow process, the molten resin once merges and then rejoins. Therefore, the weld line is generated due to the incomplete fusion of the joining surfaces at the flow fronts of the molten resin to be joined. Concerned. In particular, in an injection molded product having a longitudinal rectangular frame shape such as the resin molded product 10, in many cases, for example, when a gate mark is formed in the vicinity of any one of the four corners ( When a gate port is provided at any one of the four corners of the molding cavity), a weld line is generated in the vicinity of the corner located diagonally to the one corner. However, the resin molded product 10 is injection-molded using an injection mold that is manufactured according to the method of the present invention and has measures for preventing the occurrence of weld lines. Therefore, in such a resin molded product 10, although the gate mark 15 is formed in the connection part of the long side part 12a and the short side part 14a, generation | occurrence | production of a weld line is not recognized in any location. .

  FIG. 2 shows, in a longitudinal cross-sectional form, an injection molding die 16 that can advantageously injection-mold the resin molded product 10 without such a weld line. As apparent from FIG. 2, the injection mold 16 is divided into a fixed mold 20 attached to a fixed platen 18 that is fixed in position and a movable platen 22 that can move toward and away from the fixed platen 18. A fixed die 20 and a movable die 24 arranged opposite to each other are attached.

  The stationary platen 18 of the injection molding die 16 is provided with a sprue bush 28 including a sprue 26 communicating with a nozzle hole of a nozzle of an injection device (not shown). The fixed mold 20 is formed with a sub sprue 30 communicating with the sprue 26 of the sprue bush 28 so as to extend toward the movable mold 24.

  In addition, as shown in FIG. 3, a cavity forming recess 32 is formed on the die mating surface 31 (opposing surface) of the movable die 24 with the fixed die 20. The cavity forming recess 32 has a shape of a longitudinal rectangular annular groove corresponding to the resin molded product 10, and includes two longitudinal groove portions 34a and 34b extending in the longitudinal direction and two transverse groove portions 36a extending orthogonally to them. , 36b. Further, an injection gate forming recess 38 and a runner forming recess 40 are formed on the side of the cavity forming recess 32 on the mold matching surface 31 of the movable mold 24 so as to communicate with each other. The injection gate forming recess 38 opens into the cavity forming recess 32 through a gate port 52 that opens into the cavity forming recess 32 at a corner formed between the vertical groove portion 34a and the lateral groove portion 36a. is doing.

  As shown in FIG. 2, in the injection mold 16, the movable mold 24 and the fixed mold 20 are closed based on the approaching movement of the movable plate 22 to the fixed plate 18, and the movable mold 22 is closed. The cavity forming recess 32 of 24 is covered with a surface facing the movable mold 24 of the fixed mold 20, so that a shape corresponding to the resin molded product 10 is formed between the facing surfaces of the movable mold 24 and the fixed mold 20. A molding cavity 42 is formed. In the molding cavity 42, the portions formed by covering the two longitudinal groove portions 34 a and 34 b of the cavity forming recess 32 with the fixed mold 20 form the two long side portions 12 a and 12 b of the resin molded product 10, respectively. The long side molding cavity portions 44 a and 44 b are formed, and the two lateral groove portions 36 a and 36 b of the cavity forming recess 32 are covered with the fixed mold 20, and the two short side portions of the resin molded product 10 are formed. Short side molding cavity portions 46a and 46b that form 14a and 14b, respectively.

  In the injection mold 16, the injection gate forming recess 38 and the runner forming recess 40 are connected to the movable mold 24 of the fixed mold 20 in the closed state of the movable mold 24 and the fixed mold 20. The injection gate 48 is formed in communication with the molding cavity 42, and the runner 50 is formed in communication with the injection gate 48 and the sub sprue 30 of the fixed mold 20. It has come to be. Furthermore, here, a gate port 52 that is an opening into the molding cavity 42 of the injection gate 48 is formed at a corner formed between the long side molding cavity portion 44a and the short side molding cavity portion 46a. ing.

  Thus, in the injection mold 16, molten resin injected from a nozzle of an injection device (not shown) is introduced into the runner 50 from the sprue 26 and the sub sprue 30, and the injection gate 48 and the gate are inserted from the runner 50. It is guided into the molding cavity 42 through the mouth 52. Further, the molten resin introduced into the molding cavity 42 is diverted from the gate port 52 into the long side part molding cavity part 44a and the short side part molding cavity part 46a, and flows in the molding cavity 42. -ing

  In the injection mold 16 of the present embodiment, in particular, the electric heater 54 as a heating means and the cooling pipe 56 constituting the cooling flow path are installed with a special arrangement form with respect to the movable mold 24. ing.

  That is, the electric heater 54 has, for example, a known resistance heating type structure, and as shown in FIGS. 2 and 4, the mating surface of the movable mold 24 of the injection mold 16 with the fixed mold 20. It is embedded in a specific portion of a portion between the back surface opposite to 31 and the bottom surface of the cavity forming recess 32. The electric heater 54 may be embedded in the fixed mold 20.

  More specifically, here, in the injection molding die 16, at the time of injection molding, the flow is divided from the gate port 52 into the long side molding cavity portion 44a and the short side molding cavity portion 46a, thereby forming the molding cavity 42. The joint location of the molten resin flowing inside is formed at a location diagonally to the gate port 52 in the molding cavity 42, that is, between the long side molding cavity portion 44b and the short side molding cavity portion 46b. It is an end side portion in the extending direction of the long side portion molding cavity portion 44b including the corner portion. Further, such a joining point of the molten resin in the molding cavity 42 is a weld line generating cavity portion 58 that generates a weld line in the resin molded product 10 by the joining of the molten resin.

  In the movable mold 24 of the injection mold 16, the height (thickness) positioned between the bottom surface of the vertical groove 34 b portion of the cavity forming recess 32 corresponding to the weld line generating cavity portion 58 and the back surface. ) In the intermediate portion in the direction, a housing hole 60 as a housing portion is formed so as to open on the side surface of the movable mold 24 and extend along the vertical groove portion 34b. Further, the electric heater 54 is accommodated in the accommodation hole 60, and the electric heater 54 is bolted to the side surface of the movable mold 24 at an outer flange portion integrally formed at one end portion in the length direction.

  Thus, the electric heater 54 is embedded in the movable die 24 at a location near the weld line generating cavity portion 58. As a result, the inner surface of the longitudinal groove portion 34 b of the cavity forming recess 32 that forms the weld line generating cavity portion 58 is heated by the electric heater 54.

  On the other hand, the cooling pipe 56 is composed of a single long pipe (steel pipe, hose, etc.), and one end side opening is connected to a supply device (not shown) of a cooling medium such as cooling water, for example. On the other hand, the opening at the other end is a discharge port (not shown) for discharging the cooling medium. In addition, in the intermediate portion in the height direction of the movable mold 24 in which the cooling pipe 56 is to be embedded, there are three portions penetrating the intermediate portion at three positions spaced from each other in the extending direction of the lateral groove portions 36a and 36b. The insertion holes 62a, 62b, 62c are formed so as to extend along the longitudinal groove portions 34a, 34b of the cavity forming recess 32, respectively.

  The three insertion holes 62a, 62b, and 62c are formed so that the position in the height direction of the movable mold 24 is substantially the same as the position in the height direction of the movable mold 24 of the electric heater 54 embedded in the movable mold 24. However, the formation position in the direction perpendicular to the height direction of the movable mold 24 is different from the formation position of the electric heater 54. That is, one insertion hole 62a is formed so as to extend straight along the vertical groove 34a of the cavity forming recess 32 in which the gate port 52 is provided. Another insertion hole 62b is formed so as to extend straight along the longitudinal groove 34b at a position corresponding to the intermediate portion in the extending direction of each of the two lateral grooves 36a, 36b. Further, the remaining one insertion hole 62c is located along the vertical groove 34b at the side opposite to the vertical groove 34a, that is, at the side of the cavity forming recess 32 with the vertical groove 34b interposed therebetween. It is formed so as to extend straight.

  The cooling pipes 56 are respectively inserted into the three insertion holes 62 a, 62 b, and 62 c, so that the cooling pipe 56 is embedded in the intermediate portion in the height direction of the movable mold 24. Further, under such an embedded state, the cooling pipe 56 has the embedded position in the height direction of the movable die 24 at substantially the same position as the electric heater 54, while being perpendicular to the height direction. Is different from the electric heater 54. Therefore, the cooling pipe 56 is embedded at a position close to the molding cavity 42 (the bottom surface of the cavity forming recess 32) and at a position separated from the electric heater 54. The three insertion holes 62a, 62b, and 62c can be used as a part of the cooling pipe 56 without inserting the cooling pipe 56 into the three insertion holes 62a, 62b, and 62c. That is, one steel pipe or hose connected to the cooling medium supply device at one end is connected to one opening of the insertion hole 62a at the other end, and the other opening of the insertion hole 62a One opening of the insertion hole 62b is connected to each other by another steel pipe or hose, and the other opening of the insertion hole 62b and one opening of the insertion hole 62c are further connected to another steel pipe or Connected to each other by a hose or the like, and another steel pipe or hose whose one end is a discharge port is connected to the other opening of the insertion hole 62c at the other end. As a result, the cooling pipe 56 is configured by the insertion holes 62a, 62b, 62c and the steel pipes or hoses connecting them, and a cooling flow path is formed inside the movable mold 24 by such a cooling pipe 56. You can do it.

  Thus, in the injection mold 16, a cooling medium such as cooling water is circulated in the cooling pipe 56, so that the electric heater 54 and the movable mold 24 in which it is embedded can be moved without unnecessary cooling. The entire mold 24, particularly the inner surface of the cavity forming recess 32 that forms the molding cavity 42 except the long side molding cavity portion 44b including the weld line generating cavity portion 58, can be efficiently cooled. .

  In such an injection molding die 16, at the time of injection molding, it is injected into the molding cavity 42 through the injection gate 48, and the long side molding cavity part 44 a and the short side molding cavity part from the gate port 52. 46a and the molten resin flowing in the molding cavity 42 is introduced into the weld line generation cavity portion 58, the molten resin in the weld line generation cavity portion 58 is sufficiently absorbed by the electric heater 54. It can be heated. At this time, the heating by the electric heater 54 is not disturbed by the cooling by the cooling pipe 56. As a result, the joining surfaces at the flow fronts of the molten resin that merge in the weld line generating cavity portion 58 are surely and completely fused, so that the design surface of the injection-molded resin molded article 10 is obtained. Generation of weld lines can be effectively prevented.

  By the way, when such an injection mold 16 is manufactured, for example, the operation is advanced as follows. Note that the injection mold 16 of this embodiment has a feature that is not seen in the prior art in the arrangement structure of the cooling pipe 56 and the electric heater 54 in the movable mold 24. Therefore, in the following, only the manufacturing process of the movable mold 24 will be described in detail, and the manufacturing method of components or parts of the injection mold 16 other than the movable mold 24 will be omitted.

  That is, first, as shown in FIGS. 5 and 6, the cavity forming recess 32, the injection gate forming recess 38, and the runner forming recess 40 are formed on the mating surface 31 of the movable mold 24 with the fixed mold 20. And formed according to a known technique.

  Next, a flow analysis of the molten resin injected into the molding cavity 42 formed by closing the movable mold 24 and the fixed mold 20 is performed by, for example, CAE using a computer. And the position of the weld line generation | occurrence | production cavity part 58 in the shaping | molding cavity 42 is estimated from the result of this flow analysis, and the electric heater 54 is embed | buried with respect to the movable mold | type 24 after that based on such an estimated position. Determine the approximate position.

  Specifically, these operations are performed as follows. That is, according to the flow analysis, the joining portion of the molten resin flowing in the molding cavity 42 at the time of injection molding is, for example, a part of the molding cavity 42 located diagonally to the gate port 52, that is, the long side part molding cavity part 44b and the short side. An end side portion in the extending direction of the long side molding cavity portion 44b including a corner portion formed between the side molding cavity portion 46b and shown in FIG. If the result is that the region A is surrounded by the region A, the position of the region A in the molding cavity 42 (cavity formation recess 32) is the position of the weld line generation cavity portion 58. Predict.

  Thereafter, of the cavity forming recesses 32 provided in the movable mold 24, a location including a portion corresponding to the predicted position of the weld line generating cavity portion 58, specifically, the longitudinal groove portion 34 b and the lateral groove portion of the cavity forming recess 32. FIG. 5 and FIG. 5 are composed of an intermediate portion in the height direction of the movable die 24 located corresponding to a portion including the extending direction end portion side portion of the longitudinal groove portion 34b including the corner portion formed between the movable die 24 and FIG. 6 is determined as the approximate position where the electric heater 54 is embedded, that is, the approximate position where the accommodation hole 60 is formed.

  Note that the position of the weld line generating cavity portion 58 is only predicted from the assumed flow behavior of the molten resin in the molding cavity 42. Therefore, a flow analysis using software other than the CAE exemplified above can be performed, and the position of the weld line generation cavity portion 58 can be predicted from the result of the flow analysis. Further, the position of the weld line generating cavity portion 58 may be predicted from the flow behavior of the molten resin in the molding cavity 42 that is assumed by experience or various experiments without using a computer or the like. .

  Further, the approximate embedded position of the electric heater 54 determined from the predicted position of the weld line generation cavity 58 is usually the cavity forming recess 32 corresponding to the weld line generation cavity 58 (the extension of the vertical groove 34b). It is set at a position separated from the bottom surface of the exit end portion) by an appropriate distance in the height direction of the movable mold 24. From the bottom surface of the cavity forming recess 32 to the approximate embedded position of the electric heater 54 (The dimension indicated by D in FIG. 6) is the strength of the bottom of the cavity forming recess 32 portion where the wall thickness is reduced by the formation of the accommodation hole 60 at the approximate embedded position of the electric heater 54, and so on. This is appropriately determined in consideration of heat transfer properties based on the material of the movable mold 24 that provides the bottom of the cavity forming recess 32 portion.

  When the approximate embedded position (B region) of the electric heater 54 is determined, three insertion holes 62a, 62b, 62c for inserting the cooling pipe 56 are formed at positions avoiding the approximate embedded position of the electric heater 54. . As a result, an area in which a housing hole 60 capable of housing the electric heater 54 can be formed in the intermediate portion in the height direction of the movable mold 24 including the approximate position of the embedded electric heater 54 without being interrupted by the cooling pipe 56. Secure.

  Thereafter, as shown in FIG. 7, one end of each of the three insertion holes 62 a, 62 b, and 62 c formed in the movable mold 24 is connected to a cooling medium supply device (not shown), and the other end is the cooling medium. Is inserted through one cooling pipe 56. As a result, the cooling pipe 56 through which the cooling medium can circulate is extended near the bottom of the cavity forming recess 32 in the movable mold 24 in a meandering manner so as to avoid a region where the accommodation hole 60 of the electric heater 54 can be formed. In the state, bury it.

  And although the cooling pipe 56 was incorporated and the formation area of the accommodation hole 60 of the electric heater 54 was ensured, the electric heater 54 was not embedded yet, and the movable mold 24 was manufactured according to a known method. The movable plate 22, the fixed mold 20, the fixed plate 18 and the like are used and assembled to each other to produce a preforming mold 64 (see FIG. 8).

  Next, as shown in FIG. 8, the preforming mold 64 thus prepared is used to perform preforming in which the molten resin 66 injected from an injection device (not shown) is filled into the molding cavity 42, and the preforming is performed. A product (not shown) is formed. An electric heater 54 for heating the molten resin in the weld line generating cavity portion 58 is not yet embedded in the movable mold 24 of the preforming mold 64 used in the preforming. For this reason, a weld line is generated in the preform from the merged molten resin in the weld line generating cavity portion 58. Therefore, after the preforming, the preform is visually observed to confirm the occurrence position of the weld line. And the exact position of the weld line generation | occurrence | production cavity part 58 in the molding cavity 42 is found from the weld line generation | occurrence | production position in such a preform.

  Here, since the cooling pipe 56 is installed in the preforming mold 64, the preformed product is cooled by a cooling medium flowing in the cooling pipe 56. Therefore, the preformed product is molded under conditions close to those of the actual resin molded product 10. Thereby, the weld line occurrence position in the target resin molded product 10 can be grasped more accurately by the weld line occurrence position in the preformed product.

  Next, in the embedded approximate position (B area) of the electric heater 54 secured as an area where the accommodation hole 60 can be formed, the weld line generating cavity portion 58 found by observation of the preform is accurately positioned. The accommodation hole 60 is formed at the nearest location so as to open on the side surface of the movable mold 24. That is, if the exact position of the weld line generating cavity portion 58 found by observing the preform is, for example, the C region surrounded by a thin line in FIGS. The accommodation hole 60 is formed in the intermediate portion in the height direction of the movable mold 24 so that the electric heater 54 can be accommodated in a state where the heat generating portion of the heater 54 is disposed closest to the C region. In forming the accommodation hole 60, the cooling pipe 56 is already provided in the movable mold 24, but such a cooling pipe 56 is formed in the region (B) in which the accommodation hole 60 can be formed in the movable mold 24. It is installed in the part except area. Therefore, the cooling pipe 56 does not interfere with the formation of the accommodation hole 60.

  Then, as shown in FIG. 2, the electric heater 54 is inserted and accommodated in the accommodation hole 60, and the outer flange portion formed integrally with the end portion of the electric heater 54 is bolted to the side surface of the movable die 24. To do. As a result, the movable mold 24 is obtained in which the electric heater 54 is embedded in the vicinity of the weld line generating cavity portion 58 formed of a part of the molding cavity 42. Then, the movable mold 24 is assembled to the movable platen 22, the fixed die 20, and the fixed platen 18 to obtain the target injection molding die 16 having the structure as shown in FIGS. It is.

  As described above, in the injection mold 16 of the present embodiment, the electric heater 54 that heats the molten resin in the weld line generating cavity portion 58 at the time of injection molding includes the weld line generating cavity portion in the movable mold 24. Embedded in a location sufficiently close to the exact position of 58, and the operation at the time of embedding such an electric heater 54 is not obstructed by the cooling pipe 56 already installed in the movable mold 24, It can be done easily and quickly.

  Therefore, by using the injection molding die 16 of the present embodiment as described above, the resin molded product 10 made of a resin material can be injection-molded extremely stably with excellent appearance performance without a weld line. Moreover, the injection mold 16 itself is also easily and reliably disposed at a location sufficiently close to the exact position of the weld line generating cavity portion 58, unlike the conventional product, in the production of the injection mold 16 itself. Therefore, facilitation of the manufacturing operation can be achieved very effectively.

  The specific configuration of the present invention has been described in detail above. However, this is merely an example, and the present invention is not limited by the above description.

  For example, if the heating means embedded in the injection mold 16 is capable of heating the molten resin in the weld line generating cavity portion 58 formed of a part of the molding cavity 42, the resistance heating type illustrated may be used. Instead of or in addition to the electric heater 54, any heating means having a known structure can be used.

  Further, such a heating means may be embedded in the fixed mold 20 instead of the movable mold 24 or embedded in both the movable mold 24 and the fixed mold 20.

  Furthermore, if the area where the accommodation hole 60 can be formed is secured, the cooling pipe 56 is disposed in the injection mold 16 even after the electric heater 54 is embedded in the injection mold 16. good.

  Furthermore, in the said embodiment, although the accommodating part was comprised by the accommodation hole 60 formed so that it might open to the side surface with respect to the movable mold | type 24, for example, two division bodies consist of the movable mold | type 24. A groove portion that has a structure that is assembled and forms a hole portion that can accommodate the heating means when the two divided bodies are assembled to the corresponding portions of the respective divided surfaces of the two divided bodies. And the housing portion may be constituted by the groove portions.

  In addition, the present invention is not limited to a method for producing an injection mold used for injection molding of a resin molded product having a long rectangular frame shape, and various resin molded products in which the occurrence of weld lines is a problem. The present invention can be advantageously applied to any method of manufacturing an injection mold used for injection molding.

  In addition, although not enumerated one by one, the present invention can be carried out in a mode to which various changes, modifications, improvements, etc. are added based on the knowledge of those skilled in the art. It goes without saying that all are included in the scope of the present invention without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 10 Resin molded product 16 Injection mold 20 Fixed mold 24 Movable mold 32 Cavity formation recess 42 Molding cavity 54 Electric heater 56 Cooling pipe 58 Weld line generation cavity part 60 Accommodating hole 64 Preliminary molding mold

Claims (3)

A mold cavity having a shape corresponding to the resin molded product to be injection-molded is formed inside, and a weld line generating cavity portion including a part of the molding cavity is generated in the resin molded product. A method for manufacturing an injection mold in which a heating means for heating the molten resin introduced into the weld line generation cavity portion is embedded in a corresponding portion,
Predicting the position of the weld line generating cavity part from the assumed flow behavior of the molten resin in the molding cavity, and determining a rough position for embedding the heating means based on the predicted position;
A step of producing a preforming mold in which an area where the accommodating portion for accommodating the heating means can be formed is secured at a location including the approximate embedded position of the heating means, but the accommodating portion is not yet formed. When,
The resin molded product is preformed by injection molding using the preforming mold, and the exact position of the weld line generating cavity portion is found from the weld line generating position in the preformed resin molded product. Process,
Of the formable region of the housing portion secured in the preforming mold, the closest position to the exact position of the weld line generating cavity portion found by the preforming of the resin molded product, Embedding the heating means in a portion corresponding to the weld line generating cavity portion by accommodating the heating means in the accommodating portion after forming the accommodating portion;
The manufacturing method of the injection mold characterized by including these.   The position of the weld line generation cavity portion is predicted from the analysis result of the flow behavior of the molten resin in the molding cavity obtained by analyzing the flow of the molten resin injected into the molding cavity. 2. A method for producing an injection mold according to 1. The preforming mold in which a cooling channel through which a cooling medium for cooling the molten resin injected and filled in the molding cavity flows is formed in a portion excluding the region where the housing portion can be formed. The method for producing an injection mold according to claim 1 or 2, wherein the resin molded product is preformed by using.

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