JPH02292014A - Injection molding mold - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an injection mold for producing an injection molded product having a boss.

BACKGROUND ART When producing an injection molded product having this type of boss, problems arise from sink marks and weld lines that occur around the boss of the injection molded product. Although sink marks and weld lines both affect the appearance of injection molded products, weld lines also pose a problem in terms of strength. The reason why flakes occur around the boss is that the flesh pressure in this area is greater than in the surrounding area, and the molten plastic in this area cools more slowly than in the surrounding area.In other words,
This is because after the surrounding area has solidified, it gradually solidifies while being accompanied by contraction. FIG. 3 shows a plastic molded product a having a boss b, and a slight depression appears as a brush A on the surface of the plastic molded product a. As a measure to prevent this problem, a method has been adopted in which the wall pressure on the base side of the boss b is adjusted by providing a convex portion around the core pin of the mold, as shown in FIG. 4.

Problems to be Solved by the Invention> However, although the above conventional method can uniformly cool the molten plastic and prevent the occurrence of flakes A, as shown in FIG. There is a drawback that a weld line B with a linear pattern is generated on the surface. The cause of weld line B is:
The molten plastic branches and flows at boss b (fifth
(The arrows shown in the figure indicate the flow of molten plastic)
This is because the welding of the branched molten plastic becomes insufficient. Although various measures to prevent this weld line B have been reported, they have the disadvantage that brush marks A occur. That is, the current situation is that it is not possible to simultaneously prevent brush A and weld line B, which occur due to different causes, and one must be prioritized over the other.

The present invention was devised in view of the above circumstances, and an object of the present invention is to provide an injection mold that can prevent both the occurrence of flakes and weld lines.

Means for Solving the Problems> The injection mold according to the present invention is composed of a core and a cavity, and the core is equipped with a core pin for forming a boss that is a part of the injection molded product. A protrusion for preventing sinking is provided on the cavity-facing surface of the core corresponding to the outer edge of the base of the boss, while a protrusion is provided on the cavity-facing surface of the core corresponding to the outer edge of the core on the base side of the boss. Grooves for bypassing the molten resin are provided on the surface of the core facing the cavity in the direction in which the molten resin flows.

<Operation> Molten resin is poured into the core and cavity with the mold closed. Although some of the molten resin during the pouring process is bypassed by the core pin, most of it flows through the grooves provided in the core pin and the core. Since this groove runs in the direction along the flow of the molten resin, turbulence in the flow of the molten resin around the core pin is eliminated to some extent, and weld lines are prevented from occurring. On the other hand, since the convex portion is provided around the core pin, the internal pressure on the root side of the boss is adjusted, and the occurrence of /S is prevented through uniform cooling of the molten resin.

Embodiment> Hereinafter, an embodiment of the injection mold according to the present invention will be described with reference to the drawings. FIG. 1 is a simplified sectional view of an injection mold, and FIG. 2 is a simplified perspective view of portion C shown in FIG.

The injection mold shown in FIG. 1 is broadly divided into a core 10 and a cavity 20, both of which are connected to an injection molding machine (not shown), so that the core 10 and the cavity 20 can be opened and closed. A recess 30 corresponding to the outer shape of the injection molded product a is formed in the core 10 and the cavity 20,
Molten plastic is poured into the recess 30 from the injection molding machine through a sprue 21 provided at a predetermined location in the cavity 20, so that a plastic molded product a is manufactured.

This plastic molded product a has a boss b, and the boss b is molded by a core pin 1l fixed to a predetermined location of the core 10.

Next, the mold structure around the tip of the core pin 1l will be explained with reference to FIG. 2. A convex portion 12 is provided in the shape of an outer ring on a surface of the core 11 facing the concave portion 30 .

This convex portion 12 forms a groove on the outer edge of the base of the boss b. Further, a groove 111 having a U-shaped cross section is provided on the tip surface of the core pin 11, and a similar groove 121 is also provided on a portion of the convex portion 12.

By the way, the direction in which the molten plastic flows during the process of being poured into the recess 30 is determined by the positional relationship of the sprue 21, etc., and the groove directions of the grooves 111 and 121 are set in the direction along the flow of the molten plastic.

When the injection molding die having the above-mentioned basic configuration is used, sink marks and weld lines will not occur around the boss b of the plastic molded product a, and this principle will be explained below.

With the core 10 and cavity 20 closed, the recess 3
Pour molten plastic into 0. In the process of the molten plastic spreading into the inner space of the recess 30, the core pin 3
Although some of the water is bypassed by 0, most of the water flows through the grooves 111 and 121 provided in the core pin 30 and the core 10, respectively. Moreover, since the grooves 111 and 121 are cut in the direction along the flow of the molten plastic, the turbulence of the molten plastic around the core pin 30 is eliminated to some extent, and weld lines are prevented from forming there.

In addition, in the process in which the poured molten plastic solidifies around the core pin 30, since the protrusion 12 is provided on the core 10 and the wall pressure on the base side of the boss b is adjusted, The plastic will be cooled evenly, and the occurrence of flakes will be prevented.

Therefore, neither sink marks nor weld lines occur in the plastic molded product a, the appearance of the plastic molded product a does not deteriorate, and there is no problem in terms of strength, and product defects can be reduced. Furthermore, since the above merits can be obtained with a slight design change, it becomes possible to provide an inexpensive and high-performance injection mold.

Note that the injection molding die according to the present invention is not limited to the above-mentioned embodiments, but can be applied to any type of injection molding die as long as it has a core pin.

Effects of the Invention As described above, when using the injection mold according to the present invention,
Since the structure is such that disturbances in the flow of the molten resin around the core pin are eliminated to some extent and uniform cooling of the molten resin is achieved, the occurrence of both weld lines and flakes can be suppressed. Therefore, it has advantages in terms of appearance and strength of injection molded products, and is of great significance in reducing product defects.

[Brief explanation of drawings]

1 and 2 are diagrams for explaining an embodiment of an injection mold according to the present invention, in which FIG. 1 is a schematic cross-sectional view of the injection mold, and FIG. FIG. 1 is a simplified perspective view of portion C shown in FIG. 3 and 4 are cross-sectional views of the plastic molded product around the boss.
The figure shows how a conventional injection mold was used to suppress the occurrence of weld lines, and FIG. 5 shows how weld lines appeared on the product surface of a plastic molded product. 10・ 11・ 12・ 20・ a1 b ・ Core・Core pin・・Groove・Protrusion・Groove・Cavity・Plastic molded product・Boss Patent applicant Sharp Corporation

Claims (1)

[Claims] (1) An injection mold consisting of a core and a cavity, the core having a core pin for molding a boss that is a part of the injection molded product, in which the core is located at the outer edge of the core corresponding to the base side outer edge of the boss. A convex portion for preventing sink marks is provided on the surface facing the cavity, while a convex portion is provided on the surface facing the cavity of the core corresponding to the tip of the core pin and the outer edge of the root side of the boss in the direction of inflow of the molten resin. An injection mold characterized by having grooves for bypassing molten resin.