JPH0675893B2 - Injection mold - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an injection mold for producing an injection molded product having a boss.

<Prior Art> When manufacturing an injection-molded product having this kind of boss, a problem is a sink mark or a weld line generated around the boss of the injection-molded product. Both the sink mark and the weld line are the same in that the appearance of the injection molded product is impaired, but the weld line is also problematic in terms of strength. The cause of the brush around the boss is that the meat pressure in this part is larger than that in the surroundings, and the molten plastic in this part cools slower than the surrounding part.In other words, the surrounding part solidifies and shrinks. However, it gradually solidifies. 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 for preventing the brush A, a method of adjusting the wall pressure on the base side of the boss b as shown in FIG. 4 is provided by providing a convex portion around the core pin of the mold.

<Problems to be Solved by the Invention> However, in the above-mentioned conventional method, since the cooling of the molten plastic can be made uniform, the occurrence of the brush A can be prevented, but as shown in FIG. There is a drawback that a line-shaped weld line B is generated on the surface. The cause of the weld line B is
Molten plastic diverges at the boss b and flows (5th
This is because the arrows in the figure show the flow of molten plastic), and the welding of branched molten plastic is insufficient. Although various measures have been reported to prevent the weld line B, there is a drawback that the brush A is generated. That is, the current situation is that the brush A and the weld line B, which are caused by different causes, cannot be prevented at the same time, and one of them must be prioritized.

The present invention has been devised in view of the above circumstances, and an object thereof is to provide an injection molding die that can prevent both a brush and a weld line.

<Means for Solving the Problems> An injection molding die according to the present invention comprises a core and a cavity, and the core is provided with a core pin for molding a boss which is a part of an injection molded product. There is provided a convex portion for sink mark prevention on the cavity facing surface of the core corresponding to the root side outer edge portion of the boss, while the tip end portion of the core pin and the root side outer edge portion of the boss are provided. Grooves for bypassing the molten resin are provided in the cavity facing surface of the core in the inflow direction of the molten resin.

<Operation> In the state where the core and the cavity are closed, the molten resin is poured. The molten resin in the pouring process may be bypassed by the core pin, but most of it flows through the core pin and the groove provided in the core. Since this groove is in the direction along the flow of the molten resin, the disturbance of the flow of the molten resin around the core pin is eliminated to some extent, and the occurrence of weld lines is prevented. On the other hand, since the protrusion is provided around the core pin, the wall pressure on the base side of the boss is adjusted, and the occurrence of brushing is prevented through uniform cooling of the molten resin.

<Example> Hereinafter, an example of an injection mold according to the present invention will be described with reference to the drawings. FIG. 1 is a simplified cross-sectional view of an injection molding die, and FIG. 2 is a simplified perspective view of portion C shown in FIG.

The injection molding die shown in FIG. 1 is roughly divided into a core 10 and a cavity 20, both of which are connected to an injection molding machine (not shown), and 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, and molten plastic is injected into the recess 30 from the injection molding machine side through a sprue 21 provided at a predetermined position of the cavity 20. It is poured, and the plastic molded product a is made by this. This plastic molded product a has a boss b, and the boss b
Is molded by a core pin 11 fixed to a predetermined portion of the core 10.

Next, regarding the mold structure around the tip of the core pin 11,
It will be described with reference to the drawings. On the surface of the core 11 facing the recess 30 is provided an outer ring mountain-shaped protrusion 12. This convex portion 12 forms a groove on the outer edge of the boss b on the root side. A groove 111 having a U-shaped cross section is provided on the tip end surface of the core pin 11, while a similar groove 121 is provided on a part of the convex portion 12. By the way, the flow direction of the molten plastic in the process of being poured into the recess 30 is determined by the positional relationship of the sprue 21 and the like, but the groove directions of the grooves 111 and 121 are set along the flow of the molten plastic.

When an injection molding die having the above-described basic structure is used, no sink mark or weld line is generated around the boss b of the plastic molded product a. This principle will be described below.

Molten plastic is poured into the recess 30 with the core 10 and the cavity 20 closed. 30 recesses in molten plastic
Some of them are bypassed by the core pin 30 in the process of reaching the inner space of the
Through the grooves 111 and 121 respectively provided in the. Moreover, this groove 11
Since 1 and 121 are cut in the direction along the flow of the molten plastic, the disturbance of the molten plastic around the core pin 30 is eliminated to some extent, and the occurrence of weld lines is prevented here.

Further, in the process in which the poured molten plastic is solidified around the core pin 30, since the convex portion 12 is provided on the core 10 and the meat pressure on the base side of the boss b is adjusted, the melting around the boss b is adjusted. The plastic is cooled uniformly, and the occurrence of brushing is prevented.

Therefore, both the sink mark and the weld line are not generated in the plastic molded product a, the appearance of the plastic molded product a is not deteriorated, and there is no problem in terms of strength, and product defects can be reduced. Furthermore, since the above merit can be obtained by a slight design change, it is possible to provide an inexpensive and high-performance injection mold.

The injection-molding die according to the present invention is not limited to the above-mentioned embodiment, and can be applied to any kind of injection-molding die as long as it has a core pin.

<Effects of the Invention> As described above, in the case of the injection molding die according to the present invention,
Since the disturbance of the flow of the molten resin around the core pin is eliminated to some extent and the cooling of the molten resin is made uniform, the occurrence of both weld lines and brushes can be suppressed. Therefore, there are advantages in terms of appearance and strength of the injection-molded product, which is of great significance in reducing product defects.

[Brief description of drawings]

FIGS. 1 and 2 are views for explaining an embodiment of an injection molding die according to the present invention. FIG. 1 is a simplified sectional view of the injection molding die, and FIG. FIG. 3 is a simplified perspective view of a C portion shown in FIG. 1. 3 and 4 are cross-sectional views of the plastic molded product around the boss, and FIG. 3 is a diagram showing the appearance of a brush generated on the product surface of the plastic molded product.
FIG. 5 is a diagram showing a state in which the occurrence of brushing is suppressed by a conventional injection molding die, and FIG. 5 is a diagram showing a state of a weld line generated on the product surface of a plastic molded product. 10 …… Core 11 …… Core pin 111 …… Groove 12 …… Convex portion 121 …… Groove 20 …… Cavity a …… Plastic molding b …… Boss

Claims (1)

[Claims] 1. An injection molding die comprising a core and a cavity, the core including a core pin for molding a boss which is a part of an injection-molded product, wherein the core corresponds to an outer edge of the boss. The core facing surface of the cavity is provided with a convex portion for sink mark prevention, while the tip of the core pin is
An injection mold, wherein grooves for molten resin bypass are provided in the cavity facing surface of the core corresponding to the outer edge of the boss on the root side, respectively, in the direction of inflow of molten resin.