JPH0732433A - Molded product possessing boss part, its manufacture and mold device to be used for that - Google Patents

Abstract

PURPOSE:To obtain a molded product which prevents generation of a weld, is free from a sink and has excellent capacity, by a method wherein a synthetic resin is cast into a mold and a boss part is formed while separating a boss mold part from the mold by molten resin pressure. CONSTITUTION:A boss mold part 3 forming a boss part is made contactable and separatable freely to and from a cavity 1 forming a base. Then at the time of uninflow of molten resin, a mold device which is being energized so as to join to the cavity 1 is used. The mold device is constituted so that melting resin is melted and cast into the mold device and the boss part is formed while separating the boss mold part 3 by molten resin pressure. Thus it is preferable that the boss part mold part 3 is constituted so as to be energized by a spring 5. As for flow movement, when a molded product base is filled with the resin. the boss mold part 3 is moved at a point of time when resin pressure becomes at least force of the spring 5 and simultaneously with formation of the cavity corresponding to the boss part, the resin is cast into the cavity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molded product having a boss portion, a method for manufacturing the molded product, and a mold device used for the molded product.

[0002]

2. Description of the Related Art Resin molding technology is characterized in that it is possible to produce a product having a complicated shape having irregularities in a short cycle by injecting a resin into a cavity of a mold. Injection molding, in which a resin is injected into a cavity at a relatively high pressure, has a wide range of applications. Taking advantage of the above characteristics, the resin product is often provided with a projection-like thickened portion around the periphery for reinforcement of inserts, screws, holes, notches, etc.,
These are collectively called the boss. The size of this boss is generally 1/2 to 2/3 of the hole diameter, and within 2/3 of the wall thickness of the molded product to prevent sink marks on the surface, and the height is 3 times the wall thickness of the molded product. Within is appropriate. Since this boss shape is engraved in the mold in advance, there are the following problems.

This boss is one of the weakest parts in the molded product, and there have been problems such as cracks due to self-tapping and cracks due to insert parts. This is not simply a problem of stress concentration, but is essentially due to the reduction in strength due to welds. FIG. 6 is a schematic diagram showing a situation of generation of a weld line in the boss portion. The arrow indicates the flow direction of the resin. It can be seen that what is equivalent to a weld line appears on the downstream side of the resin flow.
The appearance of this weld varies depending on the size of the boss,
In the injection molding in which the resin is filled from the upstream side of the resin flow, it is essentially unavoidable that a weld is generated in the hole. This weld causes a decrease in the strength of the boss portion, making it difficult to quantitatively grasp and predict, which has been a major obstacle to product design. Usually, a weld is a point where two or more flows merge, but a weld at the boss portion may not be a weld in a strict sense. However, that rather made it difficult to predict the occurrence of welds in the boss portion. FIG. 5 is a view of the state in the middle of flow viewed from the direction perpendicular to the flow direction of the resin, and the arrow indicates the flow direction of the resin. Thus, there is a time difference in the amount of resin injected into the boss portion at the upstream side and the downstream side at the boss portion, which is a factor that causes welds.

Further, in order to compensate for the decrease in strength of the boss portion,
It is possible to increase the wall thickness of the boss, but if the wall thickness is 2/3 or more of the thickness of the part that will be the substrate, the sink mark will appear significantly in the product appearance. There is a limit to the design of the boss that satisfies both the sink mark and the strength in the ordinary injection molding. Furthermore, since the weld appears strongly when the thickness of the boss is increased, the strength is not simply improved. The present invention has been made to solve the above problems, and its purpose is to overcome the reduction in the strength of the boss due to welds, and thus has a structure in which no welds occur and suppresses the occurrence of sink marks. It is to provide a molded product having a boss that can be manufactured and a manufacturing method thereof.

[0005]

The gist of the present invention is to provide an invention of a molded article having a weld line and a boss portion which does not have a sink mark in the boss portion due to the flow of resin during molding.
A boss mold part 3 forming a boss part is configured to be able to come into contact with and separate from a cavity 1 forming a substrate, and is urged so as to be bonded to the cavity 1 when a molten resin does not flow in. A method for manufacturing a molded article having a boss portion, characterized in that a synthetic resin is melt-injected into the die device using the above, and the boss portion is formed while gradually separating the boss die portion 3 by the molten resin pressure. Of the present invention and the boss die portion 3 forming the boss portion is configured to be capable of coming into contact with and separating from the cavity 1 forming the substrate, and is urged so as to be joined to the cavity (1) when no molten resin flows in. The present invention is a die apparatus.

[0006]

EXAMPLES Hereinafter, description will be given based on examples embodying the present invention. FIG. 1 is a schematic cross-sectional view showing the structure of an injection molding die of the present invention, which is in a state before injection. The boss die 3 corresponding to the tip of the boss is movable, and is adjusted by the stopper 4 so as to be on the same line as the surface 2 of the cavity 1 of the molded product substrate. A force is applied to the boss die 3 in the direction of the cavity by the spring 5, and the cavity as the boss does not exist in the state before the injection molding. When the resin is injected in this state, the state shown in FIG. 2 is obtained and the boss 6 is formed. This is because the cavity of the boss portion appears due to the movement of the boss die portion 3 due to the resin pressure, and at the same time, the resin is injected. The height of the boss is adjusted by the stopper 7. The dimensions of the boss used in the examples are the thickness of the molded product substrate 3 mm, the boss hole diameter φ2.8 mm or φ.
The diameter was 3.4 mm, the boss outer diameter was 8 mm, and the boss height was 10 mm. The resin used is FC-30 manufactured by Mitsubishi Rayon Co., Ltd., which is an alloy of PC / ABS.

In the manufacturing method of the present invention, the resin flow behavior does not become as shown in FIG. 5, and after the molded product substrate is filled with resin, when the resin pressure exceeds the force of the spring 5,
The boss mold part 3 moves to form a cavity corresponding to the boss part, and at the same time, resin is injected into the cavity. The spring 5 is 10 kgf to 800 kgf when compressed.
I used the one that can bring out the power of. In order to measure the strength of the boss, the load at which cracks occur was measured using the compression device shown in FIG. The results are shown in Table 1. The values in the table are averages of 3 points. As can be seen from the table, the strength of the boss is improved.
Furthermore, even with a load of 200 kgf or more, since the boss hole was only expanded and no crack was generated, it can be seen that the boss is isotropically formed without forming a weld.
This means that the decrease in the strength of the boss portion due to the weld could be basically solved.

[0008]

[Table 1]

Further, the conventional molding method has a problem that sink marks occur at the portion 8 in FIG. 4, but according to the present invention, the pressure is constantly applied by the spring 5 during the cooling period after filling. , The sink 8 can be eliminated. φ
In the case of a 2.8 mm boss, the maximum value of the sink mark is 198 μm by the conventional method, whereas the maximum value of the sink mark is 12.5 μm by the method of forming the boss according to the present invention.

In this embodiment, the spring 5 is used as the force for driving the die part 3, but the same effect can be obtained by a hydraulic mechanism or the like.

[0011]

As described above, the molded article having the boss portion according to the present invention has excellent performance with no weld and no sink mark.

[0012]

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing a state of an injection molding die before inflow of resin in the present invention.

FIG. 2 is a sectional view schematically showing a resin-filled state of an injection molding die in the present invention.

FIG. 3 is a schematic diagram of a method for measuring the boss strength of a molded product using an injection molding die in the present invention.

FIG. 4 is a sectional view schematically showing a resin-filled state of a boss portion by a conventional method.

FIG. 5 is a cross-sectional view schematically showing a state where a boss portion is in the course of resin flow by a conventional method.

FIG. 6 is a schematic diagram showing a weld occurrence state in a conventional method.

[Explanation of symbols]

 1 Molded Product Cavity 2 Molded Product Cavity Surface 3 Boss Mold Section 4 Stopper 5 Spring 6 Boss 7 Stopper 8 Sink 9 Weld Line

Claims (4)

[Claims] 1. A molded article having a boss portion in which the boss portion does not have a weld line or a sink along with the flow of resin during molding. 2. A boss die portion 3 forming a boss portion is configured so as to be able to come into contact with and separate from a cavity 1 forming a substrate, and is biased so as to be joined to the cavity 1 when a molten resin does not flow in. A boss portion is characterized in that a synthetic resin is melt-injected into the die device using the existing die device and the boss portion is formed while gradually separating the boss die portion 3 by the molten resin pressure. Molded article manufacturing method. 3. The manufacturing method according to claim 2, wherein the boss die part 3 is biased by a spring. 4. A boss die portion 3 forming a boss portion is configured so as to be able to come into contact with and separate from a cavity 1 forming a substrate, and is biased so as to be joined to the cavity 1 when a molten resin does not flow in. Mold equipment.