JP3036326B2 - Hollow injection molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a hollow portion inside a rib which is a part of a resin molded product by introducing a gas into a resin material in a cavity during injection molding of the resin molded product. And a hollow injection molding method.

[0002]

2. Description of the Related Art A technique of molding a bumper fascia of an automobile bumper by a hollow injection molding method is disclosed in Japanese Patent Laid-Open No. 4-7 / 1990.
No. 8511. FIGS. 2 and 3 show an example of this. Injection (not shown) through a sprue 4, a runner 5 and a gate 6 is applied to a cavity 3 formed by a core block (movable mold) 1 and a cavity block (fixed mold) 2. While injecting the resin material from the nozzle, a predetermined timing, for example, an inert gas typified by nitrogen gas in the resin material in the cavity 3 from the gas nozzle 7 previously facing the cavity 3 immediately after the injection of the resin material is completed. Is introduced.

[0003] A plurality of ribs 9, 1 protruding from the general surface are provided on the back surface of the bumper fascia 8, which is a molded product.
0, 11 and a local thick portion 12 at the center of the base of the central rib 10 are integrally formed.
Since the gas nozzle 7 is exposed to the gas nozzle 2, the inert gas introduced into the cavity 3 is a part having a small flow resistance among the parts to be formed into a molded product from the gas inlet 13, that is, relatively cooled and solidified. Flows from the thick portion 12, which tends to be late, through the inside of the root portion 14 of the rib 10 and spreads in the longitudinal direction, and the gas assists the flow of the resin material by applying an internal pressure to the resin material, and at the same time, it causes “sink” or the like. The occurrence of molding failure is prevented, and the gas passage remains as the hollow portion 15 at the root portion 14 of the rib 10 as it is, thereby exhibiting a reinforcing effect.

[0004]

In the conventional molding method as described above, the inert gas flows to the longitudinal end of the rib 10 and the hollow portion 15 is formed over the entire length of the rib 10. Ideally, the flow distance of the inert gas depends on the rib 10 in addition to the gas pressure and the gas introduction time.
Greatly depends on the size of the cross-sectional area of the base portion 14 of the base member. That is, as shown in FIG. 4, the inert gas introduced from the thick portion 12 gradually decreases in cross-sectional area of the passage as it goes away from the thick portion 12, and the viscosity of the resin material and the gas pressure are balanced. At this point, the flow of the gas stops, and the position P becomes the end of the gas passage and thus the hollow portion 15.

Accordingly, in order to extend the flow distance of the inert gas and form the hollow portion 15 up to the end of the rib 10, it is effective to further increase the thickness of the root portion 14 of the rib 10 and increase its cross-sectional area. However, increasing the thickness of the rib 10 directly leads to an increase in the weight of the molded product, and still has a problem in practicality.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and is intended to increase the activity of a gas and increase the flow distance of the gas without increasing the thickness of the entire rib. It is an object of the present invention to provide an improved molding method.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a resin material is injected into a cavity of an injection mold to form a molded article having a rib protruding from a general surface. A hollow injection molding method in which a gas is introduced into the resin material in a solidified state so as to form a hollow portion along the longitudinal direction inside the rib, wherein the gas is introduced into the rib. An intermediate thick portion thicker locally than the rib is locally formed at an intermediate position of a section from the position to the end of the rib.

[0008]

According to this molding method, the gas introduced into the portion of the molded product that is to become a rib flows and spreads along the longitudinal direction of the rib, but when the gas reaches the intermediate thick portion. Since the cross-sectional area of the intermediate thick portion is larger than the cross-sectional area of the rib, the gas flowing through the rib is temporarily stored inside the large-thickness intermediate thick portion. Then, when the gas capacity inside the intermediate thick portion reaches the limit, the gas flows out to the rib side again.

Therefore, by the gas damper or the accumulating rate function at the intermediate thick portion, the gas flow distance is greatly extended as compared with the case without the intermediate thick portion,
A hollow portion can be formed up to the end of the rib.

[0010]

FIG. 1 is a view showing one embodiment of the present invention. The point that a bumper fascia 8 itself, which is a molded product, is molded by an injection mold shown in FIG. A thick portion 12 serving as a gas introduction position is formed at a root portion 14 at a central portion in a longitudinal direction of the rib, and a rib 1 is formed from the thick portion 12.
This is different from the conventional one in that a pair of intermediate thick portions 16 and 17 are formed at a predetermined pitch until the end of zero.

The intermediate thick portions 16 and 17 are formed in a substantially rectangular shape by thickening the root portions 14 of the ribs 10 so as to locally protrude from the upper and lower surfaces.

The inert gas introduced from the gas nozzle 7 when molding the bumper fascia 8 using the injection mold of FIG. 2 first enters the thick portion 12 and After being stored in the rib 10, the rib 10 extends right and left along the base 14 of the rib 10 along the longitudinal direction of the rib 10.

The flow of the inert gas at the base 14 of the rib 10 gradually decreases as the distance from the thick portion 12 increases, but the inert gas enters one intermediate thick portion 16. Then, since the inside of the intermediate thick portion 16 has a lower viscosity and lower flow resistance of the inert gas than the rib 10, the inert gas is again stored inside the intermediate thick portion 16.

On the other hand, solidification of the intermediate thick portion 16 is also progressing in the surface layer, so that the intermediate thick portion 1
When the gas capacity of the intermediate thick portion 16, that is, the occupation of the inert gas by the inert gas is limited, the inert gas flows toward the other intermediate thick portion 17. It flows out to the root part 14 side.

When the inert gas reaches the other intermediate thick portion 17, the same behavior as the previous intermediate thick portion 16 is repeated in this intermediate thick portion 17, and the intermediate thick portion 17
When the occupation of the inert gas at the limit is reached, the inert gas flows from the intermediate thick portion 17 toward the end of the rib 10 again.

As described above, the intermediate thick portions 16 and 17 provided at the intermediate portion of the length from the position where the inert gas is introduced to the end of the rib 10 are provided with dampers or accumulators for temporarily storing the inert gas. Since the rate function is exhibited, the flow distance of the inert gas is greatly extended as compared with the case where the intermediate thick portions 16 and 17 are not provided.
Without increasing its thickness over its entire length.
The inert gas can be reliably flowed to the zero end.

The thick portion 12 and the intermediate thick portion 1
The hollow portion 15 is formed by the passage of the inert gas in the base portion 6, 17 and the root portion 14 of the rib 10 remaining inside the molded product 8 as it is.

In the above embodiment, a pair of intermediate thick portions 16 and 17 are formed between the thick portion 12 at the center in the longitudinal direction of the rib 10 and the end of the rib 10. The number of the thick portions 16 and 17 can be arbitrarily set according to the overall length of the bumper fascia 8 itself.

[0019]

As described above, according to the present invention, among the ribs protruding from the general surface of the molded article, the ribs are located more locally than the ribs at the intermediate position of the section from the gas introduction position to the longitudinal end of the rib. By forming the thick middle thick part integrally, the middle thick part temporarily functions as a damper or accumulator that temporarily stores gas, so if there is no middle thick part The flow distance of the inert gas is greatly extended as compared with the above, and the gas can be reliably flowed to the longitudinal end of the rib to form a hollow portion. Therefore, it is not necessary to increase the thickness of the root portion of the rib over its entire length, and the weight does not increase.

[Brief description of the drawings]

FIG. 1 is a view showing one embodiment of the present invention, in which (A) is a perspective view of a main part of a bumper fascia formed by the hollow injection molding method of the present invention, and (B) is a-a of FIG. Sectional explanatory drawing which follows the a line.

FIG. 2 is a cross-sectional explanatory view of a hollow injection mold used in a conventional hollow injection molding method.

FIG. 3 is an explanatory cross-sectional view of a bumper fascia formed by a conventional hollow injection molding method.

FIG. 4 is an explanatory sectional view taken along line bb in FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Core block 2 ... Cavity block 3 ... Cavity 7 ... Gas nozzle 8 ... Bumper fascia (molded product) 10 ... Rib 15 ... Hollow part 16, 17 ... Middle thick part

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-131484 (JP, A) JP-A-6-107209 (JP, A) JP-A-7-52183 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B29C 45/00-45/84 B60R 19/02-19/03 B60R 19/18-19/20

Claims (1)

(57) [Claims] 1. A resin material is injected into a cavity of an injection mold to form a molded article having a rib protruding from a general surface, and the resin is formed in an unsolidified state of the resin material in the cavity. A hollow injection molding method in which a gas is introduced into a material so as to form a hollow portion along the longitudinal direction inside the rib, wherein a gas is introduced from a gas introduction position to the rib to an end of the rib. A hollow injection molding method, wherein an intermediate thick portion thicker than the rib is locally formed at an intermediate position of the section.