JPH09323340A - Apparatus and method for injection molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to eliminate the molding fault such as a surface distortion due to the difference of shrinkage percentages without locally generating a low density area in a cavity. SOLUTION: A hydraulic cylinder 30 is driven to move a movable mold 14 downward, and mated to a stationary mold 12 to form a cavity 18. A molten resin (m) is injected from an injection molding machine 28 in the cavity 18. At the stage of the midway of plasticizing resin M, a hydraulic cylinder 36 is driven, a slide core 40 is moved to the cavity surface side in plane with the cavity surface, and pressure is applied to the resin M. Thus, since the pressure except the mold clamping pressure is forcibly applied to the resin on the way of plasticizing in the cavity 18, a low density area is eliminated, and molding fault such as surface distortion can be obviated.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an injection molding apparatus and an injection molding method.

[0002]

2. Description of the Related Art Injection molding is one of the methods for processing products such as thermoplastic resins.

In this injection molding, a resin is heated and melted in a cylinder, and then the molten resin is pressure-filled into a cavity of a mold matched with each other, and after curing, the mold is opened to form a molded product. It is something to take out.

By the way, the front bumper 5 shown in FIG.
When a product having a complicated shape is manufactured by injection molding as in No. 4, a low density (low pressure) region is locally generated, so that molding defects such as surface distortion may occur.

More specifically, when the molten resin flows in the cavity (the arrow indicates the resin flow),
The opening 86 and the thin wall portion become resistance, and the portion (for example, portion B) away from the spool (the resin injection port A) provided in the mold has a low density. For this reason, a contraction difference occurs with other parts, and surface distortion occurs.

In order to solve such a problem, as in the two-stage mold clamping molding method shown in FIG. 7, the mold clamping by the movable mold 90 and the fixed mold 92 is temporarily stopped in the middle, and the resin M is removed. There is also a method of performing final tightening after injecting into the cavity 94, or a method of filling gas together with the resin to eliminate generation of a low density region.

However, in order to use the two-stage clamping method or the gas-assisted molding method, it is necessary to drastically change the equipment.

[0008]

SUMMARY OF THE INVENTION In consideration of the above facts, the present invention has an object to eliminate a defective molding such as surface distortion by preventing local occurrence of a low density region.

[0009]

According to a first aspect of the present invention, in the fixed mold, there is provided a movable core for density adjustment which moves in and out of a part of a cavity formed by the fixed mold and the movable mold. It is provided.

The movable core is pressurized and filled with molten raw material through the gate and then pushed into the cavity, whereby a pressure other than the mold pressure is forcibly applied to the raw material in the cavity during plasticization. The low density region is eliminated, and molding defects such as surface distortion can be eliminated.

According to the second aspect of the invention, the moving core comprises:
It is located farthest from the gate. Therefore, generally, it is possible to apply pressure to a portion away from the gate where the low density region is likely to be locally generated. by this,
It is possible to prevent the occurrence of surface strain without causing a difference in shrinkage.

According to the third aspect of the invention, first, the fixed mold and the movable mold are fitted to each other to form a cavity,
The melted raw material is pressure-filled into the cavity through a gate. Next, the moving core provided at the farthest position from the gate is extruded into the cavity to apply pressure to the raw material in the process of plasticizing. This eliminates localized low density areas within the cavity.

Next, after the raw material is cured, the mold is opened and a molded product free from molding defects such as surface distortion is taken out.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION As shown in FIG. 1, an injection molding apparatus 10 according to this embodiment includes a fixed mold 12 and a movable mold 14.

The fixed mold 12 is engraved with the shape of the outer surface of a box-shaped molded product 16 (see FIG. 3).
The shape of the inner surface of the molded product 16 is engraved on this. The fixed mold 12 and the movable mold 14 are matched with each other to form a cavity 18 forming a molded product 16.

In the center of the cavity surface of the fixed mold 12,
A direct gate 20 communicating with the runner 22 is provided and serves as an inlet for the molten resin into the cavity 18. By providing such a direct gate 20, the number of sink marks on the surface of the molded product 16 is reduced, and
After molding, the gate becomes less noticeable in appearance.

The end of the runner 22 is connected to a sprue 24 which is recessed in an arc shape. This sprue 24
A nozzle 26 of an injection molding machine 28 is joined to the mold, and the molten resin M is injected into the cavity 18 through the runner 22 and the direct gate 20.

On the other hand, the movable mold 14 is the hydraulic cylinder 3
The mold clamping pressure is adjusted by a controller 32 that controls the hydraulic cylinder 30.

A part of the cavity surface of the movable mold 14 is hollowed out to accommodate a hydraulic cylinder 36.
It has been. A slide core 40, which is flush with the cavity surface of the movable mold 14, is attached to the rod 38 of the hydraulic cylinder 36, and can slide backward from the cavity surface while sliding on the wall surface of the storage portion 34.

Further, the hydraulic cylinder 36 is provided with an oil supply pipe 44.
Also, the oil discharge pipe 46 is connected to the hydraulic pump 42.
The oil supply pipe 44 and the oil discharge pipe 46 are respectively connected to the oil supply valve 4
8 and an oil drain pipe 50 are provided, and the hydraulic pump 42 is driven to open and close the oil supply valve 48 and the oil drain pipe 50 to cause the slide core 40 to move out.

Further, the hydraulic pump 42 is the controller 3
Connected to 2. A signal of resin injection completion is sent from the injection molding machine 28 to the controller 32, the timer 52 is activated by this signal, and the slide core 40 is operated after a predetermined time (until the middle of plasticizing the resin) has elapsed. Is moved to the cavity surface side to be flush with the cavity surface, and pressure is applied to the resin M in the cavity 18.

Although illustration is omitted, when the mold is completely closed and the molten resin M is injected into the cavity 18, a groove-shaped air vent that allows the air in the cavity 18 to escape to the outside is provided in the fixed mold. It is formed on a dividing surface between the movable mold 12 and the movable mold 14.

Next, the operation of the injection molding apparatus according to this embodiment will be described. As shown in FIG. 1, the hydraulic cylinder 30 is driven to move the movable mold 14 downward to move the fixed mold 12
And the cavity 18 is formed. At this time,
The slide core 40 is retracted from the cavity surface to the storage section 34 side.

Next, the molten resin M is injected from the injection molding machine 28 into the cavity 18. As a result, the air in the cavity 18 is expelled from the air vent, and the molten resin M is filled in the cavity 18 and part of the storage portion 34.

When the injection of the resin is completed, the controller 32 activates the timer 52 as shown in FIG. Here, after a lapse of a predetermined time, that is, at a stage during the plasticization of the resin, the hydraulic cylinder 36 is driven to move the slide core 40 to the cavity surface side so as to be flush with the cavity surface and apply pressure to the resin M. .

Next, when the resin M is cured, as shown in FIG. 3, the hydraulic cylinder 30 is driven to open the mold, the molded product 16 is taken out from the mold, and the sprue part S is cut out as a post-treatment. . Then, finally, the slide core 40 retracts from the cavity surface of the movable mold 14.

As described above, since the pressure other than the mold clamping pressure is forcibly applied to the resin in the cavity 18 which is in the process of being plasticized, the low density region is eliminated, and molding defects such as surface distortion can be eliminated.

Next, as shown in FIGS. 4 and 5, the front bumper 54 (see FIG. 6) is used in the injection molding apparatus according to another embodiment.
An example of molding (see) will be described.

A cavity surface corresponding to the shape of the front bumper 54 is formed on the movable mold 56 and the fixed mold 58. In addition, in this injection molding device 60, a gate 62 is provided on the outer peripheral edge of the divided surface, and the molten resin M is injected from the injection molding machine 28 through the runner 64 into the cavity 6.
It is injected into 6.

A part of the cavity surface (the portion forming the peripheral portion of the opening 86 of the front bumper 54) away from the gate 62 is hollowed out to form slide holes 72 and 74 for slidably storing the slide cores 68 and 70. ing. In addition, the slide holes 72 and 74 are provided in the movable mold 5.
6 is in communication with a housing portion 76, and the housing portion 76 is provided with hydraulic cylinders 78, 80. The slide cores 68, 70 are fixed to the rods 82, 84 of the hydraulic cylinders 78, 80.

Next, the operation of the injection molding apparatus 60 according to this embodiment will be described. The basic movement is omitted because it is the same as that of the injection molding apparatus 10 described above, but in the present embodiment, the slide cores 68 and 70 are separated from the gate 62 and the opening 8 is formed.
It is characterized in that it is arranged at the peripheral portion of 6 and a portion which becomes a thin portion.

Thus, by determining the position of the slide core in consideration of the shape of the molded product, a low density (low pressure) region may locally occur due to the difference in shape. Therefore, it is possible to prevent the occurrence of molding defects such as surface distortion.

[0033]

EFFECTS OF THE INVENTION Since the present invention has the above-mentioned structure, a low density region is not locally generated in the cavity, and molding defects such as surface strain due to the difference in shrinkage can be eliminated.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a state in which a mold of an injection molding device according to the present embodiment is matched.

FIG. 2 is a cross-sectional view showing a state where pressure is applied by the slide core of the injection molding device according to the present embodiment.

FIG. 3 is a cross-sectional view showing a state in which a molded product is taken out from the mold of the injection molding device according to the present embodiment.

FIG. 4 is a cross-sectional view showing a state in which a mold of an injection molding device according to another embodiment is matched.

FIG. 5 is a cross-sectional view showing a state where pressure is applied by a slide core of an injection molding device according to another embodiment.

FIG. 6 is a perspective view of a front bumper as a molded product.

FIG. 7 is a process drawing showing a two-stage mold clamping method.

[Explanation of reference numerals] 12 fixed mold 14 movable mold 40 slide core (moving core) 56 movable mold 58 fixed mold 68 slide core (moving core) 70 slide core (moving core)

Claims (3)

[Claims] 1. An injection molding apparatus for press-filling a molten material through a gate into a cavity formed by a fixed mold and a movable mold to mold the fixed mold, wherein a part of the cavity is formed in the fixed mold. An injection molding apparatus, which is provided with a moving core that moves in and out of. 2. The injection molding apparatus according to claim 1, wherein the moving core is provided at a position apart from the gate. 3. A step of forming a cavity with a fixed die and a movable die and pressurizing and filling a molten material into the cavity through a gate, and a moving core provided at a position away from the gate. Extruding into the cavity, applying pressure to the raw material in the process of plasticizing, and after the raw material is cured,
An injection molding method comprising the steps of opening the mold and taking out a molded product.