JPH06170902A - Injection molding method - Google Patents

Abstract

PURPOSE:To prevent a warp which is caused by orientation, by a method wherein resin is pushed back to a gate side by a compression action and the orientation generated in a filling process is allowed to disappear extending over the whole of a molding cavity. CONSTITUTION:Resin is filled into a molding cavity C of molds 4, 5 from a nozzle 1a through a gate 5a by moving a screw 2 forward. Directly after a changeover to a dwell process from a filling process, pressure of the screw 2 is reduced by a pressure valve 9 and the resin is compressed by a rod 11a by actuaing a compression mechanism 11 to operate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method for molding a molded product by injecting a molten resin into a mold.

[0002]

2. Description of the Related Art As an injection molding method, as shown in FIGS. 4 to 6, a screw 2 inserted in a heating cylinder 1 is moved forward by a hydraulic cylinder 3 to mold resin 4 at a predetermined filling pressure.
After injection into the molding cavity C of No. 5 through the nozzle 1a and the gate 5a and switching the filling process to the pressure holding process to a predetermined holding pressure, the pressure of the screw 2 is immediately lowered to lower the holding pressure, There is known an injection molding method in which the pressure of the screw 2 is increased again after a lapse of a predetermined time so that a predetermined holding pressure is applied to form a molded product. Reference numeral 6 is a control device, which controls the electromagnetic switching valve 7, the electromagnetic proportional flow valve 8, and the electromagnetic proportional pressure valve 9.

[0003]

In the above conventional injection molding method, the orientation (see (A) in FIG. 6) generated along the flow during the filling of the resin completes the filling step (see the same figure). (See (B)) When the pressure of the screw 2 is lowered in the pressure holding step, the orientation of the resin in the gate 5a portion, which is stronger than other portions in the filling step, is lost ((C) in FIG. 6). . However, in the portion far from the gate 5a, the viscosity of the resin rises due to the temperature decrease, and the pressure does not escape completely, so that the orientation is not lost (see (D)), and thus warpage is likely to occur in the molded product.

An object of the present invention is to provide an injection molding method capable of preventing warping by eliminating the orientation of the entire molding cavity.

[0005]

To achieve the above object, the present invention provides a filling step of injecting molten resin from a nozzle into a molding cavity of a mold through a gate by forward movement of a screw inserted in a heating cylinder. In the injection molding method of molding a molded product through a pressure-holding process for maintaining the resin in the molding cavity at a predetermined pressure, the pressure of the screw is reduced immediately after the pressure-holding process is entered from the filling process, and the mold is pressed. The resin inside the molding cavity is pressurized by the compression mechanism attached to the above, and then the pressure of the resin inside the molding cavity by the above compression mechanism is stopped and the pressure of the screw is increased again to a predetermined holding pressure.

[0006]

The pressure of the screw is reduced immediately after the pressure-holding step is entered from the filling step, and the resin in the molding cavity is pressurized by the compression mechanism provided in the die. By this operation, the resin in the molding cavity is pushed back to the gate side, but at this time, the orientation generated during the injection of the resin disappears. Immediately after the orientation disappears, the pressure applied by the compression mechanism is stopped and the pressure of the screw is raised again to a predetermined holding pressure.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows an injection molding machine for carrying out the injection molding method of the present invention. The same members as those of the injection molding machine of FIG. 4 are designated by the same reference numerals, and detailed description thereof will be omitted.

Reference numeral 11 is a compression mechanism provided on the fixed mold 5. The compression mechanism 11 is composed of a hydraulic cylinder, and is configured such that the resin in the molding cavity C can be pressurized by the rod (core) 11a at a position away from the gate 5a. The compression mechanism 11 can also be provided in the movable mold 4. Further, the compression mechanism 11 can be configured by a pneumatic cylinder or other actuator.

The hydraulic circuit of the compression mechanism 11 includes an electromagnetic switching valve 12, an electromagnetic proportional flow valve 13, and an electromagnetic proportional pressure valve 1.
4 are provided. The electromagnetic switching valve 12, the electromagnetic proportional flow valve 13, and the electromagnetic proportional pressure valve 14 also have the same control device 6 as the electromagnetic switching valve 7, the electromagnetic proportional flow valve 8, and the electromagnetic proportional pressure valve 9 described above. Controlled by.

Next, the injection molding method of the present invention using the above-mentioned injection molding machine will be described mainly with reference to FIG. The injection of the molten resin into the molding cavity C is performed by energizing the solenoid b of the electromagnetic switching valve 7 according to a command from the control device 6 as is well known. That is, when the solenoid b of the electromagnetic switching valve 7 is excited, the screw 2 advances and injects the resin in the heating cylinder 1 into the molding cavity C from the nozzle 1a through the gate 5a. The moving speed and pressure of the screw 2 at this time are determined by the control of the electromagnetic proportional flow valve 8 and the electromagnetic proportional pressure valve 9 by the control device 6. It is the same as in the prior art that orientation occurs along the flow during injection of resin (see FIGS. 3A and 3B).

When the above filling process is completed, the pressure maintaining process is switched to, and the control device 6 controls the electromagnetic proportional pressure valve 9 to provide a predetermined pressure maintaining pressure. When the predetermined holding pressure is reached in this manner, the pressure of the screw 2 is immediately reduced by the control of the electromagnetic proportional pressure valve 9 by the control device 6, and the solenoid a of the electromagnetic switching valve 12 is excited to cause each compression mechanism. 11 works to push the resin in the molding cavity C to the rod 1
Pressurize with 1a. The moving speed and pressure of the rod 11a at this time are determined by the control of the electromagnetic proportional flow valve 13 and the electromagnetic proportional pressure valve 14 by the control device 6.

The resin is pushed back toward the depressurized gate 5a by the pressurizing operation of each compression mechanism 11. With a slight movement at this time, the orientation of the resin completely disappears throughout the molding cavity C (see FIG. 3C). After a lapse of a predetermined time, the control device 6 causes the solenoid a of the electromagnetic switching valve 12 to operate.
Demagnetize to stop the compression operation of the compression mechanism 11,
The electromagnetic proportional pressure valve 9 raises the pressure of the screw 2 again to a predetermined holding pressure. Since the rod 11a of the compression mechanism 11 is returned to the original state by the pressure increase by the screw 2, the pressure mark by the rod 11a disappears. After the pressure-holding process is completed,
Although the molded product is taken out from each of the molds 4 and 5, warping does not occur because the orientation disappears as shown in FIG.

The above-mentioned compression mechanism 11 has a structure in which the resin is partially compressed by the rod 11a (micromolding method), but the structure is not limited to this, and the resin is filled without completely clamping the mold. After that, the sandwich method is used to perform mold clamping, and the first mold clamping force is made relatively weak, and after the resin is filled, the injection pressure of the resin is used to further pressurize and compress the expanded portion of the molding cavity. It is possible to pressurize the resin in the pressure-holding step by using a compression mechanism (Japanese Patent Laid-Open No. 1-174428) that carries out the full compression method.

[0014]

As described above, the injection molding method of the present invention comprises the filling step of injecting the molten resin from the nozzle into the molding cavity of the mold through the gate by the forward movement of the screw inserted in the heating cylinder, and the molding step. In the injection molding method of molding a molded product through a pressure-holding process that keeps the resin in the cavity at a predetermined pressure, the screw pressure is reduced immediately after entering the pressure-holding process from the filling process, and it is attached to the mold. Since it is configured to press the resin in the molding cavity by the compression mechanism and then stop the pressure of the resin in the molding cavity by the compression mechanism and increase the screw pressure again to a predetermined holding pressure, The orientation of the resin generated in the filling step can be eliminated by pushing the resin back to the gate side by the compression mechanism in the pressure holding step. Therefore, it is possible to prevent warpage due to orientation.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of an injection molding machine for carrying out the present invention.

FIG. 2 is a pressure control diagram of a filling step and a pressure holding step in the present invention.

FIG. 3 is a cross-sectional view showing various phases of the resin from the start of injection to reholding pressure in the injection molding method of the present invention.

FIG. 4 is a schematic sectional view of an injection molding machine that performs a conventional injection molding method.

FIG. 5 is a pressure control diagram of a filling step and a pressure holding step in a conventional injection molding method.

FIG. 6 is a cross-sectional view showing various phases of resin from injection start to reholding pressure in a conventional injection molding method.

[Explanation of symbols]

 1 Heating Cylinder 1a Nozzle 2 Screw 4,5 Mold 5a Gate 11 Compression Mechanism 11a Rod C Mold Cavity

Claims (1)

[Claims] 1. A filling step of injecting molten resin from a nozzle into a molding cavity of a mold through a gate by forward movement of a screw inserted in a heating cylinder, and a pressure holding step of maintaining the resin in the molding cavity at a predetermined pressure. In the injection molding method of molding a molded article through the, the pressure of the screw is reduced immediately after entering the pressure-holding step from the filling step, and the resin in the molding cavity is pressurized by the compression mechanism attached to the mold, and then An injection molding method, characterized in that the pressure of the resin in the molding cavity by the compression mechanism is stopped and the pressure of the screw is increased again to a predetermined holding pressure.