JP3300891B2 - Control method by injection pressure of injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for an injection molding machine, and more particularly to a method for controlling a thin molded product by high-speed compression molding, in which the thickness of the molded product is made uniform and the shape of the molded product is prevented from being warped. And a control method for the purpose.

[0002]

2. Description of the Related Art In general, injection molding of a resin product is performed in a process of plasticizing resin, filling, holding pressure, and cooling.

Hereinafter, a control method of a general injection molding machine will be described with reference to FIGS. FIG. 6 shows a schematic configuration of an injection device and a mold clamping device of a hydraulic injection molding machine. In the injection device, the resin injected from the hopper 11 is melted in the heating cylinder 12, and the screw 13 is rotated while kneading and measuring, and the molten resin is stored in front of the screw 13. The stored resin was formed by a fixed mold 17 and a movable mold 18 through a nozzle 16 by moving the screw 13 forward, that is, the mold side by a mold clamping cylinder mechanism including an injection cylinder 14 and a piston 15. Filled in the cavity. The injection cylinder 14 has an inflow / outflow portion 14 according to the filling and pressure-holding processes.
Drive oil whose flow rate or pressure is controlled flows in and out through -1. In FIG. 6, a drive mechanism for rotating the screw 13 is not shown.

On the other hand, the mold clamping device is fixed to a frame (not shown), and a rear platen 22 has four tie bars 23 (2 in the figure) with respect to a fixed platen 21 having a fixed mold 17.
(Only the book is shown). A hydraulic piston 25 is disposed in a mold clamping cylinder 24 fixed to the rear platen 22, and a movable platen 26 to which the movable mold 18 is fixed is connected to the hydraulic piston 25.
The movable platen 26 is configured to be slidable on the tie bar 23 with the movement of the hydraulic piston 25. That is, the movable platen 26 moves in the mold closing direction when the driving oil is injected from the inflow / outlet 24-1 of the mold clamping cylinder 24 through a pressure control valve (not shown), and moves in the mold opening direction when the driving oil is injected from the inflow / outflow 24-2. Go to

[0005] The mold clamping cylinder 24 is provided with a pressure sensor 27 for detecting oil pressure as a mold clamping force or a mold clamping pressure. With the mold closed, the mold clamping force can be controlled by adjusting the oil pressure in the mold clamping cylinder on the inflow / outflow section 24-1 based on the detection value of the pressure sensor 27. The fixed platen 21 and the movable platen 26 are provided with a distance sensor 28 for detecting a distance L between the platens, and measure a delicate opening amount between each parting surface of the fixed mold 17 and the movable mold 18. I can do it. Here, the distance between the platens means the distance between the parting surfaces, that is, a mold thickness or a partial mold thickness including a so-called mold opening amount, and its behavior is almost the same as the behavior of the mold opening amount. It is.

The injection device and the mold clamping device include a screw position sensor (not shown) for detecting the screw position, a resin in the nozzle 16 or in the mold, in addition to the pressure sensor 27 and the distance sensor 28 described above. Various sensors such as a resin pressure sensor for detecting the pressure and an injection pressure sensor for detecting the oil pressure of the injection cylinder 14 are provided.

FIG. 7 shows an example of a laser type distance sensor. The laser type distance sensor shown in FIG. 7 is a laser transmission / reception laser head 28-1 provided on the fixed platen 21.
And a reflector 28-2 for laser reflection provided on the movable platen 26, and a detection signal of the distance between the platens is transmitted from the laser head 28-1 to a control unit described later. Such a laser method has a long measurement span,
It is possible to measure up to the maximum mold opening.
1. The reflector 28-2 is not a fixed mold 17 and a movable mold 18, but a fixed platen 21 and a movable platen 2, respectively.
6, the distance sensor does not need to be adjusted even when the mold is replaced.

FIG. 8 shows the configuration of a control system necessary for controlling the above-mentioned injection molding machine. The control system includes a setting signal from a setting device 41 for inputting a distance between platens, a mold clamping force, and the like, a pressure detection signal from a pressure sensor 27, a distance detection signal between platens from a distance sensor 28, and various signals described above. The sequence processing of the injection molding machine is performed based on the detection signal from the sensor and the like, and the pressure control valve 4
A microprocessing unit 43 for outputting a command value to the control unit 2, a memory 44 for storing data such as a distance between platens and a mold clamping force.

Such an injection molding machine is disclosed, for example, in Japanese Patent Application No.
-84370, and the detailed description is omitted.

[0010]

In the case of thin-wall molding, unless injection is performed at a high speed, the molten resin solidifies before being completely filled in the mold. As conventional methods for solving such problems, an injection compression method and an in-mold pressure feedback method are known.

The injection compression method is a method of detecting the pressure of the mold clamping cylinder, the opening amount of the mold, and the position of the screw, and controlling the pressure control valve of the mold clamping cylinder to control the mold clamping cylinder pressure. On the other hand, the mold pressure feedback method is
In this method, the resin pressure in the mold is detected by a resin pressure sensor, and the pressure control valve of the injection cylinder is controlled to control the mold internal pressure.

However, the above method cannot be said to be able to solve the above problems in any case.
This is because the resin pressure in the mold cannot be known by the injection compression method. On the other hand, even in the mold pressure feedback method, the resin pressure in the mold is detected only at one point. However, there is a difference between the mold internal pressure near the gate at the entrance of the mold and the mold internal pressure at a position away from the gate. And while this difference may have an adverse effect on the quality of the molded product, it is not possible to know whether or not any adverse effect is caused by such a difference.

Accordingly, an object of the present invention is to provide a control method capable of making the thickness of a molded product uniform and preventing shape defects such as warpage, particularly when a thin molded product is molded by high-speed compression molding. Is to provide.

[0014]

SUMMARY OF THE INVENTION The present invention relates to a control method for an injection molding machine for performing high-speed compression molding on a thin molded product. 1. A second mold pressure sensor is installed, and the mold clamping force before injection is set to a value sufficiently smaller than the maximum mold clamping force. Value, or when the screw reaches a predetermined position, the mold clamping pressure is increased to perform high-speed compression,
Monitoring the difference between the detected pressure of the first mold internal pressure sensor and the detected pressure of the second mold internal pressure sensor, and executing the screw retreat operation when the difference becomes a preset value. This is a control method based on the internal pressure of the injection molding machine.

[0015] The time for increasing the mold clamping pressure during the high-speed compression may be adjusted based on the difference.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A control system for implementing a control method according to the present invention will be described with reference to FIG. The control method according to the present invention is applied to the hydraulic injection molding machine shown in FIG. The control device 1 corresponds to the microprocessing unit 43 described with reference to FIG. 8 and performs control described later. 8, a pressure sensor 2 for detecting a pressure in the injection cylinder 14 not shown in FIG. 8, and a screw position sensor 8 in addition to a setting device 41, a memory 44, a pressure sensor 27, and a distance sensor 28 are provided. Is shown. In addition, the injection cylinder 14, the mold clamping cylinder 2
As means for supplying hydraulic oil to the cylinder 4, in addition to the accumulator, a large-capacity high-speed servo valve 3 as a pressure control valve is provided in the hydraulic pipe of the injection cylinder 14, Provided on the pipe. According to the present invention, as will be described later with reference to FIG. A second mold pressure sensor 7 is provided in the mold. The control system further
A display device 5 for displaying various data is provided.

The concept of the control method according to the present invention will be described with reference to FIG. In the present invention, the first mold pressure sensor 6 is provided near the gate in the mold, and the second mold pressure sensor 7 is provided in the mold away from the gate.

In the injection device, the position of the screw 13 and the pressure of the injection cylinder 14 are controlled using a screw position detection signal from the screw position sensor 8, a pressure detection signal from the pressure sensor 2, and the like. In the mold clamping device, control of the mold opening amount is performed by using a detection signal of the mold opening amount from the distance sensor 28, a pressure detection signal from the pressure sensor 27, and the like.
Pressure control of the mold clamping cylinder 24 is performed.

Further, in addition to the above detection signals, first,
Using the detection signals of the second in-mold pressure sensors 6 and 7, control for making the resin pressure in the mold uniform is performed.

In order to make the resin pressure in the mold uniform, the pressure detected by the mold internal pressure sensor 6 near the gate and the mold internal pressure sensor 7 away from the gate are controlled in high-speed compression molding.
This is realized by controlling the screw position on the injection device side in accordance with the high-speed compression operation on the mold clamping device side, in order to reduce the difference from the pressure detected in step (1).

A control method in high-speed compression molding will be described below.

1. The mold clamping force before injection in the mold clamping device is
About 10 to 20% of the maximum mold clamping force is applied in advance.

2. After the injection, when the resin reaches the predetermined mold pressure (the value detected by the mold pressure sensor 6 near the gate) with respect to the cavity, or when it is detected that the screw 13 has reached the predetermined position, the mold clamping pressure is reduced. The pressure is increased (high-speed compression) at a response speed corresponding to the filling time.

3. The resin in the mold compressed by high-speed compression from the mold clamping device side flows back to the screw 13 side through the gate after the inside of the mold is filled with the resin.

4. Here, the mold pressure during filling shows the largest value near the gate due to the effect of filling, but is detected by the two mold pressure sensors 6 and 7 because the resin flows in the mold by high-speed compression. The difference in the mold internal pressure is smaller than in normal molding.

[5] However, since the pressure in the vicinity of the gate still indicates a large pressure, in order to equalize the pressure difference in the mold, the pressure inside the mold at a position away from the gate and
By monitoring the pressure difference obtained by the two in-mold pressure sensors 6 and 7, the retraction operation timing of the screw 13 is determined, and the pressure near the gate is reduced by retreating the screw 13, so that the in-mold pressure is uniform. Can be realized. That is, the control device 1 monitors the pressure difference detected by the two mold pressure sensors 6 and 7, and when the pressure difference reaches a preset value, the screw 1
3 to perform a retreat operation.

The set value of the pressure difference is set by the operator through the setting unit 41. When the injection molding machine is started, the operator changes the pressure difference according to the mold. Repeat the molding operation while
Select a set value suitable for equalizing the pressure difference in the mold.

FIG. 3 is a functional block diagram for realizing the above control method. The arithmetic unit 1-1 on the mold clamping device side outputs a servo command to the large-capacity high-speed servo valve 4 when detecting that the value detected by the mold pressure sensor 6 near the gate has reached a predetermined mold pressure. To increase the mold clamping force (see 2.
Operation) to execute high-speed compression. The high-speed compression start timing may be determined by detecting that the screw 13 has reached a predetermined position. In this case, a detection signal of the screw position sensor 8 is output to the calculation unit 1-1.
The arithmetic unit 1-1 includes an in-mold pressure sensor 6 near the gate.
In addition, the output of the mold pressure sensor 7 at a location away from the gate is also given. This is for adjusting the pressure-increasing time of the mold clamping pressure during the high-speed compression based on the pressure difference detected by the two in-mold pressure sensors 6 and 7 in the arithmetic unit 1-1.

On the other hand, on the injection device side, the arithmetic unit 1-2 monitors the pressure difference between the two in-mold pressure sensors 6 and 7, and when the pressure difference reaches a preset value, the large-capacity high-speed servo valve 3 is turned on. And the screw 13 is retracted (operation of the above 5).

FIG. 4A shows an example of the mold clamping pressure displayed on the display device 5 and the pressure detection patterns of the two in-mold pressure sensors 6 and 7. For comparison, FIG.
The figure shows the mold clamping pressure in normal molding, the mold internal pressure near the gate, and the mold internal pressure at a location away from the gate. As described above, it has been shown that the mold pressure near the gate is reduced by retracting the screw. The operator repeats the operation of determining a set value relating to the pressure difference while observing the pressure detection pattern shown in FIG.

FIG. 5 shows another form of the functional block diagram of FIG. Here, the pressure difference detection for calculating the pressure difference between the two mold pressure sensors 6 and 7 without directly outputting the detection signals of the two mold pressure sensors 6 and 7 to the calculation units 1-1 and 1-2. Give to section 1-3. The pressure difference detection section 1-3 outputs the pressure difference between the two in-mold pressure sensors 6 and 7 to the calculation sections 1-1 and 1-2. Here, the timing of the start of the high-speed compression is determined based on the position of the screw 13 described with reference to FIG. The operation units 1-1 and 1-2 and the pressure difference detection unit 1
-3 is realized by the control device 1 shown in FIG.

[0032]

According to the present invention, the difference in internal pressure between the mold near the gate and at a position distant from the gate can be reduced, so that an ultra-thin molded product which cannot be realized by a conventional injection molding machine can be realized. It is possible to improve the uniformity of the thickness of the sheet and to form the sheet so as to prevent a shape defect such as a warp.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a control system for implementing a control method according to the present invention.

FIG. 2 is a diagram for explaining the concept of a control method according to the present invention.

FIG. 3 is a functional block diagram for realizing a control method according to the present invention.

FIG. 4 is a diagram showing an example of a mold clamping pressure displayed on a display device and pressure detection patterns of two in-mold pressure sensors according to the present invention (FIG. A), and, for comparison, a mold clamping pressure in normal molding; FIG. 4 is a diagram (FIG. B) showing the mold pressure near the gate and the mold pressure at a location away from the gate.

FIG. 5 is a diagram showing another form of the functional block diagram of FIG. 3;

FIG. 6 is a diagram showing a schematic configuration of a hydraulic injection molding machine to which the present invention is applied.

FIG. 7 is a diagram for explaining an example of a distance sensor in FIG. 6;

FIG. 8 is a block diagram showing a configuration of a conventional control system for controlling the injection molding machine of FIG.

[Explanation of symbols]

 6, 7 type internal pressure sensor 11 hopper 12 heating cylinder 13 screw 14 injection cylinder 15 piston 16 nozzle 17 fixed mold 18 movable mold 21 fixed platen 22 rear platen 23 tie bar 24 mold clamping cylinder 25 hydraulic piston 26 movable platen 27 pressure sensor 28 distance Sensor

Claims (2)

(57) [Claims] 1. A method for controlling an injection molding machine for performing high-speed compression molding on a thin molded product, wherein a first and a second internal pressure sensor are provided near and apart from a gate in a mold, respectively. The mold clamping force before injection is set to a value sufficiently smaller than the maximum mold clamping force. After injection, the value detected by the first mold pressure sensor reaches a predetermined value or the screw When the position reaches the position, the mold clamping pressure is increased to perform high-speed compression, and further, the difference between the detected pressure of the first mold internal pressure sensor and the detected pressure of the second mold internal pressure sensor is monitored, A method of controlling the injection molding machine by using an in-mold pressure, wherein a retreat operation of the screw is performed when the difference has reached a preset value. 2. The control method according to claim 1, wherein a time for increasing a mold clamping pressure during the high-speed compression is adjusted based on the difference.