JPS6130891B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method and a control device for an injection molding machine, and in particular, detects the hydraulic pressure of the injection cylinder during the injection process of the injection molding machine, and uses the information to control the injection molding material. The present invention relates to a control method for controlling a plasticization state and a control device thereof.

So-called injection molding plasticizes and melts the molding material using thermal energy from the band heater of the injection cylinder in the injection molding machine and mechanical energy from the rotational movement of the injection screw and its back pressure, and the molten resin is It is injected and filled into the mold at high speed and high pressure. and,
Thereafter, the molten resin is cooled and shaped in a mold to form a desired shape.

In order to continuously produce stable quality products using the above-mentioned molding process, injection molding machines constantly adjust the molding conditions such as heating cylinder temperature, filling pressure, filling speed, or injection amount. It is necessary to maintain it constant. For this reason, various control methods, such as those exemplified below, which are less susceptible to disturbances such as fluctuations in room temperature, power supply voltage, or water temperature, have been adopted and put into practice.

(1) By detecting the forward position of the injection screw and controlling the pressure or flow rate of the injection hydraulic circuit,
A method of controlling the process in which molten resin is injected into a mold.

(2) By detecting the resin pressure when molten resin is injected into the mold and controlling the pressure or flow rate of the injection hydraulic circuit when the resin pressure matches a predetermined setting value, A method of controlling the process in which molten resin is injected into a mold.

(3) Detects the deformation inside the mold due to the injection pressure of molten resin, and uses a control signal proportional to the deformation to
A method of controlling the pressure or flow rate of an injection hydraulic circuit to control the process of injecting and filling molten resin into a mold.

(4) A method of detecting the resin temperature or mold temperature near the nozzle of an injection molding machine and adjusting the injection pressure according to the deviation between this detected value and a predetermined set value.

(5) A method of detecting the injection screw position at the time of completion of injection and adjusting the next molten resin metering stroke according to the deviation between this detected value and a predetermined set value.

However, the injection molding process is related to the various factors mentioned above and is susceptible to variations thereof. Therefore, in any of the conventional methods exemplified above, it is difficult to maintain the molded state optimally.

That is, the method (1) above is a control device having a so-called multi-stage injection mechanism, and controls the flow rate of hydraulic oil supplied to the injection cylinder using a servo valve or a proportional solenoid valve. This method of controlling only the hydraulic oil flow rate has an unstable element due to fluctuations in the hydraulic oil temperature, and a decrease in control reproducibility and accuracy is observed due to changes in the hydraulic oil viscosity. In addition, it is difficult to cope with the pressure loss of the molten resin due to fluctuations in mold temperature and resin temperature, and it is difficult to control molding defects such as short shots and burrs.

In addition, methods (2) and (3) above include a method of detecting a certain point in the molding state in the mold and controlling the switch from the injection process to the holding pressure process, but it depends on the setting location of the detector. It is difficult to properly grasp the molding state because it is susceptible to regional deviations in mold internal pressure or mold displacement depending on the shape of the molded product. In addition to this, since the injection filling process is not controlled, flow marks (flow patterns related to temperature, speed, etc.),
It is impossible to deal with molding defects caused by the flow of the molten resin, such as weld lines (lines formed at the stop portion when filling from both directions).

Furthermore, the method (4) above is related to the heat capacity of the detector, has a poor response speed, and induces hunting of control factors due to a control time delay, making it difficult to stably control the molding state.

Finally, method (5) above is effective for controlling the shot size, but it does not deal with fluctuations in the temperature and kneading state of the molten resin due to cylinder temperature, screw rotation speed, etc., and fluctuations in the filling behavior of the molten resin. I can't. Therefore, it is not possible to deal with molding defects such as flow marks, burns, warping, and deformation caused by the above factors.

Therefore, in addition to the above-mentioned methods, the injection molding processing method also requires the control of the injection filling process described above in order to continuously mold molded products that have good physical and external quality. , it is necessary to maintain a constant plasticization state of the molten resin to be injected and filled.

That is, the degree of plasticization of the molten resin must be maintained at a constant level by controlling the thermal energy of the heating cylinder, the rotational speed of the injection screw, and the mechanical energy of the back pressure.

However, in this regard, none of the conventional methods described above accurately controls the degree of plasticization of the molten resin. Therefore, it is not possible to deal with unstable factors such as fluctuations in cylinder temperature caused by various disturbances such as power supply voltage and ambient temperature, or fluctuations in screw rotation speed and back pressure due to changes in hydraulic oil temperature. Furthermore, variations in the degree of plasticization affect the flow state of the molten resin, resulting in molding defects such as flow marks and weld lines that are unfavorable in terms of appearance and design. Conventional control methods that do not have a mechanism for controlling the degree of plasticization are unable to deal with the above-mentioned molding defects related to fluctuations in plasticization.

The present invention solves the above-mentioned drawbacks of the prior art.In short, by maintaining a constant degree of plasticization of the molten resin inside the injection cylinder, molded products with excellent physical properties and appearance can be continuously produced. A method for controlling an injection molding machine, which enables molding to be carried out in a controlled manner, and
The object is to provide a control device that implements the control method.

A feature of the present invention is that the degree of plasticization of the molten resin inside the injection cylinder is indicated by simultaneous measurement of the injection cylinder hydraulic pressure and the resin pressure inside the mold during the injection molding process by an injection molding machine. detects the working oil pressure of the injection cylinder at the time when it is filled into the mold, and controls the plasticization degree control factor of the molten resin according to the deviation between this detected value and a separately predetermined set value; A method of controlling an injection molding machine maintains a constant plasticization state of molten resin.

Furthermore, means for simultaneously measuring the injection cylinder hydraulic oil pressure and the resin pressure in the mold in the injection molding machine, thereby detecting the injection cylinder operating pressure;
An injection molding system equipped with a means for comparing the detected value and a preset value and converting it into a deviation, and a means for controlling the plasticization degree control factors according to the deviation to maintain the plasticization degree of the molten resin constant. It is in the control device of the molding machine.

An embodiment of the control method according to the present invention will be described next along with an embodiment of the control device thereof.

In the block diagram shown in FIG. 1, 1 is a movable plate, 2 is a movable type, 3 is a fixed type, 4 is a fixed plate, 5 is a pressure transmission pin, and 6 is an in-mold pressure sensor. 7 is a band heater, 8
is an operating oil pressure sensor, 9 is a hydraulic motor, 10
is an injection screw, 11 is an injection cylinder, 1
2 is a molded resin, and 13 is a molten resin.

Also, as mentioned later, 14,1
4 is an amplifier, 15 is a timing setter, 16
is a comparator, 17 is a pressure setting device, 18 is a calculator, 19 is a control signal amplifier, 20 is a hydraulic control device, 21 is a temperature control device, 22 is a proportional electromagnetic pressure valve, 23 is, The proportional electromagnetic flow valve 24 represents a hydraulic drive source.

That is, first, the movable mold 2 is fixed to the movable plate 1, and the fixed mold 3 is fixed to the fixed plate 4.
The mold consists of a pressure sensor 6 connected to a pressure transmission pin 5 to detect the pressure inside the mold.
It is equipped with

In addition, the molding resin 12, which is the molding material, is charged into the hopper provided in the injection cylinder 11 equipped with the band heater 7 and the working oil pressure sensor 8.
Due to the rotational movement of the injection screw 10 connected to the hydraulic motor 9 and the back pressure generated in the injection cylinder 11, the resin is plasticized and kneaded, becomes molten resin 13, and is stored in the front part of the injection screw 10. It's summery. Then, when the injection screw 10 retreats and the molten resin 13 is charged by a predetermined amount, the molten resin 13 is
It is designed to be injected and filled into the above-mentioned mold at high speed and high pressure.

Now, as a preliminary explanation of the operation with the above configuration, if the hydraulic oil pressure of the injection cylinder 11 and the mold internal pressure during the injection filling are measured by the hydraulic pressure sensor 8 and the mold internal pressure sensor 6, respectively, the time An example of such a change is shown in FIG. Here, 26 and 27 in FIG. 2 are curve diagrams showing temporal changes in the injection cylinder hydraulic oil pressure and the mold internal pressure.

That is, the hydraulic pressure curve 26 increases linearly at the same time as the injection starts, and reaches the inflection point P _pf after T _f . The molten resin 13 starts filling the mold only when the working oil pressure reaches P _pf , and the pressure inside the mold gradually increases. Immediately before the molten resin 13 is completely filled into the mold, the injection hydraulic circuit is switched to the holding pressure, and the injection cylinder hydraulic pressure and mold internal pressure are then changed to 26, 27 as shown in FIG. It changes like a curve.

Regarding the above transition, according to the results of experiments conducted by the inventors, the hydraulic pressure P _pf of the injection cylinder 11 at the time T _f when the molten resin 13 starts to be filled into the mold depends on the degree of plasticization of the molten resin 13. It turns out that these are closely related physical quantities.

In other words, in addition to molding conditions such as mold temperature and injection speed, injection cylinder temperature, screw back pressure,
Even if the plasticization conditions such as screw rotation speed and screw rotation speed vary individually, if the plasticization state of the molten resin 13 is ultimately at the same level, when the molten resin 13 starts filling into the mold. The working oil pressure P _pf always shows the same pressure. As a result, if P _pf is maintained at a constant value by controlling factors such as injection cylinder temperature, screw rotation speed, and screw back pressure against disturbance fluctuations, a molded product in the same state will always be stable. It turned out that it can be obtained by

In summary, the present invention is based on the above-mentioned development and knowledge, and has the above-mentioned structure.
The plasticization state of the molten resin 13 is detected by the hydraulic oil pressure P _pf , and based on this information, the rotation speed of the injection screw 10, back pressure, and injection cylinder temperature, which affect plasticization, are controlled to determine the plasticization state of the molten resin 13. It is nothing but a method and device for maintaining the temperature constant.

That is, returning to the circuit diagram of FIG. 1 again, the principle of operation will be explained below along with the configuration.

Detection of P _pf , which is the hydraulic fluid pressure, is performed by simultaneous measurement.
The information from the in-mold pressure sensor 6 and the operating oil pressure sensor 8 is transmitted to the timing setter 15 via amplifiers 14 and 14, respectively, and the injection cylinder 1 at the time T _f when the molten resin 13 starts to be filled into the mold is transmitted.
Detected as hydraulic pressure of 1. The detected working oil pressure P _pf is determined by the comparator 16 and the pressure setting device 17
It is converted into a deviation from the set pressure set in , and sent to the calculator 18. In the computing unit 18, the temperature of the injection cylinder 11,
It generates signals that control the screw rotation speed and screw back pressure.

Then, the injection cylinder temperature is corrected and set by controlling the band heater 7 via the arithmetic unit 18, the control signal amplifier 19, and the temperature control device 21. The screw rotation speed is determined by the arithmetic unit 18, the control signal amplifier 19, and the hydraulic control device 20.
It is corrected and set by driving the proportional electromagnetic flow valve 23 and controlling the flow rate of the hydraulic drive source 24. Similarly, the screw back pressure is controlled via the computing unit 18, the control signal amplifier 19, and the hydraulic control device 20.
It is corrected and set by driving the proportional electromagnetic pressure valve 22 and controlling the pressure of the hydraulic drive source 24.

By using the control method described above and the control device used to implement this method, the present invention can maintain a constant degree of plasticization of the molten resin, which was conventionally impossible to detect and control. As a result, it is possible to prevent molding defects such as flow marks, weld lines, and burns caused by fluctuations in the degree of plasticization of the molten resin, and to continuously produce molded products with good physical and external appearance. It can be said to be a novel, useful, and excellent invention based on new knowledge and technical ideas.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the method and apparatus of the present invention, and Fig. 2 is a curve diagram showing temporal changes in injection cylinder hydraulic oil pressure and mold internal pressure in the injection molding process. be. 1...Movable plate, 2...Movable type, 3...Fixed type, 4...Fixed plate, 5...Pressure transmission pin, 6...In-mold pressure sensor, 7...Band heater, 8...Operating oil pressure Sensor, 9... Hydraulic motor, 10... Injection screw, 11... Injection cylinder, 12... Molded resin, 13... Molten resin, 1
4, 14...Amplifier, 15...Timing setter, 16...Comparator, 17...Pressure setting device, 18
... Arithmetic unit, 19 ... Control signal amplifier, 20 ...
Hydraulic control device, 21... Temperature control device, 22...
Proportional electromagnetic pressure valve, 23... Proportional electromagnetic flow valve, 24
...Hydraulic drive source.

Claims (1)

[Scope of Claims] 1 Simultaneous measurement of the injection cylinder hydraulic pressure and the resin pressure in the mold during the injection molding process by an injection molding machine indicates the degree of plasticization of the molten resin inside the injection cylinder. The operating pressure of the injection cylinder at the time when resin starts filling into the mold is detected, and the factors controlling the degree of plasticization of the molten resin are controlled according to the deviation between this detected value and a separately predetermined set value. A method for controlling an injection molding machine, characterized in that a plasticized state of molten resin is maintained constant. 2 In an injection molding machine in which the injection cylinder temperature, screw rotation speed, and screw back pressure, which are factors for controlling the degree of plasticization of molten resin, are controlled by electrical signals, both the injection cylinder hydraulic pressure and the resin pressure in the mold are controlled. The working pressure of the injection cylinder at the time when the molten resin starts to be filled into the mold is detected based on both information, and the detected value indicating the degree of plasticization of the molten resin inside the injection cylinder is determined separately in advance. According to the first aspect of the present invention, the control factors are controlled according to the deviation from the set value set, so that the plasticized state of the molten resin is maintained constant and a stable molded product is continuously provided. Control method for an injection molding machine described in Section. 3. Means for simultaneously measuring the injection cylinder hydraulic pressure and the resin pressure in the mold in an injection molding machine to detect the injection cylinder operating pressure, and comparing this detected value with a preset value to determine the deviation. 1. A control device for an injection molding machine, comprising means for converting the plasticization degree, and means for controlling a plasticization degree control factor according to the deviation to maintain a constant plasticization degree of a molten resin. 4. The injection molding machine according to claim 3, which is configured to control the injection cylinder temperature, screw rotation speed, and screw back pressure, which are factors for controlling the degree of plasticization of the molten resin, by electric signals. control device.