JPS6326686B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a holding pressure control method for an injection molding machine and a device for carrying out the same, and particularly to an improved and novel injection molding machine that injection molds a plurality of molded products at the same time. The present invention relates to a pressure holding control method and device.

In the process of injection molding of synthetic resins, etc., various factors are usually intricately related to each other, making control thereof extremely difficult. Therefore, there is a need to develop a control method for controlling unstable factors involved in the injection molding process and stably and continuously molding injection molded products. For this reason, various control methods for controlling these factors have been proposed in the past. That is, (a) a method in which the resin pressure in the mold is detected by a pressure sensor via an extrusion pin, etc., and when the resin pressure reaches a set value, the control is switched to the pressure holding process at that point.

(b) A method of detecting the hydraulic oil pressure supplied to the injection cylinder and switching control to the pressure holding process at that point when the hydraulic oil pressure reaches a set value.

(c) A method of detecting the amount of opening of the mold parting surface or the amount of deformation of the mold due to resin pressure during injection, and switching control to the pressure holding process at that point when these measured values reach a set value, etc. .

Each of the above methods can be expected to give relatively good results when the injection mold consists of one cavity or multiple cavities that are the same or almost the same shape. I can do it. However, in the method proposed in the prior art as described above, as a mold for molding,
In the case of so-called simultaneous molding of different shapes, in which a plurality of cavities with widely different wall thicknesses, dimensions, shapes, and sizes are used, it becomes impossible to control individual molded products. As a result, molded products that are properly managed and controlled will be of good quality, but other molded products may have variations depending on the shape of each shot, or may have burrs, shot shots, etc. There were many cases where molding defects occurred. In particular, when multiple molded products of different shapes are injection molded at the same time, the resin filling situation in each cavity of the mold is different, so the allowable range of variation in the molding conditions is smaller than in single molding processing. For this reason, various problems have been observed, such as an increased risk of molding defects due to slight variations in molding conditions.

The present invention aims to solve the problems seen in the prior art described in detail above.
A novel and improved injection molding method and its implementation that can continuously and properly and efficiently injection mold molded products without causing molding defects or molding defects caused by changes in molding conditions, etc. The aim is to propose a new device for this purpose.

The holding pressure control method for an injection molding machine and the device for carrying out the same according to the present invention set target values of a filling pressure gradient and a holding pressure drop gradient of molten resin for each cavity part in a mold, The gist of the system is to control the pressure and flow rate of the hydraulic oil supplied to the injection cylinder so that the behavior of the molten resin in each cavity becomes a predetermined value.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The pressure holding control method and device for an injection molding machine according to the present invention will be described in more detail below with reference to the accompanying drawings.

FIG. 1 is an explanatory diagram of a system for implementing the holding pressure control method for an injection molding machine according to the present invention, and FIGS. FIG. 3 is a diagram showing the pressure behavior of hydraulic oil supplied to a cylinder in relation to elapsed time.

First, in FIG. 1, the injection mold includes cavities 1a, 1d, and 1c, and in-mold pressure transmitting pins 2a, 2b, and 2c are provided in each cavity portion. Further, in-mold pressure sensors 3a, 3b, and 3c are connected to the pins 2a to 2c, respectively, and are configured to detect the respective resin pressures in the in-mold cavities. That is, the pressure sensor 3a
The signals detected by ~3c are the pressure transducers 4a, 4b,
4c and input as input signals to filling pressure gradient setting devices 5a, 5b, 5c and holding pressure gradient setting devices 6a, 6b, 6c.

The displacement of the injection screw is detected by a displacement sensor 7 and inputted to a controller 9 via a displacement converter 8. The power amplifier 10 is connected to an electro-hydraulic control valve 11, which is connected to an operating hydraulic pressure source.

The injection molding machine 13 is a main body portion to which the present invention is implemented, and has an injection screw 14 and an injection cylinder 15 for feeding resin to the cavities 1a to 1c as main parts, and is a molding machine including the cavities 1a to 1c. The mold 16 corresponds to the shape, dimensions, etc. of the injection molded product. In addition, a sprue 17, a runner 18, etc. are provided in the molding die 16,
In addition, the speed pattern setting device 19 is connected to the controller 9.
connected to.

The pressure holding control system of the injection molding machine according to the present invention can be roughly divided into three mechanical parts: a detection section, a calculation section, and a control section, depending on their functions.
a to 3c, pressure transmitting pins 2a to 2c related to the front and rear of the sensor, and pressure transducers 4a to 4c for amplifying detection signals, as well as a displacement sensor 7 for detecting the displacement of the injection screw 14, and its This is a mechanical part including the displacement converter 8 and the like that amplify the displacement signal, and both are connected to the controller 9.

The calculation part is a mechanism including the filling pressure gradient setting devices 5a to 5c for specifying the state of the mold pressure pattern, the holding pressure gradient setting devices 6a to 6c, the speed pattern setting device 19 for specifying the injection speed pattern, etc. Furthermore, the controller 9, which performs calculations based on input signals from the detection section and outputs control signals for the injection molding machine 13, is also part of this calculation mechanism.

On the other hand, the control mechanism section is a mechanism section that includes the power amplifier 10 that amplifies the control signal from the controller 9, the electrohydraulic control valve 11 that converts the control signal into a state quantity of hydraulic oil, and the like.

In the above, when the injection start signal for starting the injection molding operation in the injection molding machine 13 is sent,
The controller 9 controls the forward speed pattern of the injection screw 14 based on information from the speed pattern setting device 19. Through the above operations, the molten resin material passes through the sprue 17 and the runner 18 and is filled into the individual cavities 1a to 1c of the molding die 16. The controller 9 controls the filling pressure of the resin from the time when the injection molding state satisfies the conditions for completing the speed control. Furthermore, pressure holding process control is performed from the time when the mold internal pressure satisfies the conditions for completing the filling process. That is, the fluctuation behavior of the detected value of the mold pressure is compared with the preset target value of the holding pressure drop gradient, and if a deviation occurs between the two, a correction signal is output in accordance with the deviation. By outputting the correction signal in this way,
It controls and adjusts the pressure and flow rate of the hydraulic oil fed to the injection cylinder 15. In the above-described pressure holding control process, the method of determining the control target from the plurality of cavities 1a to 1c is to measure the pressure gradients of all the cavities constituting the molding die 16, and set target values relative to those measured values. This is done by automatically selecting one of the cavities in an intermediate condition.

However, in the above control process, the control factor is only the state quantity of the hydraulic oil in the injection cylinder, whereas the object of management or monitoring is the amount of molten resin in the multiple cavities that make up the molding die. Therefore, a situation may occur in which the state of the molten resin in a cavity other than the cavity selected as the control target for the holding pressure gradient is significantly different from the state of the cavity that is the control target. In such a situation, the behavior of the molten resin in cavities other than the cavities selected as the management target may exhibit an upward trend even during the pressure holding process. When such a phenomenon occurs,
This is related to the fact that the molded product in the corresponding cavity is molded in an overfilled state, and therefore causes problems such as the occurrence of internal distortion in the molded product.
For this reason, the controller 9 monitors the state of the molten resin in all the cavities 1a to 1c constituting the molding die 16, and if a problem occurs such as overfilling of one cavity, this problem will be corrected. When this occurs, it is desirable to stop controlling the state variables such as the pressure and flow rate of the hydraulic oil as described above, and to maintain the initial condition of the hydraulic oil at the start of pressure holding.

FIGS. 2a to 2d illustrate the above-described pressure holding control process using changes in hydraulic oil pressure and mold pressure over time.
That is, in FIGS. 2a to d, each cavity 1
The temporal changes in the pressure of the molten resin in a to 1c and the pressure of the hydraulic fluid fed to the injection cylinder 15 are shown as a line diagram.

In Fig. 2, a hydraulic pressure curve 21, a control switching point 22, a pressure holding control stop point 23, a pressure holding control stop section 24, a holding pressure initial pressure 25, etc. are shown as lines and points, respectively. . In addition, the pressure curves 31a, 31b, and 31c are for cavity 1, respectively.
It shows the change in molten resin pressure in a, 1b, and 1c over time, and also shows the holding pressure gradient 32.
a, 32b, 32c are the respective cavities 1
It shows the holding pressure gradient of the molten resin in a, 1b, and 1c. Also, the elapsed time on the horizontal axis is
Each includes an injection process 41, a filling process 42, a pressure holding process 43, and a cooling process 44.

In the controller 9, the injection speed control step,
Through the filling pressure control step, pressure holding control is performed from the control switching point 22 when the conditions for completing the filling pressure control step are satisfied. That is, the molding die 16
The in-mold pressure behavior of the constituent cavities 1a to 1c,
The deviation from the target value of the holding pressure gradients 32a to 32c is calculated, and the deviation exhibits an intermediate value among the cavities 1a to 1c constituting the molding die 16, for example, the cavity 1c is arbitrarily selected and set as the target value. Adjustment control is performed such that the hydraulic fluid pressure 21 curve changes so that the in-mold pressure curve 31c of the cavity 1c follows the holding pressure gradient 32c.

For example, the cooling conditions, state, etc. of the molding die 16 change, and as a result, the state of the molten resin in the cavities 1b and 1c differs greatly, and the in-mold pressure curve 31b of the cavity 1b increases in the pressure holding process. If the trend starts to show, the holding pressure control stop point 23 at which this upward trend has occurred is determined.
From then on, during the pressure holding control stop section 24 until the end of the pressure holding control time, the hydraulic oil pressure is changed to the hydraulic oil pressure curve 2.
1, the portion corresponding to the section 24 is held at the initial holding pressure 25 as shown by the broken line.

As described above in detail, the holding pressure control method and device for an injection molding machine according to the present invention sets the target values of the filling pressure gradient and holding pressure drop gradient of molten resin to the cavity portion of the mold. The gist of the system is to control the pressure and flow rate of the hydraulic oil supplied to the injection cylinder so that the behavior of the molten resin in each cavity becomes a predetermined value. Therefore, it has become possible to adjust and control the pressure and flow rate of the hydraulic oil supplied to the injection cylinder, and to maintain the holding pressure drop gradient, etc., which has an important influence on the quality of the molded product, in an appropriate state. Furthermore, even if a mutation occurs in the molten resin filled in the cavity, it is now possible to immediately deal with such a mutation.

As described above, by applying the holding pressure control method and device for an injection molding machine according to the present invention, it has become possible to injection mold and supply good molded products continuously and in a stable state. Furthermore, since the injection molding condition is tracked and controlled, it is possible to minimize variations in the molding condition for each molding shot. Therefore, as a result, the defect rate of injection molding was reduced to less than 1/5 of the conventional rate, and a great effect of improving productivity was obtained.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a system for implementing the pressure holding control method for an injection molding machine according to the present invention, Fig. 2 a, b,
c and d are diagrams showing the behavior of the pressure inside the mold of the molten resin and the behavior of the pressure of the hydraulic oil supplied to the injection cylinder in relation to the elapsed time in one embodiment of the present invention. 1... Cavity, 3... In-mold pressure sensor, 4
...Mold pressure transducer, 5...Filling pressure gradient setting device, 6...Holding pressure gradient setting device, 9...Controller, 10...Power amplifier, 11...Electro-hydraulic control valve, 12...Working oil pressure Source, 13... Injection molding machine, 14... Injection screw, 15... Injection cylinder, 16... Molding mold, 19... Speed pattern setting device.

Claims (1)

[Claims] 1. A method of simultaneously injecting a plurality of molded products by repeating the steps of injection, filling, holding pressure, and cooling using a molding die consisting of a plurality of cavities and an injection cylinder including an injection screw. In a holding pressure control method for an injection molding machine that performs molding; a step of setting target values for the molten resin filling pressure gradient and holding pressure drop gradient for each cavity, and controlling the in-mold pressure behavior of each cavity and the holding pressure. A step of comparing and calculating the deviation with the target setting value of the descending gradient, and selecting one of the deviations from the target setting value for each cavity that represents an intermediate value as the management target value, and A stage of controlling the state quantity of the hydraulic oil supplied to the injection cylinder so that each mold internal pressure follows the management target value, and the behavior of the mold internal pressure increases in cavities other than the cavity for which the management target value is set. A pressure holding control method for an injection molding machine, comprising the steps of: stopping control of the state quantity of hydraulic oil when a tendency is shown, and maintaining the initial condition of the state quantity of the hydraulic oil at the time of starting pressure holding. 2. An injection molding machine that uses a mold consisting of a plurality of cavities and an injection cylinder containing an injection screw to simultaneously injection mold a plurality of molded products by repeating the steps of injection, filling, holding pressure, and cooling. The holding pressure control device includes a detection mechanism for detecting and amplifying the mold internal pressure of each cavity and inputting it to the controller, and means for specifying and setting the mold internal pressure pattern; Based on the pressure detection input signal, a comparison calculation with the set value is performed, and among the deviations from the above target set value for each cavity, one cavity that shows an intermediate value is selected and set as the management target value, and the corresponding an arithmetic mechanism including a controller that outputs a control signal to the injection molding machine so as to follow a target value; and a state quantity of hydraulic oil that amplifies the control signal from the controller and controls the injection screw of the injection cylinder. A control mechanism for controlling an injection molding machine.