JPS636341B2 - - 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 an apparatus for implementing the same.

In the process of injection molding of synthetic resins, etc., various factors are intricately interrelated, making management and control extremely difficult.
Therefore, there is also a need for the development of a control method that can control the unstable factors involved in the injection molding process and continuously injection mold injection molded products in a stable state at all times. For this reason, many various control methods have been proposed to control and manage these factors. For example, (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 when the hydraulic oil pressure reaches a set value.

(c) There is 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 holding pressure process when these measured values reach a set value. .

Each of the above methods is expected to yield good results in controlling the filling process for filling the mold cavity with molten resin. That is, it was effective in reducing the rate of occurrence of various molding defects such as jetting, flow marks, and discoloration. However, in the conventional method described above, problems such as internal distortion, easy deformation, or lack of dimensional stability that occurs in the injection molded product obtained by this method are caused by the pressure holding process of the molten resin. It has been difficult to take satisfactory measures against molding defects caused by molding. Therefore, with conventional technology, it is difficult to mold precision structural parts such as cams and gears that require high dimensional accuracy, or optical parts such as plastic lenses that have problems with uniformity and the presence of internal distortion. Therefore, there were many cases where the application was not desirable.

The present invention was proposed in view of the problems seen in the prior art described in detail above, and it solves the drawbacks seen in the prior art and is applicable to injection molding of precision mechanical parts and optical parts. It includes improvements, improved new processes, and configurations. The object of the present invention is to obtain a pressure holding control method and device for an injection molding machine.

The holding pressure control method for an injection molding machine and the apparatus for implementing the same according to the present invention control the pressure and flow rate of hydraulic oil supplied to the injection cylinder so that the holding pressure drop gradient of the molten resin becomes a predetermined value. In addition, in order to carry out the above control method, there is an in-mold pressure sensor that detects the molten resin pressure in the cavity, an in-mold pressure transducer, and a holding pressure that sets the injection molding state. descent gradient setter,
The main feature of the system is that it is equipped with an electro-hydraulic control valve for controlling hydraulic fluid.

That is, in the holding pressure control method and device for an injection molding method according to the present invention, the state of the molten resin in the holding pressure process is constantly monitored and controlled, and the occurrence of injection molding defects and molding defects caused by changes in molding conditions is eliminated. , it becomes possible to continuously mold appropriate and good molded products.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for controlling pressure holding in an injection molding machine according to the present invention and an apparatus for carrying out the method 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 pressure holding control method according to the present invention. Figures 2a and 2b are diagrams showing temporal changes in the behavior of the pressure inside the mold of the molten resin and the behavior of the hydraulic fluid pressure supplied to the injection cylinder in one embodiment of the present invention, and Figures 3a, b, and c are FIG. 6 is a diagram showing the behavior of the pressure of the molten resin in the mold, the behavior of the hydraulic oil pressure supplied to the injection cylinder, and the temporal change in the displacement of the injection screw in another embodiment of the present invention.

Before explaining the drawings, basic considerations for completing the present invention will be explained. That is, when completing the present invention, the shape of the injection molded product, the injection molding material, and the injection molding conditions were variously changed, and the correlation between the injection molding conditions and the condition and state of the injection molded product was examined in detail. This is because it is known that the molten resin in the pressure holding step passes through a semi-molten state and the melt viscosity changes greatly from moment to moment while it cools and solidifies. As a result of the above consideration,
The behavior of the molten resin during the pressure holding process of the molten resin,
The transfer function between the injection molding machine's hydraulic oil pressure, hydraulic oil flow rate, and other molding conditions includes what is called a "dead time system," and if appropriate and effective feedback control is not performed, the control system It was determined that the entire system caused a hunting phenomenon. Furthermore, it has been known that at the stage of transition from the filling process to the pressure holding process, the target value is in a transient state where it changes, so the transient deviation becomes large, resulting in particularly complex behavior. Therefore, by constantly detecting the injection molding state and adjusting the hydraulic pressure and flow rate supplied to the injection cylinder based on the information, the holding pressure drop gradient can be controlled, and the entire system can therefore be effectively controlled. This is what I did.

The control system shown in Fig. 1 was obtained as a result of the above basic study, and the injection molding machine 1 includes an injection screw 2 and an injection cylinder 3, and also supplies hydraulic oil to these mechanisms. The hydraulic pressure source 4 is the main component mechanism.

On the other hand, the injection mold 5 includes a cavity 6. For control, a basic configuration of three systems is normally required: information detection, calculation, and control based on the information, and the pressure holding control system of the present invention also includes the basic configuration of these three systems.

The detection section includes an in-mold pressure sensor 8 that detects the molten resin pressure in the cavity 6 via an in-mold pressure transmission pin 7, and an in-mold pressure transducer that amplifies the signal detected by this in-mold pressure sensor 8. 9, a displacement sensor 10 for detecting the displacement of the injection screw 2, a displacement converter 11, etc. On the other hand, the calculation section includes a speed pattern setting device 13 for specifying the injection speed pattern, and a filling pressure gradient setting device 1 for molten resin for specifying the pressure state in the mold.
4, holding pressure drop gradient setting device 15, holding pressure transient period setting device 16, which is set in the transient period until the control target becomes stable when transitioning from the filling process to the holding pressure process;
The input information from the holding pressure initial condition setter 17 for specifying the molding conditions of the transient section and the above-mentioned detection section is compared with the input setting values to each of the above-mentioned setting devices, and the difference between these values is calculated. When a deviation occurs, the controller 12 is a component, mechanism, etc. for outputting a corrected control signal according to the deviation.

Further, the control section is composed of a power amplifier 18 for amplifying correction and control signals outputted from the controller 12, and an electro-hydraulic control valve 19 for converting the control signals into state quantities of hydraulic fluid.

In the above configuration, the controller 12 controls the forward speed pattern of the injection screw 2 based on the information from the speed pattern setting device 13 in response to the molded product injection start signal. Filling pressure control is performed from the time when the molding state satisfies the conditions for completing the speed control process. Further, from the time when the mold internal pressure satisfies the conditions for completing the filling process, pressure holding process control is carried out. This is to set the pressure and flow rate of the hydraulic oil supplied to the injection cylinder 3 as the pressure initial conditions for the period specified by the pressure transient period setting device 16 immediately after the start of the pressure holding process. control so that the value is always maintained at the specified value in the device 17. Thereafter, the pressure and flow rate of the hydraulic oil supplied to the injection cylinder 3 are adjusted and controlled so that the fluctuation behavior of the mold pressure follows the pressure drop gradient specified by the holding pressure drop gradient setting device 15. It means that.

The above control process is schematically shown in the diagrams of FIGS. 2a and 2b, with the elapsed time plotted on the horizontal axis and the amount of state change plotted on the vertical axis. In FIG. 2a, the mold pressure behavior is shown as a curve 21 versus elapsed time on the horizontal axis. The control switching point 22 corresponds to the end-of-filling pressure 23 of the molten resin, after which the mold pressure exhibits a pressure change indicated as a holding pressure drop gradient 24 . On the other hand, in FIG. 2b, the hydraulic pressure behavior is shown as a curve 31 with respect to the elapsed time on the horizontal axis, and a holding pressure transient section 32 and a holding pressure initial pressure 33 are curves showing the pressure behavior of the hydraulic oil. 31. Corresponding to the above, the process elapsed time on the horizontal axis in FIG. 2b is also divided into an injection process 41, a filling process 42, a pressure holding control process 43, a cooling process 44, etc. The controller 12 maintains the hydraulic fluid pressure at the initial holding pressure 33 over a period of time from the time when the mold internal pressure satisfies the conditions for completing the filling process, that is, from the control switching point 22 to the holding pressure transient period 32. do. That is, the filling process 42 corresponds to this. During this period, the curve 21 showing the in-mold pressure behavior of the molten resin slightly exceeds the filling completion pressure 23, and then almost reaches the holding pressure drop gradient 24, which is the management target for pressure holding process control. This results in a similar behavior. After the holding pressure transient period 32 is completed and has elapsed, the controller 12 adjusts the hydraulic pressure to the curve 31 so as to follow the holding pressure drop gradient 24, as shown by the curve 21 showing the in-mold pressure behavior. Adjust and control like.

In addition to setting the elapsed time from the control switching point 22 as schematically shown in FIG. 2, the holding pressure transient section 32 is set by a relative value to the filling completion pressure 23 or by setting the pressure behavior inside the mold. Curve 21 shown
It is also possible to set the pressure drop rate given by .

Furthermore, FIGS. 3a, b, and c schematically show another embodiment of the present invention, including the displacement of the injection screw (vertical axis in FIG. 3b). In addition, in Fig. 3 a, b, and c, those indicated by the same reference numerals as those in Fig. 2 a, b mentioned above all have the same behavior.
This indicates changes, etc. That is, the third
Figures a and b roughly correspond to the aforementioned Figures 2 a and b, and Figure 3 c schematically shows the correlation between the displacement of the injection screw 2 and the passage of time corresponding to the above-mentioned changes. There is.

In FIG. 3c, the vertical axis shows the displacement of the injection screw 2 as described above, and the horizontal axis shows the screw displacement behavior with respect to elapsed time as a curve 51. A cushion amount 52 of the displacement of the injection screw 2, a pressure holding control stop point 53 and a pressure holding control stop period 54 of the hydraulic fluid pressure supplied to the injection screw 2 are also illustrated in FIG. 3c.

In the above, the controller 12 changes the curve 21 indicating the mold pressure change from the control switching point 22 at which the filling completion pressure 23 is satisfied to the pressure holding control step 43.
It functions to carry out the following. That is, adjustment control is performed such that the curve 31 representing the hydraulic fluid pressure behavior changes so that the curve 21 representing the in-mold pressure behavior follows the holding pressure drop gradient 24 set in advance.

However, when so-called external factors such as water temperature and room temperature change significantly, and the injection molding condition changes,
As a result, the displacement behavior of the injection screw 2 is 5
There are cases where the injection screw 2 changes as shown by the broken line 1a and reaches the cushioning amount 52 of the injection screw 2 set in the holding pressure transient section setting device 16. In this case, a curve 5 representing the displacement behavior of the screw 2 is used.
The working pressure of the hydraulic oil exhibits the above displacement behavior over the pressure holding control stop period 54 from the holding pressure control stop time point 53 when 1a reaches the above-mentioned cushion amount 52 until the completion of the pressure holding control step 43. As shown by the curve 31a, the pressure is maintained at the initial pressure 33.
Control takes place.

Further, the temperature of the injection molding die 5 or the temperature of the molten resin changes over time, and for example, before the pressure holding control step 43 is completed, the curve 31 showing the behavior of the pressure inside the mold of the molten resin changes during the pressure holding control step. When the pressure has dropped to the completion pressure of , the above-mentioned pressure holding control stop signal is issued and executed from that point on.

As explained in detail above, when the pressure holding control method for an injection molding machine according to the present invention and the device for carrying out the same are applied, the pressure and flow rate of the hydraulic oil fed to the injection cylinder can be appropriately controlled, and It has become possible to properly control the holding pressure drop gradient, which has an important effect on the quality of injection molded products. Therefore, by applying the present invention, it has become possible to supply injection molded products of good quality continuously and always in a stable state. Furthermore, since the system controls the injection molding state while following it, it has become possible to minimize variations in the molding state for each shot of injection molding. 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 reduce the incidence of defects in injection molding to 1/5 or less of molding by conventional technology.

[Brief explanation of the drawing]

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. Diagrams 3a, b, and c showing time changes in cylinder hydraulic oil pressure behavior are similar to the in-mold pressure behavior in another embodiment of the present invention.
FIG. 4 is a graph showing the behavior of the hydraulic oil pressure in the injection cylinder and the displacement of the injection screw over time. 1...Injection molding machine, 2...Injection screw, 3
...Injection cylinder, 4...Operating oil pressure source, 5...Forming mold, 6...Cavity, 8...In-mold pressure sensor, 10...Displacement sensor, 12...Controller, 13...Speed pattern setting device , 14... Filling pressure gradient setting device, 15... Holding pressure drop gradient setting device, 16... Holding pressure transient section setting device, 17... Holding pressure initial condition setting device, 19... Electro-hydraulic control valve.

Claims (1)

[Scope of Claims] 1. An injection molding machine that includes an injection cylinder including an injection screw and a mold, and performs injection molding of molten resin while repeating the steps of injection, filling, holding pressure, and cooling of molten resin. A state quantity of hydraulic oil to be supplied to the cylinder so that the target value of the holding pressure drop gradient of the molten resin in the pressure holding process of the molten resin is set in advance, and the in-mold pressure behavior of the molten resin follows the target value. In a holding pressure control method for an injection molding machine, when the pressure inside the mold of the molten resin drops to the set value or the displacement of the screw reaches a preset amount of cushion, the state of the hydraulic fluid is controlled. 1. A pressure holding control method for an injection molding machine, comprising: stopping control of the amount, and maintaining the initial value of the state amount of hydraulic oil at the time of starting pressure holding for a predetermined period of time from the start of holding pressure. 2. Pressure holding control of molten resin in an injection molding machine that includes an injection cylinder including an injection screw and a molding die, and performs injection molding of molten resin while repeating the steps of injection, filling, holding pressure, and cooling of molten resin. An injection method in which the target value of the holding pressure drop gradient of the molten resin in the process is set in advance, and the state quantity of the hydraulic oil supplied to the cylinder is controlled so that the in-mold pressure behavior of the molten resin follows the target value. In a holding pressure control device for a molding machine; a detection mechanism including a means for detecting and amplifying the pressure inside the mold of the molten resin and a means for detecting and amplifying the displacement of the screw; A means for predefining and setting the internal pressure behavior, and calculating a deviation between the input signal from the detection section and the set input value to each of the setting means, and a correction control signal corresponding to the deviation. A pressure holding control device for an injection molding machine, comprising: a calculation mechanism including a controller for outputting a control signal; and a control mechanism including means for amplifying a control signal from the controller and converting it into a state quantity of hydraulic oil.