JPH0622845B2 - Control method of injection molding machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a resin pressure control method for an injection molding machine using a resin pressure sensor in a mold, and more particularly to a control method having a learning function.

<Prior Art> Conventionally, there is the following in-mold feed back injection molding method in which injection pressure is controlled by a resin pressure sensor.

(A) One-stage constant setting of holding pressure by the mold internal pressure setting method (Fig. 3) (B) Multi-stage constant setting of holding pressure by the mold internal pressure setting method (Fig. 4) (C) Based on mold internal pressure setting method Multi-step setting of holding pressure and pseudo-setting between settings using a straight line or a function of some kind <Problems to be solved by the invention> By the way, in the method (A), especially optical element and warp are used. It is inconvenient to perform molding while reducing the holding pressure to prevent distortion in the vicinity of the gate, such as molded products that are easily deformed, etc., and depending on the position of the mold pressure sensor,
For example, if the sensor is installed behind the gate due to complicated mold structure restrictions, etc., the pressure transfer characteristics to the molded product will deteriorate as the gate seal progresses. Then, the hydraulic pressure suddenly rises, and at that time, the hydraulic pressure must be detected and turned off, or held at a certain level. In other words, the sensor position was limited to the runner section and the like.

In order to remedy these drawbacks, methods (B) and (C) have been proposed. In these methods, when changing the in-die pressure setting or when changing from a set value to the next set value, If you try to increase the internal pressure setting greatly, the pressure transmission characteristics to the molded product will start to deteriorate due to the increase in the viscosity of the resin, so it is impossible to predict how much hydraulic operation will correspond to the mold internal pressure setting, and the servo will Fully open, damage the mold and molding machine. On the other hand, if the setting is lowered too low, the resin pressure gets closer to T _g (glass transition point), and the viscoelastic property is different between when pushing and when pulling. The hydraulic pressure drops to zero. Therefore, in these cases, it cannot be said that the resin pressure is controlled anymore, and it is determined by the cooling state in the mold that has nothing to do with the hydraulic pressure.

In practice, the operator does not do this, so test the setting level of the resin pressure step by step by trial and error and gradually change the setting to make it optimal and make an effort while watching the waveform monitor of the resin pressure and hydraulic pressure. I had to. Furthermore, even in these setting patterns, the patterns of non-defective products differ greatly depending on the shape of the molded product.Therefore, the pattern of mold pressure of non-defective products should be repeated for each molded product while being careful not to exceed the above range. I had to test. Also, this setting becomes difficult as it approaches the final stage of the pressure waveform inside the mold, and thus requires a lot of effort and skill.

Therefore, in cases where the wall thickness, cross-sectional area, etc. of the molded product change, changes in the flow velocity of the flow front in the filling process and pressure holding process, partial changes in the pressure transfer characteristics during cooling due to the difference in wall thickness, and at the interface In order to prevent distortion and the like due to the generated stress, it is necessary to change the pressure in the time axis direction in various ways according to the shape of the molded product, instead of using a constant pressure effect model based on a simple PVT curve.

The present invention eliminates the above-mentioned drawbacks of the conventional example, and in order to obtain a molded article with higher accuracy, it is possible to perform molding using a program by mold pressure control easily without control and without requiring any skill. It is an object of the present invention to provide a control method of an injection molding machine that enables the above.

<Means for Solving Problems> A control method of the injection molding machine of the present invention for achieving the above-mentioned object will be described with reference to FIGS. 1 and 2.

The present invention relates to an injection speed program setting device for controlling a resin injection speed into a mold in a molding method of molding an injection resin by switching an injection ram 5 for injecting a resin into a mold from an injection speed control operation to a hydraulic pressure control operation. 24 and injection speed sensor 7
Injection speed servo controller 2 for controlling the injection speed by the signal from the signal and the signal from the injection speed program setter 24.
3, a hydraulic pressure program setter 18 for controlling the resin pressure into the mold, a hydraulic pressure sensor 6 for detecting the injection hydraulic pressure, a hydraulic servo controller 17 for controlling the hydraulic pressure by a signal from the hydraulic pressure sensor 6, and an in-mold Of the in-mold pressure sensor 2, the memory 15 for storing the in-mold pressure of a non-defective product as a molding condition of the molded product in a waveform set in multiple stages at each divided time in the pressure-holding step, and the in-mold pressure sensor 2 The mold internal pressure servo controller 12 that calculates a set value for controlling the injection hydraulic pressure based on the detected value and the signal of the memory 15 is provided. First, the pressure holding step after switching from the injection speed control operation to the hydraulic pressure control is performed for a plurality of hours. the division (t ₀ ~t _4), and the pressure of each divided time (P ₁ ~P ₄₎ memory 15 the mold internal pressure detected by the mold internal pressure sensor 2 when molded in as a molding condition of good
In order to start the resin injection into the mold, the injection speed program setter 24 and the injection speed servo controller 23 control the injection speed, and after the resin is injected into the mold, the signal from the in-mold pressure sensor 2 is output. Based on this, the injection speed control is switched to the hydraulic pressure control, and the pressure control process of the hydraulic pressure control using the hydraulic pressure sensor 6 and the hydraulic servo controller 17 is performed, and the memory 15 is connected to the mold internal pressure servo controller 12. Then, the detected value of the in-mold pressure sensor 2 and the molding condition, which is the target value stored in the memory, are input to the in-mold pressure servo controller 12, and a control signal is calculated for each divided time. A hydraulic signal from the hydraulic sensor 6 is input to the hydraulic servo controller 17 to control the pressure in the pressure holding process.

<Operation> First, in order to perform molding using the multistage program setting of hydraulic pressure for the pressure holding process after switching from the injection speed control operation to the hydraulic pressure control, a plurality of pressure holding processes are performed as shown in FIG. 2 (a). time _{t 0 ~t 1, t 1 ~t} 2, t 2 ~t 3, t 3 is divided into ~t _4, P ₁ a hydraulic pressure setting value for each divided time as a molding condition good, respectively, P The waveform of the mold internal pressure detected by the mold internal pressure sensor 2 when the molding is performed by setting ₂ , P ₃ and P ₄ is stored in the mold internal pressure memory 15.

Therefore, control the injection speed to start the resin injection into the mold,
After the resin is injected, molding is performed by the in-mold pressure control method, the injection speed control is switched to the hydraulic control based on the signal of the in-mold pressure sensor 2, and after the transition to the pressure-holding process, every time divided in the pressure-holding process. A precision molded product can be obtained by controlling the set value of the hydraulic pressure in the pressure holding process by the hydraulic servo controller 17 based on the detected value of the in-mold pressure sensor 2 and the molding condition of the non-defective product which is the target value from the memory 15. Trace molding conditions as good products.

By doing so, the control becomes more stable than before, and it becomes possible for anyone to easily perform molding using a program by mold internal pressure control without requiring skill.

<Example> An example of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a block diagram of an injection molding machine in which the control method of the present invention is implemented, and FIGS. 2 (a), (b), and (c) are hydraulic program settings and hydraulic pressure change waveforms, respectively, internal mold pressure waveforms during hydraulic program molding, FIG. 7 is a diagram showing a change in hydraulic pressure during in-mold pressure control.

An in-mold pressure sensor 2 for detecting the pressure of the resin is embedded in the cavity 1a (or in the flow path) of the mold 1, and the injection hydraulic pressure is detected in the hydraulic circuit of the injection ram 5 that pushes the screw 4 in the injection cylinder 3. Is provided with a hydraulic sensor 6 and a speed sensor 7 is provided on the screw 4.
In the hydraulic circuit of, the hydraulic pressure is controlled by the injection speed control → pressure control changeover switch 10 to servo valve drive servo amplifier 9
The pressure is adjusted by the servo valve 8 to a pressure proportional to the output of. The changeover switch 10 is first connected so that the speed set by the injection speed program setter 24 and the signal from the speed sensor 7 form an injection speed feedback back molding through the injection speed servo controller 23. When the fact that the pressure P ₀ set by the injection speed control → pressure control switching pressure setter 21 has been reached is detected through the in-mold pressure sensor 2 and the amplifier 11, the hydraulic pressure sensor 6 and the hydraulic servo controller 17 are connected via the first comparator 19. It is designed to switch to the used hydraulic control side.

Then, in the case of molding by hydraulic control first, the hydraulic mold internal pressure control changeover switches 13 and 14 are set to the hydraulic pressure side, the changeover switch 13 is connected to the digital internal pressure waveform memory 15, and the changeover switch 14 is set to the hydraulic pressure program. Setting device 18
Connected to, and performing molding only by the hydraulic servo controller 17 according to the set hydraulic program (hydraulic set values P _{1 to} P ₄ and time t _{1 to} t ₄ ), the molding condition of the molded product that becomes a good product is The output of the mold internal pressure sensor 2 is guided to the digital mold internal pressure waveform memory 15 via the amplifier 11 and the changeover switch 13 to store the internal mold pressure waveform. Reference numeral 17 is adapted to perform PID calculation using the output from the hydraulic sensor 6.

The mold internal pressure servo controller 12 sets the set value of the mold internal pressure, that is, the detected value of the mold internal pressure waveform and the resin pressure stored in the digital mold internal pressure waveform memory 15, that is, the setting of the hydraulic servo controller 17 rather than the output from the mold internal pressure sensor 2. A value (target value) is calculated.

The second comparator 20 switches the changeover switch 16 so that the target value of the hydraulic servo controller 17 becomes P ₅ when the hydraulic pressure reaches the value P ₅ set by the mold internal pressure control → hydraulic pressure control switching pressure setter 22.

In the above configuration, first, the hydraulic type internal pressure control changeover switches 13 and 14 are set to the hydraulic pressure side, and the hydraulic pressure program setter 18 sets the hydraulic pressure values P _{1 to} P ₄ indicated by the one-dot chain line in FIG. And the times t _{1 to} t ₄ are set, and the hydraulic servo controller 17 is used without using the mold internal pressure servo controller 12.
After the resin is melted and weighed in the injection cylinder 3, the injection speed feed back molding is performed using the speed sensor 7, the injection speed program setter 24 and the injection speed servo controller 23. When it is detected that the internal pressure of the mold ₁ has reached the pressure P ₀ set by the injection speed control → pressure control switching pressure setting device 21 (time t ₀ ), it is detected through the internal mold pressure sensor 2 and the amplifier 11 that the first comparator The changeover switch 10 is switched from the injection speed control to the hydraulic pressure control via 19 and switches to the hydraulic pressure holding process using the hydraulic pressure sensor 6 and the hydraulic servo controller 17. Meanwhile, the output from the in-mold pressure sensor 2 is the amplifier 1
1, it is guided to the digital mold internal pressure waveform memory 15 through the changeover switch 13 and stores the mold internal pressure waveform as shown in FIG. 2 (b) of the molding conditions of the molded product when a good product is made.

Next, in order to perform molding by controlling the mold internal pressure, the hydraulic mold internal pressure control changeover switches 13 and 14 are set to the mold internal pressure side, the hydraulic program setter 18 is turned off, and the digital mold internal pressure waveform memory 15 is read. Become.

Therefore, as described above, first, the injection is started by the injection speed control, and when the in-mold pressure detects the pressure P ₀ through the in-mold pressure sensor 2 and the amplifier 11, the first comparator 19 controls the changeover switch 10 to perform the injection speed control. Mold pressure control is performed by switching to mold internal pressure control.

The in-mold pressure signal (detection value of the in-mold pressure sensor 2) at the time of molding keeps a deviation from the target signal of the in-mold pressure waveform stored in the aforementioned digital in-mold pressure waveform memory 15 in the in-mold pressure servo controller 12. During the pressure step, PID calculation is performed to continuously set how much the hydraulic pressure should be set at that time, and the control signal for that is set to the changeover switch 14,
It is sent to the hydraulic servo controller 17 through 16.
The hydraulic servo controller 17 calculates the deviation between the hydraulic signal from the hydraulic sensor 6 and the set value from the mold internal pressure servo controller 12, sends it to the servo amplifier 9 through the changeover switch 10, and drives the servo valve 8 to control the hydraulic pressure. To do.

In this way, it is possible to continuously trace the in-mold pressure waveform of a good product. The hydraulic pressure waveform of the molding at the time of controlling the in-mold pressure is as shown in FIG. 2 (c), and the initial stage of injection (in this example,
Up to t ₂ ), the hydraulic pressure waveform (solid line) shown in Fig. 2 (a) changes almost the same, but at t ₃ and t ₄ , the gate seal starts and the hydraulic pressure gradually increases. Come on.

Then, when the hydraulic pressure rises, and at t ₄ , the hydraulic pressure reaches the pressure P ₅ set by the mold internal pressure control → hydraulic control switching pressure setting device 22, the second
The comparator 20 operates, the changeover switch 16 is changed over, the target value of the hydraulic servo controller 17 is changed from the set value from the mold internal pressure servo controller 12 to P ₅ , and hydraulic control is performed. When the pressure holding time ends, the cooling process is started. Move to.

It should be noted that if a good product pattern is once determined by recording the data in the digital type internal pressure waveform memory 15 on a floppy disk or the like, a good product can be molded at any time. Also,
The same control may be performed not only for injection molding but also for injection compression molding or a non-defective pattern of in-mold pressure in compression molding. Furthermore, when it is desired to make the in-mold pressure waveform a smooth curve without steps, it is possible to use a setting circuit that smoothly changes the hydraulic pressure program pattern by an integrating circuit or the like.

<Effects of the Invention> The present invention is provided with a memory for storing the mold internal pressure as a molding condition for a non-defective product as described above, and the actual internal mold pressure pattern of the non-defective product stored in the memory is used as a target value, particularly in the pressure-holding step. By adjusting the pressure in the mold for each divided time of and tracing a good product pattern, it becomes possible to easily set the program with the mold internal pressure feedback, which was difficult in the past, over the entire area of the mold internal pressure waveform. Such a molded product can be molded into a high-accuracy non-defective product, and since the mold internal pressure waveform is controlled based on the mold internal pressure pattern in hydraulic control, unlike the pseudo pattern etc., an unexpected hydraulic pressure peak It will not stand and will not damage the mold or molding machine.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an injection molding machine using a control method according to the present invention, FIG. 2 is a diagram of operation waveforms of an embodiment of the control method of the present invention, and (a) is a hydraulic program setting and hydraulic pressure. Waveform of change, (b) Waveform of mold pressure during hydraulic program molding,
(C) shows a hydraulic pressure waveform at the time of mold internal pressure control, FIG. 3 is a diagram of an operation waveform with respect to time in a conventional one-stage constant setting, (a) is a mold internal pressure waveform, and (b) is an injection hydraulic pressure waveform. 4 (a) and 4 (b) are operation waveform diagrams of the mold internal pressure and the injection hydraulic pressure in the conventional multi-stage program setting. 1 ... Mold, 1a ... Cavity, 2 ... Mold pressure sensor, 3 ... Injection cylinder, 4 ... Screw, 5 ... Injection ram, 6 ... Hydraulic sensor, 7 ... Speed sensor, 8 ... …
Servo valve, 9 ... Servo amplifier for driving servo valve, 10 ... Injection speed control → pressure control changeover switch, 1
1 ... Amplifier, 12 ... Type internal pressure servo controller, 1
3, 14 ... Hydraulic pressure control switch, 15 ...
… Digital type internal pressure waveform memory, 17… Hydraulic servo controller, 18… Hydraulic program setter, 19… First comparator, 20… Second comparator, 21 ……
Injection speed control-> pressure control switching pressure setter, 22 ... mold pressure control-> hydraulic control switching pressure setter, 23 ... injection speed servo controller, 24 ... injection speed program setter.

Claims (1)

[Claims] 1. A molding method for molding an injection resin by switching an injection ram (5) for injecting resin into a mold from an injection speed control operation to a hydraulic pressure control operation, the injection speed controlling the resin injection speed into the mold. A program setter (24), an injection speed servo controller (23) for controlling the injection speed by a signal from the injection speed sensor (7) and a signal from the injection speed program setter (24), and a resin into the mold A hydraulic pressure program setter (18) for controlling pressure, a hydraulic pressure sensor (6) for detecting injection hydraulic pressure, a hydraulic servo controller (17) for controlling hydraulic pressure by a signal from the hydraulic pressure sensor (6), An in-mold pressure sensor (2) for detecting the pressure, and a memory (15) for storing the in-mold pressure of a non-defective product as a molding condition for the molded product in a waveform set in multiple stages at each divided time in the pressure holding process. ), The detection value of the in-mold pressure sensor (2) and the memory (1
And a mold internal pressure servo controller (12) that calculates a set value for controlling the injection hydraulic pressure based on the signal of 5). First, the pressure holding process after switching from the injection speed control operation to the hydraulic pressure control is divided into a plurality of times. (t ₀ ~t _4), and stores the mold internal pressure detected by the mold internal pressure sensor (2) when molded in the divided every time pressure as the molding condition good (P ₁ to P ₄₎ in the memory (15) Then, the injection speed control by the injection speed program setter (24) and the injection speed servo controller (23) is performed to start the resin injection into the mold, and after the resin is injected into the mold, the in-mold pressure sensor (2 ), The injection speed control is switched to the hydraulic pressure control, and the process proceeds to the hydraulic pressure holding step using the hydraulic pressure sensor (6) and the hydraulic servo controller (17). ) In front It is connected to an in-mold pressure servo controller (12), and a molding condition that is a detection value of the in-mold pressure sensor (2) and a target value stored in the memory is input to the in-mold pressure servo controller (12) to divide each division. A control signal is calculated for each time, and the control signal and the hydraulic signal from the hydraulic sensor (6) are input to the hydraulic servo controller (17) to control the pressure in the pressure holding step. Control method of injection molding machine.