JPH0780897A - Injection molding machine and controlling method therefor - Google Patents

Abstract

PURPOSE:To control in-mold pressure of resin at the time of injection molding to an optimum level by packing the mold with resin by an open loop on the basis of a specific speed command value, stopping the application of pressure to the resin at a point of time when the timing of stopping the application of pressure comes, and controlling the maintenance of pressure by a closed loop when the in-mold pressure is changed to negative. CONSTITUTION:A pressure sensor 30 is disposed to a mold 21 and, for example, the in-mold pressure of resin in a runner 26 is detected. A speed command value in which the resin can reach a specific in-mold pressure in a preset period of time is found according to experiments p, and a timing from a point of time when the resin in the mold 21 is pressurized to a point of time when the application of pressure is stopped is also found according to the speed command value, thereby setting these value and timing to a control unit, respectively. The mold 21 is packed with the resin by an open loop on the basis of the speed command value and, when the timing of stopping the application of pressure comes, the application of pressure is stopped. Thereafter, when the in-mold pressure is changed to negative, the maintenance of pressure is controlled for a preset period of time so that the intended in-mold pressure is maintained by a closed loop.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding machine and a control method therefor, and more particularly to an injection molding machine and a control method therefor capable of optimally controlling a mold internal pressure during injection molding.

[0002]

2. Description of the Related Art Generally, in plastic injection molding,
Material is sent into the heating cylinder with a screw, and it is heated from the outside and mechanical internal frictional heat due to the rotation of the screw,
Melt. Then, mechanical energy is applied to the material in the molten state, and the material is injected into the mold to be filled and pressurized,
Cool to obtain a shaped article with the desired shape and quality. In this injection molding, a uniform amount of plasticized molten resin is charged into the mold with appropriate injection energy according to the structure of the mold, the filling pressure is accurately maintained, and the proper cooling temperature is maintained. It is important to cool for a suitable time.

By the way, the state function of the plastic in the injection molding process to be controlled includes the resin pressure, the resin capacity and the resin temperature as variables. When controlling such an injection molding process, it has been known that it is realistic to control the resin pressure among these variables from the feasibility of the control and the mutual relationship of these variables. Has been.

Regarding the control of resin pressure in injection molding, there is a technique disclosed in Japanese Patent Application Laid-Open No. 52-14658. In this technique, first, a pressure transducer is used to measure the resin pressure from when a molten resin is injected into a mold from a nozzle of a molding machine to when it is filled up to the cavity end and cooled and solidified. Then, for each stage of filling, holding pressure, and cooling in the injection molding process, based on the obtained measurements, find a desired necessary setting pressure within the maximum allowable range of in-mold pressure that does not cause insufficient filling or overfilling, Obtain the waveform (graph) of the in-mold pressure. During actual injection molding,
A target value is given to the controller according to the graph showing the set pressure at each time, and feedback control is performed so that the mold internal pressure becomes the target value. As a result, the method of controlling by the mold internal pressure was shown for the injection molding process which was not controlled until then.

[0005]

When the control target value is an amount that changes with time, the control target value is given by using a function of time. Generally, it is given by an exponential function or a linear function for reasons such as ease of handling. The same applies when controlling the in-mold pressure.

Further, in the feedback control, the loop gain is increased in order to speed up the response and eliminate the control deviation. Also in the case of injection molding, it is necessary to increase the loop gain for the same purpose because it is necessary to increase the production efficiency.

However, in the case of injection molding, the state of the resin in the mold greatly differs between the filling process and the pressure holding process. Therefore, if the loop gain is unnecessarily increased, there is a problem of oscillation. In this case, it is possible to deal with it by adjusting the parameter of the controller so as not to oscillate, but the adjustment is not easy and there is a problem that a great burden is imposed on the operator.

Further, if the loop gain is increased more than necessary, the characteristics of the resin and the mold will be ignored, and the filling will be forced. As a result, a peak pressure is generated even if oscillation does not occur, which causes a problem that it adversely affects the quality of the mold and the molded product.

An object of the present invention is to provide an injection molding machine capable of preventing oscillation and generation of peak pressure, filling a resin without overloading a mold, and obtaining a high-quality molded product, and its control. To provide a method.

Another object of the present invention is to provide an injection molding machine and a control method therefor capable of obtaining the conditions for performing the above-mentioned injection molding without imposing a heavy burden on the operator. .

[0011]

In order to achieve the above object, according to the present invention, a mold to be used when injection molding is performed by filling a molten resin in a mold and performing a pressure-holding process and a cooling process. For the resin, the resin is pressurized in an open loop to fill the mold based on a speed command value that is set in advance to reach the target mold pressure within the set time, and the resin is applied in the mold. When the preset pressure stop timing is reached from the time the pressure is applied, the pressure on the resin is stopped, and then when the mold internal pressure turns negative, the mold is closed loop for a predetermined time. There is provided a method for controlling an injection molding machine, which is characterized in that a holding pressure control is performed so as to maintain a target in-mold pressure on a resin inside.

The speed command value commands a filling speed at which the mold pressure can reach a value within an allowable range including the set pressure for the mold and resin to be used within a set filling time. Can be a value.

Further, the pressurization stop timing can be set as a time point at which a pressurizing time obtained in advance by an experiment has elapsed from the time point when the resin was pressed in the mold. In this case, the pressurizing time is the pressurizing time when pressurizing the resin according to the set speed command value,
The maximum value of the in-mold pressure thereby can be the pressurizing time to be a value within the allowable range including the set pressure.

According to another aspect of the present invention, in an injection molding machine having an injection mechanism for melting resin and filling it in a mold, a screw for melting resin and filling it in the mold is used. The control device includes an injection part having a pressurizing mechanism that pressurizes the screw, a control device that controls the operation of the pressurizing mechanism, and a pressure sensor that detects the pressure of the resin in the mold. At least a central processing unit and a memory unit are provided. The memory unit is a pressurizing command given to the pressurizing mechanism, and reaches a target mold pressure within a set time for a mold and resin to be used. The predetermined speed command value and the pressurization stop timing that gives the timing to stop the pressurization by the speed command value given to the pressurizing mechanism are stored in advance, and the central processing unit stores the memory unit. The speed command value read from is given to the pressurizing mechanism, the mold internal pressure output from the sensor is monitored, and the elapsed time is monitored from the time when the mold internal pressure becomes measurable. When the pressurization stop timing stored in the memory unit is reached, the pressurization mechanism is stopped, and the mold pressure is monitored to confirm that the change has become negative. Upon detection, an injection molding machine is provided, which controls the pressurizing mechanism in a closed loop so as to maintain the internal pressure of the mold at a constant value.

The control device can have a mode for obtaining a speed command value and a mode for obtaining a pressurization stop timing, in addition to a mode for performing actual injection molding. In the mode for obtaining the speed command value, the speed command value is sequentially changed until the speed command value that reaches the target mold pressure within the preset allowable range is found for the mold and resin used. , The injection can be repeated to obtain the speed command value. Further, in the mode for obtaining the pressurization stop timing, until the pressurization time by the obtained speed command value is found until the maximum value of the mold internal pressure exists within the predetermined allowable range including the set pressure, By changing the pressure stop timing in sequence and repeating injection,
The pressurization stop timing can be obtained.

In the memory unit, there is provided a test speed command value storage area for storing the speed command value used in the mode for obtaining the speed command value while sequentially updating the initial value given first and thereafter. The pressurization stop timing used in the mode for obtaining the pressurization stop timing,
It is possible to have a test pressurization stop timing storage area for storing the initial value given first while sequentially updating it thereafter.

[0017]

According to the research conducted by the present inventors, it has been found that it is important that the in-mold pressure rises up to the set pressure in the set time in the resin filling process. It has been clarified that there is no particular basis for the characteristics of the resin and the mold to make the pressure gradient in the state of linear function or exponential function, which has been conventionally performed. The present invention has been made based on the findings of the inventors.

That is, according to the present invention, the mold and the resin to be used are pressurized in an open loop with the resin on the basis of a speed command value predetermined so as to reach a target mold pressure within a set time, and the metal is used. Fill the mold. The speed command value is previously obtained by an experiment. For example, for the mold and resin used, the speed command value is sequentially changed until the speed command value that reaches the target mold pressure within a predetermined allowable range is found within the set time, and the injection is repeated, Find the speed command value that meets the conditions. This is stored in the memory, and is used when the pressurization stop timing is obtained and during the actual injection molding. The operation of obtaining the speed command value can also be performed by the present invention.

Further, the pressing of the resin is stopped at the time when the preset pressing stop timing is reached from the time when the resin is pressed in the mold. This timing is experimentally obtained in advance. For example, until the pressurization time by the obtained speed command value is found, the pressurization stop timing is sequentially changed until the maximum value of the mold internal pressure exists within a predetermined allowable range including the set pressure, The injection is repeated to obtain the pressurization stop timing that satisfies the conditions.
This is stored in the memory and used at the time of actual injection molding. Regarding the operation for obtaining this pressurization stop timing,
It is possible to carry out according to the present invention.

After the pressurization is stopped, the pressurization is continued due to the inertia or the like, and the internal load is increased to shift to the equilibrium state. Then, the mold internal pressure is monitored, and when the change becomes negative, the holding pressure control is performed in a closed loop so as to maintain the target mold internal pressure in the resin in the mold.

As described above, according to the present invention, in the region where the change in the mold pressure occurs rapidly, the control is performed in an open loop according to the speed command and the pressurization stop timing which are determined in advance. Therefore, oscillation and generation of peak pressure do not occur.

Further, during the pressure holding period, the pressure can be finely controlled by the closed loop.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view schematically showing an injection molding machine to which an embodiment of the present invention is applied.

The injection molding machine to which this embodiment is applied includes a main body 10 having a mold 21 and a mold clamping mechanism 11, and a mold 2.
Injection mechanism 40 for injecting and filling resin into 1 and applying pressure
And a control device 60 for controlling the injection mechanism 40.

The mold 21 includes a fixed mold plate 22 and a movable mold plate 2.
3 and 3. The fixed mold plate 22 is provided with a spool 25, a runner 26, and a pin gate 27. Also,
A pressure sensor 30 is arranged in the mold 21, and the runner 26
A pressure detecting pin 29 is provided at a position communicating with the. The pressure sensor 30 is connected to the runner 2 via the pressure detection pin 29.
The in-mold pressure of the resin in 6 is detected. The movable template 23 is provided with a cavity 24 communicating with the runner 26 via a pin gate 27.

The mold clamping mechanism 11 includes a fixed die plate 15 and a movable die plate 14 which sandwich the mold 21, and a mold clamping ram 1 for pressing the movable die plate 14 to perform mold clamping.
3 and a hydraulic cylinder 1 for driving the mold clamping ram 13.
2, a fixing rod 16 for fixing the hydraulic cylinder 12 and the fixed die plate 15 by sandwiching the movable die plate 14 in a displaceable manner, and a hydraulic device (not shown). The movable die plate 14 is guided and displaced by the fixing rod 16.

The injection mechanism 40 includes an injection section 41 and an injection section 4
1 and a pressure mechanism 50 for pressing the resin. The injection unit 41 includes a screw 42, a cylindrical body 43 that holds the screw 42 axially displaceable, a hopper 44 for charging resin into the cylindrical body 43, and a spool provided at the tip of the cylindrical body 43. It has a nozzle 45 for injecting resin into the mold 21 via 25, a hydraulic motor 46 for rotating the screw 42, and a heating device (not shown) arranged outside the cylindrical body 43.

The pressurizing mechanism 50 includes a cylinder 51, a piston 52 provided at the base end of the screw 42, and a servo valve 5 for controlling the amount of hydraulic oil flowing into the cylinder 51.
3 and a hydraulic device such as a hydraulic pump (not shown).
The servo valve 53 can change the flow rate of hydraulic oil according to the voltage.

The controller 60 is composed of a computer system, as shown in FIG. That is, A / C that converts the signals from the central processing unit (CPU) 61, the memory unit 62, and the pressure sensor 30 into digital signals.
A D converter 63, a D / A converter 64 for converting a command from the CPU 61 into an analog signal, an input device 65 for setting various conditions, and an output device 66 for indicating a state at the time of injection. , And a clock device 67 for measuring time output and elapsed time. In addition to this, an interface for connecting to another computer system, an external storage device, or the like can be provided.

The D / A converter 64 has a built-in latch circuit (not shown) for holding the speed command value output from the CPU 61. The speed command value latched by the latch circuit is sampled at a constant cycle, converted into an analog voltage value, and output. Here, the speed command value is set such that the mold pressure reaches the target set pressure SP at the set time ST.

The input device 65 can be composed of, for example, a keyboard having keys such as a numeric keypad, a digital switch and the like. The input device 65 can be omitted. In that case, various settings may be made in another computer system and the data may be transferred to the control device 60.

The output device 66 is composed of a display device such as a liquid crystal display or a CRT display. The output device can display a waveform diagram or the like showing changes in the mold internal pressure data at the time of injection. Further, it is also possible to display a guide or the like regarding the operation of the device and provide it for the convenience of the operator.

Next, the operation of this embodiment will be described.
In the injection molding by the control method of the present embodiment, prior to the actual molding, first, the speed command value for determining the injection speed of the screw 42 for the mold and the resin to be used (speed command value determination mode) and the screw are determined. The pressurization stop timing for stopping pressurization of 42 is determined (pressurization stop timing determination mode). These are determined by experiment. Then, using those results, the actual injection molding (running mode) is performed. Hereinafter, these will be described in order.

First, the mold 21 is mounted on the molding machine main body 10, hydraulic pressure is introduced into the cylinder 12, and the movable die plate 14 is pressed toward the fixed die plate 15 by the die clamping ram 13 to move the movable die plate. 23 is brought into close contact with the fixed template 22. In this state, conditions other than injection are set.

Further, in the control device 60, the mold 21 is filled with the resin via the input device 65, and the mold 21 is filled with the set pressure SP which is the set mold internal pressure for maintaining a constant pressure. At this time, data of a set filling time ST which is a preset required time and a holding pressure time HT which is a time for keeping the in-mold pressure of the resin after filling constant are set. Then, before collecting the test data, the resin is put into the hopper 44 and the molding is tried several times to stabilize the state of the system.

After that, the above-mentioned injection for data collection is performed. This injection is performed under the control of the control device 60. That is, the control device 60 determines the condition, and if the condition is acceptable, the data is stored in the memory unit 6.
Store in 2. If it fails, correct the conditions based on the data, perform test molding again, and repeat until it passes.

FIG. 3 is a flow chart showing the procedure of speed command value setting operation of the CPU 61.

The CPU 61 first accepts the setting of initial conditions. That is, at the set pressure SP and the set filling time ST set above, the initial value of the speed command value defining the displacement speed of the screw of the injection unit 41 and the pressurization to the screw 42 are stopped, that is, the servo is stopped. The initial value of the pressurization stop timing SZT, which is the timing for setting the command to the valve 53 to 0, is set. (Step 301). This value is input from the input device 65,
It is stored in the test speed command value storage area and the test pressurization stop timing storage area of the memory unit 62.
A permissible range ± α of the internal pressure of the mold with respect to the set pressure SP and a permissible range ± β of the maximum value of the internal pressure with respect to the set pressure SP are given in advance and written in the program. It should be noted that this may be set at the time of initial setting. The values of α and β are determined according to the desired accuracy of injection molding. In this embodiment, both are set to 5%.

Upon injection, first, the resin charged into the hopper 44 is rotated in the direction of the nozzle 45 by rotating the screw 42 by the hydraulic motor 46 and stirring,
At this time, a molten state is achieved by heating with a heating device (not shown). As a result, the molten resin accumulates on the nozzle 45 side of the cylindrical body 43. Along with this, the screw 42 is retracted in the direction of the cylinder 51. In this state, the rotation of the screw 42 is stopped.

First, the CPU 61 gives an instruction to start injection based on the set initial velocity command value (step 30).
2). That is, the CPU 61 outputs the speed command value to the servo valve 63 via the D / A converter 64. Specifically, the speed command value is given in the form of an operating voltage value of the servo valve 53. In response to this, the servo valve 53 operates so that the flow rate of the hydraulic oil becomes a flow rate according to the operating voltage value.

After that, the CPU 61 takes in the measured value sent from the pressure sensor 30 and monitors whether or not the mold internal pressure becomes positive. This is because when the resin is injected into the mold 21, there is a delay in reaching the runner portion 26 where the pressure detection pin 29 is located. Here, the fact that the in-mold pressure becomes positive does not mean that the sign has any meaning, but means that the value which was 0 until then has a certain value. When the mold pressure becomes positive, C
After that, the PU 61 fetches the pressure value at a constant cycle, fetches the time at the time of fetching from the clock device 67, and stores them in the memory unit 62 in association with each other (step 303). This value is used as monitoring data in the running mode when the condition of this time is adopted. The stored time is represented by the elapsed time with reference to the time when the mold internal pressure becomes positive. Also,
These values can be displayed on the display screen of the output device 66. The display is performed, for example, in the form of a graph as shown in FIG.

Next, the CPU 61 monitors the output from the sensor 30 and stops the pressurization of the screw 42 when the mold internal pressure reaches the set pressure SP (step 304). That is, with respect to the D / A converter 64, the servo valve 53
Is output as a command value, for example, "0".
When the output value from the D / A converter 64 changes to the voltage value indicating the neutral position, the servo valve 53 receives this and shifts to the neutral state, and stops the pressurization of the screw 42.

Next, the CPU 61 reads the in-mold pressure value at that time from the memory unit 62 at the timing when the set time ST elapses (hereinafter referred to as ST elapse time), and the pressure becomes (the set pressure SP ± α ) Is included in the range (step 305). When the mold internal pressure value at the time ST has passed is within this range, the speed command value used this time is adopted, and then the pressurization stop timing determination mode is entered. The adopted value is stored in the set speed command value storage area of the memory unit 62 as the speed command value in this injection.

On the other hand, the mold internal pressure value at the time of ST is
If not included in this range, the speed command value is reset and the above procedure is repeated. In the resetting, when the time to reach the set pressure is short, the speed command value is decreased, and when the time is long, the speed command value is increased. The reset speed command value is stored in the test speed command value storage area of the memory unit 62, and the initial value is updated. Such a procedure is repeated until a value that can be adopted is obtained in step 305.

Here, the above steps 305 and 306.
The processing procedure in step 1 will be described in more detail with reference to FIG.

In FIG. 5, the CPU 61 determines the mold internal pressure value CVP (ST) at the time ST has elapsed,

[0047]

## EQU1 ## It is determined whether or not | CVP (ST) -SP | <α (1) is satisfied (step 305). If it is satisfied, the test speed command value PSV (test) is stored in the corresponding area of the memory as the set speed command value (step 307).

If the condition of the expression (1) is not satisfied, whether the mold pressure value is smaller than the minimum allowable range of the set pressure SP,
That is, whether or not it is under is checked by the equation (2) (step 3061).

[0049]

[Equation 2] (CVP (ST) + α) <SP (2) If under, the speed command value at that time is PSV (unde
r) is stored in the PSV (under) storage area of the memory unit 62 (step 3062). Then, in this test, it is determined whether or not it has been over in the past by checking the PSV (over) storage area of the memory unit 63 (step 3063). If it has never been over in the past, a predetermined change amount is set as ΔPSV, and a new speed command value PSV (new) is calculated from the following formula for the test speed command value PSV (test).
Is determined (step 3064).

[0050]

## EQU00003 ## PSV (new) = PSV (test) +. DELTA.PSV (3) On the other hand, when it is determined in step 3063 that the past has been exceeded, the CPU 61 causes the PSV
Using (test) and PSV (over),
A new speed command value PSV (new) is determined (step 3065).

[0051]

## EQU4 ## PSV (new) = (PSV (test) + PSV (over)) / 2 (4) The test is performed again with this new speed command value (step 302).

When it is over at step 3061, the speed command value at the time of over is stored in the corresponding area of the memory unit 62 as PSV (over) (step 3066). Then, it is determined whether the PSV (unde
r) The area is examined and judged (step 3067). Then, if it has never been under in the past, the predetermined change amount is set as ΔPSV, and the test speed command value P is set.
For SV (test), a new speed command value PSV (new) is determined by the following equation (step 3068).

[0053]

## EQU00005 ## PSV (new) = PSV (test)-. DELTA.PSV (5) On the other hand, in step 3067, when it is determined that there has been an undershoot in the past, the CPU 61 causes PS
A new speed command value PSV (new) is determined by the following equation using V (test) and PSV (under) (step 3069).

[0054]

## EQU6 ## PSV (new) = (PSV (test) + PSV (under)) / 2 (6) The test is performed again with this new speed command value (step 302).

Next, the setting of the pressurization stop timing for stopping the pressurization of the screw 42 will be described. The pressurization stop timing is set after the speed command value is determined as described above. First, the resin is in a molten state,
Injectable. The CPU 61 performs injection using the speed command value PSV determined by the above procedure (step 601). Initially set screw 4
When the pressurization stop timing SZT of 2 is reached, the servo valve 53 is set to the neutral position and the operation of the screw 42 is stopped (step 602). Further, after instructing the injection, the CPU 61 takes in the measured value sent from the pressure sensor 30 and monitors whether or not the mold internal pressure becomes positive. When the in-mold pressure becomes positive, the CPU 61 thereafter fetches the pressure value at a constant cycle, fetches the time at the time of fetching from the time measuring device 67, and stores them in the memory unit 62 in association with each other (step). 603). This value is used as monitoring data in the running mode when the condition of this time is adopted. The stored time is represented by the elapsed time with reference to the time when the mold internal pressure becomes positive. Further, these values can be displayed on the display screen of the output device 66. The display is performed, for example, in the form of a graph as shown in FIG. 7 or 8.

The CPU 61 monitors whether or not the pressure holding time HT has elapsed. Here, the holding pressure time HT is calculated from the set filling time ST. When the holding time HT elapses, CP
The U 61 checks the in-mold pressure data stored in the memory unit 62 and determines whether the maximum value is within the range of (SP ± β) (step 605). When the maximum mold internal pressure value falls within this range, the screw pressurization stop timing SZT used this time is stored in the set stop timing storage area of the memory unit 62 as data to be used for actual injection molding.

On the other hand, when the maximum mold internal pressure value is not within this range, the stop timing is reset and the above procedure is repeated. In resetting, if the maximum value is higher than the above range, the stop timing is advanced, and if the maximum value is lower than the above range, the stop timing is delayed. The reset stop timing is stored in the test stop timing storage area of the memory unit 62, and the initial value is updated. Such a procedure is repeated in step 605 until a value that can be adopted is obtained.

Here, the above steps 605 and 606 are performed.
The processing procedure in step 1 will be described in more detail with reference to FIG.

In FIG. 9, the CPU 61 determines the mold pressure value CVP (max) within the pressure holding time,

[0060]

[Equation 7] | CVP (max) -SP | <β (7) It is determined whether or not (7) is satisfied. If satisfied, pressurization stop timing for testing SZT (test)
Is stored in the corresponding area of the memory as the set pressurization stop timing (step 607).

When the condition of the expression (7) is not satisfied, whether the mold pressure value is smaller than the minimum allowable range of the set pressure SP,
That is, whether or not it is under is checked by the equation (8) (step 6061).

[0062]

[Equation 8] (CVP (max) + β) <SP (8) If under, pressurization stop timing at that time is SZ
As T (under), SZT (und
er) storage area (step 6062). Then, in this test, it is determined whether or not the memory has been over in the past in the SZT (ov
er) The storage area is checked to make a determination (step 6063).
If it has never been over in the past, a predetermined change amount is set as ΔSZT, and a new pressurization stop timing SZT (new) is determined by the following formula for the test pressurization stop timing SZT (test). Yes (Step 60)
64).

[0063]

## EQU00009 ## SZT (new) = SZT (test) +. DELTA.SZT (9) On the other hand, when it is determined in step 6063 that the past overtime has occurred, the CPU 61 causes the SZT
Using (test) and SZT (over),
A new pressurization stop timing SZT (new) is determined (step 6065).

[0064]

SZT (new) = (SZT (test) + SZT (over)) / 2 (10) At this new pressurization stop timing, the test is performed again (step 602).

When step 6061 is over, the pressurization stop timing at the time of over is SZT (ove
r) is stored in the corresponding area of the memory unit 62 (step 6066). Then, the SZ of the memory unit 62 is checked to see if it has ever been under.
The T (under) area is examined and determined (step 606).
7). Then, if it has never been under in the past, a predetermined change amount is set as ΔSZT, and a test pressurization stop timing SZT (test) is newly calculated by the following equation. Is determined (step 6068).

[0066]

SZT (new) = SZT (test) −ΔSZT (11) On the other hand, when it is determined in step 6067 that the underflow has occurred in the past, the CPU 61 causes the SZT
Using T (test) and SZT (under), a new pressurization stop timing SZT (new) is determined by the following equation (step 6069).

[0067]

SZT (new) = (SZT (test) + SZT (under)) / 2 (12) At this new pressurization stop timing, the test is performed again (step 602).

By the above procedure, the speed command and the pressurization stop timing are set for the mold and resin used in the injection molding machine. Using this set value, actual injection molding is performed. Next, this will be described.

FIG. 10 shows an operation flowchart of the control device during actual injection molding.

First, as in the test, the resin is melted and prepared for injection. In this state, the CPU 61
Reads the speed command value data obtained in the above test from the memory unit 62 (step 1001). Then, the speed command value is output to the servo valve 53 to start injection (step 1002). To the cylinder 51 of the pressurizing mechanism 50, the actuation is sent from the hydraulic pump within the drawing via the servo valve 53. As a result, screw 4
2 presses the inside of the cylinder 43 toward the nozzle 45. Then, the molten resin accumulated in the cylindrical body 43 is discharged from the nozzle 45.
Is injected into the mold 21.

Then, the CPU 61 monitors the measured value of the in-mold pressure from the pressure sensor 30. However, at this point, the control is based on open loop. Then, when the mold pressure becomes positive, time measurement is started (step 100).
3). That is, the CPU 61 reads out the pressurization stop timing SZT of the screw 42 from the memory unit 62, sets SZT in the timer 67, and activates it as a timer.

Further, the CPU 61 compares the mold internal pressure data accumulated in the memory at the time of the test after the mold internal pressure becomes positive with the data currently being measured. A warning is displayed on the screen (step 1004). In this case, if the deviation is abnormally large due to the influence of disturbance or the like, a warning is given and the operation is stopped. Note that the warning may be an alarm sound, a message, or the like when the sound device is included.

The CPU 61 monitors the output of the time measuring device 67, and when a signal indicating that the elapsed time has reached SZT is output from the time measuring device 67, the D / A to stop the pressurization of the screw 42. "0" is set in the converter 64 as a speed command value (step 1005). As a result, the servo valve 53 is set to the neutral position and the pressurization of the screw 42 is stopped. After that, due to the elastic energy of the remaining resin and the inertia of the screw 42, the pressurization is continued and the load on the system is increased.
The velocity decays and the pressure-holding process naturally shifts.

After that, the CPU 61 takes in the measured value from the pressure sensor 30 and monitors whether the change gradient of the mold internal pressure becomes negative (step 1006). That is, if the change gradient of the mold internal pressure does not become negative, the screw position is maintained as it is and the pressure monitoring is continued (step 1
007). On the other hand, when it becomes negative, the process moves to the mold pressure control by the closed loop (step 1008). The in-mold control by the closed loop is performed by, for example, proportional control. Thereafter, the control is stopped at the time when the predetermined pressure holding time HT has elapsed.

FIG. 11 shows changes in the mold pressure in this example. FIG. 11 is an example of a display screen of the output device 66.

After that, the process shifts to the cooling process to cool the molded product. After cooling, the mold clamping mechanism 11 is activated, the movable die plate 14 is retracted, the movable mold plate 23 is moved, and the molded product is taken out from the kana mold 21.

At the time when the cooling process is performed, preparation for the next injection is started. That is, the resin is charged from the hopper 44 and the molten resin is accumulated in the vicinity of the nozzle 45 as described above. Then, after the mold 21 is mounted again, injection is performed by the above-mentioned procedure. Next, a specific example of injection molding to which the above embodiment is applied will be described. In this example, a mold for molding a lens having a volume of 4 cm ³ is used as the mold 21, and polypropylene is used as the resin.

In the first example, the set pressure SP is 250 kg /
cm ² and the set filling time ST is 0.5 sec,
Test injection molding was performed in the above-described procedure, and a servo valve voltage of 750 mV and a pressurization stop timing SZT of 0.3 sec were obtained as a speed command value. Therefore, when the pressure holding time HT was set to 2 sec and injection molding was performed, the results shown in FIGS. 12 (A) and 12 (B) were obtained. That is, as shown in FIG. 12A, the CPU instructs the servo valve to apply a voltage of 750 mV, and then outputs about 0.6
After a lapse of sec, it was detected that SZT became positive, and after 0.3 sec, the pressurization to the screw was stopped. Here, after a lapse of about 0.6 sec after the voltage of the servo valve dropped, the CPU detected that the change in the mold pressure became negative, and shifted to the control by the closed loop. As a result, the servo valve was finely driven. The change in the mold pressure at this time is shown in FIG.
It shows in (B). The maximum mold pressure in this example is 24
It was 0 kg / cm ² . Here, TV is the target value, MV
Indicates an actual measurement value. In this example, a good quality product was obtained.

FIG. 13 shows that the set pressure SP is 450 kg / cm.
² , the set filling time ST was set to 0.4 sec, and test injection molding was performed in the above-described procedure to obtain a servo valve voltage of 750 mV as a speed command value and a pressurization stop timing SZT of 0.3 sec. Then, when the pressure holding time HT was set to 2 sec and injection molding was performed, the results shown in FIGS. 13 (A) and 13 (B) were obtained. That is,
As shown in FIG. 13 (A), the CPU detected that SZT became positive, and thereafter, after 0.3 sec had elapsed, stopped pressing the screw. Here, after about 0.3 sec has elapsed after the voltage of the servo valve has fallen, control by a closed loop is performed,
The servo valve was finely driven. The change in the mold pressure at this time is shown in FIG. Where TV is the target value, M
V represents an actually measured value. In this example, a good quality product was obtained.

As a comparative example, using the same mold and resin, the set pressure SP was set to 450 kg / cm ² , the target value of the set pressure was given by a linear function, and the internal pressure of the mold when feedback control was performed was performed. The changes are shown in FIG. 14
In the example, it can be seen that the measured value MV vibrates with respect to the target value TV.

In the above-mentioned embodiment, an example of one kind of resin and mold is described, but the present invention can be applied to various kinds of resin and mold. Further, it is possible to obtain the speed command value and the pressurization stop timing by the above-mentioned procedure for a plurality of types of resins and molds, and store this data in the memory unit. In this case, it is preferable to store the data by adding a reference code to each combination. As a result, the necessary data can be retrieved by inputting the reference code at the time of actual injection molding. As the reference code, for example, one associated with a product number, an order number, a lot number, or the like can be used.

[0082]

As described above, according to the present invention,
It is possible to prevent the generation of oscillation and peak pressure, to fill the resin without overloading the mold, and to perform injection molding in which a high-quality molded product can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing an injection molding machine to which an embodiment of the present invention is applied.

FIG. 2 is a block diagram showing a hardware system configuration of a control device used in this embodiment.

FIG. 3 is a flowchart showing a speed command value setting operation procedure of the control device.

FIG. 4 is an explanatory diagram showing a display example of a change in mold pressure during an experiment for obtaining a speed command.

FIG. 5 is a flowchart showing a procedure for resetting a speed command value of the control device.

FIG. 6 is a flowchart showing a procedure for setting a pressurization stop timing of the control device.

FIG. 7 is an explanatory diagram showing a display example of a change in mold pressure when obtaining pressurization stop timing.

FIG. 8 is an explanatory diagram showing a display example of a change in mold pressure when obtaining pressurization stop timing.

FIG. 9 is a flowchart showing a procedure for resetting the pressurization stop timing of the control device.

FIG. 10 is a flowchart showing an operation procedure of a control device in actual injection molding.

FIG. 11 is an explanatory diagram showing a display example of change in mold pressure during actual injection molding.

FIG. 12 is a graph showing changes in servo valve voltage and in-mold pressure in a first specific example of actual injection molding.

FIG. 13 is a graph showing changes in servo valve voltage and in-mold pressure in a second specific example of actual injection molding.

FIG. 14 is a graph showing changes in mold pressure in conventional closed loop control.

[Explanation of symbols]

10 ... Injection molding machine main body, 11 ... Mold clamping mechanism, 21 ... Mold, 23 ... Movable template, 22 ... Fixed template, 24 ... Cavity, 26 ... Runner, 30 ... Pressure sensor, 40 ... Injection mechanism, 41 ... Injection part, 42 ... Screw, 43 ... Cylindrical body, 4
4 ... Hopper, 45 ... Nozzle, 46 ... Hydraulic motor, 50 ...
Pressure mechanism, 51 ... Cylinder, 52 ... Piston, 53 ... Servo valve, 60 ... Control device, 61 ... Central processing unit (C
PU), 62 ... Memory unit, 63 ... A / D converter,
64 ... D / A converter, 65 ... Input device, 66 ... Output device, 67 ... Timing device.

Claims (6)

[Claims] 1. When a molten resin is filled in a mold, and injection molding is carried out through a pressure-holding process and a cooling process, the mold and the resin to be used are designed to reach a target mold pressure within a set time. The open loop is used to pressurize the resin to fill the mold based on the speed command value set in advance, and the preset pressurization stop timing is reached from the time when the resin is pressed in the mold. At this point, the pressurization to the resin is stopped, and when the mold internal pressure turns negative after that, the holding pressure control is performed to keep the target internal mold pressure against the resin in the mold in a closed loop for a predetermined time. A method for controlling an injection molding machine, the method comprising: 2. The speed command value according to claim 1, wherein the mold pressure reaches a value within a permissible range including the set pressure of the mold and the resin to be used within a set filling time. A method for controlling an injection molding machine, which is a value that commands the speed of filling that can be performed. 3. The pressurization stop timing according to claim 2, wherein the pressurization stop timing is a time point at which a pressurization time previously obtained by an experiment has elapsed from the time point when the resin was pressurized in the mold. Is the pressurizing time when pressurizing the resin according to the set speed command value, and the maximum value of the in-mold pressure thereby becomes the value within the allowable range including the set pressure. A method of controlling an injection molding machine. 4. An injection molding machine having an injection mechanism for melting resin and filling it in a mold, wherein an injection section having a screw for melting resin and filling the mold, and a screw, A pressure mechanism that performs pressure, a control device that controls the operation of the pressure mechanism, and a pressure sensor that detects the pressure of the resin in the mold are provided. The control device includes at least a central processing unit and a memory unit. , The memory unit is a pressurizing command given to the pressurizing mechanism, and has a speed command value which is predetermined so that the target mold pressure is reached within a set time for the mold and resin used. , A pressurization stop timing for giving a timing for stopping pressurization by the speed command value given to the pressurizing mechanism is stored in advance, and the central processing unit adds the speed command value read from the memory unit. The pressure is applied to the pressure mechanism and the internal pressure of the mold output from the sensor is monitored. From the time when the internal pressure of the mold becomes measurable, the elapsed time is monitored and the elapsed time is stored in the memory unit. When the stop timing is reached, the pressurizing mechanism is stopped,
And when the mold pressure is monitored and it is detected that the change has become negative, it is closed loop to the pressurizing mechanism.
An injection molding machine characterized by controlling the in-mold pressure to be maintained at a constant value. 5. The control device according to claim 4, wherein the control device has a mode for obtaining a speed command value and a mode for obtaining a pressurization stop timing, in addition to a mode for performing actual injection molding. In the mode, for the mold and resin used, the speed command value is sequentially changed and injection is repeated until the speed command value that reaches the target mold pressure within the predetermined allowable range is found within the set time. In the mode for obtaining the speed command value and for determining the pressurization stop timing, the maximum value of the mold internal pressure is within the predetermined allowable range including the set pressure, and the pressurizing time by the obtained speed command value The injection molding machine is characterized in that the pressurization stop timing is sequentially changed and injection is repeated until the pressurization stop timing is found until is found. 6. The memory unit according to claim 5, wherein the memory unit is for a test for storing a speed command value used in a mode for obtaining the speed command value while sequentially updating an initial value given first. A speed command value storage area, and a test pressurization stop timing storage area for storing the pressurization stop timing used in the mode for obtaining the pressurization stop timing while sequentially updating the initial value given first. An injection molding machine characterized by having.