JPH0361018A - Automatic control method and its device for injection molding - Google Patents

Abstract

PURPOSE:To contrive confirmation of gate sealing point of time by measuring a speed change of a supersonic wave of resin, by a method wherein reflection of the supersonic wave dispatched toward the resin in a gate is detected by making use of a supersonic probe. CONSTITUTION:When a pulse is dispatched from a supersonic flaw detector 16 along with starting of injection into a mold 2, dispatching of a supersonic wave and receiving of a reflecting wave are performed by a supersonic probe 9. A speed change of the supersonic wave is measured based on the reflecting wave from the supersonic prode 9 and applied to a comparator 17 in the supersonic flaw detector 16. Comparative operation of a set up speed valve and a speed value from the supersonic flaw detector 16 is performed in the comparator 17 and a control signal is sent out to a signal generator 18 at a gate sealing time when resin is solidified. An instruction signal instructing dwell release to a controller 19 is sent out with a control signal from the comparator 17, in the signal generator 18. A hydraulic device is actuated based on the instruction signal, pressure of a hydraulic ram mechanism 14 is decompressed and dwell of an injection molding apparatus 1 is released in the controller 19.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an automatic injection molding control method and apparatus.

(Prior Art) Conventionally, as an automatic control method for injection molding, a method using mold internal pressure pattern control is known, for example, as described in Japanese Patent Application Laid-open No. 198217/1983.

In this control method, in an injection control circuit consisting of an injection filling process and a holding pressure filling process, switching from the injection filling process to the holding pressure filling process is performed when the resin pressure in the mold reaches a predetermined value. At the same time, the hydraulic pressure of the injection cylinder is feedback-controlled so that the same pressure during the holding pressure filling process follows a predetermined pattern over time. In other words, the resin pressure inside the mold during the holding pressure filling process is directly detected, compared with the set mold internal pressure pattern over time, and if it deviates from the mold internal pressure pattern, the injection cylinder hydraulic pressure is controlled and the mold is The molded product is designed to hold pressure according to the internal pressure pattern, even if the resin temperature in the injection cylinder, mold temperature, and resin front fluctuate at each point 4σ and the cavity pressure fluctuates. The aim is to prevent variations in weight.

(Problem to be Solved by the Invention) However, the injection molding control method in the above-mentioned conventional technology only performs control based on the mold internal pressure pattern by keeping the pressure holding time constant in the pressure holding process, so the molded product There are still variations in size and weight, making it insufficient for application to precision molded products that require high accuracy.

That is, if the pressure holding time is constant, the holding pressure may be released before the resin is completely solidified. This causes the resin filled into the mold to flow back through the gate, resulting in variations in product weight and quality deterioration. Conversely, if a holding pressure is forcibly applied in a so-called gate-sealed state in which the resin in the gate portion is cooled and solidified, the molded product itself may be deformed or warped. It goes without saying that it is best to release the holding pressure when the gate is sealed, but in order to know the timing of releasing the holding pressure, we have molded a sample in advance and measured the weight change. It is determined by the gravimetric method, etc., which measures Generally, this pressure holding time is set constant, but the state of cooling and solidification of the resin in the gate part varies depending on the resin temperature in the injection cylinder, mold temperature, and resin rhondo. Therefore, the gate sealing time differs for each injection shot, causing variations in the dimensions and weight of the molded product.

The present invention has been made to solve the above problems, and its purpose is to improve the dimensional and weight accuracy of molded products and to provide an automatic control method and apparatus for injection molding that enables high-precision molding. Our goal is to provide the following.

(Means for Solving the Problems) The automatic control method for injection molding of the present invention is an injection molding control method for controlling the resin pressure in an injection mold in a pressure-holding filling process by adjusting it to a predetermined mold internal pressure pattern. An ultrasonic probe installed near the gate of the mold continuously detects changes over time in the reflected waves of ultrasonic waves emitted toward the resin inside the gate, and measures them as changes in speed or amplitude. The present invention is characterized in that the time of gate sealing is determined by arithmetic processing from the measured value, and the holding pressure of the mold internal pressure pattern is released based on the signal that reaches the gate sealing time.

Further, the automatic control device for injection molding of the present invention is an injection molding control device that feedback-controls the hydraulic pressure of the opening cylinder so that the resin pressure in the injection mold during the holding pressure filling process becomes a predetermined mold internal pressure pattern. , by detecting the reflected waves of the ultrasonic waves emitted by the ultrasonic probe installed near the gate of the mold toward the resin inside the gate, the melted state of the resin can be detected. A measuring means for constantly measuring speed changes or amplitude changes of ultrasonic waves up to the solidification state, a calculating means for calculating a gate sealing point from the measurement value measured by the measuring means, and a result of the calculating means being output as the gate sealing point. The present invention is characterized in that it is equipped with a controller that releases the holding pressure when the pressure is released.

In the present invention, the mold internal pressure pattern used is one in which the pressure in the mold obtained during molding of a good product is set as a reference waveform over time, and a pattern in which no command to release holding pressure is issued is particularly preferred.

As an ultrasonic probe, a vibrator made of crystal, ceramic, lithium sulfate, or the like is generally used, and is connected to a measuring means such as an ultrasonic flaw detector having a pulse reception/transmission function.

In addition, as a calculation means for calculating the gate seal time,
A comparator is used to calculate the measured value obtained by measuring the velocity change from the reflected wave using the measuring means, and a differential comparator is used to calculate the measured value obtained by measuring the amplitude change from the reflected wave. A vessel is used. The comparator performs a comparison calculation with the preset ultrasonic velocity value obtained during molding of a good product, and the differentiator calculates the reflected wave of the ultrasonic wave as an amplitude value derived over time. The minimum point is calculated by performing differentiation once.

(Function) Using an ultrasonic probe installed near the gate of the injection mold, the reflection of the ultrasonic waves emitted toward the resin inside the gate is detected, thereby changing the resin from a molten state to a solidified state. It is possible to measure changes in velocity or amplitude of ultrasonic waves. This measured value is calculated by a calculation means,
When the set condition is met, it is output as the gate seal time.

In other words, in the process in which the resin filled in the gate part changes from a molten state to a solidified state, the speed or amplitude of the reflected ultrasound wave detected by the ultrasonic probe changes, so the state of the change can be determined. The gate seal point can be confirmed by checking .

When the above-mentioned gate sealing point is reached, the holding pressure controlled based on the reference wave of the mold internal pressure butterfly control is released. At this time, there is no possibility that the resin will flow back from the gate or that holding pressure will be forced into the mold. (Blank below) (Embodiment) An embodiment of the automatic control device for injection molding of the present invention will be described with reference to the drawings.

FIG. 1 shows an injection molding apparatus to which an automatic control device for injection molding according to the present invention is applied.

In the figure, reference numeral 1 denotes an injection molding machine, in which resin stored in a hopper 11 is sequentially supplied into an injection cylinder 12, and is melted while being sent to the tip of the injection cylinder 12 by the rotation of a screw 13. The resin is injected from the nozzle 1a at the tip of the injection cylinder 12 by advancing the resin with a hydraulic ram mechanism 14.

2 is the mold, which is a direct gate type gate bush 4
It consists of a stationary mold 21 in which a mold is attached, and a movable mold 22 having a cavity 23. The fixed side mold 21 is attached to the injection tip of the nozzle 1a of the injection molding machine 1, and the movable side mold 22 is arranged opposite to the fixed side mold 21, and is clamped by a mold clamping device 16 such as a hydraulic cylinder. It can be moved back and forth in the figure.

A pressure sensor 3 that detects the resin pressure in the cavity 23 is provided in the movable mold 22 via an eject turbine 24, and the pressure horn sensor 3 controls the operation of the hydraulic ram mechanism 14 via an amplifier 6 based on the mold internal pressure. It is connected to a controller 19 which performs feedback control based on the pattern.

A gate 5, which is a resin flow path, penetrates through the gate bush 4 from the nozzle 1a side to the cavity 23 side, and as shown in an enlarged view in FIG. An aluminum rod 7 is buried flush with the side surface of the flow path. An ultrasonic probe 9 is attached to the rear end surface of the Al ξ rod 7 via a coupling agent 8. The ultrasonic flaw detector 16 is connected to the ultrasonic probe 9, and the ultrasonic flaw detector [16
For example, the ultrasonic probe 9 emits a pulse every 0.01 to 1 second, and the ultrasonic flaw detector 16 transmits a pulse of 5M1l.
It emits ultrasonic waves of z and detects the reflected waves.

Although not shown, the ultrasonic flaw detector 16 also detects ultrasonic waves from the molten state to the solidified state of the resin based on the reflected waves of the ultrasonic waves received by the ultrasonic probe 9. Measuring means for measuring speed changes at any time is provided, and this measuring means is configured by software.

The output of the ultrasonic flaw detector 16 indicates an ultrasonic velocity value corresponding to the state of the resin filled in the gate 5, and is used as a calculation means in which the ultrasonic velocity value obtained during molding of a non-defective product is preset. It is connected to a comparator 17, and the output of the comparator 17 is led to a signal generator 18 which sends out an instruction signal for releasing the holding pressure based on the led signal.

The output of this signal generator 18 is led to a controller 19 of the injection molding machine 1. Based on the signal from the signal generator 18, the controller 19:
The holding pressure of the injection molding machine 1, which is controlled based on the above-mentioned mold internal pressure pattern, is released.

For example, 5 MHz ultrasonic waves (pulse waves) emitted from the ultrasonic probe 9 every 0.01 seconds are transmitted to the interface 71 between the resin 10 filled in the gate 5 and the aluminum rod 7, and the resin 10.
is reflected at the boundary surface 51 between the gate 5 and the side surface of the flow path opposite to the aluminum rod 7 (the upper side surface in the drawing), and the reflected wave passes through the aluminum rod 7 again to the ultrasonic probe 9. It is meant to be guided. The reflected waves of the ultrasonic waves received by the ultrasonic probe 9 are as shown in FIGS. 3 and 4.

Here, FIG. 3 is a waveform diagram of the reflected wave when the gate 5 is not filled with the resin 10, and FIG. 4 is a waveform diagram of the reflected wave when the gate 5 is filled with the resin 10. be. That is, FIG. 3 shows the transmission pulse 3 when the resin is not filled.
The state of the -order echo wave 31 and the secondary echo wave 32 from the surface (front end surface) of the aluminum rod 7 with respect to 0 is shown. In addition, FIG. 4 shows a −-second echo wave 34 from the surface of the aluminum rod 7, an interface echo wave 35 from the boundary surface 51, and a second echo wave 35 from the surface of the aluminum rod 7 in response to the transmitted pulse 33 when the resin is filled. The state of the secondary echo wave 36 is shown.

Each echo wave shown in FIG. It is guided to the ultrasonic flaw detector 19 by passing through the probe.

Among these guided echo waves, the boundary surface echo wave 35 is
When the resin 10 filled in the gate 5 is solidified from a molten state, a -order echo wave 34 and an interface echo wave 35 are generated.
Since the time interval T changes, the −th echo wave 34
and the boundary surface echo wave 35 using the ultrasonic flaw detector 1.
9, and the speed of the reflected wave is calculated in real time from this digital value and the width of the gate portion where the ultrasonic probe 9 is provided. However, the width of the gate 5 portion is inputted in advance.

FIG. 5 shows the velocity values of the reflected waves determined in this way. In the figure, at time t1 when the molten resin is filled into the mold, the speed of the reflected wave is approximately 1100 m/
sec, and as the resin gradually solidifies from time t1, the speed of the reflected wave increases substantially linearly, and reaches approximately 2500 m/sec at time tz when the resin solidifies (that is, at the time of gate sealing).

The velocity value of the reflected wave obtained in this way is led to the comparator 17. The comparator 17 compares the velocity value of the guided reflected wave with a preset velocity value of the ultrasonic wave obtained during molding of a non-defective product. In this case, since 2500 m/sec is set as the velocity value of the ultrasonic wave obtained during molding of a non-defective product, the comparator 17 indicates that the signal generator 18 Sends control signals to.

The signal generator 18 uses the control signal from the comparator 17 to activate the controller 19 at gate seal time L2.
Sends an instruction signal instructing to release the holding pressure. The controller 19 operates a hydraulic device (not shown) based on this instruction signal to reduce the pressure of the hydraulic ram mechanism and release the pressure holding of the injection molding machine 1.

In the above embodiment, the gate on which the ultrasonic probe 9 is provided is a direct gate, but it may also be a film gate, for example. The position where the ultrasonic probe 9 is provided is not particularly limited as long as it is near the gate, and may be provided, for example, from the cavity 4 toward the gate.

Further, the mounting position of the pressure sensor 3 is not limited to the above embodiment as long as it is a position where the pressure inside the cavity 23 can be accurately detected. For example, it may be provided at a direct gate opposite to the ultrasound probe 9.

Next, a method of controlling the injection molding apparatus in the above embodiment will be explained based on the drawings.

The solid line shown in FIG. 8 shows an example of the mold internal pressure pattern in the injection molding automatic control method of the present invention. The mold internal pressure pattern has a reference waveform indicated by a predetermined solid line Q set in the controller 19 in advance.

First, when resin is injected into the cavity 23 of the mold 2 by the injection molding machine 1, the resin is filled and compressed, and the pressure sensor 3 detects the resin pressure in the mold 2.

The detected mold internal pressure is the holding pressure switching point Q in FIG. When the pressure is reached, the controller 19 switches from filling to holding pressure, and controls the hydraulic ram mechanism 14 to maintain the pressure of waveform Q of the mold internal pressure pattern. When the ultrasonic flaw detector 16 emits a pulse, the ultrasonic probe 9 near the gate transmits the ultrasonic wave and receives the reflected wave. In the ultrasonic flaw detector 16, the ultrasonic probe 9
The change in velocity of the ultrasonic wave is measured as shown in FIG. 5, and is output to the comparator 17.

The comparator 17 compares and calculates the set speed value and the speed value from the ultrasonic flaw detector 16 every moment, and as shown in FIG. 5, the set speed (a 2500 m /sec, a control signal is sent to the signal generator 18.

The signal generator 18 uses the control signal from the comparator 17 to set the reference waveform P of the mold internal pressure pattern at gate seal time t2. At this point, an instruction signal is sent to the controller 19 to instruct release of the holding pressure.

The controller 19 operates a hydraulic device (not shown) based on the instruction signal to reduce the pressure in the hydraulic ram mechanism 146 and release the holding pressure in the injection molding machine 1.

The resin pressure within the mold decreases according to a dashed line curve P.

In the above embodiment, the comparator 17 was used as the calculation means, but a differentiator 17a may also be used as shown in FIG.

In this case, the reflected wave of the ultrasonic wave received by the ultrasonic probe 9 is measured as an amplitude value and guided to the differentiator 17a.

That is, among the echo waves shown in FIG. 4, boundary surface wave echo 3
5, the amplitude value also changes during the process in which the resin 1° filled in the gate 5 changes from a molten state to a solidified state. Therefore, the ratio of the amplitude α of the −th order echo wave 34 to the amplitude β of the boundary surface echo wave 35 is measured for each transmitted pulse, and the ratio of the amplitude β of the boundary surface echo wave 35 to the amplitude α of the −th order echo wave 34 is measured. By measuring the point in time when the value becomes the minimum value, it is possible to determine when the gate is sealed.

Specifically, when the aluminum rod 7 is used, the change in the amplitude α of the -order echo wave 34 is approximately constant7, so the ultrasonic flaw detector 16 as shown in FIG. 7(a) is used. The amplitude change of the boundary surface echo 35 detected by is input to the differentiator 17a in the next step, and by differentiating the amplitude change of the boundary surface echo 35 once in the differentiator 17a, the sign month is changed from negative to negative. Point B when it turned positive [
Refer to FIG. 7(b)] can be used as the time of gate sealing.

The signal generator 18 can send a signal instructing the controller 19 to release the holding pressure when the sign of the signal from the differentiator 17a changes from negative to positive.

(Effects of the Invention) Since the automatic control method and device for injection molding of the present invention are configured as described above, it is possible to release the holding pressure at the point when the gate is reliably sealed, and to maintain the conventional mold internal pressure pattern. Compared to the original control, the occurrence of deformation and warpage, which are problematic in molded products, can be corrected, dimensional accuracy and weight accuracy are improved, and precision molded products that require high precision can be obtained.

[Brief explanation of drawings]

18 Figure 1 is a schematic explanatory diagram of the control device for injection molding of the present invention, Figure 2
The figure is an enlarged view of the gate bushing part, Figure 3 is a diagram showing each echo wave in response to the transmitted pulse when resin is not filled, Figure 4 is a diagram showing each echo wave in response to the transmitted pulse when resin is filled, FIG. 5 is a diagram showing changes in the speed of reflected waves over time after resin is filled, and FIG. 6 is a diagram showing another embodiment of the gate seal time measuring method used in the injection molding control device of the present invention. , FIG. 7(a) is a curve diagram showing the change in amplitude of the measured boundary surface echo wave over time.
Figure (b) is a curve diagram showing a value obtained by once differentiating the temporal change in the amplitude of ``-''. FIG. 8 is a diagram showing an example of pressure cover turn over time in a cavity in injection molding. Explanation of symbols 1: Injection molding machine, 2: Mold, 21: Fixed side mold,
22...Moving side mold, 23...Cavity, 3...Pressure sensor, 4...Gate bush, 5...Gate, 6...
・Amplifier, 7...Aluminum rod, 9...Ultrasonic probe, 10
・・Resin, 14・・Hydraulic pressure 1. Mechanism, 16...Ultrasonic flaw detector, 17...Comparator, 17a...Differentiator, 18...Signal generator, 19...Controller.

Claims (1)

[Claims] 1. In an injection molding control method for controlling the resin pressure in an injection molding mold in a holding pressure filling process based on a predetermined mold internal pressure pattern, An ultrasonic probe continuously detects changes over time in the reflected waves of ultrasonic waves emitted toward the resin inside the gate, measures them as changes in speed or amplitude, and performs arithmetic processing based on the measured values to seal the gate. 1. An automatic control method for injection molding, characterized in that the holding pressure of the mold internal pressure pattern is released based on a signal that reaches the gate sealing point. 2. In the injection molding control device that feedback controls the oil pressure of the injection cylinder so that the resin pressure inside the injection mold during the holding pressure filling process becomes a predetermined mold internal pressure pattern, it is installed near the gate of the mold. an ultrasound probe;
A measurement that constantly measures changes in speed or amplitude of ultrasonic waves from the molten state to the solidified state of the resin by detecting the reflected waves of the ultrasonic waves emitted toward the resin in the gate by the ultrasonic probe. A calculating means for calculating the gate sealing point from the measured value measured by the measuring means, and a controller for releasing the holding pressure when the result of the calculating means is output as the gate sealing point. Automatic control equipment for injection molding.