JPH07214612A - Injection control method in injection molding machine - Google Patents

Abstract

PURPOSE:To embody an optimum injection stage and stably obtain a required conforming article by a method wherein a resin sensor is provided in the path of a resin flow in a mold, and an injection condition is corrected by changing over an injection stage from a speed control to a pressure control at a reference time when a leading end of a resin flow passes through the resin sensor. CONSTITUTION:A resin sensor 6 is provided in a resin path 11 of a stationary mold 10a at the top of a nozzle 4. The passing of the leading end of an injected melt resin through the resin sensor 6 is detected by the resin sensor 6. The resin sensor 6 transmits a signal to a controller of an injection molding machine. From the time of reception of the signal, a speed control is changed over to a pressure control. Similarly, the progressed position of a screw 1, an injection pressure, and the like are measured in a period from the start of injection to the passing of the melt resin through the resin sensor 6. The obtained measured values are compared with theoretical values in the calculation of operational conditions for the injection stage. If a difference exists, a set value from then is appropriately corrected by the difference. In this manner, a stable action in an injection stage can be embodied.

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 for molding plastic products, and more particularly to an injection control method for controlling the injection process with high accuracy.

[0002]

2. Description of the Related Art In an injection process of an injection molding machine, it is possible to obtain a desired high quality molded product by setting and controlling a resin speed and a resin pressure to optimum conditions in a process of injecting and filling a molten resin in a mold. Is very important for.

In order to obtain the optimum injection speed and pressure of the molten resin, depending on the experience of a skilled person, or by using CAE (Computer Assisted Technology) calculation, the ideal molding conditions are set and the set values are set. It was controlled based on.

[0004]

By the way, in the injection process of the experiment, at the start of the injection process, that is, when the screw advance starts due to the backflow of the resin due to the delay of the closing of the check ring or the gap generated at the nozzle tip by the suck back operation. There is a difference between the time and the start time of inflow of the resin into the mold, which causes a problem that the injection process as set cannot be realized no matter how the optimum injection conditions are set. In particular, when the pressure control is performed, the resin pressure stored in the front portion of the screw head does not rise until the check ring is closed and the gap at the nozzle tip portion caused by the suck back operation disappears, and the control becomes unstable.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide an injection control method in an injection molding machine for correcting an injection condition to realize an optimum injection process. is there.

[0006]

In order to achieve the above object, in the first aspect of the present invention, a resin sensor for detecting the presence / absence of resin is attached in the middle of a resin flow path in a mold to remove the resin. The time when the flow front passes is detected, and the injection process is switched from speed control to pressure control based on that time. In the second invention, the measured resin pressure and the theoretical resin pressure are used based on the time of the first invention. The difference from the resin pressure is corrected and controlled so as to be reflected in the subsequent pressure control target value.

[0007]

[Function] By detecting the delay in closing the check ring and the filling delay at the start of injection caused by the space in the nozzle tip portion caused by the suck back operation, the time is detected by the resin sensor provided in the middle of the resin flow path in the mold. Based on the above, the injection process is switched from speed control to pressure control, and the difference between the actually measured resin pressure and the theoretical resin pressure is corrected for subsequent injection conditions to realize the optimum injection process. .

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A concrete embodiment of an injection control method in an injection molding machine according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic diagram showing a simplified structure of a main part of an injection molding machine, FIG. 2 is an explanatory diagram showing a state immediately before the start of an injection process, and FIG. 3 is a flow front of a molten resin passed through a resin sensor. FIG. 4 is an explanatory diagram showing an instantaneous state, FIG. 4 is a relationship diagram of set injection speed and time in speed control in the initial stage of injection, FIG. 5 is a relationship diagram of target pressure and time after switching from speed control to pressure control, and FIG. Is a diagram for correcting the screw position and the theoretical position at the time when the flow front has passed the resin sensor, FIG. 6 is a diagram for correcting the injection pressure, and FIG. 8 is a diagram for correcting the speed switching time during injection.
FIG. 9 is a correction diagram for correcting the set pressure from the time difference.

In FIG. 1, a screw 1 is inserted in a heating cylinder 3 which constitutes an injection device 20 so as to be able to move forward and backward with respect to rotation, a nozzle 4 is attached to the tip of the heating cylinder 3, and a rear end of the heating cylinder 3 is attached. An injection cylinder 16 in which a piston 14 in which the screw 1 is axially movable and is rotatably attached is inserted is attached to the.

A resin sensor 6 is disposed so as to face the resin passage 11 of the fixed mold 10a at the tip of the nozzle 4. The resin sensor 6 is provided to confirm whether or not the flow front end of the molten resin stored in the screw head space portion 22 has passed over the resin sensor 6 after the injection process is started. It should be noted that the installation position of the resin sensor 6 is as close to the nozzle 4 as possible in consideration of the fact that the feedback control has better response when the time difference between the start of the injection process and the passage of the flow sensor through the resin sensor 6 is smaller. Is preferable.

A resin pressure sensor 7 used to control the resin pressure of the molten resin stored in the screw head space 22 at the time of completion of the measurement is arranged near the tip of the nozzle 4. On the other hand, when controlling the hydraulic pressure on the screw rear side as a reaction force of the resin pressure, the injection cylinder head side hydraulic chamber 16a
It is designed to control the hydraulic pressure.

A check sheet 1a is attached to the tip of the screw 1.
The screw head 18 is screwed on, and the screw head 18 has a substantially conical shape toward the tip, and the rear side (right side in the figure) of the conical shape is stepped to have a small diameter. A check ring 2 which is slidable in the axial direction is inserted. Reference numeral 12 is a hopper, 12a is a pellet, and 8 is a cavity formed between the fixed mold 10a and the movable mold 10b when the mold is closed.

Next, the operation of the present invention will be described. At the start of the weighing process, the screw 1 is on the right side of the position shown in FIG. 2, and when the screw 1 is rotated with back pressure applied to the hydraulic chamber, the pellets 12a are supplied from the hopper 12 to the right end side of the screw 1. The pellets 12a become molten resin and are stored in the front portion 22 of the screw head while being sent to the left by the screw 1.

The screw 1 retracts as it is stored in the front portion 22 of the screw head. For example, when a limit switch (not shown) detects this, the rotation of the screw 1 is stopped and the measurement of the molten resin is completed.

After that, when the screw 1 is further retracted to perform suck back operation, a gap 9 is formed at the tip of the nozzle 4. When the injection process is started from this state, the check ring 2 comes into contact with the screw head 18 side and then comes into contact with the check sheet 1a side as the screw 1 advances as shown in FIG. Due to the closing, the molten resin stored in the screw head front portion 22 is injected to the mold 10 side.

When the flow front of the injected molten resin passes through the resin sensor 6 (FIG. 3), the resin sensor 6 detects this and transmits a signal to the controller of the injection molding machine.

Upon receipt of the signal, the control device of the injection molding machine switches from speed control to pressure control from that time. Similarly,
The time from the start of injection until the molten resin passes through the resin sensor 6, the screw advancing position, the injection pressure, etc. were measured, and the measured values obtained were compared with the theoretical values when these operating conditions for injection were calculated. However, if there is a difference, it is aimed to realize a stable injection process operation by appropriately correcting the subsequent set values from the difference.

The above-mentioned theoretical value is such that the reverse flow rate due to the closing delay of the check ring 2 accompanying the advancement of the screw 1 at the start of the injection process and the void 9 etc. generated at the tip of the nozzle 4 due to the suck back operation at the completion of the metering process are zero. The injection conditions under the theoretical conditions are shown.

On the other hand, in the actually measured value, the void 9 generated by the back flow rate due to the closing delay of the check ring 2 and the suck back operation is actually contained under the injection process starting condition.

Thus, the above-mentioned theoretical values and measured values are
It depends on the reverse flow rate due to the delay in closing the check ring 2 at the start of injection and the presence or absence of the void 9 at the tip of the nozzle 4.

First, after the start of the injection process, as shown in FIG. 4, speed control of a constant injection speed V _O is performed. In theory, although the flow front at the time the molten resin injection step starts after t _AO passes through resin sensor 6, actually delayed because of the reverse flow and the nozzle 4 the tip of the air gap 9 from the check ring 2 times t _A
Then, it passes through the resin sensor 6, and the signal at this time is transmitted to the control device of the injection molding machine. The control device controls the target value of the injection pressure after the time t _{A as} the target value of the injection pressure after the theoretical time t _AO shown in FIG.

Further, the measured injection pressure P _A at time t _A shown in FIG. 6, when there is a difference of injection pressure P _AO and △ P theoretical time t _AO, the target injection pressure of the subsequent △ P only It is controlled so that the injection pressure is corrected.

When the injection speed is set and controlled with reference to the screw 1 position as shown in FIG. 7, the theoretical screw 1 position X _AO at time t _A is calculated. Next, actually perform the injection process, measure the screw 1 moving position X _A at the time t _A actually measured, calculate the difference _ΔX between X _AO and X _A , and change the theoretical speed after t _A time. Point X
_{1 to} X ₄ (shown by the solid line in FIG. 7) are corrected by ΔX to X ₁ ′ to X ₄ ′ shown by the dotted line in FIG. 7 for control.

Further, as shown by the solid line in FIG. 8, when the injection speed of the screw 1 is set as a target value and controlled with respect to the elapsed time after the start of injection, the theoretical resin passage time t _AO of the resin sensor 6 is calculated. The difference Δt is calculated from the measured value t _A of the actually measured resin passage time. Then, the subsequent speed switching points t ₁ to t ₄ are corrected by Δt to be speed switching points t ₁ ′ to t ₄ ′ shown by the dotted line, and the target value is corrected and controlled as shown by the dotted line in FIG.

As shown by the solid line in FIG. 9, when the injection pressure of the screw 1 is set as a target value with respect to the elapsed time after the start of injection, the theoretical resin passage time t _AO of the resin sensor 6 is calculated in advance. , Actually measured value t of the resin passing time
_From the difference Δt with respect to _A , thereafter, the difference Δt is corrected to the injection pressure shown by the dotted line, and this is controlled as a target set value.

[0027]

As is apparent from the above description, in the first aspect of the invention, the time when the flow front of the resin passes by mounting the resin sensor for detecting the presence or absence of the resin in the resin flow path in the mold Is detected and the injection process is switched from speed control to pressure control based on the time, and in the second invention, the measured resin pressure and the theoretical resin pressure are based on the time of the first invention. Since the difference is corrected and controlled so as to be reflected in the pressure control target value thereafter, a desired non-defective product can be stably obtained because an injection process close to an ideal can be realized.

[Brief description of drawings]

FIG. 1 is a schematic view showing a simplified configuration of a main part of an injection molding machine.

FIG. 2 is an explanatory diagram showing a state immediately before the start of an injection process.

FIG. 3 is an explanatory diagram showing a state at a moment when a flow front of a molten resin passes a resin sensor.

FIG. 4 is a diagram showing a relationship between a set injection speed and time in speed control at the initial stage of injection.

FIG. 5 is a relationship diagram between a target pressure and time after switching from speed control to pressure control.

FIG. 6 is a diagram for correcting the screw position and the theoretical position at the time when the flow front passes through the resin sensor.

FIG. 7 is a diagram for correcting an injection pressure.

FIG. 8 is a diagram for correcting a speed switching time at the time of injection.

FIG. 9 is a correction diagram for correcting a set pressure from a time difference.

[Explanation of symbols]

 1 Screw 1a Check Sheet 2 Check Ring 3 Heating Cylinder 4 Nozzle 6 Resin Sensor 7 Resin Pressure Sensor 8 Cavity 9 Gap 10 Mold 10a Fixed Mold 10b Movable Mold 11 Resin Passage 12 Hopper 14 Piston 16 Injection Cylinder 16a Injection Cylinder Head Side Hydraulic chamber 18 Screw head 20 Injection device 22 Screw head front part

Claims (2)

[Claims] 1. A resin sensor for detecting the presence / absence of resin is mounted in the middle of a resin flow path in a mold to detect the time when a flow front of the resin passes, and the injection process is pressure-controlled by speed control based on the time. An injection control method in an injection molding machine, characterized in that the control is switched. 2. The method according to claim 1, wherein the difference between the actually measured resin pressure and the theoretical resin pressure is corrected and controlled so as to be reflected in the subsequent pressure control target value, based on the time. Injection control method for injection molding machine.