WO2013051098A1

WO2013051098A1 - Method of controlling pressure-maintaining step for injection-molding machine

Info

Publication number: WO2013051098A1
Application number: PCT/JP2011/072822
Authority: WO
Inventors: 貴政西崎
Original assignee: 東洋機械金属株式会社
Priority date: 2011-10-04
Filing date: 2011-10-04
Publication date: 2013-04-11
Also published as: JPWO2013051098A1; JP5815040B2; CN103857516A; CN103857516B

Abstract

Provided is a method of controlling a pressure-maintaining step for an injection-molding machine capable of molding a high quality molded body, pressure control in a pressure maintaining step executed after an injection step being performed with high precision. A control method in an injection molding machine in which there are performed an injection-filling step for advancing a screw and injecting molten resin to fill a die cavity and a pressure maintaining step for retracting the screw and reducing the pressure, wherein a switch is made to the pressure maintaining step after injection filling has concluded in the injection filling step, the screw is rapidly retracted by reducing a primary pressure through pressure control in a primary pressure maintaining step which is the initial stage after the switch to the pressure maintaining step has been made, and pressure reduction is controlled so that the reduced primary pressure reaches in a short time a set pressure for a secondary pressure maintaining step performed after the primary pressure maintaining step.

Description

Pressure holding process control method in injection molding machine

The present invention relates to a pressure control method in a pressure-holding process performed immediately after injection and filling of a molten resin into a mold cavity, and occurs when molding a thin material such as a light guide plate used in a display panel such as a liquid crystal panel. The present invention relates to a pressure holding process control method in an injection molding machine that can control the residual stress to be performed with high accuracy.

In recent years, a light guide plate that uniformly emits light is used in a relatively small liquid crystal display monitor. When molding thin plate materials such as light guide plates, or in precision molding where high-precision molding is required, in order to eliminate the residual stress that occurs after filling the cavity with molten resin, the high-pressure state is changed to the low-pressure state. For example, when the pressure reduction is slow, residual stress due to the pressure remaining in the mold causes warpage or uneven thickness of the molded body. In addition, if the pressure reduction is too fast, excessive overshoot and hunting after reaching a predetermined pressure occur, and there is a problem that molding defects and gate clogging occur.

As related to the above technique, Patent Document 1 discloses that in the filling step performed before the pressure holding step, when the screw moves forward and reaches a predetermined position, the screw is returned to the set position at a set speed, so that V A method for controlling a filling process of an injection molding machine that performs pressure release immediately before -P switching (switching from speed control to pressure control) is disclosed. Patent Document 2 discloses a technique in injection molding in which a screw is temporarily stopped or retracted after high-pressure high-speed injection, and pressure reduction control is performed after high-pressure high-speed injection.

Japanese Patent No. 34044652 JP 59-165634 A

The technique of Patent Document 1 is a technique for retracting the screw in the filling process, and a technique for controlling the pressure in the pressure holding process performed after the filling process is not disclosed, that is, the residual generated in the pressure holding process. A technique for controlling the stress is not disclosed. Further, in the technique of Patent Document 2, pressure reduction is performed before the pressure holding process, and it is not a technique for controlling the residual stress generated in the pressure holding process as in Patent Document 1. Further, in Patent Document 2, when the screw is retracted and decompressed, the decompression control is simply performed based only on the measured value of the sensor or timer that detects the screw movement position (retracted position). Therefore, it is difficult to perform fine pressure reduction control, and it must be said that it is substantially difficult to obtain a high-quality molded product.

The present invention has been made in view of the above-described problems, and the pressure control in the pressure-holding step executed after the injection-filling step is performed with high accuracy, and the holding in the injection molding machine capable of molding a high-quality molded body. An object of the present invention is to provide a pressure process control method.

The pressure holding process control method in the injection molding machine is
A control method in an injection molding machine that performs an injection filling process in which a screw is advanced to inject and fill a molten resin into a cavity of a mold, and a pressure holding process by reducing the pressure by retreating the screw,
After completion of injection filling in the injection filling process, switching to the pressure holding process,
In the primary pressure-holding process, which is the initial stage after switching to the pressure-holding process, the primary pressure is reduced by pressure control and the screw is rapidly retracted. The pressure reduction control is performed so that the set pressure in the secondary pressure holding process performed after the next pressure holding process is reached in a short time.

The pressure holding process control method in the injection molding machine is
In the injection filling process, the forward movement of the screw is performed by speed control, while in the pressure holding process, the backward movement of the screw is performed by pressure control, so that the switching from the injection filling process to the pressure holding process is performed. VP switching is performed.

The pressure holding process control method in the injection molding machine is
In the primary pressure holding step in which the screw is moved backward by the pressure reduction, when the measured pressure of the primary pressure holding pressure does not reach the set pressure, the screw retracting width B when the pressure is reduced by moving the screw backward is set as follows: The following formula 1 is used to calculate, and the screw is moved backward with the receding width B calculated using the formula 1;
On the other hand, when the measured pressure of the primary holding pressure reaches the set pressure in the primary pressure holding step in which the screw is retracted by the pressure reduction, the following formula 2 is used to calculate:
When the mathematical formula 2 is not satisfied,
The retraction width B of the screw when the screw is retreated and decompressed is calculated by the following mathematical expression 3, and the screw is retreated by the retraction width B calculated by the mathematical expression 3. .

A: Movement width (mm) of the screw moved from the time of VP switching before one shot to when the primary pressure holding process and the secondary pressure holding process are switched.
C: Set screw retraction width (mm) before one shot
a: Differential pressure (MPa) between the measured VP switching pressure at the time of VP switching before one shot and the measured pressure at the primary holding pressure process one shot before
b: Differential pressure (MPa) between the measured VP switching pressure at the time of VP switching before one shot and the set pressure in the secondary holding pressure process

The pressure holding process control method in the injection molding machine is
When satisfying the mathematical formula of Equation 2,
The number of shots is k, the time when the measured pressure reaches the set pressure in the secondary pressure holding process is t, the retreating width of the screw retreating at time t is X (t), and the injection speed at time t is V ( t), injection pressure P (t) at time t, learning coefficients arbitrarily determined as α, β, and evaluation function f (t) = αV (t) + βP (t),
Using this evaluation function, the receding width X (t) is calculated for each shot in the direction of f (t) ≈0 by the following equation (4), and the receding width of the screw is calculated based on the calculated value for each shot. Is automatically adjusted.

According to the pressure-holding process control method in the injection molding machine of the present invention, after switching from the injection filling process to the pressure-holding process, in the primary pressure-holding process in the initial stage of the pressure-holding process, Since the primary holding pressure is rapidly reduced and the pressure reduction control is performed so that the primary holding pressure reaches the set pressure of the secondary holding pressure in a short time, such high-precision pressure control (holding pressure) is maintained in the holding pressure process. By controlling the residual stress generated in the pressing step), it is possible to manufacture a high-quality molded product (thinly mold the thickness of the thin molded product).

Furthermore, when performing the pressure reduction control of the screw using the measured pressure value of the primary holding pressure and the above mathematical formula, the self-learning is performed based on the measured pressure value, and the screw retraction width is optimum based on the result obtained therefrom. Reduce pressure by performing automatic adjustment (fine adjustment) to set the retreat width. Therefore, fine pressure control is possible in the pressure-holding step, and the quality of the manufactured molded product can be improved.

It is a schematic block diagram which shows the injection unit of an injection molding machine. It is a graph which shows the injection filling process and pressure holding process of the injection unit of an injection molding machine. It is a flowchart which shows operation | movement when adjusting the retreat width | variety of a screw in a primary pressure holding process. It is explanatory drawing which shows operation | movement of the primary pressure holding | maintenance process at the time of adjusting the backward movement width of a screw, applying Formula 1 in order to enlarge the said backward movement width when the backward movement width of a screw is too small, The axis represents the speed of the screw and the horizontal axis represents the moving position of the screw as the position. In the primary pressure-holding process, the waveform when the screw is retreated with the retraction width calculated by Equation 1 is represented by a solid line. The waveform when the screw is retracted with the previously set screw retraction width is represented by a dotted line. It is explanatory drawing which shows operation | movement of the primary pressure holding | maintenance process at the time of adjusting the backward movement width of a screw, applying Formula 1 in order to enlarge the said backward movement width when the backward movement width of a screw is too small, The axis represents the pressure and speed of the screw, the axis represents the time, the axis represents the time, and the pressure waveform when the screw is retracted with the receding width calculated by Equation 1 is represented by a solid line above the time axis. The waveform of the pressure when the screw is retreated with the previously set retreat width of the screw is represented by a dotted line above the time axis. In addition, the speed waveform when the screw is retracted with the retraction width calculated by the mathematical formula 1 is represented by a solid line below the time axis, and the screw is retreated with the set retraction width of the screw one shot before. The velocity waveform at the time is represented by a dotted line below the time axis. It is explanatory drawing which shows operation | movement of the primary pressure holding | maintenance process at the time of adjusting the backward movement width of a screw, applying Formula 3 in order to make the said backward movement width small, when the backward movement width of a screw is too large, The axis represents the speed of the screw and the horizontal axis represents the moving position of the screw as the position. In the primary pressure-holding process, the waveform when the screw is retreated with the retraction width calculated by Equation 1 is represented by a solid line. The waveform when the screw is retracted with the previously set screw retraction width is represented by a dotted line. It is explanatory drawing which shows operation | movement of the primary pressure holding | maintenance process at the time of adjusting the backward movement width of a screw, applying Formula 3 in order to make the said backward movement width small, when the backward movement width of a screw is too large, The axis represents the pressure and speed of the screw, the axis represents the time, the axis represents the time, and the pressure waveform when the screw is retracted with the receding width calculated by Equation 3 is represented by a solid line above the time axis. The waveform of the pressure when the screw is retreated with the previously set retreat width of the screw is represented by a dotted line above the time axis. Also, the speed waveform when the screw is retracted with the retraction width calculated by the mathematical formula 3 is represented by a solid line below the time axis, and the screw is retracted with the set retraction width of the screw one shot before. The velocity waveform at the time is represented by a dotted line below the time axis. It is a graph which shows the variable inclination of a learning coefficient. It is a graph which shows the operation | movement when adjusting numerical formula 1 of Formula, and adjusting the retreat width | variety of a screw, The speed of a screw is shown as speed measurement on the vertical axis | shaft, and the moving position of the screw is shown on the horizontal axis as a position. It is a graph which shows the operation | movement when adjusting numerical formula 1 of Formula, and adjusting the retreat width | variety of a screw, The pressure of a screw is shown as a pressure measurement on the vertical axis | shaft, and the moving position of the screw is shown on the horizontal axis | shaft as a position. It is a graph which shows operation | movement when adjusting numerical formula 1 of Formula, and adjusting the retreat width | variety of a screw, the speed of a screw is shown as speed measurement on the vertical axis | shaft, and the time is shown on the horizontal axis. It is a graph which shows the operation | movement when adjusting numerical formula 1 of Formula, and adjusting the retreat width | variety of a screw, The pressure of a screw is shown as a pressure measurement on the vertical axis | shaft, and the time is shown on the horizontal axis. It is a graph which shows operation | movement when adjusting numerical formula of Formula 3 and adjusting the retreat width | variety of a screw, The speed of a screw is shown as speed measurement on the vertical axis | shaft, and the moving position of the screw is shown on the horizontal axis as a position. It is a graph which shows the operation | movement when adjusting numerical formula 3 of Formula, and adjusting the retreat width | variety of a screw, The pressure of a screw is shown as a pressure measurement on the vertical axis | shaft, and the moving position of the screw is shown on the horizontal axis | shaft as a position. It is a graph which shows the operation | movement when adjusting numerical formula of Formula 3 and adjusting the retreat width | variety of a screw, The speed of a screw is shown as speed measurement on the vertical axis | shaft, and the time is shown on the horizontal axis. It is a graph which shows the operation | movement when adjusting the retraction width | variety of a screw by applying several 3 Formula, the pressure of a screw is shown as a pressure measurement on the vertical axis | shaft, and the time is shown on the horizontal axis.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. Of course, it goes without saying that the present invention can be easily applied to configurations other than those described in the embodiments without departing from the spirit of the invention.

FIG. 1 is a front view showing an injection unit 2 configured in an injection molding machine 1. As shown in FIG. 1, a hopper 3 into which resin (pellet) that is a granular raw material is charged, A cylindrical heating cylinder 4 to which granular resin is supplied from the hopper 3, a screw 5 for measuring the molten resin supplied into the heating cylinder 4 and plasticized by heat, and the measured molten resin to the cavity of the mold An injection nozzle 6 mounted at the tip of the heating cylinder 4 for injection filling, a metering motor 8 as a driving source for rotating the screw 5 via a timing belt 7 when kneading the molten resin in the heating cylinder 4, and the like When injecting the molten resin from the tip of the injection nozzle 6, the injection motor 1 as a drive source for advancing the screw 5 via the timing belt 9 and the ball screw mechanism 10 The load cell 12 serving as a pressure sensor that detects the force (injection pressure) for extruding the molten resin as the screw 5 moves forward is used as a reaction force. The control means 13, various numerical values such as actually measured values of the injection molding machine 1, storage means 14 in which the mathematical formulas and the like are stored are configured.

Next, the pressure holding process of the injection molding machine 1 of the present embodiment will be described below. FIG. 2 is a graph in which the vertical axis represents pressure and speed, and the horizontal axis represents time. As shown in FIG. 2, the injection filling process in which the screw 5 is advanced to inject and fill the molten resin into the mold cavity is shown. After being performed, the pressure holding process is performed. When the injection filling process is completed, the screw 5 whose speed is controlled in the injection filling process is switched to VP at that timing. In the process, pressure control is performed instead of speed control. In FIG. 2, the pressure waveform is indicated by a solid line, and the velocity waveform is indicated by a dotted line.

In the pressure holding process, the primary pressure holding process is performed at an initial stage switched from the injection filling process, and the secondary pressure holding process (main pressure holding process) is performed after the primary pressure holding process. In the primary pressure holding process, the control means 13 rapidly retracts the screw so that the primary pressure in the primary pressure holding process reaches the set pressure in the secondary pressure holding process in a short time. The next holding pressure is reduced.

Here, the primary pressure holding step will be further described with reference to FIGS. The adjustment of the backward width B of the screw 5 when the pressure is reduced by the backward movement of the screw 5 in the primary pressure-holding step is performed in the operation order shown in the flowchart of FIG. When the measured actual pressure in the primary pressure holding process does not reach the preset pressure in the secondary pressure holding process due to the operation of the injection molding machine 1 (step 1), the process proceeds to step 2 and the screw 5 The backward width B of the screw 5 when the pressure is reduced by retreating is calculated by the control unit 13 according to the following equation (1).

C: Set screw retraction width (mm) before one shot
a: Differential pressure (MPa) between the measured VP switching pressure at the time of VP switching before one shot and the measured pressure at the primary holding pressure process one shot before
b: Differential pressure (MPa) between the measured VP switching pressure at the time of VP switching before one shot and the set pressure in the secondary holding pressure process

Then, the primary holding pressure in the primary holding pressure process is rapidly reduced by the screw 5 being retracted by the retreating width B calculated by the mathematical formula 1. The fine adjustment of the retraction width B (when the retraction width B is too small) when the screw 5 is retreated with the retraction width B calculated by the mathematical formula 1 will be further described here with reference to FIGS. 4A and 4B. . FIG. 4A shows the speed of the screw 5 on the vertical axis and the moving position of the screw 5 on the horizontal axis as the position, and when the screw 5 is moved backward by the backward width B calculated by the mathematical formula 1 in the primary pressure holding step. Is represented by a solid line, and the waveform when the screw 5 is retreated by the set retreat width C of the screw 5 one shot before is represented by a dotted line. FIG. The pressure and speed are shown, the time is shown on the horizontal axis, and the pressure waveform when the screw 5 is retracted with the receding width B calculated by the mathematical formula 1 is shown as a solid line above the time axis, one shot before The pressure waveform when the screw 5 is retracted with the set receding width C of the screw 5 is represented by a dotted line above the time axis, and the screw 5 is retracted with the receding width B calculated by the mathematical formula 1 The velocity waveform when A solid line is shown below the axis, and a velocity waveform when the screw 5 is retracted by the set retreat width C of the screw 5 one shot before is shown by a dotted line below the time axis. . Then, as shown in FIG. 4B, the screw 5 can be operated with an appropriate receding width B by finely adjusting the receding width of the screw 5 based on the receding width calculated by the mathematical expression of Formula 1. .

Further, when the actually measured pressure in the primary pressure holding process in Step 1 reaches the preset pressure in the secondary pressure holding process, the process proceeds to Step 3 and the control means 13 uses the following formula. It is performed by the calculation of 2.

A: Movement width (mm) of the screw moved from the time of VP switching before one shot to when the primary pressure holding process and the secondary pressure holding process are switched.

When the mathematical expression 2 is not satisfied (step 3), the process proceeds to step 4 where the control unit calculates the backward width B of the screw 5 when the screw 5 is retracted to reduce the pressure. It is.

Then, the primary holding pressure in the primary holding pressure process is rapidly reduced by the screw 5 being retracted by the retreating width B calculated by the mathematical expression of Formula 3. Note that fine adjustment of the retraction width B (when the retraction width B is too large) when the screw 5 is retreated with the retraction width B calculated by the mathematical formula 3 is further described here with reference to FIGS. 5A and 5B. . FIG. 5A shows the speed of the screw 5 on the vertical axis and the moving position of the screw 5 on the horizontal axis as the position, and when the screw 5 is retracted by the receding width B calculated by the mathematical formula 1 in the primary pressure holding step. Is represented by a solid line, and the waveform when the screw 5 is retreated by the set retreat width C of the screw 5 one shot before is represented by a dotted line. FIG. 5B shows the screw 5 on the vertical axis. The pressure and velocity of the screw 5 are shown, the time is shown on the horizontal axis, and the pressure waveform when the screw 5 is retracted with the receding width B calculated by the mathematical formula 3 is shown as a solid line above the time axis, one shot before The pressure waveform when the screw 5 is retracted with the set receding width C of the screw 5 is represented by a dotted line above the time axis, and the screw 5 is receded with the receding width B calculated by the mathematical formula 3 The velocity waveform when A solid line is shown below the axis, and a speed waveform when the screw 5 is retracted by the set receding width C of the screw 5 one shot before is shown by a dotted line below the time axis. . Then, as shown in FIG. 5B, the screw 5 can be operated with an appropriate backward width B by finely adjusting the backward width of the screw 5 based on the backward width calculated by the mathematical formula 3 .

Further, when satisfying the mathematical expression 2 in Step 3, the process proceeds to Step 5.

(Fine adjustment by gradient method)
In Step 5, even if fine adjustment of the retraction width of the screw 5 is performed in Step 2 or Step 4, if the fine adjustment is not optimal, an unstable pressure behavior is shown after switching to pressure control. There is. As a fine-tuning means for solving this problem, a steepest descent method effective for obtaining a polar solution is used. Here, the steepest descent method is represented by the following formula.

k: Number of shots t: Time when the measured pressure reaches the set pressure of the secondary pressure holding process X (t): Retreating width of the screw retreating at time t f (t): Evaluation value used in this specification Outputs the adjustment amount of the receding width.
Here, the following functions are prepared as evaluation functions.
f (t) = αV (t) + βP (t)
V (t): injection speed at time t P (t): injection pressure at time t α, β: learning coefficient to be arbitrarily determined And, using the above evaluation function, retreat in the direction of f (t) ≈0 When the width X (t) is updated for each shot, Equation 4 is obtained.

At this time, the learning coefficients α and β suppress the overlearning when the constants are made variable as shown in the graph of FIG.
Here, parameters are determined according to the following specifications.

Then, using the above evaluation function, the control means calculates the receding width X (t) for each shot in the direction of f (t) ≈0 according to the mathematical formula 4, and based on the calculated value for each shot. The retraction width of the screw 5 is automatically adjusted.

Next, an example of the operation when the receding width B is finely adjusted using the mathematical formula 1 will be described with reference to FIG. 7A shows the speed of the screw 5 on the vertical axis as a speed measurement, the horizontal axis shows the moving position of the screw 5 as a position, FIG. 7B shows the pressure of the screw 5 on the vertical axis as a pressure measurement, and the horizontal axis shows the screw 5 7C shows the speed of the screw 5 as a speed measurement, the horizontal axis shows the time, FIG. 7D shows the pressure of the screw 5 as a pressure measurement on the vertical axis, and the horizontal axis Shows time. 7A to 7D, the waveform of the first shot (1.00 mm) is represented by a solid line, the waveform of the second shot (2.70 mm) is represented by a dotted line, and the waveform of the third shot (3.38 mm) is represented by a dashed line. ing. Then, the injection molding machine 1 is operated to perform molding by setting the receding width of the screw 5 in the first shot to 1 mm and the target pressure corresponding to the set pressure in the secondary pressure holding process to 10 MPa. Then, from FIG. 7B, since the pressure is about 66 MPa at the position of 1 mm, the target pressure is not reached in the first shot. Therefore, in order to adjust the retraction width of the screw 5 to be large, the mathematical formula (B = Cb / 0.9a) of the formula 1 is used.

Here, C = 1.0 mm, the measured VP switching pressure at the time of VP switching before 1 shot is 105 aMPa, and the measured VP switching pressure at the time of VP switching before 1 shot is 1 The differential pressure (MPa) from the measured pressure in the primary pressure holding process before the shot is 105 MPa−66 MPa = 39 MPa, a = 39 MPa, b = 95 MPa (105 MPa−10 MPa (set pressure in the secondary pressure holding process)) Because
B = Cb / 0.9a = (1.0 × 95) / (0.9 × 39) ≈2.70 mm
Therefore, in the second shot, molding is performed with B = 2.70 mm and a target pressure of 10 MPa.

As a result, when B = 2.70 mm, the pressure is about 20.7 MPa, and when it cannot reach the target pressure of 10 MPa, the equation 1 is again applied so as to reach the target pressure of 10 MPa. Using the formula (B = Cb / 0.9a)
C = 2.7 mm, the actually measured VP switching pressure at the time of VP switching before one shot is 105 aMPa, and as shown in FIG. 7B, the pressure is 20 at the position of 2.70 mm in the second shot. Since the pressure is 0.7 MPa, the differential pressure (MPa) between the measured VP switching pressure at the time of VP switching one shot before and the measured pressure in the primary pressure holding process one shot before is 105 MPa-20. Since 7 MPa = 84.3 MPa, a = 84.3 MPa, b = 95 MPa (105 MPa-10 MPa (set pressure in the secondary pressure holding process)),
B = Cb / 0.9a = (2.7 × 95) / (0.9 × 84.3) ≈3.38 mm
The third shot is molded at B = 3.38 mm and a target pressure of 10 MPa. When B = 3.38 mm, the pressure is 12.2 MPa as a result, but this 12.2 MPa (in the primary pressure holding step). Since the pressure does not reach the target pressure (set pressure in the secondary pressure holding process), the pressure converges while performing the fine adjustment of the retraction width of the screw 5 using the mathematical formula 1.

On the other hand, when the pressure in the primary pressure-holding process reaches the set pressure in the secondary pressure-holding process, the process proceeds from step 1 to step 3 as shown in the flow of FIG. Whether or not the requirement of the mathematical formula (A / B> 0.98) is satisfied is determined by the control means 13, and when the requirement is not satisfied, fine adjustment of the retraction width of the screw 5 using the mathematical formula 3 Is done. An example of the operation when performing the fine adjustment will be described below with reference to FIG.

8A shows the speed of the screw 5 as a speed measurement on the vertical axis, the moving position of the screw 5 as a position on the horizontal axis, and FIG. 8B shows the pressure of the screw 5 as a pressure measurement on the vertical axis, and the screw 5 on the horizontal axis. 8C shows the speed of the screw 5 as a speed measurement, the horizontal axis shows the time, FIG. 8D shows the pressure of the screw 5 as a pressure measurement on the vertical axis, and the horizontal axis Shows time. 8A to 8D, the waveform of the first shot (5.00 mm) is represented by a solid line, the waveform of the second shot (4.05 mm) is represented by a dotted line, and the waveform of the third shot (3.57 mm) is represented by a dashed line. ing. Then, for example, when molding is performed with the receding width of the screw in the first shot set to 5.00 mm and the target pressure corresponding to the set pressure of the secondary pressure holding process to 10 MPa, the primary pressure holding process of the primary pressure holding process is performed. In order for the pressure to reach the set pressure of the secondary pressure holding process, the receding width B is reached at 4.01 mm, but in the first shot, B = 5.00 and A = 3.97 Therefore, since the requirement of the mathematical formula 2 (A / B> 0.98) is not satisfied, in order to adjust the retraction width of the screw 5 to be small, the mathematical formula 3 (B = A / 0.99) is used. ) Is used.

Then, when the second shot is molded with the mathematical formula (B = A / 0.99), the receding width B = 4.05 mm, the target pressure of 10 MPa, the primary holding pressure in the primary holding step is 2. Since the receding width B when reaching the set pressure in the next pressure-holding step is 3.53 mm, the calculation is performed again using the mathematical formula (B = A / 0.99) of Equation 3.

As a result, since B = 3.57 mm, in the third shot, B = 3.57 mm, the target pressure is molded at 10 MPa, the receding width B is 3.57 mm, and the primary holding pressure in the primary holding step. When the pressure reaches 10 MPa, which is the set pressure (target pressure) in the secondary pressure-holding step, the fine adjustment of the retreat width of the screw 5 using the mathematical formula 3 is finished.

DESCRIPTION OF SYMBOLS 1 Injection molding machine 2 Injection unit 3 Hopper 4 Heating cylinder 5 Screw 6 Injection nozzle 7 Timing belt 8 Metering motor 9 Timing belt 10 Ball screw mechanism 11 Injection motor 12 Load cell 13 Control means 14 Storage means

Claims

A control method in an injection molding machine that performs an injection filling process in which a screw is advanced to inject and fill a molten resin into a cavity of a mold, and a pressure holding process by reducing the pressure by retreating the screw,
After completion of injection filling in the injection filling process, switching to the pressure holding process,
In the primary pressure-holding process, which is the initial stage after switching to the pressure-holding process, the primary pressure is reduced by pressure control and the screw is rapidly retracted. A pressure-holding process control method in an injection molding machine, wherein pressure reduction control is performed so as to reach a set pressure in a secondary pressure-holding process performed after the next pressure-holding process in a short time.
In the injection filling process, the forward movement of the screw is performed by speed control, while in the pressure holding process, the backward movement of the screw is performed by pressure control, so that the switching from the injection filling process to the pressure holding process is performed. 2. The pressure holding process control method in an injection molding machine according to claim 1, wherein VP switching is performed.
In the primary pressure holding step in which the screw is moved backward by the pressure reduction, when the measured pressure of the primary pressure holding pressure does not reach the set pressure, the screw backward width B when the pressure is reduced by moving the screw backward is set as follows: The following formula 1 is used to calculate, and the screw is moved backward with the receding width B calculated using the formula 1;
On the other hand, when the measured pressure of the primary holding pressure reaches the set pressure in the primary pressure holding step in which the screw is retracted by the pressure reduction, the following formula 2 is used to calculate:
When the mathematical formula 2 is not satisfied,
The retraction width B of the screw when the screw is retreated and decompressed is calculated by the following mathematical expression 3, and the screw is retreated by the retraction width B calculated by the mathematical expression 3. The pressure holding process control method in the injection molding machine according to claim 2.

A: Movement width (mm) of the screw moved from the time of VP switching before one shot to when the primary pressure holding process and the secondary pressure holding process are switched.
C: Set screw retraction width (mm) before one shot
a: Differential pressure (MPa) between the measured VP switching pressure at the time of VP switching before one shot and the measured pressure at the primary holding pressure process one shot before
b: Differential pressure (MPa) between the measured VP switching pressure at the time of VP switching before one shot and the set pressure in the secondary holding pressure process
When satisfying the mathematical formula of Equation 2,
The number of shots is k, the time when the measured pressure reaches the set pressure in the secondary pressure holding process is t, the retreat width of the screw retreat at time t is X (t), and the injection speed at time t is V ( t), injection pressure P (t) at time t, learning coefficients arbitrarily determined as α, β, and evaluation function f (t) = αV (t) + βP (t),
Using this evaluation function, the receding width X (t) is calculated for each shot in the direction of f (t) ≈0 by the following equation (4), and the receding width of the screw is calculated based on the calculated value for each shot. The pressure holding process control method for an injection molding machine according to claim 3, wherein the pressure is automatically adjusted.