KR101160561B1 - A control method for injection molding machine - Google Patents

Abstract

PURPOSE: A controlling method of an injection molding machine is provided to accurately set a driving time and an operation ranges of a servo motor by accurately setting a charging space. CONSTITUTION: A controlling method of an injection molding machine includes a screw position controlling step and a one time injection amount determining step. The screw position controlling step is as follows. A measured pressure value is output to a differentiator and the pressure value temporally changed is calculated by the differentiator. A speed of an injection servo motor is decreased when the pressure value input to the differentiator. A one time injection amount determining step is as follows. The pressure value inside a cavity in the injection is measured. The measured pressure value is compared with a pre-set critical pressure value. A position of a screw changed when the measured pressure value reaches the critical pressure value is input.

Description

Control method of injection molding machine {A CONTROL METHOD FOR INJECTION MOLDING MACHINE}

The present invention relates to a molding production method using an injection molding machine, and more particularly to a setting method for setting the amount that can be injected once in the injection step of the injection molding process.

In general, an injection molding machine is composed of an injection part, a mold part, and a control part, and the mold part includes a fixed mold provided adjacent to the injection part and a movable mold disposed corresponding to the fixed mold. A cavity having a specific shape is formed therebetween, and the resin injected from the injection portion is filled in the cavity, and the resin solidifies by cooling the mold portion to form a desired molding.

In the injection molding machine, the process of injection molding is briefly described. A measurement process of melting and accumulating resin in front of a heating cylinder inside an injection unit, and accumulated resin are ejected from a nozzle provided at the front end of a heating cylinder to be melted in a cavity of a mold unit. The resin is filled with a filling process, and after the mold part is cooled, the resin occupying the space of the cavity is hardened, so that a pressure retention process for maintaining a constant pressure on the resin for a certain period of time can be achieved.

In order to obtain moldings in good condition, proper pressure maintenance or pressure control is required until the moldings in the cavity are completely hardened.

In this pressure holding process, molten resin occupying the filling space provided at the front end of the heating cylinder is pressurized and injected into the cavity of the mold part by the forward operation of the injection servo motor, and the resin of the cavity is solidified by cooling the mold part. It is a process for maintaining a constant pressure until a complete molding can be achieved, and it is a process for maintaining the pressure for a predetermined period until the molding is hardened after injection.

In the process, this is called V-P switching, which means that the acceleration operation due to the forward movement of the screw in the heating cylinder is converted to the operation for maintaining the pressure which is made later.

This pressure maintenance requires continuous maintenance for a certain period of time after the forward operation of the screw for injection is completed.

On the other hand, when the molten resin is injected from the nozzle of the heating cylinder into the cavity formed in the mold portion, the pressure received by the mold portion gradually increases as the resin is filled in the cavity, and when the cavity is completely filled, the pressure received by the mold portion is It will increase rapidly.

At this time, excessive pressure may cause an imbalance in the density distribution of the finished molding.

In addition, there may be a difference between the design capacity of the cavity formed between the stationary mold and the movable mold, and the injection amount of the injection molding machine.

KR10-2008-0042013 A KR10-2000-0006337 A KR10-2010-0055502 A KR10-2000-0006223 A

An object of the present invention is to accurately set the injection amount of the resin injected into the mold part. Accordingly, it is possible to accurately set the initial position of the injection servomotor in the weighing step before the injection step, and to set the drive of the servomotor of the mold clamping device attached to the mold part. Therefore, the whole process can be optimized in time.

The control method of the injection molding machine according to the present invention comprises the steps of measuring the pressure value in the cavity during injection, comparing the measured pressure value with a predetermined threshold pressure value, the measured pressure value is a threshold pressure value Receiving an input of the position of the screw when reaching.

According to the molding production method using an injection molding machine according to the present invention, it is possible to calculate the filling amount once and to set the filling space inside the heating cylinder accurately.

In addition, the setting of the filling space can accurately determine the operation range and the driving time of the servo motor added to the injection part, the mold part, and the mold clamping device.

1 shows an injection molding machine according to an embodiment of the present invention.
2 is a view showing the control of the injection molding machine for determining the one-time injection amount of the injection molding machine according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, the terms defined are defined in consideration of functions in the present invention, and should not be interpreted as meanings limiting the technical configurations of the present invention.

1 is a view showing an injection molding machine according to an embodiment of the present invention.

As shown in Fig. 1, the injection molding machine according to the present invention is divided into an injection part, a mold part, and a control part, and the injection part is composed of a resin supply hopper, a heating cylinder, an injection servo motor, and a screw rotation servo motor. The mold part is composed of a stationary mold and a movable mold, and a desired shape is engraved in the space where the stationary mold and the movable mold meet, that is, the cavity.

The movable mold is provided with a clamping device which enables forward and backward movement in the direction in which the movable mold is formed to take out the finished molding.

The control unit includes a control circuit for controlling the electrical devices provided in the injection unit, the mold unit, and the mold clamping device.

The hopper provided in the injection part is added to one side of the heating cylinder, and is a place for temporarily storing the resin, which is a material of the injection molding, to be supplied into the heating cylinder.

The resin stored in the hopper is stored in the amount of one injection into the filling space formed between one end of the heating cylinder, that is, the part where the nozzle is formed and the front end of the screw, by the rotation of the screw formed inside the heating cylinder. In addition, they are melted and plasticized by heat.

The filling space is equipped with a temperature sensor and a pressure sensor for detecting the temperature and pressure of the molten resin.

A nozzle is formed at one side of the heating cylinder, and a screw is provided at the other side, and is formed at the inner center of the heating cylinder to enable the screw to rotate and move forward and backward.

In order to maintain the molten state of the resin for injection, the heating cylinder is provided with a heater for converting electrical energy into thermal energy, thereby maintaining a constant temperature until injection.

A screw rotation servomotor is connected to the rear of the screw and controls the rotation of the screw according to the operation start signal of the controller.

The resin supplied from the hopper is moved to the filling space by the rotation of the screw.

In addition, an injection servomotor, which will be described later, is added to the screw, and the filled resin is injected into the mold through the nozzle.

At this time, the screw operation advances the screw in the direction in which the nozzle is formed to pressurize the resin to complete the injection operation.

In order to convert the rotational motion of the motor into linear motion, the injection servomotor has a nut formed on one side of the screw so that the screw can be moved forward and backward according to the rotation of the screw mounted on the rotational shaft of the servomotor. The screw rotates and the screw moves forward by engaging the fixed nut.

If the injection servomotor reverses, it reverses.

The forward and backward movements of the screw affect the quality of the moldings because the pressure changes to the resin by the pressure injected from the nozzle during injection.

Since the injection servomotor requires a linear motion, a linear motor capable of linear motion may be used instead of the mechanical structure of the screw and the rotating shaft having the screw as described above.

In addition, a position sensor is provided between the screw and the servomotor to detect the exact position of the screw, so that the operation of the injection servomotor can be controlled by the control unit.

Meanwhile, the mold part includes a fixed mold formed adjacent to the nozzle of the heating cylinder and a movable mold disposed corresponding to the fixed mold, and the movable mold is matched with the fixed mold to form a predetermined space, that is, a cavity therein.

The movable mold is provided with a mold clamping device so as to perform mold opening, mold closing, and mold clamping.

During the mold clamping operation, a temperature control device such as a heater and cooling water is added so that the resin inside the mold part hardens to form a certain shape.

In particular, the resin injected from the nozzle should be maintained at an appropriate temperature to fill the entire cavity while maintaining the molten state, after which the cooling rate should be adjusted to solidify while maintaining a uniform density within a short time.

The controller receives the measured values detected by the temperature sensor, the pressure sensor, and the position sensor, which are added to the injection part and the mold part described above, and based on this, the controller controls the electric flow of the servo motor, the heater, and the cooling device. To control.

The molding process using the injection molding machine according to an embodiment of the present invention formed as described above will be described based on the flow of resin and the molding process based on time flow. Molding of the resin according to the present invention consists of a metering step, injection step, mold step and molding separation step.

The metering step is a process of transferring the resin to the filling space formed in the front end of the heating cylinder, the resin stored in the hopper is transferred to the filling space by the rotation of the screw rotation servomotor provided inside the heating cylinder.

In this process, the resin is heated to melt and plasticize.

When approximately one injection amount is filled in the filling space, the rotation of the screw rotation servomotor is stopped.

At this time, the mold closing operation of the mold clamping device is in progress so that the fixed mold and the movable mold are matched with each other.

The mold closing operation must be completed and the mold clamping operation performed before the subsequent injection step.

The injection step is a process in which the molten resin filled in the filling space is injected into the mold part through the nozzle, and the resin filled in the filling space is injected through the nozzle by the forward operation of the injection servo motor, and is formed between the fixed mold and the movable mold of the mold part. Resin is filled in the cavity to be formed.

During this period, the resin is subjected to a constant molding pressure, which is due to the forward speed of the injection servomotor.

At this time, the mold die is closed and the movable mold is closed, and a mold clamping operation in which the mold is under constant pressure from the mold clamp is in progress.

The mold stage is to solidify the resin inside the cavity. After the resin is filled in the cavity, which is a space formed between the stationary mold and the movable mold, the resin is solidified by lowering the temperature with a cooling device using the cooling water formed in the stationary mold and the movable mold. do.

On the other hand, in the injection part, the injection servomotor is advanced after injection of the resin, and the pressure is maintained until the solidification is completed, that is, the speed operation of the injection servomotor is converted to the pressure maintenance (VP conversion). It is placed under the packing process.

At this time, the mold mold and the movable mold are closed, and the mold movement under constant pressure from the mold clamping apparatus continues after the injection step.

After the mold step, the molding separation step is followed.

In the molding separation step, the stationary mold and the movable mold are separated, and the finished molding is taken out from the cavity, and at the same time, the metering process is performed by driving the screw servo.

At this time, the mold clamping device performs a mold opening operation so that the molding is separated from the mold and a mold closing operation is performed for the next molding.

In the injection molding composed of the above configuration and manufacturing method, the filling space of the heating cylinder is determined according to the determined injection quantity, and the initial position and injection time of the injection servomotor are determined, and subsequent mold clamping operation of the molding apparatus is performed. The time of the clamping operation and the mold opening operation is followed by one cycle.

Therefore, the determination of the single injection amount is based on the control setting of the molding production method using an injection molding machine.

Hereinafter, referring to FIG. 2, a method for determining a single injection amount will be described. The injection amount is determined by the position of the screw because it is determined by the space between the nozzle and the front end of the screw. Therefore, the single injection amount is determined based on the position of the screw.

The resin material stored from the hopper is plasticized and melted while being moved to the filling space by the rotation of the screw in the heating cylinder.

This filling space is the space between the nozzle and the front end of the screw, the size of which is determined by one injection amount.

First of all, the position of the screw should be determined so that it can contain more than the capacity of the mold cavity design.

When the molten resin is filled in the filling space, the injection servomotor pressurizes the molten resin to inject through the nozzle into the cavity formed in the mold part.

The mold cavity is provided with a pressure sensor to continuously detect the pressure received from the cavity from the nozzle of the heating cylinder and output the measured pressure value to the differentiator and the comparator.

Here, when looking at the pressure change in the cavity, the pressure in the cavity gradually increases as the molten resin is filled in the cavity, but the measured pressure value rapidly increases when the cavity is filled.

The differentiator calculates the pressure value that changes in time and transmits it to the servomotor drive unit to control the speed of the injection servomotor.

As a result, when the pressure value input to the differentiator starts to increase, the forward speed of the screw connected to the injection servomotor can be reduced according to the output value from the differentiator.

Accordingly, the measured pressure value can reduce the rapid change. In more detail, since the inertia force acts as a rotating electric machine, it is difficult to accurately measure the screw connected to the injection servomotor.

The measured pressure values are also sent to the comparator. The comparison unit determines whether the measured pressure value reaches a threshold pressure value by comparing with a preset threshold pressure value, and if the measured pressure value reaches the threshold pressure value, the control unit detects the position of the screw from the position sensor. Input the position value of screw.

Here, the critical pressure value is a pressure value in which the pressure is rapidly increased when the molten resin is completely filled in the cavity of the mold part, and is selected from a pressure value range for maintaining the clamping force during the clamping operation of the mold clamping device, and the precision of the molded product solidified by the user. It is decided in consideration of.

As described above, the injection amount to be injected once is determined from the position value of the screw when the pressure value measured in the cavity reaches the critical pressure value, and the control unit subsequently determines the position based on the position value of the screw. The ongoing processes, that is, injection quantity, injection timing, mold closing operation, mold opening operation, and clamping operation of the clamping device can be set.

As described above, the control method of the injection molding machine according to the present invention can be variously modified within the scope of the technical idea as those skilled in the art.

M1: Injection Servo Motor
M2: Servomotor for Screw Rotation
M3: Servomotor for Clamping Device
C: Cavity
S: Filling space
ps: pressure sensor
aps: position sensor
100: injection part
110: heating cylinder
120: screw
130: Hopper
140: nozzle
200: mold part
210: movable mold
220: fixed mold
300: clamping device
310: toggle mechanism

Claims (10)

In the control method of the injection molding machine,
(a-1) measuring the pressure value in the cavity during injection;
(a-2) calculating the pressure value which is output to the differentiator and the time value is changed in the differentiator;
(a-3) controlling the position of the screw, including decreasing the speed of the injection servomotor when the pressure value input to the differentiator increases;
(b-1) measuring the pressure value in the cavity during injection;
(b-2) comparing the measured pressure value with a preset threshold pressure value,
(b-3) A method of controlling the injection molding machine, characterized in that the injection amount is determined once, including the step of receiving the position of the screw when the measured pressure value reaches the critical pressure value.
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