JP7133387B2 - Injection molding machine and its control method - Google Patents

Description

The present invention relates to an injection molding machine and its control method.

An example of a conventional injection molding machine is disclosed in Patent Document 1. The injection molding machine of Patent Document 1 includes an in-mold resin pressure closed loop control means for controlling the resin pressure in the mold based on the measured value of the resin pressure in the mold, and a resin pressure measurement in the reservoir of the injection cylinder. a reservoir resin pressure closed loop control means for controlling the resin pressure in the reservoir based on the value. In the pressure holding operation, the injection molding machine performs switching interval control for switching from the operation amount by the in-mold resin pressure closed loop control means to the operation amount by the reservoir resin pressure closed loop control means without causing a turning point. It further has means.

JP-A-3-83621

In the injection molding machine, the control is complicated because the control is switched from the control based on the resin pressure in the mold to the control based on the resin pressure in the reservoir of the injection cylinder.

Therefore, the inventors of the present invention have extensively studied the relationship between the state of the resin material injected and filled into the cavity of the mold and the pressure inside the mold. As a result, they found that by appropriately setting and controlling the target value of the pressure of the resin material in the mold, it is possible to obtain a good molded product without switching to control of the pressure of the resin material in the injection cylinder. rice field. However, depending on the setting of the target value of the pressure of the resin material inside the mold, the resin material may be pushed in by the screw even after the resin material inside the mold has solidified, and the pressure of the resin material inside the injection cylinder may increase. There was a risk that the price would rise more than necessary. This may lead to deterioration of the quality of the molded product.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an injection molding machine and a control method for the injection molding machine that can effectively suppress deterioration in the quality of molded products through simple control.

In order to achieve the above object, an injection molding machine according to an aspect of the present invention comprises an injection cylinder having a nozzle at its tip that communicates with a mold cavity, a screw accommodated in the injection cylinder, and the screw. a screw drive unit that rotates and advances back and forth; a mold pressure detection unit that detects the pressure of the resin material in the cavity; an injection cylinder pressure detection unit that detects the pressure of the resin material in the injection cylinder; a control unit that controls the screw driving unit to perform an injection operation of injecting the resin material into the cavity by means of a screw, and a holding pressure operation of applying pressure to the resin material filled in the cavity by means of the screw; wherein the control unit controls the screw drive unit so that the pressure detected by the mold internal pressure detection unit during the pressure holding operation becomes a pressure holding target pressure value, and during the pressure holding operation (1) controlling the screw drive unit to immediately terminate the pressure holding operation, or ( 2) The screw drive unit is controlled so as to restrict forward and backward movement of the screw until an execution period of the pressure holding operation elapses.

According to the present invention, the screw driving section is controlled so that the pressure of the resin material in the mold becomes the pressure holding target pressure value during the pressure holding operation. When the pressure of the resin material in the injection cylinder reaches the holding pressure upper limit pressure value during the holding pressure operation, the holding pressure operation is terminated immediately, or the screw is rotated until the execution period of the holding pressure operation elapses. Control forward and backward movement. Because of this, if the screw drive unit is controlled based on the pressure of the resin material in the mold, the resin material will be pushed in by the screw even after the resin material in the mold has solidified during the pressure holding operation. However, it is possible to prevent the pressure of the resin material in the injection cylinder from exceeding the holding pressure upper limit pressure value. Therefore, it is possible to prevent the pressure of the resin material in the injection cylinder from increasing more than necessary.

In the present invention, the control unit detects the pressure detected by the injection cylinder pressure detection unit during the pressure holding operation and after the pressure detected by the mold pressure detection unit has decreased to a monitoring start pressure value. When the pressure reaches the holding pressure upper limit pressure value, (1) the screw driving unit is controlled so as to immediately end the holding pressure operation, or (2) the execution period of the holding pressure operation elapses. The screw drive unit is controlled so as to restrict forward and backward movement of the screw up to . By doing so, the pressure of the resin material in the injection cylinder can be detected at a more appropriate timing, and erroneous detection of an increase in the pressure of the resin material in the injection cylinder can be suppressed.

The present invention further comprises a screw position detection section that detects the position of the screw, and the control section detects the position detected by the screw position detection section during the injection operation and the in-mold pressure detection section. It is preferable to control the screw driving section so as to switch from the injection operation to the holding pressure operation when the detected pressure satisfies an operation switching condition. By doing so, it is possible to switch from the injection operation to the holding pressure operation at an appropriate timing.

In the present invention, it is preferable that the holding pressure upper limit pressure value is set within a range of ±10% of the pressure detected by the injection cylinder internal pressure detecting section when the operation switching condition is satisfied. By doing so, it is possible to more effectively prevent the pressure of the resin material in the injection cylinder from increasing more than necessary.

In the present invention, it is preferable that the injection cylinder internal pressure detection section is a load cell attached to the screw or the screw driving section. By doing so, the pressure of the resin material in the injection cylinder can be detected by the load cell provided outside the injection cylinder, so the pressure can be detected with a simple configuration.

In order to achieve the above object, a control method for an injection molding machine according to another aspect of the present invention includes an injection cylinder having a nozzle at its tip that communicates with a mold cavity; a screw accommodated in the cavity, the injection step of advancing the screw to inject a resin material into the cavity; and applying pressure to the resin material filled in the cavity. and a holding pressure step of moving the screw forward and backward so as to apply pressure, and in the holding pressure step, the pressure of the resin material in the mold (hereinafter referred to as "in-mold resin pressure") reaches the holding pressure target pressure value During the holding pressure process and after the resin pressure in the mold has decreased to the monitoring start pressure value, the pressure of the resin material in the injection cylinder reaches the holding pressure upper limit pressure value (1) the pressure holding process is terminated immediately, or (2) forward and backward movement of the screw is restricted until the execution period of the pressure holding process elapses.

According to the present invention, in the holding pressure process, the screw is moved forward and backward so that the pressure of the resin material in the mold reaches the holding pressure target pressure value. Then, when the pressure of the resin material in the injection cylinder reaches the holding pressure upper limit pressure value during the holding pressure process, the holding pressure process is immediately terminated, or the screw is held until the execution period of the holding pressure process elapses. to regulate the forward and backward movement of the Because of this, when the screw is moved back and forth (especially forward) based on the pressure of the resin material inside the mold, the resin material is still pushed by the screw even after the resin material inside the mold has solidified during the holding pressure process. Although it may be pushed in, the pressure of the resin material in the injection cylinder does not exceed the holding pressure upper limit pressure value. Therefore, it is possible to prevent the pressure of the resin material in the injection cylinder from increasing more than necessary.

According to the present invention, when the pressure of the resin material in the mold is controlled based on the pressure of the resin material in the mold, the pressure of the resin material in the injection cylinder does not increase more than necessary. It is possible to effectively suppress the deterioration of the quality of the molded product.

1 is a front view of an injection molding machine according to one embodiment of the present invention; FIG. FIG. 2 is an enlarged cross-sectional view of the main part of the injection molding machine of FIG. 1; 2 is a diagram illustrating functional blocks of the injection molding machine of FIG. 1; FIG. FIG. 2 is a diagram for explaining a pressure holding operation of the injection molding machine of FIG. 1;

An injection molding machine according to an embodiment of the present invention will be described below with reference to FIGS. 1 to 4. FIG.

FIG. 1 is a front view of an injection molding machine according to one embodiment of the present invention. 2 is an enlarged cross-sectional view of the main part of the injection molding machine of FIG. 1. FIG. FIG. 3 is a diagram illustrating functional blocks of the injection molding machine of FIG. FIG. 4 is a diagram for explaining the pressure holding operation of the injection molding machine of FIG. In this specification, the lower side of FIGS. 1 and 2 is defined as the front, and the upper side is defined as the rear.

An injection molding machine 1 according to the present embodiment shown in FIGS. 1 and 2 injects a molten resin material into a cavity 4 formed by clamping an upper mold 2 and a lower mold 3 to cool and solidify. A molded product is obtained by converting the Although this embodiment shows an example of a configuration in which the present invention is applied to a vertical injection molding machine in which the injection cylinders are arranged in the vertical direction, the injection cylinders are arranged in the horizontal direction. The present invention may be applied to a horizontal injection molding machine.

In the injection molding machine 1, an injection unit 10 for injecting a resin material, and an upper mold 2 and a lower mold 3 are brought into contact with each other on a machine base 6 to generate a mold clamping force to perform mold clamping. It has a mold clamping unit 20 and a display operation unit 30 for.

The injection unit 10 has an injection cylinder 11 having a nozzle 11a facing downward at its tip, and a screw 12 housed in the injection cylinder 11 so as to be rotatable and forward and backward. The nozzle 11a communicates with the cavity 4 through a resin channel 5 having runners, spools, gates, and the like. The injection unit 10 also has a cylinder driving section 13 having an electric motor for moving the injection cylinder 11 up and down, and a screw driving section 14 having an electric motor for rotating and moving the screw 12 forward and backward within the injection cylinder 11. ing. Moving the injection unit 10 downward to approach the upper mold 2 is called advance, and moving upward to leave the upper mold 2 is called retreat. The cylinder driving section 13 and the screw driving section 14 are connected to the control section 40 and operate according to control signals from the control section 40 .

The injection unit 10 has a load cell 16 as an injection cylinder internal pressure detection section between the screw 12 and the screw driving section 14 . The load cell 16 detects the pressure of the resin material acting on the screw 12 within the injection cylinder 11 , is attached to the screw 12 or the screw driving section 14 and is provided outside the injection cylinder 11 . The load cell 16 is connected to the control unit 40 , detects an injection-cylinder resin pressure Pi, which is the pressure of the resin material in the injection cylinder 11 , and transmits a signal indicating the injection-cylinder resin pressure Pi to the control unit 40 . . Instead of the load cell 16, for example, a configuration in which a pressure sensor is embedded in the inner wall of the injection cylinder 11 may be used. , the resin pressure Pi in the injection cylinder can be detected.

The injection unit 10 has a position sensor 17 as a screw position detector that detects the position of the screw 12 in the front-rear direction (vertical direction in FIG. 1) within the injection cylinder 11 . The position sensor 17 is connected to the control unit 40 , detects a screw position L, which is the position of the screw 12 within the injection cylinder 11 , and transmits a signal indicating the screw position L to the control unit 40 .

The mold clamping unit 20 includes a movable plate 21 as a flat upper plate to which the upper mold 2 is attached to the lower surface 21a, and a lower plate to which the lower mold 3 to which the upper mold 2 is clamped is attached to the upper surface 22a. and a rotary table 22 of . A cavity 4 is formed by clamping the upper mold 2 and the lower mold 3 together. A plurality of lower molds 3 are attached to the rotary table 22 , and by rotating, the plurality of lower molds 3 are sequentially transported to a position facing the upper mold 2 . The mold clamping unit 20 has actuators (not shown) for opening and closing the upper mold 2 and the lower mold 3 and taking out the product.

An injection cylinder 11 is arranged above the movable plate 21 . A through-hole 21b is formed in the center of the movable plate 21 and has a size into which the nozzle 11a of the injection cylinder 11 can be inserted. The upper portion of through hole 21b is formed in a mortar shape. A nozzle 11 a is inserted through the through hole 21 b , and the molten resin material is injected into the cavity 4 while the nozzle 11 a is in contact with the upper mold 2 .

The mold clamping unit 20 has a cubic box-shaped cover 23 provided on the upper surface 21c of the movable plate 21 so as to surround the nozzle 11a.

The mold clamping unit 20 is a mold internal pressure sensor as a mold internal pressure detection unit that detects the pressure of the resin material in the cavity 4 formed by clamping the upper mold 2 and the lower mold 3. 26. The in-mold pressure sensor 26 is connected to the control unit 40, detects the in-mold resin pressure Pc, which is the pressure of the resin material in the cavity 4, and sends a signal indicating the in-mold resin pressure Pc to the control unit 40. to send.

The display operation unit 30 has a display section 31 for displaying information related to the injection molding machine 1 and an operation section 32 for inputting operations. The display section 31 and the operation section 32 are connected to the control section 40 . The display unit 31 displays various screens on the display area based on the control signal from the control unit 40 . The operation unit 32 has a plurality of keys, and transmits a signal to the control unit 40 according to the operation input to each key. The display/operation unit 30 may include a touch panel as the operation unit 32, and may have a software switch configured by combining a touch panel superimposed on the display area of the display unit 31 and icons displayed thereon.

The injection molding machine 1 also has a control section 40 that controls the overall operation. The control unit 40 includes, for example, a microcomputer for built-in equipment having a CPU, ROM, RAM, EEPROM, and various I/O interfaces. The control unit 40 controls the cylinder driving unit 13 and the screw driving unit 14 of the injection unit 10 and the mold clamping unit 20 in each process such as the mold closing process, the weighing process, the injection process, the pressure holding process, the mold opening process, and the take-out process. It controls the operation of each driving device such as an actuator (not shown).

Next, an example of the operation (control method) according to the present invention in the injection molding machine 1 of this embodiment described above will be described with reference to FIG.

First, the control section 40 of the injection molding machine 1 controls the cylinder drive section 13 to move the injection cylinder 11 forward to approach the upper mold 2 so that the nozzle 11 a touches the upper mold 2 . In this state, the nozzle 11a and the cavity 4 are communicated through the resin flow path 5, and the screw 12 is at the initial position (for example, 0 mm position). The injection cylinder 11 is heated by a heater (not shown), and the resin material in the injection cylinder 11 is kneaded by the screw 12, so that the resin material near the tip of the injection cylinder 11 is in a molten state.

Then, in the mold closing process, the control unit 40 controls a mold clamping drive unit (not shown) to overlap and clamp the upper mold 2 and the lower mold 3 (mold closing operation).

In the metering process, the control unit 40 controls the screw driving unit 14 to rotate the screw 12 while retracting it to a metering position (for example, a position of 50 mm), and injects the amount of resin material required for one injection. Supply to the tip of the cylinder 11 (metering operation).

In the injection process, the control unit 40 controls the screw driving unit 14 to advance the screw 12, thereby injecting the resin material at the tip of the injection cylinder 11 into the cavity 4 through the resin flow path 5 (injection operation). .

Specifically, the control unit 40 acquires the screw position L based on the signal transmitted from the position sensor 17 during the injection operation. Then, the screw drive unit 14 is controlled based on the screw position L to advance the screw 12 so that the screw speed V becomes the target speed.

Further, the control unit 40 acquires the injection cylinder internal resin pressure Pi based on a signal transmitted from the load cell 16 during the injection operation. In order to detect an abnormality such as clogging of the nozzle 11a, the injection cylinder internal resin pressure Pi is monitored. When the resin pressure Pi in the injection cylinder rises and reaches a predetermined abnormality detection pressure value Pm, the control unit 40 determines that an abnormality has occurred and stops all operations related to molding. That is, the abnormality detection pressure value Pm is used for abnormality detection of the injection molding machine 1 .

Further, the control unit 40 acquires the in-mold resin pressure Pc, which is the pressure of the resin material in the cavity 4, based on the signal transmitted from the in-mold pressure sensor 26 during the injection operation. Then, the control unit 40 determines that the screw position L is within an operation switching range W within X mm (for example, X=5 mm) forward and backward from the VP switching position Lvp, which is a predetermined operation switching position, and the resin in the mold When the pressure Pc is equal to or higher than a predetermined operation switching pressure value Pvp, it is assumed that the screw position L and the in-mold resin pressure Pc satisfy the operation switching condition, and the operation is switched to the holding pressure operation. By doing so, it is possible to switch from the injection operation to the holding pressure operation at an appropriate timing. The operation switching pressure value Pvp is preferably the initial value of the holding pressure target pressure value Ps. By doing so, the screw 12 can be smoothly switched from the speed control operation to the pressure control operation.

In the pressure holding process, the control unit 40 controls the screw driving unit 14 to move the screw 12 back and forth, thereby applying pressure to the resin material filled in the cavity 4 (pressure holding operation). Specifically, the control unit 40 obtains the in-mold resin pressure Pc based on the signal transmitted from the in-mold pressure sensor 26, and feedback-controls the screw driving unit 14 to control the in-mold resin pressure Pc. is the holding pressure target pressure value Ps. The control unit 40 executes the pressure holding operation for a predetermined execution period (pressure holding period Th, for example, 5 seconds).

Then, the control unit 40 controls the resin pressure Pi in the injection cylinder to increase during the pressure holding operation (during the pressure holding process) to reach a predetermined holding pressure upper limit pressure value Pu set to a value higher than the holding pressure target pressure value Ps. When the pressure is reached, the forward and backward movement (movement) of the screw is restricted until the pressure holding period Th elapses, that is, the screw driving section 14 is controlled so as to keep the screw 12 in place. Alternatively, when the resin pressure Pi in the injection cylinder rises during the pressure holding operation and reaches a predetermined holding pressure upper limit pressure value Pu, the control unit 40 immediately ends the pressure holding operation and proceeds to the next mold opening step. The screw drive 14 may be controlled to advance.

Alternatively, the control unit 40 starts monitoring the injection cylinder internal resin pressure Pi after the mold internal resin pressure Pc has decreased to a predetermined monitoring start pressure value Pd during the pressure holding operation. has reached the holding pressure upper limit pressure value Pu. By doing so, it is possible to detect the resin pressure Pi in the injection cylinder at a more appropriate timing. Detection can be suppressed.

In this embodiment, the holding upper limit pressure value Pu is set in advance to a value lower than the abnormality detection pressure value Pm. Alternatively, the holding pressure upper limit pressure value Pu is, for example, within a range of ±10% of the resin pressure Pi in the injection cylinder detected by the load cell 16 when the screw position L and the resin pressure Pc in the mold satisfy the operation switching condition. can be dynamically set to the value of For example, the holding pressure upper limit pressure value Pu is set to a value that is 105% of the resin pressure Pi in the injection cylinder when the operation switching condition is satisfied. By doing so, it is possible to more effectively prevent the injection cylinder internal resin pressure Pi from increasing more than necessary.

Next, in the mold opening process, the control unit 40 controls the mold clamping drive unit to vertically open the upper mold 2 and the lower mold 3 (mold opening operation). Then, in the take-out process, the control unit 40 takes out the molded product from the cavity 4 by an eject pin (not shown) (take-out operation).

After that, the mold closing step to the taking-out step are repeated to form a molded product.

As described above, according to the injection molding machine 1 of the present embodiment, the control unit 40 controls the in-mold resin pressure Pc, which is the pressure of the resin material in the cavity 4, to be the holding pressure target pressure in the holding pressure operation (pressure holding step). The screw drive unit 14 is controlled so as to obtain the value Ps. During the pressure holding operation, when the injection cylinder internal resin pressure Pi, which is the pressure of the resin material in the injection cylinder 11, reaches the holding pressure upper limit pressure value Pu, the holding pressure period Th, which is the execution period of the pressure holding operation, is The screw drive unit 14 is controlled so as to restrict forward and backward movement of the screw 12 until the time elapses. Because of this, when the screw drive unit 14 is controlled based on the resin pressure Pc in the mold, the screw 12 pushes in the resin material even after the resin material in the cavity 4 has solidified during the pressure holding operation. However, it is possible to prevent the injection cylinder internal resin pressure Pi from exceeding the holding pressure upper limit pressure value Pu. Therefore, it is possible to prevent the injection cylinder internal resin pressure Pi from increasing more than necessary. Therefore, it is possible to effectively suppress deterioration of the quality of the molded product with simple control.

Although embodiments of the present invention have been described above, the present invention is not limited to these examples. A person skilled in the art can add, delete, or change the design of the above-described embodiment as appropriate, or combine the features of the embodiment as appropriate, as long as it has the gist of the present invention. Included within the scope of the invention.

DESCRIPTION OF SYMBOLS 1... Injection molding machine, 2... Upper mold, 3... Lower mold, 4... Cavity, 5... Resin channel, 6... Machine stand, 10... Injection unit, 11... Injection cylinder, 11a... Nozzle, 12... Screw , 13... Cylinder drive part, 14... Screw drive part, 16... Load cell, 17... Position sensor, 20... Mold clamping unit, 21... Movable plate, 21a... Lower surface, 21b... Through hole, 21c... Upper surface, 22... Rotary table , 22a... upper surface, 23... cover, 26... mold internal pressure sensor, 30... display operation unit, 31... display section, 32... operation section, 40... control section, V... screw speed, L... screw position, Lvp... VP switching position, W: Operation switching range, Pi: Resin pressure in injection cylinder, Pc: Resin pressure in mold, Ps: Holding pressure target pressure value, Pm: Abnormal detection pressure value, Pu: Holding pressure upper limit pressure value , Pvp... Operation switching pressure value, Pd... Monitoring start pressure value

Claims (5)

an injection cylinder having a nozzle at its tip that communicates with the mold cavity;
a screw housed in the injection cylinder;
a screw drive unit that rotates and moves the screw forward and backward;
an in-mold pressure detection unit that detects the pressure of the resin material in the cavity;
an injection cylinder internal pressure detection unit that detects the pressure of the resin material in the injection cylinder;
a control unit that controls the screw driving unit to perform an injection operation of injecting the resin material into the cavity by the screw and a pressure holding operation of applying pressure to the resin material filled in the cavity by the screw; , and
The control unit
controlling the screw drive unit so that the pressure detected by the mold internal pressure detection unit in the pressure holding operation becomes a pressure holding target pressure value;
During the holding pressure operation and after the pressure detected by the mold internal pressure detecting section has decreased to the monitoring start pressure value , the pressure detected by the injection cylinder internal pressure detecting section reaches the holding pressure upper limit pressure value. (1) controlling the screw drive unit to immediately terminate the holding pressure operation, or (2) restricting forward and backward movement of the screw until the execution period of the holding pressure operation has elapsed. An injection molding machine characterized in that the screw driving section is controlled as follows. further comprising a screw position detection unit that detects the position of the screw;
When the position detected by the screw position detection unit and the pressure detected by the mold internal pressure detection unit during the injection operation satisfy an operation switching condition, the control unit switches from the injection operation to the maintenance. 2. The injection molding machine according to claim 1 , wherein said screw drive is controlled to switch to pressure operation. 3. The injection molding according to claim 2 , wherein said holding pressure upper limit pressure value is set within a range of ±10% of said pressure detected by said injection cylinder internal pressure detecting section when said operation switching condition is satisfied. machine. The injection molding machine according to any one of claims 1 to 3 , wherein the injection cylinder internal pressure detection section is a load cell attached to the screw or the screw driving section. A control method for an injection molding machine having an injection cylinder provided at its tip with a nozzle communicating with a mold cavity, and a screw accommodated in the injection cylinder so as to be rotatable and forward and backward,
an injection step of advancing the screw to inject the resin material into the cavity;
a holding pressure step of moving the screw forward and backward so as to apply pressure to the resin material filled in the cavity;
In the holding pressure step, the screw is moved forward and backward so that the pressure of the resin material in the mold (hereinafter referred to as "in-mold resin pressure") reaches the holding pressure target pressure value,
When the pressure of the resin material in the injection cylinder reaches the holding pressure upper limit pressure value during the holding pressure process and after the resin pressure in the mold has decreased to the monitoring start pressure value , (1) the holding pressure; or (2) restricting forward and backward movement of the screw until an execution period of the holding pressure process has elapsed.

Images