JP3437907B2 - Insulation control method and apparatus for injection molding machine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure holding control method and device in a pressure holding step after resin filling into a mold cavity in an injection molding machine.

[0002]

2. Description of the Related Art Generally, the pressure holding control in an injection molding machine is configured to detect the position of the injection screw or the pressure in the mold cavity to control the hydraulic pressure set in the molding machine.

Therefore, in this type of holding pressure control, for example, the resin pressure in the mold cavity detected by a pressure sensor is that of the surface of the molded product to be molded by the mold, and the resin pressure in the mold is The pressure distribution is non-uniform with respect to time and position, especially in the latter stage after the resin in the gate section is solidified in the pressure holding step, the pressure application section (hydraulic pressure on the molding machine side) and the detection section (pressure sensor). Since a pressure difference between the molded product and the above-mentioned is large, excessive pressure is applied to a local portion of the molded product, and burrs, sink marks, etc. are generated, and a molded product having an uneven density is molded.

However, in the pressure holding step, the hydraulic pressure on the molding machine side and the resin pressure in the mold cavity are greatly different, and the pressure set value (holding pressure set value) on the molding machine side is lowered. However, the pressure in the cavity does not decrease, but tends to increase as the resin filling progresses.

That is, when the pressure set value on the molding machine side is lower than the pressure in the cavity at the time of switching the holding pressure, as shown in FIG. 3 (a), the switching from the filling step of the injection step to the holding step is performed. After the pressure is switched, the pressure in the cavity temporarily drops, and the injection screw temporarily stops or retracts, which causes problems such as sink marks and short shots in the molded product, and there is a problem that this problem cannot be solved. is there.

On the other hand, when the pressure set value on the molding machine side is higher than the pressure in the cavity at the time of switching the holding pressure, the resin filling amount at the time of switching the holding pressure is small as shown in FIG. 3 (b). When the holding pressure is switched to the holding pressure, it operates so as to reach the holding pressure set value, so the injection screw moves at a high speed and the pressure inside the cavity reaches the set pressure, which causes burr on the molded product. is there. Also, when switching to holding pressure due to a large amount of resin filling when switching holding pressure, the pressure inside the cavity tends to become higher than the pressure when switching holding pressure. There is a problem that burr is generated.

Therefore, conventionally, the quality of the molded product is made uniform by smoothly switching from the resin pressure control means for controlling the resin pressure in the mold to the hydraulic pressure control means for controlling the hydraulic pressure of the injection cylinder. A holding pressure control device that can be used has been proposed (Japanese Patent Laid-Open No. 3-45327).

That is, the proposed pressure maintaining control device detects the resin pressure closed loop control means for controlling the resin pressure based on the detection value of the pressure sensor for detecting the resin pressure in the mold, and the hydraulic pressure of the injection cylinder. The hydraulic pressure closed loop control means for controlling the hydraulic pressure based on the detection value of the hydraulic pressure sensor, and the switching section control means for switching between them. The switching section control means controls the operation amount and the hydraulic pressure by the resin pressure closed loop control means. The closed loop control means is provided with control switching means for controlling the operation amount so as not to generate a node with respect to the operation amount.

[0009]

However, the pressure holding control device according to the above proposal is provided with a target value setting device for inputting information such as a resin pressure target value and a hydraulic pressure target value, and the target value setting device sets the target value setting device. In addition, since the means for compensating each target value with the detection value detected by the sensor and compensating for the respective target values are provided, the device configuration becomes complicated and the control operation becomes complicated. There are difficulties.

Therefore, as a result of intensive studies, the inventor of the present invention detected the pressure in the mold cavity at the time of switching the holding pressure, and kept this pressure for a certain period of time so that the pressure in the cavity was constant or gentle. It was found that it is possible to prevent problems such as burrs and sink marks in the molded product.

Therefore, the object of the present invention is to control the pressure in the cavity until the resin is sufficiently filled into the mold cavity without immediately controlling the hydraulic pressure on the molding machine side when the holding pressure is switched. An object of the present invention is to provide a pressure holding control method and device for an injection molding machine, which can controlly control and mold an optimum molded product that does not cause burrs or sink marks.

[0012]

In order to achieve the above-mentioned object, a pressure holding control method for an injection molding machine according to the present invention comprises a first pressure sensor for detecting a resin pressure in a mold cavity and an injection method. A second pressure sensor for detecting the control hydraulic pressure of the cylinder, a holding pressure switching control means for controlling the switching from the filling process to the holding process in the injection process, and the injection cylinder after the holding pressure is switched. Inside the cavity to control the multi-stage hydraulic
In a holding pressure control method for an injection molding machine equipped with a constant pressure control unit and a timer switching unit, the timer switching unit is activated when the holding pressure is switched.
The first pressure by connecting to the constant pressure inside the cavity
Cavity pressure based on the pressure detected by the sensor
By controlling the pressure for a certain time by the constant control unit, gold
After maintaining the pressure in the mold cavity for a certain period of time, the injection cylinder is switched to multistage hydraulic control.

As a device for carrying out the above-mentioned pressure holding control method, a first pressure sensor for detecting the resin pressure in the mold cavity and a second pressure sensor for detecting the control hydraulic pressure of the injection cylinder. A holding pressure of an injection molding machine, which is provided with a sensor and a holding pressure switching control means for controlling switching from a filling process to a pressure holding process in the injection process, and is configured to perform multistage hydraulic control of the injection cylinder after the holding pressure is switched. In the control device, the holding pressure switching control means includes a multi-stage hydraulic pressure control unit having a holding pressure setting unit, a constant cavity pressure control unit, a timer switch, and an A / D conversion output unit, and when holding pressure is switched. The timer switch is connected to the cavity constant pressure control section side, and the cavity constant pressure control section controls the pressure for a predetermined time based on the pressure detected by the first pressure sensor. Characterized by configured to perform multi-stage hydraulic control and switching connected in multiple stages hydraulic control unit side.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a pressure holding control method for an injection molding machine according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows a schematic configuration of a control system for carrying out a pressure holding control method for an injection molding machine according to the present invention.

Referring to FIG. 1, the injection molding machine according to this embodiment has a mold 10, a heating barrel 12, and an injection screw 1.
4 and the injection cylinder 16 basically. However, with respect to the mold 10, the cavity 1
A pressure sensor 18 for detecting the pressure in 0a is provided, and a pressure sensor 22 for detecting the control hydraulic pressure supplied from the variable displacement hydraulic pump 20 is provided for the injection cylinder 16. Further, a position sensor 24 for detecting the screw position of the injection screw 14 and switching from the filling process of the injection process to the pressure holding process is provided. A control device 26 is provided for controlling the variable displacement hydraulic pump 20 for supplying the required control hydraulic pressure to the injection cylinder 16 by inputting the outputs of the respective sensors 18, 22, 24.

The pressure sensor 18 for detecting the pressure in the cavity 10a can be provided for a part of the molded product in the mold or for the runner portion of the mold.

In the present embodiment, the control device 26 is
As means for performing the holding pressure control, a multistage hydraulic control unit 30 having a holding pressure setting unit 28 and a constant cavity pressure control unit 32.
And two control systems, and these control systems are selectively switched by the timer switch 34 to output the D / A conversion output section 36.
A more required control signal is output to control the variable displacement hydraulic pump 20.

Therefore, in the present embodiment, at the time of switching the holding pressure when switching from the filling process to the holding process in the injection process,
The timer switch 34 is connected to the cavity constant pressure control section 32 side, the pressure in the mold cavity 10a is detected by the pressure sensor 18, and this pressure is held.
The detection value is input to the constant cavity pressure control unit 32, and the variable displacement hydraulic pump 20 is configured to perform constant control of the pressure detection value of the pressure sensor 18 at a preset time. Then, after the lapse of the set time, the timer switch 34 is switched and connected to the multi-stage hydraulic control unit 30 side to perform multi-stage hydraulic control on the variable displacement hydraulic pump 20.

Next, the change state of the pressure in the mold cavity 10a at the time of switching the holding pressure according to the present invention will be described with reference to FIG.
The description will be made with reference to (a) to (d).

First, FIG. 2 (a) is a characteristic diagram of the pressure inside the cavity 10a in which the embodiment of the standard pressure-holding process is shown by a solid line and the conventional example is shown by a broken line. In this case, at the time of switching the holding pressure, the constant cavity pressure control unit 32 controls the cavity 10 via the timer switch 34.
By controlling the pressure in a to be constant, the pressure in the cavity immediately after switching the holding pressure smoothly rises, and after a lapse of a fixed time (t), the multi-stage hydraulic control unit 30 presets the multi-stage hydraulic pressure. The control is performed, and the holding pressure control for obtaining the optimum molded product in which burrs and sink marks are not generated is achieved.

Therefore, under the conditions of the standard pressure-holding process shown in FIG. 2A, when the injection filling speed in the previous stage at the time of pressure-holding switching changes, for example, as shown in FIG. 2B. As described above, the pressure inside the cavity changes when the holding pressure is switched. That is, even if the injection filling speed is changed, the pressure in the cavity at the time of switching the holding pressure can be smoothly changed.

When the position of the pressure-holding switching screw is changed under the standard pressure-holding process conditions shown in FIG. 2A, as shown in FIGS. 2C and 2D. In addition, the pressure inside the cavity changes when the holding pressure is switched. That is, (c) of FIG. 2 shows a characteristic diagram when the holding pressure switching screw position is before the standard time, and (d) of FIG. 2 shows a characteristic diagram when the holding pressure switching screw position is after the standard time. Show.

As described above, according to the present invention, it is not necessary to set the target value for the resin pressure or the hydraulic pressure at the time of switching the holding pressure each time under any injection molding condition, and it is not necessary to set the target value for the switching of the holding pressure. By detecting the pressure in the mold cavity,
By performing constant pressure control in the cavity for a certain period of time based on this detected value, it is possible to mold an optimum molded product that does not cause burrs or sink marks.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and many design changes can be made without departing from the spirit of the present invention.

[0026]

As described above, according to the pressure holding control method of the injection molding machine according to the present invention, the first pressure sensor for detecting the resin pressure in the mold cavity and the control hydraulic pressure of the injection cylinder are used. A second pressure sensor for detecting, a holding pressure switching control means for controlling the switching from the filling process to the holding pressure process in the injection process, and a constant cavity pressure so as to perform multi-stage hydraulic control of the injection cylinder after switching the holding pressure. Control unit and Thailand
In a pressure control method for an injection molding machine equipped with a switch, a timer switch keeps the cavity pressure constant when switching the pressure.
It is connected to the control side and detected by the first pressure sensor.
Based on the generated pressure
After the pressure in the mold cavity is maintained for a certain period of time by controlling the pressure for a certain period of time, the injection cylinder is switched to the multi-stage hydraulic control so that the pressure on the molding machine side is immediately changed when the holding pressure is switched. By controlling the pressure in the cavity until the resin is sufficiently filled in the mold cavity without controlling the hydraulic pressure, it is possible to mold an optimal molded product that does not cause burrs or sink marks. .

The apparatus for carrying out the holding pressure control method of the present invention also has an advantage that it can be manufactured at a low cost with a simple structure.

[Brief description of drawings]

FIG. 1 is a main part system diagram of a control circuit that implements a pressure holding control method for an injection molding machine according to the present invention.

FIG. 2 is a diagram showing a change state of pressure in a cavity by the pressure holding control method of the present invention, (a) is a characteristic diagram in a standard case, and (b) is a condition of (a). Is a characteristic diagram in the case where the injection filling speed is changed, and (c) is (a).
FIG. 4 is a characteristic diagram when the pressure holding switching screw position is before standard time under the condition (1), and (d) is a characteristic diagram when the pressure holding switching screw position is after standard time under the condition (a).

3 (a) and 3 (b) are characteristic diagrams respectively showing a change state of the pressure in the cavity by the conventional holding pressure control method.

[Explanation of symbols]

10 mold 10a cavity 12 heating barrel 14 Injection screw 16 injection cylinder 18 Pressure sensor (inside cavity) 20 Variable displacement hydraulic pump 22 Pressure sensor (hydraulic) 24 position sensor 26 Control device 28 Holding pressure setting section 30 Multi-stage hydraulic control unit 32 Constant pressure control unit in cavity 34 Timer switch 36 D / A conversion output section

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-7-164496 (JP, A) JP-A-3-45327 (JP, A) JP-A-4-347615 (JP, A) JP-A-1- 228821 (JP, A) JP 64-14016 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B29C 45/77 B29C 45/50 B29C 45/57

Claims (2)

(57) [Claims] 1. A first pressure sensor for detecting a resin pressure in a mold cavity, a second pressure sensor for detecting a control hydraulic pressure of an injection cylinder, and a filling step to a pressure holding step in an injection step. a pressure-holding control means for controlling the switching to, and a timer switcher cavity pressure constant control unit to multistage hydraulic control the injection cylinder to the pressure-holding換後
Pressure control method for injection molding machine equipped with
Sometimes the timer switch is connected to the cavity pressure control unit side.
Then, based on the pressure detected by the first pressure sensor,
The pressure inside the cavity is kept constant for a certain time by the control unit.
A holding pressure control method for an injection molding machine, characterized in that the injection cylinder is switched to multistage hydraulic control after the pressure in the mold cavity is held for a certain time by controlling. 2. A first pressure sensor for detecting a resin pressure in a mold cavity, a second pressure sensor for detecting a control hydraulic pressure of an injection cylinder, and a filling process to a pressure-holding process in an injection process. In the pressure holding control device of the injection molding machine, which is configured to perform multi-stage hydraulic control of the injection cylinder after the pressure holding switching, the pressure holding switching control means is provided. A multi-stage hydraulic control unit having a pressure setting unit, a constant cavity pressure control unit, a timer switching unit, and an A / D conversion output unit are provided. By connecting and controlling the pressure in the cavity for a fixed period of time based on the pressure detected by the first pressure sensor, the timer switch is switched to the multi-stage hydraulic control unit side and connected to the multi-stage hydraulic control. A holding pressure control device for an injection molding machine, which is configured to perform.