JP2815182B2 - Injection pressure control method and device for injection molding machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for controlling an injection pressure of an injection molding machine, and more particularly, to an injection pressure for performing injection molding of a material having a relatively high viscosity such as rubber. The present invention relates to a method and a device for controlling an injection pressure of an injection molding machine suitable for controlling in accordance with a filling process.

[Conventional technology]

Conventionally, when performing injection molding of a material having a relatively high viscosity such as rubber in an injection molding machine, injection pressure control is also performed in a filling process, unlike injection molding of a resin having a low viscosity.

That is, at the start of filling, filling is performed with a high injection pressure (primary injection pressure), and thereafter, control is performed to lower the injection pressure (secondary injection pressure) to perform filling.

When such injection pressure control is performed, it is desired that filling be completed at a lower injection pressure at the time of completion of filling in order to reduce the mold clamping force during injection molding.

This is because the required mold clamping force (F) = the injection pressure (P) × the projected area of the product (S) is roughly estimated.

[Problems to be solved by the invention]

However, with the conventional injection pressure control, it is difficult to accurately detect the filling completion time, and in order to make the injection pressure low at the filling completion time, the injection pressure must be set to a low injection pressure from a point much earlier than the filling completion time. No.

When such injection pressure control is used, the filling speed becomes exponentially slow, and the injection pressure at the completion of filling is extremely changed in consideration of the switching accuracy of the injection pressure and the fluctuation of the material viscosity between lots. It is difficult to do.

SUMMARY OF THE INVENTION An object of the present invention is to provide an injection pressure control method and apparatus for an injection molding machine capable of changing an injection pressure to a required pressure at the time of completion of filling.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a prescribed injection pressure to an injection molding machine according to a filling command, and thereafter monitors the pressure in the molding die to determine the pressure inside the mold at a predetermined position before reaching the gate. A control method for changing the injection pressure to the injection molding machine to the required pressure at the time of filling completion when the difference between the pressure in the mold at the position on the gate side of this position and the pressure corresponding to the filling completion time has been reached. It has been adopted.

Further, as a control device, a pressure sensor that detects the pressure inside the mold runner, a pressure sensor that detects the pressure on the gate side, and a detection output of both pressure sensors are compared. A switching command circuit for outputting a switching command when a pressure corresponding to the filling completion time is reached, and a prescribed injection pressure is given to the injection molding machine by the filling command, and this injection pressure is changed to the required pressure at the filling completion time by the switching command. A control device having a pressure adjusting circuit for changing the pressure is constituted.

[Action]

Since the present invention has the above configuration, the filling completion time is detected based on the detection outputs of the plurality of pressure sensors that detect the pressure in the molding die, and the injection pressure is changed to the required pressure at the filling completion time. Thus, the injection pressure at the time of completion of filling can be changed to the required pressure without reducing the filling speed.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, a molding die 10 has an upper die 11 and a lower die 12, and a disc-shaped runner 13 and a gate 14 are formed between the upper die 11 and the lower die 12. 11 sprue
15 are formed.

An injection molding machine 16 is arranged above the upper mold 11.

The injection molding machine 16 includes an injection cylinder 17 and an injection cylinder 18.

Further, a plurality of pressure sensors 19 and 20 are arranged on the lower mold 12.

The pressure sensor 20 detects an in-mold pressure at a predetermined position in the runner 13 of the molding die 10, and the pressure sensor 19 detects an in-mold pressure closer to the gate 14 than the pressure sensor 20. Each detection output of the sensors 19 and 20 is supplied to the comparison setter 21.

The comparison setter 21 takes in the detection outputs from the pressure sensors 19 and 20, and when the difference between the pressure sensors 19 and 20 becomes a pressure corresponding to the filling completion time, for example, the detection of the two pressure sensors 19 and 20 is performed. It is configured as a switching command circuit that outputs a switching command to the amplifier 22 when the outputs become substantially equal, at the time of filling completion.

That is, as shown in FIGS. 2 and 3, the product by the molding die 10 was filled through the runner 13, and the injection was performed using the injection pressure of the injection molding machine 16 as the primary injection pressure and the secondary injection pressure. In this case, the pressure in the mold is as low as about 1/2 of the injection pressure (secondary injection pressure) until the filling is completed, and when the filling is completed, the pressure in the mold rapidly increases to approach the injection pressure.

Then, at the time of completion of filling, it was confirmed that the detection output of the pressure sensor 19 approached the detection output of the pressure sensor 20, and thereafter the pressure level was reversed.

From this, in the present embodiment, the pressure sensor 19,
Pressure control is performed by setting the time when the outputs 20 become substantially equal to the time when the filling is completed.

The amplifier 22 amplifies the switching command and outputs the amplified signal to the direction switching valve 23.

The direction switching valve 23 is inserted into a hydraulic circuit of the injection cylinder 18 so that hydraulic pressure from a hydraulic pump 25 by operation of a motor 24 is supplied.

A primary pressure setting electromagnetic relief valve 26 is provided in a hydraulic circuit connecting the hydraulic pump 25 and the direction switching valve 23, and a direction switching valve is provided in the hydraulic circuit connecting the direction switching valve 23 and the injection cylinder 18. 27 and a secondary pressure setting electromagnetic relief valve 28 are provided.

These are configured as a pressure circuit for adjusting the injection pressure of the injection molding machine 16.

In the above configuration, when an excitation signal is output to the direction switching valve 23 according to the filling command, the solenoid 23A is excited, and the port of the switching valve 23 is switched.

With this switching, the oil pressure from the hydraulic pump 25 is released from the relief valve.
The primary pressure is adjusted by 26 and the adjusted pressure is applied to the injection cylinder 18.

This pressure causes the piston 18A of the injection cylinder 18 to move toward the injection cylinder 17, and the pressure in the mold 10 is adjusted to the primary injection pressure.

At this time, since the direction switching 27 is off, the switching valve 27 is removed from the hydraulic circuit connecting the hydraulic pump 25 and the injection cylinder 18.

With the progress of filling, when a preset screw position or set time is reached, the direction switching valve 27 is excited,
The switching of the port of the switching valve 27 is performed.

That is, the hydraulic pressure from the hydraulic pump 25 is supplied to the relief valve 28 via the direction switching valve 27.

Thereby, the hydraulic pressure supplied from the hydraulic pump 27 to the injection cylinder 18 is adjusted to the secondary injection pressure.

Thereafter, the filling of the mold 10 further proceeds, and the pressure sensor 1
When the outputs of 9 and 20 become substantially equal, a switching command is output from the comparison setter 21 and supplied to the amplifier 22.

As a result, the amplifier 22 stops outputting the excitation signal, and turns off the solenoid 23A of the direction switching valve 23.

When the solenoid 23A is turned off, the hydraulic circuit connecting the hydraulic pump 25 and the hydraulic cylinder 18 is cut off, and the injection is completed.

That is, at the time of completion of the injection, an injection pressure extremely lower than the secondary injection pressure can be applied to the mold 10.

As a result, the injection pressure can be changed to the required pressure at the time of completion of the filling without reducing the filling speed.

Further, in the case of performing the molding requiring the holding pressure even after the filling is completed, it is possible to construct a circuit for switching the output of the injection molding machine 16 to the holding pressure by the output from the comparison setting device 21.

Further, if a response delay is expected in the direction switching valves 23 and 27, the switching signal is output when the output of the pressure sensor 19 is slightly smaller than the output of the pressure sensor 20, for example, when the output becomes 10 kgf / cm ^2. If the set value of the comparison setter 21 is adjusted so that is output, the in-mold pressure at the time of completion of filling can be further reduced.

〔The invention's effect〕

As described above, according to the present invention, since the injection pressure is accurately detected to change the injection pressure to the required pressure at the time of filling completion, without reducing the filling speed,
The pressure inside the mold at the time of filling completion can be set to the required pressure,
It is possible to improve the quality of the molded product and reduce the mold clamping force during molding.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing one embodiment of the present invention, FIG. 2 is a configuration diagram of a main part of a molding die, and FIG. 3 is a diagram showing a relationship between an injection pressure and a detection output of a pressure sensor. 10 Molding mold 11 Upper mold 12 Lower mold 13 Runner 14 Gate 15 Sprue 16 Injection molding machine 17 Injection cylinder 18 Injection cylinder 19, 20 Pressure sensor 21… Comparative set value 22… Amplifier 23, 27… Directional switching valve 23A… Solenoid 25… Hydraulic pump 26, 28 …… Relief valve

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B29C 45/00-45/84

Claims (2)

(57) [Claims] A prescribed injection pressure is applied to an injection molding machine (16) according to a filling command, and thereafter, a pressure in a molding die (10) is monitored, and a mold at a predetermined position before reaching a gate (14) is monitored. When the difference between the internal pressure and the in-mold pressure at a position closer to the gate (14) than this position reaches a pressure corresponding to the filling completion time, the injection pressure for the injection molding machine (16) is increased at the filling completion time. An injection pressure control method characterized by changing the pressure to the required pressure. 2. A pressure sensor (20) for detecting an in-mold pressure in a runner (13) of a molding die (10) and a gate (1).
4) Compare the detection output of the pressure sensor (19) that detects the pressure on the side with the detection outputs of the two pressure sensors (19) and (20). When the difference between the two reaches the pressure corresponding to the time when the filling is completed, the switching command A switching command circuit (21) for outputting a predetermined injection pressure to the injection molding machine (16) according to a filling command, and changing the injection pressure to a required pressure at the time of filling completion according to the switching command (22). An injection pressure control device comprising (23), (25), (26), (27) and (28).