JPH081733A - Injection mold device - Google Patents

Abstract

PURPOSE:To control freely a flow speed of a molten resin filled into a mold through adjustment of a gap of a gate within the mold. CONSTITUTION:A valve stem 6 provide movably freely on a movable mold side in an axial direction is provided on a position facing on a sprue bushing 5 on a stationary mold side, an inner end face of which faces the center of a cavity 2. A gate 7 of the cavity 2 is formed of a circumferential part between the sprue bushing 5 and valve stem 6. A driving device 9 moving the valve stem 6 by advancing and retreating is provided on an outer end of the valve stem 6. A position detector 12 is provided on the valve stem 6. The driving device 9 is operated by performing feedback of a detecting position of the valve stem to a set position and a gap of a gate is adjusted to a set gap by making the valve stem 6 movabe to the set position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection mold apparatus suitable for molding a flat molded product, particularly a disk-shaped molded product such as a compact disk or a video disk, which is required to have a high molding accuracy.

[0002]

2. Description of the Related Art In injection molding of a compact disk or the like which requires molding accuracy, when filling a cavity with a resin, a screw advancing speed is controlled in multiple stages to control a flow speed of the filled resin. This multi-stage control is for responding to a change in flow from the time when the molten resin reaches the outer peripheral portion of the cavity from the sprue, and is considered to be an essential requirement for molding a good product in a good molding state. .

[0003]

However, in the conventional multi-stage control, since the gate gap of the cavity is constant, the screw of the injection device is controlled in multiple stages, and the set value of the control is as follows. Since it is determined based on the results of repeated trial shots and flow analysis results, it tends to be an all-round intermediate value. For example, in order to keep the melt front (flow front of resin) constant, the injection speed The upper limit value is limited by the capacity limit of the injection device, and depending on the molded product, flow marks, silver, warpage, etc. may occur, and product evaluation values such as birefringence, uneven weight, transfer, etc. There are things that cannot be achieved.

[0004] In particular, when a disk-shaped and fixed-wall molded article such as a compact disk is molded by injecting it from the center, the speed of the melt front of the resin in the cavity becomes a function as the filling progresses. This tends to result in a difference in the density between the inner peripheral side and the outer peripheral side of the molded product, which makes it difficult to obtain a constant birefringence.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to adjust the gate gap in a mold and thereby freely control the flow rate of the molten resin filled in the mold. It is to provide a new injection molding die apparatus which can be used.

[0006]

SUMMARY OF THE INVENTION According to the present invention, there is provided a stationary mold having a sprue bush whose inner end face faces the center of a cavity, and a valve shaft which is movable in the axial direction at a position opposed to the sprue bush. An injection mold formed of a movable mold provided with a gate of a cavity formed by a peripheral portion between the sprue bush and the valve shaft; A drive device, a valve shaft position detector provided in the injection mold, and a valve shaft detection position fed back to a set position to operate the drive device, move the valve shaft to the set position, and move the gate to the set position. And a servo position controller for adjusting the gap to the set gap.

Further, the present invention comprises a fixed mold having an axially movable sprue bush whose inner end face faces the center of the cavity, and a movable mold having a valve shaft at a position opposite to the sprue bush. An injection mold in which the gate of the cavity is formed by a peripheral portion between the sprue bush and the valve shaft, a drive device for moving the sprue bush forward and backward, and a position detector for the sprue bush provided in the injection mold. And a servo position controller for moving the sprue bush to the set position to adjust the gate gap to the set gap by feeding back the detection position of the sprue bush to the set position and operating the drive device. On the device.

[0008] The injection mold of the above-described injection mold apparatus has a configuration in which the cavity volume can be varied by moving the movable mold.

[0009]

[Operation] In the above configuration, a command from the injection control device is input to the servo position control device before the start of injection, and the valve shaft or the sprue bush is advanced by the drive device to the set position to limit the gate gap to be narrow. Or when the injection of the molten resin is started by closing, the resin pressure reaches the set pressure. At that time, the drive device is moved backward by the action of the servo position control device, and the valve shaft or the sprue bush 6 is moved backward to the set position. With this, the gate gap is also formed to be as wide as the amount of retreat, so that the molten resin in the sprue portion flows into the cavity from the gate.

[0010] The resin pressure acting on the valve shaft or the sprue bush is reduced by the resin flowing into the cavity, but when the filling amount is increased, the resin pressure again acts on the valve shaft or the sprue bush, and this resin pressure is reduced to the set pressure. , The valve shaft or the sprue bush is retracted to the set position by the operation of the servo position control device in the same manner as described above, so that the gate gap is widened to facilitate the resin inflow. Such gradual adjustments are made to a final set position, which will ultimately close the gate gap and shift to holding pressure.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS This embodiment specifically describes an injection molding die apparatus for adjusting a gate gap by moving a valve shaft in a movable die in an axial direction.

In FIG. 1, reference numeral 1 denotes an injection mold, which comprises a fixed mold 3 and a movable mold 4 which are fitted to each other to form a disk-shaped cavity 2.

A sprue bush 5 whose inner end surface faces the center of the cavity 2 is fitted and inserted in the central portion of the fixed mold 3. A valve shaft 6 having the same diameter as the sprue bush 5 and also serving as a punch is fitted in the center of the movable mold 4 so as to face the sprue bush 5 so as to be movable in the axial direction. An annular gate 7 located at the center of the cavity by a peripheral portion between the sprue bush 6 and
Is formed.

An outer end of the valve shaft 6 is connected via a load cell 8 to a piston 10 of a hydraulically actuated driving device 9 for moving the valve shaft 6 forward and backward, and the load cell 8 acts on the valve shaft 6. The resin pressure can be detected.

The valve shaft 6 is connected to a position detector 12 such as a linear encoder provided outside the mold via a member 11 attached to an outer end portion, so that a gate gap is always detected from a position electrically detected. You can now know.

The position and pressure detection signals from the position detector 12 and the load cell 8 are input to a servo amplifier 13 which receives a command signal from the injection device, and feeds back the position of the valve shaft 6 to the set position. A signal is input to the servo valve 14, and the drive device 9 is operated to move the valve shaft 6 forward and backward so that the gate gap can be adjusted to the set gap.

Reference numeral 15 denotes an injection cylinder, which is a melt zone 17.
An injection screw 19 having a check valve 18 for preventing backflow of the measuring resin 16 is provided, and the nozzle is in contact with the outer end of the sprue bush 5.

Reference numeral 20 denotes a sleeve, 21 denotes a protruding sleeve, 2
Reference numeral 2 denotes a knockout pin inserted through the valve shaft 6, and reference numeral 23 denotes a stamper inner circumference press.

Although the load cell 8 detects the resin pressure in the illustrated example, a resin pressure sensor 24 may be provided in the cavity 2 to detect the resin pressure, as shown by the chain line. Further, although the hydraulically actuated drive device 9 and the servo valve 14 are used for the position control of the valve shaft 6, the drive device 9 has a ball screw structure, and the position control can be performed by driving this with an AC servomotor. In the invention, the position control is not particularly limited to hydraulic drive.

Next, the injection molding operation of the above injection mold apparatus will be described. First, before the start of injection, a command from the injection control device is input to the servo valve 14 via the servo amplifier 13, and the valve shaft 6 is advanced by the driving device 9 to the set position, and the gate gap is shown in FIG. Or tightly closed to create flow resistance. Also the valve shaft 6
Is always measured by the position detector, and the measured value is input to the servo amplifier 13 and fed back to the set value.

When the injection of the molten resin is started in this state, due to the flow resistance in the gate 7, the pressure of the metering resin in front of the screw is the resin on the melt zone side even if the screw 19 in the initial stage of injection is slightly moved forward. The pressure becomes larger than the pressure, and a pressure difference occurs between the resin pressures before and after the check valve 18. This differential pressure causes the check valve 18 to close,
Backflow of the metering resin 16 to the melt zone side is prevented.

The resin pressure acting on the valve shaft 6 is detected by the load cell 8, and the detected value is input to the servo amplifier 13.

When the resin pressure reaches the set pressure, the drive device 9 moves backward by the action of the servo valve 13 according to the command, and the valve shaft 6 moves backward to the set position. Accordingly, the gate gap is formed to be as wide as the retreat amount, so that the molten resin in the sprue portion flows into the cavity 2 from the gate 7.

Also, due to the resin flowing into the cavity 2,
The resin pressure acting on the valve shaft 6 decreases, but when the filling amount increases, the resin pressure acts on the valve shaft 6 again. When the resin pressure reaches the set pressure, the servo valve 13 acts to set the resin in the same position as described above. The valve shaft 6 retreats until the gate gap is widened to facilitate the inflow of the resin. After such stepwise adjustment is performed to the final set position shown in FIG.
Is detected, the drive device 9 is operated by the servo control to move the valve shaft 6 forward, thereby narrowing the gap between the gates 7.

As a result, the flow of the resin is restricted, and improper resin pressure is prevented from being applied to the resin in the cavity 2.
Finally, the gate gap is closed to further maintain the pressure, and thereafter, the process proceeds to a gate pushing-off process using the valve shaft 6.
Therefore, the flow rate of the resin into the cavity 2 can be arbitrarily controlled by controlling the retreat amount. At this time, the resin generates heat by shearing due to the edge around the valve side 6.

In the above embodiment, the gap between the gates 7 is adjusted in multiple stages according to the resin pressure in the cavity. However, this adjustment may be made continuously, and the embodiment is omitted.
The adjustment may be performed according to the screw position of the injection device 15.

When adjusting the gate gap by moving the sprue bush side, a drive device, a position detector, a servo position control device, etc. provided on the valve shaft side are provided on the sprue bush side under the same configuration. . If necessary, both can be moved relatively in the axial direction to adjust the gate gap.

[0028]

As described above, according to the present invention, a valve shaft is provided at a position opposite to a sprue bush whose inner end face faces the center of the cavity, and a gate of the cavity is formed by a peripheral portion between the sprue bush and the valve shaft. The valve shaft or the sprue bush is made movable in the axial direction so that it can be moved forward and backward by the driving device, and their positions can be detected by a detector. The following effects are provided by providing a servo position control device that feeds back the detection position to the set position, activates the driving device, moves the valve shaft or the sprue bush to the set position, and adjusts the gate gap to the set gap. To play.

A gate is formed in a peripheral portion between the sprue bush and the valve shaft, and is adjacent to a portion for molding a main portion of the molded product, and the weight of the movable portion is small. Since the flow control of the resin is performed quickly and is performed in a short stroke, it is possible to prevent the occurrence of burrs on the outer periphery of the molded product, which is caused by high-speed filling of the high-flowable resin.

The detection signal from the position detector is input to the servo amplifier, the advance / retreat position of the valve shaft or the sprue bush is fed back to the set position and input to the servo valve, and the drive device is operated to set the gate gap. Since it can be adjusted to the gap, it can be used together with multi-stage process control on the injection side, making it possible to make the conventional injection control where the set value was limited to an intermediate one more strict. As a result, it is possible to set an optimum molding condition according to the molded product and to mold a molded product such as a compact disc which is thin and requires molding precision.

Since the gate gap can be adjusted arbitrarily by operating the driving device, the resin temperature can be prevented from lowering due to the shear heat generation of the resin, and the skin layer can be formed uniformly and the pressure from the central portion of the gate to the outer periphery can be reduced. The occurrence of the gradient is also small. Therefore, a uniform and good molded product with little internal distortion such as birefringence and transfer can be obtained. Also, low-pressure injection can be performed by increasing the gate gap, and the occurrence of flow marks or the like due to the gate gap and the flow velocity can be prevented.

Since the pressure receiving area of the inner end surface of the valve shaft and the sprue bush forming the gate is extremely small, the driving output of the valve shaft can be small, and the servo control can be performed at a small output, so that the efficiency and the responsiveness are improved. In addition, since the driving output is small, the stability is excellent, and the driving device can be designed to be small, which is advantageous in terms of cost.

Since the flow of the molten resin into the cavity can be restricted by reducing or closing the gate gap at the beginning of the injection, even if the injection screw is slightly moved forward, the pressure of the metering resin is increased, and the pressure of the screw is higher than the melt zone side. Since the resin pressure of the injection valve increases and a differential pressure is generated therein, the closing operation of the check valve accompanying the advancement of the injection screw occurs promptly and reliably. Therefore, there is no excess or deficiency in the filling amount of the resin, and it is possible to accurately mold a thin molded product.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of one embodiment of an injection mold device according to the present invention.

FIG. 2 is a sectional view of a gate portion when a gate gap is adjusted to be small.

FIG. 3 is a sectional view of a gate portion when a gate gap is adjusted to be the widest.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mold 2 cavity 3 fixed mold 4 movable mold 5 sprue bush 6 valve shaft 7 gate 8 load cell 9 drive device 10 piston 12 position detector 13 servo amplifier 14 servo valve

Claims (3)

[Claims] 1. A fixed mold having a sprue bush whose inner end face faces the center of a cavity, and a movable mold having a valve shaft movably in the axial direction at a position facing the sprue bush. An injection mold in which a gate is formed by a peripheral portion between the sprue bush and the valve shaft,
A drive device positioned at the outer end of the valve shaft to move the valve shaft forward and backward, a valve shaft position detector provided in the injection mold,
An injection characterized by comprising a servo position control device for adjusting the gate gap to the set gap by moving the valve shaft to the set position by feeding back the detected position of the valve shaft to the set position Molding die equipment. 2. A fixed mold having an axially movable sprue bush whose inner end face faces the center of the cavity, and a movable mold having a valve shaft at a position facing the sprue bush. An injection mold in which a gate is formed by a peripheral portion between the sprue bush and the valve shaft,
A drive device for moving the sprue bush forward and backward, a sprue bush position detector provided on the injection mold, and a feed back of the sprue bushing detection position with respect to a set position to operate the driving device, and the sprue bush is operated. An injection mold apparatus, comprising: a servo position control device that moves to a set position to adjust a gate gap to the set gap. 3. The injection mold apparatus according to claim 1, wherein the injection mold has a structure in which the cavity volume is variable by the movement of the movable mold.