JPH049652B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a mold clamping device for an injection compression molding machine suitable for use in molding video discs, draw discs, lenses, and the like.

[Prior art] In injection compression molding, which is generally used to mold the above-mentioned molded products, molten resin is injected and filled into a closed mold under low pressure, the mold is opened slightly by injection pressure, and then high pressure is applied to a movable platen. A method of compressing by applying
Alternatively, there is a method in which molten resin is injected and filled into a mold that is slightly open in advance, and after filling is completed, the mold is strongly clamped to perform compression.

In any of the above cases, it is important to accurately determine the slightly open position of the mold. Therefore, in order to prevent the movable platen from retreating from a predetermined position due to injection pressure, it is necessary to mechanically hold the mold. Alternatively, by position feedback control, the pressure in the chamber after the mold clamping ram is controlled by a servo valve to maintain it hydraulically.

[Problems to be Solved by the Invention] However, in the above conventional method, the force acting on the rear chamber of the mold clamping ram during the injection process is zero if it is held mechanically, and is zero if it is held hydraulically. In this case, the pressure is very low, just enough to balance the injection pressure, so when moving to the compression process, it is necessary to switch from low pressure to high pressure, so it takes time to increase the pressure, and during that time, the molten resin solidifies, causing the transfer There were problems that resulted in deterioration of the properties and generation of distortion due to internal stress.

This invention has been made in view of the above circumstances, and is a new mold clamping device for an injection compression molding machine that can shorten the pressure increase time when transitioning from the injection process to the compression process and improve transferability and distortion. The purpose is to provide.

[Means for Solving the Problems] The present invention, which achieves the above-mentioned objects, provides a mold clamping device for an injection compression molding machine, which is equipped with a fixed plate and a movable plate whose cavity volume can be varied by moving one of the molds. A high-speed moving means for moving the movable platen back and forth at high speed, a first pressure source selectively connected to a front chamber of a mold clamping ram for moving the movable platen forward and backward, and a servo connected to the rear chamber of the mold clamping ram. a second pressure source connected via a valve, a pressure detector that detects the pressure in the mold clamping ram rear chamber, and a position detector that detects the position of the movable platen;
The gist of the present invention is to include a control device that is connected to the pressure detector and the position detector and provides a command signal to the servo valve by calculating each detected value and a set value.

[Function] With the above configuration, both the front and rear chambers of the mold clamping ram can be pressurized by separate pressure sources during the injection process, so the rear chamber of the mold clamping ram has a force that balances the injection pressure and a mold clamping force. A force is generated that balances the output of the ram front chamber.

When moving to the compression process, the pressurization of the mold clamping ram front chamber is stopped and released to the oil tank.

As a result, the pressure in the rear chamber of the mold clamping ram is instantaneously added to the pressure that was canceled out by the output of the front chamber, and only the differential pressure from that pressure to the predetermined pressure is generated by the second pressure source. Boosted.

[Example] The movable platen 2 is provided so as to be able to slide back and forth on a tie bar 5 that is horizontally suspended between the fixed platen 1 and the mold clamping cylinder 3, and the movable platen 2 is provided so as to be able to slide back and forth on a tie bar 5 that is horizontally suspended between the fixed platen 1 and the mold clamping cylinder 3. It is connected to the ram 4.

The mold clamping ram 4 has a small diameter cylinder part inside, and a booster ram 6 is inserted into the cylinder part from the rear.
is inserted, and the cylinder portion is divided into two oil chambers, a C chamber and a D chamber, by the large diameter portion at the tip of the booster ram 6.

Further, the mold clamping ram 4 divides the interior of the mold clamping cylinder 3 into two oil chambers, A chamber and B chamber.

The C chamber and D chamber form a differential circuit with switching valves 26 and 27, and are connected to a pressure source 34 and an oil tank 33, which are composed of a pump 20, a motor 21, a relief valve 24, a flow valve 25, and an oil tank 33. The A chamber is connected via the servo valve 28 to a pressure source 35 other than the above consisting of an oil tank 33, the pump 22, and the motor 23, and is also connected to the oil tank 33, and the B chamber is connected to the switching valve 31. , is connected to the hydraulic pressure source 34 and oil tank 33 via a relief valve 32.

The rear portions of the valve parts of the pre-fill valves 10, 11 are connected to each other and to an oil tank 33, and the opening oil chambers E, F of each pre-fill valve 10, 11 are connected to a pressure source via switching valves 29, 30, respectively. 34 and the oil tank 33.

Further, a pressure detector 40 that detects the pressure in the A chamber, a position detector 41 that detects the position of the movable platen 2, amplifiers 42, 43, an analog switch 44, a comparator 45, a characteristic compensator 46, an amplifier 47, a controller 48, A control device 50 that includes setting devices 49a to 49n and provides signals to the servo valve 28.
It has been passed down to

The mold mounting surface of the movable platen 2 is equipped with a stamper (omitted in the drawing) on the cavity surface, and a movable mold 7 is integrally formed with a flange that protrudes outside the cavity surface.
The stationary platen 1 is provided with a fixed die having an outer part that fits with the inner circumferential surface of the flange, a stamper, and a sprue hole communicating with the cavity surface on the opposite surface of the fixed platen 1 to the movable die 7.

Further, the movable mold 7 and the fixed mold 8 have a temperature control circuit, although not shown in the drawing. The temperature control circuit heats the mold with pressure-controlled steam to a temperature above the softening point of the material resin before injection starts, and after injection filling, controls the temperature to a temperature lower than the softening point of the material resin with cooling water. do.

Setting values for the mold closing primary stop position, mold clamping filling speed, and compression pressure (multistage) are set in the setting devices 49a, 49b to 49n.

Relief valve 24, flow valve 25, switching valve 2
6, 27, 29, 30, and 31 are connected to a control device equipped with a separate setter group (not shown).

Next, the operation will be explained.

[High-speed mold closing]

In the mold open state shown in FIGS. 1 and 2, the switching valves 26 are r, 27 is l, 29 is r, 30 is r,
31 to n and the servo valve 28 to OFF.

Thereby, pressure oil from the pressure source 34 is supplied to the D chamber, and the movable platen 2 moves forward at high speed. In addition, the oil in the C chamber, which is reduced as the movable platen 2 moves forward, is removed by the switching valve 2.
6 and 27 to move the movable platen 2 at a higher speed.

At the same time, the E and F chambers are pressurized and the prefill valves 10 and 11 are opened, so the A becomes negative pressure.
Inside the room, there is oil discharged from room B and oil tank 3.
The oil inside 3 will be sucked in.

[Mold closing primary stop: Injection start]

When the movable platen 2 reaches a preset position (the position where the fixed mold 8 and the movable mold 7 are fitted as shown in FIG. 3) due to high-speed mold closing, the switching valves 26, 27 are turned to n, 29, 30, 31 is l, and the servo valve 28 is
Turn on to temporarily stop the movable platen 2, and start injection while maintaining the position by position feedback control.

That is, the B chamber is connected to the pressure source 34 via the switching valve 31.
The A chamber is pressurized by introducing pressure oil, and the A chamber is pressurized by the servo valve 28.
It is pressurized by pressure oil from a pressure source 35 introduced through the servo valve 28, and the position is controlled by balancing the pressure between both oil chambers by a servo valve 28.

In this state, the cavity 5 is
Since the volume of 1 is larger than the final dimensional state shown in Fig. 5 and the dimensional state shown in Fig. 4 taking into account the compression allowance, better fluidity can be obtained than by conventional injection compression molding. Furthermore, since injection can be performed at high speed and low pressure, distortion due to flow resistance is reduced.

[Mold clamping filling]

As shown in Fig. 3, when a predetermined amount of molten resin 52 that does not fill the cavity is injected, the movable platen is switched to speed feedback control (when the screw advances to a predetermined position) and is moved forward again at a predetermined speed. .

That is, while chamber B is pressurized by the pressure source 34, the pressurizing force of chamber A is increased, and the output of chamber A is changed to B.
The output is made larger than the output of the chamber and is moved forward by differential pressure.

At this time, the pressure in chamber B increases, but the increased pressure is discharged from the relief valve 32 to the oil tank 33.

In this state, the cavity volume is reduced as the mold closes, and the molten resin in the cavity 51 is spread out, so that the decrease in the spreading speed of the molten resin tip as injection filling progresses is alleviated, and the molten resin 52 is subjected to a force perpendicular to the flow direction, thereby reducing orientation in the flow direction.

Further, the spreading speed of the resin in this state is controlled by controlling the forward speed of the movable platen.

Then, the injection is completed just before the cavity is completely filled, and the movable platen moves forward further, as shown in Figure 4, and the mold has a cavity volume that takes into account the compression amount. It is filled with molten resin 52.

〔compression〕

When the completion of mold clamping filling is detected by monitoring the position of the movable platen, the pressure in the A room, etc., the servo valve 28 is switched to pressure feedback control, controlled by the compression force command signal, and the switching valve 31 is moved to the r side. Switch.

As a result, the pressure of the movable platen is controlled, so the molten resin 52 in the cavity is compressed under pressure, and the P-V-T
A curve (a property of plastic materials that shows the relationship between pressure, specific volume, and temperature; the horizontal axis is temperature, the vertical axis is specific volume, and the specific volume at each temperature under a predetermined pressure is plotted there. As a result, when the temperature is lowered under a certain pressure, it can be seen that the specific volume decreases accordingly.) The compression force is controlled in multiple stages to cool and solidify. As a result, distortion due to residual stress is further reduced, cooling shrinkage and orientation are alleviated, and a molded article 53 with improved transferability is molded (state in FIG. 5).

In addition, when moving to the compression process, both chambers A and B were pressurized in the previous process, and chamber A was under a predetermined pressure, so the moment chamber B was depressurized, chamber B was Since the force that was canceled by the output is added to chamber A, the pressure is quickly increased to the compression pressure, and the transfer performance can be further improved.

[Pressure relief]

When the cooling and solidification is completed, the control device 50 sends a zero pressure command to the servo valve 28 to relieve the pressure in the A chamber.

[Strong mold opening]

Next, turn off the servo valve 28, and turn off the switching valve 29.
Switch 31 to r and 31 to l.

As a result, the B chamber is pressurized by the pressure of the pressure source 34 and forcefully opened. At this time, the oil in the A chamber accompanying the retreat of the mold clamping ram 4 is transferred to the oil tank 33 via the prefill valve 10 opened by the pressurization of the E chamber.
will be returned to. Also, C room, D room and oil tank 3
3 is connected, oil is discharged from the D chamber, and the C chamber sucks oil from the D chamber and the oil tank 33.

As a result, the molded disk is released from the fixed mold 8.

[High-speed mold opening]

When the movable platen 2 retreats to the predetermined position by force opening, turn the switching valve 26 to l, the switching valve 27 to r, the servo valve 28 to OFF, the switching valve 29 to r, the switching valve 30 to r, and the switching valve 31 to n. Switch to

As a result, the C chamber is pressurized by the pressure source 34, so the movable platen 2 moves back at high speed, and the oil in the D chamber is released from the switching valve 2.
6, 27 and is returned to the oil tank 33.

In addition, since the E chamber and the F chamber are pressurized and the prefill valves 10 and 11 are opened, the oil in the A chamber is discharged from the prefill valves 10 and 1 as the mold clamping ram 4 retreats.
1 to the B chamber and returned to the tank.

〔take out〕

When the movable platen 2 reaches the predetermined mold opening stop position, turn the switching valves 26 and 27 to n, and turn off the servo valve 28.
The mold is opened and stopped with the switching valves 29 and 30 set to l and the switching valve 31 set to n, and the molded product is taken out from the movable mold 7.

The above steps are repeated to perform continuous molding.

In this embodiment, an apparatus as shown in FIG. 1 was used, but the apparatus is not limited thereto, and any apparatus may be used as long as it can carry out the method according to the present invention.

Furthermore, since the temperature of the mold is controlled by heating and cooling, the formation of a skin layer can be suppressed, which is better, but this can be done by cooling only.

Furthermore, it is more preferable to perform injection process control on the injection device 9 side in the same way as usual to ensure suitable molding conditions, and to modify the structure to enable high-speed injection.

[Effects of the Invention] According to the present invention, since the pressure can be quickly increased during the transition from the injection process to the compression process, it is possible to prevent deterioration of transferability and distortion due to progress of cooling and solidification, and improve molding. Product quality improves.

[Brief explanation of drawings]

The drawings illustrate a mold clamping device for an injection compression molding machine according to the present invention, and FIG. 1 is a schematic cross-sectional view thereof;
FIGS. 2 to 5 are cross-sectional views of the mold sequentially showing the injection compression process. 1... fixed plate, 2... movable plate, 3... mold clamping cylinder,
4... Mold clamping ram, 5... Tie bar, 6... Booster ram, 7... Movable type, 8... Fixed type, 9... Injection device, 1
0, 11... Prefill valve, 20, 22... Pump, 21, 23... Motor, 24, 32... Relief valve, 25... Flow rate valve, 26, 27, 29, 31
...Switching valve, 28...Servo valve, 34, 35...Pressure source, 40...Pressure detector, 41...Position detector, 4
2, 43, 47...Amplifier, 44...Analog switch, 45...Comparator, 46...Characteristic compensation section, 4
8... Controller, 49a, 49b, 49n... Setting device, 50... Control device.

Claims (1)

[Scope of Claims] 1. A mold clamping device for an injection compression molding machine, which is equipped with molds on a fixed plate and a movable plate whose cavity volume can be varied by moving one of the molds, wherein the movable plate is moved back and forth at high speed. a first pressure source selectively connected to the front chamber of the clamping ram that moves the movable platen forward and backward; and a second pressure source connected to the rear chamber of the clamping ram via a servo valve. A pressure detector that detects the pressure in the rear chamber of the mold clamping ram, a position detector that detects the position of the movable platen, and is connected to the above pressure detector and position detector, and calculates each detected value and set value. 1. A mold clamping device for an injection compression molding machine, comprising: a control device for giving a command signal to a servo valve.