JPH0126327B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydraulic circuit for an injection molding machine, and particularly to control of an injection process.

In the injection process of an injection molding machine, it is extremely difficult to reliably stop the filling operation when filling of the resin into the mold cavity is completed because the inertia of the injection plunger must be completely absorbed. If the injection plunger does not stop reliably when the filling operation is completed, the plunger will hit the cylinder end face, which will not only cause a large shock, but also
It can even lead to damage to the machine. In addition, excess resin is packed into the mold cavity, resulting in overpacking and burrs, which also affects the pressure holding process in the next process.

Particularly when ultra-high-speed injection molding is performed, the plunger moves at high speed, resulting in large inertia, and it is difficult to reliably stop the plunger when filling is completed.

Therefore, the conventional method of attaching an accumulator to a normal molding machine and performing ultra-high-speed injection has not been able to absorb the inertia of the plunger during filling.

There are also molding machines that incorporate servo valves to speed up the speed control response, but in this case, the servo valve controls the amount of oil to advance the injection plunger, but Since the servo valve does not control the amount of oil discharged from the injection cylinder, even if the servo valve controls the amount of oil supplied to the injection cylinder in a responsive manner, the inertia of the injection plunger cannot be sufficiently removed, resulting in It was not possible to efficiently control the deceleration at the time of completion, and it was not possible to prevent the occurrence of a shock like the above-mentioned molding machine.

In an injection molding machine, in order to fill a cold mold with high temperature molten resin, the molten resin being filled is cooled, its viscosity increases, and cooling and solidification begins from the surface. Therefore, in the case of thin-walled molded products, the viscosity may increase to the point where it no longer flows before it is sufficiently filled, and there is a limit to the shape of the product that can be molded using normal molding.

Additionally, once a skin layer is formed that has begun to cool and solidify during injection, it is difficult to completely re-fuse this part, so the flow rate during filling should be made as fast as possible to maintain the shape of the mold. It is necessary to prevent such phenomena by making changes accordingly.

Ultra-high-speed filling makes it possible to complete the filling before the molten resin cools and begins to solidify, eliminating the need to consider the above problems and greatly expanding the molding limits of thin-walled molded products. This means that it can be expanded to.

The purpose of the present invention is to eliminate the drawbacks seen in conventional ultra-high-speed molding, and to provide a hydraulic circuit for controlling the injection process of an injection molding machine that reliably stops the injection plunger when the filling process is completed. To explain the circuit of the present invention in more detail, a plurality of hydraulic oil return ports are provided for the injection hydraulic cylinder during the injection process, and if necessary, some of the plurality of return ports are used, and the area of the return port is It is configured so that it can be switched between a large cross-sectional area and a small cross-sectional area, and the large cross-sectional area is used during filling, and when filling is completed, it is switched to the small cross-sectional area to rapidly decelerate and perform ultra-high-speed filling operation. This is to ensure that it stops.

Next, referring to FIG. 1, one embodiment of the present invention will be explained by taking as an example the case where two return ports have different cross-sectional areas, one large and one small. 1 is an injection cylinder, and the actuation that acts on the hydraulic cylinder 3 on the inner diameter surface. An injection plunger 2 that moves forward and backward with oil is inserted. A potentiometer 5 rotated by a rack and pinion is provided on the rod of the hydraulic plunger 4 of the hydraulic cylinder 3.
The position of can now be detected. Further, the hydraulic oil return side chamber 3a of the hydraulic cylinder 3 is provided with a small cross-sectional area return port 6 and a large cross-sectional area return port 7, and the hydraulic oil acts on the filling side oil chamber 3b, and the hydraulic plunger 4
moves to the left in the figure and when filling is completed, the hydraulic plunger 4 is arranged to close the large cross-sectional area return port 7, so during filling, the large cross-sectional area return port 7 is closed.
After filling is completed, the hydraulic oil returns to the tank via the small cross-sectional area return port 6, so that rapid deceleration is possible and the inertia of the hydraulic plunger 4, that is, the injection plunger 2 can be absorbed.

Reference numeral 8 denotes a pressure switch that detects the hydraulic pressure at the return port of the hydraulic oil, and issues a signal indicating the completion of the filling process, which serves as a signal for switching to the next process, the pressure holding process.

Reference numeral 9 denotes a reference value setting device for switching to the pressure holding process, which sets the position of the hydraulic plunger 4 detected by the potentiometer 5 or the pressure detected by the pressure switch 8 as a reference value. 1
0 is a comparator that compares the value set by the reference value setting device 9 with the value detected by the potentiometer 5 or the pressure switch 8, and when they match, it issues a signal, and the solenoid valve 11 and the flow control valve 12 The pressure is switched from the primary pressure relief valve 13 to the pressure set in the secondary pressure relief valve 14, and the amount of oil acting on the hydraulic cylinder 3 is switched to the speed for the pressure holding process.

With the structure described above, the injection plunger is decelerated in advance before stopping and its inertia is small, so the conventional drawback that the injection plunger does not stop accurately due to its inertia when the filling process is completed can be eliminated. removed.

Furthermore, as a result of the filling process being performed accurately, it is possible to accurately control the next pressure holding process, and it is also possible to switch the pressure holding process based on the filling process completion signal.

In addition, in order to reliably control this deceleration operation, a second
As shown in the figure, a timer 15 is provided to set the time during which the return of hydraulic oil is switched to the small cross-sectional area return port 6.
For example, the timing is started by the a position input signal of the electromagnetic switching valve 16 from the sequence control circuit 18 so as to operate from the start of the injection process. Same timer 1
When the timing of step 5 is completed, open the large cross-sectional area return port 7 again.
If the timer controls the directional switching valve 17 or the flow rate control valve, etc. provided in the pipeline of the small cross-sectional area return port 6 so that the return port 6 has a small cross-section, the degree of throttling and the By changing the set value of the timer, it is possible to provide arbitrary deceleration characteristics, making it possible to perform reliable and stable injection control.

It goes without saying that this control can be used for injection control not only in ultra-high-speed molding but also in normal molding.

[Brief explanation of drawings]

FIG. 1 is a diagram showing one embodiment of the present invention. FIG. 2 is a diagram showing another embodiment according to the present invention. 2... Injection plunger, 3... Hydraulic cylinder for injection, 4... Hydraulic plunger, 5... Potentiometer, 6... Small cross-sectional area return port, 7... Large cross-sectional area return port,
8...Pressure switch, 9...Reference value setting device, 10...
Comparator, 11... Solenoid switching valve, 12... Flow rate control valve,
13, 14...Relief valve.

Claims (1)

[Scope of Claims] 1. A plasticized resin raw material is supplied to the front part of an injection plunger, and after the injection plunger is retreated and a predetermined amount of resin raw material is measured, the injection plunger is advanced by an injection hydraulic cylinder to measure the amount of the resin raw material. In an injection process control circuit of an injection molding machine configured to inject resin raw material, the hydraulic cylinder has a plurality of hydraulic oil return ports during the injection process, and each return port has a pipe communicating with a tank. An injection process control circuit characterized in that a circuit is provided. 2. The hydraulic plunger itself closes a portion of a plurality of hydraulic oil return ports in the hydraulic cylinder when the hydraulic plunger in the hydraulic cylinder moves to a predetermined position. The injection process control circuit according to scope 1. 3. When the hydraulic plunger in the hydraulic cylinder moves to a predetermined position and closes some of the plurality of hydraulic oil return ports in the hydraulic cylinder, the pressure and speed of the filling process are maintained. 2. The injection process control circuit according to claim 1, wherein the injection process control circuit switches to a set value for a pressure process. 4. When the hydraulic oil pressure at the return port of the hydraulic oil during the injection process of the injection hydraulic cylinder rises to a preset value, or when the position of the hydraulic plunger reaches the preset value, during the injection process. The injection process control circuit according to Claims 1 and 2, characterized in that the filling pressure and speed are switched to the set pressure and speed during the pressure holding process. 5 The injection hydraulic cylinder has two return ports for hydraulic oil during the injection process, a small cross-sectional area port and a large cross-sectional area port, and a directional control valve or flow rate control is installed in the pipe line of the small cross-sectional area return port. 5. The injection process control circuit according to claim 3, further comprising a valve. 6. When the directional control valve or flow rate control valve provided in the pipeline of the small cross-sectional area return port switches from the pressure and speed for the filling process to the pressure and speed for the pressure holding process,
It is characterized by having a timer that starts the timing, and operating the directional switching valve or flow control valve in response to a timeout signal of the timer, and changing the hydraulic oil return port from a small cross-sectional area to a large cross-sectional area again during the injection process. An injection process control circuit according to claim 5.