JPH0134775B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) This invention relates to an injection compression molding machine used for molding synthetic resin.

(Prior Art) In injection molding using normal means, large stress during injection remains in the molded product as residual internal strain around the gate portion. As a means for reducing this distortion, a method of applying compressive force to the resin filled in the mold is already known. One method is to close the mold with a slightly low pressure, then open the mold slightly using the filling pressure, then increase the clamping pressure to completely close the mold, and then fill the mold with the resin. There are two methods: applying a compressive force to the resin, and press-fitting a plunger that also serves as an ejector pin into the filled resin after injection using the normal method, both of which apply a predetermined compressive force to the resin. I was just giving.

(Problems to be Solved by the Invention) In the above method, pressure is applied to the resin while it is still in a molten state after injection and filling, so before the gate sealing is completed as the gate part cools and solidifies. It is said that gate stress (internal stress) is discharged from the gate portion, and after the gate is sealed, sink marks, voids, etc. due to heat shrinkage are eliminated in the pressure-receiving areas of the molded product.

However, during actual molding, if excessive pressure is applied before the gate seal, not only the gate strain will be discharged from the gate, but also the resin equivalent to the compression allowance will be discharged, which will cause heat shrinkage after the gate seal. Compensation will not be possible. If the pressure before gate sealing is too low, gate sealing will be performed too quickly and gate stress will not be completely discharged, resulting in insufficient pressure in compression after gate sealing, making it difficult to compensate for thermal contraction.

In addition, the appropriate pressure during gate sealing and the appropriate pressure during compression almost never match, and if the compression force is applied only during the compression process, pressure will be applied to the molded product after solidification, which will cause internal stress. may remain.

As described above, in injection compression molding, it is difficult to set the compression force, so the excellent effects of injection compression molding cannot be fully utilized, which has been a problem.

(Means for Solving the Problems) This invention was conceived in view of the above circumstances, and its purpose is to provide an injection compression molding machine that can optimally control the compression force in injection compression molding. Our goal is to provide the following.

The present invention for the above purpose includes a hydraulic cylinder that moves a part of the mold to apply compressive force to the molten resin injected and filled into the mold cavity, and a plurality of hydraulic cylinders that set the hydraulic pressure supplied to the hydraulic cylinder. A pressure setting device, a signal generator that sequentially selects a plurality of set pressures set in the pressure setting device and issues a pressure command signal corresponding to the set pressure for an appropriate time, and supplies the pressure command signal to the hydraulic cylinder. It has an electromagnetic pressure regulating valve that controls the supplied hydraulic pressure.

(Function) In the above configuration, the compressive force determined by the shape and material of the molded product is applied from the time of injection filling to the completion of gate sealing, and from the completion of gate sealing to the middle of solidification.
The compression pressure can be divided into multiple stages, such as from the middle of solidification to the completion of solidification, and the most suitable compression force can be set for each process, and the compression force can be changed by sequentially switching according to the process.

(Example) The present invention will be described in detail below using illustrated examples.

1 is a fixed mold attached to a fixed platen 2; 3 is a movable mold attached to a mold clamping plate 5 on which tie bars 4, 4 slide; and a plunger 6 forming a part of the movable mold 3 is located in the center of the cavity. This makes it a movable cavity. It is preferable that this movable cavity has a size (area) of a portion of the molded product that requires particularly high precision or low internal distortion.

7 is the hydraulic cylinder of the movable cavity,
A plunger is attached to a plate 9 connected to the ram 8. Reference numeral 10 denotes a knockout pin, which is operated by a ram 12 of a hydraulic cylinder 11 housed in the mold clamping plate 5.

Figure 2 shows the circuit of the hydraulic cylinder 7, where _V1 is a switching valve, _V2 is a pressing force adjustment valve,
V ₃ is an electromagnetic relief valve whose pressing force is changed by a control signal, and the pressure is set by three pressure setting devices (not shown), and the set pressure is sequentially selected by a signal generator (not shown) to change the pressure to the electromagnetic relief valve. send a signal.

13 is the plunger 6 of the movable cavity.
This is an abnormal advance detector consisting of a limit switch or a photoelectronic switch that prevents the filler from advancing beyond a set value and unduly pressing the filled resin.

The method of the present invention will be described below using the molding of the optical component 14 shown in FIG. 3 as an example. In the case of the optical component 14, the movable cavity applies more pressure to the light transmitting portion 14b in the center than to the periphery 14a. First, the nozzle of the injection device 15 is touched to the gate of the mold 1 to inject molten resin. At this time, the molds 1 and 3 are completely and strongly closed with the mold clamping plate 5, and the plunger 6 is set in the retracted position.

Next, when the filling is completed, the hydraulic cylinder 11 is operated while the nozzle of the injection device 5 is kept pressed, and the plunger 6 is pushed out into the filled resin 16.
Pressure is applied to the filled resin 16 before curing. In addition, the output of the hydraulic cylinder 7 at this time may be about 1/10 to 1/20 of the mold clamping force, and the extrusion stroke of the plunger 6 is limited to the molds 1 and 3, the material resin,
Although it varies depending on the molding conditions, it is usually about 0.01 to 0.2 mm.

In addition, in this example, the pressure setting is the period from the completion of injection filling to the completion of gate sealing (section A).
There are three stages: an interval from the completion of gate sealing until 70% solidification (interval B), and an interval from 70% solidification to completion of solidification (interval C), and in interval A, only gate strain is applied from the gate. In section B, a pressure higher than that in section A is applied to compensate for voids and sink marks caused by heat shrinkage after gate sealing, and in section C, internal stress due to compressive force is applied to the cooled and solidified molded product. The pressure is set to be lower than that in section B so as not to leave any residue.

Furthermore, the hydraulic cylinder 7 is operated by timing based on the injection pressure holding pressure switching signal. The holding pressure switching signal is transmitted when the position of the injection plunger or the injection pressure reaches the set pressure of the pressure monitor, or when the mold internal pressure sensor senses the set pressure.

When the above-mentioned holding pressure switching signal is input to the signal generator, the signal generator changes from the set pressure in the A section to the B section.
The set pressure of section C is sequentially selected, and a pressure signal is generated for each set time of a pressurization time setting device provided separately for each section. This signal sets the pressure in the electromagnetic relief valve _V3 , and the hydraulic cylinder 7
The pressure of oil supplied to is adjusted. In the unlikely event that the plunger 6 abnormally advances beyond the set position during operation and presses the filled resin 16 more than necessary, the detector 13 is activated and the hydraulic cylinder Automatically stop the operation of 7.

Filled resin 1 subjected to pressure as described above
In No. 6, since the gate and the injection cylinder 15a of the injection device 15 are connected by the nozzle touch, the internal pressure escapes from the gate to the injection cylinder side. The release of pressure from this gate is due to the pressing force in the movable cavity and the injection cylinder 1.
It is controlled by the holding force of the movable cavity 5a, and the pressing force of the movable cavity is appropriately adjusted by changing the oil pressure of the hydraulic cylinder 7 in multiple stages.

The optical component 14 molded with reduced internal pressure as described above has high precision because the residual pressure that causes distortion is removed, and in particular, no distortion occurs in the light transmitting portion 14b.

In this embodiment, the compression force is changed in three stages, with sections A and C being set low and section B being set high, but the finer the division of the compression force, the better. However, if it is too finely divided, the machine cost will increase, the number of settings will increase, and the operation will become troublesome, so it is better to decide appropriately depending on the properties of the molded product.

(Effects of the Invention) As described above, this invention is configured so that the compression force in injection compression molding can be controlled in multiple stages, so molding can be performed at the pressure most suitable for each condition during the compression process, making it suitable for injection filling. The accompanying gate stress can be removed, a molded product with little orientation distortion, no voids, sink marks, etc. and good transferability can be easily obtained, and injection compression molding can be performed more effectively.

[Brief explanation of drawings]

The drawings illustrate an apparatus that can carry out the injection molding method of the present invention, and FIG. 1 is a vertical cross-sectional plan view when molding is completed, FIG. 2 is a circuit diagram of a hydraulic cylinder for pressing, and FIG. 3 is a diagram of a molded product. FIG. DESCRIPTION OF SYMBOLS 1... Fixed mold, 3... Movable mold, 5... Mold clamping plate, 6... Plunger, 7... Hydraulic cylinder for pressing, 8... Ram for pressing, 14... Optical component, 15 ... Injection device, 15a ... Injection cylinder, 16 ... Filled resin, V ₁ ... Switching valve, V ₂
……Press force adjustment valve, V ₃ ……Solenoid relief valve.

Claims (1)

[Claims] 1. A hydraulic cylinder that moves a part of the mold to apply compressive force to the molten resin injected and filled into the mold cavity, and a plurality of pressure setting devices that set the hydraulic pressure supplied to the hydraulic cylinders. A signal generator that sequentially selects a plurality of set pressures set on a pressure setting device and issues a pressure command signal corresponding to the set pressure for an appropriate time, and controls the supply hydraulic pressure supplied to the hydraulic cylinder by the pressure command signal. An injection compression molding machine characterized by having an electromagnetic pressure regulating valve.