JPS6313726A - Method and equipment for injection compression molding - Google Patents

Abstract

PURPOSE:To enable performance of injection compression molding whose dimensional accuracy is high by avoiding complication of mold structure, by a method wherein injection is suspended in a compression process after completion of filling and closed loop control of the same is performed so as to hold a screw position at the time of suspension of the injection. CONSTITUTION:When completion time of filling is detected, a sequencer 13 instructs a speed setting instrument 31 and turns speed instructions zero. Consequently, supply of hydraulic oil to an injection cylinder 17 is suspended by working a speed control instrument 33 and an injection speed is decelerated. When the injection speed V turns zero, a contact point of a changeover switching circuit 24 is changed over to a contact point 24b on the side of a position control equipment 23 from a contact point 24a on the side of an injection speed control equipment 22 by instructions of the sequencer 13, and a servo valve 26 is operated by output of the position control equipment 23. Then mold clamping pressure is raised and changed over to a compression process. Therefore, as compression is applied to the same when a resin temperature is highest and viscosity is lowest at the time of completion of filling, optimum molding conditions can be set up and dimensional accuracy can be obtained sufficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an injection compression molding method and an apparatus thereof applied to an injection molding machine.

(Prior art) In conventional injection compression molding using an injection molding machine whose mold clamping device is a hydraulic cylinder, the clamping pressure is initially set to a low pressure to close the mold joint surface. Start injection in this state.

The pressure of the resin filled into the mold cavity causes the bonding surface to open the mold and promote gas release, making it possible to perform filling at a low injection pressure.

Next, after the timer that operates at the same time as injection starts times out, the mold clamping pressure is set to high pressure to compress the open mold until the joint surface closes, and pressurizes the molten resin in the mold cavity to melt the molten resin. The aim is to compensate for the shrinkage that accompanies cooling.

This will be explained in detail based on the drawings.

FIG. 5 is a system diagram schematically showing a conventional injection pressure '4VJ device. The mold 1 includes a sprue 2, a cavity 3, a gate 4, and a gate cylinder 19 that closes a passage between the cavity 3 and the gate 4.

The mold 1 is divided into a movable side and a fixed side by a joint surface 5, with the movable side being fixed to a movable platen 6 and the fixed side being fixed to a fixed platen 7. The movable platen 6 is fastened and fixed to a mold clamping ram 9 that fits into a mold clamping cylinder 8 and slides thereon. Therefore,
The movable side moves with the joint surface 5 as a boundary due to the movement of the mold clamping ram 9, and the mold is opened and closed in the left and right directions in the figure.

First, before starting injection, the solenoid a of the directional control valve 10 is energized, and the amount of oil from the pump 11 is supplied to the left side of the mold clamping cylinder 8 in the figure, and the mold clamping ram 9 moves to the right. The mold is clamped at a low pressure set by the proportional solenoid pressure valve 12. Next, pressure oil is supplied to the injection cylinder 17 according to a command from the sequencer 13, and the injection ram 18 connected to the screw 16
moves to the left in the diagram. As a result, the resin that has been heated and melted in advance in the screw cylinder 14 is injected into the mold 1 through the nozzle 15.

During injection, the mold clamping force is lost due to the resin pressure filled in the cavity 3 and the mold opens.

When this state continues, the sequencer 13 operates the gate cut cylinder 19 in response to a signal when the screw reaches a preset screw position or a timeout signal from a timer that operates simultaneously with the start of injection. As shown in the detailed view inside the mold, the gate 4 is closed to prevent the molten resin from flowing back from the cavity 3 through the sprue 2 to the nozzle 15 during the compression process.

After closing the gate 4 in this way, the proportional solenoid pressure valve 12
The command value is changed to high mold clamping pressure for the compression process, the mold 1 is closed, and the resin in the cavity 3 is compressed.

However, the conventional injection compression molding apparatus described above has the following problems.

(1) Since the gate cut cylinder is provided inside the mold, the structure of the mold becomes complicated and costs increase.

(2) Once the resin has been filled into the mold cavity,
As the molten resin continues to cool, a solidified layer called a skin layer or a high viscosity layer begins to form from the cavity surface. When the gate cut cylinder is operated when filling is completed, pulsation is generated in the resin in the cavity near the gate, so that abrasion stress is generated in the skin layer and residual stress is generated. This causes deformation called "warpage" and molding defects such as deterioration of birefringence in disk-shaped recording medium bases such as compact disks and optical disks.

(3) Since the compression process cannot be started until after the operation of the gate cut cylinder is completed, the delay due to the operation time of the gate cut cylinder progresses cooling of the molten resin in the cavity and increases the viscosity, resulting in a uniform Compression cannot be applied.

Therefore, compensation for shrinkage due to cooling cannot be consistently performed, resulting in poor dimensional accuracy.

(Problems to be solved by the invention) As described above, in this type of conventional injection compression molding, the existence of the gate cut cylinder complicates the structure of the mold, and the operation of the cylinder causes pulsations in the resin in the cavity. Furthermore, due to the delay in the operation of the cylinder, the viscosity of the resin increases in some parts, making it impossible to apply uniform compression and making it difficult to obtain products with high dimensional accuracy.

The present invention was developed to solve these problems at the same time. ! The present invention aims to provide an injection compression molding method and apparatus that avoids complication and enables molding with high dimensional accuracy.

(Means for solving the problem) Therefore, the present invention, as the first invention, starts injection by clamping the mold at low pressure, and during filling, the filling pressure causes the mold to open, and the filling is completed. In the injection compression molding method, in which the mold clamping pressure is later increased to compress the resin in the mold, injection is stopped in the compression process after filling is completed, and closed-loop control is used to maintain the screw position at the same time. , second
The second invention is injection compression molding, in which injection is started by clamping the mold at low pressure, and during filling, the filling pressure causes the mold to open, and after filling is completed, the clamping pressure is increased to compress the resin in the mold. In the device, there is a position control device that inputs the screw position signal when injection is stopped in response to a filling completion signal and controls the screw position to be maintained at the time of stop, and the injection mechanism is controlled by the output of the control device. In each case, a closed-loop iTE mechanism equipped with a servo valve is provided, and these are used as means for solving the above-mentioned problems.

(Function) In the same injection compression molding as usual, the movement of the screw is stopped during the compression process and controlled to maintain a constant position, thereby preventing backflow of molten resin from the cavity during the compression process.

This eliminates the need for a gate cut cylinder, making it possible to use a cylindrical mold structure, thereby solving the above-mentioned problems.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a system diagram that is an embodiment of the present invention. Here, the explanation will focus on the points that are different from the conventional one shown in FIG.

Characteristic parts of the device of this embodiment include a position detector 20 such as an encoder that detects the position of the screw attached to the injection ram, and an F/F/20 that calculates the injection speed by differentiating the pulse output S of the position detector 20. The output of the differentiator 21 using a V converter (frequency/voltage converter) or the like, the injection speed control device 22 or the position control device 23 is connected to the amplifier 25, and the output of the switching circuit 24 and the amplifier 25 is used to send the output to the injection cylinder 17. This part is composed of a servo valve 26 that adjusts the pressure oil of the accumulator 27, a check valve 28 that prevents backflow from the accumulator 27 to the pump 30, and a relief valve 29 that sets the accumulated pressure of the accumulator 27.

The mold 1 according to this embodiment differs from the conventional example shown in FIG. 5 only in that a gate cut cylinder 19 is not provided.

Among the above parts, the injection speed control device 22 is a speed setter 31, as shown in FIG. 32, and a speed setting device 33 which performs proportional, integral, and differential control on the deviation ev and outputs it.

On the other hand, in the position control device 23, the output of the position detector 20 is input to a launch circuit 35 via a switching circuit 34, as shown in FIG. It is comprised of a comparator 36 that subtracts the output of the position detector 20 from the output of the latch circuit 35 and outputs a deviation e, and a position controller 37 that performs proportional, integral, and differential control on the deviation e and outputs it.

In the above configuration, the control operation thereof will be explained with reference to the control characteristic diagram in FIG. 4.

Initially, mold clamping is performed at low pressure before injection starts, as in the conventional method. Injection speed control device 2 according to commands from sequencer 13
The speed setter 31 in 2 operates and outputs a preset injection speed command, and the deviation ev from the output value of the differentiator 21 is calculated.
Based on this, the speed controller 33 adjusts the servo valve 26 to a predetermined speed. At this time, the contacts of the switching circuit 24 are connected to the contacts 24a on the injection speed control device 22 side. As a means for detecting the completion of filling, a timeout of a timer that operates simultaneously with the screw 16 reaching a preset screw position or the start of injection is employed.

When the completion of filling is detected, the sequencer 13 issues a command to the speed setter 31 to set the speed command to zero. As a result, the speed controller 33 operates to stop the supply of pressure oil to the injection cylinder 17, and the injection speed is reduced. When the injection speed ■ becomes zero, the switching circuit 34 of the position control device 23 is turned off by a command from the sequencer 13, and at the same time the contact of the switching circuit 24 changes from the contact 24a on the injection speed side all device 22 side to the position control device 23 side. The servo valve 26 is operated by the output of the position control device 23.

The launch circuit 35 has a function of always taking in an input signal and outputting it as is to the comparator 36. When the switching circuit 34 of the position control device 23 is turned off, it takes in the input signal immediately before turning off, that is, the screw position at zero injection speed (this is 80), and then a new signal is input manually. Therefore, the latch circuit 35 holds the output of So.

Therefore, the deviation es with respect to So calculated by the comparator 36
(=s0 S) By the operation of the position controller 37 which receives the signal as input, closed loop control is performed so that the screw position is set to S0.

Here, as for the clamping pressure of the mold l, following completion of filling, the clamping pressure is increased by a command from the sequencer 13, as in the conventional case, and the process is switched to the compression process.

In the above embodiments, the filling completion detection means need not be limited to the above-mentioned means, and means for comparing detected values such as mold cavity pressure, mold cavity resin temperature, mold opening amount, etc. with preset values. You may also use

(Effects of the Invention) As described above in detail, according to the present invention, the present invention enables
Backflow of resin from the cavity can be prevented during the compression process, which simplifies the structure of the mold and reduces costs.Also, since there is no resin pulsation due to gate cuts, molding defects such as deformation and deterioration of birefringence do not occur. .

Furthermore, according to the present invention, it is not necessary to limit the start timing of the compression process to after the operating conditions of the gate cut cylinder, so when the resin temperature is highest and the viscosity is lowest at the time of completion of filling,
Since compression is applied, optimal molding conditions can be set and dimensional accuracy can be ensured.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of injection compression molding showing one embodiment of the present invention, Fig. 2 is a block diagram of an injection speed control device in the same system, and Fig. 3 is a block diagram of a position control device. Fig. 4 is a control characteristic diagram as an embodiment of the present invention, Fig. 5 is a system diagram in conventional injection compression molding, and Fig. 6 is a cross-sectional view showing the operation of a gate cut cylinder in a mold showing a conventional example. be. Explanation of the main parts of the figure 20 - position detector 21 - differentiator 22 - injection speed control device 23 - position control device 24 - switching circuit 25 - amplifier 26 - servo valve Fig. 2 Fig. 3 Figure 5 chanting

Claims (2)

[Claims] (1) An injection compression molding method in which injection is started by clamping the mold at low pressure, and during filling, the filling pressure causes the mold to open, and after filling is completed, the clamping pressure is increased to compress the resin in the mold. An injection compression molding method characterized in that in the compression step after filling is completed, injection is stopped and closed-loop control is carried out so as to maintain the screw position at the time of the stop. (2) Injection compression molding equipment that starts injection by clamping the mold at low pressure, causes the mold to open during filling due to the filling pressure, and increases the clamping pressure after filling is completed to compress the resin in the mold. , a position control device inputs a screw position signal when injection is stopped in response to a filling completion signal and controls the screw position at the time of stop, and an output from the control device controls the injection mechanism. An injection compression molding device characterized by being provided with a closed loop control mechanism including a servo valve.