JPH0622831B2 - Injection compression molding method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an injection compression molding method for forming a molded product such as a plastic lens and an optical disc that requires low distortion and high accuracy. .

(Prior Art) FIG. 6 shows an outline of a conventional injection compression molding apparatus and its control circuit diagram. In ordinary injection molding, when the molten resin flows through the mold cavity of the mold during injection, a pressure gradient occurs in the flow direction, which causes residual stress in the mold. Therefore, for molded products such as plastic lenses and optical discs that require low distortion and high accuracy, injection molding is performed by injecting molten resin into the molded product cavity and then compressing the molded product cavity to make the resin pressure uniform. Is being done. If the resin pressure in the molded product cavity is uniform, the residual stress of the molded product is reduced, and a highly accurate molded product with less distortion can be obtained.

In FIG. 6, 1 is a mold clamping cylinder, 2 is a mold clamping ram within the cylinder, 3 is a tie bar connecting the mold clamping cylinder 1 and the fixed mold plate 5, and 4 is supported by the tie bar 3 so as to be able to move forward and backward. In addition, the movable mold platen is connected to the mold clamping ram 2. 106 is a movable mold attached to the movable platen 4, 107 is a fixed mold attached to the fixed mold plate 5, 20
Is the molded product cavity.

The raw material resin is supplied from a not-shown hopper to the right side of the drawing of the screw 14 in the cylinder 13, is melted and plasticized by heating by a not-shown heater and rotation of the screw 14 driven by the hydraulic motor 18, and the It is sent to the front and stored as the molten resin 12.

On the other hand, by sending pressure oil from the hydraulic inflow source 34 to the illustrated side of the injection cylinder 15 via the servo valve 38, the screw 14 is advanced to the left in the drawing via the injection ram 16 and the bearing box 17, and the screw is moved to the left side of the drawing. The molten resin 12 at the tip of 14 is injected into the molded product cavity 20. In the figure, 130 is a controller, 19 is a position sensor, 31 and 32 are hydraulic sensors,
33 is a hydraulic pressure inflow source, 35 is a proportional electromagnetic relief valve, 37 is a relief valve, and 36 is a switching valve.

After the molten resin 12 is injected and filled into the molded product cavity 20, pressure oil is sent to the compression cylinder 150 in the movable mold 106 through the switching valve 160, thereby moving the compression ram 151 toward the molded product cavity 20, The resin in the cavity 20 is compressed.

However, in this conventional example, since a compression cylinder for compressing the resin in the molded product cavity is provided in each mold, the mold cost is high, and it may be difficult to assemble the compression cylinder due to the structure of the mold. . Furthermore, since it is not easy to finely adjust the stroke of the compression cylinder that determines the amount of resin compression, it is difficult to find appropriate molding conditions.

(Problems to be Solved by the Invention) As described above, in the conventional injection compression forming apparatus in which the compression cylinder is provided in the die, the die cost for installing the compression cylinder is high and the stroke adjustment of the cylinder is not easy. However, there is a problem that it is difficult to obtain appropriate molding conditions. The present invention solves this problem and provides an injection compression molding apparatus which has a simple structure and is inexpensive, and which can easily obtain appropriate molding conditions.

(Means and Actions for Solving Problems) Therefore, according to the present invention, the mold clamping reference point is set by the value of the mold clamping hydraulic pressure or the value of the mold clamping force, and the mold clamping hydraulic pressure or the mold clamping force when the mold clamping pressure is increased. Detecting the displacement of the mold parting surface when the detected value of reaches the set value and storing it as the reference point of the mold parting surface displacement, lowering the mold clamping force in the injection filling section, and after the middle of the injection filling section. In the part, the injection hydraulic circuit is controlled with the target of the mold parting surface displacement value that has changed from the mold parting surface displacement reference point in the mold opening direction by the set value of the mold opening amount, and the mold clamping force in the subsequent injection pressure holding section. Higher,
The displacement control of the mold parting surface of the mold opening is stopped, and this is used as means and action for solving the problem.

(Embodiment) The present invention will be described below with reference to the embodiments of the drawings. Figs. 1 to 3 show an embodiment of the present invention. Fig. 1 shows an outline of an injection molding machine and its control circuit. FIG. 3 is an enlarged cross-sectional view of a portion in which the parting surface displacement detection device which is the main part of the present invention is incorporated, and FIG. 3 shows the main part circuit of the controller of the present invention.

1 is the same as the conventional device shown in FIG. 6 except for the mold 7, the parting surface displacement detecting device 8 which will be described later, and the lead wire 21a and the controller 30 which will also be described later. Description of parts is omitted. However, the compression cylinder 150 and its switching valve 160 shown in FIG. 6 are not provided in this embodiment.

Next, in FIG. 1 which is the main part of the present invention, a portion indicated by A will be described in detail. The details of the portion indicated by A are shown in FIG. 2, 6P is a parting surface of the movable side mold, and 7P is a parting surface. Is a fixed-side mold parting surface, and 21 is a displacement sensor, which is fitted into a mounting sleeve 22. The outer periphery of the mounting sleeve 22 is divided into a large-diameter portion and a small-diameter portion via a shoulder portion 22a, one side of the small-diameter portion is fixed to the stationary mold 7, and the other end of the mounting sleeve 22 is detached from the large-diameter portion. A rubber pad 23 is attached for prevention, and the dimensional relationship is such that the rubber pad 23 is slightly compressed before the mold is closed as shown in the figure.

A set screw 24 is provided to prevent the displacement sensor 21 from coming off the mounting sleeve 22. 21a
Is a lead wire of the displacement sensor 21, which is guided to the outside of the mold,
It is connected to the controller 30 shown in FIG. The mounting sleeve 22 is press-fitted into, for example, the fixed-side mold 7, and the shoulder portion 22a of the mounting sleeve 22 is in close contact with the mold 7 evenly. However, if the shoulder 22a is loosely adhered during use, it causes an error in the measurement of the gear. Therefore, in order to prevent this, the mounting sleeve 22 is always attached before the mold is closed.
The rubber pad 23 is pressed toward the shoulder 22a.

In FIG. 3, 31 is the same hydraulic sensor as shown in FIG. 1, and 21 is the same displacement sensor as shown in FIG. Reference numeral 50 is a setter for the mold closing hydraulic pressure Pc for starting the mold opening amount control in the injection filling section, and 51 is a setter for the mold closing hydraulic pressure Ps that gives the mold closing reference point. 40 and 41 are amplifiers. Reference numeral 70 denotes a signal line, and when the mold clamping pressure P ≧ Pc, the comparator 55
Signal is output (ON). A storage unit 60 stores the parting surface displacement input δ from the signal line 65 when the signal from the signal line 70 is switched from OFF to ON, and outputs the value δc at that time to the signal line 75. The value of δc is cleared to 0 when a reset signal is input from the signal line 80. Similarly, 71 is a signal line, and when the mold clamping pressure P ≧ Ps, a signal is output (ON) from the comparator 56, and at that time, the memory 61
Stores the parting surface displacement input δ from the signal line 66, outputs the value δs to the signal line 76, and holds the value of δs while the reset signal is not input from the signal line 81.
The reset signal to the signal lines 80 and 81 is input at the start of each injection molding cycle (at the start of mold closing).
Further, the displacement δ of the parting surface is constantly output from the signal line 42. On the other hand, 52 is a setter of the mold opening amount y, and the adder 57 adds the input y from 52 and the parting surface displacement reference value δs from the signal line 77, and the total value Sy is the signal line 78.
Is output to.

Next, the operation of the above embodiment will be described. In FIG. 1, the switching valve 36 allows the pressure oil from the hydraulic inflow source 33 to close the mold (the left side of the drawing) or the mold open side (the right side of the drawing) of the mold clamping cylinder 1. ) And supply. That is, when the solenoid a is excited, the pressure oil from the hydraulic pressure inflow source 33 flows to the left side of the mold clamping cylinder 1, and the mold clamping ram 2, and accordingly the movable mold platen 4 and the movable side mold 6 connected to the mold clamping ram 2. Move it to the right,
Performs mold closing operation. On the contrary, when the solenoid b is excited, the pressure oil from the hydraulic inflow source 33 flows to the right side of the mold clamping cylinder 1, and the mold clamping ram 2, the movable mold plate 4, the movable mold 6
Move to the left to open the mold. At the neutral position where neither solenoid a nor b is excited, the mold clamping side,
Both oils on the mold opening side are open to the tank.

When the solenoid a is excited to perform the mold closing operation as described above, after the mold is closed, the mold clamping pressure is increased to and maintained at the set pressure of the proportional electromagnetic relief valve 35. The set pressure of the relief valve 35 is changed by an electric signal from the controller 30. Moreover, the injection operation is performed after the mold clamping pressure is sufficiently increased.

Next, the injection operation will be described. By sending pressure oil from the hydraulic inflow source 34 to the illustrated side of the injection cylinder 15 via the servo valve 38, the screw 14 is moved to the left side of the drawing via the injection ram 16 and the bearing box 17. The molten resin 12 at the tip of the screw 14 is advanced and injected into the molded product cavity 20. The relief valve 37 is a safety valve that relieves when the hydraulic pressure rises too much.

The parting surface displacement detecting device 8 detects the gap δ in FIG. That is, in FIG.
The displacement sensor 21 generates an output (voltage or current) proportional to the gap δ through the lead wire 21a. Now, in FIG. 1, the displacement (gap δ in FIG. 2) detected by the parting surface displacement detection device 8 is sent to the controller 30, and the controller 30 injects as shown in FIG. 4 by the circuit in FIG. Performs compression control.

In FIG. 4, the diagrams of the mold clamping hydraulic pressure and the parting surface displacement have a common time axis, and the points where the suffixes 1 and 2 are added to the same alphabet symbols in both diagrams represent the same time points. In the figure, δ _D is the displacement of the parting surface immediately after the molds 6 and 7 are closed and the mold clamping force is not applied. Further, in the mold clamping pressure increasing section a, due to the compressive deformation of the mold due to the increase of the pressure applied to the parting surface, the parting surface displacement represented by the gap δ in FIG. 2 decreases, and the parting surface displacement corresponding to the mold clamping oil pressure P _G. reach δ _G.

Subsequently, in the injection filling section i, the molded article cavity 20
Since the resin pressure of the above acts in the direction of opening the mold, the compression deformation is reduced, and accordingly, the displacement of the parting surface starts to increase.
It enters the section j where the mold opening amount is controlled at the point C where the displacement δ _c is reached. In the section j, the mold is opened by the resin pressure in the molded article cavity, and the hydraulic pressure acting on the injection cylinder 16 is controlled by the servo valve 38 in FIG. 1 so that the displacement of the parting surface maintains δ _y (constant value). In the injection filling section i,
The injection speed is controlled in the same manner as the conventional method until the section j in which the mold opening amount is controlled is entered.

The length of the section j that controls the mold opening amount is set by a timer,
When the section j ends, the mold clamping hydraulic pressure is raised to P _E , the control of the mold opening amount is stopped, and the injection holding pressure section K is switched to control the injection hydraulic pressure. The length of the pressure keeping section K is also set by the timer.

As described above, in the injection filling section i, the mold is opened by the resin pressure in the molded product cavity as a low mold clamping force by the mold clamping hydraulic pressure P _G , and the mold opening amount becomes the parting surface displacement δ _y. To control.

In the next injection holding pressure section K, the mold clamping hydraulic pressure P _E is set to a higher mold clamping force, and the control of the mold opening amount is stopped to shift to the injection hydraulic pressure control, whereby the mold opening by the resin pressure in the molded product cavity is performed. The mold clamping force becomes larger than the force, the mold closes,
The resin in the molded product cavity is compressed accordingly.

Here, in this embodiment, the point that the mold parting surface displacement reference point δ _s corresponds to the setting hydraulic pressure Ps of the mold clamping reference point is that the parting surface displacement δ _D corresponding to the mold clamping hydraulic pressure 0.
In this point, since there is a possibility that the mold parting both sides are not evenly contacted and the mold is not completely closed, it is considered that it is better to set the mold clamping hydraulic pressure as a reference point. is there.

In detecting the parting surface displacement δ, an error occurs due to temperature and other environments, but in this machine, the set mold clamping hydraulic pressure for the mold opening amount control start point and the mold clamping reference diversion is used in each cycle of injection molding. Since the parting surface displacements δ _c and δ _s corresponding to Pc and Ps are detected and used, the error is 1
Only a few things in the cycle, good accuracy.

Incidentally, the mold opening degree control starting point, without using a parting plane displacement [delta] _c as in the present embodiment, it is also possible to determine the setting of Sukuriyu position and time. Further, since the mold clamping hydraulic pressure and the mold clamping force are in a proportional relationship, it is possible to easily use the mold clamping force instead of the mold clamping hydraulic pressure in this embodiment by incorporating the conversion circuit.

FIG. 5 is a characteristic diagram of injection control of another embodiment.
In the injection pressure holding section K, the constant value control of the parting surface displacement δ _F is different from the embodiment of FIG. 4 in which the injection hydraulic pressure control is performed in the same section. Incidentally, the [delta] _F is the embodiment and sets the similarly mold clamping hydraulic P _F, P _F during clamping boost
Is calculated by detecting the displacement of the parting surface corresponding to, or a compression amount Z from the parting surface reference displacement δ _s is set, and δ _s -Z is taken as the value. Therefore, in the embodiment of FIG. 5, the compression displacement amount of the resin of the molded product cavity is δ _y −.
Since δ _F is kept constant, there is an advantage that the variation in compression for each molding cycle is smaller than that in the above-mentioned embodiment.

(Effects of the Invention) The present invention is configured as described above in detail. A parting surface displacement sensor is incorporated in a mold to lower the mold clamping force at the time of injection filling to open the mold, and the mold opening amount is parted. Since it controls accurately by surface displacement, increases the mold clamping force in the injection pressure holding section, and closes the mold by stopping the control of the mold opening amount to compress the resin of the molded product cavity,
An injection compression molding device with a simple structure and safe can be realized. Further, since the mold opening amount can be changed only by changing the set value, it is possible to easily find an appropriate molding condition. Furthermore, since the precision of the above-mentioned mold opening amount is good, many excellent effects such as a small molding variation can be obtained.

[Brief description of drawings]

FIG. 1 is a side sectional view of an injection compression molding apparatus showing an embodiment of the present invention and a system diagram including its control circuit, FIG. 2 is an enlarged view of part A of FIG. 1, and FIG. 3 is a controller of the present invention. Main part circuit diagram, FIG. 4 is an injection compression control characteristic diagram of the present invention, FIG. 5 is an injection compression control characteristic diagram in another embodiment of the present invention, and FIG. 6 is a side view of a conventional injection compression molding apparatus. It is a system diagram containing the control circuit. Explanation of the main parts of the figure 6,7 …… Mold 8 …… Parting surface displacement detection device 21 …… Displacement sensor, 21a …… Lead wire 22 …… Sleeve, 30 …… Controller 31 …… Hydraulic sensor 35 …… Proportion Electromagnetic relief valve 50, 51, 52 ... setting device, 55, 56 ... comparator 57 ... adder, 60, 61 ... storage device

Claims (1)

[Claims] 1. A mold clamping reference point is set by a value of a mold clamping hydraulic pressure or a value of a mold clamping force, and a gold when the detected value of the mold clamping hydraulic pressure or the mold clamping force at the time of pressurizing the mold clamping reaches the set value. The mold parting surface displacement is detected and stored as the mold parting surface displacement reference point, the mold clamping force is lowered in the injection filling section, and the mold parting surface displacement reference point is used in the part after the injection filling section. The displacement value of the mold parting surface changed in the mold opening direction by the set value of the opening amount is controlled by the injection hydraulic circuit, and the mold clamping force is increased in the injection pressure holding section after that, and the displacement of the mold parting surface of the mold opening is controlled. An injection compression molding method characterized by stopping control.