JPH0622832B2 - Injection compression molding method and apparatus - Google Patents

Description

TECHNICAL FIELD The present invention relates to an injection compression molding method applied to an injection molding machine and an apparatus thereof.

(Prior Art) In injection molding, molten resin undergoes large shrinkage as it cools. Therefore, if the shape accuracy of the mold is now secured, it is an important issue in injection molding to control the molding shrinkage amount and reproduce the dimensional accuracy of the same shape of the mold as the shape of the molded product every cycle.

This molding shrinkage amount is a change in the specific volume of the resin, and the specific volume is a function of the resin pressure. Therefore, compression and holding pressure of the molten resin have been conventionally performed as means for compensating for the shrinkage amount.

The third example of the conventional pressure holding control by the injection mechanism, which is one of them,
Shown in the figure.

The mold 1 is composed of a sprue 2, a cavity 3 and a gate 4, and a mold internal pressure detector 14 for detecting the pressure (mold internal pressure) of the mold cavity 3 is provided near the gate of the cavity 3. The output P _m from the in-mold pressure detector 14 is the comparator 16
Is sent to the comparator 16, and the in-mold pressure command value in the in-mold pressure control section after the output P _m of the in-mold pressure detector 14 reaches the control start pressure P _mo is output to the comparator 16, and both outputs are output. Is compared and subtracted by the comparator 16 to obtain the deviation e _p from the controller 1
Output 7, and outputs the deviation _{e p} in the control 17 PID (P ... proportional, I ... integral, D ... differential) control to the amplifier 18. The servo valve 20 changes the opening according to the output of the amplifier 18, and adjusts the oil supplied from the accumulator 19.

The mold 1 is divided into a movable side and a fixed side from the joining surface 5, the movable side is fixed to the movable platen 6, and the fixed side is fixed to the fixed platen 7, respectively. The movable plate 6 is fastened and fixed to a mold clamping ram 9 which is fitted into a mold clamping cylinder 8 and slides.

A screw 10 for plasticizing and injecting a resin is slidably inserted in a screw cylinder 11 on the right side of the die 1 in the figure, and an injection cylinder 12 is provided at the right end of the screw cylinder 11 in the figure. . The right end of the screw 10 is fixed to an injection ram 13 that fits into the injection cylinder 12 and slides.

In the figure, 21 is a check valve that prevents backflow from the accumulator 19 to the pump 22, 23 is a relief valve that sets the accumulated pressure of the accumulator 19, and 24 is a relief that sets the hydraulic pressure (clamping pressure) of the mold clamping cylinder 8. It is a valve.

In the above configuration, the control operation will be described based on the control curve shown in FIG.

First, in the pressurizing step, the mold 1 is closed and the mold clamping pressure according to the setting of the relief valve 24 is applied to the mold 1. The mold clamping force at this time is set to a sufficiently large value that does not open due to the pressure in the cavity in the process of filling and holding the mold 1. Next, the filling process is started, and the injection is started in the first half of the filling region at a speed determined by the opening degree of the servo valve 20.

When the mold internal pressure P _m reaches the control start pressure P _mo , the command device 15
Outputs a mold internal pressure command value, mold internal pressure P _m is closed loop controlled to gradually increase the holding pressure P _mH during time t _s. The control start pressure P _mo has a detection lower limit value of the in-mold pressure detector 14.

Then enter the dwelling step, between the mold internal pressure P _mH in dwell time between t _H, closed-loop controlled so that isomorphic pressure P _mH is constant.

Here, there is the following relationship between the mold pressure P _m and the filling resin amount V in the steam filling process.

P _m …… Internal pressure kgf / cm ² K …… Resin bulk modulus kgf / cm ² V _m …… Mold cavity volume cm ³ Q …… Filling resin flow rate cm ³ / sec (V .... Filling resin amount cm ³ ) As can be understood from the equation (2), detecting the mold internal pressure P _m means detecting the filling resin amount V, and therefore the mold internal pressure P _m
The amount of resin to be filled in the cavity 3 can be controlled to be constant by performing the closed loop control so as to reach the target value of the in-mold pressure by gradually increasing in a fixed pattern.

Although the pressure holding control by the injection mechanism has been described above, injection compression molding is known as another pressure holding control by the mold clamping force. This conventional example is shown in FIG.

In the figure, 26 is a proportional electromagnetic flow valve for adjusting the injection speed, 27 is a proportional electromagnetic pressure valve for adjusting the mold clamping pressure,
The sequencer 25 outputs a command value to both the valves 26 and 27 to control the injection speed and the mold clamping force in a closed loop.

The operation will be described based on the control curve diagram of FIG.

First, the mold 1 is closed in the step of boosting, and at this time, the mold clamping pressure is set and maintained at the low pressure mold clamping pressure by the proportional electromagnetic pressure valve 27 based on the command of the sequencer 25.

Here, the filling process is started, and the screw 10 moves leftward at the injection speed set by the proportional electromagnetic flow valve 26 based on the command of the sequencer 25, and injection is started. At this time,
The resin pressure (mold internal pressure) filled in the cavity 3 exceeds the mold clamping force, and the mold 1 slightly opens. This opening amount is called the mold opening amount.

In the subsequent compression process, when the screw reaches the injection completion position or when the timer that starts at the same time as the injection starts has timed out at a preset time, the sequencer 2
5, the set pressure of the proportional electromagnetic pressure valve 27 is changed to the high mold clamping pressure, the mold clamping ram 9 moves to the right, the cavity 9 of the mold 1 is pressurized, and the molten resin is compressed. .

During the pressure holding step following this compression step and the cooling step which is the next step, the same high mold clamping pressure as described above is maintained.

This method uses the gate 4 like the pressure holding by the injection mechanism described above.
Since the cavity volume V _m is reduced and pressurized instead of supplying the molten resin held under pressure through the compression process,
There is an advantage that the mold internal pressure in the pressure holding step becomes uniform in each part of the cavity 3.

However, each of the above pressure holding controls has the following problems.

(1) In case of holding pressure control by injection mechanism.

After the filling is completed, the molten resin is cooled by the mold, the viscosity of the resin increases with time, and a pressure gradient is generated in the flow direction.

Therefore, with the holding pressure by injection, a sufficient pressure cannot be applied to the end of the cavity, and the holding pressure becomes non-uniform, so the compensation of the shrinkage amount is not constant, and the shape and dimensional accuracy of the molded product are poor. Occurs.

(2) For holding pressure control by the mold clamping mechanism.

Since the filling state of the resin changes from shot to shot due to changes in the calculated position of the screw and the resin temperature, the mold internal pressure also changes. For this reason, since the mold opening amount, that is, the compression margin of the resin cannot be accurately controlled, the amount of pressurization in the compression step changes and the holding pressure also changes. Further, when the mold opening amount is the same, if the filling amount is different, even if the mold clamping pressure is the same, the pressurizing amount changes and the holding pressure also changes. Therefore, in any case, dimensional accuracy becomes poor.

(Problems to be Solved by the Invention) As described above, in the pressure-holding control that has been conventionally performed, when the injection mechanism is used, the pressure-holding cannot be performed uniformly, the compensation of the resin shrinkage amount is not constant, and In the case of the other mold clamping, it is difficult to adapt to the filling condition of the resin, and further, the accurate compression allowance according to the filling amount cannot be controlled, and in any case, there is a problem that a dimensional defect of the molded product occurs.

The present invention aims to solve the above problems by taking advantage of the control by both of these methods and eliminating the drawbacks.

(Means and Actions for Solving Problems) Therefore, the present invention uses, as an invention of a method, a mold provided with a mold internal pressure detector for detecting a resin pressure (mold internal pressure) in a mold cavity. In the injection compression molding process that goes through a series of processes including the filling process, the compression process, the pressure holding process, and the cooling process, the injection mechanism is designed so that the mold internal pressure gradually increases to the target mold internal pressure value at the time of filling according to a preset function pattern Closed loop control by adjusting the mold clamping mechanism so as to gradually increase the mold internal pressure from the target value to the mold internal pressure holding pressure target value in accordance with a preset function pattern following the filling step. Controlling the compression process,
During the subsequent pressure-holding period, a pressure-holding step of controlling the mold clamping mechanism so that the mold internal pressure is maintained at the pressure-holding target value and performing closed-loop control,
The holding step is followed by a cooling step of controlling the mold clamping force so as to follow a preset function pattern, and as the invention of the device, the internal pressure of the mold detected from the internal mold pressure detector provided in the mold. A mold clamping pressure that detects the mold clamping pressure in an injection molding machine that has a closed-loop controller for the injection mechanism that controls the servo valve of the injection cylinder based on the deviation from the command value of the preset function pattern from the mold pressure commander. A mold including a detector and a mold clamping pressure command device, which controls a servo valve of a mold clamping cylinder based on a deviation between a detected mold clamping pressure and a mold clamping pressure command value of a preset function pattern or a deviation of the mold internal pressure. In addition to having a closed-loop control device for the clamping mechanism, it is equipped with a changeover switching circuit that can select either the deviation of the mold pressure or the deviation of the mold clamping pressure. The injection mechanism is controlled by the injection mold internal pressure, the mold clamping mechanism is controlled by the detected mold internal pressure in the compression and pressure holding processes, and the mold clamping mechanism is controlled by the detected mold clamping pressure in the cooling process. It is a means of solving problems.

This is a combination of both control methods described above as a conventional example,
By controlling the in-mold pressure so that it has a constant pattern, the advantages of the two are taken advantage of while simultaneously attempting to solve the problems that the two have.

Specifically, in the injection compression molding, (1) in the filling step, the injection mechanism is controlled so that the mold internal pressure at the time of filling is gradually increased to the mold internal pressure target value, and the filling amount is stabilized.

(2) In the compression step, the mold clamping force is controlled so that the pattern has a pattern that gradually increases from the value of the mold internal pressure to the target value of the mold internal pressure, and the cavity is uniformly compressed.

(3) In the pressure-holding step, control is performed so that the internal pressure of the mold is kept constant during the pressure-holding period to the preset value of the internal pressure-holding pressure preset by adjusting the mold clamping force.

In this pressure-holding process, cooling progresses and a solidified layer or high-viscosity layer called a skin layer begins to be generated from the cavity surface, but this impedes pressure transmission to the mold internal pressure detector, so the mold internal pressure detector Output decreases, and the correspondence with the actual mold pressure is lost. Therefore, the mold clamping force increases,
This causes excessive thickness, which causes deformation and poor dimensional accuracy of the molded product.

(4) To prevent this, after the pressure holding time has elapsed, the mold clamping force at the end of the pressure holding process is detected in the cooling process and this mold clamping force is used to keep the mold clamping force constant until the cooling completion time. Is controlled so that becomes a function that gradually decreases to zero when cooling is completed.

From the above, in each process, the mold pressure was controlled so as to follow a fixed pattern for each shot, and the holding pressure could be uniformly applied to the entire surface of the cavity. It becomes possible to continuously mold the molded product of.

(Example) Hereinafter, the Example of this invention is concretely described based on drawing.

FIG. 1 shows an embodiment of the present invention.

In this embodiment, the pressure detector 35 for detecting the mold clamping pressure of the mold clamping cylinder 8 and the command value of the mold clamping pressure are compared with the system of the pressure holding control by the injection mechanism as the conventional example shown in FIG. Mold clamping pressure command device 30 for outputting and the pressure detector 3
5, the output P _c of the mold clamping pressure commander 30 is compared and subtracted to output the deviation e _c , the switching circuit 32, the deviation e _c or the output P of the mold pressure detector 14. the deviation e _r obtained by comparing subtracts the output of _m and mold internal pressure command unit 15 and the controller 33 to the PID control to output, an amplifier 34 which receives the output of the controller 33, the amplifier 34
A mold clamping force control mechanism including a servo valve 36 for adjusting the opening degree by adjusting the output of the accumulator 19 to adjust the oil supplied from the accumulator 19 and a sequencer 37 is additionally provided.

The control operation in the above configuration will be described based on the control curve diagram shown in FIG.

First, in the boosting step, the mold 1 is closed and the mold clamping pressure command device 3
By the command of 0, closed loop control is performed via the comparator 31, the contact 32b, the controller 33, the amplifier 34, and the servo valve 36 so that the preset low mold clamping pressure is obtained.

In the next filling step, in accordance with a command from the mold internal pressure commander 15, similarly to the conventional example shown in FIG. 3, the mold internal pressure P _m is set to a preset control start P _mo (detection value of the mold internal pressure detector 14). From the lower limit value) until the target value P _m1 for filling mold internal pressure is reached, t
_The amount of oil supplied to the injection cylinder 12 is adjusted to perform a closed loop control so that the pattern gradually increases within _one hour. Here, as the gradually increasing pattern, an optimum pattern is selected from polygonal lines, exponential functions, a combination of the two, etc. depending on the mold and resin conditions.

Then it enters the compression step, the mold internal pressure in this process reaches the filling time type pressure target value P _m1, commander 15 mold internal pressure holding pressure from the filling-time type pressure target value P _m1 in response to a command from the sequencer 37 A command value of a pattern that gradually increases within t ₂ time until reaching the target value P _mH (this is also selected by the mold / resin condition by the same function as above) is output. At this time,
At the same time, the contact of the changeover switching circuit 32 is switched from the contact 32b on the mold clamping pressure control circuit side to the contact 32a on the mold internal pressure control circuit side by the command of the sequencer 37, and the input of the mold clamping pressure to the controller 33 is the mold clamping pressure. Since the comparison deviation e _c of the mold internal pressure is switched to the comparison deviation e _p of the mold internal pressure, the mold internal pressure command value pattern from the mold internal pressure target value P _m1 during filling to the mold internal pressure holding pressure target value P _mH is _traced to the mold. The closing pressure will be controlled by the servo valve 36. Further, the sequencer 37 outputs a command to the controller 17 at the same time when the switching circuit 32 is switched,
The output of the controller 17 is set to zero, the supply of hydraulic pressure to the injection cylinder 12 is decreased, the injection speed and the injection pressure are decreased, and the screw 10 is stopped.

In the subsequent pressure-holding step, the mold-clamping force is adjusted during the pressure-holding time t _{H so that} the internal pressure of the mold is maintained at the target internal pressure-holding value P _mH similar to that in the compression step, and closed-loop control is performed.

In the final cooling step, the clamping pressure P _H detected by the mold clamping pressure detector 35 at the final time of the pressure holding process and instructs the clamping pressure command unit 30 via the sequencer 37, the clamping pressure at the same time to output a command of P _H, the contact 32a contacts the mold internal pressure control circuit side of the switching the switching circuit 32
To the contact 32b on the mold clamping pressure control circuit side. Since then, as the clamping pressure P _H until the completion of cooling time is constant, it is a closed loop control by the controller 33 of the mold clamping pressure.

At this time, as shown by the chain double-dashed line in FIG. 2, the mold clamping pressure curve is set as a function consisting of an exponential function, a broken line, etc., and the mold clamping pressure is controlled so as to gradually decrease along the pattern of the function. Is also good. This method is more effective in preventing excessive pressure during resin contraction, repeated stability of elastic deformation due to mold clamping force of the mold, and preventing deformation of the molded product during mold release.

(Effect of the Invention) As described above in detail, according to the present invention, the amount of molten resin filled in the cavity can be made constant by controlling the mold internal pressure in the filling step so as to match the preset pattern. In the pressure-holding step, the cavity is compressed by adjusting the mold clamping force so that the internal pressure of the die matches a preset pattern, so that uniform pressure can be applied to the entire surface of the cavity. Further, in the cooling step following this holding pressure, the mold clamping pressure is controlled in accordance with a preset pattern while detecting the mold clamping pressure instead of the mold internal pressure, so that proper control can be performed.

As a result, according to the present invention, since injection compression molding can be performed with an optimum mold internal pressure for each shot, it is possible to continuously produce molded products having excellent shape dimensional accuracy.

[Brief description of drawings]

FIG. 1 is a schematic system diagram of injection compression molding showing an embodiment of the present invention, FIG. 2 is a control curve diagram thereof, FIG. 3 is a schematic system diagram of pressure holding control by a conventional injection mechanism, and FIG. The control curve diagram, FIG. 5 is a schematic system diagram of the pressure holding control by the conventional mold clamping force, and FIG. 6 is the control curve diagram. Description of main parts of the figure 14 …… Mold pressure detector 15 …… (mold pressure) commander 16 …… Comparator 17 …… Controller 20 …… Servo valve 30 …… Mold clamping pressure commander 31 …… Comparator 32 …… Switching switching circuit 33 …… Controller 35 …… Clamping pressure detector 36 …… Servo valve 37 …… Sequencer

Claims (2)

[Claims] 1. A series of steps of a filling step, a compression step, a pressure holding step and a cooling step are performed by using a mold having an internal mold pressure detector for detecting a resin pressure (mold internal pressure) in a mold cavity. In the subsequent injection compression molding process, the filling process of adjusting the injection mechanism so that the mold internal pressure gradually increases to the target value of the mold internal pressure at the time of filling according to the preset function pattern, and the mold internal pressure following the filling process. A compression step of controlling the mold clamping mechanism to perform a closed loop control so that the target value to the target value of the mold pressure holding pressure is gradually increased according to a preset function pattern, and the mold pressure is maintained during the subsequent pressure holding period. It consists of a pressure-holding process that adjusts the mold clamping mechanism so that it is maintained at a target value and performs closed-loop control, and a cooling process that controls the mold-clamping force so that the mold clamping force follows a preset function pattern. Injection pressure characterized by Molding method. 2. An injection mechanism for controlling a servo valve of an injection cylinder based on a deviation between a mold internal pressure detected by a mold internal pressure detector provided in a mold and a command value of a preset function pattern from a mold internal pressure command device. In an injection molding machine having a closed-loop control device, a mold clamping pressure detector for detecting the mold clamping pressure and a mold clamping pressure commander are provided, and the detected mold clamping pressure and the mold clamping pressure command value of a preset function pattern are Of a mold clamping mechanism for controlling a servo valve of a mold clamping cylinder on the basis of the deviation of the mold pressure or the deviation of the mold pressure, and a switch capable of selecting either the deviation of the mold pressure or the deviation of the mold pressure. A switching circuit is provided, and by switching the switching circuit, the injection mechanism is controlled by the detection mold internal pressure in the filling process, the mold clamping mechanism is controlled by the detection mold internal pressure in the compression and pressure holding processes, and the detection mold clamping pressure is controlled in the cooling process. Ri clamping mechanism injection compression molding apparatus being characterized in that the manner respectively controlled.