JPH0976314A - Control method of mold clamping pressure in injection compression molding - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To control a mold clamping pressure corresponding to a mold opening amount during injection filling, and to perform a mold clamping pressure control corresponding to a resin flowing time in a cavity after completion of injection. Enables the minimum required mold clamping pressure control. SOLUTION: After a movable mold is brought into contact with a fixed mold, a molten resin is injected and filled in a cavity, and a mold opening amount of the first pressure is clamped so that a mold opening amount does not exceed a predetermined value until the injection is completed. Feedback control of pressure is performed, and after injection filling is completed, molding is started 1
In the second cycle, the mold clamping pressure of the first pressure at the time of injection completion is continuously maintained as the second mold clamping pressure, and in the second and subsequent cycles, the mold until the inflection point at which the moving speed change rate of the movable mold becomes constant. When the closing time is equal to or longer than the predetermined value, the second mold clamping pressure is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a mold clamping pressure in injection compression molding.

[0002]

2. Description of the Related Art Conventionally, a method of controlling a mold clamping pressure at the time of injection compression molding by a single pressure or a multi-stage pressure is generally used. However, such a control method is performed by an operator based on past experience. The mold clamping pressure determined in advance was used as the set value.

Further, in the injection compression molding machine in which the mold clamping pressure is feedback-controlled on the basis of the mold opening amount,
When injecting and filling the cavity with the molten resin, only the mold opening amount was controlled.

[0004]

By the way, controlling the mold opening amount during injection compression molding is an important control item, but controlling the mold opening amount alone is not sufficient to obtain a good molded product. There is an excess or deficiency in the required mold clamping force.
Therefore, if an excessive mold clamping force is applied, the flow velocity of the resin in the cavity will increase, and as a result, a molded product with a large internal stress due to freezing of the flow orientation will be obtained. There is a problem that a desired molded product cannot be obtained when the property is deteriorated and further severe.

The present invention has been made in view of the above problems, and an object thereof is to control the mold clamping pressure corresponding to the mold opening amount during injection filling and to control the resin in the cavity after the injection is completed. By controlling the mold clamping pressure according to the flow time, the minimum necessary mold clamping pressure control is possible.

[0006]

The present invention has been made in order to achieve the above object. In the present invention, a molten resin is injected and filled in a cavity after a movable mold is brought into contact with a fixed mold. , The first mold clamping pressure is feedback-controlled so that the mold opening amount does not exceed the predetermined value until the injection is completed, and after the injection filling is completed, the first pressure after the molding is started is the first pressure at the completion of the injection. If the mold closing time up to the inflection point at which the moving speed change rate of the movable mold becomes constant after the second cycle is equal to or more than the predetermined value, the eye mold clamping pressure is continuously maintained as the second mold clamping pressure. The mold clamping pressure of the second pressure is increased, and conversely, when the mold closing time is a predetermined value or less, the mold clamping pressure of the second pressure is reduced to control the mold clamping speed.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION During injection and filling of molten resin into a cavity, feedback control is performed on the mold clamping pressure of the first pressure so that the mold opening amount does not exceed a predetermined value, and molding is started after completion of injection and filling. In the first cycle after that, the mold clamping pressure of the first pressure at the time of injection completion is continuously maintained as the mold clamping pressure of the second pressure, and in the second cycle and thereafter, up to the inflection point where the moving speed change rate of the movable mold becomes constant When the mold closing time is equal to or more than a predetermined value, the second mold clamping pressure is increased, and conversely, when the mold closing time is less than the predetermined value, the second mold clamping pressure is reduced. By doing so, it is possible to obtain a low-distortion molded product with less internal stress without applying an excessive mold clamping pressure.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A concrete embodiment of a method for controlling a mold clamping pressure in injection compression molding according to the present invention will be described in detail below with reference to FIGS.

FIG. 1 is an explanatory view for explaining an inflection point of a mold opening / closing increase / decrease characteristic curve of a mold opening amount according to the present invention, and FIG. 2 is a mold opening / closing increase / decrease characteristic curve of a mold opening amount according to an embodiment of the present invention. 3 is an explanatory view for explaining the inflection point, FIG. 3 is a control conceptual diagram according to the embodiment of the present invention, and FIG. 4 is a control flow chart at the time of injection compression molding according to the embodiment of the present invention.

The fixed mold 3 is attached to a fixed platen 5 fixed to one end of a machine base (not shown), while the movable mold 2 is provided at the other end of the machine base so as to face the fixed platen 5. It is attached to the movable platen 4.

A mold clamping cylinder 6 is provided on the rear surface of the movable platen 4.
The movable platen 4 is fixed to the piston 6a that moves back and forth inside and the tip of the piston rod 6b of this piston 6a, and the movable platen 4 is movable back and forth by introducing pressure oil before and after the piston 6a. There is. Reference numeral 35 indicates a cavity portion.

Reference numeral 10 denotes an injection device, which is composed of a screw 11, an injection cylinder 12, a forward / reverse rotation motor 13, a hopper 14a and a barrel 14.

A screw 11 is rotatably provided in a barrel 14, a resin raw material in a hopper 14a is heated and compressed in a supply zone and a compression zone, melt-measured in a measuring zone, and injected into a nozzle 15 through an injection zone. It is configured to be.

A heater for externally heating the resin raw material is provided on the outer peripheral surface of the barrel 14, and the resin raw material is sent forward by the rotation of the screw 11 while being melted. Reference numeral 11a indicates a screw head. The screw 11 is normally and reversely rotated by a forward / reverse rotation motor 13 directly connected to the screw 11. Reference numeral 30 indicates a shutoff valve. Reference numeral 12 is an injection cylinder, 12a is a piston, and 13 is a forward / reverse rotation motor, which is directly connected to the screw 11 and rotates the screw 11 forward and backward.

Reference numeral 17 denotes a control unit, and 8 and 16 are hydraulic control valve, position sensor 7, mold position detection unit 18, shut-off valve control unit 19, screw position detection unit 20, injection control unit 21, injection pressure detection. Unit 22, mold clamping pressure control unit 23, mold clamping pressure detection unit 24, input / output interface 25, arithmetic processing unit 26, storage unit 27, input keyboard 2
8 and a display unit 29.

The position sensor 7 is connected to a mold position detecting unit 18, and the mold position detecting unit 18 is connected to an input / output interface 25. Further, the input / output interface 25 is connected to an arithmetic processing unit 26 capable of obtaining the change rate δn of the moving speed of the movable mold 2 from the moving amount of the movable mold 2 detected by the mold position detection unit 18. There is.

Further, the injection control section 21 connected to the hydraulic control valve 16 for controlling the drive of the injection cylinder 12 and the forward / reverse rotation motor 13 and the injection pressure detection section 22 for detecting the oil pressure of the injection cylinder 12 are respectively provided. It is connected to the input / output interface 25.

On the other hand, the mold clamping pressure control unit 23 is connected to the hydraulic control valve 8 for controlling the drive of the mold clamping cylinder 6, and the mold clamping pressure control unit 23 is connected to the input / output interface 25. Further, the mold clamping pressure detector 24 for detecting the hydraulic pressure of the mold clamping cylinder 6 is connected to the input / output interface 25. Reference numeral 20 denotes a screw position detection unit provided to notify the injection start position and the injection end position, and the screw position detection unit 20 is connected to the input / output interface 25.

An input / output interface 25 for inputting / outputting control signals output to the respective drive units of the mold clamping cylinder 6, the injection cylinder 12 and the shutoff valve 30, an input keyboard 28 for inputting setting conditions, and a display for displaying this. The unit 29 is connected to the input / output interface 25, and the input / output interface 25 is connected to an arithmetic processing unit 26 that performs a comparative arithmetic operation on a set value and a detection signal and outputs a control signal.

The storage unit 27 is connected to the arithmetic processing unit 26, and sets and calculates the upper limit value of the mold opening amount, the mold clamping pressure, the change rate of the mold movement, the upper and lower limit values of the flow time of the resin in the cavity. The value is stored.

A method for controlling the mold clamping pressure using the injection compression molding apparatus described above will be described.

In this embodiment, the movable mold 2 is clamped in advance.
A low-pressure injection compression molding method in which a molten resin is injected and filled in the fixed mold 3 and then compression is performed on the mold clamping side will be described.

FIG. 1 shows a typical characteristic curve of the change over time of the mold opening amount during injection compression molding when the mold clamping pressure is controlled at 1 pressure. In FIG. 1, the movable mold 2 is pushed back by the resin pressure injected into the cavity 35, and the mold opening amount shows the maximum value immediately after the completion of injection filling.

The resin injected and filled in the cavity 35 is pressed by the mold clamping pressure applied to the movable mold 2 before the injection is started, and the resin is spread to every corner in the cavity 35. At the same time as the filling thickness of No. 1 is decreased, the mold opening amount is gradually decreased due to the decrease in resin volume due to cooling.

Eventually, the resin in the mold cavity 35 is cooled and loses its fluidity, and the cavity is filled with the resin, so that the flow behavior is stopped. It depends only on the volume reduction due to. Therefore, by measuring the rate of change of the mold opening amount, that is, the rate of change δn of the moving speed of the movable mold 2, the flow end time of the resin in the mold cavity 35 can be estimated.

Further, if the flow end time is too late, flow marks will appear on the surface of the molded product, and if the flow end time is further delayed, it will be impossible to fully fill the mold cavity 35 with the resin.
It appears as a defective molded product.

On the contrary, if the flow end time is too fast, the mold clamping pressure is applied more than necessary, and at the same time, after this flow end time, the mold cavity 35 is used to promote the flow behavior of the resin. It is not necessary to control the clamping pressure, and only the minimum required clamping pressure for advancing the movable mold 2 until the cavity 35 has the same volume as the molded product in accordance with the solidification shrinkage of the resin is required. .

Based on this concept, a detailed description will be given with reference to FIGS. 3 and 4. First, pressure oil is introduced into the mold clamping cylinder 6 to move the movable mold 2 forward to the fixed mold 3 side.
Touch the fixed mold 3.

On the other hand, the injection filling amount is defined by detecting the forward / backward movement position of the screw 11 by the screw position detecting section 20. Then, after the die touch is completed, the hydraulic pressure control valve 16 is controlled via the injection control unit 21 while the hydraulic pressure value is detected by the injection pressure detection unit 22, and the forward / reverse rotation motor 13 is controlled.
And a cavity part 3 formed by a movable mold 2 and a fixed mold 3 by driving a piston of the injection cylinder 12.
Injection filling into 5.

During injection, the mold position detecting section 18 continues to measure the mold opening amount Xn, and if the mold opening amount Xn exceeds an arbitrary set value X1, a command for increasing the mold clamping pressure Pn is calculated. 26 to the mold clamping pressure control unit 23.

After the injection is completed, the shut-off valve 30 is closed, and at the same time, the mold clamping pressure P2 of the second pressure is transferred. However, in the first cycle after the start of molding, the mold clamping pressure Pn at that time is changed to the second pressure. It is added as it is as the mold clamping pressure P2.
As a result, during injection, the movable mold 2 moves in the direction away from the fixed mold 3 due to the resin pressure (mold opening behavior), but maintains a constant value as the mold clamping pressure increases.
Eventually, after the injection is completed, the movable mold 2 starts moving forward again due to the mold clamping force.

The mold opening amount of the movable mold 2 and the fixed mold 3 is detected by the position sensor 7 to obtain a mold opening / closing increase / decrease characteristic curve D as shown in FIG. The mold opening / closing increase / decrease characteristic curve D is
When the injection molding of the molten resin is started in the cavity portion 35 formed by closing the molds 2 and 3, the movable mold 2 moves in the direction away from the fixed mold 3 as described above. However, the mold opening increasing characteristic curve E is controlled so that the mold opening amount Xn does not exceed the predetermined value X1, and when the injection is completed, the resin flow in the cavity 35 advances due to the mold clamping pressure and the resin filling thickness decreases. And the mold shrinkage causes the movable mold 2 to move closer to the fixed mold 3,
The rate of change of the moving speed of the movable mold 2 (referred to as the rate of change of the movable mold 2 per unit time) gradually decreases and becomes constant until a so-called inflection point H. It can be displayed by the mold closing decrease characteristic curve C.

In the present invention, paying attention to the mold closing decrease characteristic curve C, the moving amount of the movable mold 2 in the closing direction per unit time, that is, the change rate of the moving speed of the movable mold 2 with respect to the fixed mold 3. (Or the rate of change of the mold opening amount) Δn is calculated, and the calculation is continued until the rate of change Δn becomes a constant value. Thus, the mold closing time Tx from the completion of injection to the inflection point H at which the rate of change δn of the moving speed becomes constant from the time of completion of injection is obtained.

The second clamping pressure of injection compression molding in the next molding cycle is controlled on the basis of the time Tx from the end of injection thus determined to the inflection point.

The mold closing time Tx is provided with a maximum setting value T3 as an upper limit value and a minimum setting value T4 as a lower limit value. If the mold closing time Tx is longer than the maximum setting value T3 (Tx≥T3). Indicates that the mold clamping pressure is smaller than the resin pressure that shrinks by cooling. Therefore, in order to increase the mold clamping pressure in the next molding cycle by a certain percentage, the value obtained by multiplying the mold clamping pressure P2 of the current molding cycle by the variation coefficient b larger than 1 is newly stored in the storage unit 27 as the new model clamping pressure P2. Fix it.

On the contrary, when the mold closing time Tx is shorter than the minimum set value T4 (Tx≤T4), it means that the mold clamping pressure is larger than the resin pressure which shrinks by cooling. Therefore, in order to reduce the mold clamping pressure in the next molding cycle by a certain percentage,
The value obtained by multiplying the mold clamping pressure P2 of the current molding cycle by the variation coefficient a smaller than 1 is set as the new model clamping pressure P2, and the storage unit 2
It is remembered again to 7.

When Tx becomes T4 <Tx <T3, the mold clamping pressure P2 of the current molding cycle is maintained as it is in the next molding cycle. In this case, the mold clamping stored in the memory unit 27 is held. The pressure P2 is maintained as it is.

After that, the mold clamping pressure P2 is applied as at least the second pressure up to the inflection point H as shown in FIG. 1, but normally, the resin flow is stopped after the inflection point H has passed. Therefore, the third mold clamping pressure P3 may be small.

Therefore, when the holding time T1 of the second pressure to which the mold clamping pressure P2 is applied becomes T1 = Tx, the mold pressure shifts to the third mold clamping pressure P3. The mold clamping pressure P3 of P3 = P2 × X2 (however, the rate of change X2 shows a value smaller than 1) is given by the arithmetic processing unit 2
6 to the mold clamping pressure control unit 23, and the mold clamping pressure P3 is applied for a certain period of time T2 in order to continue the mold clamping.

However, as described above, it is preferable when the inside of the cavity 35 has a simple shape and the behavior of the resin flow is relatively easy to grasp, but the behavior of the resin flow is partially affected by the difference in the product thickness. When there is a difference, the inflection point H is unlikely to occur, and the inflection point H is determined from the obtained mold opening / closing increase / decrease characteristic curve A
Is difficult to specify, so for safety, the second mold clamping pressure P
2 may continue to be added so that T1> Tx.

After holding the second pressure for T1 time in this way, after the point which is recognized as the inflection point H based on the past experience, the second pressure is switched to the third pressure. The third pressure is the mold clamping pressure P3 described above.

In addition to the above-described operation, on the injection device 10 side, the screw 11 is rotated and retracted by rotating the forward / reverse rotation motor 13, and a predetermined amount of molten resin is measured in front of the screw head 11a. After this, the third clamping time T
When step 3 is completed, the process goes directly to the end of mold clamping described above.

In this way, on the mold clamping side 1, after the resin in the cavity 35 is cooled and solidified, the movable platen 4 and the movable mold 2 are retracted by the mold clamping cylinder 6, the product is taken out, and the next molding cycle is started. . By repeating the molding cycle, the time during which the rate of change of the moving speed of the movable mold 2 becomes constant converges within the set range, and stable molding is possible.

[0044]

As is apparent from the above description, in the present invention, after the movable mold is brought into contact with the fixed mold, the cavity is filled with the molten resin and the mold opening amount is maintained until the injection is completed. Feedback control of the first mold clamping pressure so that does not exceed a predetermined value, and after the completion of injection filling, the first mold clamping pressure at the completion of injection is the second mold clamping pressure after the start of molding. It is continuously maintained as the mold clamping pressure, and after the second cycle, if the mold closing time to the inflection point where the moving speed change rate of the movable mold becomes constant is a predetermined value or more, the second mold clamping pressure is increased. When the mold closing time is equal to or less than a predetermined value, the mold clamping pressure of the second pressure is reduced to control the mold clamping speed. Since molding is possible, we were skilled in producing good molded products with little internal stress. It is possible to obtain without Pereta. Further energy saving can be achieved by lowering the mold clamping pressure after the flow is stopped. Further, by repeating the molding cycle, the mold clamping pressure converges and becomes constant, and there is no variation between cycles.

[Brief description of drawings]

FIG. 1 is an explanatory diagram for explaining an inflection point of a mold opening / closing increase / decrease characteristic curve of a mold opening amount according to the present invention.

FIG. 2 is an explanatory diagram for explaining an inflection point of a mold opening / closing increase / decrease characteristic curve of a mold opening amount according to the embodiment of the present invention.

FIG. 3 is a control conceptual diagram according to an embodiment of the present invention.

FIG. 4 is a control flow chart at the time of injection compression molding according to the embodiment of the present invention.

[Explanation of symbols]

 2 Movable mold 3 Fixed mold 4 Movable plate 5 Fixed plate 6 Mold clamping cylinder 6a Piston 6b Piston rod 7 Position sensor 8, 16 Hydraulic control valve 10 Injection device 11 Screw 11a Screw head 12 Injection cylinder 13 Forward / reverse motor 14 Barrel 14a Hopper 15 Nozzle 17 Control part 18 Mold position detection part 19 Shut-off valve control part 20 Screw position detection part 21 Injection control part 22 Injection pressure detection part 23 Mold clamping pressure control part 24 Mold clamping pressure detection part 25 Input / output interface 26 Arithmetic processing unit 27 Storage unit 28 Input keyboard 29 Display section 32 Shut-off valve 35 Cavity section

Claims (1)

[Claims] 1. A mold for the first pressure so that a mold opening amount does not exceed a predetermined value until a movable resin is brought into contact with a fixed mold, a molten resin is injected and filled into a cavity, and injection is completed. The clamping pressure is feedback-controlled, and after the completion of injection filling, the mold clamping pressure of the first pressure at the completion of injection is continuously maintained as the mold clamping pressure of the second pressure in the first cycle after the molding is started, and it is movable after the second cycle. When the mold closing time up to the inflection point where the rate of change of the moving speed of the mold becomes constant is more than the predetermined value, the second mold clamping pressure is increased, and conversely the mold closing time is less than the predetermined value. In this case, the method for controlling the mold clamping pressure in injection compression molding is characterized in that the mold clamping pressure is controlled by reducing the second mold clamping pressure.