JP3232550B2 - Control method of mold clamping pressure in injection compression molding - Google Patents

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, in an injection compression molding method, a method of controlling a mold clamping pressure by a single pressure or a multi-stage pressure is generally used. However, such a control method is performed by an operator on a trial and error basis based on past experience. The mold clamping pressure and the mold clamping pressure switching time which were determined in advance were used as set values.

Further, in an injection compression molding machine that performs feedback control of the mold clamping pressure based on the amount of mold opening, only the amount of mold opening when the molten resin is injected and filled into the cavity is to be controlled.

[0004]

In the former method in which the former operator sets the mold clamping pressure and the mold clamping pressure switching time based on past experience, the mold clamping pressure is likely to be set higher than necessary. As a result, the mold-clamping speed by the mold-clamping force is increased, so that the flow speed of the resin flowing in the mold cavity is increased, and there is a problem that the flow orientation is frozen in the molded product, which causes warpage and breakage. .

If re-clamping starts before the completion of the flow of the resin in the mold cavity, the resin flow in the mold cavity is promoted, and the same problem as described above occurs. After the completion of the flow of the resin, the compression effect due to the re-clamping decreases with the lapse of time, and there is a problem that generation of sinks cannot be prevented.

On the other hand, even when the mold clamping pressure is feedback-controlled based on the amount of mold opening as in the latter case, attention has not been focused on the flow behavior of the resin in the mold cavity. In such a case, there is a problem that the mold clamping pressure is insufficient or insufficient to make the fluid flow, and a desired molded product cannot be obtained, or the same problem as described above.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and pays attention to the end time of the flow of the resin in the mold cavity, determines the mold clamping pressure and the additional time, and inputs an initial set value. It is an object of the present invention to provide a method of controlling a mold clamping pressure in an injection compression molding method which can be performed only by using the method.

[0008]

In order to achieve the above object, in a first aspect of the present invention, a preset clamping force is applied to a movable platen while a movable mold is in contact with a fixed mold. In addition, in this state, the molten resin is injected and filled, and after the movable mold is retracted by the resin pressure, the resin in the mold cavity is caused to flow by the mold clamping force, and the movable mold is again advanced by injection compression molding. The amount of movement of the movable mold during mold clamping is detected by the position sensor, and the mold clamping pressure at that time is increased based on the time when the rate of change in the moving speed of the movable mold becomes constant. I did it. In the second invention, if the time at which the rate of change of the moving speed of the movable mold in the first invention becomes constant is equal to or longer than a preset time, the mold clamping pressure during injection in the next cycle is increased. Conversely, when the time is shorter than a separately set time, the mold clamping pressure is reduced to control the mold clamping speed.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A flow completion time of a resin in a cavity is estimated from a movement curve of a movable mold after completion of injection, and a mold clamping in a next molding cycle is performed so that the flow completion time converges to a predetermined range. By changing the pressure, molding can be performed with a minimum required mold clamping pressure. As a result, the flow speed of the resin in the cavity due to the mold clamping force is minimized, the flow orientation of the molded product is reduced, and a molded product with a small warp can be obtained. Furthermore, by increasing the mold clamping pressure while the resin in the cavity immediately after the flow completion time maintains the fluidity, the resin in the cavity can be compressed without flowing, thereby suppressing the flow orientation. It becomes possible to prevent sink marks and improve surface properties.

[0010]

1 to 3 show a specific embodiment of a method for controlling a mold clamping pressure in an injection compression molding method according to the present invention.
This will be described in detail with reference to FIG.

FIG. 1 is a diagram for explaining an inflection point according to the present invention, FIG. 2 is a conceptual diagram of control according to an embodiment of the present invention, and FIG. 3 is control during injection compression molding according to the embodiment of the present invention. FIG.

The fixed mold 3 is mounted on a fixed platen 5 fixed on one end of a machine base (not shown), while the movable mold 2 is mounted on the other end of the machine base in opposition to the fixed platen 5. It is attached to the movable platen 4.

A mold clamping cylinder 6 is provided on the back of the movable platen 4.
The movable platen 4 is fixed to the tip of a piston 6a that moves back and forth inside and a piston rod 6b of the piston 6a, and pressure oil is introduced before and after the piston 6a so that the movable platen 4 can be moved back and forth. I have. Reference numeral 35 indicates a cavity.

An injection device 10 comprises 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, and a resin material in a hopper 14a is heated and compressed in a supply zone and a compression zone, melted and 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 fed forward by the rotation of the screw 11 while being melted. Reference numeral 11a indicates a screw head. The screw 11 is rotated forward and backward by a forward / reverse rotation motor 13 directly connected to the screw 11. Reference numeral 30 indicates a shut-off valve. Reference numeral 12 denotes an injection cylinder, 12a denotes a piston, and 13 denotes 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. The hydraulic control valves 8 and 16, the position sensor 7, the mold position detection unit 18, the shut-off valve control unit 19, the screw position detection unit 20, the injection control unit 21, and the injection pressure detection unit 22, mold clamping pressure control unit 23,
Mold clamping pressure detector 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 section 18, and the mold position detecting section 18 is connected to an input / output interface 25. Further, the input / output interface 25 is connected to an arithmetic processing unit 26 which can obtain a rate of change δ _n of the moving speed of the movable mold 2 from the amount of movement of the movable mold 2 detected by the mold position detection unit 18. ing.

An injection control unit 21 connected to a hydraulic control valve 16 for controlling the driving of the injection cylinder 12 and the forward / reverse rotation motor 13 and an injection pressure detection unit 22 for detecting the hydraulic 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 controller 23 is connected to the hydraulic control valve 8 for controlling the driving of the mold clamping cylinder 6, and the mold clamping pressure controller 23 is connected to an input / output interface 25. Further, a 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 completion position. The screw position detection unit 20 is connected to the input / output interface 25.

An input / output interface 25 for inputting / outputting a control signal to be output to each drive unit 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 the same. A unit 29 is connected, and the input / output interface 25 is connected to an arithmetic processing device 26 that performs a comparison 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 stores the set values of the mold clamping pressure, the rate of change of the mold movement, the upper and lower limits of the flow time of the resin in the cavity, and the calculated values.

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

In this embodiment, the movable mold 2 previously clamped
And a low-pressure injection compression molding method in which a molten resin is injected and filled into the fixed mold 3 and then compressed on the mold clamping side.

FIG. 1 shows a typical characteristic curve of the change over time of the mold opening during injection compression molding when the mold clamping pressure is controlled at one pressure. In FIG. 1, the movable mold 2 is pushed back in the direction away from the fixed mold 3 by the pressure of the resin injected and filled into the cavity portion 35, and the mold opening amount shows the maximum value immediately after the injection and filling is completed.

Since the resin in the mold cavity 35 flows due to the mold clamping force and fills the inside of the cavity, and the resin is cooled and loses fluidity, the flow behavior stops. Of the mold opening depends only on the volume reduction due to the cooling of the resin. Therefore, by measuring the change rate of the mold opening amount, that is, the change rate δ _n of the moving speed of the movable mold 2, it is possible to estimate the flow end time of the resin in the mold cavity 35.

If the flow completion time is too late, a flow mark appears on the surface of the molded product, and if the flow completion time is further delayed, it becomes impossible to completely fill the mold cavity 35 with the resin. Appears.

Conversely, if the flow completion time is too fast, an excessive clamping pressure is applied, and as a result, the mold clamping speed is increased, which promotes flow orientation and causes warpage of the molded product. Becomes

Further, when the mold clamping pressure after the flow completion time is increased, it is possible to compress the resin without flowing, and it is possible to prevent sink marks and improve surface properties without flow orientation. If the switching time of the clamping pressure is too fast, the flow orientation is promoted. If the time is too slow, the fluidity is lost due to cooling of the resin, and the effect of compression cannot be expected.

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

After the movable mold 2 and the fixed mold 3 touch each other, the hydraulic control valve 8 is controlled based on the oil pressure value detected by the mold clamping pressure detector 24 to send pressure oil to the mold clamping cylinder 6. The movable mold 2 is pressed toward the fixed mold 3 so that the mold clamping pressure P ₁ is set at the beginning of the injection start or in the pre-molding cycle, and the mold clamping pressure is increased.

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 detection unit 20. After that, after the mold clamping pressure reaches the set value, the injection pressure detecting unit 22 detects the oil pressure value while the injection control unit 21 detects the oil pressure value.
The hydraulic control valve 16 is controlled via the
3 and the piston of the injection cylinder 12 are driven to perform injection filling into the cavity 35 formed by the movable mold 2 and the fixed mold 3.

After the injection is completed, the shutoff valve 30 is closed, and at the same time, the mold clamping pressure P ₁ is maintained. Due to the balance between the filled resin pressure and the mold clamping force applied by the mold clamping cylinder 6 during the injection filling, the movable mold 2 moves in a direction away from the fixed mold 3 (mold opening behavior). After the injection is completed, the movable mold 2 starts to advance again by the mold clamping force.

At this time, the 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 A as shown in FIG. The mold opening / closing increase / decrease characteristic curve A is obtained by injecting and filling the molten resin into the cavity 35 formed by the movable mold 2 and the fixed mold 3 so that the movable mold 2 The mold opening increase characteristic curve B in which the mold opening amount becomes maximum immediately after the injection is completed by moving in the separating direction, the resin in the cavity flows due to the mold clamping force after the injection is completed, and the volume is reduced by cooling the resin. The movable mold 2 moves in a direction approaching the fixed mold 3, and the amount of movement decreases every moment, and the mold closes at an inflection point at which the rate of change of the moving speed of the movable mold 2 becomes constant. It can be represented by a decreasing characteristic curve C.

In the embodiment according to the present invention, focusing on 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 movement of the movable mold 2 with respect to the fixed mold 3 is described. Change rate of moving speed (or change rate of mold opening) δ
seek _n, continued operation until the change rate [delta] _n is constant, obtaining the mold closing time T _X from completion of injection up to the inflection point X of the change rate [delta] _n of the moving speed becomes constant.

More specifically, referring to FIG. 3, the mold closing pressure of the injection compression molding in the next molding cycle is controlled based on the mold closing time T _X obtained at the first pressure.

The mold closing time T _X is previously provided with a set value T ₃ as an upper limit value and a set value T ₄ as a lower limit value. If the mold closing time T _X is longer than the maximum set value T ₃ (T _X >
T ₃ ) indicates that the mold clamping pressure is smaller than the resin pressure that contracts upon cooling. Therefore, to the clamping pressure in the next molding cycle is constant percentage increase, the value obtained by multiplying a greater than one change coefficient b on clamping pressure P ₁ in the current molding cycle as new clamping pressure P _1, again in the storage unit 27 You have to remember it again.

On the other hand, when the mold closing time T _X is shorter than the minimum set value T ₄ (T _X <T ₄ ), it indicates that the mold clamping pressure is larger than the resin pressure for cooling and shrinking. Therefore, to the clamping pressure in the next molding cycle is constant percentage decrease, the value obtained by multiplying 1 smaller change coefficient a in clamping pressure P ₁ in the current molding cycle as new clamping pressure P _1, again in the storage unit 27 You have to remember it again.

When the mold closing time T _X satisfies T ₄ <T _X <T ₃ , the mold clamping pressure P ₁ of the current molding cycle is maintained as it is in the next molding cycle. the clamping pressure P ₁ stored in the unit 27 is directly hold.

Thereafter, the mold clamping pressure P ₁ is applied as the _first pressure up to the inflection point X shown in FIG. 1, but after reaching the inflection point X, the mold pressure P ₂ shifts to the _second pressure P ₂ . . The 2 clamping pressure P ₂ of圧目the clamping than P ₂ = P ₁ × X ₁ (provided that the rate of change X ₁ is a preset value greater than 1) and a kind of command the processing unit 26 out to the pressure control unit 23, subsequently the clamping pressure P ₂ a predetermined time T ₂ is added.

Separately from the above-described operation, the injection device 10 rotates the screw 11 by rotating the forward / reverse rotation motor 13 to measure a predetermined amount of the molten resin in front of the screw head 11a.

On the other hand, 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, and after the product is taken out, the process proceeds to the next molding cycle.

By repeating the molding cycle in this way, the rate of change in the moving speed of the movable mold 2 is converged within a range set for a constant time, thereby enabling stable molding.

The same effect can be expected at the inflection point of the opening amount between the dies in the present invention at the inflection point of the opening amount between the platens. The present invention is also applicable to an injection press molding method in which injection is performed in a state in which a mold is opened in advance, and then a mold clamping operation is performed.

[0045]

As is evident from the above description, the present invention controls the mold clamping pressure in the next molding cycle by the time required for the resin in the cavity to complete the flow after the injection, thereby minimizing the necessary amount. Molding with mold clamping pressure becomes possible. As a result, the flow speed of the resin in the cavity due to the mold clamping force is minimized, the flow orientation of the molded product is reduced, and a molded product with a small warp can be obtained. Furthermore, by increasing the mold clamping pressure while the fluidity of the resin in the cavity is high immediately after the flow completion time, the resin in the cavity can be efficiently compressed without flowing, while suppressing the flow orientation. It becomes possible to prevent sink marks and improve surface properties.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an inflection point of a mold opening amount according to the present invention.

FIG. 2 is a control conceptual diagram according to the embodiment of the present invention.

FIG. 3 is a control flow chart during injection compression molding according to an 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 unit 18 Mold position detection unit 19 Shut-off valve control unit 20 Screw position detection unit 21 Injection control unit 22 Injection pressure detection unit 23 Mold clamping pressure control unit 24 Mold clamping pressure detection unit 25 Input / output interface 26 Arithmetic processing unit 27 Storage unit 28 Input keyboard 29 Display unit 30 Shut-off valve 35 Cavity unit

Claims (2)

(57) [Claims] 1. A predetermined mold clamping force is applied to a movable platen in a state where a movable mold is in contact with a fixed mold, and molten resin is injected and filled in this state, and the movable mold is retracted by resin pressure. After that, the resin in the mold cavity is caused to flow by the mold clamping force, and the movable mold is injection compression molding in which the movable mold advances again, and the movement amount of the movable mold during the mold clamping is detected by the position sensor. A method for controlling a mold clamping pressure in injection compression molding, wherein the mold clamping pressure at that time is increased based on a time when the rate of change of the moving speed of the movable mold becomes constant. 2. The method according to claim 1, wherein when the rate of change of the moving speed of the movable mold is constant is equal to or longer than a preset time, the mold clamping pressure at the time of injection in the next cycle is increased. A method of controlling a mold clamping pressure in injection compression molding, wherein the mold clamping speed is controlled by reducing the mold clamping pressure when the time is equal to or less than a separately set time.