JPH0976277A - Method for control of clamping pressure in injection compression molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine clamping pressure and its application time by only inputting an initial set value by a method wherein a transfer distance of a movable mold during clamping is detected with a positional sensor, time when a rate of change in a transfer speed of the movable mold becomes constant is taken as a reference, and clamping force at that point of time is increased. SOLUTION: A rate of change δn of transfer speed of a movable mold to a fixed mold is obtained. Operation is continued until the rate of change δn becomes constant, and a clamping time Tx from completion of injection to an inflection point X wherein the rate of change δn of the transfer speed becomes constant is obtained. Clamping time Tx on the first pressure obtained thus is taken as a reference, and control of clamping pressure of injection compression molding in a next molding cycle is carried out. Therefore, molding by the necessary minimum clamping pressure can be carried out, a flow speed of resin in a cavity by clamping force becomes consequently lowest, and a flow orientation of a molded product is decreased. Then, the molded product of small warpage can be obtained thereby.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method of controlling a mold clamping pressure in injection compression molding.

[0002]

2. Description of the Related Art Conventionally, in the injection compression molding method, a method of controlling the mold clamping pressure with a single pressure or multiple pressures is generally used. However, such a control method is performed by an operator based on past experience. The mold clamping pressure and the mold clamping pressure switching time, which are determined in advance, were used as set values.

Further, in an injection compression molding machine which performs feedback control of the mold clamping pressure based on the mold opening amount, only the mold opening amount at the time of injecting and filling the cavity with the molten resin is the control target.

[0004]

By the way, in the former operator's method of setting 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 force is increased by the mold clamping force, which increases the flow velocity of the resin flowing in the mold cavity, causing the flow orientation of the molded product to freeze and causing warpage and breakage. .

If the mold clamping pressure switching time starts before the mold is re-clamped before the completion of the resin flow in the mold cavity, the resin flow in the mold cavity is promoted, causing the same problem as described above. After the completion time of the resin flow, there was a problem that the compression effect due to re-molding was reduced with the passage of time, and the occurrence of sink marks could not be prevented.

On the other hand, even when the mold clamping pressure is feedback-controlled based on the mold opening amount as in the latter case, conventionally, no attention has been paid to the flow behavior of the resin in the mold cavity, and the resin in the mold cavity has not been paid attention to. There was a problem that the desired clamping product could not be obtained due to excess or deficiency in the mold clamping pressure sufficient to cause the flow of the resin, and the same problem as described above.

An object of the present invention is to solve the above problems, and paying attention to the end time of the flow of the resin in the mold cavity, the mold clamping pressure and the additional time are determined by inputting the initial set values. It is to provide a method of controlling a mold clamping pressure in an injection compression molding method which is possible only by the above.

[0008]

In order to achieve the above object, in the first aspect of the present invention, a preset mold clamping force is applied to the movable platen with the movable mold being in contact with the fixed mold. In addition, in this state, the molten resin is injected and filled, the movable mold is retracted by the resin pressure, then the resin in the mold cavity is caused to flow by the mold clamping force, and the movable mold is advanced again by injection compression molding. Therefore, 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 of the moving speed of the movable mold becomes constant. I did it. Further, in the second invention, when the rate of change of the moving speed of the movable mold in the first invention becomes constant or longer than a preset time, the mold clamping pressure at the time of injection in the next cycle is increased. On the contrary, when the time is not longer than the separately set time, the mold clamping pressure is reduced to control the mold clamping speed.

[0009]

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

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A concrete embodiment of a method for controlling a mold clamping pressure in an injection compression molding method according to the present invention will be described below with reference to FIGS.
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 a control during injection compression molding according to the embodiment of the present invention. A flow chart is shown.

The fixed mold 3 is attached to a fixed platen 5 fixed on one end of a machine base (not shown), while the movable mold 2 is opposite to the fixed platen 5 at the other end of the machine base. 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, which includes hydraulic control valves 8 and 16, a position sensor 7, a mold position detection unit 18, a shutoff valve control unit 19, a screw position detection unit 20, an injection control unit 21, and an 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 capable of obtaining the rate of change δ _n 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. ing.

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 completion 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 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 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 stores the mold clamping pressure, the change rate of the mold movement, the set values of the upper and lower limit values of the resin flow time in the cavity, and the calculated values.

A method of 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.
Then, a low-pressure injection compression molding method will be described in which the molten resin is injected and filled into the fixed mold 3, and thereafter compression is performed on the mold clamping side.

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 in the direction away from the fixed mold 3 by the resin pressure injected and filled in the cavity 35, and the mold opening amount shows the maximum value immediately after the completion of the injection and filling.

Eventually, the resin in the mold cavity 35 flows due to the mold clamping force and the cavity is filled with the resin, or the resin cools and loses its fluidity, so that the flow behavior stops. The reduction of the mold opening amount 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.

Here, if the flow completion time is too late, flow marks will appear on the surface of the molded product, and if it is further delayed, it will be impossible to completely fill the mold cavity 35 with resin, resulting in a defective molded product. Appears.

On the other hand, if the flow completion time is too fast, the mold clamping pressure is applied more than necessary. As a result, the mold clamping speed is increased, which promotes flow orientation and causes warpage of the molded product. Becomes

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

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

After the movable mold 2 and the fixed mold 3 are touched, the hydraulic pressure control valve 8 is controlled by the hydraulic pressure value detected by the mold clamping pressure detection unit 24 to send the 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 initial stage of injection 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 rise reaches the set value, the injection pressure detection unit 22 detects the hydraulic pressure value and the injection control unit 21
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 portion 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. Along with the injection filling, the movable mold 2 moves in a direction away from the fixed mold 3 (mold opening behavior) due to the balance between the filled resin pressure and the mold clamping force applied by the mold clamping cylinder 6. After the injection is completed, the movable mold 2 starts to move forward again by the mold clamping force.

The opening amount of the movable mold 2 and the fixed mold 3 at this time is detected by the position sensor 7 to obtain the 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 the molten resin into the cavity portion 35 formed by the movable mold 2 and the fixed mold 3 to fill the movable mold 2 with respect to the fixed mold 3. The mold opening increase characteristic curve B that maximizes the mold opening amount immediately after completion of injection after moving in the separating direction, the resin in the cavity flowing due to the mold clamping force after completion of injection, and the volume decrease due to cooling of the resin The movable mold 2 moves in a direction closer to the fixed mold 3, and the moving amount decreases with time, and eventually the mold closing reaches an inflection point where the rate of change of the moving speed of the movable mold 2 becomes constant. The decrease characteristic curve C can be displayed.

In the embodiment according to the present invention, paying attention to the mold closing reduction characteristic curve C, the moving amount of the movable mold 2 in the closing direction per unit time, that is, the movable mold 2 relative to the fixed mold 3. Change rate of movement speed (or change rate of mold opening amount) 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.

As will be described in detail with reference to FIG. 3, the mold clamping pressure for injection compression molding in the next molding cycle is controlled on the basis of the mold closing time T _X of the first pressure thus obtained.

[0037] When this type closing time T set value as previously upper limit in _X T ₃ and the set value T ₄ as the lower limit value is provided, 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 shrinks by cooling. For this reason, in order to increase the mold clamping pressure in the next molding cycle by a certain ratio, a value obtained by multiplying the mold clamping pressure P ₁ in the current molding cycle by the change coefficient b larger than ₁ is set as the new model clamping pressure P ₁ in the storage unit 27 again. Remember it again.

On the contrary, when the mold closing time T _X is shorter than the minimum set value T ₄ (T _X <T ₄ ), 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 ratio, a value obtained by multiplying the mold clamping pressure P ₁ in the current molding cycle by the variation coefficient a smaller than ₁ is set as the new model clamping pressure P ₁ and stored in the storage unit 27 again. Remember it again.

Further, when the mold closing time T _X is T ₄ <T _X <T ₃ , the mold clamping pressure P ₁ of the current molding cycle is kept as it is in the next molding cycle. The mold clamping pressure P ₁ stored in the unit 27 is maintained as it is.

After that, the mold clamping pressure P ₁ is added as the first pressure up to the inflection point X shown in FIG. 1, but after reaching the inflection point X, it shifts to the _second pressure clamping pressure P ₂ . . The mold clamping pressure from the arithmetic processing unit 26 is such that the _second mold clamping pressure P ₂ becomes P ₂ = P ₁ × X ₁ (however, the rate of change X ₁ indicates a value larger than _{1 which} is set in advance). It is sent to the pressure control unit 23, and the mold clamping pressure P ₂ is continuously applied for a certain period of time T ₂ .

In addition to the operation described above, 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.

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, the product is taken out, and the next molding cycle is started.

By repeating the molding cycle in this manner, stable molding is possible by making the rate of change of the moving speed of the movable mold 2 converge within a set range within a constant time.

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

[0045]

As is apparent from the above description, in the present invention, the mold clamping pressure in the next molding cycle is controlled by the time required for the resin in the cavity to complete the flow after injection. Molding with mold clamping pressure is possible. As a result, the flow velocity of the resin in the cavity due to the mold clamping force becomes the minimum, and the flow orientation of the molded product becomes small, so that 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, it is possible to efficiently compress the resin in the cavity without causing it to flow, while suppressing the flow orientation. It is possible to prevent sink marks and improve surface properties.

[Brief description of drawings]

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

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

FIG. 3 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 rotation 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 30 Shut-off valve 35 Cavity section

Claims (2)

[Claims] 1. A preset mold clamping force is applied to a movable platen while the movable mold is in contact with a fixed mold, and molten resin is injected and filled in this condition, and the movable mold is retracted by resin pressure. After that, it is an injection compression molding in which the resin in the mold cavity is caused to flow by the mold clamping force and the movable mold advances again, and the position sensor detects the amount of movement of the movable mold during mold clamping, A method for controlling a mold clamping pressure in injection compression molding, wherein the mold clamping pressure at that time is increased based on the time when the rate of change of the moving speed of the movable mold becomes constant. 2. When the rate of change of the moving speed of the movable mold according to claim 1 is constant for a preset time or longer, the mold clamping pressure at the time of injection in the next cycle is increased to a reverse value. A method for controlling a mold clamping pressure in injection compression molding, wherein the mold clamping pressure is controlled by reducing the mold clamping pressure when the time is not more than a separately set time.