JPH0929805A - Control method of mold clamping pressure in injection compression molding - Google Patents

Abstract

(57) [Summary] [Purpose] The mold clamping pressure can be controlled simply by inputting molding with the minimum necessary mold clamping pressure as the initial setting value. [Structure] Find the inflection point from the rate of change of the moving speed of the movable mold, estimate the resin flow time in the cavity, and change the mold clamping pressure in the next molding cycle so that this time converges within a certain range. At the same time, the mold clamping pressure after this time is changed.

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 that was 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]

However, when the former operator sets the mold clamping pressure based on past experience, the mold clamping pressure is set higher than necessary, or the mold clamping pressure is required. As a result of the state of being applied for a time or longer, there is a problem that the internal pressure of the mold cavity becomes unnecessarily high, and in a severe case, internal stress remains in the molded product and causes deformation or destruction.

On the other hand, in the latter case where the feedback control of the mold clamping pressure is performed with the mold opening amount as a reference, conventionally, no attention has been paid to the flow behavior of the resin in the mold cavity. There is a problem that a desired molded product cannot be obtained due to insufficient mold clamping pressure for flowing the resin in the cavity.

Further, even after the resin in the mold cavity has flowed out and the mold cavity has been filled with the resin, a very expensive detection device is required to detect the filled state of the resin, and therefore, it continues. Since a high mold clamping pressure must be continuously applied, there is a problem in that much energy is wasted.

The present invention has been made in view of the above problems, and an object of the present invention is to pay attention to the flow end time of the resin in the mold cavity and to set the mold clamping pressure and the mold clamping pressure application time to the initial stage. It is an object of the present invention to provide a method of controlling a mold clamping pressure in injection compression molding, which is only input and set as a set value.

[0008]

In order to achieve the above object, in the first aspect of the present invention, the movable platen is provided with a preset mold clamping pressure in a state where the movable mold is brought into 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, and then the movable mold is advanced again as the resin thickness in the filled cavity changes. During molding, the amount of movement of the movable mold is detected by the position sensor during mold clamping, and the mold clamping pressure at that time is based on the time when the rate of change of the moving speed of the movable mold becomes constant. Was changed to an arbitrary value to change the mold clamping pressure. In the second invention, which is mainly based on the first invention, when the time during which the rate of change of the moving speed of the movable mold becomes constant exceeds a preset time, the mold clamping during injection in the next molding cycle is performed. The pressure is increased, and conversely, when the time is less than or equal to a preset time, the mold clamping pressure is reduced to control the mold clamping speed.

[0009]

[Function] The flow end time of the resin in the cavity is estimated from the movement curve of the movable mold after the injection is completed, and the mold clamping pressure in the next molding cycle is changed so that the flow end time converges within a predetermined range. Since this is done, molding can be performed with the minimum required mold clamping pressure. Furthermore, by reducing the mold clamping pressure after the converged flow end time, it is possible to save the mold clamping pressure energy without affecting the shape of the molded product. On the other hand, by increasing the mold clamping pressure after the end of flow, the resin can be compressed without the flow orientation of the resin in the cavity, preventing the occurrence of sink marks on the surface of the molded product and improving transferability. It becomes possible.

[0010]

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 according to the present invention, FIG. 2 is a conceptual view of control according to an embodiment of the present invention, and FIGS. The control flow diagram at the time of such injection compression molding 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, 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 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 δn of the moving speed of the movable mold 2 from the moving amount of the movable mold 2 detected by the mold position detector 18. There is.

The injection control unit 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 unit 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 section 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 section 23 is connected to the input / output interface 25.

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 is a screw position detector provided for notifying the injection start position and the injection completion position,
The screw position detector 20 is connected to the input / output interface 25.

An input / output interface 25 for inputting / outputting control signals to be 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 stores the mold clamping pressure, the mold position change rate, the set values of the upper and lower limit values of the flow time of the resin 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, a low-pressure injection compression molding method will be described in which the movable mold 2 and the fixed mold 3 that have been clamped in advance are filled with a molten resin, and then 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 backward by the resin pressure injected and filled in the cavity portion 35, and the mold opening amount shows the maximum value immediately after the completion of injection and filling.

By the mold clamping pressure applied to both the molds 2 and 3 before the injection is started, the resin once injected and filled in the cavity 35 receives a pressing force and spreads to every corner of the cavity 35. At the same time as the resin filling thickness decreases, the mold opening amount gradually decreases due to the decrease in the resin volume due to cooling.

The flow behavior stops as the resin in the mold cavity 35 cools, but the reduction of the mold opening amount at this time depends only on the volume reduction due to the cooling of the resin.

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 end time of the resin flow 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 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, in order to promote the flow behavior of the resin in the mold cavity 35, It is not necessary to control the clamping pressure, and only the clamping pressure applied to the movable mold 2 to hold the volume of the cavity 35 having the same volume as the molded product is required.

On the contrary, even if the mold clamping pressure after the flow end time is increased, a large flow does not occur in the resin in the cavity, so that the compression operation is not accompanied by the flow orientation that causes the deformation or destruction of the molded product. Is possible.

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 detector 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. 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 injection 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 moving forward again by 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 A as shown in FIG.

The mold opening / closing increase / decrease characteristic curve A shows that when the injection filling of the molten resin into the cavity portion 35 formed by closing the molds 2 and 3 is started, the movable mold 2 is moved as described above.
Moves in the direction away from the fixed mold 3 and the mold opening increase characteristic curve B that maximizes the mold opening amount between the two molds 2 and 3 when the injection is completed, and the resin that has been injected and filled with the injection resin are The movable mold 2 to which the mold pressure is added as the resin pressure is cooled and to which the mold clamping pressure is applied moves closer to the fixed mold 3 and changes every moment in the deceleration direction. The rate (which means the rate of change of the moving amount of the movable mold 2 per unit time) becomes smaller. It can be displayed with a mold closing decrease characteristic curve C up to the so-called inflection point X.

In the embodiment according to the present invention, paying particular 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 movable mold 2 with respect to the fixed mold 3. Of the moving speed (or the changing rate of the mold opening amount) δn, the calculation is continued until the changing rate δn becomes constant, and the change from the completion of injection when the moving speed change rate δn becomes constant. The mold closing time Tx to the bending point X is obtained.

The mold clamping pressure for injection compression molding in the next molding cycle is controlled on the basis of the mold closing time Tx of 1 pressure thus obtained.

The mold closing time Tx is provided with a maximum setting value T ₃ as an upper limit value and a minimum setting value T ₄ as a lower limit value. If the mold closing time Tx is longer than the maximum setting value T ₃ (Tx> T ₃ ) 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 P ₁ of the current molding cycle by the variation coefficient b larger than ₁ is set as the new model clamping pressure P ₁ and is stored in the storage unit 27 again. Remember it again.

On the contrary, the mold closing time Tx is the minimum set value T_FourThan
When short (Tx ≦ T_Four), To the acupressure to shrink and shrink
It shows that the mold clamping pressure is higher than that. Therefore, the next molding
In order to reduce the mold clamping pressure in the cycle by a certain percentage,
Clamping pressure P of the current molding cycle ₁Coefficient of change less than 1
The value obtained by multiplying a is the new clamping pressure P₁As storage unit 2
It is remembered again to 7. And Tx> T_Fourof
When the mold clamping pressure P₁Storage unit 2 as
Do not change the setting value entered in 7.
You.

When Tx is in the range of T ₄ <Tx <T ₃ , the mold clamping pressure P ₁ of the current molding cycle is maintained as it is in the next molding cycle. In this case, the memory unit 27 stores it. Clamping pressure set to the set initial setting (control based on the initial setting value during the first molding cycle) or the pre-molding cycle (controlling based on the pre-molding cycle from the second molding cycle) P ₁
Is retained as is.

Thereafter, the mold clamping pressure P ₁ is applied as at least one pressure up to the inflection point X as shown in FIG. 1, but normally, the resin flow is stopped after the inflection point X has passed. Therefore, the mold clamping pressure P ₁ may be small.

Therefore, when the holding time T ₁ of _one pressure to which the mold clamping pressure P ₁ is applied becomes T ₁ = Tx, the mold clamping pressure P _{2 which} is ₂ pressures is P ₂ = P ₁ × X ₁ (However, change rate X
A command such that 1 indicates a value smaller than ₁ ) is issued from the arithmetic processing unit 26 to the mold clamping pressure control unit 23, and the mold clamping pressure P ₂ is added for a fixed time T ₂ in order to continue the mold clamping. is there.

On the other hand, depending on the shape of the molded product and the presence / absence of surface treatment, the occurrence of sink marks and the surface transferability may become a problem. In such a case, the rate of change X ₁ for obtaining the mold clamping pressure P ₂ is input as a value larger than 1 so that P ₂ ≧ P ₁ and the mold clamping pressure P ₂ is added for a certain period of time T ₂ .

However, as described above, it is preferable if 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 different due to the difference in the product thickness. T the mold opening and closing decrease characteristic from the curve a look at the safety since the inflection point X is difficult to identify one pressure clamping pressure P ₁ which inflection point X is obtained hardly occurs if the results
Continue to add so that ₁ > Tx.

After maintaining 1 pressure for T ₁ hour in this way, after the point determined to be the inflection point X based on the past experience, the pressure is switched from 1 pressure to 2 pressure. Becomes the above-mentioned mold clamping pressure P ₂ .

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.

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, the rate of change of the moving speed of the movable mold 2 converges within a set range of time, and stable molding becomes possible.

Next, a second embodiment shown in FIG. 4 will be described.
Since the mold closing time Tx in which the rate of change δn of the moving speed of the movable mold 2 when the movable mold 2 advances after the completion of injection is not changed is the same as that in the first embodiment, the description thereof will be omitted.

The mold closing time Tx is provided with a maximum setting value T ₃ as an upper limit value and a minimum setting value T ₄ as a lower limit value. If the mold closing time Tx is longer than the maximum setting value T ₃ (Tx> T ₃ ) 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 constant value, a value obtained by adding an appropriate mold clamping pressure ΔP ₁ to the mold clamping pressure P ₁ of the current molding cycle is set as a new mold clamping pressure P ₁ in the storage unit. It is stored again in 27.

On the contrary, the mold closing time Tx is the minimum set value T_FourShorter
Case (Tx ≤ T_Four) Is the ratio of tree pressure that shrinks when cooled
All indicate that the mold clamping pressure is high. Therefore, the next molding service
In order to reduce the mold clamping pressure in the icle by a certain value,
Clamping pressure P of the current molding cycle ₁More appropriate mold clamping pressure ΔP
₁Is the new mold clamping pressure P₁As storage unit
It is stored again in 27. And T_Four<Tx
Clamping pressure P₁Memory is determined to be appropriate.
Do not change the setting value by inputting to
Of.

When Tx is in the range of T ₄ <Tx <T ₃ , the mold clamping pressure P ₁ of the current molding cycle is maintained as it is in the next molding cycle. In this case, the memory unit 27 stores it. Clamping pressure set to the set initial setting (control based on the initial setting value during the first molding cycle) or the pre-molding cycle (controlling based on the pre-molding cycle from the second molding cycle) P ₁
Is retained as is.

In this embodiment, the inflection point X is set to the movable mold 2
Although it was assumed that the rate of change of the moving speed of was constant, it goes without saying that the same idea can be applied to the movable platen 4.

Further, in this embodiment, the mold clamping operation is performed after the movable resin 2 is injected and filled in the cavity 35 with the fixed mold 3 having a constant mold opening amount. It can also be applied to the above injection press molding.

[0060]

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 when the resin in the cavity finishes flowing after injection, so that the minimum necessary mold can be obtained. It is possible to mold at the clamping pressure. As a result, a good molded product with a small internal stress can be obtained without a skilled operator. Further energy saving can be achieved by lowering the mold clamping pressure after the end of flow. On the contrary, by increasing the mold clamping pressure after the end of the flow, the resin can be compressed without the flow orientation of the resin, and it is possible to prevent sink marks and improve the surface property.

[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 a control conceptual diagram according to an embodiment of the present invention.

FIG. 3 is a control flow chart during injection compression molding according to the first embodiment of the present invention.

FIG. 4 is a control flow chart at the time of injection compression molding according to the second 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 mold clamping pressure set in advance in a state where the movable mold is brought into contact with a fixed mold is applied to the movable platen, and in this state, molten resin is injected and filled to retract the movable mold by the resin pressure. After that, it is an injection compression molding in which the movable die moves forward again with the change of the resin thickness in the filled cavity, and the movement amount of the movable die is detected by the position sensor during the mold clamping. The injection is characterized in that, based on the time when the rate of change of the moving speed of the movable mold becomes constant, the mold clamping pressure is multiplied by an arbitrary value to change the mold clamping pressure. Control method of mold clamping pressure in compression molding. 2. When the rate of change of the moving speed of the movable mold according to claim 1 becomes constant over a preset time, the mold clamping pressure at the time of injection in the next molding cycle is increased, On the contrary, when the time is equal to or shorter than a preset time, the mold clamping speed is controlled by decreasing the mold clamping pressure to control the mold clamping pressure in injection compression molding.