JPH0957807A - Controlling method for mold clamping pressure of injection compression molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the necessary minimum mold clamping pressure by controlling the mold clamping pressure corresponding to the mold opening amount during injection charging and controlling the mold clamping pressure corresponding to the flowing time of resin in a cavity after the injection is completed. SOLUTION: The method for controlling the mold clamping pressure of injection compression molding comprises the steps of bringing a movable mold into contact with a stationary mold, then injection charging melted resin in the cavity, so feedback controlling the first mold clamping pressure that the mold opening amount does not exceed a predetermined value until the injection is completed, and switching to the second mold clamping pressure obtained by multiplying the first mold clamping pressure at the time of completion of the injection by a change rate after the completion of the injection to increase or decrease the mold clamping pressure of next molding cycle according to the mold closing time up to a point of contraflexure that the moving speed change rate of the movable mold becomes constant from the completion of the injection charging.

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, 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 will be excess or deficiency with respect to 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, resulting in a molded product with a large internal stress due to freezing of the flow orientation, or with an excessive mold clamping force. However, there is a problem in that the desired molded product cannot be obtained if the surface property is deteriorated.

The present invention has been made in view of the above problems, and its purpose is to control a mold clamping pressure corresponding to a mold opening amount during injection filling, and to flow a resin in a cavity after completion of injection. To provide a method of controlling a mold clamping pressure in injection compression molding which enables a minimum necessary mold clamping pressure control by performing a mold clamping pressure control corresponding to time.

[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 completion of injection filling, the rate of change to the first mold clamping pressure at the time of injection completion. When the mold closing time from the completion of injection filling to the inflection point where the moving speed change rate of the movable mold becomes constant after switching to the second mold clamping pressure multiplied by Then, the rate of change of the mold clamping pressure at the second pressure is multiplied by a change constant greater than 1, and conversely, when the mold closing time becomes equal to or less than a predetermined value, the mold clamping pressure at the second pressure is changed in the next molding cycle. Change the rate of change of mold clamping pressure by multiplying the rate of change by a change constant smaller than 1. And to control the mold clamping speed by.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The mold clamping pressure is controlled so that the mold opening amount does not exceed a predetermined value during injection and filling of resin into a cavity, and after the injection is completed, the mold clamping pressure is switched to the second mold clamping pressure. If the mold closing time from the completion of injection filling 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 changes by more than 1 in the next molding cycle. If the mold closing time is equal to or less than a predetermined value by multiplying by a constant, on the other hand, in the next molding cycle, the mold clamping pressure of the second pressure is changed to a rate of change of the mold clamping pressure multiplied by a change constant smaller than 1. 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 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 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.

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 is a screw position detector provided for informing 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 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 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 a movable mold 2 and a fixed mold 3 that have been clamped in advance are injected and 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 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.

The resin in the mold cavity 35 is eventually 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. At the same time, after this flow end time, in order to promote the flow behavior of the resin in the mold cavity 35, the mold is closed. 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 portion 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 detector 18 continues to measure the mold opening amount Xn, and when the mold opening amount Xn exceeds an arbitrary set value X1, a command for increasing the mold clamping pressure Pn is issued to the arithmetic processing unit. 26 to the mold clamping pressure control unit 23.

After the injection is completed, the shutoff valve 30 is closed, and at the same time, the mold clamping pressure Pn at that time is changed to the mold clamping pressure P2 multiplied by the change rate X2. During this period, the movable mold 2 moves in the direction in which it separates from the fixed mold 3 due to the filling resin pressure accompanying the injection filling (mold opening behavior), but maintains a constant value as the mold clamping pressure increases. After the injection is completed, the movable mold 2 starts to move 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 the mold opening / closing increase / decrease characteristic curve D as shown in FIG.

The mold opening / closing increase / decrease characteristic curve D 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, but the mold opening increasing characteristic curve E is controlled so that the mold opening amount Xn does not exceed a predetermined value X1, and when the injection is completed The flow of the resin progresses, the filling thickness of the resin decreases, and the cooling shrinkage of the resin causes the movable mold 2 to move in the direction closer to the fixed mold 3 and change in the decelerating direction from moment to moment. The change rate of the moving speed of the mold 2 (which means the change rate of the movable mold 2 per unit time) can be reduced by a so-called inflection point H, which can be represented by a mold closing decrease characteristic curve C.

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

The mold closing pressure for injection compression molding in the next molding cycle is controlled on the basis of the mold closing time Tx of 1 pressure and 2 pressure thus obtained.

The mold closing time Tx is provided with a maximum set value T3 as an upper limit value and a minimum set value T4 as a lower limit value. If the mold close time Tx is longer than the maximum set 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 rate of change of the mold clamping pressure in the next molding cycle by a certain ratio, the value obtained by multiplying the rate of change of the mold clamping pressure X2 of the current molding cycle by the coefficient of variation b larger than 1 is used. As
It is stored again in the storage unit 27.

On the other hand, 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 tree finger pressure that causes cooling contraction. Therefore, in order to reduce the rate of change of the mold clamping pressure in the next molding cycle by a certain ratio, a value obtained by multiplying the rate of change X2 of the mold clamping pressure in the current molding cycle by a coefficient of variation a smaller than 1 is used.
2 is stored again in the storage unit 27.

When Tx is between T4 <Tx <T3, the rate of change X2 of the mold clamping pressure in the current molding cycle is maintained as it is in the next molding cycle.
In this case, the initial setting (control based on the initial setting value in the first molding cycle) set in the storage unit 27 or the pre-molding cycle (controlling based on the pre-molding cycle from the second molding cycle) is performed. The change rate X2 of the set mold clamping pressure is maintained as it is.

Thereafter, the mold clamping pressure P ₂ is applied as at least the second pressure up to the inflection point H as shown in FIG. 1, but normally, after the inflection point H has passed, the resin flow is stopped. Therefore, the third clamping pressure P3 may be small.

Therefore, when the mold clamping pressure P ₂ is applied and the second pressure holding time T ₁ becomes T ₁ = Tx, the third mold clamping pressure P 3 is P 3 = P 2 × X 3 (however, , The rate of change X3 is smaller than 1) is issued from the arithmetic processing unit 26 to the mold clamping pressure control unit 23, and the mold clamping pressure P3 is added for a certain period of time T2 in order to continue the mold clamping. Of.

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. If there is a difference, the inflection point H is unlikely to occur, and it is difficult to specify the inflection point H from the obtained mold opening / closing increase / decrease characteristic curve A. Therefore, for safety, the second mold clamping pressure P2
May be continuously added so that T1> Tx.

After holding the second pressure for T1 time in this way, the second pressure is switched to the third pressure after the point which is recognized as the inflection point H based on the past experience. 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 the installation of 3 is completed, it goes directly to the above-mentioned mold clamping completion.

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 and the product is taken out.
Move on to the next molding cycle.

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.

If the value of the final mold clamping force of the first pressure / projected area of the mold cavity (average cavity internal pressure) in this embodiment is too large, the injection speed on the injection device 10 side is lowered to reduce the average cavity. By adjusting the internal pressure to an appropriate value, it is possible to prevent the flow orientation from freezing and obtain a molded product with no residual stress.

[0052]

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 completion of injection filling, the second mold clamping pressure obtained by multiplying the change rate to the first mold clamping pressure at the completion of injection. If the mold closing time from the completion of injection filling to the inflection point where the moving speed change rate of the movable mold becomes constant after the completion of the injection filling becomes a predetermined value or more, in the next molding cycle, the second mold clamping pressure If the rate of change is multiplied by a change constant greater than 1, and conversely the mold closing time is less than or equal to a predetermined value, the rate of change of the second clamping pressure is multiplied by a change constant less than 1 in the next molding cycle. The mold clamping speed is controlled by changing the mold clamping pressure change rate. By, it is possible to mold in the clamping pressure of the minimum required. As a result, a good molded product with less internal stress can be obtained without a skilled operator. Further, further energy saving can be achieved by reducing the mold clamping pressure after the flow is stopped. Further, when the mold clamping pressure is converged by repeating the molding cycle, the mold clamping pressure becomes constant and the variation between the cycles becomes small.

[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 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 (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. After the completion of injection filling, the clamping pressure is feedback-controlled, and after the completion of injection filling, the mold clamping pressure of the first pressure is multiplied by the change rate to switch to the second clamping pressure, and the moving speed of the movable mold changes from the completion of injection filling. When the mold closing time up to the inflection point where the rate becomes constant becomes a predetermined value or more, in the next molding cycle, the rate of change of the mold clamping pressure at the second pressure is multiplied by a change constant larger than 1, and conversely the above. When the mold closing time becomes equal to or less than a predetermined value, in the next molding cycle, the mold clamping pressure change rate is changed by multiplying the second mold clamping pressure change rate by a change constant smaller than 1. Control of clamping pressure in injection compression molding characterized by controlling clamping speed Your way.