JP2001018271A - Injection molding method and injection molding machin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high molding quality by excluding the inferiority of a skin layer caused by the weight irregularity, strain or density difference of a molded article. SOLUTION: The dwelling target value Ps in a dwelling process is preset and, in the dwelling process at a time of molding, the dwelling force based on the dwelling target value Ps is applied while the resin pressure Pg on the side of a gate in a mold cavity and the resin pressure Po on the side opposite to the gate therein are detected and, when the resin pressure Po on the side opposite to the gate begins to lower, pressure control is performed so that the resin pressure Pg on the side of the gate coincides with the resin pressure Po on the side opposite to the gate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method and an injection molding machine suitable for molding a long molded product or the like.

[0002]

2. Description of the Related Art Generally, in a molding cycle of an injection molding machine, an injection step of injecting and filling a resin (molten resin) measured in front of the screw into a mold cavity by advancing a screw in a heating cylinder. And a pressure holding step of applying a pressure holding force to the resin injected and filled in the mold cavity.

In the pressure holding process in a conventional injection molding machine, for example, as disclosed in Japanese Patent Application Laid-Open No. 63-114618, a target value for the pressure holding is set in advance, and the process proceeds to the pressure holding process during molding. Then, feedback control is performed such that the detected value matches the target value by comparing the target value with a detected value of the holding pressure detected based on the hydraulic pressure of the injection cylinder.

[0004]

By the way, the reference numeral Pcr shown by a dotted line in FIG. 1 indicates the holding pressure characteristic when it is set at one stage in a conventional injection molding machine (injection molding method). In the cavity, the filling of the resin on the opposite side of the gate (the end of the cavity separated from the gate) is later than on the gate side (near the gate). The resin pressure Por on the side opposite to the gate decreases as a whole from the resin pressure Pgr on the side of the gate, and the resin pressure Por on the side opposite to the gate starts to decrease earlier than the resin pressure Pgr on the side of the gate. It shows the characteristic that the resin pressure Pgr decreases.

For this reason, in a conventional injection molding machine (injection molding method), particularly when a highly elastic resin such as an elastomer is used or when a long molded product is molded, the gate side resin pressure Pgr is reduced. The difference in the resin pressure Por on the anti-gate side increases, and eventually the unevenness of the resin pressure causes unevenness in weight and distortion of the molded product, and the occurrence of a defective skin layer due to the difference in density, resulting in high molding quality. There was no problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems existing in the prior art, and makes the resin pressure in the mold cavity uniform, and causes a failure of the skin layer due to weight variation, distortion or density difference of the molded product. By eliminating
It is an object of the present invention to provide an injection molding method and an injection molding machine capable of obtaining high molding quality.

[0007]

In the injection molding method according to the present invention, in the pressure-holding step of applying a pressure-holding pressure Pc to the resin L injected and filled in the mold cavity C, Set a target pressure Ps in the pressure-holding process, and set the target pressure Ps if the process proceeds to the pressure-holding process during molding.
The resin pressure Pg on the gate side and the resin pressure Po on the opposite side of the gate in the mold cavity C are detected, and when the resin pressure Po on the opposite side of the gate begins to decrease, the gate pressure is reduced. Is characterized in that pressure control is performed so that the resin pressure Pg of the above-mentioned resin coincides with the resin pressure Po on the side opposite to the gate.

In this case, according to a preferred embodiment, the resin pressure Po on the side opposite to the gate in the pressure holding step is differentiated by the time t, and the obtained differential value Do = dPo / dt reaches the preset value Ds. Then, the above pressure control is performed. Also,
When the process shifts to the pressure holding process, first, the resin pressure P on the gate side
The pressing force is reduced until the difference To between the pressure g and the resin pressure Po on the opposite gate side reaches a preset set value Ts, and thereafter, the holding pressure Pc based on the holding pressure target value Ps can be applied, and furthermore, The pressure can be controlled so that the gate-side resin pressure Pg does not exceed a preset upper-limit target value Pu until the process proceeds to the pressure-holding step.

On the other hand, the injection molding machine 1 according to the present invention comprises a gate side pressure sensor 2 for detecting the gate side resin pressure Pg in the mold cavity C, and a gate side resin pressure Po in the mold cavity C opposite to the gate side. , A detection function unit 4 for detecting that the resin pressure Po on the side opposite to the gate in the pressure-holding step has started to decrease, and a pre-set pressure-holding value when the process proceeds to the pressure-holding step. A pressure at which the holding pressure Pc based on the target value Ps is applied, and when the detection function unit 4 detects a decrease in the resin pressure Po, the pressure is controlled so that the gate-side resin pressure Pg matches the anti-gate-side resin pressure Po. It is characterized by having a control function unit 5.

In this case, according to a preferred embodiment, the detection function section 4 differentiates the resin pressure Po on the side opposite to the gate with respect to time t, and obtains the obtained differential value Do = dPo / dt and a preset set value Ds And has a function of detecting a decrease in the resin pressure Po. Further, when the control function unit 5 shifts to the pressure-holding step, first, the pressure is applied until the difference To between the gate-side resin pressure Pg and the opposite-gate-side resin pressure Po reaches a preset set value Ts. The pressure can be reduced, and thereafter, a function of giving a holding pressure Pc based on the holding pressure target value Ps can be provided. In addition, the resin pressure Pg on the gate side is set to a predetermined upper limit target value before shifting to the holding pressure process. A function of controlling pressure so as not to exceed Pu can be provided.

As a result, in the pressure holding step, the resin pressure Pg on the gate side in the mold cavity C and the resin pressure Po on the opposite side of the gate coincide with each other, and the resin pressure in the mold cavity C is made uniform. After shifting to the pressure-holding step, first, the gate-side resin pressure Pg and the opposite-gate-side resin pressure Po
The pressure is reduced until the difference To reaches the preset set value Ts, and the pressure is controlled so that the resin pressure Pg on the gate side does not exceed the preset upper limit target value Pu until the process proceeds to the pressure holding step. If this is the case, the resin pressure can be further uniformed temporally and qualitatively.

[0012]

Next, preferred embodiments according to the present invention will be described in detail with reference to the drawings.

First, the configuration of the injection molding machine 1 according to the present embodiment will be described with reference to FIGS.

In FIG. 2, Mi is an injection device, which is an injection device main body 20, a hydraulic circuit 21 connected to the injection device main body 20, and a control circuit which controls the whole of the injection molding machine 1 including the hydraulic circuit 21. 22. Further, a mold 23 supported by a mold clamping device (not shown) is provided in front of the injection device Mi, and the injection molding machine 1 is provided by the mold clamping device and the injection device Mi.
Is configured.

The injection device body 20 has an injection nozzle 3 at the front end.
1 is provided with heating cylinders 33 each having a hopper 32 at the rear. A screw 34 is built in the heating cylinder 33, and a screw driving unit 35 is connected to a rear end of the heating cylinder 33. The screw drive unit 35 is a double rod type piston 3.
6, the front rod 36f of the piston 36 is connected to the rear end of the screw 34, and the rear rod 36r is connected to the drive shaft of an oil motor 38 disposed at the rear end of the injection cylinder 37. Spline join. The mold 23 has a fixed mold 23c and a movable mold 23m.
And a mold cavity C formed by the fixed mold 23c and the movable mold 23m. One end of the mold cavity C communicates with the runner R via the gate G.

On the other hand, the injection cylinder 37 has a hydraulic circuit 21.
Connect. The hydraulic circuit 21 includes a four-port servo valve 41, and the A port of the servo valve 41 is connected to the injection cylinder 37.
The B port is connected to the rear oil chamber 37r of the injection cylinder 37, and the P port and T port of the servo valve 41 are connected to a hydraulic accessory circuit 42 including a logic valve, a check valve, an accumulator, and the like. Are connected to the hydraulic pump 43 and the oil tank 44 via the.

The control circuit 22 further includes a sequence controller 51 using a microcomputer. The sequence controller 51 is connected to an operation panel 52 including a setting unit and a display unit, and is connected to a servo controller 53. And the servo controller 5
The output side of 3 is connected to the four-port servo valve 41, and the input side of the servo controller 53 is connected to various sensors,
That is, a position sensor 54 for detecting the position of the screw 34,
A front oil chamber pressure sensor 55 for detecting the oil pressure of the front oil chamber 37f of the injection cylinder 37, a rear oil chamber pressure sensor 56 for detecting the oil pressure of the rear oil chamber 37r of the injection cylinder 37, a gate side (gate) in the mold cavity C. Resin pressure Pg)
Pressure sensor 2 and mold cavity C for detecting pressure
The anti-gate side pressure sensors 3 for detecting the resin pressure Po on the side opposite to the gate (at the end of the cavity separated from the gate G) are connected.

FIG. 3 is a block diagram of the control circuit 22 in which portions related to the present invention are extracted. 61 is
A loop switching unit incorporated in the servo controller 53. The input side of the loop switching unit 61 is provided from the sequence controller 51 by a position setting value Xs and a pressure setting value Xp (a pressure holding target value Ps, an upper limit target value Pu) set in advance. ) And the speed set value Xv. Thereby, each set value X
s, Xp, and Xv are selectively input through the loop switching unit 61 and are provided as one of the input units of the deviation calculation unit 62 as the target value X. Further, various detection values obtained by the operation of the injection cylinder 37, that is, the position detection value Ys obtained from the position sensor 54, and the pressure obtained from the difference between the detection value of the front oil chamber pressure sensor 55 and the detection value of the rear oil chamber pressure sensor 56. A speed detection value Yv obtained by differentiating the detection value Yp and the position detection value Ys is supplied to a deviation calculation unit 6 via a data conversion circuit (data switching circuit) 63.
2 is selectively provided to the other input unit. Deviation calculator 6
An operation amount Dd is obtained on the output side of No. 2 and the operation amount Dd is converted into a control amount Dc and provided to the four-port servo valve 41, and the injection cylinder 37 is drive-controlled based on this.

On the other hand, the gate side resin pressure Pg in the mold cavity C detected by the gate side pressure sensor 2
The resin pressure Po on the side opposite to the gate in the mold cavity C detected by the pressure sensor 3 on the side opposite to the gate is applied to the detection function unit 4. The detection function unit 4 has a function of detecting a decrease in the input resin pressure Po in the pressure holding step,
The output of the detection function unit 4 is provided to a target value setting unit 64. In this case, the target value setting unit 64 sets the resin pressure Po on the side opposite to the gate as a target value based on the detection result of the detection function unit 4, and sets the set target value via the loop switching unit 61 to the deviation calculation unit. 62 to one input unit. If the target pressure setting unit 64 sets the resin pressure Po on the side opposite to the gate as a target value, the pressure control is performed based on this so that the resin pressure Pg on the gate side matches the resin pressure Po on the side opposite to the gate. The control system at this time constitutes the pressure control function unit 5.

Next, an injection molding method according to the present embodiment including the operation of the injection molding machine 1 will be described with reference to FIGS.

First, the sequence controller 51 includes:
Using the setting unit of the operation panel 52, the target pressure Ps in the pressure holding step is set in advance. This holding pressure target value Ps
Is set as molding conditions corresponding to each molded article.
Further, an upper limit target value Pu for limiting an increase in the gate-side resin pressure Pg is set until the process proceeds to the pressure holding process, that is, in the injection process. This upper limit target value Pu can also be set as molding conditions corresponding to each molded product. FIG. 1 shows the holding pressure target value Ps and the upper limit target value Pu. Further, in the pressure holding step, the detection function unit 4 differentiates the resin pressure Po on the side opposite to the gate with respect to time t, and the obtained differential value Do = dPo / dt.
Reaches a preset set value Ds, the set value Ds is set in advance in order to control the resin pressure Pg on the gate side to match the resin pressure Po on the opposite gate side. Also,
At the beginning of the pressure-holding step, the control function unit 5 reduces the pressure-holding pressure Pc until the difference To between the gate-side resin pressure Pg and the counter-gate-side resin pressure Po reaches a preset set value Ts. In order to apply the holding pressure Pc based on the holding pressure target value Ps, the set value Ts is set in advance. Others
Necessary molding conditions such as a pressure set value Xp, a speed set value Xv, and a position set value Xs are set.

On the other hand, the operation of the injection molding machine 1 for executing the molding cycle is as follows. Now, it is assumed that the measuring process is completed and the process shifts to the injection process. The screw 34 moves forward from the injection start position at an injection speed V (see FIG. 1) based on a preset speed set value Xv. In this case, while the speed setting value Xv is given as the target value X to one input unit of the deviation calculating unit 62 by the loop switching unit 61,
The speed detection value Yv is provided to the other input unit of the deviation calculation unit 62. As a result, feedback control for the injection speed V is performed. It is desirable to set the injection speed to a high speed and to shorten the injection filling time as much as possible. FIG.
In the figure, S indicates the position of the screw 34.

On the other hand, as the screw 34 advances, the resin (molten resin) L measured in front of the screw 34 becomes
The injection cavity 31 is injected and filled into the mold cavity C. As the resin L is injected and filled into the mold cavity C, the gate-side resin pressure Pg detected by the gate-side pressure sensor 2 gradually increases. Detected resin pressure P on the opposite gate side
o gradually increases (see FIG. 1). When the gate-side resin pressure Pg reaches a preset upper limit target value Pu, pressure control is performed so that the resin pressure Pg does not exceed the upper limit target value Pu. Therefore, speed control is performed until the gate-side resin pressure Pg reaches the upper limit target value Pu, and pressure control is performed after the gate-side resin pressure Pg reaches the upper limit target value Pu. By performing such control, the difference between the resin pressure Pg on the gate side and the resin pressure Po on the side opposite to the gate when the screw 34 reaches the speed-pressure switching position Sc can be reduced (see FIG. 1).

When the screw 34 reaches the speed-pressure switching position Sc, the pressure is switched to the pressure holding step. After shifting to the pressure holding step, first, a pressure adjustment step of reducing the pressing force until the difference To between the gate-side resin pressure Pg and the opposite-gate-side resin pressure Po reaches a preset value Ts is performed. That is, a process of slightly retracting the screw 34 is performed. As a result, the resin pressure Pg on the gate side quickly decreases,
Since the resin pressure Po on the opposite gate side does not decrease, the difference To between the resin pressure Pg on the gate side and the resin pressure Po on the opposite gate side becomes smaller. When the difference To between the resin pressure Pg on the gate side and the resin pressure Po on the opposite side of the gate reaches the set value Ts, the screw 34 is advanced again to apply the holding pressure Pc based on the holding pressure target value Ps. In this case, for example, the differential value dPo / d
t and dPg / dt are determined, and the resin pressure P is increased by increasing the pressure with a relatively gradual pressure increase characteristic that eliminates the difference between the two values.
Care is taken so that no pressure deviation occurs between g and Po. In addition,
The resin pressure Pg for giving the holding pressure Pc is equal to the holding pressure target value P.
When s, the difference To between the gate-side resin pressure Pg and the opposite-gate-side resin pressure Po hardly occurs (see FIG. 1). In the pressure-holding step, the pressure setting value Xp is provided as a target value X to one input of the deviation calculating unit 62 by the loop switching unit 61, and the detected pressure value Yp is applied to the other input of the deviation calculating unit 62. And feedback control is performed on the detected pressure value Yp.

In the pressure-holding step, the detection function unit 4 monitors the resin pressure Pg on the gate side and the resin pressure Po on the opposite side of the gate, and detects that the resin pressure Po on the opposite side of the gate has begun to decrease. . In this case, the detection function unit 4 differentiates the resin pressure Po on the side opposite to the gate with respect to time t, and obtains the obtained differential value Do =
When dPo / dt reaches a preset value Ds,
It is determined that the resin pressure Po has started to decrease. As a result, a decrease in the resin pressure Po can be detected stably and reliably. When the detection function unit 4 detects that the resin pressure Po has started to decrease, the resin pressure Po on the opposite gate side is set to the target value X such that the resin pressure Pg on the gate side becomes equal to the resin pressure Po on the opposite gate side. Pressure control for the gate side resin pressure Pg. That is, the target value setting unit 64 sets the resin pressure Po on the opposite side of the gate as a target value, and provides the set target value to one input unit of the deviation calculation unit 62 via the loop switching unit 61. As a result, the resin pressure Po on the opposite gate side is set as a target value, and the feedback control on the resin pressure Pg on the gate side is performed so that the resin pressure Pg on the gate side matches the resin pressure Po on the opposite gate side. Therefore, the resin pressure P
After o starts to decrease, the holding pressure Pc also gradually decreases,
In particular, after the gate is sealed, the holding pressure Pc drops sharply, and the pressure holding step can be terminated with this behavior.

As described above, the injection molding machine 1 according to the present embodiment
According to the (injection molding method), the gate-side resin pressure Pg and the opposite-gate-side resin pressure Po in the pressure-holding step match, and the resin pressure (and temperature) in the mold cavity C can be made uniform. it can. Therefore, the defect of the skin layer due to the weight variation, distortion or density difference of the molded product is eliminated,
A high level of molding quality can be obtained, and it is optimal when a highly elastic resin such as an elastomer is used or when a long molded product is molded. In particular, the pressure control is performed so that the gate-side resin pressure Pg does not exceed the preset upper limit target value Pu until the pressure-holding step is performed. Since the pressure is reduced until the difference To between the pressure Pg and the resin pressure Po on the opposite side to the gate reaches the set value Ts, the resin pressure can be further uniformed temporally and qualitatively.

The embodiment has been described in detail above.
The present invention is not limited to such an embodiment,
It is possible to arbitrarily change, add, and delete the details of the configuration, the method, and the like without departing from the gist of the present invention. For example, pressure control in which the upper limit target value Pu is set or control in which the pressure is reduced until the difference To between the gate-side resin pressure Pg and the counter-gate-side resin pressure Po reaches the set value Ts can be selectively adopted. And it is not necessarily required.

[0028]

As described above, according to the injection molding method (injection molding machine) according to the present invention, the preservation target value in the preservation step is set in advance, and if the process proceeds to the preservation step during molding, the preservation target value is obtained. The resin pressure on the gate side and the resin pressure on the opposite side of the gate in the mold cavity are detected, and if the resin pressure on the opposite side of the gate starts to decrease, the resin pressure on the gate side becomes lower. Since the pressure control is performed so as to match the resin pressure on the gate side, the following remarkable effects are obtained.

By equalizing the resin pressure (and temperature) in the mold cavity, and eliminating defects in the skin layer due to weight variation, distortion or density difference of the molded product,
High molding quality can be obtained.

According to a preferred embodiment, in the pressure-holding step, if the resin pressure on the side opposite to the gate is differentiated with respect to time and the obtained differential value is compared with a preset value to detect a decrease in the resin pressure, In addition, a decrease in resin pressure can be detected stably and reliably.

According to a preferred embodiment, in the pressure-holding step, first, the pressure is reduced until the difference between the resin pressure on the gate side and the resin pressure on the opposite side of the gate reaches a preset value. Along with applying the holding pressure based on the holding pressure target value, and before shifting to the pressure holding step, if the pressure is controlled so that the resin pressure on the gate side does not exceed the preset upper limit target value, time and quality can be improved. Further uniform resin pressure can be achieved.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram of each physical quantity when an injection molding method according to a preferred embodiment of the present invention is performed,

FIG. 2 is a schematic configuration diagram of an injection molding machine according to a preferred embodiment of the present invention;

FIG. 3 is a block diagram of a control device in the injection molding machine;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Injection molding machine 2 Gate side pressure sensor 3 Anti-gate side pressure sensor 4 Detection function part 5 Pressure control function part C Mold cavity L Resin Pc Holding pressure Ps Holding pressure target value Pu Upper target value Pg Gate side resin pressure Po Anti Gate side resin pressure

Claims (8)

[Claims] In an injection molding method having a pressure-holding step of applying a pressure-holding force to a resin injected and filled in a mold cavity, a pressure-holding target value in the pressure-holding step is set in advance, and at the time of molding, When the process shifts to the pressure-holding step, a pressure-holding pressure based on the pressure-holding target value is applied, and the gate-side resin pressure and the opposite-gate-side resin pressure in the mold cavity are detected. , The pressure control is performed so that the resin pressure on the gate side matches the resin pressure on the opposite gate side. 2. The pressure control according to claim 1, wherein the resin pressure on the side opposite to the gate in the pressure holding step is differentiated with time, and the pressure control is performed when the obtained differential value reaches a preset value. Injection molding method. 3. When the process proceeds to the pressure-holding step, first, the pressure is reduced until the difference between the resin pressure on the gate side and the resin pressure on the opposite side of the gate reaches a preset set value. The injection molding method according to claim 1, wherein a holding pressure based on the pressure target value is applied. 4. The injection molding method according to claim 1, wherein the pressure is controlled so that the resin pressure on the gate side does not exceed a preset upper limit target value until the pressure holding step. 5. A gate-side pressure sensor for detecting a gate-side resin pressure in a mold cavity in an injection molding machine having a pressure-holding step of applying a holding pressure to resin injected and filled in a mold cavity. An anti-gate side pressure sensor for detecting an anti-gate side resin pressure in the mold cavity; a detection function unit for detecting that the anti-gate side resin pressure in the pressure holding step has started to decrease; If the detection function unit detects a decrease in resin pressure, the resin pressure on the gate side matches the resin pressure on the opposite gate side if the detection function unit detects a decrease in resin pressure. An injection molding machine comprising a pressure control function unit for performing pressure control. 6. The detecting function unit has a function of differentiating the resin pressure on the side opposite to the gate with respect to time, and comparing the obtained differential value with a preset set value to detect a decrease in the resin pressure. The injection molding machine according to claim 5, wherein: 7. The control function section, when the process shifts to the pressure-holding step, first reduces the pressure until the difference between the resin pressure on the gate side and the resin pressure on the opposite side of the gate reaches a preset value. The injection molding machine according to claim 5, further comprising a function of applying a holding pressure based on the holding pressure target value thereafter. 8. The control function unit has a function of performing pressure control so that the resin pressure on the gate side does not exceed a preset upper limit target value until the process shifts to a pressure holding step. 5. The injection molding machine according to 5.