JPH06170900A - Screw preplaticizing injection molding machine and metering method therefor - Google Patents

Abstract

PURPOSE:To stabilize metering by correcting a variation of a metering position of resin, and correcting a change of the variation by using a real metering position in a preceding molding cycle even when the variation of the metered resin corresponding to a specific forward distance of a screw is changed. CONSTITUTION:When an operation of an injection molding machine is started, a screw 12 is rotated to melt resin in a plasticizing chamber 10, and melted resin is fed from the chamber 10 to an injection chamber 20 through a connecting passage 11. The resin fed to the chamber 20 retracts a plunger 22. When the plunger 22 reaches a designed metering position So or Sa, the rotation of the screw 12 is stopped, the screw 12 is moved forward to close the passage 11 at an end of the screw. That is, a gap 13 between the screw 12 and the passage 11 is closed to prevent the melted resin from reversely flowing from the chamber 20 to the chamber 10 by a pressure at the time of injecting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to weighing in an injection device of a screw preplasticizer type injection molding machine, and further, to further increase the amount of material (resin) accumulated in each injection cycle when the material (resin) is accumulated in the injection device. The present invention relates to a control means for stabilizing.

[0002]

2. Description of the Related Art A screw pre-plastic injection molding machine has a plasticizing section for melting a synthetic resin material and an injection section for accumulating the plasticized resin and then injecting it into a mold cavity. There is. Therefore, as compared with the in-line screw type injection molding machine, the screw pre-plastic type injection molding machine has a feature that a large ejection force can be obtained.

The applicant of the present application discloses in Japanese Patent Laid-Open No. 3-97518 that a communication passage connecting a plasticizing chamber and an injection chamber is opened at a position facing a tip of a plasticizing screw (hereinafter simply referred to as a screw) to rotate the screw. In addition to the motor, a hydraulic actuator that moves the screw in the axial direction is provided, and in the plasticizing / measuring process, the screw is retracted to open the communication passage to send the molten resin to the injection chamber, and to the injection process. In that case, we propose an injection molding machine that prevents the backflow of molten resin into the plasticizing chamber during the injection process without advancing the screw and closing the communication path at the screw tip, without using a ball valve or check valve. did.

In the above-mentioned injection molding machine, a hydraulic cylinder device is used as a drive source for the injection part, and the molten resin sent from the plasticizing chamber to the injection chamber causes the injection plunger (hereinafter simply referred to as the plunger) to retract, and thereafter. The molten resin is weighed by the amount of withdrawal, and then the plunger is moved forward to inject and fill the molten resin in the cavity and hold the pressure. In this pressure holding, the molten resin is left on the tip side of the plunger of the injection chamber, and the resin filled in the cavity is pressed and held by the plunger. That is, in the injection chamber, the amount of resin, which is obtained by adding the volume of the molded product and the cushion for holding pressure, is measured for each measurement.

As described above, in the plasticizing section, the screw rotates to melt the resin material, and the pressure of the melted material causes the screw to slightly retract, leaving a gap (usually about 1 mm) between the screw tip and the communicating passage. ) Is formed, and the resin is caused to flow into the injection chamber through the communication passage. Then, the plunger inserted into the injection chamber is retracted by the pressure of the resin flowing into the injection chamber, and the retracted position is detected by a detector such as a linear scale or limit switch to measure the amount of resin required for one injection. Weighing. When the plunger reaches the set position (set metering position), the rotation of the screw that was rotating to melt the material is stopped, and at the same time, the screw is advanced to close the resin communication passage with the tip of the screw. The resin is prevented from flowing backward from the injection chamber to the plasticizing chamber through the communication passage when the measured resin is injected by the plunger.

[0006]

However, in the conventional apparatus, the screw rotation stops after the plunger retracts to reach the set metering position, and the screw advances to close the communication passage. The amount of resin used will be greater than the planned amount. The amount of molten resin extruded into the injection chamber due to the operation of closing the communication passage with the screw changes due to changes in the viscosity and fluidity of the resin, so it is not constant, and the measured amount of resin varies. Occurs. If there is variation in measurement, it directly affects the quality of the molded product.For example, if the measurement is insufficient, the injection volume will be insufficient and it will be a short cut. , Bending and twisting occur. In addition, when the amount is excessive, burrs are generated due to overfilling, which causes defective molding.

It is sufficient that a fixed amount of resin corresponding to the volume of the molded product and the cushion amount required for holding pressure is constantly measured in the injection chamber. However, if the measurement is unstable, the ejection force, the injection time, and the holding pressure are increased. Since the pressure holding time is slightly affected and they themselves become unstable, it is considered that variations occur in the molded product. Therefore, an appropriate amount of stable weighing needs to be performed.

That is, the stabilization of measurement is an important factor in obtaining the reproducibility of a molded product, and in the present invention,
The challenge is to stabilize this measurement.

[0009]

The pre-plastic injection molding machine of the present invention comprises a plasticizing chamber 1 for plasticizing and melting a synthetic resin material.
0, an injection chamber 20 for measuring and injecting the molten material,
It has a detector 3 for detecting the retracted position of the plunger 22, and the plasticizing chamber 10 and the injection chamber 20 are connected by a communication passage 11 opening at the front end of the plasticizing chamber 10, and the screw 12 is advanced during injection. In the screw pre-plastic type injection molding machine in which the communication passage 11 is closed, the reference metering position S set as a reference value for the molten material accumulated in the injection chamber 20, the screw 1 for each molding cycle.
A storage means for storing the set measuring position (detection position So and / or the end position Sa) for stopping the rotation of 2 and the actual measuring position Sb after the screw 12 is moved forward and the communication passage 11 is closed. Further, there is provided a calculating means for calculating a weighing position So or Sa to be newly set from the above-mentioned weighing position, and an updating means for updating the stored value of the previous setting weighing position at the calculated setting weighing position So or Sa. .

Further, according to the measuring method of the screw pre-plastic type injection molding machine of the present invention, the plasticizing chamber 10 for plasticizing and melting the synthetic resin material and the injection chamber 20 for measuring and injecting the molten material.
And the plasticizing chamber 10 and the injection chamber 20 have a screw 1
In the screw pre-plastic injection molding machine, which is communicated with each other by the communication passage 11 opening to the front of 2, the screw 12 is rotated to cause the molten material to flow from the plasticizing chamber 10 to the injection chamber 20, and is detected by the detector 3. Plunger 22
The screw 12 that has stopped rotating at the set measuring position So or Sa is moved forward to close the communication passage 11,
The actual measurement position Sb of the plunger 22 after closing 1 is detected, and the set measurement position So or Sa of the plunger 22 in the subsequent molding cycle is determined based on the variation ΔS between the set measurement position So or Sa and the actual measurement position Sb. It is characterized by making a decision.

[0011]

When the operation of the injection molding machine is started, the screw 12
The resin in the plasticizing chamber 10 is melted by rotating the
The molten resin flows from the plasticizing chamber 10 through the communication passage 11 into the injection chamber 20. The resin flowing into the injection chamber 20 causes the plunger 22 to retract. When the plunger 22 reaches the set measuring position So or Sa (the reference measuring position S in the first molding cycle), the screw 12
Is stopped and the screw 12 is moved forward to close the communication passage 11 at the tip of the screw. That is, the gap 13 (which is usually adjusted to be about 1 mm) between the screw 12 and the communication passage 11 is closed, and the molten resin flows back from the injection chamber 20 to the plasticizing chamber 10 due to the pressure at the time of injection. Prevent. When the gap 13 is closed, the screw 12 momentarily pushes the molten resin into the communication passage 11 that is open forward of the tip thereof, so that the plunger 22 further moves from the set measuring position So or Sa. The position of the plunger 22 after this movement is detected as the actual weighing position Sb.

In the first molding cycle, in addition to the volume of the actual molded product and the cushion amount required for holding pressure, the amount of resin corresponding to the variation ΔS is accumulated and measured in the injection chamber 20. Therefore, after the first injection molding operation,
At least an amount of molten resin corresponding to the variation ΔS remains in the injection chamber 20. Therefore, the second set weighing position So ′ or Sa ′ is a position obtained by subtracting the variation ΔS from the first set weighing position So or Sa. Then, in the second molding cycle, when the plunger 22 reaches the set measuring position So ′ or Sa ′, the rotation of the screw 12 is stopped similarly to the previous time, and the screw 12 is advanced to close the communication passage 11, Since the resin is extruded by this operation, the set second set measuring position So ′ or Sa ′ + the variation ΔS ′ remains in the injection chamber 20, and the volume of the actual molded product in the injection chamber 20 is Resin equivalent to the cushion amount will be accumulated and measured. After that, the next measurement end position is calculated and calculated based on the previous variation ΔS each time.

That is, the variation ΔS (= Sb-S) due to the forward movement of the screw 12 when closing the communication passage 11 in the previous molding cycle from the set measuring position So or Sa.
The position Sa ′ (= S− (Sb−Sa)) obtained by subtracting a) is set as the next set measuring position, and the position is moved forward by the amount of the molten resin flowing into the injection chamber 20 due to the forward movement of the screw 12. The measurement is ended by, and the set measurement position is made to follow the change of the variation ΔS due to the change of the viscosity and the fluidity of the resin.
Therefore, the accumulated amount of each time becomes constant.

The above-mentioned reference numerals are for the purpose of contrasting with the drawings, but do not limit the configuration of the present invention in any way.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made to FIG. 1, which shows a screw pre-plastic injection molding machine and its apparatus of the present invention, FIG. 2 which shows a flow chart at the time of weighing of the present invention, and FIG. Will be described in detail.

In FIG. 1, the injection molding machine includes a plasticizing section 1
And the injection part 2. Plasticizing chamber 10 of plasticizing section 1
The injection chamber 20 of the injection unit 2 is connected and integrated by a communication passage 11 that communicates the front portions of the chambers 10 and 20 with each other. A screw 12 is rotatably inserted in the plasticizing chamber 10, and a piston 15 for advancing the screw 12 and a motor 16 for rotating the screw 12 are connected to a rear portion of the screw 12 via a connecting shaft.

The screw 12 can be moved slightly in the plasticizing chamber 10 in the axial direction, and the screw 12 rotates to cause the plasticizing chamber 10 to rotate.
By the reaction force generated by melting the material inside,
The screw 12 retracts and a gap 13 (about 1 mm) is formed between the screw 12 and the opening of the communication passage 11. The retracted position of the screw 12 during rotation is set by adjusting the position of the connecting shaft by the adjusting unit 18. The piston 15 is a cylinder 14 formed between the plasticizing chamber 10 and the motor 16.
It is built in, and supplies hydraulic pressure from the pipe line 19 to move the screw 12 forward to block the gap 13,
The communication passage 11 can be closed. Although details are omitted in the drawing, the screw 12 and the connecting shaft, and the connecting shaft and the motor 16 are spline-connected to each other, and
The rotation of 6 is transmitted to the screw 12 via the connecting shaft, and the forward / backward movement of the connecting shaft is not transmitted to the motor 16. A piston 15 for advancing the screw 12 is supported by a connecting shaft via a bearing and is non-rotatably fitted in the cylinder 14. The rotation speed of the screw 12 is measured by the rotary encoder 17.

The injection part 2 has an injection chamber 20 which is communicated with the plasticizing chamber 10 by the communication passage 11 which is open at the front end as described above.
The injection chamber 20 is provided with a nozzle 23 on the tip side.
Is connected to the nozzle hole 21 of the resin in the injection chamber 20.
Through a cavity (not shown) of the mold. Further, the injection chamber 20 has a plunger 22.
And the plunger 22 is inserted into the cylinder 2 behind it.
It is connected with the piston 28 in 4 through the joint 27. The piston 28 advances or retracts the plunger 22 by supplying pressure oil to the advancing oil chamber 25 or the retreating oil chamber 26 (the retreat is not required when forced retraction such as purging is required). Is not used during normal operation). The position of the plunger 22 is detected by the rotary encoder 3 connected to the joint 27 via the rack 3a and the pinion 3b, and the detection signal is passed through the input interface circuit 4 and a control microcomputer (hereinafter referred to as a microcomputer) 5 Entered in.

The output of the detector 3 input to the microcomputer 5 is counted by a counter (not shown), the count value is read as a measurement value, compared with the weighing position S or Sa, So stored in the memory, and It is stored as the actual weighing position Sb. In this embodiment, the memory is provided with a storage area for a reference weighing position S, a position set as a weighing position (weighing detection position) So, a position where the weighing operation actually ends (weighing end position) Sa, and an actual weighing position Sb. The microcomputer 5 is provided with at least a comparing means for comparing the contents of the counter with the stored value and a calculating means for calculating a set measuring position So or Sa for each molding cycle described later. A keyboard K and a display L are connected to the microcomputer 5, and a ROM storing a control program is built in the microcomputer 5.
Based on this control program and the data in the memory, the CPU of the driver circuit 7 issues a rotation stop command of the motor 16 via the output interface circuit 6, a hydraulic operation command to the flow rate adjusting valve 8 for moving the screw 12 forward, An operation command for exciting the electromagnetic valve 9 to move the injection plunger 22 forward and for injection is output.

Next, the differential of the above device will be described.

First, the motor 16 is driven to drive the screw 12
When is rotated, the resin in the plasticizing chamber 10 is melted by the heat of a heater (not shown) wound around the outer wall of the plasticizing chamber 10 and the shear heat generated by the rotation of the screw 12, and The screw 12 is pushed down by the pressure to form a gap 13 on the tip end side of the screw 12, and the molten resin flows into the injection chamber 20 through the gap 13 and the communication passage 11 and retracts the plunger 22. The reference measurement position S of the injection volume calculated from the volume of the molded product and the cushion amount required for holding pressure is input from the keyboard K or the like and stored in the memory in advance, and this reference measurement position S is the measurement detection position So. It is given as an initial value. Plunger 22
When the detected value reaches the measurement detection position So, the motor 16 is instructed to stop, and the position of the plunger 22 at the time when the motor 16 is stopped is detected and the measurement ends. It is stored as the position Sa.
Next, a pipe line 19 leading from the flow rate adjusting valve 8 to the cylinder 14
Supplies hydraulic pressure to move the screw 12 forward, the screw 12 closes the gap 13 and closes the communication passage 11.
The material melted at the time of this blockage is discharged from the communication passage 11 into the injection chamber 2
It will be pushed to 0 (hereinafter, the operation of advancing the screw 12 to close the communication passage 11 is referred to as "return operation").

The amount of resin in the injection chamber 20 becomes larger than the amount of resin at the measuring end position Sa due to the material pushed in with the check operation, and the plunger 22 retracts by that amount to the actual measuring position Sb. . The detector 3 uses this actual weighing position Sb.
Detected, the input interface circuit 4 to the microcomputer 5
The detection value is sent and the microcomputer 5 stores this value in the memory. The calculating means of the microcomputer 5 calculates the measurement detection position So in the next molding cycle by So = S- (Sb-Sa) using the stored reference measurement position S, measurement end position Sa and actual measurement position Sb. The stored value of the weighing detection position So is updated.

When the measurement is completed, the solenoid valve 9 is excited to send the pressure oil to the oil chamber 25, and the plunger 22 is moved forward to move the resin in the injection cylinder 20 into the mold cavity through the nozzle hole 21 of the nozzle 23. After injecting, holding the pressure and cooling the molded product, the mold is opened and the molded product is taken out (released). At the time of injection, since the screw 12 advances and the check operation works, the plunger 22 advances and pushes the material, but the resin in the injection chamber 20 flows back to the plasticizing chamber 10 through the communication passage 11. There is nothing to do.

Next, when the second operation is started, the supply of hydraulic pressure from the flow rate adjusting valve 8 and the electromagnetic valve 9 is stopped, and the screw 12 starts to rotate again in the depressurized state. By starting the rotation of the screw 12, as shown in FIG. 2, the measurement is started, and the measurement is started in the same manner as the last time. When the position of the plunger 22 reaches the measurement detection position So updated last time by the detector 3, after stopping the screw 12, the position of the plunger 22 is detected to update the measurement end position Sa and the screw 12 moves forward. Activate the check mechanism. Then, the position of the plunger 22 is detected again and the actual measurement position S
The stored value of b is updated, and the updated (updated) value is used to update the next (here, the third time) weighing detection position So by the same formula So = S- (Sb-Sa) as in the first time. When the measurement is completed, the plunger 22 is moved forward to inject and hold the resin, cool the molded product, take out the molded product, and complete the second molding cycle. After that, the measurement detection position So for each molding cycle is calculated by the same control continuously, and the injection amount is measured based on this.

According to the procedure of the above-described embodiment, in the first molding cycle, the actual measuring position Sb increases by the amount of flow into the injection chamber 20 due to the check operation, but in the second and subsequent measuring steps. , The value smaller than the reference weighing position S by the variation ΔS (= Sb−Sa) due to the non-return operation in the previous molding cycle is set as the weighing detection position So. Corrected weighing is always performed so as not to deviate from the weighing position S. Further, in the above embodiment, after the rotation of the screw 12 is stopped at the measurement detection position So, the measurement end position Sa is detected and the difference between the measurement detection position So and the measurement end position Sa (measurement due to inertia rotation of the screw 12). However, since the difference is usually small, there is almost no problem even if the metering detection position So and the metering end position Sa are controlled to be the same.

FIG. 3 schematically shows the position of the plunger 22 in the first to fourth molding cycles under the above control, with dashes and double dashes attached to the metering positions of the second and subsequent times. , At the end of measurement in each molding cycle, the measurement end positions Sa, Sa '... are detected and the actual measurement positions Sb, Sb' after the check operation are performed.
.. is detected to calculate fluctuations .DELTA.S, .DELTA.S '..., and the next measurement detection positions So, So' ... are corrected and calculated, and the actual measurement position is determined by the change in resin viscosity over time. S
b is not displaced from the reference weighing position S. That is, for example, at the time of the second weighing, the actual measurement position is Sb ′ due to the variation due to the check operation added to the measurement end position Sa ′, and the difference between the actual measurement position Sb ′ and the reference measurement position S is The third weighing detection position So ″ is set to zero at the weighing end position Sa ′ + (reference weighing position S−S).
b '). That is, if the n-th measurement detection position So ends the measurement at the position subtracted from the reference measurement position S by the variation between the (n-1) th measurement end position Sa and the actual measurement position Sb, It is possible to perform stable weighing without causing a shift in the weighing position due to the variation due to the stop operation.

[0027]

As described in detail above, according to the present invention, in the screw pre-plastic injection molding machine having a structure in which the screw is advanced to close the communication passage communicating from the plasticizing chamber to the injection chamber, the screw is advanced. The fluctuation of the resin measuring position due to the operation is promptly corrected, and also when the fluctuation of the measuring resin corresponding to the constant advance amount of the screw changes due to the change of resin viscosity, etc. Since the change in minute is corrected using the actual measurement position in the preceding molding cycle, it is possible to measure the resin in each molding cycle extremely accurately, and the amount of resin accumulated in the injection chamber is stable, As a result, the temperature of the molten resin accumulated becomes more uniform, so that the ejection force and the holding pressure are stable and the reproducibility of the molded product is improved.

[Brief description of drawings]

FIG. 1 is a block diagram schematically showing a screw pre-plastic injection machine and a control device.

FIG. 2 is a flowchart showing a control procedure of the present invention.

FIG. 3 is an explanatory diagram showing a change in the weighing position of the present invention.

[Explanation of symbols]

 1 Plasticizing part 2 Injection part 3 Detector 10 Plasticizing chamber 11 Communication passage 12 Screw 20 Injection chamber 22 Plunger S Reference measurement position So, So '... Measurement detection position Sa, Sa' ... Measurement end position Sb, Sb '... Actual measurement position

[Procedure amendment]

[Submission date] December 28, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

[0006]

However, in the conventional device, the screw rotation stops after the plunger moves backward and reaches the set measuring position, and the screw for closing the communication passage moves forward, so that the injection chamber enters the injection chamber. The amount of resin accumulated exceeds the planned amount to be measured. The amount of molten resin extruded into the injection chamber due to the operation of closing the communication passage with the screw changes due to changes in the viscosity and fluidity of the resin, so it is not constant, and the measured amount of resin varies. Occurs. If there is variation in measurement, it will directly affect the quality of the molded product.For example, if the measurement is insufficient, the injection volume will be insufficient and a short shot will occur. , Bending and twisting occur. In addition, when the amount is excessive, burrs are generated due to overfilling, which causes defective molding.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

In the first molding cycle, in addition to the volume of the actual molded product and the cushion amount necessary for holding pressure, the amount of resin corresponding to the variation ΔS is accumulated and measured in the injection chamber 20. Therefore, after the first injection molding operation,
At least an amount of molten resin corresponding to the fluctuation amount ΔS remains in the injection chamber 20. Therefore, the second preset metering position So 'or Sa' is a position obtained by subtracting the variation △ S from the first preset metering position So or Sa. Then, in the second molding cycle, when the plunger 22 reaches the set measuring position So ′ or Sa ′, the rotation of the screw 12 is stopped similarly to the previous time, and the screw 12 is advanced to close the communication passage 11, Since the resin is extruded by this operation, the set second set weighing position So ′ or Sa ′ + the fluctuation amount ΔS ′ remains in the injection chamber 20, and the volume of the actual molded product in the injection chamber 20. And the resin equivalent to the cushion amount will be accumulated and measured. After that, the next measurement end position is calculated and calculated based on the previous variation ΔS each time.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

Next, the operation of the above device will be described.

Claims (2)

[Claims] 1. A plasticizing chamber having a plasticizing chamber for plasticizing and melting a synthetic resin material, an injection chamber for measuring and injecting the molten material, and a detector for detecting a retracted position of an injection plunger. The injection chamber is connected to the plasticizing chamber by a communication passage that opens at the front end, and in a screw pre-plastic injection molding machine in which the plasticizing screw is advanced during injection to close the communication passage, each molding cycle Initially set reference weighing position for molten material accumulating in the injection chamber,
Storage means for storing the set measuring position when the screw stops rotating in each injection cycle and the actual measuring position after the screw is moved forward and the communication passage is closed, and a new set measuring position from the stored measuring position. A calculation means for calculating the position, and an updating means for updating the previous set weighing position with the calculated set weighing position,
Screw pre-plastic injection molding machine. 2. A plasticizing chamber for plasticizing and melting a synthetic resin material, and an injection chamber for measuring and injecting the molten material, wherein the plasticizing chamber and the injection chamber are open in front of an injection screw. In a method for measuring a molten material of a screw pre-plastic injection molding machine, which is communicated with each other by a passage, the screw is rotated to cause the molten material to flow from the plasticizing chamber to the injection chamber,
At the set measuring position of the injection plunger detected by the detector, the screw whose rotation has stopped is moved forward to close the communication passage, and the actual measuring position of the plunger after closing the communication passage is detected. A measuring method for a screw pre-plastic injection molding machine, characterized in that a measuring position of an injection plunger in a subsequent molding cycle is determined based on a difference from the measuring position.