JPH022686B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of controlling an in-line screw type injection molding machine used in manufacturing plastic molded products and the like.

[Conventional technology]

The inline screw type injection molding machine has a heating cylinder 15 equipped with a nozzle 18 at the tip as shown in FIG.
A screw 11 is disposed inside the screw 11.
A hydraulic cylinder device 12 for reciprocating drive and a hydraulic motor 13 for rotational drive are connected to each other.

The molding process using the above-mentioned injection molding machine includes a filling process in which the screw 11 is moved forward and the cavity 14 formed between the molds 1 and 10 is filled with molten resin, and the resin filled in the cavity 14 is filled with the molten resin. Screw 1 to compensate for the shrinkage that occurs during solidification.
There is a pressure holding process in which a predetermined extrusion force is applied to the hopper for a certain period of time, and for the next injection, the screw 11 is rotated and the pellets supplied from the hopper are transferred to the heating cylinder 1.
At the same time as sending it to the front part of 5, it is melted,
The method is comprised of a metering process in which the screw 11 is retreated by the pressure of the molten resin, and the required injection amount is measured by the backward stroke of the screw 11.

In the above-mentioned filling process, the forward speed of the screw 11 is changed in multiple stages according to the shape of the cavity 14, thereby creating flow marks and
Prevent defects such as wrinkles from occurring.

In addition, in the pressure holding process, by changing the driving force to the screw 11 in one or more steps and controlling the resin pressure appropriately, it is possible to prevent sink marks, burrs, etc. from occurring on the product, and to prevent stress from remaining on the product. prevent.

In a conventional injection molding machine, as disclosed in Japanese Patent Publication No. 57-59060, pressure control in the pressure holding process is performed by driving the screw 11 forward.

That is, the pressure of the forward drive source (for example, a hydraulic cylinder device) of the screw 11 is controlled according to a preset program, and thereby the cavity 14 is
This changes the pressure of the resin inside.

[Problem that the invention seeks to solve]

Although the number of defects in products has decreased by implementing the control method for the pressure holding process described above, there are large variations in product quality, and defects such as burrs and sink marks may still occur depending on the product. Ta.

The cause of the above defect is presumed to be as follows. That is, the screw 11 is attached to the tip of the screw 11.
In order to prevent backflow of molten resin when moving forward,
Although the system is equipped with a check valve 19, it is unavoidable that some leakage will occur due to clearance of the check valve, foreign matter getting caught, etc., and it is virtually impossible to completely prevent backflow. It's impossible. When the backflow flow rate of the resin fluctuates during the pressure holding process, the screw 11 moves forward to compensate for the flow rate and maintain the resin pressure at a predetermined value. The pressure does not follow the pressure sufficiently, or even if the pressure follows the pressure sufficiently, the screw 11 has an inertial force, so the advance of the screw 11 cannot fully follow this, and as a result, the resin pressure fluctuates greatly from the target value. I will do it. If the resin pressure fluctuates greatly, that is, if the resin pressure greatly exceeds the target value or decreases significantly than the target value, the intended purpose of the pressure holding process cannot be achieved, and the product may suffer from sink marks, burrs, etc. This results in a number of defects.

[Means for solving problems]

In order to solve the above-mentioned problems, the applicant repeated experiments with various methods of controlling the screw during the pressure holding process. As a result, it was discovered that the above problem could be completely solved by driving and controlling the screw as described below, leading to the completion of the present invention.

That is, in one or more stages of pressure control during the pressure holding process, the forward and backward movement of the screw 11 is stopped, and the screw 11 is rotated with a predetermined rotational force under the control of the rotation control section connected to the screw 11. , thereby maintaining the resin pressure at a predetermined value for a certain period of time.

[Effect]

Among the reasons why defects such as sink marks and burrs are prevented from occurring by the above-mentioned molded product method in the holding pressure step, the most important reason is considered to be as follows.

As mentioned above, in the conventional control method, the cause of the above-mentioned defects is the occurrence of backflow when the screw 11 moves forward during the pressure holding process. On the other hand, in the control method of the present application, the rotation of the screw 11 forces the molten resin to the front part of the heating cylinder 15, thereby compensating for the shrinkage caused by the cooling and solidification of the resin. At this time, the resin passes through the check valve 19 at the tip of the screw 11 in the forward direction and is sent to the front of the heating cylinder, so the check valve 19 does not perform a backflow prevention operation. Therefore, fluctuations in the resin pressure, which were mainly caused by leakage from the check valve 19, do not occur.

The resin pressure in the cavity is controlled by a program or feedback control of the rotary drive device connected to the screw 11 by the rotation control section, and the screw 11 is rotated with a predetermined rotational force to achieve the target with good followability. set to the value.

As a result, the amount of shrinkage that occurs when the resin in the cavity solidifies is completely compensated for, and no excessive pressure is applied to the resin.

In addition, the pressurization control by the rotation of the screw mentioned above is as follows.
It has been experimentally confirmed that it is not necessary to perform the treatment at all stages, and that similar effects can be obtained even if the treatment is performed only at the final stage, for example.

〔Effect of the invention〕

The resin pressure inside the cavity during the pressure holding process is
Since the target value is reliably set and maintained, defects such as sink marks and burrs do not occur in the molded product.

〔Example〕

FIG. 1 and FIG. 2 each show the configuration of an in-line screw type injection molding machine used for carrying out the present invention. The structure of the injection molding machine body is the same as the conventional one described above, and the casing of the hydraulic motor 13 is fixed to the output shaft of the hydraulic cylinder device 12, and the screw 11 is fixed to the output shaft of the hydraulic motor 13. are fixed so that they can rotate together.

Hydraulic motor 1, which is the reciprocating part of the injection molding machine
A rack 17 is fixed to the casing of No. 3, and a pinion 16 is pivotally supported on a base (not shown) on which an injection molding machine is placed, and meshes with the rack 17. The pinion 16 is interlocked with a potentiometer 3, which will be described later, and detects the forward position of the screw 11.

As shown in FIG. 1, the reciprocating hydraulic cylinder device 12 and the rotational driving hydraulic motor 13 are connected to the hydraulic pump 2 via a hydraulic circuit that serves as a reciprocating control section and a rotation control section. The hydraulic circuit is equipped with a control electric circuit shown in FIG.

First, the screw 1 when the screw 11 is driven using the above-mentioned hydraulic circuit and electric circuit will be described.
After explaining the operation of No. 1, changes in resin pressure, etc. using FIG. 3, the detailed configurations of the hydraulic circuit and the electric circuit will be described.

As mentioned above, the injection process consists of a filling process and a pressure holding process, and in the filling process, as shown in FIG.
This is done by moving B and C forward.

On the other hand, the pressure holding process includes a first pressure holding process in which the screw 11 is moved forward with a predetermined extrusion force while the rotation of the screw 11 is stopped, and a first pressure holding process in which the screw 11 is stopped moving forward and the screw 11 is rotated with a predetermined rotational force. It consists of a second pressure holding step. 1st
In the pressure holding process, the screw 11 moves forward in section D at a speed of Vd in the figure, thereby increasing the resin pressure P.
is maintained at a predetermined value p ₀ . Also, in the second holding pressure step,
The resin pressure P is increased to a predetermined value _p1 .

The hydraulic circuit includes a forward/reverse switching valve 22 that switches the screw 11 between forward and backward movement in the injection process and the metering process, a back pressure switching valve 23 and a relief valve 26 that control the back pressure when the screw retreats in the metering process,
It is equipped with a flow rate control circuit 20 including a throttle switching valve 21 that controls the flow rate of pressure oil supplied to the hydraulic cylinder device 12 or the hydraulic motor 13, and a pressure regulating valve 25 that controls the pressure of the pressure oil. .

On the other hand, the electric circuit shown in FIG. 2 is for sequentially controlling the hydraulic circuits for the hydraulic cylinder device 12 and the hydraulic motor 13 by exciting the solenoids installed in each of the control valves, and mainly consists of a relay circuit. has been done.

The pinion 16 installed in the injection molding machine body
are the first to fourth potentiometers 3, 30, 3
It is interlocked with the first potentiometer 3 of the injection speed switching position setter 38 consisting of 1 and 32. 2nd ~
The fourth potentiometers 30, 31, and 32 respectively set in advance the switching positions of the forward speed of the screw 11 in the filling process.

Said second to fourth potentiometers 30, 3
1 and 32 are connected to signal comparators 33, 34, and 35, respectively, and each comparator 33, 34, and 35 has relay contacts 33a, 33b, 34a, 34b, 35a, and
35b, and the third comparator 35 further comprises relay contacts 36a, 36b, 37a.

The injection speed setter group 5 is a first setter that sets the screw advance speed for each section of sections A, B, C, and D.
- Consists of fourth setting devices 53, 54, 55, and 56, and is connected via a speed control amplifier 6 to a pair of solenoids 21a and 21b that operate the throttle switching valve 21 of the flow rate control circuit 20.

In the pressure holding process, the target value of the resin pressure when pressurizing the resin by the rotation of the screw 11 is set by the back pressure setting device 60.

The output signal of the back pressure setter 60, together with the output signal from the back pressure sensor 7, is connected to a feedback control amplifier 62, which in turn is connected to the speed control amplifier 6.

The pressure setting device group 50 includes first to third pressure setting devices 57, 58, and 59 that adjust the discharge pressure of the hydraulic pump 2 in the sections A to C, the section D, and the section E, respectively.
It is connected to the solenoid 25a of the pressure regulating valve 25 via the pressure control amplifier 61.

The timer 4 switches from the D section to the E section during the pressure holding process. The timer 4 has contacts 4a, 4b, 41a, 42a, 42
It has b.

The operation of the circuits shown in FIGS. 1 and 2 will be described below with reference to FIGS. 3 and 4.

Filling Step In the injection molding apparatus, as shown in FIG. 4a, the screw 11 is retracted and the tip of the heating cylinder 15 is filled with molten resin 9.

First, the bus bar 40 is energized by a signal from a system controller (not shown) that controls the sequence control of the entire device, and the solenoid 22a of the forward/reverse switching valve 22 operates, and at the same time, the flow rate control circuit 2
0 solenoid 21b operates. As a result, the oil discharged from the hydraulic pump 2 pushes up the pilot check valve 24 and pushes up the hydraulic cylinder device 1.
The liquid flows into the cylinder chamber on the B side in FIG. 2 and advances the screw 11. At this time, the speed of the screw 11 moving through section A is preset to a speed Va in FIG. 3 by the first injection speed setting device 53.

As the screw 11 moves forward, the rack 17 moves, the pinion 16 rotates, and the voltage of the potentiometer 3 changes. When the voltage matches the preset voltage of the potentiometer 30, the comparator 33 detects this and opens the relay contact 33b and closes the relay contact 33a. As a result, the second
The excitation current of the solenoid 21b and therefore the opening degree of the throttle switching valve 21 change in proportion to the magnitude of the signal set by the injection speed setting device 54.
As a result, the discharge amount of the hydraulic pump 2 changes, and the screw 11 moves forward in section B in FIG. 3 at a speed of Vb.

When the screw 11 passes through the B section, the screw 11 moves forward through the C section at the speed Vc defined by the third injection speed setting device 55 in the same manner as described above, and moves toward the cavity 9 as shown in FIG. 4b. Complete filling.

Pressure holding process At the same time as the screw 11 passes through section C,
The signal from the comparator 35 causes the relay contact 35 to
b, 36b open, relay contacts 35a, 36a,
37a closes. As a result, at the same time as the timer 4 starts operating, the screw 11 is driven forward in section D with the target speed Vd set by the fourth injection speed setting device 56.

Further, the excitation current for the solenoid 25a of the pressure regulating valve 25 changes to a value preset by the second pressure setting device 58. As a result, the discharge pressure of the hydraulic pump 2 changes, and the hydraulic cylinder device 1
The driving force of No. 2, that is, the extrusion force of the screw 11 is set to a target value, thereby maintaining the resin pressure P at a predetermined value p ₀ (first pressure holding step).

When a certain period of time set by the timer 4 (during which time the screw 11 moves through section D in FIG. 3) has elapsed, the timer contacts 4a, 41a,
At the same time as 42a closes, contacts 4b and 42b open. As a result, solenoid 2 of flow control circuit 20
1a is excited. The excitation current at this time is defined by the set value of the back pressure setting device 60 and the magnitude of the output signal of the back pressure sensor 7. At the same time, the forward/reverse switching valve 22 returns to the neutral position due to the disappearance of the excitation current, and the closing operation of the pilot check valve 24 prevents the screw 11 from moving forward/backward and holds it at a fixed position.

Oil discharged from the hydraulic pump 2 is sent under pressure to the hydraulic motor 13 via the throttle switching valve 21. The discharge pressure at this time is defined by the magnitude of the excitation current to the pressure regulating valve 25, that is, the setting value of the third pressure setting device 59.

As a result, the screw 11 is rotationally driven by the hydraulic motor 13 and pressurizes the molten resin 9 in the cavity 14 as shown in FIG. 4c. As a result, the resin pressure P is increased to a predetermined value _p1 as shown in FIG. 3 (second pressure holding step).

In addition, in the second pressure holding step, the screw 11
When the molten resin is sent to the front part of the heating cylinder by the rotation of the screw 11, the screw 11 receives a reaction force in the backward direction due to the resin pressure. At this time, the hydraulic cylinder device 1
Check valve 2 for oil in the B side cylinder chamber of 2.
4 and 27, the oil pressure changes depending on the resin pressure, and the oil pressure is detected by the pressure sensor 7. As mentioned above, the output signal of the pressure sensor 7 is input as a control signal to the feedback control amplifier 62 together with the output signal of the back pressure setting device 60, and the amplifier 62 controls the oil pressure and thus the resin pressure P to a predetermined value _p1. The excitation current to the solenoid 21a of the pressure control circuit 20 is changed so that the rotational driving force of the screw 11 is controlled. At this time, since the excitation current of the pressure regulating valve 25 remains unchanged, the discharge pressure of the hydraulic pump 2 varies in order to keep the discharge flow rate, that is, the rotational speed of the screw 11 constant.

Time to maintain resin pressure P at predetermined value _p1 (E in Figure 3)
The period) is defined by a timer (not shown), and the operation of the timer returns the throttle switching valve 21 to the neutral position, completing the pressure holding process.

Metering process The metering for the next injection process is performed with the molds 1 and 10 in contact with the nozzle 18 as shown in FIG. 23b is activated,
The screw 11 is driven to rotate while maintaining the back pressure set by the relief valve 26. At the same time as the screw 11 returns to the predetermined position shown in FIG. 4a, the throttle switching valve 21 is returned to the neutral position, the rotation of the screw 11 is stopped, and the metering is completed.

Finally, the solenoid 21b of the flow control circuit 20
Then, the solenoid 22b of the forward/reverse switching valve 22 is operated to release pressure from the hydraulic circuit, and the system waits for the next injection process.

In the above embodiment, in the second pressure holding step, the resin pressure p ₁ is raised higher than the pressure p ₀ in the first pressure holding step, as shown in FIG. It is also possible to lower it to p ₂ (p ₂ < p ₀ < p ₁ ).

It should be noted that the injection process control method according to the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various changes can be made within the technical scope of the claims.
For example, all stages of the pressure holding process may be performed by rotating the screw 11. Although this makes the electrical circuit somewhat more complex, the quality of the injection molded product can be maintained more reliably.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a cross section and hydraulic circuit of an injection molding machine used in carrying out the present invention, Fig. 2 is an electric circuit diagram,
FIG. 3 is a diagram showing the operation of the screw and changes in resin pressure, and FIGS. 4a, b, and c are explanatory diagrams of the injection process. 11... Screw, 12... Hydraulic cylinder device, 13... Hydraulic motor, 21... Throttle switching valve, 22... Forward/forward switching valve.

[Claims]

1. A side passage is provided in the pipeline connecting the mold clamping cylinder and the hydraulic pump, and a pressure sensor and an electromagnetic relief valve for detecting the pressure in the mold clamping cylinder are provided in the side passage, and a control current for the electromagnetic relief valve is provided. a mold clamping pressure setting device for setting, a third setting device, a signal output from the mold clamping pressure setting device, a signal output from the pressure sensor, and the third setting device.
A type of an injection molding machine characterized by being provided with a computing unit that outputs a signal that causes the electromagnetic switching valve to unload the hydraulic pump when a predetermined computed value is obtained by adding the signals from the setting device. Tightening pressure boost control device.