JPH04250016A - Measuring method of injection molding machine - Google Patents

Abstract

PURPOSE:To prevent unevenness in weight or dimensions of a molded product, by preventing a back current at the beginning of an injection process by making a check valve of a blockaded state before a start of injection even under an open state of a nozzle. CONSTITUTION:Molten resin is fed to a tip side of a heating cylinder 11 while turning a screw 12 and the foregoing screw is stopped at a predetermined position. Then predetermined force is applied to the screw 12 in the direction of a nozzle port under a state where the nozzle port 27 formed on the tip of the heating cylinder is made to abut against a resin casting port 29 of a mold into which resin is injected and the screw 12 is moved forward. With this construction, pressure given in a counter press process is released and decompression of molten resin pressure on a screw tip side is performed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring method for an injection molding machine for accurately measuring the amount of injected resin to be injected into a mold cavity in an injection molding machine.

0002

[Prior Art] In a conventional injection molding machine, FIG.
), the screw 2 inserted into the heating cylinder 1
is rotated to supply the molten resin to the tip side of the heating cylinder 1, and the pressure of the molten resin causes the screw 2 to retreat, and when the screw 2 reaches a predetermined position, the rotation of the screw 2 is stopped and the screw 2 is moved to the predetermined position. I am trying to stop it at a certain position. At this time, the ring-shaped check valve 5 located between the screw head 3 and the seat ring 4 is positioned toward the screw head due to the flow of the molten resin.

[0003] When injection molding is performed, as shown in Fig. 7(b).
, As shown in (c), the screw 2 is pressed and moved toward the tip side of the heating tube 1 to apply pressure to the molten resin at the tip side of the heating tube 1, and the molten resin is injected into the cavity of the mold (not shown). I try to do that. At the beginning of the injection process,
As shown in FIG. 7(b), the check valve 5 moves from the screw head 3 side to the seat ring 4 side, and as shown in FIG. 7(c)
As shown in FIG. 2, when the screw 2 moves to a certain extent, the check valve 5 comes into contact with the seat ring 4 to block the back flow of the molten resin and apply pressure to the molten resin. Here, as shown in FIG. 7(b), at the beginning of the injection process, when the check valve 5 moves toward the seat ring 4,
A phenomenon occurs in which the molten resin at the tip side of the heating cylinder 1 flows backward to the back of the check valve 5. Here, the check valve 5 has a gap with respect to the inner diameter of the heating cylinder 1, and
Since it is not constrained in the axial direction, the backflow flow at the beginning of the injection process is not constant from molding cycle to molding cycle, and the amount of molten resin injected into the mold varies, resulting in changes in the dimensions and weight of the molded product. Variations occur.

[0004] In addition, as a method for increasing the accuracy of the stopping position of the screw 2 during measurement and improving the accuracy of measuring the molten resin, there are methods such as reducing the rotational speed of the screw 2 immediately before stopping the rotation of the screw 2, or There are known systems in which the back pressure acting on the screw 2 is set to zero or reduced immediately before the rotation of the screw 2 is stopped, or in which the stop position of the screw 2 is kept constant using a mechanical stopper. However, in these methods, when the screw 2 stops, the check valve 5 is in contact with the screw head 3 side, and at the beginning of the injection process, the check valve 5 moves toward the seat ring 4 side, causing back flow. No measures have been taken to prevent this, and it is impossible to prevent variations in the dimensions and weight of molded products due to backflow of molten resin. In order to prevent this variation, Japanese Patent Application Laid-Open No. 1-10801
As shown in Publication No. 8, a shutoff valve is provided in the nozzle formed at the tip of the heating cylinder 1 to keep the nozzle in a closed state, and just before the injection process, the screw 2 is advanced to close the heating cylinder 1. By applying extra pressure to the molten resin inside,
A method is known in which the check valve 5 is brought into close contact with the seat ring 4 immediately before the injection process.

[0005]

[Problems to be Solved by the Invention] However, the method described in Japanese Patent Application Laid-open No. 1-108018 is equipped with a shut-off valve that closes the nozzle part in order to apply extra pressure to the molten resin. A so-called open nozzle without a valve has the disadvantage that it is not possible to apply extra pressure to the molten resin. The present invention can be applied to open nozzles as well, and can prevent backflow at the beginning of the injection process by closing the check valve before injection starts, thereby preventing variations in weight and dimensions of molded products. The purpose of the present invention is to provide a method for measuring injection molding machines.

[0006]

[Means for Solving the Problems] The present invention includes a resin supply step of supplying molten resin to the tip side of a heating cylinder while rotating a screw, and stopping the screw at a predetermined position;
With the nozzle opening formed at the tip of the heating cylinder in contact with the resin injection port of the mold into which the resin is injected, a predetermined pressure is applied to the screw stopped in the resin supply step in the direction of the nozzle opening. The method is characterized by comprising a counter press step of advancing the screw, and a step of releasing the pressure applied in the counter press step and releasing the molten resin pressure on the tip end side of the screw.

[0007]

[Operation] A predetermined pressure is applied to the molten resin supplied to the tip of the heating cylinder in the resin supply process toward the nozzle opening in the counter press process. This counter press process is
Since the nozzle opening of the heating cylinder is in contact with the resin injection port of the mold into which the resin is injected, there is no need to install a valve such as a shut-off valve at the nozzle opening to prevent the resin from being injected into the mold. The closed state is maintained by the resin, and extra pressure can be applied to the molten resin. During this counter press process, the molten resin supplied to the tip of the heating cylinder flows backward, and the check valve moves to become closed. Thereafter, the residual pressure of the molten resin is removed by a pressure release step, and when the nozzle port is removed from the resin injection port of the mold, the so-called nasal drip phenomenon, in which resin leaks from the nozzle port, is prevented. As described above, according to the present invention, the backflow of molten resin that conventionally occurs at the beginning of the injection process can be prevented by performing normal injection molding after the check valve is closed in the counter press process. , variations in weight and dimensions of molded products are prevented.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. First, the apparatus for carrying out the method of the present invention will be described. As shown in FIGS. 2 and 3, a heating cylinder 11 having a nozzle 10 formed at the front end is provided. A screw 12 is inserted from the rear end of the heating cylinder 11 so as to be freely forward and backward and rotatable. A hydraulically driven motor 13 is attached to the rear end of the screw 12, and the motor 13 rotates the screw 12. Further, an injection cylinder 14 is provided at the rear end of the motor 13, and the injection cylinder 14 moves the screw 12 forward and backward. A hydraulic drive device 15 is provided for the motor 13 and the injection cylinder 14.
is connected, and the hydraulic pressure supplied to the motor 13 and injection cylinder 14 is controlled. Furthermore, a hopper 16 is attached to the rear end of the heating cylinder 11 to supply injection material to the screw 12 side.

An L-shaped rack member 17 is attached to the rear end of the screw 12, and a pinion of an encoder (position detector) 18 is rotatably engaged with this rack member 17. is control device 1
It is connected to the position sensor input circuit 40 of No. 9. Also,
A pressure sensor (not shown) is attached to the injection cylinder 14 to detect the pressure that the injection cylinder 14 loads on the screw 12, so-called back pressure, and this pressure sensor is connected to the pressure sensor input of the control device 19. circuit 41
It is connected to the. This control device 19 includes a setting device 42 for inputting various operational data of the injection molding machine, and a latch command signal by comparing the pressure value inputted to this setting device 42 with the output of the pressure sensor input circuit. a comparison circuit 43 that outputs the signal, a storage device 44 that stores the signals from the position sensor input circuit 41 and the comparison circuit 43, and a storage device 44 that stores the output signal of the storage device 44, the shift point input to the setting device 42, and the measurement completion. A calculation device 45 calculates a change point signal (described later) from a set value of a position signal such as a point, and a hydraulic control output from this change point signal and set values such as screw drive pressure and speed inputted to a setting device 42. a control circuit 47 that outputs a control signal to the hydraulic drive device 15 via the circuit 46;
It is equipped with

FIG. 3 shows a state in which the nozzle 10 of the heating cylinder 11 is in contact with a mold. A screw head 24 is formed at the tip of the screw 12, and a seat ring 23 is attached to the end opposite to the screw head 24. A ring-shaped check valve 22 is inserted between the seat ring 23 and the screw head 24 so as to be slidable on the inner peripheral surface of the heating cylinder 11 . The check valve 22 is located on the screw head 24 side during resin supply, and is located on the seat ring 23 side during injection to prevent backflow of molten resin. Moreover, the nozzle 10 formed at the tip of the heating cylinder 11 is
The nozzle 10 is inserted through the through hole 26 formed in the fixed plate 25, and the nozzle port 27 formed at the tip of the nozzle 10 contacts the resin injection port 29 of the mold 28 to inject the molten resin into the cavity of the mold 28. It looks like this. In the figure, 30 indicates a molded product formed by injection. Next, the weighing operation in this embodiment will be explained with reference to FIGS. 1 to 3.

(1) Supply of resin (see FIG. 1(a)) When the screw 12 rotates, the plasticized resin passes from the screw 12 through the gap between the screw head 24 and the check valve 22 to the heating cylinder 11. The screw 12 rotates and retreats in a state where the resin pressure P0 in the tip and the back pressure of the cylinder 14 are balanced. At this time, the check valve 22 is in contact with the screw head 24 side due to the flow of molten resin toward the tip of the heating cylinder 11 . (2) Supply stop (see FIG. 1(b)) When the metering stop position set by the setting device 42 and the screw position measured by the encoder 18 match, the calculation device 4
5 sends a control signal to the control circuit 47, the hydraulic drive device 15 is operated to stop the rotation of the screw 12, and the backward movement of the screw 12 is also stopped. This stop position is S0
shall be. At this time, similarly to the conventional example, the check valve 2
2 is in a so-called open state in contact with the screw head 24 side.

(3) Counter press (see FIG. 1(c))
After the supply is stopped, the injection cylinder 14 is driven to advance the screw 12 with a constant pressure P1. At this time, the nozzle port 27 of the nozzle 10 is in contact with the resin injection port 29 of the mold 28, and since the molded product injected just before is in a solidified state, the nozzle port 27 is in a closed state, and the injection cylinder 14, pressure is applied to the molten resin stored on the tip side of the heating cylinder 11. As a result, the pressure applied to the molten resin at the tip end of the heating cylinder 11 causes the molten resin to flow back from the screw head 24 side to the seat ring 23 side, and the back flow of this resin and the forward movement of the screw 12 prevent backflow. The valve 22 moves relatively to the right in the figure, contacts the seat ring 23, and enters the closed state. In this way, the screw 12 advances until the check valve 22 is closed, and the screw 12 stops when the pressure P1 caused by the counter press and the pressure of the molten resin at the tip of the heating cylinder 11 are balanced. The position of the screw 12 at this time is set as S1, and the amount of advance of the screw 12 from the above-mentioned position S0 is set as Δl1. In addition,
This counter press operation may be performed at any time from immediately after the supply is stopped to immediately before the mold is opened.

(4) Pressure release (see FIG. 1(d)) After the screw 12 is stopped by the counter press, the pressure applied by the injection cylinder 14 is released. That is, the resin pressure P1 in the heating cylinder 11 is set to be less than or equal to P2, which is a relatively small pressure value that does not cause nasal drip, which will be described later. Here, during the counter press, the check valve 22 contacts the seat ring 23 and is maintained in a closed state, so that the resin pressure on the tip side of the heating cylinder 11 and the pressure in the injection cylinder 14 are balanced. The pressure from the counter press is released while maintaining this state. As a result of this pressure release, the screw 12 moves back slightly and stops, completing metering. The position of the screw 12 at this time is S2, and the position of the screw 12 is S1.
Let Δl2 be the amount of retreat from the position S0, and Δl3 be the amount of advance of the screw 12 from the position S0. Note that since the pressure from the counter press is released, the residual pressure of the molten resin on the tip side of the heating cylinder 11 is removed, and the nozzle 1
0 is removed from the injection port 29 of the mold 28, the nozzle 1
It is possible to eliminate the so-called nasal drip phenomenon in which molten resin leaks from the nozzle port 27.

(5) Injection process The mold 28 is opened, the molded product injected and solidified just before is taken out, and the mold 28 is closed. Then, the injection cylinder 14 applies pressure to the molten resin stored at the tip side of the heating cylinder 11 and injects it into the cavity of the mold 28 . On this occasion,
While measuring the current position of the screw 12 with the encoder 18, this measured value is compared with the shift point value set by the setting device 42, and a control signal is issued to the hydraulic control unit 15 at a predetermined injection stroke to adjust the injection speed, etc. changes will be made. Here, either the position S1 or the position S2 of the screw may be adopted as the origin of the injection stroke.

Next, the case where injection molding is performed by controlling the injection speed as shown in FIG. 4 will be explained with reference to the flowcharts shown in FIGS. 5 and 6. The flowchart in FIG. 5 shows the processing before the injection process. Step 1 (denoted as ST1 in the figure. The same applies below.)
Now, it is determined whether the current value Sp of the injection stroke has reached the set value S0. If Sp is not S0, proceed to step 2 and rotate the screw 12. In these steps 1 and 2, the screw 12 is rotating and retracting, and Sp is at the set value S0.
This shows a resin supplying process in which the rotation of the screw 12 is stopped and the backward movement of the screw 12 is stopped when this occurs. As a result of step 2, the current injection stroke value is Sp=S0
If so, proceed to step 3. In this step 3,
The comparison circuit 43 determines whether the current value Pp of the injection cylinder pressure has reached the counter press completion pressure P1. When Pp is smaller than P1, the process advances to step 4 and the counter press is continued. These steps 3 and 4 represent a counter press step in which the screw 12 is advanced and a predetermined pressure P1 is applied to the molten resin stored at the tip of the heating cylinder 11.

When the resin pressure becomes Pp≧P1, proceed to step 5. In this step 5, the current value Sp of the injection stroke of the screw 12 when Pp=P1 is set as S
1 in the storage device 44, and the process proceeds to step 6. In step 6, hydraulic pressure to the injection cylinder is released;
It is determined whether the current value Pp of the injection cylinder pressure at that time has reached P2. When Pp is not P2, the process proceeds to step 7, and the release of the injection pressure is continued. These steps 6 and 7 represent a pressure relief step in which the pressure P1 applied to the molten resin by the injection cylinder 14 is released.

[0017] When Pp≦P2, step 8
Proceed to. In this step 8, the current value Sp of the injection stroke when Pp=P2 is set as S2 and stored in the storage device 44.
, and proceed to step 9. In step 9, it is determined whether the injection origin of the injection stroke is set at S1 or S2 based on prespecified data. If S1 is to be the injection origin, the process proceeds to step 10, and if S2 is to be the injection origin, the process is to proceed to step 11. In step 10, S1 is subtracted from S0 to obtain the amount of advance Δl1 advanced by the counter press process, and this Δl1 is calculated at predetermined injection speed change points S21, S22, S shown in FIG.
Subtract and correct from 23, S24, S25, and the changes after correction HS21, HS22, HS23, HS24, HS25
seek. Further, in step 11, S2 is subtracted from S0 to obtain the amount of advance Δl3, and this Δl3 is calculated at predetermined injection speed change points S21 and S22 shown in FIG.
, S23, S24, S25 and corrected the changes after correction HS21, HS22, HS23, HS24, HS2
Find 5. Next, the injection process will be explained based on FIG. In step 20, it is determined whether the current value Sp of the injection stroke is larger than the corrected change point HS21. H.S.
When 21<Sp, proceed to step 21;
A control signal is issued to the hydraulic control section 15, and the forward speed of the screw 12 is controlled so that the injection speed becomes V1. When HS21=Sp, the process proceeds to step 22.

In step 22, it is determined whether the current value Sp of the injection stroke is larger than the corrected change point HS22. When HS22<Sp, proceed to step 23;
In step 23, a control signal is issued to the hydraulic control section 15 so that the injection speed becomes V2, and the screw 1
The forward speed of 2 is controlled. When HS22=Sp, the process proceeds to step 24. In step 24, it is determined whether the current value Sp of the injection stroke is larger than the corrected change point HS23. When HS23<Sp, proceed to step 25, and in step 25, the injection speed is set to V3.
A control signal is issued to the hydraulic control section 15, and the forward speed of the screw 21 is controlled so that. HS23
=Sp, the process advances to step 26. In step 26, it is determined whether the current value Sp of the injection stroke is larger than the corrected change point HS24. HS24<
When Sp, the process proceeds to step 27, and in step 27, a control signal is issued to the hydraulic control section 15 to control the forward speed of the screw 12 so that the injection speed becomes V4. When HS24=Sp, step 2
Proceed to step 8. In step 28, the current value S of the injection stroke is
It is determined whether p is larger than the corrected change point HS25. When HS25<Sp, the process proceeds to step 29, and in step 29, a control signal is issued to the hydraulic control section 15 so that the injection speed becomes V5, and the screw 12
The forward speed of the is controlled. When HS25=Sp, the process proceeds to step 30. In step 30, a pressure holding step is started, and the injection pressure is controlled as time T elapses, as shown in FIG.

[0019]

As explained above, in the measuring method of the injection molding machine of the present invention, molten resin is supplied to the tip side of the heating cylinder while rotating the screw, and the resin is supplied by stopping the screw at a predetermined position. step, with the nozzle port formed at the tip of the heating cylinder in contact with the resin injection port of the mold into which the resin is injected, a predetermined pressure is applied to the screw stopped in the resin supply step in the direction of the nozzle port. The method includes a counter press step in which the screw is advanced by applying a Even in the case of a so-called open nozzle that does not have a nozzle closing mechanism, it is possible to put extra pressure on the molten resin and close the check valve before starting injection, which prevents the molten resin from flowing back toward the rear of the screw at the beginning of injection. , it is possible to eliminate variations in weight and dimensions of molded products due to variations in the amount of backflow.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the steps of the present invention.

FIG. 2 is a diagram showing the configuration of an injection molding machine used in the present invention.

FIG. 3 is a partially enlarged view of FIG. 2;

FIG. 4 is a diagram showing a program for a filling process and a pressure holding process.

FIG. 5 is a flowchart of a weighing process.

FIG. 6 is a flowchart of an injection process.

FIG. 7 is a diagram showing a conventional injection process.

[Explanation of symbols]

11 Heating tube 12 Screw 22　Return prevention valve 27 Nozzle mouth 29 Resin injection port

Claims (1)

[Claims] 1. In an injection molding machine in which a screw is rotatably inserted into a heating cylinder so as to be freely advanced and retractable, and a check valve is attached to the tip of the screw, the tip of the heating cylinder is inserted while the screw is rotated. a resin supplying step of supplying molten resin to and stopping the screw at a predetermined position, and a nozzle opening formed at the tip of the heating cylinder in contact with a resin injection port of a mold into which the resin is injected; A counter press step in which a predetermined pressure is applied to the screw stopped in the resin supply step in the direction of the nozzle opening to advance the screw, and the pressure applied in the counter press step is released to release the molten resin on the tip side of the screw. A measuring method for an injection molding machine, characterized by comprising a pressure releasing step.