JPH07323449A - Method for setting timing for starting exciting and pressing action of local pressing type injection molding machine - Google Patents

Abstract

PURPOSE:To prevent the occurrence of sink marks on a molding, in a local pressing type injection molding machine in which a pressing pin provided with its end facing toward a cavity is moved forward while being vibrated, by a method wherein a judgement is made as to whether or not a screw is in an exciting/pressing action starting region and, if so, this action is started. CONSTITUTION:In a local pressing type injection molding machine, the pressing action takes place by the vibration of pressing pins 24 caused by a pressing cylinder 32 supplied with a pulse-like hydraulic pressure, while resins are being fed from an injection nozzle forced against a sprue bush 13. In such a molding machine, when a screw is judged to have reached an exciting/pressing action starting zone from the output of a screw position detector, a predetermined amount of resin is filled in a cavity 16 and, when the injection speed reaches at most the reference value, a proportional pressure reducing valve provided in a hydraulic system is controlled to start the exciting/pressing action. By starting the exciting/pressing action at a point at which the resin is sufficiently filled in the cavity 16, the occurrence of sink marks on a molding is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibration / pressurizing operation start timing setting method for a local pressure type injection molding machine.

[0002]

2. Description of the Related Art Conventionally, a pressure pin disposed so as to face a cavity is moved forward while vibrating, and a pulsed pressure force is applied to a resin to perform various processes on a molded product. A local pressure injection molding machine is provided. In this case, a pressure pin is provided penetrating the movable mold, and the tip of the pressure pin is made to move forward and backward in the cavity so as to correspond to the processed portion of the molded product. A pressure cylinder is disposed behind the pressure pin, and pulsed hydraulic pressure is supplied to the pressure cylinder.

Therefore, after the injection process is completed, pulsed hydraulic pressure is supplied to the pressurizing cylinder in the pressure holding process or the cooling process to move the pressurizing pin forward while vibrating the pressurizing pin.
By applying a pulse-like pressure to the resin, the molded product can be subjected to predetermined processing. FIG. 2 is a diagram showing a pressing program for a pressing pin in a conventional local pressure injection molding machine. The horizontal axis represents time and the vertical axis represents the input signal of the proportional pressure reducing valve.

[0004] As shown, vibration-pressurization operation is started at the time when the injection start point or V-P from switching point pressure delay time T _d elapses, pressurized only during the pressing time T _a The set value of the pressure is increased / decreased every pressurization cycle time T _b . In this case, the pressure is gradually increased from the initial pressure P ₁ to the final pressure P ₂ to
At the end of the pressurizing operation, the final pressurizing force P ₃ is maintained for the final pressurizing time T ₃ without vibrating the pressurizing pin (not shown).

When the vibration / pressurizing operation is completed, the processing of the molded product is also completed.

[0006]

However, in the conventional local pressurization type injection molding machine, the vibration / pressurizing operation is performed at the time when the pressurization delay time T _d elapses from the injection start point or the VP switching point. Therefore, if the injection speed varies, the molded product will be defective.

For example, when the injection speed is high at the time when the pressurization delay time _Td has passed from the injection start point or the VP switching point, the resin is sufficiently filled in the cavity when the pressurization delay time _Td has passed. Since it is not filled in the mold, sink marks will occur in the molded product. If the injection speed is low at the time when the pressurization delay time _Td elapses from the injection start point or the VP switching point, the resin in the cavity starts to be hardened by that amount, making it difficult to process the molded product. Become.

The present invention solves the problems of the conventional local pressurization type injection molding machine so that even if the injection speed varies, the local pressurizing injection molding machine does not cause a defect in the molded product. It is an object of the present invention to provide a method for setting the start timing of the vibration / pressurization operation of the above.

[0009]

Therefore, in the method for setting the vibration / pressurizing operation start timing of the local pressurization type injection molding machine of the present invention, the pressurizing pin disposed with its tip facing the cavity is used. In a local pressurization type injection molding machine that moves forward while vibrating, it is determined whether the screw is in a vibration / pressurization operation start section, and whether the injection speed is equal to or lower than a reference value.

When the screw is in the vibration / pressurization operation start section and the injection speed is below the reference value,
The pressurizing operation is started.

[0011]

According to the present invention, as described above, in the method for setting the vibration / pressurizing operation start timing of the local pressurization type injection molding machine, the pressurizing pin arranged with its tip facing the cavity is vibrated. In the local pressurization type injection molding machine which is moved forward, it is judged whether the screw is in the vibration / pressurization operation start section, and it is judged whether the injection speed is equal to or lower than the reference value.

In this case, when the screw advances by a predetermined amount in the injection process, the screw reaches the vibration / pressurizing operation start section. Further, when the cavity is filled with a predetermined amount of resin, the injection speed gradually decreases, and the injection speed becomes equal to or lower than the reference value. Then, when the screw is in the vibration / pressurizing operation start section and the injection speed is equal to or lower than the reference value, the vibration / pressurizing operation is started.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 3 is a sectional view of a local pressure type injection molding machine according to an embodiment of the present invention. In the figure, 1
Reference numeral 1 denotes a fixed side mounting plate, and the fixed mold 12 is mounted on a fixed platen (not shown) via the fixed side mounting plate 11. Then, the injection nozzle of the injection device (not shown) advances in the injection process, and the tip of the injection nozzle is brought into contact with the sprue bush 13 of the fixed mold 12.

On the other hand, the movable platen (not shown) is moved forward and backward by a mold clamping device (not shown) to bring the movable mold 14 into contact with and separate from the fixed mold 12. for that reason,
The movable mold 14 is attached to the movable platen via a movable side attachment plate 15 and a spacer block (not shown). Then, the resin injected from the injection nozzle passes from the sprue through the runner and through the gate 25 to the fixed mold 12
And the movable mold 14 is filled with the cavity 16.

When the injection step is completed, a pressure holding step is subsequently performed, the resin pressure in the cavity 16 is increased, the resin is started to be cooled, and a molded product (not shown) is placed on the movable mold 14 side after a fixed time. In the left state, the fixed mold 12 and the movable mold 14 are opened, and the molded product is pushed down by the ejector device. Therefore, the sprue lock pin 17 and the ejector pin 18 are provided. The sprue lock pin 17 is arranged so as to face the sprue, and holds the molded product when the mold is opened and leaves it on the movable mold 14 side. In addition, the ejector pin 18 is provided in the cavity 1
6 and the runner are arranged with their ends facing, and the molded product is pushed down from the movable mold 14 after the mold is opened.

The sprue lock pin 17 and the ejector pin 18 penetrate the movable mold 14 and extend rearward (toward the mold clamping device), and the head portion formed at the rear end is held by the ejector plates 21 and 22. Fixed. Then, the rod 23 can be brought into contact with the ejector plates 21 and 22, and the sprue lock pin 17 and the ejector pin 18 are moved as the rod 23 moves forward (moves to the right in the figure). Can be moved forward.

By the way, in order to process the molded product in the injection process, the pressure holding process or the cooling process, the pressure pin 24 is provided. The pressure pin 24 has a cavity 1
6, a predetermined number of gates 25 and the like are provided with their tips facing each other, and the head portion formed at the rear end extends rearward through the movable mold 14 and the ejector plates 21 and 22. It is clamped and fixed by the pressure plates 27 and 28.

The pressure plates 27, 28 are arranged so as to be able to come into contact with and separate from the movable side mounting plate 15, and are moved forward and backward by two pressure cylinders 32. The pressure cylinder 3
The second pressure rod 33 penetrates the cross head 34 and the movable side mounting plate 15 and is in contact with the pressure plate 28, and the pressure pin 24 can be projected by operating the pressure cylinder 32. .

The hydraulic pressure supplied to the pressurizing cylinder 32 is controlled by a proportional pressure reducing valve or a servo valve (not shown). By electrically controlling the proportional pressure reducing valve or the servo valve, the pressurizing pin 24 is gradually advanced (moved to the right in the figure) while vibrating to apply a pulse-like application to the resin in the processed portion of the molded product. Apply pressure to excite (displace),
Predetermined processing can be performed on the molded product.

Even if the pressurizing pin 24 is moved forward by using the proportional pressure reducing valve or the servo valve, the resin cannot be excited. That is, a reaction force is required to excite the resin by the applied pressure, and the pressure pin 24
Must be forcibly retracted from the processing section. Therefore, the four return pins 29 are connected to the return pins 29.
A highly responsive return spring 30 that surrounds the pressure plate 27 is disposed between the pressure plate 27 and the movable mold 14. Both the pressure pin 24 and the return pin 29 have a head portion formed at an end thereof, and the head portion has a pressure plate 27,
It is sandwiched and fixed by 28. In this case, by arranging the four return springs 30 evenly,
The pressure plates 27 and 28 can be moved forward in parallel without tilting, and a smooth operation can be obtained.

By setting the spring constant of the return spring 30 to a predetermined value, it becomes possible to excite the resin up to around 10 Hz by the hydraulic pressure generated in the proportional pressure reducing valve. That is, since the proportional pressure reducing valve generates a pulsed pressure force, the return spring 30 having a spring constant capable of following this is selected. This spring constant is proportional to the weight of the driving unit (for example, the pressure plates 27 and 28, the pressure rod 33, the cross head 34, etc.) and the vibration / pressure frequency of pulse input. That is, when the vibration / pressurization frequency is increased or the weight of the drive unit is increased, the spring constant must be increased.

For example, the weight of the driving unit is about 18.5 [k].
g] and the vibration / pressurization frequency is 10 [Hz], the spring constant is 80 [Kgf / mm]. Also, 4
When the book has the return springs 30, the spring constant of each return spring 30 is 200 [Kgf / cm]. The preload of the return spring 30 is about 10 of the maximum pressing force (880 [Kgf]).
[%], For example, 80 [Kgf]. This preload is added to improve the controllability of the proportional pressure reducing valve.

Next, the control device for the proportional pressure reducing valve will be described. FIG. 1 is a control circuit diagram of a proportional pressure reducing valve in an embodiment of the present invention. As shown in the figure, a proportional pressure reducing valve 44 and a switching valve 45 are provided to move the pressing rod 33 forward while oscillating (moving to the right in the figure), and the oil discharged from the pump 46 is proportional to the proportional pressure reducing valve 44 and the switching valve 45. By electrically controlling the pressure reducing valve 44 and the switching valve 45, pulsed hydraulic pressure can be supplied to the oil chambers 32 a and 32 b of the pressurizing cylinder 32. Then, the pulsed hydraulic pressure gradually advances while vibrating the pressure pin 24 (FIG. 3) to excite the resin in the processed portion of the molded product, and subject the molded product (not shown) to predetermined processing. The oil chamber 32b of the pressure cylinder 32 is for retracting the pressure pin 24 to the initial position.

Incidentally, the proportional pressure reducing valve 44 has a solenoid a, and the pressure applied to the oil chamber 32a can be changed by electrically operating the solenoid a. And the solenoid a
The current supplied to is adjusted by the driver 50, and a command signal from the CPU 51 is sent to the driver 50.

Further, the timing which starts the vibration / pressurization operation
A screw position detector 61 is provided to adjust the
Detected by the screw position detector 61
The screw position is sent to the differentiator 62, and the differentiator 62
Therefore, it is differentiated and the injection speed v _Sbecome. The injection speed v_S
Is the reference value v set by the setter 65_refRatio with
It is input to the comparator 64, and both are compared.

A predetermined amount is put in the cavity 16 in the injection process.
Injection speed v _SIs gradually lower
, The injection speed v_SIs the reference value v_refCompare when
The device 64 sets the output to the high level. And the CPU
51 indicates whether the conditions for starting the vibration / pressurization operation are satisfied.
Refuse. In this case, first, the CPU 51 determines the screw position.
Position, based on the time elapsed from the injection start point, etc.
The injection molding machine can start the vibration / pressurization operation.
Is in a state, that is, the screw is vibrating / pressurizing
It is determined whether it is in the operation start section. Like this
And the injection speed is low immediately after the injection process is started.
In case the vibration / pressurization operation is not started
It

Next, the CPU 51 determines whether or not the injection speed v _S has become less than or equal to the reference value v _ref . in this case,
It is determined whether the output of the comparator 64 is high level. Therefore, since the vibration / pressurizing operation can be started at the time when the cavity 16 is sufficiently filled with the resin, it is possible to prevent the sink mark from occurring in the molded product.

Further, since the resin in the cavity 16 does not start to harden too early, the processing of the molded product does not become difficult. The determination of the vibration / pressurizing operation start condition in the CPU 51 is performed during each of the injection step, the pressure holding step, and the cooling step, and the vibration / pressurizing operation is started until the vibration / pressurizing operation start condition is satisfied. The operation is never started. On the contrary, when the vibration / pressurizing operation start condition is satisfied, the vibration / pressurizing operation is started in any of the injection step, the pressure holding step and the cooling step.

In the present embodiment, the screw position detected by the screw position detector 61 is differentiated by the differentiator 62 to calculate the injection speed v _S. However, the injection speed is directly calculated by a speed sensor (not shown). It can also be detected. Next, the operation of the local pressure type injection molding machine will be described. FIG. 4 is a flowchart of the local pressure type injection molding machine according to the embodiment of the present invention. Step S1 The injection is started. In step S2, it is determined whether the vibration / pressurizing operation start condition is satisfied. When it is satisfied, the process proceeds to step S3, and when it is not satisfied, the process proceeds to step S4. In this case, the CP
U51 (Fig. 1) determines whether the local pressurization type injection molding machine can start the vibration / pressurizing operation based on the screw position, the elapsed time from the injection start point, etc. Determine whether it is in the vibration / pressurization operation start section. Then, the CPU 51 determines whether or not the injection speed v _S has become equal to or lower than the reference value v _ref . Step S3 The vibration / pressurization operation is started. Once the vibration / pressurization operation is started (once), this step S
3 is ignored. Step S4: It is judged whether the injection process is completed. In this case, switching from the injection process to the pressure-holding process is
There are time switching, position switching, V / P switching, etc. If not completed, the process returns to step S1, and if completed, the process proceeds to step S5. Step S5: Holding pressure is started. Step S6: It is judged whether or not the conditions for starting the vibration / pressurizing operation are satisfied. When it is satisfied, the process proceeds to step S7, and when it is not satisfied, the process proceeds to step S8. In this case, the CP
U51 determines whether or not the local pressurization type injection molding machine can start the vibration / pressurizing operation based on the screw position, the elapsed time from the injection start point, and the like. It is determined whether or not it is in the pressure operation start section. Then, the CPU 51 determines that the injection speed v _S is the reference value v
_Judge whether or not it has become less than or equal to _ref . Step S7: The vibration / pressurizing operation is started. Once the vibration / pressurizing operation is started, this step S7 is ignored. Step S8: It is judged whether the pressure holding process is completed. If not completed, the process returns to step S5, and if completed, the process proceeds to step S9. Step S9 Start cooling. Step S10: It is judged whether or not the conditions for starting the vibration / pressurizing operation are satisfied. If yes, go to step S11,
If not established, the process proceeds to step S12. In this case, the CPU 51 determines whether or not the local pressurization type injection molding machine can start the vibration / pressurizing operation based on the screw position, the elapsed time from the injection start point, and the like. Determine whether it is in the vibration / pressurization operation start section. Then, the CPU 51 determines whether or not the injection speed v _S has become equal to or lower than the reference value v _ref . Step S11 The vibration / pressurization operation is started. Once the vibration / pressurizing operation is started, this step S11 is ignored. In step S12, it is determined whether the cooling process is completed. If not completed, the process returns to step S9, and if completed, the process ends.

The present invention is not limited to the above-mentioned embodiments, but can be variously modified within the scope of the present invention, and they are not excluded from the scope of the present invention.

[0031]

As described above in detail, according to the present invention, in the method for setting the vibration / pressurizing operation start timing of the local pressurization type injection molding machine, the tip is disposed so as to face the cavity. In a local pressurization type injection molding machine in which a pressurizing pin is moved forward while vibrating, it is judged whether or not the screw is in a vibration / pressurizing operation start section, and it is judged whether or not the injection speed is equal to or lower than a reference value.

In this case, when the screw advances by a predetermined amount in the injection process, the screw reaches the vibration / pressurizing operation start section. Further, when the cavity is filled with a predetermined amount of resin, the injection speed gradually decreases, and the injection speed becomes equal to or lower than the reference value. Then, when the screw is in the vibration / pressurizing operation start section and the injection speed is equal to or lower than the reference value, the vibration / pressurizing operation is started.

Therefore, since the vibration / pressurizing operation can be started at the time when the resin is sufficiently filled in the cavity, it is possible to prevent sink marks from being generated in the molded product. In addition, since the resin in the cavity does not start to cure too early, the processing of the molded product does not become difficult.

[Brief description of drawings]

FIG. 1 is a control circuit diagram of a proportional pressure reducing valve in an embodiment of the present invention.

FIG. 2 is a diagram showing a pressure program for a pressure pin in a conventional local pressure type injection molding machine.

FIG. 3 is a sectional view of a local pressure type injection molding machine according to an embodiment of the present invention.

FIG. 4 is a flowchart of a local pressure type injection molding machine according to an embodiment of the present invention.

[Explanation of symbols]

16 cavity 24 pressure pin v _S injection speed v _ref reference value

Claims (1)

[Claims] 1. A method for setting a vibration / pressurizing operation start timing of a local pressurization type injection molding machine, wherein: a screw is applied to a local pressure injection molding machine in which a pressure pin disposed with its tip facing a cavity is moved forward while vibrating. It is judged whether or not it is in the vibration / pressurization operation start section, (b) it is judged whether or not the injection speed is less than or equal to the reference value, and (c) the screw is in the vibration / pressurization operation start section, and the injection speed is A vibration / pressurizing operation start timing setting method for a local pressurization type injection molding machine, wherein the vibration / pressurizing operation is started when is less than a reference value.