JPS6317020A - Controlling method for dwelling in injection molder - Google Patents

Abstract

PURPOSE:To make it possible to apply a dwell pressure, which is scrupulously controlled in response to the cooling and setting state of the resin in a mold cavity, and consequently and especially improve the quality of a precision molded item by a method wherein the magnitude of the dwell pressure is controlled in response to the movement of an injection screw during dwell process. CONSTITUTION:When a screw 3 moves by a distance, which is obtained by dividing the predetermined movement (l) of the screw into (n) equal-length portions or mun, during dwell process, as the shrinkage of the resin in a mold cavity 5 due to cooling proceeds, the detected value of the positional detector 10 of the screw 3 coincides with the set point of an interval setter 12 to change over the dwell pressure. As a result, a switch 11 is put into acutuation so that, for example, the second relay coil 132 is demagnetized and at the same time the third relay coil 133 is excited so as to control the magnitude of the dwell pressure to P3. In such a manner as just mentioned above, the dwell pressure is controlled one after another to the preset value. Finally, when the movement of the screw 3 since the start of dwell process reaches the predetermined movement (l), the dwell pressure is changed over to zero so as to complete the dwell process.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for controlling an injection molding machine, and particularly to a method for controlling the magnitude of holding pressure in the holding process.

(Prior Art) In an injection molding machine, molten resin stored in a cylinder is injected from a nozzle by advancing an injection screw and press-fitted into a mold cavity. The molten resin filled in the mold cavity becomes a molded product by cooling and solidifying in that state. In that case, since the resin contracts as it cools and solidifies, it is necessary to compensate for the shrinkage. Therefore, the injection screw is used even after the filling process, in which the molten resin is filled until it reaches the end of the mold cavity.
It is pressed in the forward direction for a predetermined period of time to apply holding pressure.

Since this pressure holding step is an important factor in determining the quality of the molded product, the magnitude of the holding pressure needs to be controlled to an appropriate level depending on the cooling and solidification state of the resin.

When controlling the holding pressure in this way, conventionally, a timer is used to change the magnitude of the holding pressure when a set time has elapsed after switching to the holding pressure process.

(Problems to be Solved by the Invention) However, in the pressure holding control method using such a timer, in order to achieve fine control, it is necessary to provide a large number of timers, which is not only expensive but also The work of setting the time and the like becomes complicated, and for this reason, pressure control is usually only possible in two to three stages.

Further, the state of solidification and contraction of the resin is not uniquely determined by the cooling time, but varies depending on the mold temperature, the outside temperature, the temperature of the molten resin during filling, and the like.

For this reason, in the case where the holding pressure is controlled by the elapsed time after switching to the holding pressure process, the molded product may be filled with molten resin after the cooling shrinkage of the resin in the cavity has progressed, causing shrinkage or shrinkage in the molded product. Warping may occur, or excessive holding pressure may be applied before the resin shrinks, resulting in an overfilling state, which may cause burrs to form on the molded product. Such deformation and occurrence of burrs in molded products pose major problems in performing precision molding.

The present invention has been made in view of the above circumstances, and its purpose is to finely control the holding pressure in accordance with the cooling and solidification state of the resin in the mold cavity.

(Means for solving the problem) In order to achieve this objective, in the present invention, during the pressure holding process,
The displacement amount of the injection screw is detected, and the holding pressure is sequentially controlled according to the displacement amount.

(Function) With this method, when the resin in the mold cavity is cooled and solidified and the resin contracts, the injection screw moves according to the amount of contraction, so the amount of screw movement at that time The cooling and solidification state of the resin can be grasped. Therefore, by controlling the holding pressure according to the amount of screw movement, the holding pressure can be correctly controlled as the resin in the mold cavity progresses as it cools and solidifies.

By finely setting the screw position interval for switching the holding pressure, fine control of the holding pressure becomes possible.

(Example) Hereinafter, the present invention will be explained in detail using the drawings.

In the drawings, FIG. 1 is a block diagram showing an example of a control device for implementing the pressure holding control method according to the present invention.

As is clear from this figure, an injection screw 3 is inserted into the cylinder 1 of the injection molding machine, which is rotationally driven by a one-rotator (not shown) and is driven forward by an injection hydraulic cylinder 2. An injection nozzle 4 is provided at the front end of the cylinder l, and as the screw 3 advances, the molten resin stored in the cylinder l is injected through the nozzle 4, and the mold is clamped by a mold clamping device (not shown). The cavity 6 of the mold 5 is filled with the mold.

The injection hydraulic cylinder 2 is operated by hydraulic pressure supplied from a hydraulic source 7. The magnitude of the oil pressure is sequentially controlled by an electromagnetic proportional pressure control valve 8 during the filling process and the pressure holding process.

The screw drive shaft 9 connecting the piston 2a of the injection hydraulic cylinder 2 and the screw 3 is provided with a position detector 10 consisting of an encoder or the like capable of detecting the amount of movement of the drive shaft 9, that is, the position of the screw 3. There is. This position detector 10 encodes the detected position of the screw 3 internally and outputs it as a digital value. The output signal of this position detector 10 is input to a switch 11.

The output signal from the interval setter 12 is also input to the switch 11 . This interval setting device 12 is used to preset the position interval of the screw 3 at which the holding pressure should be changed according to the molding conditions, etc.
A digital signal is output at every screw movement interval of +sm or 2t+w. In the switch 11, the output values of the position detector 10 and the interval setter 12 are sequentially compared digitally, and the screw 3 is connected to the interval setter 1.
Every time it moves by the interval set in 2, the multi-stage relay coil 13 times.

The excitation of 132, . . . , 13n is switched in order.

Relay coil 13. .about.13n, by their excitation, the corresponding normally open relay contacts 141 . 142
, . . . , 14n. These relay contacts 14. ~14n is a multistage potentiometer 15. ．． 15. .

..., 15n, respectively. This potentiometer 15. ~15n, the output voltage can be set arbitrarily by adjusting the position of each slider.

Then, the output voltage is from relay contact 14t to
The signal is input to the amplifier 16 via 14n.

An output signal from a pressure head 17 that detects the oil pressure supplied to the injection hydraulic cylinder 2 is also input to the amplifier 16 . Then, in this amplifier 16, the setting values set in the potentiometers 151 to 15m are compared with the actual pressure detection value detected by the pressure controller 17, and a pressure signal is corrected so that the pressure always becomes the set pressure. is supplied to the electromagnetic proportional pressure control valve 8. The pressure control valve 8 has a set pressure switched according to the pressure signal from the amplifier 16, and controls the hydraulic pressure supplied to the injection hydraulic cylinder 2.

When injection molding a molded product using the injection molding machine configured as described above, first, a relationship diagram between the optimum position of the injection screw 3 and the holding pressure is determined according to the shape of the mold 5, molding conditions, etc. Here, we will calculate the 0th order, assuming that the diagram is a curve as shown by the solid line in Figure 2.

The amount of movement of the screw 3 that moves during the pressure holding process is n
Divide into equal parts. Then, according to the diagram in FIG.
) at the holding pressure P1 + P2 +...

Find Pn.

Next, the control position interval 1/n of the screw 3 obtained in this manner is set in the interval setting device 12, and each holding pressure P1, P2 *... is set.

Potentiometer 15 with Pn as the voltage value. .

152, . . . , 15n, respectively.

When the injection screw 3 is rotated in this condition, the plasticized and kneaded molten resin is stored in the front part of the cylinder 1, and the screw 3 is moved backward accordingly. When the amount of molten resin reaches a predetermined amount, the injection hydraulic cylinder 2 is
High pressure oil pressure is applied to the screw 3, and the screw 3 is rapidly driven forward. Thereby, the cavity 6 of the mold 5 is filled with the molten resin.

When such a filling process is completed, the screw 3 reaches a predetermined position. Then, the position is detected by the position detector IO, and the pressure holding process is switched to. Switching to this pressure holding process may be performed by a speed reduction signal of the screw 3 or a pressure signal of the pressure rad 17, etc.

When entering the pressure holding process, first, the output value of the position detector 10 becomes O.
is set, the switch 11 is activated, and the first relay coil 13. Excite. Then, the first relay contact 14. is closed and potentiometer 15. A voltage signal corresponding to the initial holding pressure P1 set to
Sent to 6. As a result, the set pressure of the electromagnetic proportional pressure rfA control valve 8 is switched, and the injection hydraulic cylinder 2
The hydraulic pressure of pressure P is now applied to. This oil pressure is detected by the pressure head 17 and returned to the amplifier 16 for feedback control.

In this way, the magnitude of the initial holding pressure is controlled to PK.

Then, the injection screw 3 is pressed in the forward direction by the holding pressure P1, and gradually moves forward as the resin in the mold cavity 6 cools and contracts. The amount of movement is detected by the position detector 10, and the detected value is input to the switch 11. On the other hand, the value of the screw position interval u/n, which is the set movement amount, is input from the interval setting device 12 to the switching device 11.

When the screw 3 moves and reaches a position where the detected value of the position detector IO and the set value of the interval setter 12 match, the switch 11 switches the first relay coil 13 . The second relay coil 132 is actuated to stop excitation of the relay coil 132 and to excite the second relay coil 132. Thereby, the first relay contact 14
1 is opened, the second relay contact 142 is closed, and a voltage corresponding to the holding pressure P2 set on the potentiometer 152 is sent to the amplifier 16. therefore.

The set pressure of the pressure control valve 8 is switched to P2, and the hydraulic pressure of the holding pressure P2 is applied to the injection hydraulic cylinder 2.

When the cooling contraction of the resin in the mold cavity 6 progresses and the screw 3 further moves by l/n, the position detector 1
The detected value of 0 and the set value of the interval setter 12 match again. Then, the switch 11 is activated to demagnetize the second relay coil 132 and energize the third relay coil 133. As a result, the holding pressure is controlled to the magnitude of P3.

In this way, the holding pressure is successively controlled to a preset magnitude according to the amount of movement of the injection screw 3. Then, when the amount of movement of the screw 3 after entering the pressure holding process reaches a limit, the holding pressure is switched to zero. That is, the pressure holding process is completed.

By performing such control, the holding pressure can be controlled in a stepwise manner as shown by the dotted line in FIG. That is, the holding pressure is controlled in a way that approximates the optimum holding pressure diagram according to the position of the screw 3. If the number of relays 131 to 13n, 141 to 14n and potentiometers 151 to 15n is increased to make the controlled screw position interval finer, control closer to the holding pressure diagram can be performed.

In addition, in the above embodiment, the magnitude of the holding pressure is switched and controlled every time the injection screw 3 moves by a fixed interval, but the position interval of the screw 3 to be controlled can also be made variable. . To do this, all the screw positions at the time points to be controlled can be set in the interval setter 12. If this is done, fine control can be performed in areas where the holding pressure changes sharply, and the holding pressure changes can be controlled finely. In loose areas, it can be controlled at large intervals.

Just by using a certain number of relays and potentiometers,
It becomes possible to perform more accurate control.

Further, as a means for switching the holding pressure, in addition to the contact type relay as in the above embodiment, a non-contact relay or the like can also be used.

(Effects of the Invention) As is clear from the above explanation, according to the present invention, during the pressure holding process, the magnitude of the holding pressure is controlled according to the amount of movement of the injection screw, so that the mold It becomes possible to apply finely controlled holding pressure according to the cooling and solidification state of the resin in the cavity, and it becomes possible to improve the quality of molded products by injection molding.

Therefore, it is extremely useful for precision molding.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a control device for an injection molding machine for implementing the holding pressure control method according to the present invention, and FIG. 2 is a holding pressure diagram for explaining its operation. l...Cylinder 2...Hydraulic cylinder for injection 3...Injection screw 5...Mold 6...
・Cavity 7... Hydraulic source 8... Electromagnetic proportional pressure control valve 10... Position detector 11... Switching device 1
2... Interval setter 13, ~13n... Relay coil 14 current ~14n... Relay contact 15, ~15n... Potency type meter Patent applicant Nikki Steel Co., Ltd. Representative Patent attorney Mori Lower end Yu Figure 2

Claims (1)

[Claims] During the holding pressure process of an injection molding machine, the amount of movement of the injection screw is detected, and each time the screw moves by a preset amount, the holding pressure is increased to a preset value. A method for controlling holding pressure in an injection molding machine, which is characterized by controlling the holding pressure in an injection molding machine.