JP4502669B2 - Injection molding machine and control method thereof - Google Patents

Description

  The present invention relates to an injection molding machine and a control method thereof.

  The molding operation for one cycle of the injection molding machine will be briefly described from the injection device side.

  (1) By rotating the screw with a screw rotating motor, a certain amount is sent to the tip of the heating cylinder, that is, the front of the screw head called a reservoir, while the resin falling from the hopper to the rear of the screw is melted (plasticization) / Weighing process). At this time, the screw moves backward while receiving the pressure (back pressure) of the molten resin accumulated in the reservoir.

  An injection shaft is directly connected to the rear end of the screw, and this injection shaft is rotatably supported. In the case of a hydraulic type, the injection shaft is also driven by a hydraulic drive system having an injection cylinder. On the other hand, in the case of an electric injection device, the injection shaft is driven in the axial direction by an injection motor. The above-mentioned back pressure of the molten resin is detected by a load cell in the case of an electric type, and is detected by an injection pressure sensor that detects a hydraulic pressure in an injection cylinder in the case of a hydraulic type. The back pressure detected in this way is used for pressure control in a closed loop.

  (2) Next, the screw is advanced, the screw head is used as a piston, and the molten resin in the reservoir is fed into the cavity in the mold (filling step).

  (3) At the end of the filling process, the molten resin fills the cavity of the mold, and the control for the screw is switched from speed control to pressure control. This is called V (speed) -P (pressure) switching.

  (4) After VP switching, the resin in the cavity of the mold is cooled under the set pressure (pressure holding step). The resin pressure is controlled in a closed loop as in the above-described back pressure control.

  In the injection apparatus, after the step (4), the process returns to the step (1) and enters the next cycle. On the other hand, on the mold clamping device side, in addition to performing mold opening / closing and mold clamping operations, in parallel with (1), after opening the mold and taking out the product cooled and solidified by the ejector mechanism, the mold is closed. The process (2) is entered.

  FIG. 3A shows the behavior of the screw speed and the injection pressure in the above one cycle, and FIG. 3B shows the behavior of the screw position.

  On the other hand, on the mold clamping device side, the movable mold is held with a certain force against the fixed mold, and in this state, the molten resin is filled into the cavity in the mold by the screw. Then, the screw forward speed is controlled until the molten resin is almost completely filled in the cavity, and then the pressure for pressing the screw is controlled to prevent the resin from contracting by moving to the pressure holding process. become.

  At this time, in the pressure holding process, the screw advance speed becomes slower than the screw advance speed in the previous speed process. Moreover, the increase of the injection pressure is also applied, and the screw may move backward. This is illustrated by the negative screw speed in FIG. When the screw moves backward, the behavior of the check ring that prevents the molten resin in the reservoir from returning to the screw side may become unstable. If the behavior of the check ring becomes unstable, the molten resin is returned to the screw side, and the amount of resin intended by the operator may not be filled in the cavity. In addition, the behavior of the check ring during the pressure holding process varies between shots depending on the state of the measured molten resin. Therefore, the dimension and weight of the molded product also vary.

  Therefore, an object of the present invention is to provide an injection molding machine and a control method therefor that can solve the problem of molding defects caused by the backward movement of the screw during the pressure-holding process.

The control method of the injection molding machine according to the present invention is characterized in that the mold clamping device is controlled so that the screw does not move backward when the molten resin flows backward into the nozzle at the tip of the heating cylinder during the pressure holding process .

In this control method, when the screw reaches the set value of the molten resin filling completion position, the process proceeds to the compression operation of the molten resin filled in the cavity space so as to maintain the position of the screw at the set value. Control.

  In the present control method, the mold clamping force is set to a low value before the molten resin filling is started, or the fixed platen and the movable platen are opened to a predetermined value.

An injection molding machine according to the present invention includes an injection device for rotating, advancing and retracting a screw, a mold clamping device for opening and closing a mold, and clamping, and a screw for detecting the position of the screw. A position sensor; an injection pressure sensor for detecting an injection pressure; a platen distance sensor for detecting a distance between platens between a fixed platen and a movable platen; In an injection molding machine comprising an injection device and a controller for controlling the mold clamping device,
The controller controls the mold clamping device so that the screw does not move backward when the molten resin flows back into the nozzle at the tip of the heating cylinder during the pressure holding process .

In the present injection molding machine, when the screw reaches the set value of the molten resin filling completion position, the controller shifts to the compression operation of the molten resin filled in the cavity space and sets the position of the screw to the set value. Control to maintain.

  In the present injection molding machine, the controller also sets the mold clamping force to a low value before starting the filling of the molten resin, or opens the fixed platen and the movable platen to a predetermined value.

  According to the present invention, since the screw does not move backward in the pressure holding process, the behavior of the check ring is stabilized, and the molten resin is not returned to the screw side, so that the quality of the molded product is improved, for example, the dimensional accuracy is improved. In addition, it is possible to reduce the occurrence of appearance defects (sinks, warpage, etc.). Further, the stress in the mold cavity is made uniform by the compression operation on the mold clamping device side.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view schematically showing an embodiment when the present invention is applied to a hydraulic injection molding machine. In FIG. 1, a fixed mold 12 is attached to the fixed platen 11, and a movable mold 14 is attached to the movable platen 13. A cavity 15 having the shape of a molded product is formed between the fixed mold 12 and the movable mold 14. The resin is heated and melted in the heating cylinder 16.

  A screw 17 is supported in the heating cylinder 16 so as to be rotatable and reciprocated. The molten resin is injected into the cavity 15 by moving the screw 17 forward. Further, the resin that has fallen into the heating cylinder 16 from a hopper (not shown) advances in the outer peripheral groove of the screw 17 as the screw 17 moves backward due to the back pressure described above, and during that time, the shear heat generation and heating of the resin itself occur. It is heated and melted by a heater arranged around the cylinder 16.

  An injection cylinder 18 is disposed at the rear end of the screw 17 and its piston is connected to the screw 17 via an injection shaft. The injection shaft and the screw 17 can rotate, but the piston in the injection cylinder 18 does not rotate. The injection cylinder 18 has two oil chambers with a piston in between. The screw 17 is retracted by supplying hydraulic oil to one oil chamber through an injection servo valve 19 and the hydraulic oil is supplied to the other oil chamber. Thus, the screw 17 can be advanced.

  On the other hand, on the mold clamping device side, the movable platen 13, in other words, the movable mold 14 is brought into contact with and separated from the fixed mold 12 by the drive shafts of the plurality of mold opening / closing cylinders 21a and 21b, and the mold opening / closing is performed. The movable mold 14 is also given a clamping force by a clamping cylinder 22. Reference numeral 23 denotes a mold clamping center rod, and 24 denotes a mechanical lock plate. The mold opening / closing cylinders 21a and 21b also have two oil chambers. By supplying hydraulic oil to one oil chamber via the mold opening / closing servo valve 25, the movable mold 14 is advanced to close the mold, and the other oil chamber is closed. By supplying hydraulic oil to the chamber, the movable mold 14 is moved backward to perform mold opening.

  In the mold clamping cylinder 22, hydraulic oil can enter and exit only through one of the two oil chambers via the mold clamping servo valve 26, and the mold clamping is performed with respect to the movable mold 14 by supplying the hydraulic oil. Giving power.

  Each of the injection servo valve 19, the mold opening / closing servo valve 25, and the mold clamping servo valve 26 is connected to an oil pump 27 serving as a hydraulic pressure supply source and controlled by a controller 30. Reference numeral 28 denotes an accumulator.

  Now, in the injection device, a screw position sensor 31 is provided for detecting a specific position in the movable part as a screw position, and a suck-back pressure sensor 32 is provided in the backward hydraulic pipe, and the forward hydraulic pipe is provided in the forward hydraulic pipe. Are each provided with an injection pressure sensor 33. On the other hand, on the mold clamping device side, a mold clamping pressure sensor 34 is provided in the hydraulic piping for the mold clamping cylinder 22, and the movable platen 13 and the fixed platen 11 are movable by detecting the position of the movable platen 13 in the movable part of the mold part. An inter-platen distance sensor 35 is provided for detecting a distance from the platen 13 (hereinafter referred to as an inter-platen distance).

  By providing the various sensors as described above, the controller 30 controls the injection servo valve 19 by receiving detection signals from the screw position sensor 31, the suck back pressure sensor 32, and the injection pressure sensor 33 on the injection device side. Thus, the screw position, suck back pressure, injection pressure and the like are controlled. On the other hand, on the mold clamping device side, the controller 30 controls the mold opening / closing servo valve 25 and the mold clamping servo valve 26 in response to detection signals from the mold clamping pressure sensor 34 and the platen distance sensor 35 in addition to the above detection signals. Thus, the mold opening / closing position, the mold clamping force, and the like are controlled.

  In the above configuration, the essential requirements for the present invention are as follows. That is, the injection device needs a mechanism capable of screw position control. On the other hand, the mold clamping device needs to be able to change the mold clamping force regardless of the operation of the injection device, and to have high responsiveness when changing the mold clamping force. This is possible in a hydraulic injection molding machine by using a servo valve in the hydraulic control system. Further, it is necessary to have an inter-platen distance sensor 35 for detecting the distance between the movable platen and the fixed platen and to be able to control the position of the movable platen 13.

  Next, the control operation of the controller 30 will be described with reference to FIG.

Prior to the start of filling, the controller 30
1. Keep low clamping force,
2. The movable mold 14 is opened to a predetermined position, that is, the distance between the platens is set to a predetermined value L1.
Set to either state.

  At the start of filling, the screw 17 is driven to move forward. At this time, in the case of the above 1, the mold clamping device is opened in a direction in which the movable mold 14 is separated from the fixed mold 12 due to an increase in injection pressure. That is, the distance between the platens increases. In this process, when the distance between the platens increases and reaches a predetermined value L1, the controller 30 starts position control of the movable platen 13, in other words, the movable mold 14, so as to maintain the predetermined value L1. That is, the controller 30 receives the detection signal from the inter-platen distance sensor 35 and controls the mold clamping servo valve 26 and the mold opening / closing servo valve 25 to drive the mold opening / closing cylinders 21a, 21b to perform the above-described position control. . The position control for maintaining the predetermined value L1 is the same as in the above case 2.

  Subsequently, the controller 30 receives the detection signal from the screw position sensor 31, and when the screw 17 moves forward to the set value of the filling completion position (position where the cavity 15 is almost completely filled) P1 (t1 in FIG. 2b), The screw position control is started so that the speed control of the screw 17 is stopped and the screw 17 maintains the set value P1 of the filling completion position. At the same time or after the delay timer has been counted up, the controller 30 causes the mold clamping device to perform a compression operation by any one of the following control methods, and realizes the same effect as the conventional pressure holding. The delay timer is built in the controller 30 and is appropriately set according to the molding conditions.

A) Control of mold clamping force B) Control of distance between platens C) Control of injection pressure Control of mold clamping force is performed by controlling the mold clamping servo valve 26 in response to a detection signal from the mold clamping pressure sensor 34. In this method, the clamping force is controlled by driving the clamping cylinder 22. Further, the control of the distance between the platens is performed so that the distance between the platens is maintained at L2 by receiving the detection signal of the distance sensor 35 between the platens and controlling the mold clamping servo valve 26 and the mold opening / closing servo valve 25. Is the method. On the other hand, regarding the control of the injection pressure, the injection pressure increases because the molten resin in the mold cavity, runner, and sprue flows back into the nozzle at the tip of the heating cylinder 16 by the high-speed compression operation of the mold clamping device. By detecting this with the injection pressure sensor 33 and controlling the mold clamping servo valve 26, it becomes possible to control the mold clamping apparatus. This can be realized by using a servo valve capable of high-speed response in the hydraulic control system of the mold clamping device.

  As described above, in this embodiment, when the screw reaches the filling completion position, the screw is maintained at that position, and the mold clamping device side controls the mold clamping force, the distance between the platens, and the injection pressure. By performing the compression operation, it is possible to prevent molding defects caused by the retreat of the screw during the pressure holding process.

  In addition, although said form is a case of a hydraulic injection molding machine, it cannot be overemphasized that this invention can be applied also to an electric injection molding machine. The difference in this case is that an injection motor is used instead of the injection cylinder, and a mold clamping motor is used on the mold clamping device side instead of the mold clamping cylinder and mold opening / closing cylinder, for example, an injection motor, Only the mold clamping motors are controlled.

It is the figure which showed schematically embodiment at the time of applying this invention to a hydraulic injection molding machine. It is the figure which showed the behavior (a) of the screw speed and injection pressure in the shaping | molding cycle by this invention, the behavior (b) of a screw position, and the behavior (c) of the distance between platens. It is the figure which showed the behavior (a) of the screw speed and the injection pressure in the conventional molding cycle, and the behavior (b) of the screw position.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Fixed platen 12 Fixed mold 13 Movable platen 14 Movable mold 16 Heating cylinder 17 Screw 18 Injection cylinder 19 Injection servo valve 21a, 21b Mold opening / closing cylinder 22 Mold clamping cylinder 23 Mold clamping center rod 24 Mechanical lock plate 25 Mold opening / closing servo valve 26 Clamping Servo Valve 27 Oil Pump 28 Accumulator 31 Screw Position Sensor 32 Suckback Pressure Sensor 33 Injection Pressure Sensor 34 Clamping Pressure Sensor 35 Platen Distance Sensor

Claims (6)

A method for controlling an injection molding machine, comprising: controlling a mold clamping device so that a screw does not move backward when molten resin flows back into a nozzle at the tip of a heating cylinder during a pressure holding process . 2. The control method according to claim 1, wherein when the screw reaches a set value of a molten resin filling completion position, the operation shifts to a compressing operation of the molten resin filled in a cavity space, and the screw position is set to the set value. A control method for an injection molding machine, wherein control is performed so as to maintain. The control method according to claim 1 or 2, to keep in a state between opened to a predetermined value with or fixed platen and the movable platen before starting filling of molten resin keep the mold clamping force to a low value A method for controlling an injection molding machine. An injection device for rotating the screw and moving forward and backward, a mold clamping device for opening and closing the mold, and clamping, a screw position sensor for detecting the position of the screw, and detecting an injection pressure An injection pressure sensor for detecting the platen distance between the fixed platen and the movable platen, and the injection device and the mold clamping device in response to detection signals from the sensors. In an injection molding machine equipped with a controller to control,
The controller controls the mold clamping device so that the screw does not move backward when the molten resin flows back into the nozzle at the tip of the heating cylinder during the pressure holding process . 5. The injection molding machine according to claim 4, wherein when the screw reaches a set value of a molten resin filling completion position, the controller shifts to a compression operation of the molten resin filled in the cavity space to position the screw. Is controlled so as to be maintained at the set value. In the injection molding machine according to claim 4 or 5, wherein the controller is filled before starting molten resin is opened between the mold clamping force or fixed platen and the movable platen keep to a low value to a predetermined value An injection molding machine characterized by being in a state.

Images