JPH0441894B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a method for controlling an injection molding machine.

(b) Conventional technology In injection molding, a pressure holding process is performed following the filling process. At that time, the first stage pressure of the pressure holding step may be set to a value significantly smaller than the filling pressure. This occurs when the projected area is large, such as a disc-shaped molded product, so there is not enough room for clamping force and burrs are likely to occur, or when the mold structure is complex and has small-diameter pins, etc., making it easy to break. This is to prevent the occurrence of burrs, overfilling, etc., by setting the first stage pressure of the pressure holding step low in cases such as cases.
The first stage pressure of the pressure holding process is maintained for a predetermined time after switching from the filling process to the pressure holding process, and then the pressure holding process is controlled in multiple stages below the second stage pressure.
The pressure in each stage below the second stage is also maintained for a preset time.

(c) Problems to be solved by the invention However, in the conventional control as described above, the first stage pressure is held for a preset period of time, so the pressure is changed from the first stage pressure to the second stage pressure. There is a problem in that the position of the screw changes when switching to. In other words, the first stage pressure in the pressure holding process is set to a value significantly lower than the filling pressure, so the screw is pushed back by the resin pressure in the filled mold, but this occurs within the set time. The amount of retraction of the screw is determined by the uneven kneading of the resin material.
It changes for each shot due to changes in the filling state due to changes in mold temperature. As a result, molding conditions become unstable, such as increased variation in weight of molded products. The present invention aims to solve these problems.

(d) Means for Solving the Problems The present invention solves the above problems by switching from the first stage pressure to the second stage pressure in the pressure holding process with reference to the position of the screw. That is, in the method for controlling an injection molding machine according to the present invention, the first stage pressure of the holding pressure step is maintained until the screw retreats to a predetermined position,
After the screw has retreated to a predetermined position, a pressure holding step is performed by maintaining the pressure equal to or lower than the second stage pressure of the pressure holding step for a set time for each stage.

(e) Operation When the filling process is completed, the pressure holding process is started by a predetermined pressure holding switching signal, and the first stage pressure is first applied. Since this first stage pressure is set lower than the filling pressure, the screw is retracted by the resin pressure. When the screw is retracted to a preset position, the state is switched to applying the second stage pressure. The state in which the second stage pressure is applied is maintained for a preset time. Each of the third and subsequent stages of the pressure holding process is also held for a predetermined set time. As a result, the amount of retraction of the screw that occurs when changing the holding pressure is always constant, and stable molding can be performed.

(f) Example FIG. 1 shows an apparatus for carrying out the method of the present invention. A screw 12 is provided within the cylinder 10 so as to be rotatable and movable in the axial direction. Screw 1
2 is connected to a piston 16 of an injection cylinder 14 by a piston rod 18, whereby the axial position of the screw 12 is controlled.
Note that illustration of a mechanism for rotationally driving the screw 12 is omitted. The bracket 20 is moved axially together with the piston rod 18.
is provided, and a screw position detector 22 is provided thereto. As a result, Screw 1
2 positions can be detected. A signal indicating the position of the screw 12 detected by the screw position detector 22 is input to the control device 24 . The operating pressure of the injection cylinder 14 is the discharge pressure of the oil pump 26, which is controlled by the electromagnetic pressure control valve 28 and the electromagnetic flow control valve 3.
0. The operation of the electromagnetic pressure control valve 28 and the electromagnetic flow control valve 30 is controlled based on signals from the control device 24. A setting signal from a condition setting device 32 is also input to the control device 24 . The condition setting device 32 includes a screw retraction setting device 34 and an injection speed switching position setting device group 36.
₍₁₎ to 36 _(o) , speed setting device group 38 ₍₁₎ to 38 _(o-1) , holding pressure setting device group 40 ₍₁₎ to 40 _(n) , holding pressure time setting device group 42 _{(2 )} to 42 _(n) and a filling pressure setting device 44. The screw retraction amount setting device 34 is a setting device that sets the amount of retraction of the screw 12 from the time of pressure holding switching. Injection speed switching position setter group 3
6 ₍₁₎ to 36 _(o) are setting devices for setting the position at which the injection speed should be changed during the filling process. Speed setting device groups 38 ₍₁₎ to 38 _(o-1) are setting devices for setting the injection speed of each stroke divided and set by injection speed switching position setting device groups 36 ₍₁₎ to 36 _(o). It is. The holding pressure setter group 40 ₍₁₎ to 40 _(n) is a setter that sets the holding pressure of each stage in the holding pressure process. The holding pressure setting device groups 42 ₍₂₎ to 42 _(n) are setting devices for setting the pressure holding time of each pressure set by the holding pressure setting device groups 40 ₍₂₎ to 40 _(n). be. The filling pressure setting device 44 is a setting device that sets the maximum pressure in the filling process.

Next, the operation of this embodiment will be explained. Before starting the filling process, a predetermined amount of resin material is kneaded and plasticized by the rotation of the screw 12.
The screw 12 retreats (moves to the right in FIG. 1) due to the pressure of the molten resin that accumulates on the tip side.
It comes to the position set by the injection speed switching position setter 36 _(o) and stops. That is, the injection speed switching position setter 36 _(o) also serves as a setter for the measured value of the molten resin. When the screw 12 is retracted to the position set by the injection speed switching position setter 36 _(o) , the filling process is started. That is, the electromagnetic pressure control valve 28 is activated by a signal from the control device 24.
Then, the electromagnetic flow control valve 30 is operated, hydraulic oil is sent to the injection cylinder 14, and the screw 12 moves forward. At that time, the speed of the screw 12 is determined by the speed setting device group 38 for each stroke separated by the injection speed switching position setting device group 36 _(o) to 36 _(1).
(o-1) ~38 Move forward at the speed set by ₍₁₎ . By doing this, when the screw 12 reaches the position set by the injection speed switching position setter 36 ₍₁₎ (the filling pressure at this time will be equal to P ₀ set by the filling pressure setter). 2), a signal is output from the control device 24 and the pressure holding process is started. That is, the control device 24 controls the first stage pressure set by the holding pressure setting device 40 _(1).
The operation of the electromagnetic pressure control valve 28 and electromagnetic flow control valve 30 is controlled so that P ₁ is achieved. This first stage pressure
Since P ₁ is set to be much smaller than the above-mentioned filling pressure P ₀ , the screw 12 is pushed back by the resin pressure on the mold side. When the retraction amount of the screw 12 matches the setting value of the screw retraction amount setting device 34, the control device 24 sets the holding pressure to the second stage pressure P ₂ set by the holding pressure setting device 40 _(2). The operation of the electromagnetic pressure control valve 28 and the electromagnetic flow control valve 30 is controlled so that the electromagnetic pressure control valve 28 and the electromagnetic flow control valve 30 are After this state of the second stage pressure P ₂ continues for the time set by the holding pressure setting device 42 ₍₂₎ , the third stage pressure set by the holding pressure setting device 40 ₍₃₎ is reached. _P3 , and this is held for the time set by the pressure holding time setting device 42 ₍₃₎ . Thereafter, in the same manner, the m-th stage pressure P _n set by the holding pressure setting device 40 _(n) is held for the time set by the holding pressure setting device 42 _(n). At this point, the pressure holding process ends. As described above, the first stage pressure P ₁ set by the holding pressure setting device 40 ₍₁₎ is not controlled based on time, but based on the amount of retraction of the screw 12. Therefore, even if variations in the kneading state of the resin material, variations in mold temperature, etc. occur, switching to the second stage pressure _P2 is always performed at the same retracted position of the screw 12. As a result, stable molding can be performed at all times, and variations in the weight of molded products can be reduced.

In this embodiment, the switching from the filling process to the pressure holding process was performed based on the position signal of the screw 12, but the pressure holding process could also be changed using the speed signal of the screw 12, the oil pressure signal of the injection cylinder 14, etc. However, the present invention can be practiced similarly. In addition, in this embodiment, the screw 1
2 is controlled by the injection cylinder 14, but this is an electric injection molding machine in which injection control is performed by converting the rotational force of the electric motor into linear force using a ball screw mechanism or the like. It is also clear that similar control can be performed by controlling the torque and rotational speed of the electric motor.

(G) Effects of the Invention As explained above, according to the present invention, the first stage pressure of the holding pressure process is maintained until the screw retreats to a predetermined position, so that the pressure generated at the time of switching the holding pressure can be reduced. The amount of screw retraction can be kept constant at all times, resulting in the effect that stable molding is possible.

[Brief explanation of the drawing]

FIG. 1 shows an apparatus for carrying out the method of the invention. 10...Cylinder, 12...Screw, 14
... Injection cylinder, 22 ... Screw position detector, 24 ... Control device, 28 ... Electromagnetic pressure control valve, 30 ... Electromagnetic flow control valve, 32 ... Condition setting device, 34 ... Screw retraction amount setting device , 36 ₍₁₎
~36 _(o) ... Injection speed switching position setter group, 38 ₍₁₎
~36 _(o-1) ... speed setting device group, 40 ₍₁₎ ~40 _(n) ...
... Holding pressure setting device group, 42 ₍₂₎ to 42 _(n) ... Holding pressure setting device group.

Claims (1)

[Claims] 1. Injection where the screw retreats immediately after switching from the filling process to the holding process because the first stage pressure of the holding process is set lower than the pressure during the filling process. In a method of controlling a molding machine, the first stage pressure of the pressure holding process is maintained until the screw retreats to a preset predetermined position, and after the screw retreats to the predetermined position, the pressure of the second stage of the pressure holding process is maintained or lower. A control method for an injection molding machine, characterized in that a pressure is maintained at each stage for a set time to perform a pressure holding process.