JP3057456B2 - Injection holding pressure control method for injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection holding pressure control method for an injection molding machine, and aims at eliminating an inertia force due to an injection speed and smoothly switching from an injection stroke to a pressure holding stroke. .

[0002]

2. Description of the Related Art In a conventional injection molding machine, as shown in FIG. 3, a hydraulic circuit for switching and controlling the injection speed and the injection pressure in multiple stages at a predetermined position of the screw 2 from the injection stroke to the pressure-holding stroke is shown. And a meter-in circuit comprising an electromagnetic flow regulating valve 6 and an electromagnetic pressure regulating valve 7 at the inlet side of the injection cylinder 1. The method includes a control device 11 for the entire stroke including the injection stroke and the pressure-holding stroke. Of the multi-stage injection control signal sent from the
, So that it was controlled in multiple stages.

[0003]

However, in the case of such a conventional method in which the injection speed and the injection pressure from the injection stroke to the pressure-holding stroke are switched by the meter-in control circuit, 1. The piston rod of the screw or the injection cylinder is used. In the movement, the higher the injection speed, the greater the inertia force,
There was a large difference between the set value and the actual injection speed immediately after switching. 2. The injection speed is controlled by the load at which the molten resin is injected from the nozzle, but the load fluctuates due to a difference in flow resistance such as a change in viscosity of the molten resin. Therefore, it is very difficult to always control the inertia force to be constant, and the screw forward speed immediately after switching from injection to holding pressure has a difference between the set value and the measured value. Also fluctuated depending on the environment. An object of the present invention is to solve such a problem.

[0004]

SUMMARY OF THE INVENTION The present invention relates to an electromagnetic flow control valve 6 provided on the inlet side of an injection cylinder 1 of an injection molding machine.
And an electromagnetic pressure adjusting valve 7, in which the injection speed and the injection pressure are switched in multiple stages at a predetermined position of the screw 2 from the injection stroke to the pressure-holding stroke. At a stage (n-1st stage) immediately before the final stage (nth stage) of the injection stroke, which is a pressure switching point, the direction switching valve 8 provided on the exit side of the injection cylinder 1 of the injection molding machine is operated. The above problem is caused by switching from the injection stroke to the pressure-holding stroke while controlling the injection pressure by the differential pressure between the pressure generated by the electromagnetic pressure control valve 9 and the pressure generated by the electromagnetic pressure control valve 7. Solve.

[0005]

By applying a back pressure when the screw 2 advances, the injection speed can be controlled without being affected by the inertial force. That is, immediately after the position switching of the screw 2, the actual injection speed and the injection speed of the control value have an error due to the influence of the previous injection speed. This is because the fluctuation occurs due to uncertainties such as the weight of the piston rod of the injection cylinder 1 and the screw 2, the sliding resistance, and the flow resistance of the molten resin.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A control method for switching from an injection stroke to a pressure-holding stroke of an injection molding machine according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a hydraulic system diagram for performing control when switching from the injection stroke to the pressure-holding stroke of the injection molding machine according to the present invention.
FIG. 2 is a diagram showing the switching positions of the screw injection speed and the injection pressure in the injection holding pressure stroke. As is clear from FIG. 1, in FIG. 1, an electromagnetic flow regulating valve 6 and an electromagnetic pressure regulating valve 7 are provided in the X-chamber inlet side pipe of the injection cylinder 1. Similarly, a direction switching valve 8 is provided in the Y-chamber outlet side pipe of the injection cylinder 1, and the passage is normally closed. It returns to the hydraulic tank via a circuit having the regulating valve 9 and the fixed throttle valve 10, or returns directly to the hydraulic tank at the position A. Various control signals are sent from the control device 11 to the electromagnetic flow control valve 6, the electromagnetic pressure control valve 7, the direction switching valve 8, and the electromagnetic flow control valve 9.

[0007] The screw 2 is disposed inside the cylinder barrel 3, and a nozzle 4 is disposed at the tip of the cylinder barrel 3. Next, the operation of the injection holding pressure control method in the injection molding machine configured as described above will be described. As shown in FIG. 2, the injection speed and the injection pressure of the screw 2 are sequentially controlled at each position of the first stage, the second stage,... In accordance with the position switching signal of the screw 2 together with the injection start signal. In general, the injection speed and the injection pressure are controlled in multiple stages. If the number of control stages is n, the control is shifted from the injection to the holding pressure at the n-th stage, and at the same time, is changed from the flow control to the pressure control.

Here, the direction switching valve 8 is operated to the position B by the screw position switching signal of the (n-1) th stage, and the pressure generated by the electromagnetic flow control valve 9 and the pressure generated by the electromagnetic pressure control valve 7 are generated. N from the (n-1) th stage due to the pressure difference
By controlling the injection pressure of the screw 1 up to the stage, the uncertainty of the flow resistance of the resin immediately after switching from the n-th stage injection to the holding pressure, and the uncertainty of the sliding resistance of the injection cylinder and the piston rod. The instability of the inertia force of the screw advance caused by the nature is eliminated. Thereby, the same control as the control value and the actual value can be achieved, stable reproducibility of molding conditions can be obtained, and control advantageous for precision molding can be performed.

[0009]

As is apparent from the above description, the injection holding pressure control method in the injection molding machine according to the present invention is capable of controlling the injection speed to the variation of the inertial force, the fluctuation of the flow resistance, and the uncertainty of the sliding resistance. Precise control can be performed without being affected, and precise molding conditions can be ensured.

[Brief description of the drawings]

FIG. 1 is a hydraulic system diagram for performing control when switching from an injection stroke to a pressure-holding stroke of an injection molding machine according to the present invention.

FIG. 2 is a diagram showing switching positions of an injection speed and an injection pressure in an injection holding pressure stroke.

FIG. 3 is a hydraulic system diagram for performing control when switching from an injection stroke to a pressure-holding stroke of a conventional injection molding machine.

[Explanation of symbols]

 1 ... Injection cylinder 2 ... Screw 3 ... Cylinder barrel 4 ... Nozzle 5 ... Hydraulic motor 6 ... Electromagnetic flow control valve 7 ... Electromagnetic Pressure regulating valve 8 ... Directional switching valve 9 ... Electromagnetic flow regulating valve 10 ... Fixed throttle valve 11 ... Control device 12 ... Directional switching valve 13 ... Fixed throttle valve

Claims (1)

(57) [Claims] An electromagnetic flow control valve (6) and an electromagnetic pressure control valve (7) provided on the inlet side of an injection cylinder (1) of an injection molding machine, a screw (2) from an injection stroke to a pressure-holding stroke. In the injection holding pressure control method for an injection molding machine, in which the injection speed and the injection pressure are switched and controlled in multiple stages at the position specified in ()), the final stage (n-th stage) of the injection stroke which is the holding pressure switching point
In the previous stage (n-1st stage), the directional control valve (8) provided on the exit side of the injection cylinder (1) of the injection molding machine is actuated and generated by the electromagnetic pressure regulating valve (9). Holding pressure in an injection molding machine, wherein switching from the injection stroke to the holding pressure stroke is performed while controlling the injection pressure by a differential pressure between the pressure thus generated and the pressure generated by the electromagnetic pressure regulating valve (7). Control method.