JPH0516200A - Method for controlling injection of injection molding machine - Google Patents

Abstract

PURPOSE:To manufacture a molded item of good quality by a method wherein a pressure control valve is provided between a flow rate control valve communicating with a hydraulic pump and an injection cylinder and the flow rate control valve and the pressure control valve are successively actuated and controlled in a section from the initial stage of the injection process to the dwelling pressure switching point. CONSTITUTION:A hydraulic oil from a hydraulic pump 1 or an accumulator is fed in an injection cylinder 5 through a flow rate control valve 3 and injection is performed. In this case, a pressure control valve 6 is provided between the flow rate control valve 3 and the injection cylinder 5. In the first section, injection and filling process is performed by means of the flow rate control valve 3 based on a speed set in accordance with the advancing position of a piston rod 5a in the injection cylinder 5 regardless of the loading pressure. On the other hand, in the second section, the injection and filling process is performed by means of the pressure control valve 6 based on a preferable filling pressure set in accordance with the advancing position of a piston rod 5a. The filling pressure at the last stage of the injection and filling process and the time for being settled to a set dwelling valve are respectively stabilized thereby.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection control method for an injection molding machine using an injection cylinder (hydraulic cylinder) as an injection actuator.

[0002]

2. Description of the Related Art In this type of hydraulically driven injection molding machine, a mold clamping cylinder (hydraulic cylinder) is used to perform mold clamping, and the injection cylinder (hydraulic cylinder) clamps molten resin at an appropriate injection timing thereafter. The molding space (cavity) in the mold is injected and filled.

FIG. 4 is a diagram showing a hydraulic circuit of an injection cylinder system of such a conventional injection molding machine. In FIG. 4, 1 is a hydraulic pump, 2 is a pressure control valve (electromagnetic proportional relief valve), 3 is a hydraulic pump.
Is a flow control valve, 4 is a direction switching valve, and 5 is an injection cylinder (hydraulic cylinder). The piston rod 5a of the injection cylinder 5 is connected to the root portion of the screw arranged in the heating cylinder through a connecting means as is well known, although not shown in the in-line screw type injection molding machine. Has been done.

In the structure shown in FIG. 4, the directional valve 4 is switched from the neutral position to the left position at a predetermined time after the completion of mold clamping, and the pressure oil from the hydraulic pump 1 is injected into the injection cylinder. 5 is supplied to the advancing oil chamber 5, and thereby the screw (not shown) is integrally advanced together with the piston rod 5a, and molten resin is also clamped from the nozzle at the tip of the heating cylinder (not shown). It is injected and filled in the cavity (molding space). Then, when the molten resin is completely filled in the cavity by the injection / filling process (primary injection process) by the screw forward movement, the known pressure holding process (secondary injection process) is switched to and the cavity is pressed by the screw pressing force. A predetermined holding pressure is applied to the molten resin so as to compensate for shrinkage and the like accompanying the cooling and solidification of the resin.

By the way, during the above-mentioned injection / filling process (primary injection process), the injection speed is often emphasized in order to prevent jetting or the like and perform good injection / filling in accordance with the shape of the mold. Therefore, during the injection / filling stroke period, the screw (the piston rod 5 of the injection cylinder 5
The injection speed is controlled by the flow rate control valve 3 so as to follow the set speed set according to the forward movement position (stroke) of a). Further, since the pressure holding process emphasizes the pressure control, after the known pressure holding switching point, the pressure control according to the time is performed by the pressure control valve 2.

FIG. 5 is a graph showing the relationship between the injection speed and the load pressure (pressure in the advancing oil chamber of the injection cylinder 5) when injection is performed with the configuration of FIG. As shown in the figure, since the speed control is performed during the injection / filling stroke period, the actual measurement data of the speed shows a characteristic curve substantially following the set value as shown by the solid line in the figure. On the other hand, since the speed control is prioritized during the injection / filling stroke period in this manner, in other words, the speed control is performed by the position regardless of the load pressure. Therefore, as shown in FIG.
During filling, even if the upstream pressure (primary pressure) of the flow control valve 3 is considerably higher than the downstream pressure (secondary pressure) (even if the so-called differential pressure is increased), the load pressure is injected.・ Although the optimum filling pressure during the filling process is not exceeded, the load reaction force (resin pressure) increases before the completion of filling when the resin has spread (clogged) into the cavity, so the load pressure increases rapidly. It exceeds the optimum filling pressure during the injection / filling process. That is, during the injection / filling stroke period, control is performed by giving priority to speed, so that the control method cannot accurately control the load pressure.

[0007]

In the prior art of FIG. 4 described above, the load pressure cannot be accurately controlled during the injection / filling stroke period, so that the load pressure is not stable and has a significant effect on the quality of the molded product. There is a problem that the filling pressure at the end of the injection / filling process and the initial stage of the pressure holding process that gives the pressure are not stable, and the density of the molded product tends to vary. Particularly, when the charge amount, the resin temperature, etc. change, the filling pressure fluctuates easily, and this tendency becomes remarkable. Further, in the above-described conventional technique of FIG. 4, since the load pressure greatly exceeds the optimum filling pressure in the vicinity of the holding pressure switching point, the filling pressure becomes excessive and burrs are likely to occur in the molded product, and Since the density of the portion near the gate becomes excessive, warpage is liable to occur, and there is a problem that defective products such as burrs and warps occur. This is remarkable as the differential pressure between the upstream side and the downstream side of the flow rate control valve 3 is set to be large in order to perform high-speed injection. Further, since the load pressure greatly exceeds the optimum filling pressure in the vicinity of the holding pressure switching point, the time T ₂ from the start of the holding pressure process until the load pressure reaches the holding pressure set value is relatively large and unstable. Therefore, also in this respect, there is a problem that the quality of the molded product is adversely affected.

The present invention has been made in view of the above points,
The purpose is to ensure that the filling pressure at the end of the injection / filling process is stable and does not exceed the appropriate value even when it approaches the completion of filling. An object of the present invention is to provide an injection control method for an injection molding machine in which the time until settling down is stable and a molded product of good quality can be manufactured.

[0009]

In order to achieve the above object, the present invention provides an injection molding machine for supplying pressure oil from a hydraulic pump or an accumulator to an injection cylinder via a flow control valve for injection. In the control method, a pressure control valve is provided in an oil passage between the flow rate control valve and the injection cylinder, and a section from the initial injection stroke to the holding pressure switching point is followed by a first injection / filling stroke section. Second shot
In the first injection / filling stroke section, injection is performed by speed control by the flow rate control valve based on the speed set according to the forward position of the piston rod of the injection cylinder in the first injection / filling stroke section. A pressure control by the pressure control valve, which executes a filling stroke and is based on a suitable filling pressure set according to the forward position of the piston rod of the injection cylinder, regardless of the speed in the second injection / filling section. The injection / filling process is executed.

[0010]

In the oil passage between the flow control valve and the injection cylinder, that is, the oil passage on the downstream side (secondary side) of the flow control valve, the oil pressure (load pressure) supplied to the injection cylinder is controlled. A pressure control valve including an electromagnetic proportional relief valve is provided. Then, the section from the initial injection stroke to the holding pressure switching point, in other words, the injection / fill stroke section, which is the primary injection stroke section, is defined as the first injection / fill stroke section and the second injection / fill zone subsequent thereto. In the first injection / filling stroke section, the injection / filling stroke is executed by the speed control by the flow rate control valve based on the speed set according to the forward position of the piston rod of the injection cylinder, regardless of the load pressure. .. As a result, accurate injection speed control is performed in the first injection / filling stroke section, and good molten resin filling speed control can be achieved according to the mold shape (product shape), and jetting etc. can be reliably generated. Be restrained by. Also, in this first injection / filling stroke section,
Of course, multistage control of the injection speed is also possible.

On the other hand, in the second injection / filling section, regardless of the speed, the injection / filling stroke is performed by the pressure control by the pressure control valve based on the suitable filling pressure set according to the advance position of the piston rod of the cylinder. Run.
As a result, in the second injection / filling section, injection / filling is performed based on pressure control so that the hydraulic pressure (load pressure) supplied to the injection cylinder matches the set optimum filling pressure, and the inside of the cavity is filled. Even if the load reaction force (resin pressure) increases before the completion of filling where the resin has spread (clogged), the hydraulic pressure (load pressure) supplied to the injection cylinder does not exceed the optimum filling pressure. It Therefore, the final filling pressure in the injection / filling process is stable, and the time from the beginning of the holding process to the set pressure is stable,
Further, since the load pressure does not exceed the optimum filling pressure, the density of the molded product is generally stable, the occurrence of burrs and warps can be suppressed as much as possible, and the quality of the molded product is improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is an explanatory diagram showing a hydraulic circuit of an injection cylinder system of an injection molding machine according to this embodiment, and FIG. 2 is an injection speed and a load pressure (for advancing the injection cylinder 5) during an injection / filling process and a pressure-holding process. It is a graph showing the relationship with the pressure of the oil chamber).

In FIG. 1, 1, 2, 3, 4, 5, 5a
Is a hydraulic pump, a pressure control valve (electromagnetic proportional relief valve), a flow control valve, a direction switching valve, an injection cylinder (hydraulic cylinder), and a piston rod, which are equivalent to the configuration of FIG. 4, respectively, and 6 is a flow control valve. 3 and the forward oil chamber of the injection cylinder 5 (downstream oil passage as viewed from the flow control valve 3)
Is a pressure control valve made up of an electromagnetic proportional relief valve installed at 1, and 7 is an injection stroke detection sensor (for example, an encoder) that detects the position of the piston rod 5a.

The above-mentioned electromagnetic control valve groups 2, 3, 4, 6 are
A microcomputer (not shown) that controls the entire machine is independently controlled via driver circuits as appropriate, and the speed (speed) of the flow rate control valve 3 is controlled according to a command from the microcomputer. Flow rate) and the hydraulic pressure upper limit value by the pressure control valves 2 and 6 can be variably set, and the switching position of the direction switching valve 4 can be selected. The measurement data from the injection stroke detection sensor 7 is taken in by the above-mentioned microcomputer so that the injection stroke (position) can be recognized.

Here, in this embodiment, since the pressure control valve 6 is added to and installed in the oil passage between the flow control valve 3 and the advancing oil chamber of the injection cylinder 5, the flow control valve 3 When the injection / filling control prioritizing the speed due to the pressure is not performed, the flow rate control valve 3 is set to an open state with a predetermined valve opening degree, so that the hydraulic pressure in accordance with the hydraulic pressure upper limit regulation value variably set by the pressure control valve 6 is set. It is possible to perform injection / filling control with priority given to (load pressure). On the other hand, when the injection / filling control that prioritizes the hydraulic pressure (load pressure) by the pressure control valve 6 is not performed, it depends on the flow rate of the flow rate control valve 3 as long as the hydraulic pressure upper limit value set in the pressure control valve 6 is not exceeded. It is possible to perform injection / filling control that prioritizes the speed at which the

In the above structure, the directional switching valve 4 is switched from the neutral position to the left position at a timing after a predetermined time has elapsed after the completion of mold clamping, and the pressure oil from the hydraulic pump 1 is injected into the injection cylinder 5. Is supplied to the forward advancing oil chamber, whereby the screw (not shown) is integrally advanced together with the piston rod 5a, and the molten resin is also blown between the die clamped from the nozzle at the tip of the heating cylinder (not shown). The cavity (molding space) begins to be injected and filled. From the start of this injection until the piston rod 5a reaches a position before the holding pressure switching point by a predetermined amount (the first in the injection / filling stroke section).
(In the injection / filling stroke section), the upper limit value of the pressure control valve 6 is set to a large value that does not affect the speed control. Based on the set injection speed value set by the above, the microcomputer controls the flow rate control valve 3 to execute the injection / filling stroke in which the injection speed is prioritized. That is, as shown in FIG. 2, in the first injection / filling stroke section, regardless of the load pressure, the injection / injection is performed by speed control by the flow rate control valve 3 based on the set speed.
A filling process is performed to stabilize the injection speed, achieve a good molten resin filling speed control according to the mold shape (product shape), and reliably prevent jetting. ..

Next, the injection / filling stroke (primary injection stroke) proceeds and the piston rod 5a reaches the end position of the first injection / filling stroke section (second injection / filling stroke section). When the start stroke position is reached) is recognized by the injection stroke detection sensor 7, the upper limit regulation value by the pressure control valve 6 is switched to a value equal to the optimum filling pressure by the command of the microcomputer, and Flow control valve 3
The flow rate control by is stopped and the flow rate control valve 3 is placed in an open state in which a constant flow rate is flowed. Then, in the second injection / filling stroke section following the first injection / filling stroke section, the microcomputer is operated based on the position detection information by the injection stroke detection sensor 7 and the set pressure value set according to the position. The pressure control valve 6 is controlled to execute an injection / filling process in which load pressure (filling pressure as injection pressure) is prioritized. That is, as shown in FIG. 2, in the second injection / filling stroke section, the injection / filling stroke is controlled by the load pressure control by the pressure control valve 6 whose upper limit regulation value is set to the optimum filling pressure, regardless of the injection speed. Run it
At the end of the filling stroke (primary injection stroke), the load pressure does not exceed the optimum filling pressure, and the load pressure is made to match the optimum filling pressure to maintain a stable filling pressure. In addition,
Since such load pressure priority control is performed, the injection speed is slightly reduced in the form of being pulled by the load pressure before the holding pressure switching point.

When the injection stroke detection sensor 7 recognizes that the piston rod 5a has reached the end position of the second injection / filling stroke section (reached the holding pressure switching point), The microcomputer enters the pressure-holding process in which the pressure control valve 6 controls the pressure according to time, and the pressure-holding process is executed for a predetermined time by setting the upper limit value of the pressure control valve 6 to the pressure-holding set value. At this time, since the load pressure at the holding pressure switching point is constant at the optimum filling pressure, the time T ₁ from the start of the holding pressure process until the load pressure reaches the holding pressure set value T ₁
Is more stable and shorter than the conventional one.

As described above, in this embodiment, accurate injection speed control is performed in the first injection / filling stroke section, and good molten resin filling speed control according to the mold shape (product shape) can be performed. This can be achieved and the occurrence of jetting, etc. can be reliably suppressed. In addition, the second injection
Since the load pressure is prioritized and controlled in the filling stroke section, even if the filling pressure at the end of the injection and filling stroke is stable and approaches the completion of filling, the filling pressure does not exceed the appropriate value, and the holding pressure is maintained. The time from the beginning of the process until the holding pressure setting value is settled down is stable, and as a whole, the density of the molded product is stable, and it is possible to manufacture a good molded product without warpage and burrs.

In the above embodiment, a hydraulic pump is used as a pressure oil supply source for injection, but as shown in FIG. 3, it is suitable for high-speed injection as a pressure oil supply source dedicated to injection. It is obvious to those skilled in the art that the accumulator 8 can be substituted.

[0021]

As described above, according to the present invention, even when the filling pressure at the final stage of the injection / filling process is stable and approaches the completion of filling, the filling pressure does not exceed the appropriate value, and the initial holding process is performed. The time from entering the pressure to the holding pressure setting value is stable,
It is possible to provide an injection control method of an injection molding machine capable of producing a molded product of good quality, and the value is great in the seed injection molding machine.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a hydraulic circuit of an injection cylinder system of an injection molding machine according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between an injection speed and a load pressure during an injection / filling process and a pressure-holding process according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a hydraulic circuit of an injection cylinder system of an injection molding machine according to another embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a hydraulic circuit of an injection cylinder system of an injection molding machine according to a conventional example.

FIG. 5 is a graph showing the relationship between the injection speed and the load pressure during the conventional injection / filling process and pressure-holding process.

[Explanation of symbols]

 1 Hydraulic Pump 2 Pressure Control Valve 3 Flow Control Valve 4 Direction Switching Valve 5 Injection Cylinder 5a Piston Rod 6 Pressure Control Valve 7 Injection Stroke Detection Sensor 8 Accumulator

Claims (1)

Claim: What is claimed is: 1. An injection control method for an injection molding machine, comprising: supplying pressure oil from a hydraulic pump or an accumulator to an injection cylinder via a flow control valve for injection. A pressure control valve is provided in an oil passage between the injection cylinder and the first injection / filling stroke section and a second injection / filling stroke section following the section from the initial injection stroke to the holding pressure switching point. In the first injection / filling stroke section, regardless of the load pressure, the injection by the speed control by the flow rate control valve based on the speed set according to the forward position of the piston rod of the injection cylinder is performed.
A filling stroke is executed, and injection is performed by the pressure control by the pressure control valve based on a suitable filling pressure set according to the forward movement position of the piston rod of the injection cylinder regardless of the speed in the second injection / filling section. An injection control method for an injection molding machine, characterized in that a filling process is executed.