JPH0560774B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to speed control when injection is performed by an accumulator in an injection molding machine or a die casting machine.

[Conventional technology]

In plastic injection molding, for thin-walled products or products with complex shapes, the faster the cavity is filled, the more accurate the dimensions and weight can be obtained. Furthermore, in die casting of aluminum or the like, filling must be completed quickly before the molten metal solidifies. For such purposes, the injection filling process is carried out using an accumulator drive source 2.
It is common to use 0. By using the accumulator injection, the injection speed can be increased to about 2 to 3 times compared to the case where the injection is performed using only the discharge amount of the hydraulic pop pump 21, and filling can be performed quickly.

[Problem that the invention seeks to solve]

However, when it comes to variation in injection speed during accumulator injection, the variation rate from shot to shot is often worse than in the case of only a hydraulic pump.

At the time of injection of the accumulator, as shown in FIG.
Since the instantaneous flow rate passing through is large, the pressure on the accumulator 20 side also drops rapidly, and the flow control valve 22 with pressure compensation, which has a configuration similar to the conventional pressure reducing valve 22b using a spring, cannot quickly follow the pressure compensation action. This results in a delay in response and, as a result, variation in injection speed, resulting in poor product quality, especially stability in product weight.

In order to reduce variations in injection speed, as shown in Figure 7, even if a servo valve 23 is used to achieve high response control through speed feedback, problems such as oscillation may occur due to the inertia of the molten resin and hydraulic oil. occurs, and the benefits of closed control are not realized. In addition, in the closed control circuit using the servo valve 23, the hydraulic oil used must be kept clean to NAS class 7 or below, which poses maintenance problems.

〔the purpose〕

In order to achieve the above object, the present invention provides a proportional solenoid valve system that can feed-control the opening degree of the valve spool inside the valve as an injection speed adjustment device when injection is performed using an accumulator in an injection molding machine or a die-casting machine. By using a flow rate directional control valve, changes in the accumulator pressure are input to the flow rate directional control valve via a microcomputer control device as an electric signal using a pressure sensor, and the injection speed can be controlled with high response and precision similar to closed control. , a method that can ensure high stability (small variation), and because it is a proportional solenoid valve system, there is no need to pay special consideration to the cleanliness management of the hydraulic oil, is extremely easy to use, and can control the accumulator injection speed with high accuracy. The object of the present invention is to provide an injection molding machine using the method.

[Means for solving problems]

In order to solve the above-mentioned problems, the method of the present invention is as follows: In injection molding in which pressure oil from an accumulator 3 is used in the injection process, the accumulator 3 and the injection cylinder 7 are connected via a proportional electromagnetic flow control valve 6. The valve opening degree is increased in accordance with the decrease in the source pressure of the accumulator 3 during the injection molding process, and the flow rate of pressure oil passing through the valve during the injection process is maintained approximately constant.

In claim 2, the injection molding machine of the present invention includes an injection cylinder 7 for driving an injection member 8 such as a screw or a plunger rod of the injection molding machine.
and accumulator 3 for use in the injection process.
and a proportional electromagnetic flow control valve 6 that controls the amount of pressure oil supplied from the accumulator 3 to the injection cylinder 7.
, a pressure sensor 4 that detects a drop in the source pressure of the accumulator 3 during the injection process, and proportional electromagnetic flow control so that the flow rate of pressure oil passing through the valve is approximately constant throughout the injection process based on the signal from the pressure sensor 4. It is composed of a microcomputer type control device 5 that increases the opening degree of the valve 6.

; is adopted as a technical means.

[Effect]

When injection is started and the piston 7c of the injection cylinder 7 begins to move forward at high speed, the source pressure of the accumulator 3 decreases accordingly. Therefore, in order to keep the injection speed constant, the opening degree of the flow rate control valve 6 is controlled to increase in proportion to the drop in the base pressure of the accumulator 3, thereby keeping the injection speed constant.

〔Example〕

Embodiments of the present invention will be described with reference to the drawings.

In FIGS. 1, 2, and 3, reference numeral 1 denotes a hydraulic pump, and a pipe line a from its discharge port is connected to a check valve 2. In FIG. Reference numeral 3 denotes an accumulator, which is connected to the conduit b on the outlet side of the check valve 2.
Usually, a Prada-type device with a built-in rubber bag for sealing the gas is used. Reference numeral 4 denotes a hydraulic pressure sensor which is attached to the accumulator conduit b and measures the source pressure moment by moment, and its electrical output is input to the microcomputer type control device 5 via a signal line k. Pipe line b is connected to the P port of a proportional electromagnetic type flow control valve 6. The flow rate control valve 6 is a proportional electromagnetic type control valve, but its interior has a structure similar to a servo valve as shown in FIG. The spool 6f that adjusts the flow rate passing between ports P→A and B→T is moved forward and backward by torque motors 6b and 6c, respectively, via positive and negative output lines m and n from a built-in ratio amplifier 6a. It operates with high response in accordance with the flow rate setting electric signal inputted via the electric signal line 1 from the microcomputer type control device 5, and the passing flow rate can be adjusted with high precision.

It also has a built-in differential transformer 6d, which is proportional to the forward and backward movement of the spool (valve opening).
Positive or negative electrical output, electrical signal input terminal 6
The valve 6 itself has a flow rate feedback function.

Moreover, it is less affected by dust and foreign matter in the hydraulic oil, which is the disadvantage of servo valves, and it is
It has the advantage of being able to use hydraulic oil of about NAS10 class and being easy to maintain.

The outlet A port of the flow rate control valve 6 is connected to the head side 7a of the injection cylinder 7 by a conduit c. From the rod side 7b of the injection cylinder 7, the pressure oil is returned to the tank via the line d. An injection member 8 such as a screw or a plunger rod is mounted in front of the piston 7c of the injection cylinder 7.

In processes other than injection, each operation is performed using pressure oil from the hydraulic pump 1, and at the same time, a charge operation is also performed to replenish the accumulator 3 with pressure oil until the start of the next injection. Charging ends when the pressure signal from the pressure sensor 4 becomes equal to the set pressure value P ₀ from the setting device 5a of the microcomputer control device 5.

When the injection process begins, the pressure oil from the accumulator 3 flows into the injection cylinder 7 through the flow path from port P to A of the flow control valve 6, and when the injection piston 7c starts moving forward, the accumulator source pressure changes to the curve shown in Fig. 4. α
It descends like this. Therefore, the injection speed of the injection cylinder 7 cannot be maintained at the set value (V ₀ ) and falls as indicated by the curve α'.

FIG. 5 is a characteristic diagram of the valve opening dmm of the proportional electromagnetic type flow rate control valve 6 versus the valve passing flow rate Q (l/min), but as is generally known, the passing flow rate Q of a hydraulic valve is: Here, Q: Passing flow rate A: Valve opening area γ: Specific gravity of hydraulic oil used P ₁ : Valve inlet pressure P ₂ : Valve outlet pressure ΔP=P ₁ −P ₂ : Valve differential pressure C: Flow rate count.

Here, in the case of the flow control valve 6 used in the present invention, it has a spool valve structure, and A〓d (d is the valve opening degree mm).
Therefore, equation (1) becomes Q=C'd√〓...(2) C: proportionality constant. Also, since the differential pressure △P is approximately proportional to the valve inlet pressure P ₁ , Q=C″d√ ₁ ……(3).

Therefore, when injection starts, the source pressure of the accumulator 3, that is, the inlet pressure _P1 of the control valve 6, decreases moment by moment, so the characteristic line x in FIG. 5 decreases to y, and the flow rate passing through the valve becomes _Q1. What should be Q drops to ₂ .

Therefore, in the present invention, in order to raise this to the original _Q1 , the valve opening degree _d1 is increased to _d2 according to the characteristic line y.

That is, the source pressure _P1 of the accumulator 3 is measured every moment by the pressure sensor 4, and is inputted to the microcomputer type control device 5 via the electric signal line k.

In the control device 5, the valve opening degree d is increased by an amount corresponding to the decrease in the input _P1 according to equation (3).
In other words, the calculation is performed so that d√ ₁ is constant.
The valve opening degree d is input to the flow rate control valve 6 via the signal line 1, and the passing flow rate Q is maintained so as not to decrease. In this way, even if the source pressure of the accumulator 3 drops to α as shown in FIG. 4, the injection speed can be maintained at the set value V ₀ (ie, the line indicated by β).

〔effect〕

As shown in claim 1, the method of the present invention connects an accumulator and an injection cylinder via a proportional electromagnetic flow control valve in injection molding using pressure oil of an accumulator in the injection process, and The valve opening is expanded as the pressure decreases, and the valve opening of the pressure oil in the injection process is expanded, and the flow rate of pressure oil passing through the valve in the injection process is maintained almost constant. Therefore, even if the accumulator source pressure decreases as the piston of the injection cylinder moves forward at high speed after injection is started, the decrease in source pressure is compensated for by the controlled expansion of the valve opening, which eliminates the conventional problem. The variation in injection speed caused by the use of an accumulator, which was thought to be a problem, has been eliminated, and high-speed molding can be performed with high precision and stability.In addition, the pressure oil supply to the injection cylinder can be controlled using a proportional electromagnetic flow control valve. Therefore, there is no need to pay special consideration to the cleanliness management of the hydraulic fluid, and there are advantages in that it is extremely easy to use, and that the accumulator injection speed can be controlled with high accuracy.
Further, in claim 2, an injection cylinder for driving an injection member such as a screw or a plunger rod of an injection molding machine, an accumulator for use in the injection process, and a proportional electromagnetic flow rate for controlling the amount of pressure oil supplied from the accumulator to the injection cylinder. A control valve and a pressure sensor to detect the drop in the source pressure of the accumulator during the injection process, and a proportional electromagnetic type flow control valve so that the flow rate of pressure oil passing through the valve is almost constant throughout the injection process based on the signal from the pressure sensor. Since a speed-controlled accumulator injection type injection molding machine is configured with a microcomputer type control device that increases the valve opening degree, the injection method described in claim 1 can be carried out.

[Brief explanation of drawings]

Fig. 1... Hydraulic control circuit diagram of the present invention, Fig. 2...
...Detailed circuit diagram of the flow control valve used in the present invention, Fig. 3...Block circuit diagram of the present invention, Fig. 4...Injection stroke (x-axis), accumulator pressure and injection speed (y-axis) in the injection process Graph showing the relationship between the valve opening degree of the flow rate control valve (x-axis) and the flow rate of pressure oil passing through the valve (y-axis) in the injection process, FIG. 6a ...Conventional hydraulic control circuit diagram using a flow control valve with pressure compensation, Fig. 6b...Block circuit diagram for Fig. 6a, Fig. 7a...Conventional hydraulic control circuit diagram using a servo valve , Fig. 7b...Block circuit diagram of Fig. 7a 1...Hydraulic pump, 2...Check valve, 3...
Accumulator, 4... Pressure sensor, 5... Microcomputer system control device, 5a... Setting device, 6... Flow rate control valve, 6a... Comparison amplifier, 6b, 6c... Torque motor, 6d... Differential transformer, 6e... Electric signal input terminal, 6f... Spool, 7... Injection cylinder, 7a... Head side, 7b... Rod side, 7c... Piston, 8... Injection member, a,
b, c, d...pipe line, kl...electric signal line, m, n
...Electric output line.

Claims (1)

[Claims] 1. In injection molding using pressure oil from an accumulator in the injection process, the accumulator and injection cylinder are connected via a proportional electromagnetic flow control valve,
A method for controlling the speed of accumulator injection, characterized in that the valve opening degree is increased in accordance with a decrease in the source pressure of the accumulator during the injection process, and the flow rate of pressure oil passing through the valve during the injection process is maintained almost constant. 2. An injection cylinder for driving an injection member such as a screw or plunger rod of an injection molding machine, an accumulator for use in the injection process, and a proportional electromagnetic type flow control valve that controls the amount of pressure oil supplied from the accumulator to the injection cylinder; A pressure sensor detects a drop in the source pressure of the accumulator during the injection process, and the valve opening of the proportional electromagnetic flow control valve is adjusted based on the signal from the pressure sensor so that the flow rate of pressure oil passing through the valve remains almost constant throughout the injection process. A speed controlled accumulator injection type injection molding machine characterized by being configured with a microcomputer type control device that expands the speed.