JPS63182122A - Control method of injection speed of injection molding machine - Google Patents

Abstract

PURPOSE:To control an injection speed swiftly and accurately without having a lag in response in a changing part at the time of building-up or falling of the injection speed, by a method wherein an opening area of a nozzle valve is controlled to a preset opening prior to control of a supply oil quantity to an extension chamber of an injection cylinder and when the opening of the nozzle valve becomes preset one, the nozzle valve is regarded to be fully opened. CONSTITUTION:A screw 2 is connected with a piston rod 8 of an injection cylinder 7, a driving shaft 10 is fitted into the piston rod 8, hydraulic oil of a hydraulic pressure source 12 is supplied within an extension chamber 11 and a flow of the hydraulic oil is controlled by a flow control valve 13. A nozzle 4 is provided with a nozzle valve 14 which controls an injection speed by changing an opening of the nozzle valve 14 by controlling an electric current to be supplied to a proportional solenoid 17. When the screw 2 has attained to a preset screw position, an opening area of the nozzle 4 is controlled to a preset opening. When the opening has attained to the preset opening, the opening area of the nozzle 4 is made maximum, and when the opening has come to a degree a little before the preset opening, a supply flow into the extension chamber 11 is controlled to a preset value. Therefore, the injection speed can be changed accurately and swiftly without having a lag in response, in a changing part between building-up and falling of the injection speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the injection speed of molten resin during the filling process in an injection molding machine that fills a cavity of a mold with molten resin.

[Conventional technology]

As shown in Japanese Unexamined Patent Publication No. 57-59060, an injection molding machine is known in which a rotatably driven screw is reciprocated by an injection cylinder and molten resin is injected from a nozzle to fill the cavity of a mold. There is.

In such an injection molding machine, it is necessary to control the injection speed at which the molten resin is filled into the cavity of the mold according to the position of the screw.

As a method of controlling such injection speed, for example, the method shown in Japanese Patent Application Laid-Open No. 59-64337 is known.

In other words,! As shown in Figure J4, there is a position detector that detects the position of the screw a, a flow control valve e that controls the flow rate supplied to the extension chamber d of the injection cylinder C, and a setting device that sets the screw speed relative to the screw position. f and outputs a control signal to the flow control valve e according to the screw position detected by the position detector to control the flow rate supplied to the extension chamber d so that the screw speed is set by the setting device f. According to this device, the speed of the molten resin filling the cavity of the mold from the nozzle g, that is, the injection speed, can be controlled in multiple stages according to the screw position.

[Problem that the invention seeks to solve]

This method of controlling the injection speed is based on the movement speed of the screw,
In other words, the injection speed is controlled by controlling the elongation speed of the injection cylinder, and since the molten resin is compressible, the moving speed of the screw and the injection speed may differ, so the accuracy of the moving speed of the screw is controlled. Even if the injection speed is well controlled, the accuracy of the injection speed may be poor and it may not be possible to control the injection speed to a preset screw position.

That is, for example, when the screw a is pressing the molten resin during the filling process in which the cavity of the mold is filled with the molten resin from the nozzle g, the molten resin pressure inside the housing i at the tip of the screw a increases. ing. Even if the screw a is stopped in this state, the pressure of the compressed molten resin inside the housing i will correspond to the load pressure inside the mold, and it will not respond until the injection speed becomes zero. There is a delay.

In addition, if the speed of the screw a is suddenly accelerated to increase the injection speed from the state where the speed of the screw a has been switched, it is necessary to increase the pressure of the molten resin inside the housing i before the injection speed corresponding to the screw speed is obtained. must rise, resulting in a response delay corresponding to the time required for the pressure of the molten resin to rise.

Specifically, when injection molding a product with two abrupt changes in shape as shown in Figure 5, surface defects such as clouding and welding may occur due to disturbances in the flow of molten resin into the mold cavity. Therefore, the injection speed pattern is controlled in four stages: v, v, v, v according to the screw positions A, B, C, and D as shown in FIG. vl, v to prevent
is set to a low speed, and v and v4 are set to a high speed so that no flow mark occurs.

To control the injection speed in this way, screw position A,
When B, C, and D are detected, the flow rate control valve is controlled to change the extension speed of the injection cylinder to control the screw speed as shown by the broken line in Figure 6, but due to the aforementioned response delay, the screw speed is shown as a solid line. The injection speed differs depending on the rising and falling transitions.

Because of this response delay, even if the screw speed is suddenly changed, the injection speed will gradually change from V3 to V4, resulting in flow mark black in the product, and at the time of falling, the injection speed will gradually change from V3 to V4. ■３
However, when the injection speed is high, the molten resin pressure inside the housing 1 is high, so even if the screw speed is suddenly reduced, injection will continue until the molten resin pressure reaches the load pressure inside the mold. As the speed increases and the voltage gradually switches from V2 to V3, weld/cumorino 1 occurs in the product. In order to prevent this, if the screw speed is switched at a screw position before switching screw position B from v2 to V3, a flow mark cross will occur.

Note that even if the screw speed is reduced before applying holding pressure after filling is completed, 1. The peak value V' occurs due to inertia due to the load of the motor etc. applied to the screw a.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an injection speed control method for an injection molding machine that allows the injection speed to be changed quickly and accurately without response delay at the transition portions of the injection speed, such as the rise and fall of the injection speed.

[Means and actions for solving the problem] Before controlling the amount of oil supplied to the extension chamber of the injection cylinder that moves the screw, the opening area of the nozzle valve is controlled to the set opening, and the opening area is adjusted to the set opening. By fully opening the injection speed, the injection speed can be quickly and precisely controlled without delay in response to changes in the rise and fall of the injection speed.

〔Example〕

In FIG. 1, a screw 2 is inserted into a cylindrical housing 1.
is slidably and rotatably inserted to melt the resin in the hopper 3 and fill the cavity 6 of the mold 5 through the nozzle 4, and the screw 2 is connected to the piston rod 8 of the injection cylinder 7. A drive shaft 10 rotated by a hydraulic motor 9 is spline-fitted to the soston rod 8, and pressure oil from a hydraulic source 12 is supplied into the extension chamber 11 via a switching valve (not shown). Moreover, the flow rate can be controlled by a flow rate control valve 13.

The nozzle 4 is provided with a flow rate control mechanism, such as a nozzle valve 14, for controlling its opening area, and the nozzle valve 14 is connected to a nozzle valve drive mechanism, such as a proportional solenoid 17, via a lever 15 and a rod 16, By controlling the current supplied to the proportional solenoid 17, the opening degree of the nozzle valve 14 can be changed, thereby increasing or decreasing the opening area of the nozzle 4 to control the injection speed.

In other words, when the opening degree of the nozzle valve 14 is large, the flow resistance of the molten resin flowing through the nozzle 4 is small, so the screw 2
moves quickly, increasing the injection speed, and the nozzle valve 14
If the opening degree is small, the flow resistance of the molten resin flowing through the nozzle 4 becomes large, and the screw 2 cannot move quickly, resulting in a slow injection speed.

A rack rod 18 is connected to the piston rod 8, and a rotation sensor 20 such as a potentiometer is provided on a pinion 19 meshing with the rack rod 18 to constitute a rack position detector 21. A rotation sensor 24 is provided on a pinion 23 meshed with a rack rod 22 fixed to a movable portion 17a of the rotor 17, and constitutes a nozzle valve opening degree detector 25.

The injection speed is then controlled by the controller 30.

The controller 30 includes a screw position setting device 31, a nozzle valve opening setting device 32, a first comparator 33, a second comparator 34, an arithmetic unit 35, a converter 36, and a gate 37. The screw position for switching the injection speed can be arbitrarily set, and the nozzle valve opening degree corresponding to a plurality of injection speeds can be arbitrarily set in the nozzle valve opening degree setting device 3°2 corresponding to the set screw position.

For example, the screw position setter 31 is set with first, second, and third screw positions SS, S and 1 2 3 , and the start position So, and the nozzle valve opening setter 32 is set with the first, second, and third screw positions SS, S and 1 2 3 , and the start position So. The third set opening degree v, v, v3 is set.

Further, the flow rate control valve 13 is fully open, that is, in a maximum flow state when no control signal is input to the control section 13a.

Next, control of injection speed will be explained.

When the injection molding start signal is input when the screw 2 is at the rearmost position, that is, at the start position, the hydraulic motor 9 is driven and the screw 2 is rotated, and at the same time, the actual screen position S detected by the screw position detector 21 is at the start position. So
Therefore, a readout signal is inputted from the first comparator 33 to the nozzle valve opening setting device 32, and a control current is supplied from the gate 37 to the proportional solenoid 17 to obtain the first set opening ■1, thereby adjusting the nozzle valve 14. When the opening changes to the closing direction and reaches the first set opening V1, the nozzle valve opening detector 2
5 matches the first set opening v1, a signal is sent from the second comparator 34 to the gate 37, the gate 37 closes, and no control current is sent to the proportional solenoid 17, and the nozzle valve 14 is fully opened.

On the other hand, the first set opening degree v1 is sent to the calculator 35, and the opening degree at one point in the middle when the nozzle valve 14 closes to the first set opening degree v1 is calculated as follows: Start flow rate switching position g(V ) is calculated and the second comparator 3
4, and when the actual opening reaches the opening V'1, a command is given to the converter 36 from the second comparator 34 to set the first set opening v.
1, the first control flow rate f corresponding to the first set opening degree v1,
(Vl), and sends a control signal to the control unit 13a of the flow control valve 13 to maintain the first control flow rate f (Vl) until the next control signal is input.

Then, the first comparator 33 compares the actual screw position S detected by the screw position detector 21 and the screw position S1 set by the screw position setting device 31, and if the two match, the nozzle valve opening setting device 32 A readout signal is issued to control the proportional solenoid 17 to set a second opening V2 corresponding to the injection speed corresponding to the first screw position S1 preset in the nozzle valve opening setting device 32 in the same manner as described above. Supplying current to the nozzle valve 14
The opening degree is closed and set to the second set opening degree V2.

At the same time, the second set opening degree v2 is input to the calculator 35, and the opening degree V', that is, the] flow rate switching position g, is determined in the same manner as described above.
(Vl) is calculated and sent to the 21st comparator 34, and when the actual opening reaches the opening V', the converter 36 calculates the first flow rate switching position g1 (Vl) and controls the flow rate control valve 13. A control signal is sent to the section 13a to maintain the second control flow m f 2 (V2) until the next control signal is input.
- On the other hand, when the opening degree of the nozzle valve 14 reaches the second set opening degree V2, a signal is sent from the second comparator 34 to the gate 37 as described above, the gate 37 is closed, and the nozzle valve 14 is closed.
is fully opened.

Similarly, when the actual screw position S becomes the second screw position S2, the opening degree of the nozzle valve 14 changes to the third set opening degree V.
3, and when it becomes slightly larger than ■'3, the second flow rate switching position g2 (V2) is set, the flow rate of the flow rate control valve 13 becomes the third control flow rate f (V3), and the flow rate of the nozzle valve 14 is changed to the third control flow rate f (V3). When the opening degree reaches the third set opening degree V3, the opening becomes fully open.

Then, the actual screw position S is the third screw position S
3, the opening degree of the nozzle valve 14 is reduced in order to switch to the pressure holding process, and when the opening degree reaches a predetermined value, the flow rate of the flow rate control valve 13 is controlled by setting the third flow rate switching position g (V3)''.

〔Effect of the invention〕

When controlling the injection speed, first the opening area of the nozzle 4 is controlled, and then the amount of oil supplied into the extension chamber 11 of the injection cylinder is controlled, so there is no response delay at the transition points at the rise and fall. The injection speed can be controlled quickly and accurately with no response delay.

In other words, the timing for switching the opening area of the nozzle 4 and the timing for switching the amount of supplied oil are not simultaneous, but the amount of supplied oil is changed at the point where the opening area of the nozzle 4 is closed to a certain degree from the fully open state (in the process of closing). If the opening area of the nozzle 4 in the next process is larger than the opening area setting value of the nozzle 4 in the process, the supply oil amount starts to increase while the nozzle 4 is closing at one end until the setting value in the next process. The oil pressure in the extension chamber 11 increases by 1, and the pressure of the molten resin at the tip of the screw also increases. In a state where the resin pressure is rising, the opening area of the nozzle 4 is closed to the set value and is fully opened at the rear, so that the resin ejected from the nozzle 4 can be rapidly accelerated.

Furthermore, if the set value for the next process is smaller than the set value for the opening area of the nozzle 4 in a certain process, the nozzle 4 starts to close the amount of supplied oil in a state where the set value for the next process is almost exceeded, so that the extension chamber 11 of the injection cylinder 7 falls, and the molten resin pressure at the tip of the screw also falls. Since the opening area of the nozzle 4 closes to a set value while the resin pressure is decreasing, the resin ejected from the nozzle 4 can be rapidly decelerated.

In addition, the nozzle 4 always has a fully open point during one process, so even if a stagnation point of the molten resin occurs when the opening area of the nozzle 4 is made small, there is always a self-cleaning action in each process, so the nozzle The resin does not stay in the opening area changing portion of the nozzle 4, and even when a material containing glass fiber is used as the resin material, the opening area of the nozzle 4 becomes smaller only when the molten resin injection speed is accelerated or decelerated. In other cases, since the nozzle 4 is in a fully open state, the life of the aperture area changing portion of the nozzle 4 against wear is significantly extended.

[Brief explanation of the drawing]

Fig. 1 is an overall explanatory diagram showing one embodiment of the present invention, Fig. 2 is a chart showing the nozzle valve opening degree, Fig. 3 is a chart showing the flow rate of the flow control valve, and Fig. 4 is a chart showing the flow rate of the conventional example. Explanatory diagram, Figure 5,
FIG. 6 is a diagram illustrating the malfunction. 2 is a screw, 4 is a nozzle, 7 is an injection cylinder, 11
is the extension room.

Claims (1)

[Claims] In an injection molding machine in which a rotatably driven screw 2 is reciprocated by an injection cylinder 7, molten resin is filled from a nozzle 4 into a cavity 6 of a mold 5 through multiple steps at different injection speeds. When the position is reached, the opening area of the nozzle 4 is controlled so that it reaches a predetermined opening, and when the opening is reached, the opening area of the nozzle 4 is maximized, and the opening is slightly before the set opening. 1. An injection speed control method for an injection molding machine, characterized in that the flow rate supplied into the extension chamber 11 of the injection cylinder 7 is controlled to a preset value when the injection speed is reached.