JPH05124080A - Control method of injection molding machine - Google Patents

Abstract

PURPOSE:To mass-produce products having high quality easily by conducting changeover from the control of an injection process to the control of a dwell process easily at a proper period on filling molding. CONSTITUTION:The change of the forward speed of an injection screw or the change of filling pressure at the time of changeover from a filling process to a dwell process is detected, the start of dwell control is quickened when there is inversion in the fluctuation of speed or pressure, and the start of dwell control is delayed when speed or pressure does not reach a set value within a fixed time after the start of dwell control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to injection control of an injection molding machine, and more particularly to control of switching from a filling process to a pressure holding process.

[0002]

2. Description of the Related Art Today, in injection molding of molten resin or the like, as shown in FIG. 4, the horizontal axis represents position l or time t, and the vertical axis represents forward speed v and pressure P of the injection screw, as shown in FIG. Filling process L1 for filling the mold cavity with molten resin in
And a holding pressure L2 that adjusts the molding by applying pressure after the molten resin is filled. In many cases, the filling process L1 opens the pressure control valve of the hydraulic circuit widely and the elapsed time from the start of injection. Alternatively, the opening of the flow control valve is set to change over time so as to change the speed in multiple stages based on the forward position of the injection screw, etc., and the piston of the injection cylinder and thus the injection screw is adjusted by adjusting the flow control valve. It is assumed that the molten resin is filled into the cavity at such a high speed that the resin in the cavity does not entrain air, and the flow control valve is fixed after the molten resin is filled into the cavity. A pressure-holding step L2 is performed in which the hydraulic pressure is adjusted by a pressure adjusting valve, and this pressure-holding step L2 may apply a predetermined pressure to the molten resin filled in the cavity as time passes. The opening of the pressure adjustment valve is changed to prevent the resin from shrinking due to the molten resin being cooled in the cavity, causing an error in the shape of the product with respect to the shape of the cavity. We try not to generate a large residual stress inside the product.

By the way, when switching from the filling process to the pressure-holding process, if this switching is delayed, burrs are produced in the product, and if the switching is quick, sink marks and short shots occur. Therefore, proper switching timing is required. As shown in FIG. 5, where the horizontal axis represents time t and the vertical axis represents pressure P, the filling pressure of the hydraulic circuit in the filling process and the pressure holding process is detected, and the hydraulic pressure is determined by the completion of the molten resin filling in the filling process. It is detected that the
A control method is also adopted in which the switching is performed when the temperature reaches.

Further, in a state where the molten resin has not been completely filled in the cavity, when the hydraulic pressure reaches a predetermined value P0 due to a temporary increase in the filling pressure due to disturbance, the pressure control is erroneously switched to. In order to prevent the operation, the hydraulic pressure is controlled to switch when the hydraulic pressure reaches a predetermined value P0 after a predetermined time from the start of injection, or the filling pressure is detected after the injection screw has advanced to a predetermined position. Zone control is also adopted so that when the temperature reaches a predetermined value P0, the injection pressure of the molten resin, the pressure of the pressure oil in the hydraulic circuit for injection, or the mold of the fixed mold and the movable mold are adopted. There is also a control method of detecting the opening of the mold matching surface and adjusting so as to correct the pressure in the pressure holding process when these detected values exceed a predetermined allowable range (for example, Japanese Patent Publication No. 53-53). No. 9905).

[0005]

As described above, the conventional control method for switching the speed control to the pressure control based on the filling pressure detects that the filling pressure or the like has reached a predetermined set value. If the pressure rises to an abnormal value, the hydraulic pressure is adjusted during the next injection molding, but the internal stress is reduced and high-precision products that prevent distortion etc. The injection control was still insufficient for mass production.

Further, when the zone control is adopted, skill is required to set the zone range and the set value P0 of the pressure, and depending on the shape and size of the mold cavity, the type of resin, etc. However, since the set value P0 is different, injection preparation such as initial setting is complicated and difficult. The present invention eliminates these drawbacks, makes it possible to set the switching control relatively easily, and enables high-accuracy products to be easily mass-produced.

[0007]

According to the present invention, when the injection screw or the like reaches a predetermined range position, the filling speed control is switched to the pressure holding control, and the screw filling speed or the filling pressure is changed immediately after the switching. If the speed or pressure exceeds the target value at the time of holding pressure and the speed or pressure change is reversed, the switching pressure is slightly lowered to speed up the switching timing in the next injection, and after switching If the speed or pressure does not reach the target value for holding pressure within the required time, the switching pressure is slightly increased so that the switching timing is delayed.

[0008]

According to the present invention, when the injection screw or the like reaches a predetermined position, the pressure control is switched to start the pressure holding. Therefore, the screw between the backward limit position of the injection screw and the predetermined position is controlled. By matching the volume to the cavity volume, calculation and setting of the predetermined position can be easily performed.

Further, the forward speed of the injection screw immediately after the switching, the filling pressure, etc. are detected, and when the change in the speed or the pressure is reversed, the next switching timing is advanced, so that a correction to prevent overshoot is made. If the speed or pressure does not reach the target value within the predetermined time, the next switching timing is delayed, so that a correction to prevent a short shot can be made.

[0010]

As an embodiment of the present invention, injection control of an injection molding machine having a screw-in-line type injection device provided with a pressure detector for detecting an injection pressure is performed. In injection molding by this control, the retreat limit position of the injection screw is set according to the size of the cavity to regulate the required amount of molten resin, and the opening control of the pressure control valve and the flow rate adjusting valve is performed as shown in FIG.
As shown in, the position of the injection screw is changed so that the injection speed in the filling process L1 for filling the cavity with the molten resin from the start of injection is changed in several stages based on the size and shape of the cavity, the type of resin, the injection temperature, and the like. The opening of the flow rate control valve is set accordingly, and after the injection screw reaches the setting switching pressure at which the molten resin is sufficiently filled in the cavity, the opening of the pressure adjusting valve is adjusted and changed to adjust the pressure of the pressure holding process L2. To be adjustable.

The filling speed in the injection molding is the low-speed filling speed corresponding to the opening setting of the flow rate control valve and the high-speed filling speed corresponding to the valve opening set to be changed according to the cavity shape. After the molten resin is filled into the cavity and the required amount of the molten resin is filled into the cavity, the filling speed rapidly decreases, and the horizontal axis is the time axis and the vertical axis is the forward speed. As shown by the curve, the injection screw advances at an ultra-low speed so as to supplement the amount of the molten resin in the cavity that is cooled and contracts.

However, when the injection screw reaches a predetermined position due to delicate compression of the molten resin, thermal expansion, etc., even if the holding pressure is switched to the holding pressure control and the holding pressure is started, the filling amount into the cavity is slightly increased. In some cases, the cavities may be insufficient, or the cavity may be filled with molten resin before switching to holding pressure control. When this filling amount is slightly insufficient, the forward speed of the injection screw after switching to the pressure-holding control is such that the injection screw is made to replenish the cooling contraction of the molten resin as shown by the curve C in FIG. The forward movement of the injection screw for advancing and replenishing the shortage of the molten resin is combined, and as compared with the graph of the above A, it takes time to decay the forward speed immediately after switching when the holding pressure control is started.
The stability of reaching ultra-low speed for replenishing the shrinkage of the resin due to cooling is delayed, and if the cavity is filled with molten resin immediately after switching to the holding pressure control, the molten resin will momentarily disappear. Is over-compressed, the forward speed of the injection screw drops sharply, and after the molten resin returns to the proper compressed state, it advances at a predetermined slow speed to supplement the cooling compression, as shown by the curve B in FIG. As described above, the injection speed rapidly decreases and becomes slower than the predetermined speed, and then the injection speed is increased once to increase the speed and then changes to advance at the predetermined speed.

It should be noted that the predetermined advancing speed during this pressure-holding process is determined by the size of the cavity, the type of resin, the cooling rate,
It can be calculated in advance from the diameter of the injection screw and the like. Therefore, in this embodiment, the predetermined forward speed at the time of holding pressure is registered in advance in the control computer as a set value, and the pressure behavior immediately after switching from the speed control to the pressure control after the completion of filling is indicated by B in FIG. As shown by the curve in Fig. 2, when the set value is reached after the speed change is reversed so that the injection speed becomes slow once and then the set value is reached, the pressure control valve or flow control valve is used for holding pressure. , The timing of starting the pressure holding control is accelerated, and the set value stored in the control computer is reduced so that the setting switching pressure of the injection screw set for switching to the pressure holding process is lowered by a certain amount. In order to detect the speed of the injection screw immediately after switching to the pressure holding process in the injection,
If the forward speed of the injection screw gradually decreases and reaches a predetermined speed and there is no reversal in speed change, it is judged whether or not the set speed is reached within the required time. If the set speed is not reached within the required time. Is to delay the timing to start the pressure holding control, modify the set value so that the set switching pressure of the injection screw set to switch to the pressure holding process is increased by a certain amount, and in the next injection, The screw is switched to the pressure-holding process at a position where the screw has advanced to the advance limit position slightly from the set position.

In this embodiment, the backward limit position of the injection screw and the injection screw position for starting the pressure holding control are set in advance in accordance with the volume of the cavity, and are registered in the control computer. When a change in the injection screw speed is detected and the injection speed drops sharply and then falls below the set speed and then reverses and reaches the set speed, the pressure is switched to holding pressure control. Change to lower to eliminate overfilling, and the change in injection speed immediately after the start of pressure holding control is slow,
If the injection speed does not reach the set speed within the predetermined time, the pressure is switched to the pressure holding control.The setting switching pressure of the injection screw is changed to a certain fixed amount to correct it so as to eliminate insufficient filling. It is extremely easy to determine when to switch to an appropriate switching position, and it is possible to easily perform switching control that enables mass production of highly accurate products.

The reversal of the speed is performed by continuously detecting the speed immediately after the start of the pressure-holding control, comparing the new detection value with the previous detection value, and the new detection value is smaller than the previous detection value. If the reversal is detected when it becomes, speed reversal can be easily detected. Further, in the above embodiment, the forward speed of the injection screw is detected to correct the start time of the pressure holding control, but the resin pressure in the mold can be detected to make the correction.

As shown in FIG. 3, in which the horizontal axis is the time axis and the vertical axis is the pressure P, the resin pressure is low before the molten resin is completely filled when the molten resin is filled in the cavity. After the completion, the molten resin is maintained at a predetermined set pressure to be cooled and solidified. When appropriate switching control is performed, the set pressure is smoothly reached as shown by the curve A in FIG. When the switching to the holding pressure control is early, the arrival at the set pressure is delayed as shown by the curve C in FIG. 3, and when the switching is delayed, the set pressure is exceeded as shown by the curve B in FIG. Peak pressure will occur once.

Conventionally, the peak value of such a peak pressure is detected, and when the peak value is an abnormally high pressure exceeding the allowable set value, the filling pressure, the filling speed or the holding pressure is corrected to generate the abnormally high pressure. However, in the present embodiment, as in the case of the detection of the filling speed, when the pressure change immediately after the start of the pressure holding control is detected and the reversal drop occurs in the pressure, it is performed from the next time. The switching timing of the
If the set value is not reached within a predetermined time from the start of the pressure holding control due to the delay of the pressure increase to the set value, the changeover timing from the next time is corrected so as to detect the change of the filling speed. Similar to the case, the switching control from the filling speed control to the pressure holding control is performed.

That is, in the injection control of the injection molding machine, the speed control is switched to the pressure control when the injection screw or the like reaches a predetermined set range position. Immediately after this switching, the pressure sensor provided in the mold is used. When the molten resin pressure is detected and it is detected that the change in the detected resin pressure exceeds the holding pressure settling pressure and then settles to the holding pressure settling pressure, the switching set pressure to the holding pressure control at the next injection is set. If the resin pressure does not reach the holding pressure settling pressure within a predetermined time from the start of the holding pressure control, the set pressure for switching to the holding pressure control at the next injection is fixed by a certain amount. It is modified so that the amount is increased.

The detection of the pressure of the molten resin is not limited to the case of measuring in the mold, but the injection pressure of the resin can be detected at the barrel tip or the like, and the injection pressure of the resin can be detected. In doing so, the pressure of the pressure oil to the injection cylinder can be detected to indirectly detect the resin filling pressure, and the timing of switching from speed control to pressure holding control can be corrected accordingly.

Further, when the speed control in the filling process is switched to the pressure control in the pressure holding process by the speed detection or the pressure detection, the switch setting position is obtained based on the shape and volume of the cavity, and then the injection at the switch setting position is performed. The control pressure of the screw or the like may be detected, and thereafter, the switching control may be performed by using the pressure value as a set pressure for switching from the speed control to the pressure control.

Further, the injection control is not limited to the screw-in-line type injection device, but can be performed so as to perform injection control of an injection molding machine having various injection devices.

[0022]

According to the present invention, when the speed control in the filling process is switched to the pressure control in the pressure maintaining process, a change in injection speed or a change in injection pressure is detected, and the speed or pressure is changed immediately after switching the pressure maintaining control. When the reversal occurs, the switching is corrected so as to be faster, and the switching is slowed when the set speed or the set pressure is not reached within a predetermined time after switching the holding pressure control. With the injection control method of the injection molding machine, it is possible to switch from speed control to pressure holding control at an appropriate timing when the filling of the cavity is completed, and it is possible to perform injection molding of high quality products with extremely easy switching timing setting. is there.

[Brief description of drawings]

FIG. 1 is a graph showing an example of an injection speed in injection molding according to the present invention.

FIG. 2 is a graph showing changes in injection speed at the start of pressure holding control in injection molding according to the present invention.

FIG. 3 is a graph showing changes in pressure at the start of pressure holding control in injection molding according to the present invention.

FIG. 4 is a graph showing an example of speed control and pressure control during injection molding.

FIG. 5 is a graph illustrating conventional switching control.

Claims (1)

[Claims] 1. In injection control of an injection molding machine, when an injection screw or the like reaches a predetermined setting range position, or when the injection screw or the like reaches a preset control switching allowable value and a control hydraulic pressure is predetermined. When the switching pressure is reached, the injection speed control is switched to the holding pressure control, the screw filling speed or filling pressure immediately after the switching is detected, and when it is detected that the speed change or pressure change has been reversed. At the next injection, the set pressure for switching to the pressure holding control is corrected to a value lower by a predetermined pressure so that the switching timing is advanced, and the speed or pressure does not reach the set value within a predetermined time after starting the pressure holding control. In this case, the control of the injection molding machine is characterized in that at the next injection, the set pressure for switching to the pressure holding control is corrected to a value higher by a predetermined pressure so that the switching timing is delayed. Method.