JP2649115B2 - Control method of 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 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 At present, in injection molding of a molten resin or the like, as shown in FIG. 4, a horizontal axis represents a position 1 or a time t, and a vertical axis represents a forward speed v and a pressure P of an injection screw. Filling step L1 for filling the mold cavity with molten resin
Injection molding is performed with a pressure L2 for adjusting the molding by applying pressure after filling with the molten resin. In many cases, the filling step L1 is performed by opening the pressure regulating valve of the hydraulic circuit widely and elapse of 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 a plurality of steps based on the forward position of the injection screw or the like, and the piston of the injection cylinder and, consequently, the injection screw are adjusted by adjusting the flow control valve. The molten resin is filled into the cavity at such a high speed that the resin in the cavity is not entrained by air. After the molten resin is filled into the cavity, the flow control valve is fixed. A pressure-holding step L2 for adjusting the oil pressure by a pressure-regulating valve is provided. This pressure-holding step L2 can apply a predetermined pressure to the molten resin filled in the cavity as time passes. The opening degree of the pressure regulating valve is changed to prevent the resin from shrinking due to the cooling of the molten resin in the cavity, thereby preventing the product's shape and dimensions from causing errors in the dimensions of the cavity. Prevents large residual stress from occurring inside the product.

By the way, when switching from the filling process to the pressure-holding process, if the switching is delayed, burrs will be generated on the product, and if the switching is fast, sink marks and short shots will occur. Therefore, appropriate switching timing is required. As shown in FIG. 5 in which the horizontal axis represents time t and the vertical axis represents pressure P, the filling pressure of the hydraulic circuit in the filling step and the pressure-holding step is detected. Is detected to rise, and the hydraulic pressure is increased to a predetermined value P0.
A control method is also adopted in which the switching is performed when the number of times has been reached.

In addition, in a state where the filling of the molten resin into the cavity is not completed, if the oil pressure reaches a predetermined value P0 due to a temporary increase in the filling pressure due to disturbance, switching to the pressure holding control is erroneously performed. In order to prevent this, a method of controlling the oil pressure to be switched when the oil pressure reaches a predetermined value P0 after a certain period of time from the start of injection, or by detecting a charging pressure after the injection screw has advanced to a predetermined position, and Is switched when the pressure reaches a predetermined value P0. In addition, the injection pressure of the molten resin, the pressure of the pressure oil in the injection hydraulic circuit, or the mold between the fixed mold and the movable mold is adopted. There is also a control method that detects the opening of the mold-matching surface and adjusts the pressure in the pressure-holding process so that the pressure is corrected when the detected value exceeds a predetermined allowable range (for example, Japanese Patent Publication No. No. 9905).

[0005]

As described above, the conventional control method for switching from speed control to pressure control based on the filling pressure detects the fact that the filling pressure or the like has reached a predetermined set value. High-precision products that reduce the internal stress and prevent the product from being distorted, even if the pressure rises to an abnormal value. Injection control was still insufficient to mass-produce.

When zone control is employed, skill is required to set the zone range and set pressure P0, and the shape and size of the mold cavity, and the type of resin, etc. Also, since the set value P0 is different, preparation for injection such as initial setting is made complicated and difficult. An object of the present invention is to eliminate such disadvantages, relatively easily set the switching control, and easily mass-produce high-precision products.

[0007]

SUMMARY OF THE INVENTION According to the present invention, when an injection screw or the like reaches a predetermined range position, switching from filling speed control to holding pressure control is performed. When the speed or pressure once exceeds the target value at the time of holding pressure and the speed change or pressure change reverses, the switching pressure is slightly reduced so that the switching timing is advanced in the next injection, and If the speed or pressure does not reach the target value at the time of holding pressure within the required time, the switching pressure is slightly increased so as to delay the switching timing.

[0008]

According to the present invention, since the pressure is controlled by switching to the pressure holding control when the injection screw or the like reaches the predetermined position, the screw between the retreat limit position and the predetermined position of the injection screw or the like is started. By adjusting the volume to the cavity volume, calculation and setting of the predetermined position can be easily performed.

Furthermore, the forward speed of the injection screw, the charging pressure, etc., immediately after the switching 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. When the speed and pressure do not reach the target values within a predetermined time, the next switching timing is delayed, so that a correction for preventing a short shot can be made.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 the injection molding by this control, the retreat limit position of the injection screw is determined in accordance with the size of the cavity to regulate the required amount of the molten resin.
As shown in the figure, based on the size and shape of the cavity, the type of resin, the injection temperature, and the like, the injection speed in the filling step L1 for filling the cavity with the molten resin from the start of injection is changed in several steps so as to change the injection speed. The opening of the flow control valve is set accordingly, and after the injection screw has reached the set switching pressure at which the cavity is sufficiently filled with the molten resin, the opening of the pressure regulating valve is adjusted and changed to change the pressure in the pressure holding step L2. Is set so that can be adjusted.

The filling speed at the time of the injection molding is set at a low filling speed according to the opening setting of the flow control valve and at a high filling speed corresponding to the valve opening set to be changed according to the cavity shape. After the cavity is filled with the molten resin and the required amount of the molten resin is filled, the filling speed drops rapidly, and the horizontal axis represents the time axis, and the vertical axis represents the forward speed. As shown by the curve, the injection screw advances at a very low speed so as to replenish the amount of cooling and shrinkage of the molten resin in the cavity.

However, even when the injection screw reaches a predetermined position due to a delicate compression state or thermal expansion of the molten resin, even if the pressure is switched to the pressure holding control and the pressure holding is started, the filling amount in the cavity is slightly reduced. In some cases, there may be a shortage, or the cavity may be filled with molten resin before switching to pressure-holding control. When the filling amount is slightly insufficient, the forward speed of the injection screw after switching to the holding pressure control is adjusted so that the injection screw replenishes the cooling shrinkage of the molten resin as shown by the curve C in FIG. Along with the advance of the injection screw for advancing and replenishing the shortage of the molten resin, it takes time to attenuate the advance speed immediately after the switching when the pressure-holding control is started, as compared with the graph of A,
If the cavities are filled with molten resin immediately after switching to the pressure-holding control, the molten resin will not be instantaneously stable. In the state shown in FIG. 1, the injection screw advances rapidly at a predetermined very low speed to replenish the cooling and compression after the molten resin returns to the proper compression state, and the forward speed of the injection screw rapidly decreases. As described above, after the injection speed suddenly decreases and becomes lower than the predetermined speed, the injection speed is temporarily increased so as to increase the speed, and then changes so as to advance at the predetermined speed.

The predetermined forward speed during the pressure-holding step depends on the size of the cavity, the type of resin, the cooling speed,
It can be calculated in advance based on the diameter of the injection screw and the like. Therefore, in this embodiment, the predetermined forward speed at the time of the pressure holding is registered in advance in the control computer as a set value, and the pressure behavior immediately after switching from speed control to pressure control after filling is completed is represented by B in FIG. As shown by the curve, if the injection speed is once slowed down so that the speed change reverses and then settles to the predetermined speed and reaches the set value, the pressure regulating valve or flow control valve is used for holding pressure. The control value is stored in the control computer so that the injection screw setting switching pressure 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 step in the injection,
If the forward speed of the injection screw gradually decreases and reaches the specified speed, and no reversal occurs in the speed change, it is determined 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 for switching to the pressure-holding process is increased by a certain amount, and in the next injection, The pressure is switched to the pressure-holding step at a position where the screw has advanced slightly to the forward limit position from the set position.

In this embodiment, the retraction limit position of the injection screw and the injection screw position at which the pressure-holding control is started are determined in advance in accordance with the volume of the cavity and registered in the control computer. When the change in injection screw speed is detected, the injection speed suddenly drops and then reverses to reach the set speed once the speed is lower than the set speed. In order to eliminate overfilling by changing to lower, the injection speed change immediately
If the injection speed does not reach the set speed within the specified time, switch to the pressure holding control. Change the injection screw setting switching pressure to a certain amount higher and correct it to eliminate insufficient filling. It is extremely easy to determine the time of switching to an appropriate switching position, and it is possible to easily perform switching control that enables mass production of high-precision products.

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

As shown in FIG. 3 in which the horizontal axis represents the time axis and the vertical axis represents the pressure P, the pressure of the resin is low before filling the cavity with the molten resin. After completion, the molten resin is maintained at a predetermined set pressure to cool and solidify the molten resin. When appropriate switching control is performed, the set pressure smoothly reaches the set pressure as shown by curve A in FIG. When the switching to the holding pressure control is quick, the arrival at the set pressure is delayed as shown by the curve C in FIG. 3, and when the switching is delayed, the pressure exceeds the set pressure as shown by the curve B in FIG. A 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 an allowable set value, the filling pressure, the filling speed or the holding pressure is corrected to generate an abnormally high pressure. In this embodiment, similarly to the detection of the filling speed, the present embodiment detects a pressure change immediately after the start of the pressure-holding control, and when a reversal drop occurs in the pressure, the present embodiment starts the next operation. Switching timing, and
If the set value does not reach the set value within a predetermined time from the start of the pressure-holding control due to a delay in the pressure rise to the set value, a correction is made to delay the switching timing from the next time, thereby detecting the change in the filling speed. As in 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, when the injection screw or the like reaches a predetermined set range position, the control is switched from the speed control to the pressure control. Immediately after this switching, a pressure sensor provided in the mold is used. When the molten resin pressure is detected, and when it is detected that the change in the detected resin pressure once exceeds the holding pressure stabilizing pressure and then settles to the holding pressure stabilizing pressure, the switching setting pressure to the holding pressure control at the next injection is detected. Is adjusted to be lower by a certain amount, and when the resin pressure does not reach the holding pressure settling pressure within a predetermined time from the start of the holding pressure control, the switching set pressure to the holding pressure control at the next injection is changed to a certain value. It is modified to increase by the amount.

It should be noted that the detection of the pressure of the molten resin is not limited to the measurement in the mold, but the injection pressure of the resin at the tip of the barrel or the like can also be detected. At this time, the pressure of the pressurized oil to the injection cylinder is detected to indirectly detect the filling pressure of the resin, whereby the timing of switching from the speed control to the holding pressure control can be corrected.

When switching from speed control in the filling process to pressure control in the dwelling process based on the speed detection and pressure detection, a switching set position is obtained based on the shape and volume of the cavity, and then injection at the switching set position is performed. In some cases, the control pressure of the screw or the like is detected, and thereafter the switching control is performed using the pressure value as a switching set pressure from speed control to pressure control.

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

[0022]

According to the present invention, when switching from speed control in the filling process to pressure control in the pressure holding process, a change in the injection speed or a change in the injection pressure is detected, and the speed change or the pressure change immediately after the pressure control is switched. If the reversal occurs, the switching is corrected to be faster, and if the pressure does not reach the set speed or the set pressure within a predetermined time after switching the holding pressure control, the switching is corrected to be slower. With the injection control method of an injection molding machine, it is possible to switch from speed control to holding pressure control at the appropriate timing when the cavity has been filled, and it is extremely easy to set the timing of the switching and injection molding of high quality products. is there.

[Brief description of the 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 a change in an injection speed at the start of pressure-holding control in injection molding according to the present invention.

FIG. 3 is a graph showing a pressure change 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)

(57) [Claims] In an injection control of an injection molding machine, when an injection screw or the like reaches a predetermined set range position, or when the injection screw or the like reaches within a preset control switching allowable value and a control oil 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 pressure immediately after the switching is detected, and when it is detected that the speed change or the pressure change is reversed, At the time of the next injection, the switching set pressure to the holding pressure 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 from the start of the holding pressure control. Control of the injection molding machine at the time of the next injection, wherein the switching set pressure to the pressure holding control is corrected to a value higher by a predetermined pressure so that the switching timing is delayed. Method.