JP2917088B2 - 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 a method for controlling an injection molding machine.

[0002]

2. Description of the Related Art In general, in injection molding of a resin, if the injection is performed while maintaining the injection speed at a high speed, an overpack phenomenon is likely to appear. That is, the injection speed is switched to a low speed immediately before the filling is completed. This switching timing is set empirically. If the switching is performed too early, the thin portion of the molded product is solidified, and an unfilled phenomenon occurs.

In consideration of this point, there has been proposed a method of detecting the injection speed and switching from the injection process to the pressure holding process when the injection speed drops to a low speed. However, the decrease in the injection speed is caused by the resin pressure in the mold. As the resistance rises due to the rise, the switching timing is liable to be delayed.

As a control method for solving the above-mentioned drawbacks, there has been known a method which pays attention to a mold opening amount as described below.

[0005] That is, attention is paid to the fact that the mold is opened by a very small amount when the mold is filled with the molten resin, and the injection pressure and the holding pressure are controlled by setting the mold opening amount.
No. 29415.

[0006]

According to the above-described control method, when the injection pressure is corrected, if the resin pressure in the mold is low, the degree of change in the mold opening amount is large, and a large correction effect can be obtained. However, as the resin pressure in the mold increases, the resin pressure in the mold is increased by the injection pressure, which is the pressure outside the molded product. Therefore, there is a limit to the effect of correcting the mold opening amount. Problems such as uneven thickness may occur.

[0007] In view of the above problems, an object of the present invention is to change the timing of switching the injection speed and injection pressure required immediately before the completion of filling of the resin with the change amount of the mold opening amount that changes within the molding cycle. An object of the present invention is to provide a control method for an injection molding machine which can be monitored and automatically determined.

[0008]

According to the present invention, there is provided a control method of an injection molding machine for automatically correcting a molding condition by detecting a mold opening amount , wherein a change of the mold opening amount with respect to time during an injection step in each molding cycle. Amount, or a value correlated with the change amount, and based on a comparison result between the calculation result and a predetermined set value, a rapid rise phenomenon of the mold opening amount is detected.
However, when the rapid rise phenomenon is detected,
And performing correction control of the injection speed and injection pressure that.

As a value correlated with the change amount, a ratio between the change amount at a certain time and the change amount calculated one time before the change amount is used.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing embodiments of the present invention, the background on which the present invention is made will be described. FIG. 1 shows a time change of the mold opening amount (indicated by a solid line) and the injection speed (indicated by a dashed line) in one molding cycle, and a region P1 exhibiting a sharp rise is a mold opening when the resin is completely filled. It shows the phenomenon of quantity increase. Speaking of the mold opening amount, while the resin is being filled after the injection is started at the time T1, the value remains almost at 0,
Immediately before the complete filling, it was found that the mold opening amount suddenly rises at time T2 while a gas such as a gas that still cannot escape in the mold cavity exists as a kind of damper. In addition, it has been found that this time is a timing suitable for switching the injection speed indicated by T3 to a low speed.

Based on the above knowledge, the present invention monitors the amount of change in the mold opening that changes within the molding cycle to determine the timing of switching the injection speed. This will be described with reference to FIG.

The platen 2 is moved by the mold clamping cylinder 1 to clamp the mold 3. The screw 5 advances to the nozzle 6 side by the injection cylinder 4, and the molten resin 7 is filled in the cavity of the mold 3. At this time, it is well known that a small amount of mold opening occurs at the joint between the pair of molds 3. This mold opening is detected by the position detector 9 and the abutment block 10 provided on the mold 3 and the platen 2. The control device 20 controls the switching of the injection speed, which will be described later, based on the detection signal from the position detector 9.

In this embodiment, in addition to the position detector 9, a mold clamping force detector 21 and an injection pressure detector 22 are provided.
0 controls the drive source 23 of the mold clamping cylinder 1 and the drive source 24 of the injection cylinder 4 based on the detection signals from these detectors, but since these controls are known, the description is omitted. The setting unit 25 is for inputting a set value required for control described later.

Hereinafter, the switching control of the injection speed will be described. Assuming that the mold opening amount is L in a section from the start of injection to the switching to the pressure-holding step, the control device 20 detects the position by the position detector 9 at an arbitrary sampling cycle sufficiently shorter than one cycle time for each molding cycle. The mold opening is sampled. Then, the difference in mold opening amount of the mold opening amount L _n and the next period of a time L _{(n + 1)} to _{(L (n + 1) -L} n) ( change amount) [Delta] L
When _n, to calculate the ratio of the immediately preceding difference ΔL _(n-1). The control device 20 performs an operation of determining whether or not the above ratio is within the range set by the setting unit 25. When the above ratio is within the set range, the injection speed is switched to a low speed or the injection system is braked. Control operations such as switching the injection pressure are performed.

[0015] The detected value of the mold opening amount usually shows at least a five-fold difference when measuring between the tie bars as compared with when measuring only between the platens of the mold. However, by employing the method of the present invention, it is possible to cancel the absolute value of the mold opening amount, and it is not affected by the mounting method of the position detector, the mounting accuracy, and the like. There is no need to change the setting values accordingly. Also,
When noise enters, the above ratio shows an excessive value, but by setting a range for the above ratio, in the case of noise, the above ratio falls out of the set range, so that there is less erroneous recognition. As this range, a value of 1 or more and 10 or less is usually selected. In addition, the sampling period of the mold opening amount can be reduced to the shortest time in which the time required for the above-described ratio calculation and determination operation in the control device 20 can be secured.

As described above, according to the present invention, it is not necessary to change the set value each time the shape of the mold 3 or the molded article portion 8 changes, and the mold opening amount immediately rises immediately before the filling is completed (see FIG. 2). (Time point indicated by T2) can be accurately detected based on the amount of time change of the mold opening amount due to the reaction force F from the molded article portion 8.

[0017]

As described above, according to the present invention, the timing detection immediately before the completion of the filling of the resin can be accurately performed without being affected by the shape change of the mold and the molded product. Switching of the injection speed can be performed with good timing. As a result, burrs and overpack can be reduced, and short shots and the like can be reduced.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing a time change of a mold opening amount and an injection speed in one molding cycle in order to explain the principle of the present invention.

FIG. 2 is a diagram showing a schematic configuration of an embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mold clamping cylinder 2 platen 3 mold 4 injection cylinder 5 screw 6 nozzle 7 molten resin 8 molded part 9 position detector 10 butting block 22 mold clamping force detector 22 injection pressure detector 23, 24 drive source

Claims (2)

(57) [Claims] 1. A method of controlling an injection molding machine for automatically correcting a molding condition by detecting a mold opening amount , wherein the mold opening amount changes with time or correlates with the change amount during an injection step in each molding cycle. value is calculated, the type based on a comparison result between the set value determined in advance and the result output the calculated
Detecting the rapid rise of the opening amount,
A control method for an injection molding machine, wherein correction control of an injection speed and an injection pressure in an injection cylinder is performed upon detection . 2. The control method for an injection molding machine according to claim 1, wherein a ratio between the change amount at a certain time and the change amount calculated one time before the change amount is set as a value correlated with the change amount. A method for controlling an injection molding machine, which is used.