JPH0462020A - Method of setting change-over point for dwelling process in injection molding - Google Patents

Abstract

PURPOSE:To improve the quality and yield of a molding by sending an ultrasonic wave toward a part of the cavity by a probe, and detecting the reflected wave of the ultrasonic wave for calculating sound velocity, and therefore setting the change-over point from an injection process to a dwelling process on the basis of the sound velocity value. CONSTITUTION:At the same time of a commencement of the injection process in which resin is injected from an injection molding machine 1 to the cavity 3 of a mold 2, an ultrasonic wave of, for example, 5MHZ is sent per every 0.001 seconds toward a part of the cavity 3 from an ultrasonic probe 5 by an ultrasonic flaw detector 6. The ultrasonic wave sent in this fashion passes through the resin within the cavity 3 and reflects on the inner surface of the cavity 3 and then the reflected wave is detected by the ultrasonic flaw detector 6 via the ultrasonic probe 5. At the ultrasonic flaw detector 6, an ultrasonic velocity value is calculated on the basis of the reflected wave. The sound velocity value calculated herein is once differentiated by a differentiator 7, and the once differentiated value and aforementioned sound velocity value are recorded by a recorder 8. By observing the characteristic denoted by the sound velocity value and time, the operator can simply set the switching point from the injection process to the dwelling process.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a switching-free method for setting a switching point from an injection process to a pressure holding process in injection molding.

(Prior Art) In injection molding, the switching point from the injection process to the holding process in an injection molding machine is one of the factors that has a large influence on the quality of the molded product. For example, if the switching point is early, it will lead to incomplete filling, and if the switching point is late, it will lead to overfilling, which will cause cracks and deformation.

Conventionally, the switching point from the injection process to the pressure holding process has generally been set at any time by an operator based on experience and intuition while observing the quality of the molded product.

(Problem to be solved by the invention) However, if the switching point is set based on the experience and intuition of the operator, only a skilled operator can set the switching point. This poses a problem in that efficiency is lowered and it is difficult to determine whether or not the switching point determined by this is optimal.

(Means for Solving the Problems) The method without setting for switching to the holding pressure step in injection molding of the present invention uses an ultrasonic probe provided in the mold to transmit ultrasonic waves to a part of the cavity. Then, the reflected waves of the ultrasonic waves are detected to calculate the sound velocity, and the switching point from the injection process to the pressure holding process is set based on this sound velocity value.

(Function) In injection molding, when the injection process starts, an ultrasonic probe emits ultrasonic waves toward a part of the cavity.
The reflected wave of the ultrasonic wave is detected to calculate the sound velocity, and the switching point from the injection process to the pressure holding process is set based on the sound velocity value.

For example, as shown in Figure 3 (al), if the sound speed value increases in a substantially parabolic manner, it is determined that the switching point is set appropriately. is time t
If it decreases between 1 and t2, it is determined that the switching point is too early, and settings are made to obtain the characteristics shown in FIG. 3(a). Furthermore, as shown in FIG. 4(a), the sound velocity value changes over time t.
If it increases rapidly between 1 and t2, it is determined that the switching point is too late, and the setting is made so that the characteristics as shown in FIG. 3(a) are obtained. (Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows the overall configuration of an injection molding system using the method for setting a switching point to a pressure holding process according to the present invention.

In the figure, reference numeral 1 denotes an injection molding machine, and a mold 2 is disposed opposite to the nozzle tip of the injection molding machine 1.

The mold 2 is composed of a pair of divided fixed molds 21 and a movable mold 22, and the movable mold 22 is provided so as to be movable back and forth in the direction of arrow A in the figure by a hydraulic cylinder 4. A cavity 3 is formed facing the dividing plane between the fixed mold 21 and the movable mold 22.

The fixed mold 21 is provided with an ultrasonic probe 5, and the ultrasonic probe 5 is connected to an ultrasonic flaw detector 6. The ultrasonic probe 5 transmits 5 MHz ultrasonic waves toward a part of the cavity 3 using an ultrasonic flaw detector 6, for example, every o, ooi seconds (this transmission interval can be changed arbitrarily). This reflected wave (echo wave) is then input to the ultrasonic flaw detector 6. The ultrasonic flaw detector 6 calculates the sound velocity value based on this reflected wave. By transmitting ultrasonic waves to the cavity 3 and calculating the sound velocity value in this manner, the solidification state of the resin injected and filled into the cavity 3 can be measured.

Then, the sound velocity value of the ultrasonic flaw detector 6 is outputted to a differentiator 7, and a recorder 8 records the sound velocity value and its differential value obtained by dividing the same by the differentiator 7.

Next, a method for setting the switching point from the injection process to the pressure holding process using the injection molding system described above will be described.

At the same time as the injection process of injecting resin from the injection molding machine 1 into the cavity 3 of the mold 2 starts, the ultrasonic flaw detector 6 injects 5M from the ultrasonic probe 5 toward a part of the cavity 3.
Hz ultrasonic waves are transmitted every 0.001 seconds. The ultrasonic waves thus transmitted pass through the resin in the cavity 3 and are reflected on the inner surface of the cavity 3, and the reflected waves are detected by the ultrasonic flaw detector 6 via the ultrasonic probe 5. Ultrasonic flaw detector 6
Now, the sound speed value is calculated based on this reflected wave. and,
The calculated sound velocity value is differentiated once by a differentiator 7, and this -same machine value and the sound velocity value are recorded by a recorder 8.

FIG. 2 to FIG. 4 show the relationship between the sound velocity value calculated as described above, its minus aircraft component value, and time. FIG. 2(a) shows the relationship between the sound speed value and time when the switching point is too early, and FIG. 2(b) shows the relationship between the one-time differential value of the sound speed value and time. Figure 3(a) shows the relationship between the sound velocity value and time when the switching point is set appropriately, and the third
Figure ('b) shows the relationship between the first differential value of the sound speed value and time. FIG. 4(a) shows the relationship between the sound speed value and time when the switching point is too slow, and FIG. 4 (bl) shows the relationship between the one-time differential value of the sound speed value and time.

In FIGS. 2 to 4, tl indicates the time when the injection process is switched to the pressure holding process.

Here, if the switching point is too early, the resin filled in the cavity 3 will flow backwards, and the density of the resin in the cavity 3 will become small (as a result, the sound velocity value will change from time t1 as shown in Figure 2 (al). During t2, the appearance temporarily decreases.

In addition, if the switching point is too late, the cavity 3 will be filled with a large amount of resin, resulting in overpacking (overfilling), and the density of the resin will become thick (as a result, the sound velocity value will increase as shown in Figure 4 + a). It shows a characteristic that increases rapidly between time t1 and t2.

On the other hand, when the switching point is appropriate, as shown in FIG. 3(a), the sound velocity value exhibits a characteristic in which it increases substantially in a parabolic manner.

Therefore, during injection molding, the operator can easily set the switching point from the injection process to the holding pressure process by looking at the characteristics shown by the relationship between the sound velocity value and time described above.

In other words, during injection molding, if the characteristics shown in Figure 2 (a) appear, the switching point is set to be late, and if the characteristics shown in Figure 4 (a) appear, the switching point is set to be late. It is only necessary to set the speed to be faster so that the characteristics shown in FIG. 3 (al) are obtained.

This characteristic is shown in Figures 2(b) and 3) and 4(b).
As shown in Figure 2, this becomes noticeable when the sound velocity value is differentiated once. In other words, if the switching point is appropriate, the differential value will gradually decrease without an inflection point, as shown in Figure 3(b), and if the switching point is too early, the differential value will gradually decrease as shown in Figure 2(b). The differential value has an inflection point and becomes negative between time t1 and t2, and if the switching point is too late, the differential value has an inflection point and becomes negative at time t1, as shown in Figure 4 (bl). to t2.

Next, a description will be given of an application of the above-described method for setting a switching point to the pressure holding step of the present invention to injection molding of polycarbonate bathroom goods.

FIG. 5 shows a schematic configuration of a mold for molding bathroom supplies.

In FIG. 5, reference numeral 10 indicates a movable mold 11 and a fixed mold 12.
The cavity 13 of the mold 10 is formed in the shape of a bathroom article (bath tub). 14 is an ultrasonic probe.

Then, using this mold, the relationship between the sound velocity value and time when molding is performed with the above-mentioned injection molding system with the switching position set to 7, 5, 3, 1n, and the differential obtained by once differentiating the sound velocity value. The relationship between values and time is shown in FIGS. 6 to 9. The switching position here refers to the distance X from the position X1 when the injection screw moves to the frontmost position to the tip x2 of the injection screw when the injection screw is stopped to switch to holding pressure in Fig. 1. This switching position is the switching point to the pressure holding process.

Figure 6+8) shows the relationship between the sound velocity value and time when the switching position is set to 7 cranes, and Figure 6) shows the relationship between the single differential value of the sound velocity value and time. FIG. 7 (al) shows the relationship between the sound speed value and time when the switching position is set to 5n, and FIG. 7(b) shows the relationship between the one-time differential value of the sound speed value and time. FIG. 8(a) shows the relationship between the sound velocity value and time when the switching position is set to 3 m, and the part in FIG. 8) shows the relationship between the one-time differential value of the sound velocity value and time. Figure 9 (a) shows the relationship between the sound speed value and time when the switching position is set to 3 cranes, and Figure 9 (b) shows the relationship between the single differential value of the sound speed value and time. There is.

As a result, the switching position is changed to 5fl as shown in FIG. 7(a).
When set to , the sound velocity value exhibits a characteristic that increases almost parabolically as in the case where the switching position shown in Fig. 3 fa) is appropriate, and from this it can be determined that the switching position is appropriate. . A molded product (bathtub) was molded under these conditions.
The filling and appearance were both good.

In addition, when the switching position is set to 7 cranes as shown in Figure 6 (al), the sound velocity value is temporarily changed between time t1 and t2 as in the case where the switching position is too early as shown in Figure 2 (al). As a result, the appearance showed a characteristic of decreasing upwards, and from this it can be determined that the switching position was too early.Furthermore, molded products molded under these conditions had poor filling.

Furthermore, when the switching positions are set to 3 fl and 11 m as shown in Figure 8 (a) and Figure 9 (al), the sound velocity value is different from that when the switching position 1 shown in Figure 4 (a) is too slow. Similarly, it shows a characteristic that increases rapidly between time t1 and t2, and from this it can be determined that the switching position is too late.Furthermore, molded products molded under this condition have cracks and deformation.This phenomenon is caused by the switching This was more noticeable in the switching position 1n than in the switching position 3fl.

In this way, it is possible to easily determine whether or not the switching point from the injection process to the pressure holding process is appropriate based on the relationship between the sound velocity value and time, and this makes it easy to set the switching point. .

In this example, the differentiator 7 differentiates the sound velocity value once to clearly express the characteristics, but it is not necessarily necessary to differentiate the sound velocity value once, and the switching position can be determined only by the relationship between the sound velocity value and time. may be set. However, by differentiating, the characteristics can be clearly shown as described above, and it is effective for automatic control.

(Effects of the Invention) As described above, according to the method of the present invention, the switching point from the injection process to the pressure holding process can be quickly and easily appropriately set in injection molding.

By appropriately setting the switching point in this way, it is possible to improve the quality and yield of molded products.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the outline of an injection molding system for performing injection molding by the method of the present invention, and Fig. 2 (a) is a characteristic diagram showing the relationship between the sound velocity value and time when the switching point is too early. , Fig. 2('b) is a characteristic diagram showing the relationship between the first differential value of the sound speed value and time, and Fig. 3(a) is a characteristic diagram showing the relationship between the sound speed value and time when the switching point is appropriately set. A characteristic diagram showing the relationship between
Figure 3 (bl is a characteristic diagram showing the relationship between the first differential value of the sound velocity value and time, Figure 4 (al is a characteristic diagram showing the relationship between the sound velocity value and time when the switching point is too slow, Figure 4 (bl is a characteristic diagram showing the relationship between the first differential value of the sound velocity and time, Figure 5 is a sectional view showing the schematic configuration of a mold for molding bathroom goods, and Figure 6 (a) is a switching diagram. Point (advanced position of injection screw)
A characteristic diagram showing the relationship between the sound velocity value and time when 7 cranes are set, Fig. 6 (bl is a characteristic diagram showing the relationship between the single differential value of the sound velocity value and time, Fig. 7 (al is A characteristic diagram showing the relationship between the sound speed value and time when the switching point is set to 5fi, FIG. 7(b) is a characteristic diagram showing the relationship between the one-time differential value of the sound speed value and time, and FIG. al is a characteristic diagram showing the relationship between the sound velocity value and time when the switching point is set to 3H, Fig. 8 ('b
) is a characteristic diagram showing the relationship between the first differential value of the sound speed value and time, and FIG. 9 (al is a characteristic diagram showing the relationship between the sound speed value and time when the switching point is set to 1 fl, FIG. 9 (b) is a characteristic diagram showing the relationship between the first differential value of the sound velocity value and time. 1... Injection molding machine 2.10... Mold 3.13... Cavity 4.14... ...Ultrasonic probe patent applicant Sekisui Chemical Co., Ltd. Representative Hiroshi 1) Kaoru Figure 1 Figure 6 Figure 7 Figure 8 Figure 9 Prisoner

Claims (1)

[Claims] 1) An ultrasonic probe installed in the mold emits ultrasonic waves toward a part of the cavity, detects the reflected waves of the ultrasonic waves, calculates the sound speed, and performs injection based on this sound speed value. A method for setting a switching point from a process to a pressure holding process in injection molding, the method comprising setting a switching point from a process to a pressure holding process.