JPH0399821A - Method for judging quality of molded product in injection molding - Google Patents

Abstract

PURPOSE:To accurately judge the quality of a product by judging that a good product is molded when a measured filling time enters the tolerance range of the filling time at the time of the molding of a good product and a measured gate seal time enters the tolerance range of the gate seal time at the time of the molding of the good product. CONSTITUTION:In the first comparator 19, the output value measured by the first timer circuit 18 is compared with the tolerance range of a filling time and, when the measured value enterse the tolerance range, a good product signal is sent out. The output of an ultrasonic flaw detector 16 is connected to the second comparator 20 to which the speed value of an ultrasonic wave obtained at the time of the molding of a good product is preset and the output of the second comparator 20 is guided to the second timer circuit 25. In the third comparator 26, the measured output value from the second timer circuit 25 is compared with the tolerance range of a set gate seal time and, when the measured value enters the tolerance range, a good product signal is sent out. In a signal generator 27, only when the output signal of a good product from both of the third comparator 26 and the first comparator 19 are sent out, a good product is judged.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for determining the quality of molded products in injection molding.

(Prior Art) Generally, in an injection molding machine, a molded product is formed by filling a mold with molten synthetic resin, cooling and solidifying the resin, sealing the gate, and then releasing the resin from the mold. Recently, the technological progress of injection molding machines has been remarkable, and products that require high precision9
For example, compact discs and the like can also be molded by injection molding. As described above, when injection molding a high-precision product, it is important to determine whether the molded product is good or bad.

Conventionally, methods for determining the quality of molded products in injection molding include, for example, detecting the temperature of the injection nozzle as described in JP-A-60-217125;
By monitoring the mold temperature as described in JP-A-232923, or by detecting the mold opening force during mold opening as described in JP-A-61-182916,
It is known that the quality of molded products is determined by comparing them with respective set reference values.

(Problem to be solved by the invention) However, it is not possible to directly know the state of the resin filled into the mold by detecting the temperature of the injection nozzle, the temperature of the mold, the mold opening force when opening the mold, etc. , it is difficult to accurately monitor the molding of non-defective products.

In other words, data such as detected mold temperature and mold opening force are
There is a timing lag with the state of the resin in the mold during molding, and high accuracy is required based on the detected data. To determine the quality of precision molded products, it is necessary to repeatedly compare the results with actual molding. It required acquired experiential know-how and advanced molding knowledge.

The present invention has been made to solve the above problems, and its purpose is to accurately monitor the quality of the product by monitoring the resin filled into the injection mold from the melting state to the solidifying state. An object of the present invention is to provide a method for determining the quality of molded products in injection molding.

(Means for solving the problem) The method for determining the quality of molded products in injection molding of the present invention detects the resin pressure injected into the mold over time using a pressure sensor, and the rate of increase over time accelerates from a constant trend. The inflection point where the trend changes is determined by differentiation, the time from the start of filling to the inflection point is measured as the filling time, and the measured filling time is compared with a preset allowable range of filling time when forming a good product. The comparison process involves detecting the velocity value of the reflected wave of the ultrasonic wave emitted toward the resin in the gate by an ultrasonic probe installed near the gate of the injection mold, and comparing the detected value with the preset value. The gate sealing time is measured by comparing it with the set speed value of the ultrasonic wave obtained during molding of a good product, and the gate sealing time to reach the gate sealing time and the preset allowable gate sealing time during molding of a good product are measured. A process of comparing with the range,
This method is characterized by the step of determining a non-defective product when the measured values of the filling time and the gate sealing time fall within their respective allowable ranges during molding of a non-defective product.

(Function) The method for determining the quality of a molded product in the injection molding of the present invention configured as described above is such that the filling time from when the resin is injected into the mold to when it is filled is detected by a pressure sensor, and when the resin is The gate seal time is measured by an ultrasonic probe. It is determined that a non-defective product has been molded when the measured filling time falls within the allowable range for the filling time when molding a non-defective product and the measured gate seal time falls within the permissible range for the gate seal time during molding a non-defective product. Ru.

(Example) An example of a method for determining the quality of a molded product in injection molding of the present invention will be described with reference to the drawings.

FIG. 1 shows an injection molding apparatus to which the method for determining the quality of molded products in injection molding according to the present invention is applied.

In the figure, reference numeral 1 denotes an injection molding machine, in which resin stored in a hopper 11 is sequentially supplied into an injection cylinder 12, and is melted while being sent to the tip of the injection cylinder 12 by the rotation of a screw 13. The resin is injected from the nozzle 1a at the tip of the injection cylinder 12 by advancing the resin with a hydraulic ram mechanism 14.

2 is the mold, which is a direct gate type gate bush 4
It consists of a stationary mold 21 in which a mold is attached, and a movable mold 22 having a cavity 23.

The fixed side mold 21 is attached to the injection tip of the nozzle 1a of the injection molding machine 1, and the movable side mold 22 is attached to the fixed side mold 21.
A mold clamping device 15 such as a hydraulic cylinder is disposed facing the
It is possible to reciprocate back and forth in the figure.

A pressure sensor 3 that detects the resin pressure in the cavity 23 is provided in the movable mold 22 via an ejector turbine 24, and the pressure sensor 3 is connected to a differentiator 7 via an amplifier 6.
It is connected to the.

The output side of the differentiator 7 is connected to a first timer circuit 18 and a second timer circuit 25, which will be described later. The output of the first timer circuit 18 is determined by measuring the time between the injection start, that is, filling start, instruction signal from the controller 17 of the injection molding machine 1 and the output signal from the differentiator 7 as the filling time. is led to a comparator 19.

The first comparator 19 has a filling time set in advance when molding a non-defective product, and the filling time is the time from the start of injection of the injection molding machine 1 to the end of filling the cavity 23 with resin. As the filling time when molding a non-defective product, an allowable range of the filling time that satisfies the dimensional accuracy required by the product is set.

In the first comparator 19, the output value measured by the first timer circuit 18 is compared with the set tolerance range of the filling time, and when the measured value is within the tolerance range, a good product signal is sent out. be done.

On the other hand, the gate bush 4 has a gate 5 which is a resin flow path.
penetrates from the nozzle 1a side to the cavity 23 side,
As shown in an enlarged view in FIG. 2, an aluminum rod 8 is embedded in the side surface of the flow path of the gate 5 so that its front end surface is flush with the side surface of the flow path. An ultrasonic probe 9 is attached to the rear end surface of this aluminum rod 8 via a coupling agent. An ultrasonic flaw detector 16 is connected to the ultrasonic probe 9, and the ultrasonic flaw detector 16 emits a pulse every 0.01 to 1 second, for example. The probe 9 is 5M detected by the ultrasonic flaw detector 16.
It emits Hz ultrasonic waves and detects the reflected waves.

In addition, although not shown in the diagram, the ultrasonic flaw detector 16 includes:
Based on the reflected waves of the ultrasonic waves received by the ultrasonic probe 9, a measuring means is provided that measures the change in the velocity of the ultrasonic waves from the molten state to the solidified state at any time, and this measuring means is implemented by software. It is made up of.

The output of the ultrasonic flaw detector 16 indicates an ultrasonic velocity value corresponding to the state of the resin filled in the gate 5.
The output of the second comparator 20 is led to a second timer circuit 25 which operates based on the output signal from the differentiator 7 mentioned above.

The output of the second timer circuit 25 is guided to a third comparator 26 where the time between the output signal from the differentiator 7 and the output signal from the first comparator 20 is measured as a gate seal time.

This third comparator 26 is preset with a gate sealing time during molding of a non-defective product. As the gate sealing time during molding of a non-defective product, an allowable range of gate sealing time that satisfies the dimensional accuracy required by the product is set.

In the third comparator 26, the measured output value from the second timer circuit 25 is compared with the set tolerance range of the gate seal time, and when the measured value is within the tolerance range, a good product signal is sent out. be done.

The outputs of the third comparator 26 and the first comparator 19 are led to a signal generator 27. This signal generator 27 is
The good signal from the first comparator 19 and the third comparator 26
It is constituted by an AND circuit which determines that the product is non-defective and sends out an instruction signal when both the non-defective product signal and the non-defective product signal from the product are led together.

The output of this signal generator 27 is led to a controller 28 of a molded product removal device 29. The controller 28 controls the molded product removal device 29 based on the signal from the signal generator 27.

The molded product take-out device 29 is configured to feed molded products determined to be good products to a normal line, and to take out molded products determined to be defective products to a different line for processing.

In the above embodiment, the gate on which the ultrasonic probe 9 is provided is a direct gate, but it may also be a film gate, for example. The position where the ultrasonic probe 9 is provided is not particularly limited as long as it is near the gate, and may be provided, for example, from the cavity toward the gate.

Further, the mounting position of the pressure sensor 3 is not limited to the above embodiment as long as it is a position where the pressure inside the cavity 23 can be accurately detected. For example, it may be provided at a direct gate opposite to the ultrasound probe 9.

Next, a method for determining the quality of a molded product in injection molding according to the above embodiment will be explained based on the drawings.

First, when resin is injected into the cavity 23 of the mold 2 by the injection molding machine 1, the resin is filled and compressed, and the pressure sensor 3 detects the resin pressure in the mold 2 over time. At this time, the controller 17 of the injection molding machine 1 sends a filling start instruction signal to the first timer circuit on the 1st, and the first timer circuit 18 is activated. The detected change in mold pressure over time is input to a differentiator 7 via an amplifier 6. Figure 3 shows the pressure change inside the mold cavity at this time. This change in mold pressure over time is differentially calculated by a differentiator 7, and the result is shown in FIG.

In FIG. 4, an inflection point Q at which the rate of increase in mold pressure over time changes from a constant tendency to an accelerating tendency is determined, and the inflection point Q is detected as the time t1 at which filling is completed. Therefore, when the inflection point Q in FIG. 3 is reached, the differentiator 7 sends a filling end signal to the first timer circuit 18 and the second timer circuit 25.

In the first timer circuit 18, the injection start time t0
The time from t1 to time t1 when the resin is filled into the mold is measured, and this measured value is sent to the first comparator 26. This measured gate sealing time is compared with a preset allowable range of filling time when forming a non-defective product in a first comparator 19.

If the filling time is within the allowable range, the first comparator 19 sends a signal indicating a good product to the signal generator 27 .

On the other hand, as injection starts into the mold 2, the ultrasonic flaw detector 1
When a pulse is emitted from the ultrasonic probe 9, the 5 MHz ultrasonic wave (pulse wave) emitted every 0.01 seconds, for example, is transmitted to the resin 10 filled in the gate 5 and the aluminum rod 8.
and the boundary surface 51 between the resin 10 and the side surface of the flow path (the upper side surface in the drawing) on the opposite side of the aluminum rod 8 of the gate 5, and the reflected wave passes through the aluminum rod 8 again. The ultrasonic probe 9 transmits ultrasonic waves and receives reflected waves.

The reflected ultrasound waves received by the ultrasound probe 9 are
As shown in FIGS. 5 and 6. Here, FIG. 5 is a waveform diagram of the reflected wave when the gate 5 is not filled with the resin 10, and FIG. 6 is a waveform diagram of the reflected wave when the gate 5 is filled with the resin 10. be. That is, FIG. 5 shows the state of the -order echo wave 31 and the secondary echo wave 32 from the surface (front end surface) of the aluminum rod 8 in response to the transmitted pulse 30 when the resin is not filled. FIG. 6 also shows a primary echo wave 34 from the surface of the aluminum rod 8, an interface echo wave 35 from the boundary surface 51, and a secondary echo wave from the surface of the aluminum rod 8 in response to the transmitted pulse 33 when the resin is filled. The state of the next echo wave 36 is shown.

Each echo wave shown in FIG. 6 is guided to the ultrasonic flaw detector 16 via the ultrasonic probe 9.

Among these guided echo waves, the boundary surface echo wave 35 is
When the resin 10 filled in the gate 5 is solidified from a molten state, a -order echo wave 34 and an interface echo wave 35 are generated.
Since the time interval T changes, the −th echo wave 34
and the boundary surface echo wave 35 using the ultrasonic flaw detector 1.
6, and the speed of the reflected wave is calculated in real time from this digital value and the width of the gate 5 portion where the ultrasonic probe 9 is provided. However, the width of the gate 5 portion is inputted in advance.

FIG. 7 shows the velocity values of the reflected waves obtained in this manner. In the figure, time 1. when molten resin is filled into the mold. , the speed of the reflected wave is approximately 1600 m
/sec, and from this time, as the resin gradually solidifies, the speed of the reflected wave increases almost linearly, and reaches approximately 2500 m/sec at time b when the resin solidifies (i.e., at the time of gate sealing). .

The velocity value of the reflected wave determined in this way is guided to the second comparator 20. The second comparator 20 compares the speed value from the ultrasonic flaw detector 16 every moment with a preset speed value of ultrasonic waves obtained during molding of a non-defective product.

In this case, 2500 m/sec is set as the set speed value. The measured speed value is the set speed value 2500
m/sec, a deactivation instruction signal is sent to the timer circuit 25, which is activated in response to the instruction signal from the differentiator 7 mentioned above.

The timer circuit 25 measures the time from time t1 when the mold is filled with molten resin to time t2 when the resin solidifies, and sends this measured value to the third comparator 26. This measured gate sealing time is compared with a preset allowable range of gate sealing time during molding of a non-defective product in a third comparator 26.

If the third comparator 26 is within the allowable range of the gate seal time, a signal indicating a good product is sent to the signal generator 27.

In the signal generator 27, the third
The product is determined to be non-defective only when output signals indicating a non-defective product are sent out from both the comparator 26 and the first comparator 19, but the product is determined to be defective if a defective product signal is derived from at least one of them.

The controller 28 controls the molded product removal device 29 based on the signal from the signal generator 27. The molded product take-out device 29 distinguishes the molded products molded during the molding cycle into non-defective products and defective products, and takes out the defective products to a different line from the normal line.

In the above example, the overall length is 1 as the dimensional accuracy of the molded product.
If ±10μm is required for 00mm, the allowable range for the filling time is set to 2.0 to 2.3 seconds, and the allowable range for the gate seal time is set to 4.3 to 5.7 seconds.
Molding was performed with the setting set to sec.

FIG. 8 shows the quality determination status of the molded product obtained at this time.

In Figure 8, if the measured values of filling time and gate sealing time are both within the allowable range, the product is good (marked O).
A molded product (marked with an x) in the time-deficient or time-excess region is determined to be a defective product. Defective products due to insufficient time have insufficient dimensions and are molded at low temperatures, resulting in short shots and flow marks that can be seen on the outside, and are determined to be defective. In addition, it was confirmed that molded products in the excessive time range were overpacked because they were molded at high temperatures, causing cracks and the like.

(Effects of the Invention) Since the method for determining the quality of molded products in injection molding of the present invention is configured as described above, it is possible to start filling with resin during molding without requiring empirical know-how or advanced formation knowledge. It is possible to accurately monitor everything from the melting state to the solidification state, and easily determine the quality of precision molded products.

[Brief explanation of drawings]

Fig. 1 is a schematic explanatory diagram of the control device for injection molding according to the present invention;
The figure is an enlarged view of the gate bush part, Figure 3 is a diagram showing an example of the change in cavity pressure over time during injection molding, and Figure 4 is an enlarged view of the gate bushing part.
The figure is a graph of the differential value of the change in cavity pressure over time during injection molding, Figure 5 is a graph showing each echo wave in response to the emitted pulse when resin is not filled, and Figure 6 is a graph showing the echo waves when resin is filled. Figure 7 is a diagram showing the speed change of reflected waves over time after resin is filled, and Figure 8 is a scatter diagram showing the status of quality determination of molded products. be. Explanation of symbols 1: Injection molding machine, 2: Mold, 2I: Fixed side mold,
22...Moving side mold, 23...Cavity, 3...Pressure sensor, 4...Gate bush, 5...Gate, 6...
・Amplifier, 7. Differentiator, 8. Aluminum rod, 9. Ultrasonic probe, 10. Resin, 14. Hydraulic ram mechanism, 15
...Mold clamping device, 16..Ultrasonic flaw detector, 18..First timer circuit, Engineering 9..First comparator, 20..Second comparator, 25..Second timer circuit , 26...Third comparator, 27...Signal generator, 28...Controller,
29... Molded product removal device.

Claims (1)

[Claims] 1. The pressure of the resin injected into the mold is detected over time by a pressure sensor, the inflection point where the rate of increase over time changes from a constant tendency to an accelerating tendency is found by differentiation, and filling is started. A step of measuring the time required to reach an inflection point from the start of the injection mold as the filling time, and comparing the measured filling time with a preset allowable range of filling time when molding a non-defective product; The velocity value of the reflected wave of the ultrasonic wave emitted toward the resin in the gate is detected by the ultrasonic probe, and the detected value is combined with the preset speed value of the ultrasonic wave obtained during molding of a non-defective product. A step of comparing the gate sealing time to reach the gate sealing point with a preset allowable range of gate sealing time when forming a good product; A method for determining the quality of a molded product in injection molding, the method comprising the step of determining the product to be non-defective when the measured value falls within the respective tolerance range for molding a non-defective product.