JP2003039519A - Monitoring method in injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a monitoring method which hardly judges a conforming article to be a defective article even when a large wave-shaped change appears in operation data for quality control in an injection molding machine. SOLUTION: Every time when the operation data for quality control are obtained, the newest movement average value with regard to a preset number of data is calculated. When the deviation of the operation data from the average value exceeds a preset allowance limit, an alarm is raised. In the injection molding machine, for example, when this method is used in monitoring operation data such as metering time, filling time, and a cushion quantity; the precision of judgment with regard to a conforming article and a defective article can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for monitoring operational data for quality control in an injection molding machine.

[0002]

2. Description of the Related Art FIG. 2 shows a schematic structure of an injection unit portion of a hydraulic injection molding machine. In the figure, 1 is a mold, 3 is a heating barrel, 5 is a screw, and 7 is a hydraulic cylinder for injection.

The heating barrel 3 has its tip (the left end in the figure).
It is connected to the back surface of the mold 1 via the nozzle 4 provided in the. A screw 5 is incorporated inside the heating barrel 3. A hydraulic cylinder 7 for injection is connected to the rear end of the screw 5. A hopper 6 is connected near the rear end of the heating barrel 3.

At the time of measurement, the screw 5 is rotated in the forward direction in the heating barrel 3 by using a servomotor (not shown) for measuring, and the resin is introduced into the heating barrel 3 from the hopper 6. The introduced resin is melted while being heated and stirred, is sent to the front of the screw 5 (leftward in the figure), and is stored on the tip side of the heating barrel 3. Along with this, the screw 5 is gradually retracted by the pressure of the molten resin, and the molten resin is stored in the heating barrel 3. After a predetermined amount of molten resin is stored in the heating barrel 3, the screw 5 is moved forward using the hydraulic cylinder 7. As a result, the molten resin is filled in the mold 1.

Conventionally, operation data for quality control in an injection molding machine has been monitored as follows. That is, operational data (eg, weighing time, filling time,
Cushion amount, metering pressure, filling pressure, peak pressure, etc.)
With respect to, a reference value and an allowable limit of deviation from the reference value are set in advance. Whenever the actual operation data is obtained, the deviation of the operation data from the reference value is calculated, and when the value of this deviation exceeds the allowable limit, an alarm is issued, whereby
Inform the operator that the product may be defective.

Here, the measurement time is the time required to introduce a predetermined amount of molten resin into the heating barrel 3.
The filling time is the time from the start of injection of the molten resin from the heating barrel 3 into the mold 1 to the transition to the pressure holding step. The cushion amount is a distance by which the screw 5 (or the plunger) advances in the heating barrel 3 in the pressure holding step. In the pressure-holding step, the screw 5 is moved forward in the heating barrel 3 in order to compensate for the shrinkage of the molten resin after the resin is filled in the mold 1 due to the solidification.
The metering pressure is the pressure in the heating barrel 3 when charging the molten resin, or the back pressure of the screw 5 (that is, the pressure of the hydraulic cylinder 7) at that time. The filling pressure is the pressure in the heating barrel 3 when the molten resin is injected from the injection unit into the mold 1, or the back pressure of the screw 5 at that time. The peak pressure is the instantaneous maximum value of the filling pressure during one injection operation.

The reference value and the allowable limit of the deviation are fixed values, and once set, they are kept at a constant value until the operator changes the value next time.

The above-mentioned reference value has been conventionally set by the following method.

(A) The operator directly inputs the reference value on the setting screen of the operation panel. This method is adopted when a product having a past production record is produced and the previous reference value is known.

(B) When trial production is carried out and a good product can be stably produced, the average value (or latest value) of the operation data for quality control is set as a reference value. This method is used, for example, when a suitable number of products are produced after a rough condition is set and a reference value is decided while verifying whether the condition is appropriate.

Further, the allowable limit of the above deviation has been conventionally set by the following method.

(A) The operator directly inputs the reference value on the setting screen of the operation panel. This method is adopted when a product having a past production record is produced and the previous reference value is known.

(B) When the recommended value of the allowable limit of the deviation is stored in advance in the operation panel (storage device of the operation panel), the operator pushes the push button for calling the recommended value. As a result, the recommended value is set as the allowable limit of deviation in the operation panel.

There are the following two types of states in which the above recommended values are stored in the operation panel.

(B-1) When the recommended value is stored as a variable parameter: The recommended value is stored as a variable parameter in the operation panel and is not coded as a fixed value in the control program. Not in. In this case, it is usually difficult for the operator to freely change the variable parameter. However, the service personnel of the device manufacturer can switch the operation panel to the parameter setting mode without rewriting the control program.
The recommended value can be changed.

(B-2) When coded as a fixed value in the control program: The recommended value cannot be changed without rewriting the control program. Therefore, the operator cannot freely change. In addition, it is not always easy for the service personnel of the device manufacturer to rewrite the control program.

(Problems of Prior Art) In an injection molding machine, when monitoring operation data for quality control, a sudden abnormality is detected, and only a product when such an abnormality occurs is regarded as a defective product. It is desirable to judge. However, the operating data fluctuates even when a large undulation fluctuation occurs in the temperature of the mold or the injection unit under the influence of the outside air temperature or the cooling water temperature.

For example, since the fluidity of the resin in the mold increases as the temperature of the mold increases, more resin is filled in the mold and the cushion amount fluctuates. When the temperature of the injection unit rises, in the crystalline resin, the melting of the resin is accelerated and the measuring time tends to be shortened. On the other hand, in the case of the amorphous resin, the melting of the resin is accelerated, and the melting starts from the feed zone (the portion in the heating barrel 3 near the connection portion of the hopper 6 (FIG. 2)). Therefore, the frictional force between the screw and the resin is reduced, and the force to send out the resin becomes weaker,
Weighing time tends to be long.

As described above, even when the quality control operation data fluctuates under the influence of disturbance factors and deviates from the preset allowable range, the product at that time is determined to be defective. There is. However, a product that is determined to be defective due to such a cause may actually satisfy the specifications of a non-defective product. That is, there is a problem that it is determined as a defective product even though it is a good product. In particular, when the operating data shows a certain tendency of increase or decrease, or when there is a large fluctuation of waviness,
If the reference value for monitoring the operation data remains fixed, it is often the case that the product is determined to be defective from the operation data, although the product is actually a good product.

[0020]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems in the conventional method of monitoring the operation data for quality control in the injection molding machine. An object of the present invention is to provide a monitoring method that is less likely to erroneously determine a non-defective product to be a defective product even when a large undulation fluctuation appears in the operation data for quality control.

[0021]

A monitoring method for an injection molding machine according to the present invention is a method for monitoring operational data for quality control, which is preset every time operational data for quality control is obtained. The latest moving average value for the number of data is calculated, and an alarm is issued when the deviation of the obtained operation data from the moving average value exceeds a preset allowable limit.

Preferably, when the moving average value is calculated, data exceeding the allowable limit in the past operation data is excluded from the calculation.

Further, the injection molding machine according to the present invention has a monitoring function for monitoring the operation data for quality control based on the above method.

According to the monitoring method of the present invention, the measured quality control operation data is used to determine whether the product is “good” or
When making a determination of "bad", the determination is made based on the deviation from the latest moving average value. Therefore, it is possible to remove the influence of the change in the environmental condition having a relatively long cycle.
Therefore, only when a sudden abnormality occurs in the injection molding machine, the affected product can be determined as a "defective product".

According to the monitoring method of the present invention, it is possible to reduce the possibility of erroneously determining a non-defective product as a defective product, so that the yield of non-defective products can be increased and the manufacturing cost can be reduced. Further, since the labor of re-inspecting the product determined to be defective from the operation data is reduced, the production efficiency can be improved.

In the injection molding machine, for example, the measuring time,
If the method of the present invention is used to monitor the operation data such as the filling time and the cushion amount, it is possible to improve the accuracy of determination of non-defective products and defective products. In addition, here, the weighing time is
This is the time required to introduce a predetermined amount of raw material resin into the heating barrel. The filling time is the time from the start of injection of the molten resin from the heating barrel into the mold until the transition to the pressure holding step. The cushion amount is the distance that the screw advances in the heating barrel due to the shrinkage of the resin in the pressure holding step.

[0027]

FIG. 1 shows a flow chart of an example of a method for monitoring an injection molding machine according to the present invention.

First, an allowable limit K of deviation of the quality control operation data (for example, measuring time, filling time, cushion amount, etc.) from a reference value is set. The product is determined to be defective when the difference between the reference value and the actual data exceeds the allowable limit K.

An initial reference value IJ is set. This is because the actual value of the moving average IH does not exist at the start of production. As the value of the initial reference value IJ, a value determined by a preliminary test or a value obtained based on past operation data can be used.

The number of data for calculating the value of the moving average IH (in this case, the number N of shots for injection molding) is set.

With the start of operation of the injection molding machine, monitoring of operation data is started.

From the start of operation to N shots, the latest N
Since there is no moving average IH value for shots,
The value of the deviation of the actual data Mi from the initial reference value IJ is monitored. When the absolute value of this deviation exceeds the allowable limit K, it is determined that the product is defective and an alarm is issued.

After N + 1 shots from the start of operation, the moving average IH for the latest N shots is used as a reference value to monitor the deviation value of the actual data Mi from this moving average IH. When the absolute value of this deviation exceeds the allowable limit K,
The product is judged to be defective and an alarm is issued.

(Regarding Modifications of Monitoring Method) The monitoring method of the present invention is not limited to the method shown in FIG. 1 and can be carried out by adding various modifications to the above method, as shown below. .

A. Regarding the allowable limit of deviation, different values can be set for the "+" side and the "-" side of the moving average. Further, the allowable limit may be set only on one side (that is, if it is on the other side, all are judged as non-defective products).

B. Regarding the method of setting the reference value immediately after the start of operation, from 2 to N shots, the value of the moving average is sequentially calculated by using only the actual data (1 to N-1 pieces) obtained up to that point. The value can also be used as a reference value. Alternatively, the moving average value can be calculated by replacing only the portion where the actual data is insufficient with the initial reference value IJ.

C. "Good product" without setting the initial reference value K
-The determination of "defective product" may be started from the N + 1th shot. Further, according to the method described in “b”, the determination may be started from the second shot.

D. When calculating the value of the moving average, the operation data when it is determined as “defective product” may be excluded from the calculation.

E. In the flow chart shown in FIG.
Although an alarm is simply generated when it is determined to be "defective product", the injection molding machine can be stopped when it is determined to be "defective product". Further, the injection molding machine may be stopped when a predetermined number of alarms are continuously issued.

[0040]

According to the monitoring method of the present invention, it is possible to reduce the possibility of erroneously determining a non-defective product to be a defective product, so that the yield of non-defective products can be increased and the manufacturing cost can be reduced. Further, since the labor of re-inspecting the product determined to be defective on the operation data is reduced, the production efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a flowchart showing an example of a method for monitoring an injection molding machine according to the present invention.

FIG. 2 is a schematic configuration diagram of an injection unit portion of a hydraulic injection molding machine to which the monitoring method of the present invention is applied.

[Explanation of symbols]

1 ... mold 3 ... heating barrel, 4 ... Nozzle, 5 ... screw, 6 ... Hopper, 7 ... Hydraulic cylinder.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Fumiyuki Kato             2068 Ooka, Numazu City, Shizuoka Prefecture Toshiba Machine Co., Ltd.             In the company (72) Inventor Jun Koike             2068 Ooka, Numazu City, Shizuoka Prefecture Toshiba Machine Co., Ltd.             In the company (72) Inventor Hiroshi Katsuta             2068 Ooka, Numazu City, Shizuoka Prefecture Toshiba Machine Co., Ltd.             In the company F-term (reference) 4F206 AM09 AM19 AM22 AP10 AR11                       JA07 JL02 JM01 JM04 JM05                       JN03 JN11 JN21 JP01 JP12                       JP13 JP14 JP15 JP17

Claims (6)

[Claims] 1. A method for monitoring operational data for quality control in an injection molding machine, wherein the latest moving average value for a preset number of data is calculated every time operational data for quality control is obtained. A monitoring method in an injection molding machine, wherein an alarm is issued when the deviation of the obtained operation data with respect to the moving average value exceeds a preset allowable limit. 2. The injection molding machine according to claim 1, wherein, when the moving average value is calculated, data exceeding the allowable limit in the past operation data is excluded from the calculation. Monitoring method. 3. The monitoring method according to claim 1, wherein the quality control operation data is at least one of a weighing time, a filling time, and a cushion amount. 4. Every time operation data for quality control is obtained, a latest moving average value for a preset number of data is calculated, and a deviation of the obtained operation data from this moving average value is An injection molding machine having a monitoring function for issuing an alarm when a preset allowable limit is exceeded. 5. The injection molding machine according to claim 4, wherein when the moving average value is calculated, data that exceeds the allowable limit in the past operation data is excluded from the calculation. 6. The injection molding machine according to claim 4, wherein the operation data for quality control is at least one of a weighing time, a filling time, and a cushion amount.