JP2001191382A - Method for discriminating moldings and injection molding machine equipped with device for discriminating moldings - Google Patents

Abstract

PROBLEM TO BE SOLVED: To contrive discrimination of a nondefective and a defective of moldings, especially enhancement of precision of a technique discriminating short shot by utilizing the monitoring value of an injection molding machine. SOLUTION: The injection molding machine equipped with a position detector 24 for detecting transfer amount of a screw 18 in a heating cylinder 21 is equipped with a discriminating device 1 performing previously decided operation by using a detection signal sent from a position detector. The discriminating device executes a first step calculating density of a plasticized molten resin, a second step, in which product of calculated density of the molten resin and advanced distance of a screw in case of injection is calculated and weight of the molten resin inserted into a mold is calculated and a third step, in which a nondefective and a defective of moldings are discriminated by a degree of short shot from the calculated weight of the molten resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molded article discriminating method for judging the quality of a molded article in an injection molding machine and an injection molding machine provided with a molded article discriminating apparatus.

[0002]

2. Description of the Related Art Of the operations of an injection molding machine, the operation of an electric injection molding machine will be briefly described focusing on the operation of an injection device.

(1) By rotating a screw by a servomotor for driving the screw to rotate, the resin dropped from the hopper to the rear portion of the screw is fed into the tip of the heating cylinder while being melted. At this time, the screw retreats while receiving the pressure of the molten resin accumulated at the tip of the heating cylinder.

[0004] A drive shaft is directly connected to the rear end of the screw, and the drive shaft is rotatably supported by a pressure plate via a bearing. This drive shaft is driven via a timing belt by a servomotor for driving the rotation of the screw.
The pressure plate is driven by a servomotor for injection via a ball screw, and moves forward and backward along a guide bar. As described later, the pressure of the molten resin is detected by a load cell and controlled in a closed loop.

(2) Next, the pressure plate is advanced by driving the servo motor for injection, and the molten resin is fed into the mold by using the tip of the screw as a piston.

(3) At the end of the filling process, the molten resin fills the cavity of the mold, at which time the forward movement of the screw switches from speed control to pressure control.

(4) Thereafter, the resin in the mold cavity is cooled under the set pressure. The resin pressure is controlled in a closed loop as in the pressure control described above.

In the injection apparatus, after the step (4),
Returning to the step (1), the next cycle is started. On the other hand, in the mold clamping device, in parallel with (1), after opening the mold and taking out the molded product cooled and solidified by the ejector mechanism,
Close the mold and enter the step (2).

In general, an injection molding machine is provided with a pass / fail determination device that determines pass / fail of a molded product for each shot. For example, Japanese Patent Application Laid-Open No. 7-205
No. 243 discloses a method of performing pass / fail determination using a screw most forward position, that is, a minimum cushion position, and a filling peak pressure as monitor values. In addition, there are various types of quality determination of molded products. For example, there is a method of detecting short shots of molded products and performing quality determination.

The following two methods are known as methods for detecting a short shot of a molded article. The first method is a method in which the obtained molded product is photographed by a camera, and the presence or absence of a short shot in a point area is determined by image processing. The second method uses detection signals from various detectors provided in the injection molding machine as monitor values (for example, the amount of movement of the screw, the driving force when driving the screw, the fluctuation of the minimum cushion position, etc.). In this method, the quality of the molded product is determined based on the change.

However, the first method cannot detect a small short shot or a short shot in an area not captured by the camera. On the other hand, the above-mentioned second method has a problem that the relation between each monitor value and the short shot is not clear, and in the end, it is necessary to manually perform an inspection.

[0012]

The reason why the conventional short shot discriminating apparatus does not properly discriminate a molded product is considered to be as follows. This will be described using a typical discriminating device as an example.

At present, a method of making a determination at the minimum cushion position is most often used. However, this method
The determination is performed assuming the following two points. The first point is
The assumption is that the density of the plasticized molten resin is uniform and constant. The second point is that the amount of resin backflow at a screw check valve (usually those having a check valve is called an in-line type) arranged in a heating cylinder is constant. It is an assumption.

The method of performing the determination at the minimum cushion position is as follows.
Under these assumptions, a short shot is detected by detecting a change in the volume of the injected resin (entering the mold). Under the molding conditions where the above assumptions hold, it is possible to determine the acceptability with a considerable probability. However, there is a problem that the probability of discrimination decreases when the lot and the dry state of the molding material change.

A molding machine without a check valve, which has recently become a hot topic (usually referred to as a pre-plastic type), has been improved in the above-mentioned second point, and is therefore compared with an in-line type. It is said that weight fluctuation (short shot occurrence) is small.

[0016] However, since the above-mentioned first point has not yet been dealt with, it is a reality that the customer is struggling with further demands.

An object of the present invention is to improve the accuracy of a method for judging the quality of a molded product, in particular, a method for judging a short shot, using a monitor value of an injection molding machine.

[0018]

According to the present invention, there is provided a molded article discriminating method for an injection molding machine, comprising: a first step of calculating a density of a plasticized molten resin;
The second step of calculating the product of the molten resin in the mold by calculating the product of the distance the screw has traveled at the time of injection, and determining the quality of the molded product from the calculated molten resin weight based on the degree of short shot And a third step.

Further, the injection molding machine according to the present invention includes, in addition to the detecting means for detecting the amount of movement of the screw in the heating cylinder, a judging means for performing a predetermined operation using a detection signal from the detecting means. The determining means calculates a product of a first step of calculating the density of the plasticized molten resin, a product of the calculated molten resin density, and a distance traveled by the screw at the time of injection, and enters a mold. A second step of calculating the weight of the molten resin, and a third step of determining the quality of the molded product from the calculated weight of the molten resin based on the degree of a short shot.

In any of the above-described injection molding machines, the density of the molten resin in the first step is determined by setting the plasticized molten resin at a constant pressure while the backflow of the resin is prevented in the heating cylinder. Calculated based on the amount of movement of the screw obtained from the detection signal of the detection means in the state where the button is pressed.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to an injection molding machine in which a check valve of a screw is closed before injection (naturally, a pre-plastic injection molding machine is also included) when a short shot failure occurs. This is to improve the detection accuracy, and is to detect a short shot with a completely different idea from the conventional discriminating apparatus.
This is based on the following assumptions. That is, the fact that the molded product becomes a short shot means that the weight is reduced assuming that the density of the molded product is constant. According to the present invention, short shots are detected by strictly detecting the weight fluctuation of a molded article based on such a premise.

Furthermore, the present invention is based on the following principle. In general, the following equations can be applied to gases or fluids:

P × ΔV = Δn × R × ΔT where P is pressure, V is volume, n is mole number, R is constant, T
Is the temperature.

Assuming that the pressure P is constant and the temperature does not change, ΔV indicates a variation in the weight (density) of the molten resin.

An example of the electric injection molding machine will be described with reference to FIG. The injection device is a ball screw,
The rotation of the servomotor is converted into a linear motion by a nut, and the molten resin is charged. In FIG. 1, the rotation of an injection servomotor 10 is transmitted to a ball screw 11.
The nut 12 that moves forward and backward by the rotation of the ball screw 11 is fixed to a pressure plate 13, and the pressure plate 13 is movably mounted on a plurality of guide bars 14 fixed to a frame (not shown). The forward and backward movement of the pressure plate 13 is controlled by the screw 1 via the load cell 15, the bearing 16, and the drive shaft 17.
It is conveyed to 8. The drive shaft 17 is also rotationally driven via a timing belt 20 by a servo motor 19 for driving the rotation of the screw.

The screw 18 is rotated back in the heating cylinder 21 by driving the servo motor 19 for driving the rotation of the screw, so that the molten resin is stored at the tip of the heating cylinder 21. Then, the molten resin stored by advancing the screw 18 by the driving of the injection servomotor 10 is filled in the mold, and the molding is performed by applying pressure. At this time, the force pressing the resin is detected as a reaction force by the load cell 15, amplified by the load cell amplifier 22, and input to the controller 23. A position detector 24 for detecting the amount of movement of the screw 18 is attached to the pressure plate 13, and this detection signal is amplified by an amplifier 25 and input to the controller 23. The controller 23 controls the current (torque) according to each process according to the setting of the operator.
A command is output to the servo amplifiers 26 and 27, and the servo amplifiers 26 and 27 control the drive current of the servo motors 10 and 19 to control the output torque of the servo motors 10 and 19.

In this embodiment, a discriminating device 1 for detecting a short shot is provided in the above configuration. Discrimination device 1
Receives the detection signal indicating the amount of movement of the screw 18 from the amplifier 25 and executes the following steps.

First, after the measurement is completed, the screw 18 is pressed at a constant pressure. After this time, backflow of the resin inside the heating cylinder 21, particularly from the head of the screw 18 to the rear, is to be prevented. The discriminating apparatus 1 receives a detection signal indicating the amount of movement of the screw 18 from the amplifier 25, and calculates the density of the plasticized molten resin based on the distance of the screw 18 advanced at that time (first step). Here, if the molten resin density is low, the moving distance of the screw 18 is large, and if the molten resin density is high, the moving distance of the screw 18 is small. Such a relationship between the moving distance of the screw 18 and the density of the molten resin can be known in advance according to the type of the resin.

Next, the discriminating apparatus 1 calculates the weight of the molten resin entering the mold from the product of the obtained molten resin density and the distance traveled by the screw 18 at the time of injection (second). Steps). The distance the screw 18 has traveled depends on the amplifier 25
From the detection signal.

The discriminating device 1 further estimates the state of the short shot of the molded article from the calculation result of the weight. Since the ideal weight of the molded product is known in advance, a reference value indicating the degree of normality is given to the discriminating apparatus 1 in advance as a set value. The determination device 1
Compare this set value with the calculated weight of the molten resin, if the calculated weight of the molten resin exceeds the set value, it is normal,
Otherwise, a determination result indicating an abnormality, that is, a short shot is output (third step).

As described above, the discriminating apparatus 1 uses the detection signals indicating the movement amount of the screw 18, which is one of the monitor values used in the normal control operation, to perform the first to third determinations. The steps are performed for each shot of the molded article.

Conventionally, it has been a problem to determine which one of the accuracy of the quality judgment of the molded article and the monitor value is to be employed. However, in the present invention, the judgment can be performed without such troublesomeness and with high accuracy. In the present embodiment, the discrimination is mainly described. However, the controller 23 determines the above values (the molten resin density and the distance (volume) by which the screw 18 has advanced during injection).
If the main body of the injection molding machine is controlled so as to minimize the fluctuation of the product, the accuracy of the molded product naturally increases. In other words, the function of the determination device 1 may be realized by the controller 23.

The present invention can be applied not only to the electric injection molding machine but also to a hydraulic injection molding machine, and the type thereof is not limited to the in-line type, but can also be applied to a pre-plastic type injection molding machine.

[0034]

According to the present invention, a short shot can be accurately determined.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration when the present invention is applied to an electric injection molding machine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Ball screw 12 Nut 13 Pressure plate 14 Guide bar 15 Load cell 16 Bearing 17 Drive shaft 18 Screw 20 Timing belt 21 Heating cylinder 24 Position detector

Claims (4)

[Claims] 1. A first step of calculating the density of a plasticized molten resin, calculating the product of the calculated molten resin density and the distance the screw has advanced during injection, and A molded article discriminator for an injection molding machine, comprising: a second step of calculating the weight of the resin; and a third step of discriminating the quality of the molded article from the calculated weight of the molten resin based on the degree of short shot. Method. 2. The method according to claim 1, wherein the density of the molten resin in the first step is such that the backflow of the resin is prevented in the heating cylinder and the molten resin is plasticized. A molded product discriminating method for an injection molding machine, wherein the calculated value is calculated based on the amount of movement of the screw while pressing at a constant pressure. 3. An injection molding machine having a detecting means for detecting an amount of movement of a screw in a heating cylinder, comprising: a determining means for performing a predetermined operation using a detection signal from the detecting means. Calculates the product of the first step of calculating the density of the plasticized molten resin, the product of the calculated molten resin density, and the distance traveled by the screw at the time of injection, and calculates the weight of the molten resin entering the mold. And a third step of judging the quality of the molded product from the calculated molten resin weight based on the degree of short shot. 4. The injection molding machine according to claim 3, wherein the density of the molten resin in the first step is such that the backflow of the resin is prevented in the heating cylinder, and the plasticized molten resin is removed. An injection molding machine characterized in that it is calculated based on a movement amount of the screw obtained from a detection signal of the detection means in a state where the screw is pressed at a constant pressure.