JPS645823B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an injection molding method and an injection molding machine that perform injection molding under optimal conditions by controlling the operation of an injection piston in relation to the viscosity of a plastic material. .

[Conventional technology]

In injection molding, a plastic material such as plastic is heated and melted, injected under pressure into a mold cavity, and after cooling is removed from the cavity as a molded article. Recently, new materials such as ceramics have also been plasticized and molded using water, plastic, etc. as inclusions. In the molding process, it is necessary to mold a molded product of constant quality without variation.
Particularly in the technologically advanced and precise industry, there is a high need for molded products of a certain quality. Therefore, in the conventional technology, mechanical molding conditions (injection pressure, injection speed, injection amount, heating temperature,
The screw rotation speed, back pressure, holding pressure, etc.) are controlled by a computer using closed loop control. In particular, computer control is widely used in injection molding using pre-plastic injection molding machines.

However, variations in the plastic material itself make it difficult to maintain optimal conditions. For example, even if the same plastic material is used, there are variations in material particle size and intrinsic viscosity from lot to lot. Furthermore, due to slippage and retention within the screw barrel (heating cylinder), variations occur in the amount of heat and friction that the plastic material receives during plasticization and kneading, resulting in inconsistent plasticization. Furthermore, variations in the amount of water contained due to uneven drying cause variations in viscosity. In response to changes in the plastic material itself, the flow velocity of the plastic material, pressure distribution, development of the solidified layer, etc. within the cavity change. Therefore, in repeated molding, even if the mechanical molding conditions are maintained constant, dimensional variations, appearance variations, and mold release defects occur, making it difficult to completely prevent the occurrence of defective products.

Recently, injection molding methods have been provided that are computer-controlled, taking into account viscosity, which is an important factor determining flow characteristics during the injection process. However, since it is difficult to directly measure the viscosity of plastic materials, the viscosity is calculated indirectly from the temperature of the plastic material, the speed of injection unevenness, or a combination of injection speed and injection pressure. There is.
Such a method of determining viscosity indirectly cannot adequately deal with fluctuations in viscosity due to changes in the plastic material itself. In practice, there is a tendency to control more mechanical molding conditions in order to find the optimum conditions. As a result, combinations of mechanical molding conditions have become more complex and difficult to understand, making injection molding machines more expensive and molding processes more complicated.

[Means and actions for solving problems]

The present invention aims to provide an injection molding method and an injection molding machine that mold a molded product of constant quality by directly measuring the viscosity of the plastic material and effectively responding to changes in the plastic material itself. There is.

In order to achieve this purpose, in this invention,
Viscosity is measured using the melt indexer principle. That is, the injection piston is pressurized in the direction of reflection and ejection by the pressurized medium, and the plastic material is supplied into the injection cylinder against the injection piston. Then, for example, the speed of the injection piston in the reflection/output direction is detected, the viscosity is determined from the speed, and the operation of the injection piston is controlled based on the relationship with the viscosity to perform injection molding under optimal conditions. In such an injection molding method, since the viscosity is directly measured, changes in the plastic material itself can be adequately coped with, and control of mechanical molding conditions does not become complicated. By controlling the three conditions of injection pressure, injection speed, and injection time, molding of constant quality without variation can be easily achieved. These molding conditions are controlled by a program determined in advance for each plastic material in relation to viscosity.

The injection molding machine for the above injection molding method includes a heating cylinder, a feeder means disposed within the heating cylinder to feed the plastic material to the front of the heating cylinder, and a feeder means disposed in front of the heating cylinder so that the plastic material can flow into the heating cylinder. When feeding the plastic material into the injection cylinder against the injection cylinder containing the injection piston and the injection piston pressurized by the pressurized medium,
The apparatus is configured to include a control means for detecting the viscosity of the plastic material and controlling the operation of the injection piston based on the relationship with the viscosity to perform injection molding under optimal conditions.
In such a configuration, the viscosity of the plastic material is directly determined. In an injection molding machine that uses the viscosity of the plastic material as a criterion for controlling molding conditions, it is possible to mold with constant quality without variation without requiring many mechanical molding conditions to be controlled.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

As shown in the drawings, an injection molding machine 10 according to the present invention includes a heating cylinder 12, a feeder means 14 disposed within the heating cylinder to plasticize and knead the plastic material and feed the plastic material to the front part of the heating cylinder, An injection cylinder 18 is disposed in front of the heating cylinder so as to be able to flow into the injection cylinder 18 and houses an injection piston 16 therein.
and a control means 20 that detects the viscosity of the plastic material and controls the operation of the injection piston based on the relationship with the viscosity. Here, the injection molding machine 10
The machine has almost the same structure as a known injection molding machine except for the control means 20.

After rotating the feeder means 14 to plasticize and knead the plastic material, when the feeder means is advanced,
Plastic material is fed into injection cylinder 18 via check valve 19. Here, the chamber 22 on the head side of the injection cylinder is filled with a pressurized medium, for example pressurized oil. Therefore, against the pressure acting on the injection cylinder 18 in the injection direction, the plastic material flows into the injection cylinder and displaces the injection piston 16 in the reflected exit direction (in the example upwards). Incidentally, a plunger type can also be used as the feeder means 14.

Here, the viscosity of the plastic material is measured as follows using the principle of a melt indexer. The melt indexer calculates the melt index by converting the weight of the plastic resin that passes through a predetermined orifice in a predetermined time under constant temperature and pressure into grams per 10 minutes. In this invention, the temperature of the pressurized medium is kept constant, a constant pressure is applied to the injection piston 16, and the viscosity of the plastic material is determined from the amount of movement of the injection piston against the pressure. The viscosity determined in this manner is directly related to the fluidity of the plastic material, and can be grasped as a directly measured value. The amount of movement of the injection piston is determined from the movement speed, the movement distance in a predetermined time, the amount of pressurized medium flowing out from the chamber 22, and the flow rate. In the embodiment, the speed of the injection piston 16 in the reflection and exit direction is detected. In other words, the extending portion 24 extends from the injection piston 16 in the reflection direction.

The control means 20 includes a sensor 26 that detects the speed of the injection piston 16 in the injection direction and a speed of the reflection and exit direction, a sensor 28 that detects the position of the injection piston, and a sensor 28 that detects the pressure of the pressurized medium flowing into the chamber 22. It is equipped with a sensor 30 for detection. When detecting the speed of the injection piston 16 in the reflection/ejection direction, the output signal of the sensor 26 is transmitted to the arithmetic circuit 3.
Sent to 2. Further, the output signal of the sensor 26 and the output signals of the sensors 28 and 30 when detecting the speed of the injection piston 16 in the injection direction are transmitted to the arithmetic circuit 3.
Feedback is provided to 2. Here, the optimum molding conditions for each plastic material, including temperature conditions, are determined in advance and programmed into the arithmetic circuit 32. As a method of determining the optimal molding conditions in advance, a method of making a prototype using a low-viscosity plastic material may be considered, but a method of making a prototype using a wax whose comparative correlation with the plastic material is known is preferable. In the method using wax, charts etc. showing the comparative correlation between plastic materials and wax,
From the wax molding pattern obtained from the prototype, the optimal molding conditions for the plastic material can be easily determined. Here, the trial production using wax may be performed using a model mold or a mold used for actual molding. In the former case, the optimum molding conditions are determined by calculations in advance, without having to make a prototype for each mold or plastic material immediately before injection. In addition, in the latter case, a filling resistance system of the mold flow path shape including heat dissipation of the mold can be obtained, and the optimum molding conditions can be easily determined.

The control means 20 includes a flow control valve 34 and its control servo 36 that control the flow rate of pressurized oil supplied to the chamber 22, and a pressure control valve 38 and its control servo 40 that control the pressure of the pressurized oil. We are even more prepared. Here, since the speed of the injection piston 16 in the reflection and exit direction is inversely proportional to the viscosity of the plastic material, the sensor 26 determines the viscosity as the reciprocal of the speed in the reflection and exit direction. The viscosity determined from the velocity detected by the sensor 26 is sent to the arithmetic circuit 32, and the injection pressure, injection speed, and injection time for molding conditions suitable for the viscosity are determined for each predetermined plasticizer. It is determined by an arithmetic circuit according to the material program. Then, the pressure and flow rate of the pressurized oil to the chamber 22 of the injection cylinder are adjusted based on the calculation result. The pressure of the pressurized oil to the chamber 22 is detected by the sensor 30 and sent to the arithmetic circuit 32.
The pressure control valve 34 is controlled by the control servo 36 to obtain the desired injection pressure. On the other hand, the sensor 26 detects the injection speed from the speed of the injection piston 16 in the injection direction, and feeds back its output signal to the arithmetic circuit 32. Then, the control servo 40 and pressure control valve 38 are adjusted to control the amount of pressurized oil flowing into the chamber 22 so as to move the injection piston 16 in the injection direction according to the desired injection speed and injection. There is. Note that the placement positions of the sensors 26 and 28 are not limited to the positions in the example, but may be placed in other positions, such as
It may be arranged at a position where the operation of the injection piston 16 moving through the small diameter portion of the injection cylinder 18 is detected.
Further, a combination sensor having the functions of the sensors 26 and 28 may be used. Furthermore, since the operation of the injection piston 16 can also be detected from the inflow and outflow of pressurized oil into the chamber 22, instead of the sensors 26 and 28, a sensor is provided on the outflow side of the flow control valve 34 to measure either the flow rate or the flow rate. A sensor may be provided to detect whether the

〔Effect of the invention〕

As described above, in the injection molding method according to the present invention, when feeding the plastic material into the injection cylinder against the injection piston pressurized by the pressurizing medium,
It is characterized by detecting the viscosity of the plastic material and controlling the operation of the injection piston based on the relationship with the viscosity to perform injection molding under optimal conditions. In such an injection molding method, since the viscosity is directly measured, changes in the plastic material itself can be adequately coped with, and control of mechanical molding conditions does not become complicated. For example, if the three mechanical molding conditions of injection pressure, injection speed, and injection time are controlled, uniform quality molding can be easily achieved. These molding conditions are controlled by a program determined in advance for each plastic material in relation to viscosity. Additionally, since the viscosity is measured just before injection, more accurate values can be obtained.

The injection molding machine for the above-mentioned injection molding method includes a heating cylinder, a feeder means arranged in the heating cylinder for feeding the plastic material to the front of the heating cylinder, and a feeder means arranged in the heating cylinder for feeding the plastic material to the front of the heating cylinder so that the plastic material can flow into the heating cylinder. Detecting the viscosity of the plastic material when supplying the plastic material into the injection cylinder against the injection cylinder arranged and housing the injection piston therein and the injection piston pressurized by the pressurizing medium; The injection molding apparatus is configured to include a control means for controlling the operation of the injection piston in relation to the viscosity and performing injection molding under optimal conditions. In such a configuration, the viscosity of the plastic material is directly determined. In an injection molding machine that uses the viscosity of the plastic material as a criterion for controlling molding conditions, it is possible to mold with constant quality without variation without requiring many mechanical molding conditions to be controlled. Despite this, the injection molding machine can be provided at low cost.

The above-mentioned embodiments are for illustrating the present invention, and do not limit the present invention in any way, and all modifications and modifications within the technical scope of the present invention are included in the present invention. Needless to say, it will be done.

[Brief explanation of the drawing]

The drawing is a partial cross-sectional view of an injection molding machine according to the present invention. 10: injection molding machine, 12: heating cylinder, 1
4: feeder means, 16: injection piston, 18:
injection cylinder, 20: control means, 22: chamber of injection cylinder, 26, 28, 30: sensor, 3
2: Arithmetic circuit, 34: Flow rate control valve, 36, 40:
Control servo, 38: Pressure control valve.

Claims (1)

[Claims] 1. In an injection molding method using a pre-plastic type injection molding machine, when a plastic material is supplied into an injection cylinder against an injection piston pressurized by a pressurizing medium, the viscosity of the plastic material is An injection molding method characterized by determining the viscosity and controlling the operation of an injection piston in relation to viscosity to perform injection molding under optimal conditions. 2. The injection molding method according to claim 1, wherein the operation of the injection piston is controlled by adjusting the injection pressure, injection speed, and injection time of the injection piston according to a predetermined program in relation to the viscosity. . 3. The injection molding method according to claim 1 or 2, wherein the viscosity of the plastic material is determined from the velocity of the injection piston in the reflection and exit direction. 4. The viscosity of the plastic material is determined from either the flow rate or the flow velocity of the pressurized medium flowing out from the chamber of the injection cylinder when the injection piston moves in the reflected ejection direction. injection molding method. 5. A heating cylinder, a feeder means disposed within the heating cylinder to feed the molten material to the front of the heating cylinder, and an injection cylinder disposed in front of the heating cylinder so that the plastic material can flow therein and housing an injection piston therein. When feeding a plastic material into an injection cylinder against an injection piston pressurized by a pressurized medium, the viscosity of the plastic material is detected and the operation of the injection piston is controlled based on the relationship with the viscosity. An injection molding machine comprising a control means for performing injection molding under optimal conditions. 6. The control means includes a sensor that detects the speed of the injection piston in the reflection and exit direction to determine the viscosity of the plastic material;
It is controlled by a sensor that detects the speed of the injection piston in the injection direction, a sensor that detects the pressure of the pressurized medium, an arithmetic circuit to which the output signals of each sensor are fed back or simply sent, and signals from the arithmetic circuit. The injection molding machine according to claim 5, further comprising a pressurized medium circuit. 7. The control means includes a sensor that detects the viscosity of the plastic material by detecting either the flow rate or flow velocity of the pressurized medium flowing out from the injection cylinder, a sensor that detects the speed of the injection piston in the injection direction, and a sensor that detects the pressure of the sensor, and a calculation circuit to which the output signal of each sensor is fed back or simply sent;
6. The injection molding machine according to claim 5, further comprising a pressurized medium circuit controlled by a signal from an arithmetic circuit.