JPH03244522A - Method and device for controlling inner pressure of mold in injection molding machine - Google Patents

Abstract

PURPOSE:To control the resin pressure in the cavity of a mold by actuating a nozzle for heat release of resin when the resin pressure in the cavity of the mold is detected by a detector during an injection packing stage and this pressure exceeds the prescribed preset value and regulating the temp. of resin. CONSTITUTION:An initial needle pin position setter 11c is set by viscosity of resin and initial calorific value. This preset value is regulated to large value as viscosity of resin is made higher. Further this preset value is set at large value as the initial calorific value is made smaller. Thereby the position of a needle pin 21 is decided by a servovalve 29 before injection and injection is started at this position. Injection is started and a resin pressure sensor 39 provided in a cavity detects resin pressure. when the detected resin pressure reaches the preset value or more of a resin pressure lower limit setter 11b, a signal is output to the servovalve 29 from a controller 11. A hydraulic cylinder 25 is actuated and the gap d1 of a nozzle 20 and the needle pin 21 is throttled to control the internal pressure of the cavity. Further when the resin pressure reaches the value of a resin pressure upper limit setter 11a, the needle pin 21 of a nozzle 4 for heat release of resin is completely closed. Accordingly the gap d1 is made to zero and resin pressure is not transferred to the inside of the cavity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method and apparatus for controlling mold pressure in an injection molding machine.

(Prior technology) Conventional methods for detecting internal pressure and protecting the mold from excessive resin pressure during filling include lowering the hydraulic pressure supplied to the injection cylinder or stopping the hydraulic pump of the molding machine. .

In addition, in order to fill the resin to the end of the cavity without lowering the resin temperature, it is necessary to use a method to fill the resin into the cavity in a short time, but in this case, the hydraulic pressure supplied to the injection cylinder must be increased. Therefore, there was a drawback that the internal pressure of the cavity during filling became too high.

(Problem to be solved by the invention) However, if a resin heating nozzle is provided at the tip of the heating cylinder as shown in Figure 1, if the hydraulic pressure supplied to the injection cylinder is lowered, the resin will be injected into the mold accordingly. This reduces the injection pressure and the amount of resin heat generated by the resin heating nozzle.
The resin viscosity is high (and the filling resistance increases. Therefore, the internal pressure may become high. As a countermeasure to the problem of excessive resin pressure in the cavity, it was not possible to lower the injection hydraulic pressure. Also, the injection hydraulic pump of the molding machine was stopped. In this case, not only would the molded product in that shot be defective, but the several shots required to restart the bottom shape and reach a stable state would also be defective, resulting in poor productivity.

The present invention aims to solve the above-mentioned conventional problems.

(Means for Solving the Problems) Therefore, the present invention provides a mold internal pressure control method for an injection molding machine having a detector for detecting the resin pressure in the mold and a resin heating nozzle at the tip of a heating cylinder. If the resin pressure in the mold cavity detected by the detector during the injection filling process exceeds a predetermined set value, the resin heating nozzle is activated to adjust the resin temperature, thereby reducing the resin pressure in the mold cavity. It is designed to control pressure, and is used as a means to solve problems.

The present invention also provides an in-mold pressure control device for an injection molding machine having a detector for detecting resin pressure in the mold and a resin heating nozzle at the tip of a heating tube cylinder. an opening detector that detects the amount of adjustment of the opening of the resin passage; a plurality of adjustment amount setters that set the amount of adjustment of the opening of the resin passage according to the resin pressure in the mold; The adjustment amount of the resin passage is adjusted so that the adjustment amount of the resin passage is within the range of the opening adjustment amount of the resin passage set in the plurality of adjustment amount setting devices according to the resin pressure from the detector to be detected. It consists of a control section that outputs an output to the aperture adjustment drive section, and is used as a means to solve the problem.

(Function) The present invention detects the pressure at the time of filling using a resin pressure sensor provided in the cavity in the mold. When the cavity internal pressure reaches a preset value, the needle bottle of the resin heating nozzle installed at the tip of the heating tube of the molding machine is moved to the high temperature side to narrow the resin passage, thereby reducing the effective resin pressure transmitted to the cavity. can be reduced. Since the resin actively generates heat as it passes through the resin passage which has become smaller, the cavity filling resistance becomes smaller, and the cavity internal pressure can be kept below the set value. In addition, as the internal pressure of the cavity increases, that is, as the end is filled, the resin heating nozzle is narrowed, so it is possible to fill the resin with more heated high-temperature resin, and the resin temperature decreases up to the end. Although there is a decrease, the temperature distribution of the molded product at the time of completion of filling is more uniform than that of the conventional method. In this way, excessive cavity internal pressure can be prevented and a molded product with uniform temperature distribution upon completion of filling can be obtained.

(Embodiments) The present invention will be described below with reference to embodiments shown in the drawings. FIG. 1 shows a sectional view of a main part of an injection molding machine that implements the present invention. In the figure, reference numeral 1 denotes a screw, which is slidably incorporated into a closed space 2a formed by a heating tube cylinder 2, an end cap 3, and a resin heating nozzle 4.

The raw resin is supplied to the hopper 5, falls into the heating tube cylinder 2, is melted and plasticized by heating by a heater (not shown), and rotation of the screw 1 by the hydraulic motor 6, and is sent to the front of the screw 1 as molten resin 7. stored. Note that the hydraulic motor shaft 6a is connected with a spline inside the injection ram 8, so that it can rotate between the two and at the same time can freely slide in the axial direction. Further, the screw 1 feeds pressure oil from the hydraulic source 12 into the injection cylinder 15 via the electromagnetic valve 13 and the flow rate control valve 14 according to a command from the controller 11, and fills the cavity 36 with the molten resin 7.

Next, the details of the resin heating nozzle 4 are shown in FIG. 2.
20 is a nozzle, 21 is a needle pin, and 22 is a valve body, which are connected to the heating tube cylinder 2 via the end cap 3. Further, the needle pin 21 is pin-coupled to a connecting fitting 24 via a lever 23, and is driven by a hydraulic cylinder 25 shown in FIG.

The hydraulic cylinder 25 is fixed to the heating tube cylinder 2 by a bracket 26. 27 is a position sensor that detects the stroke position of the hydraulic cylinder 25 and, in turn, the needle pin 21.
Detect the position of. 20a is a nozzle hole, 20b is a resin passage, 21a is a retaining portion between the needle pin 21 and lever 23, and 22a is a resin passage, which is composed of a plurality of holes on the circumference. Further, the valve body 22 is attached to the end cap 3 with bolts 28, and the nozzle 20 is screwed into the valve body 22.

Furthermore, the needle pin 21 is slidably fitted into the valve body 22, and its tip forms a gap d between it and the nozzle 20.
It is connected to the lever 23 at the rear.

Further, in FIG. 1, reference numeral 39 is a cavity internal pressure sensor, and the resin pressure in the cavity is transmitted to the cavity internal pressure sensor 39 via a pin 38. Next, to explain the setting device connected to the controller 11, lla is the resin pressure upper limit setting device, and when the cavity internal pressure reaches this value,
The needle pin 21 of the resin heating nozzle 4 is completely tightened. Therefore, the gap d1 becomes zero, and no resin pressure is transmitted into the cavity. Ilb is a resin pressure lower limit setting device, and when the cavity internal pressure exceeds this value, the servo valve 29 is activated to operate the hydraulic cylinder 25 to reduce the gap d between the nozzle 20 and the needle pin.

Furthermore, llc is an initial needle pin position setting device, which determines where the needle pin should be set at the beginning of molding. This value corresponds to the gap d, and the smaller the value, the greater the amount of heat generated by the resin. becomes larger, the resin temperature becomes higher, and the cavity internal pressure during filling becomes smaller.

Next, the cavity internal pressure and the movement of the needle pin 21 will be explained.

First, the initial needle pin position setting device 11c is set based on the resin viscosity and initial heat generation amount. The higher the resin viscosity, the larger the initial needle pin position setting value, and the smaller the initial heat generation value, the larger the setting value. As a result, the position of the needle pin 21 is determined by the servo valve 29 before injection, and injection is started at this position. When injection starts and the resin pressure sensor 39 installed in the cavity detects the resin pressure and reaches the set value of the resin pressure lower limit setter 11b, the controller 11 outputs a signal to the servo valve 29.

As shown in FIG. 3, when the cavity internal pressure is ■, the position of the needle pin 21 changes from the initial needle pin position to the position ■. In this way, during the cavity filling process, the needle pin 21 is moved as the cavity internal pressure changes,
The cavity internal pressure is controlled by narrowing the gap d1.

(Effects of the Invention) As described above, according to the present invention, molding can be performed while keeping the resin pressure in the cavity below a certain value, so there is no mold damage due to over-puncture, and the number of stops of the molding machine is reduced.

Furthermore, since the end of the molded product is filled with a resin whose temperature decreases little, the temperature difference within the molded product is reduced, which has the effect of preventing warpage. In particular, when the mold material constituting the cavity is made of aluminum alloy, zinc alloy, copper alloy, etc., the durability of the material is low and the thermal conductivity is good, so the temperature of the resin at the end part decreases greatly. The effects of the present invention are significant.

[Brief explanation of drawings]

Fig. 1 is a system diagram of an apparatus showing an embodiment of the present invention;
The figure is a detailed sectional view of the resin heating nozzle portion in FIG. 1, and FIG. 3 is a diagram showing the relationship between the cavity internal pressure value and the needle pin position. Description of main parts in the diagram 1 - Screw 2 - Heating tube Cylinder end cap Resin heating nozzle Melting resin controller Resin pressure upper limit setter Resin pressure lower limit setter Initial needle pin position setter Hydraulic cylinder position sensor Servo Pulp cavity Resin pressure sensor 2nd Figure 3: Removal of internal pressure 2)

Claims (2)

[Claims] (1) In a mold pressure control method for an injection molding machine having a detector for detecting resin pressure in the mold and a resin heating nozzle at the tip of a heating tube cylinder, the amount of gold detected by the detector during the injection filling process is An injection molding machine characterized by controlling the resin pressure in the mold cavity by operating a resin heating nozzle to adjust the resin temperature when the resin pressure in the mold cavity exceeds a predetermined set value. Method of controlling the pressure inside the mold. (2) In a mold pressure control device for an injection molding machine having a detector for detecting resin pressure in the mold and a resin heating nozzle at the tip of a heating tube cylinder, a resin passageway into the mold that constitutes the resin heating nozzle an opening detector that detects the amount of adjustment of the opening; a plurality of adjustment amount setting devices that set the amount of adjustment of the opening of the resin passage according to the resin pressure in the mold; and a plurality of adjustment amount setting devices that detect the resin pressure in the mold. The adjustment amount of the resin passage is adjusted so that the adjustment amount of the resin passage is within the range of the opening adjustment amount of the resin passage set in the plurality of adjustment amount setting devices according to the resin pressure from the detector. An internal mold pressure control device for an injection molding machine, comprising: a control section that outputs output to an adjustment drive section.