JPH0366140B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a molding control method for an injection molding machine using a load-responsive variable flow rate hydraulic pump as a power source during an injection process.

(Prior Art) The injection process of an injection molding machine can be roughly divided into a filling process from the start of injection of molten resin until the resin reaches the end of the mold cavity, and then a filling process in which the molten resin in the cavity is cooled and solidified. It consists of a pressure holding process that compensates for shrinkage. Conventionally, the so-called programmed injection method has been known in which this filling process is controlled by controlling the injection speed of an injection screw (or plunger) according to a predetermined program. The filling speed of the molten resin is controlled by changing the molten resin. Furthermore, in the pressure holding process, a method of controlling the holding pressure in which the holding pressure is controlled in multiple stages using a timer is also known. Furthermore, the switching from the above-mentioned filling process to the pressure holding process can be controlled by changing the position of the screw,
That is, a method is adopted in which switching is performed depending on the set position of the screw in the filling process. Furthermore, a method is also known in which the switching of this process is controlled by an injection ram (hydraulic pressure) or resin pressure in a mold cavity. Recently, a switching method has also been used that involves a reduction in the moving speed of the screw.

(Problems to be Solved by the Invention) In the conventional technology, the switching from the filling process, which is the injection speed control area, to the holding pressure process, which is the holding pressure control area, is performed depending on the screw position, injection ram pressure, or cavity oil pressure, as described above. is detected and controlled.

On the other hand, what is desirable in this switching control is
At the same time as the molten resin reaches the end of the mold cavity, that is, at the same time as the actual filling is completed, the pressure control is switched to the pressure holding process. However, each of the above-mentioned conventional techniques has its own problems as described below.

First, in conventional devices that perform this switching control based on the screw position, it is difficult to detect the actual completion of filling based on the screw position. That is, the amount of molten resin filled is determined by the injection volume, which is given by the following equation.

V=π/4・D ²・S V; Injection volume D; Screw diameter S; Stroke Therefore, the injection volume is magnified by fluctuations in the injection stroke, so the actual filling amount is , even a slight change in the screw position will cause a large error. That is, in order to appropriately perform the above switching control based on the screw position, extremely delicate settings are required.
Furthermore, the injection molding machine itself requires repeatability based on this strict positional accuracy. If this delicate position setting deviates even slightly, the resin will reach the end of the cavity and filling will be completed before switching to the pressure holding process, or conversely, the process will be switched to the pressure holding process before filling is completed. In the former case, the cavity peak pressure rises to the set pressure during injection speed control, causing molding defects such as burrs, and in the latter case, the filling speed decreases before the resin filling is completed. Defects such as flow marks occur, and in any case, repeatability of the molding operation is inhibited. Since this problem has been known for a long time, a method has been adopted, for example, of switching from the injection speed control region to the pressure control region before filling is completed. In this method, the filling speed of the molten resin into the cavity before the filling is completed is controlled by pressure, and is not directly controlled by the injection speed. On the other hand, the injection speed is an important factor in controlling the surface condition of the molded product, and therefore, the above method has to reach an unstable region before filling is completed in order to obtain a high-quality molded product. I don't get it.

Next, in the conventional technology that switches from the filling process to the pressure holding process using the injection ram pressure described above, when changing the molding conditions, changing the injection speed reduces the resistance of the molten resin passing through the nozzle, sprue, gate, etc. Since it depends on the speed, the passing resistance changes,
Therefore, the ram pressure just before the filling is completed is changed. As a result, there is a problem in that every time the molding conditions are changed, the switching pressure of the injection ram that sets the pressure switching point from the filling process to the pressure holding process must be changed.

Furthermore, when the injection speed pattern is controlled in multiple stages in the filling process, the injection ram pressure, that is, the load pressure, increases and decreases with changes in the injection speed, so the injection ram pressure is detected and the pressure holding process The control method for switching to pressure-holding required a control area for switching to holding pressure. That is, this restriction area is a restriction that, even if the injection ram pressure reaches the switching set value, the switching control to pressure holding is not performed before a certain predetermined point before the actual filling is completed. These problems occur not only when switching to pressure holding based on injection ram pressure, but also when switching to pressure holding based on detection of resin pressure in the mold cavity and detection of a decrease in injection speed.

(Means for solving the problem) In order to solve the conventional problem, it is necessary to set the reference value for switching to the holding pressure process to some value at a certain point (instantaneous) during the injection process (e.g. It needs to be information that increases monotonically over time, rather than the injection ram pressure (injection ram pressure), and that has meaning for injection moldability.

In order to solve the conventional problems, the present invention integrates the power supplied to the load-responsive variable flow rate hydraulic pump over time, and switches to the pressure holding process when this integrated value reaches a reference value. It is something.

(Function) The present invention detects the amount of energy supplied to a load-responsive variable flow hydraulic pump that indicates actual injection moldability, and when the detected value reaches a preset reference value, holds pressure. Since the process is changed over, the injection moldability is constant for each shot, and the quality of the molded product is also stable.

(Example) An example of the present invention is shown in FIG. The molten resin 17 in the screw cylinder 16 is filled into the mold cavity by the hydraulic pressure of the load-responsive variable flow rate hydraulic pump 11 applied to the screw 15 via the injection plunger 14. 18 is a suction filter, and 19 is a tank.

During the injection process, the load applied to the injection plunger 14 is detected by the load pressure detection line 20, and this is fed back to the load-responsive variable flow rate hydraulic pump 11, so that the discharge amount and discharge pressure of the hydraulic pump 11 are adjusted to the load. A response is made to drive the screw 15. The power supplied to the electric motor 6 that drives the load-responsive variable flow rate hydraulic pump 11 is measured by the power detection line 7, and is sent to the integrated power calculator 3 at the same time as injection starts according to a command from the detection start trigger transmitter 22. Output. The integrated power computing unit 3 integrates the above-mentioned measured supplied power at the start of injection, thereby detecting the amount of energy required to drive the screw 15. The integrated value is output from the integrated power calculator 3 to the comparator 2. On the other hand, the comparator 2 is supplied with a predetermined switching value from the holding pressure switching value setter 1 which has previously set the switching value.

The comparator 2 compares the integrated value and the switching value, and when the two values match, issues a holding pressure switching signal to the controller 5. Further, the controller 5 controls the coil 13a of the electromagnetic flow control valve 13 which controls the moving speed of the screw 15 via the driver amplifier 4, and the coil 12a of the electromagnetic relief 12 which controls the injection pressure and holding pressure via the pressure control line 21. Then, a command value for the pressure holding process is issued.

(Effects of the Invention) With the above configuration, the present invention transfers the amount of energy required to move the screw during the filling process, that is, the amount of energy required to fill the mold cavity with molten resin, to the load-responsive variable flow rate hydraulic pump. It can be detected by the time integration of the supplied power, and the switching from the filling process to the pressure holding process can be controlled based on the detected value.

Therefore, in the present invention, the amount of energy applied to the mold cavity during the filling process can be kept constant for each shot, and the quality of the molded product can be refined and stabilized.

Furthermore, in addition to switching to the holding pressure process, it is also possible to switch the injection speed or injection pressure during the filling process using a signal that is issued when the integrated value set in advance on the switching setting device matches. , it is possible to achieve precision and stabilization of molded product quality in the same way as described above.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the invention. 1... Holding pressure switching value setter, 2... Comparator, 3...
...integrated power calculator, 4...driver amplifier, 5...
... Controller, 6 ... Electric motor, 7 ... Power detection line, 11 ... Load responsive variable flow rate hydraulic pump, 1
2... Solenoid relief valve, 13... Solenoid flow control valve, 14... Injection plunger, 15... Screw, 16... Screw cylinder, 17... Molten resin, 18... Suction filter, 19... Tank , 20...Load pressure detection line, 21...Pressure control line, 22...Detection start trigger transmitter.

Claims (1)

[Claims] 1. In a control device for an injection molding machine powered by a load-responsive variable flow rate hydraulic pump, the power supplied to the electric motor that drives the hydraulic pump is detected, and the detected value is calculated as the integrated power. 1. A molding control method for an injection molding machine, comprising integrating the integrated value using a calculator and emitting a signal when the integrated value matches a value set by a predetermined switching setting device. 2. Injection molding according to the claims set forth in paragraph 1, characterized in that the process is switched to the pressure holding process by a signal issued when the integrated value matches the value set by a predetermined switching setting device. Machine molding control method. 3. In the claim set forth in item 1, the invention is characterized in that the injection speed or injection pressure is switched by a signal issued when the integrated value matches a value set by a predetermined switching setting device. Molding control method for injection molding machine.