JP3967306B2 - Control method of injection molding machine - Google Patents

Description

  The present invention relates to a method for controlling an injection molding machine, and more particularly to a method for controlling an injection molding machine suitable for molding optical precision parts such as lenses.

Conventionally, the mold material is filled into the cavity by advancement of the screw, and measurement is performed by rotating the screw after completion of filling, and holding pressure is performed by back pressure, while the cooling time is started at the completion of filling or at the start of measurement, An injection molding method for shortening the molding cycle is disclosed (for example, see Patent Document 1).
Japanese Patent No. 2640714 (FIGS. 1 and 2)

In the conventional injection molding method, it is possible to hold the pressure in the pressure-holding step with the back pressure depending on the material and the shape of the cavity, but it is impossible because the back pressure has an upper limit pressure. There are many cases. For resins with high resin viscosity such as styrene, ABS (acrylonitrile, butadiene, styrene) and polycarbonate, the back pressure can be increased to about 500 kg / cm ^{2 in} terms of resin pressure. This is because it is impossible to mold the resin with a low resin viscosity such as a back pressure of 100 kg / cm ² or more.

  In addition, when the back pressure is used as the holding pressure, the generated back pressure varies depending on the granularity of the feed material even when the same pressure is set. Hard to get. For this reason, the back pressure varies from shot to shot, and the dimensional stability decreases. Therefore, the back pressure cannot be used as the holding pressure. In particular, in an optical precision component represented by a lens, a slight change in internal stress due to variations in coercive pressure affects the resin density of the product, and causes defective products.

  As shown by the gap between the injection secondary pressure and the back pressure in FIGS. 1 and 2 of Patent Document 1, when shifting from the pressure holding process to the metering process, the injection cylinder is released to protect the screw. Yes. When this driving force is switched from the radiant power to the back pressure, an uncontrolled state occurs during the process. Since the pressure is released in the uncontrolled state, the screw retreats due to the thermal expansion of the resin. As a result, in the weighing process for injecting the next product, the measurement is performed from the state where the screw is retracted, and the resin density of the product varies.

  The present invention can stably hold the pressure in the pressure-holding step by controlling the back pressure even when the resin viscosity is low and the particle size of the feed material is different, and occurs when the pressure-holding step shifts to the metering step. It is an object of the present invention to provide a method for controlling an injection molding machine that eliminates the uncontrolled state and can provide a stable pressure.

In order to solve the above-mentioned problems, the first aspect of the present invention stores the screw in the heating cylinder so as to be able to advance and retreat and rotate freely, and stores the material at the tip of the heating cylinder while turning the screw in the measuring process, In an injection molding machine equipped with an injection mechanism that retracts a screw and advances a screw in an injection process to inject material from a heating cylinder,
An injection mechanism (injection cylinder) in which the injection mechanism advances the screw in the injection process, and a back pressure control means (back pressure control cylinder) that controls the back pressure when the screw moves backward in the weighing process by an actuator dedicated to back pressure control. The back pressure control means is driven at an arbitrary timing so as not to cause the backward movement of the screw due to the reaction force during the injection process by the injection driving means.

  The method for controlling an injection molding machine according to claim 2 is characterized in that the injection driving means is pneumatic driving, hydraulic driving or electric driving.

The control method of the injection molding machine according to claim 3 is characterized in that the timing is an arbitrary timing in the pressure holding process in the injection process.

According to the first aspect, the injection mechanism includes the injection driving means for moving the screw forward in the injection process and the back pressure control means for controlling the back pressure when the screw moves backward in the metering process, and the injection driving means is performing the injection process. In addition, since the back pressure control means is driven at an arbitrary timing so as not to cause the backward movement of the screw due to the reaction force, it is possible to prevent the occurrence of an uncontrolled state that occurs when shifting from the pressure holding process to the weighing process, and various Optimal control can be performed for each molding, product defects are improved, and production efficiency is improved. Further, by controlling the back pressure control means with an actuator dedicated to back pressure control, it can be controlled independently from the injection pressure.

  According to the second aspect of the present invention, the control accuracy can be further improved by setting the injection driving means to pneumatic driving, hydraulic driving or electric driving.

According to claim 3 , by setting the timing to an arbitrary timing in the pressure-holding process in the injection process, the control at the time of shifting from the pressure-holding process to the measuring process is made a suitable control waveform for each molding. Can do.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a front view of an injection molding machine according to the present invention. The injection molding machine 10 includes a plurality of first tie rods 12... ), An upper fixed platen 13 fixed to the upper part of the first tie rods 12..., A first elevator plate 14 held in the air by an elevator means (not shown), and attached to the first elevator plate 14. The injection cylinder 15 and the back pressure control cylinders 16A and 16B (injection mechanism), the second lifting plate 17 suspended by these back pressure control cylinders 16A and 16B, and the upper fixed plate extending downward from the first lifting plate 14 13 through which the second tie rod 18..., The heating cylinder holding plate 19 fixed to the lower part of these second tie rods 18, the heating cylinder 20 attached to the heating cylinder holding plate 19, The heating cylinder 20 can be rotated freely A screw 21 movably accommodated, a spline shaft 22 extending from the upper end of the screw 21, a screw rotation motor 23 attached to the upper fixed plate 13 for rotating the spline shaft 22, and the screw rotation motor 23 The belt 24 and the ball nut 25 transmit power to the spline shaft 22.

  The piston of the injection cylinder 15 moves up and down, but when it moves down, it hits the second elevator 17 and lowers the second elevator 17 to lower the screw 21. Thereby, an injection action is performed. The back pressure control cylinders 16A and 16B suspend the second elevator board 17, and the vertical movement of the pistons of the back pressure control cylinders 16A and 16B directly becomes the vertical movement of the second elevator board 17 and moves the screw 21 up and down.

FIG. 2 is a simplified view of the control system of the injection molding machine. The air supplied from the air supply source 31 is controlled to a predetermined circuit pressure by the regulator 32. Air flows to the injection pressure control valve 33 side for controlling the injection pressure and the back pressure control valve 34 side for controlling the back pressure. The flow of air that has flowed to the injection pressure control valve 33 side is switched by the injection switching valve 35. Code 37a, 37b are check valves, numerals 38a, 38b are scan Phi de control valve. Air controlled by an injection pressure control valve 33 is adjusted by the scan Phi de control valve 38a, 38b, is supplied to the rear chamber or prechamber of the injection cylinder 15.

  The air that has flowed to the back pressure control valve 34 changes its flow at the back pressure switching valve 36. Air is supplied to the back chamber or the front chamber of the back pressure control cylinders 16A and 16B. The back pressure switching valve 36 is switched to the position A, and air is supplied to the rear chambers of the back pressure control cylinders 16A and 16B, whereby back pressure control is performed. The back pressure switching valve 36 is switched to the position B, and air is supplied to the front chambers of the back pressure control cylinders 16A and 16B, so that suck back is performed. In order to keep the back pressure control cylinders 16A and 16B free during the injection process, the bypass switching valve 39 opens the air. Reference numeral 40 denotes a silencer.

  Next, referring to FIG. 2 (a diagram showing the control system of the injection molding machine in a simplified manner), according to FIG. 3 (time chart of the switching table of each component and the injection pressure, back pressure, and heating cylinder pressure) The control method of the injection molding machine according to the present invention will be described. First, the entire process will be described, and then switching of each configuration will be described in detail.

  The injection process is a process of injecting resin into the cavity of the mold, and includes an injection primary process for filling the resin into the cavity of the mold and the injection secondary process for maintaining the pressure and sealing the gate of the mold. In particular, the secondary injection process is called a pressure holding process. When the injection process is completed, the screw 21 in FIG. 2 is rotationally driven, and the material is plasticized by the heating cylinder 20 while rotating, and the material is stored at the tip. The screw 21 tries to retreat by the reaction force due to this storage. In the pressure-holding step before the transition from the injection step to the metering step, the control is gradually switched from the injection pressure control to the back pressure control. That is, before the control by the injection cylinder 15 is lost, the back pressure control cylinders 16A and 16B are driven. Thereby, the non-control state which arises when transfering from a pressure holding process to a measurement process can be eliminated.

  Next, switching of each configuration will be described in detail. In the table in FIG. 3, in the primary injection process, the injection pressure control valve 33 is turned ON (injection pressure), and air flows to the injection switching valve 35. The injection switching valve 35 is in the position A, air is supplied to the rear chamber of the injection cylinder 15, and the piston of the injection cylinder 15 is driven downward. At this time, since the back pressure control cylinders 16A and 16B are in a free state, the back pressure switching valve 36 is neutral, and the bypass switching valve 39 is turned ON (atmosphere release position) to release the atmosphere.

  In the injection secondary process, which is the pressure holding process in the table, the injection pressure control valve 33 is ON (injection pressure) and the injection switching valve 35 is at the position A as in the injection primary process. By changing the voltage, the injection primary pressure and the injection secondary pressure become different injection pressures. The injection pressure time chart of FIG. 3 shows that the injection primary pressure and the injection secondary pressure are different injection pressures. Moreover, the resin pressure in the heating cylinder changes according to the injection pressure.

  The timer is activated at the time of transition from the primary injection process to the secondary injection process, and the back pressure switching valve 36 is switched to position A prior to the back pressure control. The back pressure control valve 34 starts to be driven when the timer is activated or when a certain time has passed. In the back pressure time chart of FIG. 3, the time when the timer is operated is indicated by T0, and the time when the back pressure control valve 34 is driven is indicated by T1. The back pressure control valve 34 is driven stepwise and is set to have a back pressure that should be at Tsw at the start of screw rotation. At this time, the bypass switching valve 39 is OFF.

  The above driving time T1 of the back pressure control valve 34 is an arbitrary timing of the injection process, and particularly preferably an arbitrary timing of the pressure holding process. In the pressure holding process, by driving the back pressure control valve 34, the control when shifting from the pressure holding process to the metering process can be set to a suitable control waveform for each type of molding.

  The back pressure control valve 34 is driven stepwise in the time during which no control is performed in the conventional control method (during the process transition) or in the pressure holding process before the transition. As a result, the uncontrolled state can be eliminated, and at the time Tsw at the start of screw rotation, the back pressure that should be at that time is obtained, and the pressure holding process can be smoothly shifted to the measuring process. Here, the time in the uncontrolled state is the time shown in the injection depressurization step in FIG. In this embodiment, since the screw and the injection cylinder are separated in the injection molding machine, the injection ram moves backward. However, if the injection molding machine is not a separate type, the injection ram does not move backward. It can be seen that it is only the time indicated in the injection depressurization process. The time chart of the in-cylinder resin pressure in FIG. 3 shows that there is no uncontrolled state that occurs when shifting from the pressure-holding process to the metering process, and that pressure is always applied. It shows that pressure is being applied. This prevents variations from shot to shot, and enables efficient production of optical precision parts typified by lenses.

  To disconnect the injection ram, the back pressure control valve 34 is turned ON, and the back pressure switching valve 36 is switched to the position A. Thereby, the back pressure control cylinder holds the material stored at the tip of the heating cylinder 20 at the set pressure, and then the injection ram moves backward.

  In the measuring process, the screw starts to rotate at the time Tsw at the start of screw rotation, and at the same time, the injection pressure control valve 33 and the injection switching valve 35 are turned off (neutral), and the measurement is performed by the control by the back pressure control valve 34 and the back pressure switching valve 36. Is done. Depending on the material to be filled, it is possible to control the back pressure control valve 34 so as to have a waveform like a one-dot chain line or two-dot chain line, and optimal control can be performed for each type of molding. Product defects are improved and production efficiency is improved.

  In the above-described embodiment, the control method of the pneumatic drive injection molding machine has been described. However, the present invention is not limited to the pneumatic drive, and can be applied to a hydraulic drive and electric drive injection molding machine. Thereby, control accuracy can be improved more.

  The present invention is used in a method for controlling an injection molding machine.

Front view of an injection molding machine according to the present invention Diagram showing simplified control system of injection molding machine Time chart of switching table and injection pressure, back pressure, and in-cylinder resin pressure for each configuration

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Injection molding machine, 15 ... Injection cylinder, 16A, 16B ... Back pressure control cylinder, 20 ... Heating cylinder, 21 ... Screw, 33 ... Injection pressure control valve, 34 ... Back pressure control valve, 35 ... Injection switching valve, 36 ... back pressure switching valve, 38a, 38b ... scan copy de control valve, 39 ... bypass switching valve.

Claims (3)

A screw is housed in a heating cylinder so as to be able to advance and retreat and rotate freely. In the measuring process, the material is stored at the tip of the heating cylinder while rotating the screw, and the screw is retracted by a reaction force caused by the storage. In an injection molding machine including an injection mechanism that advances a screw and injects material from the heating cylinder,
The injection mechanism is composed of injection drive means for moving the screw forward in the injection process, and back pressure control means for controlling the back pressure when the screw is retracted in the metering process by a back pressure control dedicated actuator ,
A control method for an injection molding machine, wherein the back pressure control means is driven at an arbitrary timing so as not to cause the retraction of the screw by the reaction force during the injection process by the injection drive means.   2. The method of controlling an injection molding machine according to claim 1, wherein the injection driving means is pneumatic driving, hydraulic driving or electric driving. The method of controlling an injection molding machine according to claim 1 or 2 , wherein the timing is an arbitrary timing in a pressure holding process in the injection process.

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