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US-12617139-B2 - Control method for injection molding machine and injection molding machine

US12617139B2US 12617139 B2US12617139 B2US 12617139B2US-12617139-B2

Abstract

A control method for an injection molding machine includes a measurement process of feeding a quantity of molten resin along a length of a heating barrel by moving a screw backward while rotating the screw in the heating barrel for melting a resin material, during the measurement process before the measurement process is completed, reducing a rotational speed of the screw at a same time as reducing a backward movement speed of the screw, stopping backward movement of the screw when the measurement process is completed, and the rotational speed and a rotation direction of the screw are controlled such that a back pressure becomes a target pressure at a target time lower than the back pressure that is measured at a time when the measurement process is completed, and injecting the molten resin into a mold after reaching the target time.

Inventors

  • Nobuyuki Asanuma

Assignees

  • SHIBAURA MACHINE CO., LTD.

Dates

Publication Date
20260505
Application Date
20220224
Priority Date
20210316

Claims (6)

  1. 1 . A control method for an injection molding machine, the method comprising: a metering process of accumulating a quantity of molten resin to be used in an injection cycle, the metering process includes feeding the molten resin along a length of a heating barrel by moving a screw backward while rotating the screw in the heating barrel for melting a resin material; during the metering process and before the metering process is completed, decelerating a rotational speed of the screw at a same time as decelerating a backward movement speed of the screw in order to stop backward movement of the screw at completion of the metering process; measuring a back pressure of the molten resin, which is a pressure of the molten resin metered in the metering process; controlling the rotational speed and a rotation direction of the screw so that the back pressure becomes a target pressure lower than the back pressure that is measured at a time when the metering process is completed when a target time is reached; and injecting the molten resin into a mold after reaching the target time.
  2. 2 . The control method for the injection molding machine according to claim 1 , wherein the target pressure is 0 MPa.
  3. 3 . The control method for the injection molding machine according to claim 1 , wherein the target pressure is a set pressure that is set depending on the molten resin.
  4. 4 . The control method for the injection molding machine according to claim 1 , wherein the target time is a time when cooling of molded resin is completed in a mold for molding the molten resin molten in the heating barrel.
  5. 5 . The control method for the injection molding machine according to claim 1 , wherein the target time is an offset time that is set to be earlier than a time when cooling of molded resin is completed in a mold for molding the molten resin molten in the heating barrel.
  6. 6 . An injection molding machine comprising: a heating barrel in which a resin material is heated and becomes molten resin; a screw that is disposed rotatably in the heating barrel, and movable in an axis direction of rotation in the heating barrel; a back pressure detection unit that detects a back pressure as a pressure of the molten resin ejected by the screw in the heating barrel; and a control unit that controls rotation of the screw and movement of the screw by moving the screw backward while rotating the screw to feed the molten resin along a length of the heating barrel and accumulate a quantity of molten resin to be used in an injection cycle, the control unit determines a back pressure of the accumulated quantity of molten resin based on the back pressure detected by the back pressure detection unit, wherein during a metering process before the metering process is completed, the control unit is configured to decelerate a rotational speed of the screw at a same time as a backward movement speed of the screw is decelerated, wherein the control unit is configured to stop backward movement of the screw at completion of the metering process, wherein the metering process is a process of accumulating a quantity of the molten resin to be used in an injection cycle, wherein the control unit is configured to control the rotational speed and a rotation direction of the screw so that the back pressure detected by the back pressure detection unit becomes a target pressure lower than the back pressure of when the metering process is completed when a target time is reached, and wherein the control unit is configured to control an injection of the accumulated molten resin into a mold after reaching the target time.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a national stage application of International Application No. PCT/JP2022/007609, filed Feb. 24, 2022, which designates the United States, incorporated herein by reference, and which claims the benefit of priority from Japanese Patent Application No. 2021-042725, filed Mar. 16, 2021, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD The present invention relates to a control method for an injection molding machine that injects a molten resin material to perform molding, and the injection molding machine. BACKGROUND ART In an injection molding machine, in a measurement process of measuring resin to be injected into a mold, a screw is rotated in a heating barrel to melt and knead a resin material while the screw is moved backward to a predetermined position. In this way, molten resin to be injected into the mold at the next injection process is fed to a distal end of the heating barrel, and the molten resin is measured. In some injection molding machines in the related art, the screw is made to perform a predetermined operation after the molten resin is measured for the purpose of reducing a pressure of the molten resin after the measurement, securing quality of a molded article, and the like. That is, the pressure of the molten resin positioned at the distal end of the heating barrel after the measurement is high, so that a failure may be caused such that the measured molten resin leaks out from a nozzle positioned at the distal end of the heating barrel accordingly. In this case, a resin amount used for molding may be changed, or an appearance defect may be caused in the molded article, so that some of injection molding machines in the related art cause the screw to perform a predetermined operation after the molten resin is measured for the purpose of suppressing such a failure. For example, in the injection molding machine disclosed in Patent Literature 1, after the molten resin is measured, the screw is moved backward to a backward movement stop point, and a backward movement speed is lowered in a predetermined period during backward movement and the screw is reversely rotated to prevent excessive reverse rotation and adjust pressure reduction with high accuracy. Due to this, a measurement condition for obtaining a more correct and uniform measured resin amount is determined in a short time. In the injection device disclosed in Patent Literature 2, degassing of a molten material is implemented with a simple configuration by rotating, immediately after plasticization of a molding material ends, the screw by a predetermined rotation angle in a direction opposite to a rotation direction of the plasticization to reduce the pressure of the molten material. CITATION LIST Patent Literature Patent Document 1: Japanese Patent Application Laid-open No. 2007-253606Patent Document 2: Japanese Patent Application Laid-open No. 2008-143022 SUMMARY OF INVENTION Problem to be Solved by the Invention As a method for reducing the pressure of the molten resin after measurement, as described above, exemplified are a method of moving the screw backward to a predetermined position or by a predetermined amount, what is called suck-back, and a method of reversely rotating the screw by a predetermined rotation angle. However, in a case of performing suck-back, the pressure of the molten resin positioned at the distal end side in the heating barrel after the measurement is locally and abruptly lowered, so that the molten resin positioned behind the heating barrel, that is, on a hopper side where the resin material is put into the heating barrel may pass through a check ring disposed on the screw to flow into a distal end side in the heating barrel. In this case, the measured resin amount varies, so that weight stability of the molded article may be lowered. Additionally, in a case in which the pressure of the molten resin is locally and abruptly lowered when suck-back is performed, a negative-pressure clearance like a void tends to be generated in the molten resin, and gas generated from the molten resin tends to accumulate in the clearance. In this case, the gas generated from the molten resin may lower the quality of the molded article such that a silver trace, what is called a silver streak, is generated on a surface of the molded article, or a surface of the mold is contaminated by the gas, for example. In a case of reversely rotating the screw by a predetermined rotation angle for a short time after measuring the molten resin, the entire pressure inside the heating barrel is abruptly reduced to the vicinity of atmospheric pressure, so that gas is not locally generated from the molten resin but tends to be generated from the entire molten resin, and the gas that cannot be discharged to the hopper side tends to stay inside the heating barrel. In a case of reversely rotating the screw by a predetermined rotation angle for a short time aft