JP6667976B1 - Adjustment method of holding pressure switching position of electric injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an operating method of an electric injection molding machine, in which the amount of resin filled in a cavity of a mold becomes constant even if the temperature of the mold changes, and a molded product having a constant quality can be obtained. SOLUTION: In an electric injection molding machine (1), a screw (3) is driven by speed control until the screw (3) reaches a holding pressure switching position to perform an injection process, and when it reaches, the pressure control is switched to. This is achieved by adjusting the holding pressure switching position when the molding cycle in which the holding pressure step of holding the pressure for a predetermined holding time is performed to continuously obtain a molded product is repeated. Specifically, a deviation e between the position of the screw (3) at the completion of the pressure holding step and a predetermined target screw position determined in advance is detected, and the pressure holding in the next molding cycle is eliminated so as to eliminate this deviation e. Adjust the switching position. The adjustment amount of the holding pressure switching position may be determined so as to be proportional to the deviation e. [Selection diagram] Fig. 2

Description

  The present invention relates to a method for adjusting a holding pressure switching position in an electric injection molding machine including a screw provided in an injection cylinder and an injection motor for driving the screw in an injection direction. The present invention relates to a method for adjusting a screw position for switching from an injection process for controlling speed to a pressure-holding process for controlling pressure, that is, a pressure-holding switching position.

  Electric injection molding machines are well known in the art, not to mention the name of the literature, and include an injection cylinder, a screw provided in the injection cylinder so as to be freely rotatable in a rotational direction and an axial direction, and a plasticizing machine for rotating the screw. It is composed of a motor, an injection motor driven in the axial direction, a control device for controlling these motors, and the like. Therefore, by appropriately controlling these motors, the screw can be rotationally driven by the plasticizing motor to be plasticized, and the screw can be driven in the axial direction by the injection motor to be injected, and then the pressure can be maintained.

  In the injection process, speed control for controlling the speed of the screw is performed. When the screw reaches the pressure holding switching position, the process proceeds to the pressure holding step. That is, the torque control, that is, the pressure control is performed until the predetermined dwell time expires.

  When performing the injection step and the pressure-holding step, the injection step is filled with, for example, 95% of the volume of the molten resin in the mold cavity, and in the pressure-holding step, the remaining volume is filled to reach 100%, and thereafter, Pressure is applied to compensate for the decrease in volume due to cooling of the resin. The amount of resin remaining at the tip of the injection cylinder after performing the pressure holding step is called a cushion, that is, a remaining amount, but this remaining amount is not always constant. This will be described with reference to FIG. In FIG. 3, reference numeral 60 denotes an injection cylinder, and 61 denotes a screw. When the screw 61 advances in the injection direction and reaches the set dwell switching position 63, the process proceeds to the dwelling step, where the dwell is maintained for the set dwell time. A predetermined remaining amount remains at the tip end portion 62 of the injection cylinder 60. This remaining amount can be represented by the distance (d) mm between the tip of the screw 61 and the entrance of the injection nozzle 64, or can be represented by the screw position. A state in which the remaining amount is good is indicated by a symbol X in FIG. However, for example, when the mold temperature rises, the flow resistance of the molten resin decreases and the filling becomes easier, so that even when the pressure is switched at the same pressure-holding switching position, the remaining amount may be reduced. This state is indicated by reference numeral X '. In this case, an overpack in which the cavity is excessively filled with the resin may occur, and further, molding defects such as burrs may occur. Conversely, when the temperature of the mold decreases, the filling resistance increases and the filling becomes difficult. Then, the remaining amount may increase as indicated by the symbol X ". In this case, molding defects such as short shots may occur. If the remaining amount is large, until the next molding cycle. Residual resin increases, the resin is liable to be deteriorated, and may cause other molding defects.

  Although they are not direct prior art documents of the present invention, Patent Documents 1 to 3 disclose different control methods relating to injection and holding pressure of injection molding.

JP-A-8-90619 JP-A-8-39632 JP-A-10-128812

  Patent Literature 1 discloses an injection molding apparatus that controls a hydraulic cylinder for injection and pressure holding as follows. That is, control is performed so that the screw speed drops at a constant acceleration when the internal pressure of the nozzle becomes equal to or higher than a predetermined threshold value at the end of the injection process so that the speed of the injection screw becomes constant during the injection process. Then, a control method of switching to pressure holding control when the pressure in the mold reaches a predetermined value is shown. In Patent Document 2, control is performed so that the injection pressure is maximum from the injection start position to the preliminary position, and the screw moving speed is constant from the preliminary position, and the current screw speed is set in advance. A control method for switching to pressure-holding control when the speed of the screw before the completion of filling is reduced by a predetermined amount from the speed is shown. Further, in Patent Document 3, in the injection step, the injection electric motor is controlled by position feedback control, and when the set remaining amount setting position is reached, the remaining amount setting position is maintained until the injection holding pressure timer expires. The invention to be controlled is shown in FIG. Further, the remaining amount setting position of the present invention can be automatically set as a variable.

  According to the control method described in Patent Document 1, since the final pressure in the mold becomes constant even when the viscosity of the molding material changes, the effect of improving the quality of the molded product can be obtained. However, since the pressure is switched to the pressure holding control by the internal pressure in the mold, the remaining amount of the resin remaining at the tip of the injection cylinder cannot be adjusted. In other words, the remaining amount may change depending on the mold temperature, the viscosity of the resin to be filled, and the like, but cannot be adjusted so that the remaining amount is constant.

  The invention described in Patent Document 2 includes a pressure-holding switching determination means for the pressure-holding control. However, when the current screw speed becomes smaller than a preset screw speed before the completion of filling by a predetermined amount, the pressure is maintained. It switches to pressure control and cannot control the remaining amount in the same way.

  According to the invention described in Patent Document 3, when the screw reaches the set remaining amount setting position, the screw is controlled so as to hold the remaining amount setting position until the injection holding pressure timer expires. An excellent effect is obtained in that the amount of resin is always constant. Instead of manually setting the remaining amount setting position, the remaining amount position, that is, the average value of the most advanced position of the screw can be automatically set as a variable. However, as described above, the viscosity of the injected resin changes depending on the mold temperature. The change in the remaining amount is caused by this, but simply maintaining the remaining amount setting position may cause the pressure in the holding pressure to be different from the set condition, so that the filling of the cavity is not performed. May be stable.

  Therefore, the present invention provides an electric injection molding method in which the amount of the resin filled in the cavity of the mold becomes constant even when the temperature of the mold changes, whereby a molded article having a constant quality can be formed. It is intended to provide a method of operating the machine.

  The object of the present invention is to perform an injection step by driving a screw by speed control until the screw reaches a predetermined holding pressure switching position in an electric injection molding machine, and when the screw reaches the predetermined pressure holding switching position, switch to pressure control to drive the screw. This is achieved by adjusting the pressure-holding switching position when continuously performing a molding cycle for obtaining a molded product by performing a pressure-holding step of holding the pressure for a predetermined pressure-holding time. Specifically, a deviation between the screw position at the completion of the pressure-holding step and a predetermined target screw position is detected, and the pressure-holding switching position in the next molding cycle is adjusted so as to eliminate this deviation. . The adjustment amount of the holding pressure switching position may be determined so as to be proportional to the deviation.

That is, in order to achieve the above object, the present invention provides, in an electric injection molding machine, an injection step of injecting a resin into a mold by driving the screw by speed control until the screw reaches a predetermined pressure-holding switching position. When the pressure is switched to pressure control and the screw is driven and the screw is driven to perform a pressure-holding step for a predetermined pressure-holding time, a molding cycle for obtaining a molded product is continuously repeated. At the time of the pressure-holding completion screw position, which is the position of the screw at the time, and a predetermined screw pressure-holding completion time target screw position, and detects the pressure-holding switching position in the next molding cycle so as to eliminate the deviation. adjusted, thereby characterized in that a constant amount of resin filled in the mold cavity is configured as a method for adjusting the hold pressure switching position of the electric injection molding machine
According to a second aspect of the present invention, in the adjusting method according to the first aspect, the amount of adjustment of the holding pressure switching position is determined in proportion to the deviation. It is configured as a position adjustment method.

As described above, the present invention implements an injection step of driving the screw by speed control to inject the resin into the mold until the screw reaches a predetermined pressure-holding switching position, and switching to pressure control when the screw is reached. The present invention is directed to an electric injection molding machine that continuously repeats a molding cycle of obtaining a molded product by performing a pressure holding step of driving a screw to hold a pressure for a predetermined pressure holding time. In other words, it covers all general electric injection molding machines. Then, in the present invention, a deviation between the screw position at the time of completion of the pressure holding, which is the screw position at the time of completion of the pressure holding step, and a predetermined target screw position at the time of the completion of the pressure holding is detected, and the next time the deviation is eliminated. In this case, the holding pressure switching position in the molding cycle is adjusted so that the amount of resin filled in the cavity of the mold is made constant . Then, even when conditions such as the mold temperature change, the remaining amount at the time of completion of the pressure holding is always constant. That is, it is guaranteed that the amount of the resin filled in the cavity of the mold is constant. Therefore, a short shot does not occur, and burrs and overpacks do not occur. In order to keep the filling amount of the resin constant, it is not necessary to change the screw speed in the injection step, and it is not necessary to change the pressure and the dwell time in the dwelling step. That is, the injection conditions for molding the molded article are substantially constant and are not changed. Therefore, even if the conditions such as the mold temperature are changed, it is possible to continue to mold a uniform molded product with substantially the same quality. According to another invention, since the adjustment amount of the pressure holding switching position is determined in proportion to the deviation, the adjustment amount can be easily determined, and the invention can be provided at low cost.

It is a front sectional view showing a part of electric injection molding machine concerning an embodiment of the invention. It is a block diagram which shows the adjustment method of the holding pressure switching position which concerns on embodiment of this invention implemented in a control apparatus. It is a front view which shows typically the position of the screw at the time of the conventional pressure holding end.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. As shown in FIG. 1, the electric injection molding machine 1 according to the present embodiment also includes an injection device 5 including a heating cylinder 2 and a screw 3 provided in the heating cylinder 2. The screw 3 is driven by a screw driving mechanism 7. The screw drive mechanism 7 includes a plasticizing motor 8 for rotating the screw 3 and an injection motor 9 for driving the screw 3 in the axial direction. The plasticizing motor 8 and the drive shaft 12 of the screw 3 are connected by power transmission means 11 such as a belt, and the screw 3 rotates when the plasticizing motor 8 is rotated. The drive shaft 12 of such a screw 3 is supported at its rear end by a predetermined bearing 14 that allows rotation. The bearing 14 is provided on a predetermined member 15. When the member 15 is driven in the axial direction, the screw 3 is driven in the axial direction via the bearing 14. The member 15 is fixedly provided with a ball nut 18 a of a ball screw mechanism 18, and the ball screw 18 b of the ball screw mechanism 18 is rotated by the injection motor 9 via a predetermined power transmission means 20. Therefore, when the injection motor 9 is driven, the ball screw 18b rotates, whereby the member 15 and the screw 3 are driven in the axial direction. A load cell 21 is provided in the screw driving mechanism 7 configured as described above, and an axial force acting on the screw 3, that is, an injection pressure is detected. The electric injection molding machine 1 is provided with a controller, that is, a control device 22 so that the injection pressure detected from the load cell 21 and the position of the screw 3 detected from the rotation position of the injection motor 9 are input. The plasticizing motor 8 and the injection motor 9 are controlled by the control device 22.

The adjustment method of the holding pressure switching position according to the present embodiment is performed by such a general electric injection molding machine 1. However, the following setting data is input to the control device 22 in advance by the operator. I have.
`` Pressure switching position ''
This is a condition for switching from the injection step to the pressure-holding step. When the screw position reaches the pressure-holding switching position after the injection step of driving the screw 3 by the speed control, the pressure is switched to the pressure-holding step driven by the pressure control. It has become. The initial value of the pressure-holding switching position is input by the operator, but is adjusted for each molding cycle by the adjusting method of the pressure-holding switching position according to the present embodiment, and the value is changed.
`` Target screw position when pressure is completed ''
It is a target value of the screw position of the screw 3 at the time of completion of the pressure holding step. It can also be referred to as the target value of the remaining amount d of the resin at the time of completion of the pressure holding step. The remaining amount d indicates the amount of resin remaining at the tip of the screw 3 as shown in FIG.

  A method for adjusting the pressure holding switching position according to the present embodiment will be described. The molding cycle is performed according to the molding conditions set in the electric injection molding machine 1. That is, in the injection device 5, the plasticizing motor 8 is driven to rotate the screw 3 and melt the resin. When the resin is measured at the tip of the screw 3 and the screw 3 retreats and reaches a predetermined screw position, it is determined that the set amount of resin has been measured and the rotation of the screw 3 is stopped. The resin is injected into the closed mold by driving the injection motor 9. That is, an injection step of driving the screw 3 by speed control, that is, position control, to achieve the set injection speed is performed, and when the screw 3 reaches the pressure-holding switching position, the pressure is switched to the pressure-holding step. That is, control is performed by pressure control, that is, torque control. When the set pressure holding time has elapsed, the pressure holding step is completed. When the mold is opened, a molded product is obtained. The molding cycle is completed.

In the method of adjusting the pressure-holding switching position according to the present embodiment, when the pressure-holding step is completed, the screw position at that timing, that is, the screw position 31 at the time of the pressure-holding completion, is detected. Then, as shown in FIG. 2, the control device 22 calculates a deviation e between the target screw position 30 at the time of completion of pressure holding and the screw position 31 at the time of completion of pressure maintenance. The regulator 34 adjusts the holding pressure switching position 35 in the next molding cycle so that the deviation e is eliminated. That is, the pressure holding switching position 35 in the next molding cycle is adjusted by the feedback control. In the adjuster 34, for example, PID control is performed, and respective parameters of a proportional element, an integral element, and a differential element are set. Which parameter should be set may be determined as appropriate, but only the parameter of the proportional element may be set. Specifically, when a predetermined adjustment amount u is added from the pressure-holding switching position in the current molding cycle to obtain the pressure-holding switching position in the next molding cycle, the following calculation is performed.
u = K × e
Here, u: adjustment amount, K: proportional constant, e: deviation The calculated adjustment amount u is added to the current pressure-holding switching position to obtain the pressure-holding switching position in the next molding cycle.

  The molding cycle is performed with the holding pressure switching position adjusted in this manner. At the completion of the pressure-holding step, the pressure-holding screw position 31 is detected, and the pressure-holding switching position in the next molding cycle is adjusted so that the deviation e from the target screw position 30 at the time of pressure-holding completion is eliminated. Hereinafter, the molding cycle is repeated in the same manner. When the method for adjusting the pressure-holding switching position according to the present embodiment is performed, the pressure-holding switching position is adjusted each time the molding cycle is repeated, so that the remaining amount d at the time when the pressure holding is completed is guaranteed to be constant. This means that the amount of resin filled in the mold cavity is constant. This ensures that a molded article of uniform quality is formed.

DESCRIPTION OF SYMBOLS 1 Electric injection molding machine 2 Heating cylinder 3 Screw 5 Injection device 7 Screw drive mechanism 8 Plasticization motor 9 Injection motor 21 Load cell 22 Control device

Claims (2)

In the electric injection molding machine, an injection step of driving the screw by speed control and injecting resin into a mold is performed until the screw reaches a predetermined holding pressure switching position, and when the screw reaches the predetermined pressure holding switching position, the screw is switched to pressure control to switch the screw. When continuously repeating a molding cycle to obtain a molded product by performing a pressure holding step of driving and holding a pressure for a predetermined pressure holding time,
Detect the deviation between the screw position at the time of pressure holding, which is the screw position at the time of completion of the pressure holding step, and the target screw position at the time of the pressure holding completion at a predetermined time, and in the next molding cycle so as to eliminate the deviation. A method for adjusting the pressure-holding switching position of the electric injection molding machine, wherein the pressure-holding switching position is adjusted to thereby make the amount of resin filled in the cavity of the mold constant . 2. The adjustment method of the pressure holding switching position of the electric injection molding machine according to claim 1, wherein the adjustment amount of the pressure holding switching position is determined in proportion to the deviation.

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