JPH11115020A - Method for stabilizing actual weighing completion position of injection molding machine, and weighing controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always make a weighing process correct by stabilizing the wt. of a molded product and eliminating the mixing of air with a molten resin at the tip part of a nozzle part, a resin leak or the like. SOLUTION: In an injection molding machine allowing a screw to retreat and plasticizing a raw material resin to weigh the same, the weighing start position and weighing completion position of the screw are respectively set and a rotational speed and back pressure are respectively set corresponding to the set positions and the direction changeover valve 24 provided to the hydraulic circuit 30 connected and arranged to the injection cylinder controlling the movement of the screw is held to a nutural position to allow the screw to retreat under rotation and the rotation of the screw is stopped at a weighing completion setting position to complete weighing and, further, the retreat position of the screw after the completion of weighing is set to perform control so as to block or increase the screw back pressure in the hydraulic circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to metering control of an injection molding machine, and in particular, after the injection of the injection molding machine, by rotating a screw, a raw resin is transferred from a hopper to a front of a heating cylinder, kneaded, and kneaded. The present invention relates to a method for stabilizing an actual weighing completion position and a weighing control device for optimizing a weighing process for weighing an amount and preparing for injection in a next cycle.

[0002]

2. Description of the Related Art An important requirement for determining the quality of a molded article in injection molding is stabilization of the weight of the molded article. Such stabilization of the weight is required that the raw material resin injected by the injection molding machine is always a constant amount,
In a conventional injection molding machine that requires accurate metering as a prerequisite, the raw resin in the hopper is fed into a heating cylinder, where it is retained at the tip of the screw while being melted. At this time, the front end face of the annular check ring mounted on the outer circumference of the tip of the screw is pressed by the molten resin flow and is in contact with the tip end side of the screw. Flow into the retaining chamber at the tip end of the screw.

In the injection step, when the tip of the screw advances, the check ring does not advance, and the check ring abuts against a check sheet constituting the leading edge of the screw to prevent the molten resin from flowing backward. It is configured as follows.

However, in this type of injection molding machine,
Even if the rotation of the screw is stopped after the measurement process is completed, there is a phenomenon that the screw gradually retreats. This phenomenon is caused by the fact that when the molten resin plasticized and kneaded by the rotation of the screw is sent to the retaining chamber on the front side of the screw, the molten resin stays in the screw valley even if the rotation of the screw is stopped. The pressure P1 of the resin is slightly higher (P1> P2) than the pressure P2 of the resin sent into the retaining chamber. For this reason, even if the measuring process is completed and the rotation of the screw is stopped, the molten resin is fed into the retaining chamber, and the screw slightly retreats to P1 = P2.
When it becomes, the screw retreat completely stops.

Further, in such a screw retreat phenomenon, since the condition of P1> P2 is satisfied as described above, the molten resin pressure P1 in the retaining chamber further rises and flows out of the machine through the nozzle passage. Cannot be stopped, causing drooling (a phenomenon of resin leakage from the tip of the nozzle portion), which causes a defective molded product.

In order to solve such a problem in the conventional injection molding machine, a screw is rotatably arranged in a heating cylinder so as to be able to advance and retreat, and a position for detecting a retreat position associated with the accumulation of molten resin in the screw. Providing a detecting means, in the measuring stroke from the start of the retention of the molten resin to the completion of the retention, when entering the measurement control stroke section immediately before the completion of the retention, at least the condition of the nozzle portion and the molding material are predetermined. A pattern selecting means for selecting a pattern for lowering the back pressure of the staying chamber; and means for lowering the back pressure of the staying chamber based on a signal from the pattern selecting means when the position detecting means detects that the measurement control stroke section has been entered. There has been proposed a metering control device for an injection molding machine provided with the above (Japanese Patent Publication No. 4-78090).

The metering control device for an injection molding machine according to this proposal reduces at least the back pressure of the staying chamber in a constant pattern when the metering control stroke immediately before the completion of the stay is entered in the entire metering stroke. At the same time, the screw rotation speed is reduced.

In this case, how to reduce the back pressure in the final metering control stroke section is determined by cooling the resin in the nozzle hole. That is, depending on the type of the resin, the nozzle setting temperature, the size and the shape of the nozzle hole (straight or inverted taper), the fluidity of the resin in the nozzle hole portion is reduced, and the effect of preventing the resin leakage (drooling) is caused. Since this is different, this is configured so that the operator can select one pattern from various patterns set in advance and manually determine it.

The rotation speed of the screw is determined by the amount of oil supplied from a hydraulic source that rotates the hydraulic motor at the time of metering. When the final metering control stroke section is entered, a constant low rotation speed is set. Is set to

On the other hand, in contrast to the above-described method of lowering the back pressure, a method of controlling the injection molding machine capable of measuring the molten resin with high precision is based on the screw back pressure or the screw pressure near the end of the process of plasticizing the resin. A change in the position is detected in advance, and a reference screw back pressure or a reference screw position near the end of the plasticizing process is determined and set in the control device, and the screw is retracted according to the reference screw back pressure or the reference screw position. By configuring, the screw back pressure near the end of the plasticization process of the resin by open loop control is detected, and based on the detected screw back pressure, a standard without irregular fluctuation similar to the screw back pressure during open loop control The screw back pressure is determined, and the screw back pressure is controlled to be equal to the reference screw back pressure. It is, to improve the measurement accuracy, measurement control method which make it possible to perform precision molding injection molding machine has been proposed (JP-A 5-92461 Patent Publication).

[0011]

However, in the above-described metering control of the conventional injection molding machine, in the former type in which the back pressure is reduced in the final metering control stroke section, the operator sets in advance. Since one pattern is selected from various patterns and manually determined, the control operation becomes complicated, and the resin pressure and back pressure in the heating cylinder, screw rotation speed, and screw retreat speed at the time of completion of weighing are determined. The screw stop position is difficult to stabilize due to variation.

In the latter metering control method (suck-back method) in which the screw is retracted near the end of the plasticizing step, when the screw is retracted, the supply of pressurized oil to the injection cylinder is switched. There is a difficulty in that the screw stop position at the time of retreat is difficult to stabilize.

Therefore, as a result of intensive research, the present inventor has found that the screw in the heating cylinder is retracted, and the screw is controlled in the injection molding machine for plasticizing and measuring the raw material resin to be filled in the mold. The weighing start position and the weighing completion position are set respectively, and the screw rotation speed and the screw back pressure are set respectively corresponding to the set screw positions, and the injection cylinder for controlling the movement of the screw is controlled. Holding the directional switching valve provided in the hydraulic circuit connected and arranged at the neutral position, retreating while rotating the screw to plasticize and measure the raw resin, and rotating the screw at the measurement completion setting position Stop and complete the weighing, and further set the screw retreat position after the completion of the weighing, and set the hydraulic circuit at the screw retreat set position. By controlling the screw back pressure in the block or increasing the screw back pressure, the dispersion of the actual weighing completion position can be greatly reduced, thereby greatly reducing the weight variation between shots during injection molding. It was found that it could be reduced.

Accordingly, an object of the present invention is to improve the accuracy of the actual weighing completion position, stabilize the weight of the molded product, mix air into the molten resin at the tip of the nozzle portion, and reduce the It is an object of the present invention to provide a method for stabilizing an actual weighing completion position of an injection molding machine and a weighing control device which can eliminate leaks and the like and can always optimize a weighing process.

[0015]

In order to achieve the above object, the present invention provides a method for stabilizing a position where an actual metering is completed in an injection molding machine. In a metering control method for an injection molding machine that plasticizes and measures a resin, a metering start position and a metering completion position of the screw are set, respectively, and a screw rotation speed, a screw back pressure, and a screw speed corresponding to these set screw positions. The direction switching valve provided in the hydraulic circuit connected to the injection cylinder for controlling the movement of the screw is held at a neutral position, and the screw is rotated and retracted while rotating. The rotation of the screw is stopped to complete the weighing, and the retreat position of the screw after the completion of the weighing is set. And controls so as to increase the blocking screw back pressure or screw back pressure in the hydraulic circuit Te.

Further, in the present invention, the metering control device for implementing the method for stabilizing the actual metering completion position of the injection molding machine includes connecting a hydraulic motor for controlling rotation to a screw in a heating barrel. At the same time, coupling the injection cylinder that controls the movement, retreat the screw,
In a weighing control device of an injection molding machine for plasticizing and weighing a raw material resin to be filled in a mold, a position detector for setting a weighing start position and a weighing completion position of the screw is provided, and a direction is switched with respect to the injection cylinder. A hydraulic circuit that controls the supply of pressure oil via a valve is connected and arranged, and a part of the hydraulic circuit where a back pressure acts during the screw weighing process is provided with a back pressure block switching valve and a back pressure control proportional valve. The directional switching valve provided in the hydraulic circuit is held at a neutral position from the metering start setting position to the metering completion setting position of the screw, and a hydraulic motor is provided at the metering completion setting position of the screw. Is stopped to complete the weighing. Further, the retracted position of the screw after the completion of the weighing is set in the position detector, and the back pressure block is set at the screw retracted set position. Whether to back pressure block by operating the use switching valve, or and providing a controller for controlling to increase the back pressure by operating the back pressure control proportional valve.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a method for stabilizing an actual weighing completion position of an injection molding machine according to the present invention will be described in detail with reference to the accompanying drawings in relation to a weighing control device for performing this method. explain.

FIG. 1 shows a schematic configuration of a control device of an injection molding machine for performing a method of stabilizing an actual weighing completion position according to the present invention. However, in FIG.
Reference numeral 0 denotes a heating barrel. An injection screw 12 for measuring and injecting the molten resin is inserted through the heating barrel 10.

The nozzle portion 10a of the heating barrel 10 on the tip end side of the screw 12 is disposed to face the nozzle touch portion 14a communicating with the cavity 16 of the mold 14. The other end of the screw 12 is provided with a piston portion 12a and inserted into the injection cylinder 18, and a screw rotation hydraulic motor 20 is connected to an extension shaft portion 12b of the screw 12. .

The screw 12 is provided with a screw position detector 22 for detecting a moving position of the screw 12.

On the other hand, for the injection cylinder 18,
Hydraulic circuits 30 are provided, which are connected to a hydraulic source 26 and a tank 28, respectively, for supplying pressure oil for performing an injection operation via the direction switching valve 24. A part of the hydraulic circuit 30 (the B port side of the injection cylinder 18 to which the pressurized oil is supplied at the time of the injection operation) is connected via a back pressure block switching valve 32 and a back pressure control proportional valve 34, respectively. , A branch oil passage 35 connected to the tank 28 is provided.

The position detection signal detected by the screw position detector 22 is compared with the position set value set by the position setter 36 by the comparator 38, and the back pressure block or back pressure control is performed. Each is determined. When the back pressure block is performed, the controller 42 is energized by the signal switch 40 to operate the back pressure block switching valve 32. When the back pressure control is performed, the controller 44 is energized by the signal switch 40 to operate the proportional valve 34 for back pressure control.

Next, the metering control according to the present invention by the control device of the injection molding machine having the above configuration will be described with reference to the operating characteristics shown in FIGS. 2 (a) to 2 (e).

First, as shown in FIG. 2A, a controller (not shown) of the screw rotating hydraulic motor 18 for rotating the screw 12 is rotated from a weighing start position to a weighing complete position in the weighing process. The screw rotation speed up to is set. Also, for the back pressure control proportional valve 34, FIG.
As shown in (c), the screw back pressure from the weighing start position to the weighing completion position and the retreat position after weighing completion in the weighing process is set. The set value of the screw rotational speed and the set value of the screw back pressure differ depending on the mold, the molded product, and the resin used. Further, the screw back pressure at the screw back pressure set value up to the retreat position after the completion of the weighing can be set to zero.

Therefore, now, the injection is completed and the screw 12
Is in the forward limit, the metering control is started immediately. That is, with the start of the measuring process, the direction control valve 24
Is held at the illustrated neutral position, and the screw 12 retreats with the progress of the plasticizing step of the resin raw material supplied from the hopper as appropriate. In this case, the retracted position of the screw 12 is detected by the screw position detector 22, and based on the detected screw position signal, the screw rotation speed and the screw back pressure are respectively controlled to the set values. Then, when the screw 12 reaches the weighing completion set position, the rotation of the screw is stopped.

The actual screw rotation speed and the actual screw back pressure BP actually measured in such a measuring step (plasticizing step) have characteristic curves as shown in FIGS. 2B and 2D, respectively. That is, the actual screw rotation speed and the actual screw back pressure decrease from the metering completion setting position of the screw 12 (the rotation stop of the screw 12). In this case, the measured actual resin pressure Pr of the molten resin retained in the retaining chamber of the heating barrel 10 has a characteristic curve as shown in FIG.

Therefore, in the present invention, based on the characteristic curve of the actual resin pressure Pr, the resin pressure Pr is changed from the set position for completing the metering of the screw 12 (stop of rotation of the screw 12) to the set position for retreating after the metering is completed. It was confirmed that the molten resin retained in the retaining chamber of the heating barrel 10 at the position between the pressures was not more than the resin pressure point Pr0 at which no resin leaked from the tip of the nozzle portion 10a.

However, between the weighing completion set position where the screw 12 moves and the retreat setting position after weighing completion, the controller 42 is energized by the signal switch 40,
By operating the back pressure block switching valve 32 to block the screw back pressure or to increase the screw back pressure, the screw is stopped from retreating and a fixed amount of the molten resin is always measured. As a result, optimization of the measuring step for the injection in the next cycle can be achieved.

Therefore, in the present invention, the retracted position after the completion of the weighing based on the above-mentioned set-up position (the rotation stop of the screw 12) of the screw 12 is set. Is reached, the controller 42 is energized by the signal switch 40,
The back pressure block switching valve 32 is operated to block the screw back pressure.

As an alternative, when the screw 12 reaches the retreat set position after the completion of the metering, the controller 44 is energized by the signal switch 40 to operate the back pressure control proportional valve 34. Operate to increase the screw back pressure.

As described above, according to the present invention, with a relatively simple configuration, the screw 12 is stopped at a proper retreat position after the metering completion position of the screw 12 so as to keep the proper molten resin constant. The amount can be measured, and the occurrence of resin leakage (drooling) from the tip of the nozzle portion of the molten resin can be reliably prevented.

Accordingly, when the measured values of the actual weighing completion position after successive shots by the injection molding machine according to the above-described stabilization method of the present invention and the actual weighing completion position by the conventional apparatus were compared, FIG. The results shown were obtained. That is, according to the conventional apparatus, the variation width of the actual weighing completion position is 0.40 mm with respect to the weighing completion position. The variation width can be significantly reduced to 0.03 mm, and it has been confirmed that the weight variation of the molten resin between each injection molding shot can be significantly improved.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and many design changes can be made without departing from the spirit of the present invention.

[0034]

As described above, in the method for stabilizing the actual metering completion position of the injection molding machine according to the present invention, the screw in the heating barrel is retracted to plasticize the raw resin to be filled in the mold. In a measurement control method of an injection molding machine for measuring,
A screw weighing start position and a screw weighing complete position are set, respectively, and a screw rotation speed and a screw back pressure are respectively set corresponding to these set screw positions, and connected to an injection cylinder that controls the movement of the screw. The directional control valve provided in the arranged hydraulic circuit is held at the neutral position and the screw is rotated and retracted while rotating, the screw is stopped at the weighing completion setting position to complete the weighing, and further after the weighing is completed. By controlling the screw back pressure in the hydraulic circuit at the screw retreat setting position by setting the screw retreat position in the above, or controlling the screw back pressure to increase, the variation of the actual weighing completion position is varied. Can be greatly reduced, which significantly reduces the variation in weight between shots during injection molding. It is possible to reduce, to improve the accuracy of the actual metering completion position, it is possible to achieve a stabilization of the weight of the molded article.

The metering control device for an injection molding machine according to the present invention is characterized in that a screw in the heating barrel is connected to a hydraulic motor for controlling its rotation and an injection cylinder for controlling its movement is connected to the screw. In a measurement control device of an injection molding machine for plasticizing and measuring a raw material resin to be filled in a mold, a position detector for setting a measurement start position and a measurement completion position of the screw is provided, and the injection is performed. A hydraulic circuit for controlling the supply of pressure oil is connected to the cylinder via a direction switching valve, and a switching valve for a back pressure block and a back pressure block are provided on a part of the hydraulic circuit where a back pressure acts during the screw measuring process. The oil passage provided with the control proportional valve is branched and connected, and the directional control valve provided in the hydraulic circuit is set to the neutral position from the metering start setting position to the metering completion setting position of the screw. , The drive of the hydraulic motor is stopped at the weighing completion setting position of the screw to complete the weighing, and further, the retreat position of the screw after the completion of the weighing is set in the position detector, and at the screw retreat setting position, By operating the switching valve for the back pressure block to perform the back pressure block, or by operating the proportional valve for back pressure control and by providing a controller that controls to increase the back pressure, With a relatively simple configuration, it is possible to obtain advantages such as the incorporation of air into the molten resin at the tip of the nozzle portion, the leakage of resin, and the like, and the accuracy of stopping the measurement completion position can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a control device of an injection molding machine showing one embodiment of a method of stabilizing an actual measurement completion position according to the present invention.

FIGS. 2A and 2B show a screw characteristic at the time of weighing of an injection molding machine obtained by a method of stabilizing an actual weighing completion position according to the present invention, wherein FIG. 2A is a waveform diagram of a screw rotation speed set value, and FIG. ) Is the waveform diagram of the actual screw rotation speed,
(C) is a waveform diagram of the screw back pressure set value, (d) is a waveform diagram of the actual screw back pressure, and (e) is a waveform diagram of the actual resin pressure in the heating cylinder.

FIG. 3 is a waveform diagram showing a comparison between a method of stabilizing an actual weighing completion position according to the present invention and a stabilization characteristic of an actual weighing completion position in a conventional weighing control device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Heating barrel 10a Nozzle part 12 Injection screw 12a Piston part 12b Extension shaft part 14 Die 14a Nozzle touch part 16 Cavity 18 Injection cylinder 20 Hydraulic motor for screw rotation 22 Screw position detector 24 Direction switching valve 26 Hydraulic source 28 Tank 30 Hydraulic Circuit 32 Switching valve for back pressure block 34 Proportional valve for back pressure control 35 Branch oil passage 36 Position setting device 38 Comparator 40 Signal switching device 42, 44 Controller

Claims (2)

[Claims] 1. Retracting a screw in a heating barrel,
In a measuring control method of an injection molding machine for plasticizing and measuring a raw material resin to be filled into a mold, a measuring start position and a measuring completion position of the screw are respectively set, and a screw rotation corresponding to the set screw position is performed. The speed and the screw back pressure are set respectively, the direction switching valve provided in the hydraulic circuit connected to the injection cylinder for controlling the movement of the screw is held at the neutral position, and the screw is rotated backward while rotating, and the weighing is performed. At the completion setting position, the rotation of the screw is stopped to complete the measurement, and further, the screw retreat position after the completion of the measurement is set, and the screw back pressure in the hydraulic circuit is blocked at the screw retreat setting position. Or control to increase the screw back pressure to reduce the actual metering completion position of the injection molding machine. The stabilization method. 2. A raw resin to be filled in a mold by connecting a hydraulic motor for controlling the rotation of the screw in the heating barrel and an injection cylinder for controlling the movement of the screw to retract the screw. In a measurement control device of an injection molding machine for plasticizing and measuring, a position detector for setting a measurement start position and a measurement completion position of the screw is provided, and the pressure oil is supplied to the injection cylinder via a direction switching valve. A hydraulic circuit for performing supply control is connected and arranged, and an oil passage provided with a switching valve for back pressure block and a proportional valve for back pressure control is provided in a part of the hydraulic circuit to which back pressure acts during the screw measuring process. The directional control valve provided in the hydraulic circuit is held at the neutral position from the weighing start setting position to the weighing completion setting position of the screw, and the directional control valve is set to the weighing completion setting position of the screw. The drive of the hydraulic motor is stopped to complete the weighing, and further, the retreat position of the screw after the completion of the weighing is set in the position detector, and the switching valve for the back pressure block is operated at the screw retreat set position. A metering control device for an injection molding machine, comprising a controller for performing a back pressure block or operating the back pressure control proportional valve to increase the back pressure.