JPH06328530A - Method for controlling of injection molding machine - Google Patents

Abstract

(57) [Summary] [Purpose] A molded product (product) with excellent bonding strength at the resin confluence can be reduced as much as possible, while reducing the appearance defects that tend to occur at the resin confluence such as weld lines and gas burns. To provide a control method of a moldable injection molding machine. [Structure] Until the end of the process of injecting and filling the molten resin into the cavity 6, the front-rear moving member 7a is in the retracted position, and the gas in the cavity is sucked and discharged to the outside through the gas vent hole 13 to enter the cavity. Immediately before the molten resin is completely filled (just before the molten resin reaches the confluence position), the forward / backward moving member is moved to the forward position, the gas vent hole is closed, and the front end surface of the forward / backward moving member partially covers the wall surface of the cavity. Form. Further, during the pressure-holding process after injection / filling, the front-rear moving member is oscillated and driven by a short stroke in the front-rear direction, and vibrational compressive stress is applied to the resin portion at the confluence position in the cavity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 capable of suppressing a molding defect that is likely to occur at a resin joining position in a cavity.

[0002]

2. Description of the Related Art In injection molding, when the molten resin splits in the cavity and then joins, a weld line (weld line)
line) or gas burns due to adiabatic compression, and not only the appearance is apt to deteriorate, but also the bonding strength at the resin merging portion is lowered, which easily becomes a weak point portion of the strength of the molded product.

The above-mentioned weld line is often generated by entraining the air in the cavity and the volatile gas component from the resin, and in order to reduce the generation of this weld line and the above-mentioned gas burn, the cavity is reduced. It is effective to degas the inside of the cavity. During the injection / filling process, the inside of the cavity is depressurized by degassing the gas (air) with a vacuum pump, etc. There is known an injection molding machine having a metal mold structure. In a mold having such a conventional degassing mechanism, the cavity is degassed from a gap (a small gap where resin is difficult to enter) of the die of about several hundreds of millimeters. Was common.

[0004]

As described above, in the conventional mold structure having the function of degassing the inside of the cavity, the gas is degassed from the space between the molds which is so small that the resin is difficult to enter. Therefore, there was a limit to the degassing performance. Therefore, it cannot be denied that the occurrence of weld lines, which are noticeable as a poor appearance, cannot be dramatically reduced, and that the bonding strength at the resin merging portion still tends to decrease. Particularly, in a metal injection mold (MIM) or a ceramic injection mold (CIM) in which metal powder (metal particles) or ceramic powder (ceramic particles) is kneaded in a resin and injection molding is performed, the resin merging portion (merging of the resin) In the weld part which is the joint part), the metal particles or ceramic particles in the binder (resin) are oriented perpendicular to the injection flow direction (due to the so-called fountain blow type resin behavior),
Combined with the fact that the particles do not get entangled with each other and that the polymer entanglement of the resin cannot be expected to get entangled at the resin confluence part, the degreasing (debinding) after injection molding → sintering process makes the resin confluence part A serious problem was caused that cracks were likely to occur.

Therefore, the technical problem to be solved by the present invention is to solve the above-mentioned problems of the prior art.
The purpose is to reduce the appearance defects that are likely to occur at the resin merging site such as weld lines and gas burns as much as possible, and it is possible to mold molded products (products) with excellent bond strength at the resin merging site. Another object of the present invention is to provide a method for controlling an injection molding machine.

[0006]

In order to achieve the above-mentioned object, the present invention provides a method for controlling an injection molding machine, in which a molten resin is injected and filled in a cavity which is a space for forming a molded product of a mold. A gas vent hole communicating with the cavity is formed in the mold part near the confluence position of the molten resin, and the gas vent hole is appropriately connected to the gas vent means through the communication means and the gas vent hole is closed. A forward and backward moving member that can move back and forth in the gas vent hole is provided so that it can take the open position and the open position, and the forward and backward moving member is in the retracted position until the end of the process of injecting and filling the molten resin into the cavity. , The gas in the cavity is sucked and discharged to the outside through the gas vent hole, and the molten resin is about to fill the cavity (just before the molten resin reaches the confluence position).
In the forward movement position of the front-rear moving member, the vent hole is closed, and the front end surface of the front-rear moving member forms a part of the wall surface of the cavity.
The front-rear moving member is oscillated and driven by a short stroke in the front-rear direction, thereby applying an oscillating compressive stress to the resin portion near the confluence position in the cavity.

[0007]

The ejector, which is a front-rear moving member, is driven back and forth by an ejecting servomotor through an appropriate rotation-linear motion converting mechanism such as a ball screw mechanism, and the ejector pin is placed in the retracted position before the start of injection. The degassing hole is opened, and the inside of the cavity is degassed (depressurized) by a vacuum pump (gassing means) via the degassing hole and an appropriate communicating means. When the injection start timing is reached in this state, the screw as the injection member is driven forward by the injection servomotor through an appropriate rotation-linear motion conversion mechanism such as a ball screw mechanism, and the molten resin is injected into the cavity of the mold.
Filling begins and air (gas) is evacuated by the vacuum pump even during the injection / filling process. Then, when it is recognized by the measurement information of the pulse encoder (rotation detector) attached to the injection servo motor that the state in which the molten resin is almost filled with the molten resin is recognized, the eject servo motor detects The eject pin is driven forward to block the gas vent hole to stop the air (gas) vent, and the tip end face of the eject pin forms a part of the wall surface of the cavity. After this,
The injection / filling operation is continued for a while, and the forward drive of the screw is stopped at the timing when the resin is completely filled in the cavity. After this injection / filling is completed, the pressure-holding process is started.However, during this pressure-holding process, the eject servomotor vibrates the eject pin back and forth with a short stroke, which causes it to move to the resin portion near the confluence position in the cavity. An oscillating compressive stress is applied.

By doing so, air (gas) can be released from the inside of the cavity through the gas vent hole having a relatively large cross-sectional area, so that the gas venting capacity is greatly enhanced, and moreover, just before the completion of injection / filling. Since the gas is vented up to the end, the gas generated from the air in the cavity and the resin can be efficiently discharged, the gas burn due to adiabatic compression can be almost wiped out, and a weld line that causes a poor appearance can be generated. Can be reduced. further,
Since the compressive stress is repeatedly applied to the resin confluence during the pressure-holding process, vibrational compression is transmitted to the resin near the confluence position, and the molecular orientation of the resin can be effectively changed. As a result, the bonding strength at the resin merging portion is dramatically increased, and the occurrence of weld lines can be substantially suppressed. Further, when the vibrational compressive stress is applied to the resin merging portion in this way, in the above-mentioned metal injection mold or ceramic injection mold, not only the molecular orientation of the resin but also the particle orientation in the resin (binder) It is possible to change effectively, and it becomes easier for the polymer and the particle to become entangled in the solidification process, and even for products that require the steps of injection molding → degreasing → sintering such as metal injection mold and ceramic injection mold. Also, cracks will not be generated at the portion corresponding to the resin merging portion.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is an explanatory view schematically showing a state in which a molten resin is injected and filled in a cavity of a mold of an injection molding machine according to this embodiment, and FIG. 2 is a mold of an injection molding machine according to this embodiment. FIG. 3 is an explanatory diagram showing a peripheral configuration, FIG. 3 is an explanatory diagram schematically showing a cavity of the mold of FIG. 2, and FIG. 4 is an explanatory diagram showing a drive control system of an injection servo motor and an ejection servo motor in a simplified manner. is there.

First, the structure around the mold will be described with reference to FIG. In the figure, 1 is a fixed die plate to which a fixed side die 2 is attached, 3 is a movable die plate to which a movable side die 5 is attached via a die attachment plate 4, and the movable die plate 3 is Although not shown, it is driven back and forth by an appropriate mold clamping drive source to separate the movable mold 5 from the fixed mold 2 and the mold clamping position where the movable mold 5 is brought into close contact with the fixed mold 2. It is designed so that it can be placed in a mold open position. Then, in the state where the movable side mold 5 is in close contact with the fixed side mold 2,
A cavity 6 which is a space for forming a molded product (product) is formed by the two molds 2 and 5, and the cavity 6 is normally communicated with a resin injection port 8 through an appropriate gate, runner and sprue 7 which are not shown. As shown in FIG. 3, the cavity 6 in the present embodiment is formed in such a shape that the molten resin 20 injected / filled into the cavity 6 is split once, and then merges when the filling is completed. Here, 6a in FIG. 3 indicates a resin merging portion (a weld portion which is a merging and joining portion of the resin).

A known heating cylinder 9 has a nozzle at the tip of the heating cylinder 9 pressed against the resin injection port 8. A screw 10 is arranged in the heating cylinder 9 so as to be able to rotate and move back and forth. The screw 10 can be rotationally driven by an appropriate rotary drive source (not shown), and in the present embodiment, it is an injection servo. The motor 11 can be driven forward and backward through a rotation-linear motion conversion mechanism 12 such as a ball screw mechanism. This screw 1
0 is rotationally driven in a predetermined direction by a rotary drive source (not shown) during the kneading / plasticizing / measuring process (charge process),
As a result, the resin raw material (resin pellets) fed from the hopper (not shown) to the rear end side of the screw 10 is fed to the front side of the screw 10 while being kneaded and plasticized,
As the molten resin 20 accumulates on the front side of the screw 10, it moves backward while controlling the back pressure (going to the right in FIG. 2), and when one shot of molten resin is stored on the front side of the screw 10 (at the time of completion of measurement). ) Stops the screw rotation. Then, when the injection start timing after a lapse of a predetermined time is reached, the screw 10 is driven forward by the injection servomotor 11, whereby one shot of the molten resin 20 is injected into the cavity 6 of the mold.・ It is designed to be filled.

Numeral 13 is a gas vent hole formed at a position corresponding to the resin confluence portion 6a of the movable mold 5, and the gas vent hole 13 opens and closes the movable mold 5. It is formed so as to penetrate in the direction and communicates with the cavity 6. Reference numeral 14 is also a gas flow hole formed in the movable side mold 5, and the gas flow hole 14 is orthogonal to the mold opening / closing direction so as to reach the gas vent hole 13 from the outer surface of the movable side mold 5. And is connected to a vacuum pump 16 through an appropriate pipe means 15.
Then, in the open state of the gas vent hole 13 described later, the cavity 6 is moved by the vacuum pump 16 via the conduit means 15, the gas flow hole 14, and the gas vent hole 13.
It is possible to degas (decompress) the inside.

Reference numeral 17 denotes an eject member for ejecting a molded product, which is held by the movable die plate 3 so as to be movable back and forth, and an eject pin 17a which moves back and forth integrally with the eject member 17 is It can slide back and forth in the gas vent hole 13. Reference numeral 18 denotes an eject servomotor mounted on the movable die plate 3, which is ejected by the eject servomotor 18 via a rotation-linear motion conversion mechanism 19 such as a ball screw mechanism also mounted on the movable die plate 3. The member 17 moves forward and backward with respect to the movable die plate 3 (the eject pin 17a moves with respect to the movable die 5). Then, at least immediately before the start of injection, the eject pin 17a is placed in the retracted position shown in FIG.
It is placed in a state of being communicated with the gas flow hole 14, and this state is maintained until the end of the process of injecting and filling the molten resin into the cavity 6. Also,
The eject pin 17a is driven by the eject servomotor 18 at an appropriate timing near the end of the injection / filling process.
Is driven forward, and just before the molten resin 20 is completely filled in the cavity 6 (immediately before the molten resin 20 reaches the resin merging portion 6a), the eject pin 17a closes the vent hole 13 and Eject pin 17a
The tip end surface of the cavity is flush with the wall surface of the cavity 6 and forms a part of the cavity wall surface. Further, during the pressure-holding stroke, the eject pin 17a is oscillated by the eject servomotor 18 in a short stroke back and forth, as will be described later. Further, when the mold is opened, the eject pin 17a is further moved forward by the eject servomotor 18 so that the molded product is ejected from the movable-side mold 5.

FIG. 4 shows a simplified drive control system for the injection servomotor 11 and the ejection servomotor 18. In FIG. 4, 31 is a driver amplifier for driving the injection servomotor 11, and 32 is a driver amplifier. A rotation detector such as a pulse encoder attached to the injection servomotor 11,
33 is a driver amplifier for driving the eject servomotor 18, 34 is a rotation detector such as a pulse encoder attached to the eject servomotor 18, 35, 36, 3
Reference numeral 7 is an arithmetic control circuit. Arithmetic control circuits 35, 36, 3
7 recognizes the positions of the screw 10 and the eject pin 17a in real time based on the detection information from the rotation detectors 32 and 34 according to the injection control setting condition and the eject pin control setting condition, and the injection servomotor 11 and The eject servomotor 18 is driven. In this embodiment, since the servomotors 11 and 18 are used as the injection drive source and the eject pin drive source in this manner, real-time accurate drive control can be performed according to the position of the controlled object. Instead of the rotation detectors 32 and 34, sensors for detecting the positions of the screw 10 and the eject pin 17a may be provided.

Next, the operation at the time of the injection stroke (the injection / filling stroke which is the primary injection stroke and the subsequent pressure-holding stroke) of the present embodiment based on the above-mentioned structure will be described with reference to FIG.

Before the injection is started, the fixed side mold 2 and the movable side mold 5 are closely contacted and clamped, and the cavity 6 is formed by both molds 2 and 5. At this time, The eject pin 17a is in the retracted position as shown in FIG. Therefore, the cavity 6 is in a state of being connected to the vacuum pump 18 via the gas vent hole 13, the gas flow hole 14, and the conduit means 15, and before the injection is started, the inside of the cavity 6 is a vacuum pump. Gas is degassed (depressurized) by 18 as shown by arrow A. When the injection start timing is reached in this state, the screw 10
Is driven forward by the injection servomotor 11, the molten resin 20 begins to be injected and filled into the cavity 6, and the cavity 6 is degassed by the vacuum pump 16 even during the injection and filling. As a result, the injected molten resin 20 is filled and flows into the cavity 6, and the filling proceeds as shown by an arrow B toward the resin confluence portion 6a.

When the molten resin 20 is about to be filled into the cavity 6 (for example, as shown in FIG. 1), the molten resin 20 is filled up to the vicinity of the resin merging portion 6a. The rotation detector 3
When it is recognized by the measurement information of No. 2, the eject servomotor 18 is driven and the eject pin 17a is indicated by the arrow C.
Driven forward, the eject pin 17a closes the degassing hole 13 to stop degassing, and the tip surface of the eject pin 17a moves to a position flush with the wall surface of the cavity 6, The tip surface of 17a forms a part of the wall surface of the cavity 6. After this, the injection / filling operation is continued for a short time, and the forward drive of the screw 10 by the injection servomotor 11 is stopped at the timing when the resin is completely filled in the cavity 6.

Immediately after the completion of this injection / filling (after the completion of the primary injection stroke), the pressure-holding stroke is started. During this pressure-holding stroke, the eject pin 17a is moved by the ejecting servomotor 18 as shown by the arrow D. It vibrates with a short stroke back and forth. As a result, compressive stress is repeatedly applied to the resin portion in the vicinity of the resin confluence portion 6a in the cavity 6 in a short cycle (vibrating compressive stress is added).

After the end of the pressure-holding process, the mold is opened after a proper cooling period, if necessary, and the eject pin 17a is further advanced by the eject servomotor 18 to move the molded product to the movable side metal. It is made to stick out from the mold 5.

As described above, according to this embodiment, the inside of the cavity 6 can be degassed through the gas vent hole 13 having a relatively large cross-sectional area.
Moreover, since the gas is vented until just before the injection / filling is completed, the gas generated from the air and the resin in the cavity 6 can be efficiently discharged, and the gas burn due to the adiabatic compression can be almost wiped out, and the appearance is defective. The occurrence of weld lines to a certain extent can be reduced as much as possible. Furthermore, since a compressive stress is repeatedly applied to the resin confluence part during the pressure-holding process, vibrational compression is transmitted to the resin near the confluence position, and it becomes possible to effectively change the molecular orientation of the resin, which allows the polymer molecules to coexist during the solidification process. Are easily entangled, the bonding strength at the resin merging portion is dramatically increased, and the occurrence of weld lines can be substantially suppressed. Further, when the vibrational compressive stress is applied to the resin merging portion in this way, in the above-mentioned metal injection mold or ceramic injection mold, not only the molecular orientation of the resin but also the particle orientation in the resin (binder) It is possible to change effectively, and it becomes easier for the polymer and the particle to become entangled in the solidification process, and even for products that require the steps of injection molding → degreasing → sintering such as metal injection mold and ceramic injection mold. Also, cracks will not be generated at the portion corresponding to the resin merging portion.

Although the present invention has been described above with reference to the illustrated embodiments, it goes without saying that various modifications can be made by those skilled in the art without departing from the spirit of the present invention. A different compression pressing member for opening / closing a hole and performing vibration compression, instead of opening / closing a gas vent hole and performing vibration compression, and a drive source (for example, a servomotor) therefor May be provided.

[0022]

Industrial Applicability As described above, according to the present invention, it is possible to reduce the appearance defects that are likely to occur in the resin merging portion such as weld lines and gas burns as much as possible, and the bonding strength of the resin merging portion is excellent. A control method of an injection molding machine capable of molding a molded product (product) can be provided, and its value is enormous.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing a state in which a molten resin is injected and filled in a cavity of a mold of an injection molding machine according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a configuration around a die of an injection molding machine according to an embodiment of the present invention.

FIG. 3 is an explanatory view schematically showing a cavity of the mold shown in FIG.

FIG. 4 is an explanatory view showing a simplified drive control system of an injection servo motor and an ejection servo motor according to an embodiment of the present invention.

[Explanation of symbols]

 1 Fixed Die Plate 2 Fixed Side Mold 3 Movable Die Plate 5 Movable Side Mold 6 Cavity 6a Resin Merging Site 10 Screw 11 Injection Servo Motor 12 Rotation-Linear Motion Conversion Mechanism 13 Gas Venting Hole 14 Gas Circulation Hole 15 Pipeline Means 16 Vacuum pump 17 Eject member 17a Eject pin 18 Eject servo motor 19 Rotation-linear motion conversion mechanism 32, 34 Rotation detector

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshiya Taniguchi 523 Nishinoyama, Fukusato, Futami-cho, Akashi-shi, Hyogo 1 Toyo Kikai Metal Co., Ltd.

Claims (5)

[Claims] 1. An injection molding machine for injecting and filling a molten resin into a cavity, which is a space for forming a molded product of a mold, wherein the cavity is communicated with the mold portion near the confluence position of the molten resin in the cavity. To form a degassing hole, connect the degassing hole to the degassing means through an appropriate communicating means, and degas so that the degassing hole can be closed or opened. A front-rear moving member that can move back and forth in the working hole is provided, and the front-rear moving member is in the retracted position until the end of the process of injecting and filling the molten resin into the cavity, and the gas in the cavity is degassed. The suction / exhaust to the outside through the cavity, and before the molten resin has finished filling the cavity (just before the molten resin reaches the confluence position), the forward / backward moving member is moved to the forward position. With closing the gas vent holes, method of controlling an injection molding machine wherein the front end surface of the back-and-forth movement member is characterized in that so as to form a portion of a wall surface of the cavity. 2. The injection / filling drive source is a servomotor according to claim 1, wherein a rotation amount of the servomotor or a forward stroke amount (forward position) of a member forward driven by the servomotor is detected. By doing so, the control method of the injection molding machine is characterized in that the front-rear moving member determines the timing of closing the gas vent hole. 3. The injection member according to claim 1, wherein after the injection and filling, the front-rear moving member is oscillated and driven by a short stroke back and forth, thereby applying an oscillating compressive stress to a resin portion in the cavity near the confluence position. A method for controlling an injection molding machine, characterized in that. 4. The method for controlling an injection molding machine according to claim 3, wherein the front-rear moving member is an eject pin for ejecting a molded product from a mold. 5. The method for controlling an injection molding machine according to claim 3, wherein the drive source of the front-rear moving member is a servo motor.