JP2010131812A - Injection molding method and injection molding machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an injection molding method preventing the leak of a molten resin from a valve gate at the time of molding using a mold equipped with a hot runner and the valve gate and producing no molding failure. <P>SOLUTION: A pressure sensor (34) for detecting injection pressure and a controller (35) are provided to the mold (3) equipped with the hot runner and the valve gate. When the injection pressure reaches predetermined pressure, the controller (35) retracts a valve pin (27) to open the valve gate. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an injection molding method using a mold provided with a hot runner capable of controlling the temperature of molten resin inside by a heater and a valve gate that can be opened and closed by a valve pin, and such an injection molding method. The present invention relates to an injection molding machine to be implemented.

  Sprues and runners, which are flow paths for molten resin, are formed in the mold, and a gate for injecting molten resin is opened in a cavity formed in the mold that has been clamped. Therefore, when the molten resin is injected from the nozzle of the injection molding machine, the cavity is filled from the gate through the sprue and runner. After filling, when the mold is opened after cooling and solidification, a molded product shaped in the cavity is obtained, but at the same time, unnecessary resin that is solidified in the sprue or runner and discarded is generated. In this way, the molten resin in the sprue or runner is solidified for each shot of injection molding, so the resin of the material is wasted, but as a mold that can eliminate such waste, A mold provided with a valve gate is well known.

JP 2002-337187 A

  Although it is not a direct document of the present invention, Patent Document 1 describes a mold provided with a valve gate. The valve gate is opened and closed by a valve pin. The mold is provided with a so-called hot runner having a predetermined heat insulating structure and a heater, so that the sprue and the molten resin in the runner are not cooled and solidified. Therefore, if the valve gate is opened immediately before the injection, the injection is performed, and the valve gate is closed after the injection is completed, the molten resin in the sprue and runner will not be cooled and solidified. Since the molten resin can be filled in the cavity, the resin material is not wasted.

  Such opening and closing of the valve gate is controlled by a controller provided in the injection molding machine, but will be described in detail as follows. The controller drives the mold clamping device to close and clamp the mold. When the completion of mold clamping is detected, the controller drives the valve pin. When detecting the opening of the valve gate, the controller drives the screw or plunger of the injection molding machine to inject the molten resin. A holding pressure is applied to apply a predetermined back pressure. After holding the pressure, the controller drives the valve pin to close the valve gate. After waiting for cooling and solidification, the mold is opened and the molded product is taken out.

  If the conventional valve gate opening / closing method described above is performed using a mold provided with a valve gate, the molten resin is not cooled and solidified in the sprue and the runner, and the resin material is not wasted. Further, since the injection is performed after the valve gate is opened, the mold or the like is not damaged by the injection pressure. However, there are some problems to be solved. Specifically, there is a problem because the injection is started after the opening of the valve gate is detected. That is, when the valve gate is opened, a so-called drooling phenomenon occurs in which the molten resin in the runner leaks from the valve gate into the cavity immediately after that. Then, the leaked molten resin cools in the cavity and becomes cold slag, and when the molten resin is injected immediately after that, the flow of molten resin in the cavity is hindered by the cold slag, and insufficient filling, etc. The molding defect will occur. Furthermore, the fusion between the cold slag and the molten resin becomes insufficient, and the strength of the molded product cannot be obtained sufficiently.

  If the valve gate is opened after a predetermined time has passed after issuing an injection command to the injection molding machine, the valve gate will be opened after the injection pressure of the molten resin is sufficiently high, thus preventing drooling. I can. Specifically, the opening and closing of the valve gate is controlled by a timer. That is, after the controller issues an injection command to the injection molding machine, a valve gate opening command may be issued after the time set in the timer has elapsed. If the timer is optimally set in such a system, the valve gate is opened after the injection pressure is sufficiently high, so that leakage of molten resin immediately after the valve gate is opened can be prevented. However, there are also problems with such timer control. That is, since the optimal setting time of the timer depends on molding conditions such as the injection speed, it is necessary to adjust the timer every time the molding conditions are changed, which is complicated. Furthermore, since the timer has to be adjusted every time the molding conditions are changed, the operation of finding out the optimum molding conditions, that is, the so-called molding condition determination process becomes complicated. There is also a risk of accidents. In other words, the opening and closing of the valve gate by the timer is controlled regardless of fluctuations in the injection pressure. Therefore, if the timing for opening the valve gate is delayed even a little, the injection pressure becomes abnormally high, resulting in a runner or injection molding machine. Breakage such as cracks or cracks will occur in the cylinder.

  An object of the present invention is to provide an injection molding method that solves the above-described conventional problems or problems. Specifically, a mold having a hot runner and a valve gate is used. When injection molding is performed, resin leakage does not occur from the valve gate, and after the injection pressure is sufficiently high, molten resin can be injected into the cavity, thus causing cold slag and defective molding. It is an object of the present invention to provide an injection molding method in which abnormal run pressure is not applied to a mold runner or a cylinder of an injection molding machine and breakage such as cracks or cracks does not occur. Furthermore, another object of the present invention is to provide an injection molding machine that can carry out such an injection molding method and can easily determine molding conditions.

  In order to achieve the above object, the present invention provides an injection molding method using a mold provided with a hot runner, a valve gate, and a cavity tee, in which the screw of the injection machine is driven in the axial direction for injection. The valve gate is configured to open when the injection pressure reaches a predetermined pressure. The injection molding machine includes an injection machine, a mold provided with a hot runner, a valve gate, and a cavity, a pressure sensor that detects an injection pressure of the molten resin, and a controller. When a predetermined pressure is reached, the valve gate is opened by an instruction from the controller, and injection filling is performed. Further, another invention is constituted by an injection machine and a mold provided with a hot runner, a valve gate and a cavity, and a valve pin for opening and closing the valve gate has an injection pressure of the molten resin in the hot runner. When a predetermined value is reached, the valve pin is configured to open against the biasing means that biases the valve pin in the closing direction.

  That is, in order to achieve the above object, the invention described in claim 1 uses an injection machine and a mold provided with a hot runner, a valve gate, and a cavity, and the hot runner is moved from the injection machine. When the molten resin is injected and filled from the valve gate into the cavity via the valve, when the injection pressure of the molten resin in the injection machine reaches a predetermined pressure, the valve gate is opened and filled. . According to a second aspect of the present invention, an injection machine and a mold provided with a hot runner, a valve gate, and a cavity are used, and molten resin is discharged from the valve gate from the injection machine through the hot runner. When the injection filling of the cavity is performed, when the injection pressure of the molten resin in the hot runner reaches a predetermined pressure, the valve gate is opened by this pressure to perform injection filling. The invention according to claim 3 comprises an injection machine, a mold provided with a hot runner, a valve gate and a cavity, a detection means for detecting an injection pressure of the molten resin, and a controller, The controller monitors the injection pressure detected by the detection means, and opens the valve gate when a predetermined pressure is reached, so that the hot runner communicates with the cavity. Furthermore, the invention described in claim 4 comprises an injection machine, a mold having a hot runner, a valve gate and a cavity, and a valve pin for opening and closing the valve gate is melted in the hot runner. When the resin injection pressure reaches a predetermined value, the valve pin is opened against the biasing means biasing the valve pin in the closing direction, and the hot runner communicates with the cavity.

  As described above, according to the present invention, in the injection molding method using the mold provided with the hot runner, the valve gate, and the cavity tee, when the screw of the injection machine is driven in the axial direction, the injection is performed. Since the valve gate is configured to open when the pressure reaches a predetermined pressure, the valve gate is opened after the injection pressure becomes sufficiently high. Therefore, the so-called drooling phenomenon that the molten resin leaks from the valve gate does not occur. That is, no cold slug is formed. Since the molten resin is vigorously filled into the cavity from the valve gate, molding defects such as insufficient filling do not occur. Moreover, since the valve gate is opened when the injection pressure reaches a predetermined pressure, the injection pressure does not become abnormally high, and cracks or cracks due to the injection pressure occur in the mold runner or the cylinder of the injection molding machine. There is nothing. According to another invention, an injection molding machine comprises an injection machine, a mold provided with a hot runner, a valve gate and a cavity, a detection means for detecting an injection pressure of the molten resin, and a controller. Since the controller monitors the injection pressure detected by the detection means and opens the valve gate when a predetermined pressure is reached, there is no danger of an abnormal injection pressure being generated. Therefore, so-called molding conditions can be determined with ease and easily determined by changing molding conditions such as injection speed and injection pressure to determine appropriate molding conditions. Furthermore, such an injection molding machine only needs to include a detecting means for detecting the injection pressure and a controller, and an effect that can be provided at low cost is also obtained. According to still another invention, an injection molding machine comprises an injection machine and a mold provided with a hot runner, a valve gate, and a cavity, and a valve pin that opens and closes the valve gate is formed of molten resin in the hot runner. When the injection pressure reaches a predetermined value, it is configured to open against the urging means that urges the valve pin in the closing direction, that is, the valve gate is configured to open directly by the injection pressure. Therefore, although the structure is simple, the drooping phenomenon can be easily prevented and molding defects do not occur.

  Embodiments of the present invention will be described below. As shown in FIG. 1, an injection molding control device 1 according to the present embodiment is provided in a conventionally known injection machine 2 so as to control opening and closing of a valve gate of a mold 3 during an injection process. It is configured. First, a conventionally known mold 3 having a valve gate and a hot runner will be described. The mold 3 includes a fixed mold 5 and a movable mold 6. The fixed mold 5 and the movable mold 6 are respectively attached to a fixed platen and a movable platen not shown in the drawing. The mold is opened and clamped by a mold clamping device. Since the movable mold 6 has a recess 7 having a predetermined shape in the parting line P, when the movable mold 6 is clamped to the fixed mold 5, the movable mold 6 is fixed to the recess 7. A cavity C is formed by the parting line P of the side mold 5. The fixed-side mold 5 includes a first plate 9 and a second plate 10, and the first and second plates 9 and 10 are fixed by bolts or the like. The first plate 9 is provided with a cylindrical first hole 11 having a shape that crosses the first plate 9 in the vertical direction in FIG. The first hole 11 is tapered in the vicinity of the parting line P in a tapered shape. The second plate 10 is provided with a second hole 12 including a lateral recess and a longitudinal hole penetrating from the end of the recess to the fixed platen side. Therefore, a hole 13 having a predetermined shape including the first hole 11 and the second hole 12 is formed inside the fixed-side mold 5. The holes 13 are opened on the fixed platen side and the parting line P side.

  In the hole 13, a manifold 18 in which a flow path of a molten resin composed of a first spru 15 and a runner 16 is opened, and a second spru 21 is opened inside, and a gate chip 19 is formed at the tip. And the gate nozzle 22 provided with. The manifold 18 and the gate nozzle 22 are fixed to each other, and the runner 16 and the second sprue 21 communicate with each other. Therefore, the molten resin injected into the first sprue 15 is filled into the cavity C from the gate 24 opened to the cavity C via the runner 16 and the second sprue 21. The manifold 18 and the gate nozzle 22 are provided through a predetermined gap from the inner wall of the hole 13 and are insulated from the first and second plates 9 and 10. Since the gate nozzle 22 is close to the movable mold 16 and heat is released to the movable mold 16, the heater 25 is wound around the outer peripheral surface of the gate nozzle 22 to heat the second sprue 21. It is like that. That is, the first sprue 15, the runner 16, and the second sprue 21 are so-called hot runners that are maintained at a predetermined temperature. A valve pin 27 that can be driven in the axial direction is provided in the second sprue 21 of the gate nozzle 22. The shaft diameter of the tip of the valve pin 27 is equal to the hole diameter of the gate 24. Therefore, when the piston cylinder unit 28 provided at the rear end portion of the valve pin 27 is driven to protrude the valve pin 27 in the axial direction, the gate 24 is closed and the molten resin in the second sprue 21 is prevented from leaking. When the valve pin 27 is retracted, the gate 24 can be opened. The gate 24 and the valve pin 27 constitute a so-called valve gate. A locate ring 29 is fitted in the opening of the hole 13 of the second plate 10.

  The injection machine 2 includes a heating cylinder 31, a screw provided inside the heating cylinder 31 so as to be driven in the rotational direction and the axial direction, a heater for heating the heating cylinder 31, and the like, as is well known. Yes. The screw and heater are not shown in the figure. An injection nozzle 32 is provided at the tip of the heating cylinder 31, and the injection nozzle 32 is guided by a locating ring 29 so as to touch the first sprue 15 of the fixed mold 5. The heating cylinder 31 is provided with a hole having a predetermined depth in the axial direction from the outer peripheral surface, and a pressure sensor 34 is embedded so that the resin pressure of the molten resin in the heating cylinder 31, that is, the injection pressure can be detected. It has become.

  The injection molding control device 1 according to the present embodiment includes a controller 35 and a pressure sensor 34. Specifically, the controller 35 is connected to the pressure sensor 34 through the signal line S <b> 1, and the detected injection pressure is input to the controller 35. The controller 35 is connected to the piston cylinder unit 28 by a signal line S2, and drives the piston cylinder unit 28 according to a command from the controller 35 to open and close the gate 24, that is, the valve gate.

  A molding method using an injection molding machine including the injection molding control device 1 according to the present embodiment will be described. First, the state where the gate 24 is closed by the valve pin 27 will be described. The first sprue 15, the runner 16, and the second sprue 21 are filled with molten resin, and since the temperature of the molten resin is maintained by the heater 25, the molten resin is not cooled and solidified. The movable mold 6 is clamped to the fixed mold 5 by the mold clamping device. Start weighing. That is, the heating cylinder 31 is heated, the screw is driven in the rotation direction, and the molding resin is supplied from the hopper. Then, the molding resin is melted by the heat from the heating cylinder 31 and the frictional heat generated by the shearing action caused by the rotation of the screw, and is sent to the front of the heating cylinder 31 so that the screw moves backward. When a predetermined amount of molten resin is accumulated in front of the heating cylinder 31, the measurement is completed. Start injection. The screw is driven in the axial direction with the valve gate closed. Then, as shown in the graph of FIG. 2, the injection pressure rapidly increases in a short time. In the graph, reference numeral 41 denotes a screw driving start timing, and reference numeral 42 denotes a change in injection pressure immediately after the screw driving. When the injection pressure detected from the pressure sensor 34 reaches the set pressure value, the controller 35 drives the piston cylinder unit 28 to retract the valve pin 27 and open the gate 24. Then, as shown in FIG. 3, the molten resin 49 is injected from the gate 24 into the cavity C, and after the injection pressure instantaneously decreases, the injection pressure rapidly increases again, and the cavity C of the molten resin 49 is increased. Filling is complete. In the graph, reference numeral 43 indicates a set pressure value, reference numeral 44 indicates a timing when the gate 24 is opened, reference numeral 46 indicates a change in injection pressure immediately after the gate 24 is opened, and reference numeral 47 indicates a cavity C. Changes in injection pressure when the molten resin is filled are shown. A holding pressure is applied to drive the screw in the axial direction with a predetermined force to apply a predetermined back pressure to the molten resin. Thereafter, the controller 35 drives the piston cylinder unit 28 to drive the valve pin 27 forward to close the gate 24. The temperature of the molten resin in the sprue 15 and the runners 16 and 21 is maintained by the heater 25. The mold is opened after the molten resin filled in the cavity C is cooled and solidified, and the molded product is taken out. Thereafter, molding is performed in the same manner.

  In the embodiment described above, the injection pressure detected from the pressure sensor 34 is monitored by the controller 35, and the controller 35 controls the opening of the valve gate. That is, the valve gate is opened in a controlled manner. Hereinafter, a second embodiment in which the valve gate can be mechanically opened by the injection pressure of the molten resin will be described. FIG. 4A shows a valve gate according to the second embodiment. Members having the same functions and effects as those of the apparatus according to the above-described embodiment are designated by the same reference numerals and will not be described in detail. In the valve gate according to the second embodiment, the diameter of the valve pin 27 'is relatively large, and a spring 36 is provided at the rear end of the valve pin 27'. The valve pin 27 is urged toward the gate 24 by the spring 36 and the gate 24 is closed. The vicinity of the tip of the valve pin 27 ′ is reduced in a conical shape, and only the vicinity of the tip of the cone seals the gate 24. And most of the tapered surface reduced in diameter, that is, the pressure receiving surface 37 that receives the pressure of the molten resin is located in the runner 21. When injection is started by driving the screw in the axial direction, the injection pressure of the molten resin in the runner 21 increases. Then, the injection pressure acts on the pressure receiving surface 37 and tries to push the valve pin 27 'upward in the drawing. When the injection pressure reaches a predetermined pressure, the valve pin 27 'is pushed up against the bias of the spring 36 and the gate 24 is opened. That is, the valve gate is mechanically opened.

  The position where the pressure receiving surface 37 is provided may be other than the tip of the valve pin 27 ′. As an example, the valve gate according to the third embodiment is shown in FIG. It is shown. Members having the same functions and effects as those of the apparatus according to the above-described embodiment are designated by the same reference numerals and will not be described in detail. In the third embodiment, a predetermined cylinder hole 38 is formed in a part of the manifold 18 '. A piston portion 39 fixed to a predetermined portion of the valve pin 27 ′ is slidably provided in the cylinder hole 38, and a lower surface of the piston portion 39 is exposed to the runner 16 and the second sprue 21. The pressure receiving surface 37 receives the injection pressure of the molten resin. A spring 36 is provided at the rear end of the valve pin 27 ′ and biases the valve pin 27 ′ toward the gate 24. When injection is started by driving the screw in the axial direction, the injection pressure of the molten resin in the runner 16 and the second sprue 21 increases. When the injection pressure reaches a predetermined pressure, the valve pin 27 'is pushed up by the injection pressure received by the pressure receiving surface 37 against the bias of the spring 36, and the gate 24 is opened.

  The injection molding control apparatus 1 according to the embodiment of the present invention is not limited to the above embodiment, and can be implemented in various forms. For example, although it has been described that the injection pressure of the molten resin is detected by a pressure sensor provided in the heating cylinder, a load cell is provided on a predetermined member at the rear end of the screw, and the screw is driven in the axial direction. It is also possible to detect the force to be detected and calculate the injection pressure. Furthermore, a pressure sensor may be provided in the mold to detect the injection pressure in the mold. The controller can also be configured from a conventionally known controller provided in an injection molding machine. In this case, it suffices to add software for monitoring the injection pressure and controlling the opening and closing of the valve gate to a conventionally known controller, and the injection molding control device can be configured at low cost. The valve gates according to the second and third embodiments can also be modified. For example, the urging means for urging the valve pin 27 'need not be limited to a spring, but may be elastic such as fluid pressure or rubber material. It can also be implemented by the body.

It is a front view which shows typically the metal mold | die and injection molding control apparatus which concern on embodiment of this invention. It is a graph which shows the change of the injection pressure of molten resin when injecting using the injection control apparatus which concerns on this Embodiment. It is sectional drawing of the metal mold | die which shows the state currently shape | molded using the metal mold | die which concerns on this Embodiment. The figure which shows the valve gate which concerns on this Embodiment typically, The (a) is the valve gate which concerns on 2nd Embodiment, The (a) is the valve gate which concerns on 3rd Embodiment, It is sectional drawing shown, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Injection molding control apparatus 2 Injection machine 3 Mold 5 Fixed side mold 6 Movable side mold 9 1st plate 10 2nd plate 15 1st spru 16 Runner 18 Manifold 19 Gate chip 21 2nd spru 22 Gate Nozzle 24 Gate 25 Heater 27 Valve pin 34 Pressure sensor 35 Controller

Claims (4)

When using an injection machine and a mold provided with a hot runner, a valve gate, and a cavity, when the molten resin is injected and filled from the valve gate through the hot runner from the injector into the cavity,
An injection molding method, wherein when the injection pressure of the molten resin in the injection machine reaches a predetermined pressure, the valve gate is opened to perform injection filling. When using an injection machine and a mold provided with a hot runner, a valve gate, and a cavity, when the molten resin is injected and filled from the valve gate through the hot runner from the injector into the cavity,
An injection molding method, wherein when the injection pressure of the molten resin in the hot runner reaches a predetermined pressure, the valve gate is opened by this pressure to perform injection filling. An injection machine, a mold provided with a hot runner, a valve gate and a cavity, a detection means for detecting an injection pressure of the molten resin, and a controller,
The controller monitors the injection pressure detected by the detection means, opens the valve gate when a predetermined pressure is reached, and the hot runner communicates with the cavity. It consists of an injection machine and a mold provided with a hot runner, valve gate and cavity,
When the injection pressure of the molten resin in the hot runner reaches a predetermined value, the valve pin that opens and closes the valve gate opens against the biasing means that biases the valve pin in the closing direction, and the hot runner An injection molding machine characterized by communicating with a cavity.

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