JP5354333B2 - Injection molding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that an electric motor becomes overloaded and a plasticized material may be leaked from a cavity of a mold when a mold clamping force is generated by using the electric motor. <P>SOLUTION: An injection molding method includes a mold clamping step of driving a movable mold 11<SB>M</SB>by a driving torque T<SB>1</SB>to closely contact a fixed mold 11<SB>S</SB>, a pressure holding step of pressing the movable mold 11<SB>M</SB>to the fixed mold 11<SB>S</SB>by a second driving torque T<SB>2</SB>smaller than the first driving torque T<SB>1</SB>, and an injection step of injecting the plasticized material in the cavity 14 formed between these two molds 11<SB>M</SB>, 11<SB>S</SB>at least during the pressure holding step. The injection molding method also includes a step of reducing a driving torque with respect to the movable mold 11<SB>M</SB>from the first driving torque T<SB>1</SB>to the second driving torque T<SB>2</SB>between the mold clamping step and the pressure holding step, and an ending time period t<SB>3</SB>of the torque reduction step is set before the ending time period t<SB>4</SB>of the injection step. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an injection molding method in which a plasticized material is injected into a cavity defined between a fixed side mold and a movable side mold and molded into a shape corresponding to the cavity, and in particular, an electric motor is used. Therefore, it is suitable for a small injection molding machine that performs mold clamping.

  The injection molding machine has a basic configuration of an injection device that melts and kneads resin and injects the resin into a mold, and a mold clamping device that can fix and hold the mold so that the mold can be released from the injection device.

  In the operation procedure, a cassette mold is set in the injection molding machine, and the temperature of the injection cylinder, nozzle, mold, etc. is set. Subsequently, the material is set in the hopper, and when the temperature of the injection cylinder or the like reaches the set molding temperature, purging is performed to check whether or not the molten resin is smoothly injected from the injection cylinder. Thereafter, molding conditions such as injection pressure are set, and the molding operation is started.

  As a mold clamping apparatus for opening and closing a mold, a so-called direct pressure type apparatus that performs mold clamping using only an electric motor is disclosed in Patent Document 1. In such a direct pressure type clamping device, the toggle mechanism is unnecessary, and even if it is a direct pressure type, the installation space is not required as in the case of using a long hydraulic cylinder. Can be reduced in size and weight.

  Also, after injecting the plasticized material into the mold cavity, it is generally performed to keep the mold clamping pressure lowered in order to protect the mold and save power consumption. Yes.

JP 2000-94488 A

  In an injection molding machine that uses a mold clamping device to open and close a mold, an injection pressure is applied to the mold as the molding material is injected. This injection pressure causes the mold to open and the material to leak out. there is a possibility. For this reason, the mold clamping device must continue to generate the mold clamping force from the start of the mold clamping operation to the end of the injection operation.

  However, in the case of a direct pressure type mold clamping mechanism using an electric motor as disclosed in Patent Document 1, if the electric motor continues to generate a high driving torque for mold clamping during the injection period of the molding material, the compact size is reduced. Therefore, the electric motor is overloaded. As a result, the safety device works and the operation of the injection molding machine is stopped, which may lead to a reduction in the operation rate. When an electric motor having a sufficiently large rating is used, such a problem can be avoided, but the injection molding machine cannot be reduced in size and weight.

  Therefore, in order to shorten the time for performing mold clamping with a high driving torque, the present inventors have attempted to reduce the driving torque for the electric motor before the injection operation is completed. In this case, it goes without saying that the driving torque provided by the electric motor needs to be a clamping force that can overcome the injection pressure of the molding material and keep the mold closed. However, if the driving torque for the electric motor is drastically reduced before the injection operation is finished, a repulsive force may act on the mold released from the high driving torque, and the mold may open. In some cases, problems such as leakage occurred.

  In view of such a viewpoint, the object of the present invention is to operate the safety device with an overload of the electric motor even when a direct pressure type clamping device using a small electric motor with a small rating is used. An object of the present invention is to provide an injection molding method that avoids such problems and prevents leakage of a molding material from a mold during an injection operation and enables more stable molding.

  The injection molding method according to the present invention includes a mold clamping step in which a movable mold is driven with a first driving torque so that the movable mold is brought into close contact with the fixed mold, and is smaller than the first driving torque. A pressure holding step of pressing the movable mold against the fixed mold with a second driving torque, and a plasticized material is defined between the movable mold and the fixed mold. An injection molding method comprising an injection step of injecting into the cavity, wherein the movable side is moved from the first driving torque to the second driving torque between the mold clamping step and the pressure holding step. A torque reduction step for reducing the driving torque for the mold is further provided, and the end time of the torque reduction step is set before the end time of the injection step.

  In the present invention, the injection step is started after the start point of the torque reduction step for reducing the drive torque for the movable mold from the first drive torque to the second drive torque.

  In the injection molding method according to the present invention, the injection step may include at least a part of the torque reduction step. That is, the injection step may be started at least halfway through the torque reduction step.

  The torque reduction step preferably reduces the drive torque continuously or stepwise at a rate of 10% or less of the first drive torque per 10 milliseconds. When the driving torque is suddenly reduced at a rate exceeding 10% of the first driving torque per 10 milliseconds, the mold is slightly caused by inertia in combination with the injection pressure of the material injected into the cavity. There is a possibility of opening.

  A cooling step for cooling the material injected into the cavity and a step of opening the mold by pulling the movable die away from the fixed die, and a third step in which the cooling step is smaller than the second driving torque. It may include a second pressure holding step of pressing the movable side mold against the fixed side mold with the driving torque.

  The start time of the torque reduction step is preferably between the contact start time of the movable mold with respect to the fixed mold and the intermediate point of the period from the contact start time to the start of the cooling step. When the start time of the torque reduction step is after the intermediate point of the period from the contact start time of the movable mold to the fixed mold to the start time of the cooling step, the drive torque for the movable side is the first drive torque. As a result, the safety device may be activated as a result of the longer holding period and the drive source being held in a high load state.

  The movable mold may be driven by an electric motor and the drive torque may be controlled by changing the current value.

  According to the injection molding method of the present invention, there is provided a torque reduction step for reducing the drive torque for the movable mold from the first drive torque to the second drive torque between the mold clamping step and the pressure holding step. Since the end time of the torque reduction step is set before the end time of the injection step, there is no need to hold the drive torque for the movable mold at the first drive torque during the injection step. It is possible to reduce the load on the drive source for driving the.

  When the injection step includes at least a part of the torque reduction step, the cycle of injection molding the material can be further shortened.

  In the torque reduction step, when the drive torque is reduced continuously or stepwise at a rate of 10% or less of the first drive torque per 10 milliseconds, a part of the material injected into the cavity leaks. Can be prevented.

  A cooling step for cooling the material injected into the cavity, and a step of opening the movable side mold away from the fixed side mold to open the mold, wherein the cooling step is smaller than the second driving torque. In the case where the second holding pressure step of pressing the movable side mold against the fixed side mold with the driving torque is included, an injection molded product with stable quality can be obtained.

  When the start time of the torque reduction step is between the contact start time of the movable mold with respect to the fixed mold and the intermediate point between the contact start time and the start time of the cooling step, the movable mold It is possible to more reliably reduce the load on the drive source for driving the.

  When the movable mold is driven by an electric motor and the drive torque is controlled by changing the current value, continuous injection is performed without operating the safety mechanism of the injection molding machine due to overload of the electric motor. The molding machine can be operated. As a result, it is possible to easily control the drive torque for the movable mold, and it is possible to make the whole injection molding machine more compact by using a smaller electric motor.

  An embodiment of an injection molding machine capable of performing an injection molding method according to the present invention will be described in detail with reference to FIGS. However, the method of the present invention is not limited to such an injection molding machine, but can be implemented by any injection molding machine. In particular, the type using a small electric motor as a drive source for opening and closing the mold. It is effective in the injection molding machine.

  The external appearance of the injection molding machine in this embodiment is shown in FIG. 1, the plane shape is partially broken and shown in FIG. 2, and the side shape of the part of the mold clamping device is extracted and enlarged and shown in FIG. That is, the injection molding machine 10 in the present embodiment performs plastic clamping of the mold unit 11 and an injection device 12 for plasticizing a resin as a molding material and injecting the resin into the mold unit 11 by a predetermined amount. The mold clamping device 13 is included.

The mold unit 11 has a fixed mold 11 _S and a movable mold 11 _M, and a cavity 14 corresponding to the shape of the molded product is defined between them.

  The injection device 12 includes a metering injection unit 15 for pumping a predetermined amount of molten resin into the cavity 14 defined in the mold unit 11, and plasticization for plasticizing the resin material and sending it to the metering injection unit 15. And a sending unit 16.

The plasticizing delivery unit 16 includes a barrel 19 that is accommodated across a fixed die plate 17 and a casing 18 to be described later, a rotor 20, a spiral groove 21, a rotor drive motor 22, and a heater 23 for heating. Including. As shown in the barrel 19 and 4 extracted enlarged portion of the rotor 20 in FIG. 2, the barrel 19, the resin inlet passage 24 is open to the end face 19 _F. In the middle of the resin inflow passage 24, a check valve 25 for preventing the backflow of the molten resin is incorporated. The check valve 25 is disposed on the upstream side of the resin inflow passage 24 with respect to a connection portion between the resin inflow passage 24 and a chamber 27 to which resin is supplied from the plasticization kneading passage 26 described later. A rotor 20 rotatably accommodated in a casing 18 assembled integrally with the fixed-side die plate 17 has an end surface 20 _F that is in sliding contact with one end surface 19 _F of the barrel 19. The spiral groove 21 is formed on the end surface 20 _F of the rotor 20, and defines a plasticized kneading passage 26 between the end surface 19 _F of the barrel 19 and the resin. The spiral groove 21 is supplied with resin from the outer end portion 21 _O, and the inner end portion 21 _I communicates with the resin inflow passage 24 of the barrel 19. A rotor drive motor 22 installed in the casing 18 drives and rotates the rotor 20 around the resin inflow passage 24 of the barrel 19. The resin flow principle by the rotation of the rotor 20 is well known as described in detail in, for example, Japanese Patent Application Laid-Open No. 2005-306028. The heater 23 incorporated in the barrel 19 is for heating and softening and melting the resin present in the resin inflow passage 24 and the plasticizing kneading passage 26.

The resin material in the form of pellets is stored in a hopper 28 attached to the casing 18, and is supplied from here to the outer end portion 21 _O of the spiral groove 21 of the rotor 20 through the casing 18. Then, along with the rotation of the rotor 20 by the operation of the rotor drive motor 22, the fluid flows in the plasticization kneading passage 26 formed between the rotor 20 and the barrel 19. During this time, the rotor 20 moves to or near the rotation center of the rotor 20 while being softened and melted by the heater and kneaded.

Metering injecting portion 15 includes a fixed die plate 17 which holds the fixed mold 11 _S, the nozzle 29 to be inserted into the fixed mold 11 _S, the injection plunger 30, an exit-metering motor 31 Including. The nozzle 29 with the tip facing the cavity 14 has a resin passage 32 communicating with the resin inflow passage 24 formed in the barrel 19. As described above, the barrel 19 is formed with a chamber 27 communicating with the resin inflow passage 24 on its side, and the injection plunger 30 is slidably fitted to the chamber 27. The resin intervening in the nozzle 27 is pumped by a predetermined amount to the resin passage 32 side of the nozzle 29. The injection plunger 30 is mechanically connected to an injection / metering motor 31 via a speed reducer 33 and a power transmission mechanism (not shown), and has an advance end for injecting resin into the cavity 14 and resin in the chamber. It moves between the retracted end for measuring and pulling into 27.

  Accordingly, the rotation of the rotor 20 by the previous rotor drive motor 22 and the backward movement of the injection plunger 30 by the reverse rotation drive of the injection / metering motor 31 (moving in the right direction in FIG. 4) are combined to produce the plasticizing kneading passage 26. The resin guided from the resin to the resin inflow passage 24 is accommodated in the chamber 27. Thereafter, the resin contained in the chamber 27 is moved from the nozzle 29 to the cavity of the mold unit 11 by the forward movement of the injection plunger 30 by the forward rotation drive of the injection / metering motor 31 (moving leftward in FIG. 4). 14 can be injected.

The mold clamping device 13 in this embodiment includes a base 34, a mold clamping motor 35 attached to the base 34, a movable side die plate 36, and the movable side die plate 36 and the mold clamping motor 35. And a ball screw mechanism 37 to be connected to each other. The movable side die plate 36 that holds the movable side mold 11 _M of the mold unit 11 is slidably fitted to a column 38 protruding from the base 34, and an advanced end where mold clamping is performed, It reciprocates between the retracted end where the mold is open. The ball screw mechanism 37 detects the position of the ball screw shaft 37 _A connected to the mold clamping motor 35, the ball nut 37 _N attached to the movable die plate 36, and the position closest to the forward end of the movable die plate 36. And a sensor (not shown). Moving speed of the movable die plate 36 at the forward end than the sensor, as slower than the moving speed of the movable die plate 36 at the rear end side of the sensor, the rotational speed of the ball screw shaft 37 _A is controlled Is done. The driving torque applied to the movable mold 11 _M via the movable die plate 36 during mold clamping is controlled by changing the current value supplied to the mold clamping motor 35.

Therefore, by driving the mold-clamping motor 35 as an electric motor in the present invention, it is possible to move the movable die plate 36 with the movable mold 11 _M along the column 38. More specifically, in the case of the mold clamping operation, the movable die 11 _M at the retracted end is advanced at a high speed to a predetermined position, and when the sensor detects the position of the movable die plate 36, the advance speed is increased. Lowering and continuing the advancement until the movable side mold 11 _M is pressed against the fixed side mold 11 _S , and applying a predetermined current value to the mold clamping motor 35, a predetermined mold clamping force is obtained. For mold opening operation, separate the movable mold 11 _M from the fixed mold 11 _S.

Incidentally, the movable die plate 36, the ejector device 39 for taking out a molded product from the movable mold 11 _M are incorporated. In the ejector device 39, the ejector plate 40 moves relative to the movable mold 11 _M via a spring 41 using the mold opening operation of the mold unit 11. As a result, the ejector pin 42 slidably penetrating the movable mold 11 _M moves so as to protrude into the cavity 14, whereby the molded product is discharged out of the movable mold 11 _M. ing. With respect to the mold unit 11, the mold clamping device 13, and the ejector device 39, those having the same configuration as other known injection molding machines can be adopted.

The change of a given driving torque for such clamping the movable mold 11 reaches the mold opening from _M schematically shown in FIG. First, the mold clamping motor 35 is energized, and the movable mold 11 _M at the retracted end is advanced to a predetermined position at a high speed. When the sensor detects the position of the movable die plate 36, the advance speed is reduced. . In this way, when the movable mold 11 _M that continues to move forward at a low speed presses against the fixed mold 11 _S , the current value rises rapidly and is given to the mold clamping motor 35 so that it becomes a predetermined current value. Control the current value. As a result, the movable mold 11 _M comes into close contact with the fixed mold 11 _S with the first drive torque T ₁ (see time t ₁ ), and mold clamping starts.

The movable mold 11 _M is pressed against the fixed mold 11 _S at the first drive torque T _{1 for a} predetermined time (t ₂ −t ₁ ) until time t ₂ to continue the mold clamping step. That is, in the mold clamping step according to the present invention, the movable die plate 36 moves from the retracted end to the advanced end, and the movable die 11 _M is fixed to the fixed die 11 _S with the first drive torque T ₁ . Corresponds to the time pushing operation. Thereafter, the value of the current supplied to the mold clamping motor 35 is changed, and the driving torque applied to the movable mold 11 _M is reduced to a _second driving torque T ₂ smaller than the first driving torque T _1. Then, a pressure holding step for holding this for a predetermined time (t ₄ -t ₃ ) until time t ₄ is performed.

When the driving torque applied to the movable mold 11 _M is reduced to the _second driving torque T ₂ smaller than the first driving torque T ₁ , the driving torque is rapidly reduced from the mold clamping step to the pressure holding step. Then, a repulsive force acts on the mold released from the high-pressure mold clamping force, and the mold unit 11 is opened, causing problems such as resin leakage. For this reason, a torque reduction step is executed in which the drive torque is reduced continuously or stepwise at a rate of 10% or less of the _first drive torque T ₁ per 10 milliseconds. That is, the period from time t ₂ to time t ₃ is the torque reduction step, and the period from time t ₃ to time t ₄ is the pressure holding step. In this case, end time t ₃ of the torque reduction step, before the end timing of the injection step is set before the words of at least a time t _4. In addition, the start time of the torque reduction step is the contact start time t ₁ of the movable mold 11 _M with respect to the fixed mold 11 _S and the period from the contact start time t ₁ to the start time t ₄ of the cooling step. It is preferably between the intermediate point ((t ₄ −t ₁ ) / 2). If the torque reduction step is started after the intermediate point ((t ₄ -t ₁ ) / 2), the above-described mold clamping step period becomes too long, and the mold clamping motor 35 becomes overloaded and the safety device. This causes a problem that the operation of the injection molding machine 10 is forcibly stopped.

Simultaneously with the start of the previous torque reduction step, the injection / metering motor 31 is driven to move the injection plunger 30 from the retracted end to the advanced end, and the resin contained in the chamber 27 is transferred from the nozzle 29 to the mold unit. An injection step for injection into the 11 cavities 14 is performed. In the injection step of the present invention, the injection plunger 30 moves from the retracted end to the advanced end, and the resin accommodated in the chamber 27 is injected from the nozzle 29 into the cavity 14 of the mold unit 11 for injection and metering. This corresponds to a period during which the drive torque to the injection plunger 30 by the motor 31 is continuously applied. The time required for this pressure holding step is set in advance, and the period (t ₄ -t ₂ ) is slightly longer than the time required for the movement of the injection plunger 30 to the forward end, that is, the time at t ₄ . The pressure holding step end timing t ₄ is set so that the injection plunger 30 has almost moved to its forward end.

  In this embodiment, the injection step is started simultaneously with the torque reduction step. However, the injection step may be started from the middle of the torque reduction step, or the injection step may be started after the start of the pressure holding step. Is possible.

After the pressure holding step, the process proceeds to a cooling step for cooling the material injected into the cavity 14. In this cooling step, the second pressure holding step of pressing than the second drive torque T ₂ at a small third driving torque T ₃ to time t ₅ the movable mold 11 _M to the fixed mold 11 _S And a third pressure holding step for holding the mold clamping motor 35 until time t ₆ with the power supply to the mold clamping motor 35 being cut off. When shifting from the pressure holding step to the second pressure holding step, it is not particularly problematic to rapidly reduce the torque from the _second driving torque T ₂ to the third driving torque T ₃ . Similarly, when shifting from the second pressure holding step to the third pressure holding step, it is not particularly problematic to perform a torque reduction from the _third driving torque T ₃ rapidly. In the present embodiment, even in the second pressure holding step, a predetermined drive torque is given to the injection plunger 30 by the injection / metering motor 31, and no sink due to resin cooling in the cavity 14 occurs. Consideration is taken.

At time t ₆ the cooling step is completed, performs a mold opening pull the movable mold 11 _M from the fixed mold 11 _S by reversing the mold clamping motor 35, the cavity the products that are formed by the ejector device 39 Take out from.

In this way, by performing the torque reduction step between the mold clamping step and the pressure holding step, the mold clamping motor 35 becomes overloaded and the safety device operates to bring about a reduction in the operating rate of the injection molding machine 10. Such problems can be prevented in advance. Moreover, by gradually reducing the torque in the torque reduction step during the predetermined period (t ₃ -t ₂ ), it is possible to prevent the resin from leaking and maintain the mold clamping state. As a result, a small servo motor can be used as the mold clamping motor 35, and the entire injection molding machine 10 can be downsized.

The moving speed and the movable mold 11 _M up to mold clamping start, with respect to a control of the driving torque of the subsequent pressure holding step is not limited to this embodiment, optionally employed if desired a known method be able to. In the above-described embodiment, the so-called scroll-type injection molding machine 10 using the barrel 19 and the rotor 20 as the injection device 12 has been described. Of course, it is also possible to apply the present invention to an injection molding machine using the above.

  As described above, the present invention should be construed only from the matters described in the scope of the claims, and in the above-described embodiments, the matters described in all the changes and modifications included in the concept of the present invention are described. Other than possible. That is, all matters in the above-described embodiment are not intended to limit the present invention, and include any configuration not directly related to the present invention. To get.

It is a three-dimensional projection figure showing the external appearance of one Embodiment of the injection molding machine which can implement the injection molding method by this invention. It is a fracture | rupture top view which represents typically the internal structure of the principal part in embodiment shown in FIG. It is a fracture front view showing typically the internal structure of the principal part in the embodiment shown in FIG. FIG. 3 is a cross-sectional view in which the main part shown in FIG. 2 is further extracted and enlarged. It is a graph which represents typically an example of the change of the drive torque given to a movable side metal mold | die.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Injection molding machine 11 _S Fixed side metal mold 11 _M Movable side metal mold 12 Injection device 13 Clamping device 14 Cavity 17 Fixed side die plate 19 Barrel 20 Rotor 22 Rotor drive motor 27 Chamber 30 Injection plunger 31 Motor for injection and measurement 35 mold clamping motor 36 movable die plate 37 ball screw mechanism T ₁ through T ₃ type driving torque t ₁ ~t ₆ time given to clamping motor

Claims (6)

A mold clamping step of driving the movable side mold with a first driving torque to bring the movable side mold into close contact with the fixed side mold;
A pressure-holding step of pressing the movable-side mold against the fixed-side mold with a second drive torque smaller than the first drive torque;
An injection molding method comprising: an injection step of injecting a plasticized material into a cavity defined between the movable side mold and the fixed side mold, wherein the mold clamping step and the holding step are performed. A torque reduction step for reducing the drive torque for the movable mold from the first drive torque to the second drive torque during the pressure step, and the end time of the torque reduction step is the injection step. An injection molding method characterized in that the injection molding method is set before the end time.   The injection molding method according to claim 1, wherein the injection step includes at least a part of the torque reduction step.   3. The injection according to claim 1, wherein the torque reduction step reduces the drive torque continuously or stepwise at a rate of 10% or less of the first drive torque per 10 milliseconds. Molding method. A cooling step for cooling the material injected into the cavity;
A step of opening the movable-side mold away from the fixed-side mold, and the cooling step includes the step of cooling the movable-side mold with a third driving torque smaller than the second driving torque. The injection molding method according to any one of claims 1 to 3, further comprising a second pressure holding step of pressing the pressure against the fixed mold.   The start time of the torque reduction step is between the contact start time of the movable mold with respect to the fixed mold and the midpoint of the period from the contact start time to the start time of the cooling step. The injection molding method according to any one of claims 1 to 4, wherein the injection molding method is characterized.   The injection molding method according to any one of claims 1 to 5, wherein the movable side mold is driven by an electric motor, and a driving torque is controlled by changing a current value.

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