JP5086307B2 - Injection mechanism of metal injection molding machine - Google Patents

Description

  The present invention relates to an injection mechanism of a metal injection molding machine that performs injection molding of a metal such as a magnesium alloy or an aluminum alloy.

  The injection mechanism of the metal injection molding machine includes a heating cylinder that melts the molding material, a screw that can be moved in the heating cylinder along the axial direction of the heating cylinder, and that can rotate about the axis of the heating cylinder, and the screw is a screw shaft. And an injection piston that moves along the direction. The piston is disposed in an injection hydraulic cylinder and can move forward and backward in the cylinder. Further, the injection mechanism includes a motor that rotates the injection piston around the axis of the injection piston in order to rotationally drive the screw. In addition, a mold for molding a molded product can be installed at the injection destination of the heating cylinder (see Patent Document 1 and Patent Document 2).

  In such an injection molding machine, a measurement process, an injection process, and a pressure holding process are performed. The measuring step is a step of storing and measuring an amount of the molding material corresponding to the volume of the molded product. A solid molding material is put into a heating cylinder, and the screw is driven to rotate by a motor. At the same time, the screw is moved along the axis of the screw in the direction opposite to the injection destination by the injection piston in the injection hydraulic cylinder. Thus, the storage amount of the molding material in the heating cylinder is measured. The injection step is a step of injecting the molding material melted in the metering step into the mold cavity by moving the screw in the injection direction with the injection piston. The pressure holding step is a step of holding pressure in order to compensate for shrinkage accompanying cooling of the material after the molding material is injected.

  In injection molding, if the molten molding material is not injected at a high speed, the molding material rapidly cools in the cavity during the injection process and the viscosity increases, and the molding material does not reach the cavity sufficiently. Occurs. Furthermore, the temperature deviation of the molding material in the cavity becomes large. As a result, it has been a problem that appearance defects such as sink marks and variations in the mass of the molded product occur. Therefore, in the injection molding method, it is required to perform injection of the molding material at high speed and to shorten the injection process.

  The injection process consists of the rise time until the screw that pushes out the molding material reaches the maximum speed from the stopped state, the constant speed drive time during which the screw is driven to move at a constant speed at the maximum speed, and until the screw stops from the moving state. It can be divided into the fall time.

  In Patent Document 3, as a method of shortening the injection process, a method of focusing on the fall time and decelerating the screw and the injection piston abruptly to shorten the fall time is disclosed. Specifically, the oil discharge port provided in the injection hydraulic cylinder is closed by the injection piston that moves in the injection direction in order to inject the molding material, and the discharge of hydraulic oil from the hydraulic cylinder is stopped to stop the injection piston. Is decelerated rapidly.

  Further, paying attention to the startup time of the screw, a method of using an accumulator as a pressure oil supply source to the injection hydraulic cylinder is employed. By accumulating the pressure oil in the accumulator, the pressure oil can be supplied to the injection hydraulic cylinder at a higher speed than when the hydraulic pump is operated alone. That is, the injection piston and the screw connected to the injection piston can be driven at high speed in the axial direction of the screw, and the rise time is shortened.

Japanese Patent Laid-Open No. 11-47901 JP 2008-036975 A JP 2007-216285 A

  In the injection process, the method of driving the injection piston and the screw at high speed toward the injection destination using the accumulator as described above was useful for shortening the rise time in the injection process, but useful for further time reduction. A mechanism was desired. However, since the injection piston and the screw are started to move from the stopped state, it takes time to reach the maximum speed, which causes a problem in that the rise time of the injection process is hindered.

  Then, an object of this invention is to provide the injection mechanism of the metal injection molding machine which can shorten the rise time of a screw in an injection process.

In order to achieve the above object, the present invention provides a heating cylinder for melting a molding material constituting a molded product, and can be moved forward and backward in the axial direction of the heating cylinder inside the heating cylinder, and rotated around the axis of the heating cylinder. In an injection mechanism of a metal injection molding machine provided with a screw that can be provided and an injection piston that is rotatably provided around an axis and that is driven forward to advance the screw.
An engaging portion that engages the screw and the injection piston so that the injection piston can move by a predetermined distance along the axial direction with respect to the screw, and the screw can rotate according to the rotation of the injection piston;
The predetermined distance is a distance by which the injection piston moves forward after the injection piston starts to advance toward the screw and reaches a predetermined speed .

  According to the configuration as described above, the screw that injects the molding material is still stopped when the injection piston is driven forward, and the screw does not move forward until it collides with the injection piston. Further, the injection piston moves forward while accelerating a predetermined distance until it collides with the screw, and when it collides with the screw, the injection piston reaches a predetermined speed. Thereafter, the screw is advanced together with the injection piston by colliding with the injection piston reaching a predetermined speed. Therefore, it is possible to shorten the time until the screw reaches the constant speed driving time from the stopped state, compared to the case where the screw and the injection piston start to move from the stopped state in conjunction with each other.

  According to the present invention, in the injection process, it is possible to shorten the rise time until the screw for injecting the molding material reaches the maximum speed from the stopped state.

It is a figure which shows schematic structure of the metal injection molding machine of one Embodiment of this invention. In the metal injection molding machine of one embodiment of the present invention, it is a sectional view showing typically a connecting part of a screw and an injection piston. In the conventional metal injection molding machine, it is sectional drawing which shows typically the connection part of a screw and an injection piston. In the injection process of the conventional metal injection molding machine, the horizontal axis represents time, and the vertical axis represents the speed of the screw and the injection piston. In the injection process of the metal injection molding machine of one embodiment of the present invention, it is a figure showing time on a horizontal axis and speed of a screw and an injection piston on a vertical axis.

  FIG. 1A is a diagram showing a schematic configuration of an injection mechanism of a metal injection molding machine according to an embodiment of the present invention. As shown in FIG. 1A, the injection mechanism of the metal injection molding machine according to the present embodiment includes a heating cylinder 1 that heats a molding material that forms a molded product, and a forward movement in the axial direction of the heating cylinder 1 inside the heating cylinder 1. And a screw 2 provided so as to be retractable and rotatable about the axis of the heating cylinder. By moving the screw 2 in the heating cylinder 1 along the axial direction of the screw, the molding material melted in the heating cylinder 1 is injected. In the description of this document, the direction in which the molding material is injected along the axial direction of the heating cylinder 1 and the screw 2 is referred to as the front, and the opposite is the rear.

  A heater 4 for applying heat to the molding material is provided on the outer periphery of the heating cylinder 1. A nozzle 5 is attached to the front end of the heating cylinder 1. Further, a die 6 for molding a molded product is attached in front of the nozzle 5. A hopper 3 for introducing a molding material into the heating cylinder 1 is installed behind the heating cylinder 1. The molding material thrown into the hopper 3 is melted by heat applied from the heater 4 on the outer periphery of the heating cylinder 1 and frictional heat or shear heat generated with the rotation of the screw 2. Further, the molding material is kneaded by the rotation of the screw 2 and sent to the front of the heating cylinder 1. Then, the molten molding material stored in front of the heating cylinder 1 is injected into the cavity 7 of the mold 6 which is closed through the nozzle 5 at the time of injection.

  The screw 2 is connected to the injection piston 10 at the rear part of the screw 2 by a coupling 18. FIG. 1B schematically shows a connecting portion 20 between the injection piston 10 and the screw 2 at a position where the weighing process is completed and the screw 2 and the injection piston 10 are waiting for injection in the embodiment of the present invention. It is sectional drawing shown. As shown in FIG. 1B, the connection portion 20 provided at the rear portion of the screw 2 and connected to the injection piston 10 is stored in a hole 21 provided at an end portion on the forward side of the injection piston 10. The connecting portion 22 is configured by preventing the connecting portion 20 from coming out of the hole 21 by the coupling 18. The length of the connecting portion 20 is shorter than the depth of the hole 21, and therefore a gap 19 is formed between the injection piston 10 and the screw 2. Therefore, the screw 2 and the injection piston 10 can be moved relative to each other. That is, the injection piston 10 is individually movable forward or backward in the axial direction of the injection piston 10 with respect to the screw 2 in a stopped state. Further, the interval X of the gap 19 is determined until the injection piston 10 reaches a predetermined speed (for example, the maximum speed) when the measuring process is finished and the injection piston 10 starts to be driven forward in the axial direction of the injection piston 10. A distance that does not contact the screw 2 is provided. In this embodiment, the distance from which the injection piston 10 reaches the maximum speed was 10 [mm] as a result of experiments and calculations with the configuration shown in the drawing, and therefore the interval X of the gap 19 was set to 10 [mm].

  The injection piston 10 is provided with a motor 8, and the rotational movement of the motor 8 is transmitted to the screw 2 through the injection piston 10. For example, the outer peripheral surface of the connecting portion 20 of the screw 2 is provided with a groove along the axial direction of the screw 2, and the inner surface of the hole 21 of the injection piston 10 is fitted with the groove along the axial direction of the injection piston 10. A structure having protrusions that fit together is exemplified. As a result, the screw 2 and the injection piston 10 can be individually moved in the axial direction of the screw 2 and the injection piston 10, and rotate in conjunction with each other around the axis.

  An injection hydraulic cylinder 9 that drives the injection piston 10 in the axial direction of the injection piston 10 is installed on the outer periphery of the injection piston 10. In the injection hydraulic cylinder 9, a front chamber 11 a is formed in front of the injection piston 10, and a rear chamber 11 b is formed in the rear of the injection piston 10. Pressure oil accumulated in the accumulator 13 by the hydraulic pump 12 is supplied to the rear chamber 11 b via the flow rate adjustment valve 14. An oil discharge port 15 is provided in the front chamber 11 a of the injection hydraulic cylinder 9. The oil discharge port 15 is connected to the oil tank 17 via the flow rate adjusting valve 16, and has a size sufficient to discharge the hydraulic oil stored in the rear chamber 11b to the oil tank 17 in the injection process. ing.

  Next, operations from the weighing process to the injection process of the injection molding machine will be described.

  The solid molding material charged into the heating cylinder 1 from the hopper 3 is provided on the outer periphery of the heating cylinder 1 and frictional heat and shear heat generated as the screw 2 is driven to rotate by the motor 8. It is melted by the heat applied from the heater 4. When melting of the molding material corresponding to the volume of the molded product is completed, the injection piston 10 starts driving in the axial direction of the injection piston by supplying pressure oil to the injection hydraulic cylinder 9.

  FIG. 2 is a cross-sectional view schematically showing the connecting portion 22 between the injection piston 10 and the screw 2 of a conventional metal injection molding machine. As shown in FIG. 2, the conventional metal injection molding machine has a structure in which the hole 21 of the injection piston 10 and the connecting portion 20 of the screw 2 are always in contact with no gap. Therefore, at the same time when the injection piston 10 starts driving forward along the axial direction of the injection piston, the screw 2 is also started to drive forward in the axial direction of the screw 2. Since the injection piston 10 and the screw 2 start to be driven from a stopped state, a certain amount of rise time is required for the injection piston 10 and the screw 2 to reach the maximum speed. In the conventional example of FIG. 2, when the maximum speed of the screw 2 is 3 [m / s] to 5 [m / s], the rise time until reaching the maximum speed needs about 10 [ms]. As a result, the injection process is prolonged. Then, the molten molding material is rapidly cooled in the cavity 7 during the injection process, the viscosity of the molten molding material is increased, and the filling of the molding material into the cavity 7 tends to be insufficient. Furthermore, the temperature deviation of the molding material in the cavity 7 is increased, and there is a possibility that a problem such as appearance defect of the molded product occurs.

  On the other hand, in the present embodiment, as shown in FIG. 1B, the gap 19 is provided between the bottom surface of the hole 21 of the injection piston 10 and the end surface of the connection portion 20 of the screw 2 at the time when the weighing process is completed. It has become. Therefore, the operation of the screw 2 is not synchronized with the operation of the injection piston 10. At the time when the weighing process is finished and the injection piston 10 starts driving forward in the axial direction of the injection piston 10, there is a gap 19 between the hole 21 of the injection piston 10 and the connecting portion 20 of the screw 2. Therefore, the screw 2 remains stopped. After the injection piston 10 reaches a certain speed, the injection piston 10 and the screw 2 collide. Since the hydraulic cylinder 9 for injection is filled with lubricating oil, the following law of conservation of momentum holds when it is assumed that almost no friction occurs between the injection piston 10 and the screw 2.

上記の数式において、表１に示したように、Ｍ１は射出ピストン１０の質量、Ｍ２はスクリュ２の質量である。Ｖ１は射出ピストン１０とスクリュ２とが衝突する直前の射出ピストン１０の速度を、Ｖ１’は衝突した直後の射出ピストン１０の速度である。Ｖ２は射出ピストン１０とスクリュ２とが衝突する直前のスクリュ２の速度を、Ｖ２’は衝突した直後のスクリュ２の速度である。

In the above formula, as shown in Table 1, M1 is the mass of the injection piston 10, and M2 is the mass of the screw 2. V1 is the speed of the injection piston 10 immediately before the injection piston 10 and the screw 2 collide, and V1 ′ is the speed of the injection piston 10 immediately after the collision. V2 is the speed of the screw 2 immediately before the injection piston 10 and the screw 2 collide, and V2 ′ is the speed of the screw 2 immediately after the collision.

  FIG. 3A is a diagram showing speed changes of the screw 2 and the injection piston 10 in an injection process in a conventional injection molding machine, with the horizontal axis representing time and the vertical axis representing speed. FIG. 3B is a diagram showing speed changes of the screw 2 and the injection piston 10 in the injection molding machine according to the embodiment of the present invention, with the horizontal axis representing time and the vertical axis representing speed. As shown in FIG. 3B, in the mechanism of the present invention, the screw 2 is collided with the injection piston that has reached a predetermined speed, and the screw 2 starts to be driven forward in the axial direction of the screw 2. Therefore, in the mechanism of the present invention, the time to reach the maximum speed can be shortened as compared with the conventional mechanism in which the injection piston 10 and the screw 2 are interlocked to start driving from the stopped state.

  For example, the mass M1 of the injection piston 10 is 10 [kg], and the mass M2 of the screw 2 is 5 [kg]. Further, the speed V1 immediately before the collision of the injection piston 10 is 5 [m / s], the speed V1 ′ immediately after the collision of the injection piston 10 is 3 [m / s], and the speed V2 immediately before the collision of the screw 2 is 0 [m / s]. s]. From Equation 1, the velocity V2 'immediately after the collision of the screw 2 is 4 [m / s]. If the speed V2 ′ immediately after the collision of the screw 2 is the maximum speed of the screw 2 in the injection process, the conventional time of about 10 [ms] from the state where the screw is stopped until the constant speed driving time is reached is shortened. It will be.

  Thus, since the screw 2 starts to be driven forward in the axial direction of the screw 2 due to the collision of the injection piston 10 reaching a predetermined speed, the rise time of the screw 2 is shortened. As a result, cooling of the molding material in the cavity 7 during the injection process is suppressed, and the molding material can be injected into the cavity 7 at a high temperature. Therefore, insufficient filling of the molding material into the cavity 7 and uneven material temperature in the cavity 7 are suppressed, and a molded product with few appearance defects can be formed with high productivity.

DESCRIPTION OF SYMBOLS 1 Heating cylinder 2 Screw 3 Hopper 4 Heater 5 Nozzle 6 Mold 7 Cavity 8 Motor 9 Injection hydraulic cylinder 10 Injection piston 11a Front chamber 11b Rear chamber 12 Hydraulic pump 13 Accumulator 14 Flow rate adjustment valve 15 Oil discharge port 16 Flow rate adjustment valve 17 Oil tank 18 Coupling 19 Clearance 20 Connection 21 Hole 22 Connection X distance

Claims (2)

A heating cylinder for melting a molding material constituting the molded article, a screw provided inside the heating cylinder and capable of moving forward and backward in the axial direction of the heating cylinder, and rotatable about the axis of the heating cylinder; In an injection mechanism of a metal injection molding machine, which is provided rotatably around an axis and includes an injection piston which is driven forward to advance the screw.
An engaging portion that engages the screw and the injection piston so that the injection piston can move by a predetermined distance along the axial direction with respect to the screw, and the screw can be rotated according to the rotation of the injection piston. Further comprising
The predetermined distance is a distance by which the injection piston moves forward after the injection piston starts to advance toward the screw and reaches a predetermined speed. Injection mechanism.   The engaging portion includes a groove extending along the axial direction, formed on one of an outer peripheral surface of the backward end portion of the screw and the piston, an outer peripheral surface of the backward end portion of the screw, and the The injection mechanism of an injection molding machine according to claim 1, further comprising: a protrusion provided on the other of the pistons and fitted into the groove.

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