Die-casting machine and injection molding method

Abstract

To provide a die cast machine capable of guaranteeing a sufficient speed for increasing hydraulic pressure to prescribed pressure after the start of a boosting step and preventing overshooting without being equipped with a power servo motor of a size larger and an output higher than necessary.SOLUTION: Control means 58 provided in a die cast machine 10 executes a low-speed injection step of operating an injection plunger 38 by using a low-speed side flow rate adjust valve 50, then a high-speed injection step of operating the injection plunger 38 by using a high-speed side flow rate adjust valve 52, and then a boosting step of increasing hydraulic oil O in an injection cylinder 42 by a pressure piston 64. A servo motor 60 is operated before completion of the high-speed injection step so as to end the preparation operation time of a power pressure mechanism 34 at the time of completion of the high-speed injection step.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a die casting machine that injects molten metal into a mold to mold a molded product, and an injection molding method.

Background Art

[0002] In conventionally used die casting machines, molten metal melted in a melting furnace is measured and scooped up by a ladle for each shot, the scooped molten metal is supplied to a water supply port of an injection sleeve, and the molten metal is injected and filled into a cavity of a mold by the forward movement of an injection plunger provided to be able to advance and retreat in the injection sleeve, thereby molding a molded body.

[0003] An injection step of injecting molten metal into a cavity of a mold includes a low-speed injection step and a subsequent high-speed injection step. In the high-speed injection step, it is necessary to inject and fill the molten metal into the mold at a high injection speed that is one order of magnitude faster than the injection speed of an injection molding machine that molds plastic products.

[0004] Further, after the completion of the high-speed injection step, a pressure increasing step is performed in which the pressure of the molding material in the cavity is increased by the injection plunger (for example, Patent Document 1).

[0005] Consider a die casting machine in which after performing the low-speed injection step and the high-speed injection step, the final pressure increasing step is performed by a piston pressed by a ball screw driven by an electric servo motor.

[0006] When the change in the moving speed of the injection plunger in a series of injection steps and the change in the hydraulic pressure (internal pressure of the injection cylinder) pressing the injection plunger are graphed, for example, it is as shown in FIG. 4.

[0007] At the beginning of the injection molding process, a low-speed injection process of about 1 to 2 seconds is performed using hydraulic power, and the molten metal begins to fill the cavity. Then, just before the molten metal is completely filled into the cavity (a few hundredths of a second), a high-speed injection process is performed, also using hydraulic power.

[0008] After the high-speed injection process is complete, the electric servo motor rapidly increases the hydraulic pressure, and when it reaches the required pressure, the electric servo motor is rapidly decelerated to maintain a constant hydraulic pressure.

[0009] The injection process is completed by maintaining the hydraulic pressure for a predetermined time after it has stabilized. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2011-224626 [Overview of the project] [Problems that the invention aims to solve]

[0011] However, in the injection process of the conventional die-casting machine described above, the speed at which the hydraulic pressure is increased to a predetermined pressure after entering the pressure-boosting process depends on the acceleration of the electric servo motor, making it difficult to adequately guarantee the speed at which the hydraulic pressure is increased to a predetermined pressure (i.e., the pressure rise time).

[0012] In addition, equipping the machine with a large, high-power electric servo motor to speed up the pressure build-up time presented another problem: it would lead to an increase in the overall cost of the die-casting machine.

[0013] Furthermore, if one attempts to speed up the pressure rise time by relying on the acceleration of the electric servo motor, it becomes necessary to continue accelerating until the hydraulic pressure reaches a predetermined level, and then rapidly decelerate the electric servo motor when that level is reached. This acceleration-to-rapid deceleration process can easily cause an overshoot, where the hydraulic pressure spikes and exceeds the predetermined level.

[0014] This invention has been made in view of these problems, and its purpose is to provide a die-casting machine that can sufficiently ensure the speed at which the hydraulic pressure is raised to a predetermined pressure after entering the pressure-boosting process, without equipping it with an unnecessarily large and high-output electric servo motor, and that can avoid overshoot. [Means for solving the problem]

[0015] According to one aspect of the present invention, A die-casting machine having an injection mechanism, a hydraulic operating mechanism, and an electric pressurizing mechanism, The injection mechanism has an injection plunger for injecting molten metal into the cavity, The hydraulic operating mechanism comprises an injection cylinder housing the injection plunger, a hydraulic pump, an accumulator, a low-speed flow control valve, a high-speed flow control valve, and a control means. The electric pressurizing mechanism comprises an electric servo motor, a ball screw driven by the electric servo motor, and a pressurizing piston pushed out by the ball screw. The control means performs a low-speed injection step in which the injection plunger is operated using a low-speed flow control valve, a high-speed injection step in which the injection plunger is operated using a high-speed flow control valve, and a pressure-boosting step in which the hydraulic fluid in the injection cylinder is pressurized by the pressurizing piston, and operates the electric servo motor before the completion of the high-speed injection step so that the preparation time for the electric pressurizing mechanism is completed when the high-speed injection step is completed. Afterward, the speed of the electric servo motor is kept constant until the pressure inside the injection cylinder reaches a predetermined level during the pressure-boosting process, and the pressure boosting inside the injection cylinder is started from the point of completion of the high-speed injection process. Characterized by A die-casting machine will be provided.

[0016] According to another aspect of the present invention, An injection molding method using a die-casting machine having an injection mechanism, a hydraulic operating mechanism, and an electric pressurizing mechanism, The injection mechanism has an injection plunger for injecting molten metal into the cavity, The hydraulic operating mechanism comprises an injection cylinder housing the injection plunger, a hydraulic pump, an accumulator, a low-speed flow control valve, a high-speed flow control valve, and a control means. The electric pressurizing mechanism comprises an electric servo motor, a ball screw driven by the electric servo motor, and a pressurizing piston pushed out by the ball screw. A low-speed injection process in which the injection plunger is operated using a low-speed flow control valve, This is followed by a high-speed injection process in which the injection plunger is operated using a high-speed flow control valve, This is followed by a pressure-boosting step in which the hydraulic fluid in the injection cylinder is pressurized by the pressurizing piston, The control means operates the electric servo motor before the completion of the high-speed injection process so that the preparation time for the electric pressurizing mechanism is completed when the high-speed injection process is completed. Afterward, the speed of the electric servo motor is kept constant until the pressure inside the injection cylinder reaches a predetermined level during the pressure-boosting process, and the pressure boosting inside the injection cylinder is started from the point of completion of the high-speed injection process. It has steps An injection molding method is provided. [Effects of the Invention]

[0017] According to the die-casting machine of the present invention, the electric servo motor is operated before the completion of the high-speed injection process so that the preparation time for the electric pressurizing mechanism is completed when the high-speed injection process is completed. This allows the pressurization to be started at any speed of the electric servo motor. As a result, it is possible to sufficiently ensure that the hydraulic pressure is raised to a predetermined pressure after entering the pressurization process using a relatively small, low-power electric servo motor, and since deceleration can be performed from a non-accelerating state of the electric servo motor, the possibility of the hydraulic fluid pressure overshooting can also be reduced. [Brief explanation of the drawing]

[0018] [Figure 1] It is a diagram showing an example of the die casting machine 10 according to the embodiment. [Figure 2] It is a diagram showing an example of the electric pressurizing mechanism 34 in the die casting machine 10 according to the embodiment. [Figure 3] It is a graph showing changes in the moving speed of the injection plunger 38, changes in the internal pressure of the injection cylinder 42, and changes in the speed of the electric servo motor 60 during the injection step of the die casting machine 10 according to the embodiment. [Figure 4] It is a graph showing changes in the moving speed of the injection plunger, changes in the internal pressure of the injection cylinder, and changes in the speed of the electric servo motor during the injection step of the prior art. DESCRIPTION OF EMBODIMENTS

[0019] (Configuration of Die Casting Machine 10) As shown in FIG. 1, the die casting machine 10 according to the present embodiment generally includes a mold device 12 and an injection device 14.

[0020] The mold device 12 generally includes a stationary mold 22 mounted on a stationary die plate 20, and a movable mold 26 mounted on a movable die plate 24. A cavity 28 is formed when the stationary mold 22 and the movable mold 26 are clamped.

[0021] The injection device 14 generally includes an injection mechanism 30, a hydraulic operation mechanism 32, and an electric pressurizing mechanism 34.

[0022] The injection mechanism 30 includes an injection sleeve 36, an injection plunger 38, an injection piston 40, and an injection cylinder 42.

[0023] The injection sleeve 36 is a cylindrical member integrally provided to the stationary die plate 20, and has a molten metal supply port 43 formed at an upper portion thereof, through which molten metal is supplied.

[0024] The injection plunger 38 is a roughly rod-shaped member that is provided to move back and forth within the injection sleeve 36.

[0025] The injection piston 40 is formed on the rear end side of the injection plunger 38 (the end opposite to the end that contacts the molten metal) and is the part that is pressed by the hydraulic fluid O.

[0026] The injection cylinder 42 is a cylindrical member through which the injection piston 40 moves back and forth, and is filled with hydraulic fluid O. Looking at the injection piston 40, the space inside the injection piston 40 in the direction in which the injection piston 40 moves during the injection process is called the out side A, and the opposite side is called the in side B.

[0027] The hydraulic operating mechanism 32 is a mechanism that supplies hydraulic fluid O, used in the low-speed and high-speed injection processes of the injection plunger 38, to the injection cylinder 42 to act on the injection piston 40, and generally comprises oil piping 44, a hydraulic pump 46, a plurality of control valves 48, a low-speed side flow control valve 50, a high-speed side flow control valve 52, an accumulator 54, a pressure sensor 56, and a control means 58.

[0028] The oil piping 44 provides a flow path for supplying pressurized hydraulic fluid O from the hydraulic pump 46 to the injection cylinder 42 via the accumulator 54, the low-speed flow control valve 50, and the high-speed flow control valve 52, and for returning the hydraulic fluid O that has come out of the injection cylinder 42 to the original flow path via the control valve 48.

[0029] The hydraulic pump 46 is used to pressurize the hydraulic fluid O to the pressure required for the low-speed and high-speed injection processes of the injection plunger 38.

[0030] The control valve 48 includes a first control valve 48a for switching on and off a passage that sends the hydraulic fluid O discharged from the hydraulic pump 46 to the accumulator 54, and a second control valve 48b for switching on and off a passage that returns the hydraulic fluid O from the inlet side B of the injection cylinder 42 to the hydraulic pump 46 side when the injection plunger 38 is returned to the starting position, and also supplies the hydraulic fluid O discharged from the hydraulic pump 46 to the outlet side A of the injection cylinder 42.

[0031] The low-speed side flow control valve 50 is a valve for adjusting the flow rate of the hydraulic fluid O supplied from the accumulator 54, etc., to the inlet side B of the injection cylinder 42 during the low-speed injection process.

[0032] The high-speed side flow control valve 52 is a valve for adjusting the flow rate of the hydraulic fluid O supplied from the accumulator 54, etc., to the inlet side B of the injection cylinder 42 during the high-speed injection process.

[0033] The accumulator 54 is a container for temporarily storing the hydraulic fluid O that has been pressurized by the hydraulic pump 46.

[0034] The pressure sensor 56 is a device for measuring the pressure of the hydraulic fluid O inside the intake side B of the injection cylinder 42.

[0035] The control means 58 is responsible for operating the hydraulic pump 46, control valve 48, low-speed side flow control valve 50, and high-speed side flow control valve 52 while detecting the position information of the injection piston 40 and the pressure signal from the pressure sensor 56 when performing the low-speed injection process, high-speed injection process, pressure boosting process, and return process of the injection plunger 38. This control means 58 also controls the electric pressurizing mechanism 34.

[0036] The electric pressurizing mechanism 34 according to this embodiment will be described in detail with reference to Figure 2. The electric pressurizing mechanism 34 is a mechanism for further pressurizing the hydraulic fluid O sent into the inlet side B of the injection cylinder 42, and generally comprises an electric servo motor 60, a ball screw 62, a pressurizing piston 64, and a plurality of guide bars 66 (only one is shown in Figure 2). The ball screw 62 is composed of a screw shaft 68 and a nut 70.

[0037] The electric servo motor 60 rotates the screw shaft 68 of the ball screw 62 via a belt or the like (a gear may also be used), thereby causing the nut 70 to slide relative to the screw shaft 68.

[0038] In this embodiment, the electric servo motor 60 is fixed to a servo motor mount 72. The servo motor mount 72 has a screw shaft bearing 74 that holds the rotating screw shaft 68, and also has a first guide bar holding part 76 that holds one end of each guide bar 66. A drive belt 78 is stretched between the rotating shaft 77 of the electric servo motor 60 and the end of the screw shaft 68, and the rotational force of the rotating shaft 77 of the electric servo motor 60 is transmitted to the screw shaft 68 by this drive belt 78.

[0039] The nut 70 of the ball screw 62 is fixed to an intermediate retaining member 80, which has a guide bar insertion hole 82 through which a guide bar 66 is inserted. By inserting the guide bar 66 through the guide bar insertion hole 82, the intermediate retaining member 80 is guided by the guide bar 66, and the nut 70 can move forward and backward in a predetermined direction (downward in the figure) without wobbling. Also, since the intermediate retaining member 80 is guided by the guide bar 66, the pressurizing piston 64 can move forward and backward in a predetermined direction (downward in the figure) without wobbling.

[0040] Furthermore, the other end of the guide bar 66 is held by a tip holding member 84. This tip holding member 84 has a pressure piston insertion hole 86 through which a pressure piston 64 attached to a nut 70 is inserted. In addition, the injection cylinder 42 has a pressure piston guide hole 88 through which the pressure piston 64 is guided.

[0041] The pressurizing piston 64 is inserted into the inlet side B of the injection cylinder 42 in the hydraulic operating mechanism 32 so that its tip can be moved in and out. When the nut 70 of the ball screw 62 moves downward in the figure, the pressurizing piston 64 enters the inlet side B and pressurizes the hydraulic fluid O filled in the inlet side B.

[0042] As described above, in the electric pressurizing mechanism 34 according to this embodiment, the end of the pressurizing piston 64 is connected in series to the nut 70 of the ball screw 62 via an intermediate holding member 80, so that the nut 70 and the pressurizing piston 64 are in series, and the pressurizing piston 64 is pushed into the injection cylinder 42 to increase the pressure of the hydraulic fluid O. As a result, there is no need to slide the injection piston 40 itself, so the entire device can be made simpler and a die-casting machine 10 that can reduce costs can be provided.

[0043] Furthermore, by connecting the end of the pressurizing piston 64 in series with the nut 70 of the ball screw 62, the weight that the ball screw needs to drive (driving weight) can be reduced compared to a structure in which a movable plate is installed between two ball screws to press the pressurizing piston, and the pressing force from the ball screw is applied to the pressurizing piston via the movable plate. As a result, the inertial force is reduced, which prevents overshoot of the hydraulic fluid O pressure caused by the pressurizing piston.

[0044] Furthermore, in this embodiment, the ball screw 62 and the pressure piston 64 are arranged to move vertically. This makes it possible to reduce the width dimension of the electric pressure mechanism 34 and the entire die-casting machine 10, and provides a die-casting machine 10 that can be installed in relatively narrow spaces.

[0045] (Injection process of die-casting machine 10 according to this embodiment) Next, the injection step in the procedure for forming a molded body using the die-casting machine 10 according to this embodiment will be explained with reference to Figure 3.

[0046] In the die-casting machine 10 according to this embodiment, the injection process is divided into a low-speed injection process, a high-speed injection process, and a pressure boosting process.

[0047] Before entering the injection process, the control valve 48 of the hydraulic operating mechanism 32 is operated to connect the discharge side of the hydraulic pump 46 to the accumulator 54 and the suction side of the hydraulic pump 46 to the hydraulic oil tank (not shown). In addition, both the low-speed flow control valve 50 and the high-speed flow control valve 52 are closed to a zero flow rate state.

[0048] Subsequently, the hydraulic pump 46 is activated to fill the accumulator 54 with hydraulic fluid O at a predetermined pressure. At the same time, the separately prepared molten metal is filled into the injection sleeve 36.

[0049] The low-speed injection process is initiated. The low-speed flow control valve 50 in the hydraulic operating mechanism 32 is opened, and the hydraulic fluid O from the accumulator 54 (and hydraulic pump 46) is supplied to the inlet side B of the injection cylinder 42, causing the injection plunger 38 to move at a predetermined speed and filling the cavity 28 with molten metal. This low-speed injection process lasts for a few seconds (1 to 2 seconds).

[0050] Subsequently, the high-speed injection process begins. In addition to the low-speed flow control valve 50 in the hydraulic operating mechanism 32, the high-speed flow control valve 52 is opened, and the hydraulic fluid O is supplied to the inlet side B of the injection cylinder 42, moving the injection plunger 38 at a predetermined speed to fill the cavity 28 with molten metal. The high-speed injection process lasts for a few hundredths of a second. When the high-speed injection process is completed, the low-speed flow control valve 50 and the high-speed flow control valve 52 are closed.

[0051] Incidentally, the injection process of the die-casting machine 10 according to this embodiment is characterized by the operation of the electric pressurizing mechanism 34. Specifically, prior to the start of the pressurizing process, the electric servo motor 60 is started to operate, thereby starting the operation of the nut 70 and the pressurizing piston 64, so that the preparation for pressurizing the hydraulic fluid O by the pressurizing piston 64 of the electric pressurizing mechanism 34 is completed at the time the high-speed injection process described above is completed.

[0052] This is because, immediately after the electric servo motor 60 of the electric pressurizing mechanism 34 starts operating, the belt between the electric servo motor 60 and the screw shaft 68 of the ball screw 62 stretches slightly, and due to backlash between the screw shaft 68 and the nut 70, as well as inertial force due to the drive weight, the rotational force of the electric servo motor 60 is not fully transmitted to the nut 70 via the screw shaft 68. It takes some time after the electric servo motor 60 starts operating for the rotational force to be fully transmitted to the nut 70. This time is called the "preparation time".

[0053] If the pressure build-up time in the pressure-boosting process is slow, the molten metal filling the cavity 28 will solidify too quickly, raising concerns that this could degrade the quality of the finished molded product.

[0054] Therefore, if the electric servo motor 60 is started at the same time as the high-speed injection process is completed, the speed at which the hydraulic pressure is increased to a predetermined pressure after entering the pressure-boosting process depends on the acceleration of the electric servo motor, making it difficult to adequately guarantee the speed at which the hydraulic pressure is increased to a predetermined pressure (i.e., the pressure rise time).

[0055] Furthermore, equipping the die-casting machine with a large, high-power electric servo motor to speed up the pressure build-up time would lead to an increase in the overall cost of the machine.

[0056] Furthermore, if one attempts to speed up the pressure rise time by relying on the acceleration of an electric servo motor, it becomes necessary to continue accelerating until the hydraulic pressure reaches a predetermined level, and then rapidly decelerate the electric servo motor as it approaches that level. This acceleration-to-rapid deceleration process makes it easy for an overshoot to occur, where the hydraulic pressure spikes and exceeds the predetermined level.

[0057] In this regard, in the electric pressurizing mechanism 34 according to this embodiment, as described above, by starting the operation of the electric servo motor 60 and the operation of the nut 70 and pressurizing piston 64 prior to the start of the pressurizing process, the preparation time has elapsed by the time the high-speed injection process requiring pressurizing is completed, so pressurizing can be started at any speed of the electric servo motor 60.

[0058] This ensures that the relatively small, low-power electric servo motor 60 can be used to quickly raise the hydraulic pressure to a predetermined level after entering the pressure-boosting process, and also reduces the possibility of the hydraulic fluid O pressure overshooting because the electric servo motor 60 can be decelerated from a non-accelerating state.

[0059] The timing of starting the operation of the electric servo motor 60 prior to the start of the pressure-boosting process depends on the preparation time, so this start timing may be during the low-speed injection process or during the high-speed injection process. Of course, when the electric servo motor 60 starts operating, the amount of hydraulic fluid O flowing into the injection cylinder 42 through the low-speed flow control valve 50 and the high-speed flow control valve 52 is reduced by the amount that the pressurizing piston 64 moves.

[0060] (Variation 1) In the die-casting machine 10 according to the above embodiment, an example of a so-called "inlet throttle" was shown to adjust the flow rate of the hydraulic fluid O flowing into the inlet side B of the injection cylinder 42 during the low-speed injection process and the high-speed injection process. However, instead, a so-called "outlet throttle" may be used to adjust the flow rate of the hydraulic fluid O flowing out from the outlet side A of the injection cylinder 42. In the case of this "outlet throttle," the low-speed side flow control valve 50 and the high-speed side flow control valve 52 are attached to the oil piping 44 connected to the outlet side A of the injection cylinder 42.

[0061] (Modification 2) Furthermore, in the die-casting machine 10 according to the above embodiment, a pressure piston 64 was connected in series to a nut 70 constituting the ball screw 62 in the electric pressure mechanism 34, and the nut 70 and pressure piston 64 were moved vertically by rotating the screw shaft 68 with an electric servo motor 60. However, instead, the pressure piston 64 may be connected in series to the screw shaft 68, and the screw shaft 68 and pressure piston 64 may be moved vertically by rotating the nut 70 with an electric servo motor 60.

[0062] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of symbols]

[0063] 10…Die casting machine, 12…Mold device, 14…Injection device, 20…Fixed die plate, 22…Fixed mold, 24…Moving die plate, 26…Moving mold, 28…Cavity, 30…Injection mechanism, 32…Hydraulic operating mechanism, 34…Electric pressurization mechanism, 36…Injection sleeve, 38…Injection plunger, 40…Injection piston, 42…Injection cylinder, 43…Hot water inlet, 44…Oil piping, 46…Hydraulic pump, 48…Control valve, 48a…First control valve, 48b…Second control valve, 50…Low-speed side flow control valve, 52... High-speed flow control valve, 54... Accumulator, 56... Pressure sensor, 58... Control means, 60... Electric servo motor, 62... Ball screw, 64... Pressurizing piston, 66... ​​Guide bar, 68... Screw shaft, 70... Nut, 72... Servo motor mount, 74... Screw shaft bearing, 76... Guide bar first holding part, 77... Rotating shaft, 78... Drive belt, 80... Intermediate holding member, 82... Guide bar insertion hole, 84... Tip holding member, 86... Pressurizing piston insertion hole, 88... Pressurizing piston guide hole O...Hydraulic fluid, A...Outlet side of injection piston 40, B...Inlet side of injection piston 40

Claims

1. A die-casting machine having an injection mechanism, a hydraulic operating mechanism, and an electric pressurizing mechanism, The injection mechanism has an injection plunger for injecting molten metal into the cavity, The hydraulic operating mechanism comprises an injection cylinder housing the injection plunger, a hydraulic pump, an accumulator, a low-speed flow control valve, a high-speed flow control valve, and a control means. The electric pressurizing mechanism comprises an electric servo motor, a ball screw driven by the electric servo motor, and a pressurizing piston pushed out by the ball screw. The control means performs a low-speed injection step in which the injection plunger is operated using a low-speed flow control valve, a high-speed injection step in which the injection plunger is operated using a high-speed flow control valve, and a pressure-boosting step in which the hydraulic fluid in the injection cylinder is pressurized using a pressurizing piston. The electric servo motor is operated before the completion of the high-speed injection step so that the preparation time for the electric pressurizing mechanism is completed when the high-speed injection step is completed. The speed of the electric servo motor is kept constant during the pressure-boosting step until the pressure inside the injection cylinder reaches a predetermined pressure, and the pressure boosting inside the injection cylinder is started from the completion of the high-speed injection step. Die-casting machine.

2. An injection molding method using a die-casting machine having an injection mechanism, a hydraulic operating mechanism, and an electric pressurizing mechanism, The injection mechanism has an injection plunger for injecting molten metal into the cavity, The hydraulic operating mechanism comprises an injection cylinder housing the injection plunger, a hydraulic pump, an accumulator, a low-speed flow control valve, a high-speed flow control valve, and a control means. The electric pressurizing mechanism comprises an electric servo motor, a ball screw driven by the electric servo motor, and a pressurizing piston pushed out by the ball screw. A low-speed injection process in which the injection plunger is operated using a low-speed flow control valve, This is followed by a high-speed injection process in which the injection plunger is operated using a high-speed flow control valve, This is followed by a pressure-boosting step in which the hydraulic fluid in the injection cylinder is pressurized by the pressurizing piston, The control means operates the electric servo motor before the completion of the high-speed injection process so that the preparation time for the electric pressurizing mechanism is completed when the high-speed injection process is completed. The electric servo motor's speed is kept constant during the pressure-boosting process until a predetermined pressure is reached inside the injection cylinder, and the pressure-boosting process is started from the moment the high-speed injection process is completed. Injection molding method.

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