Die cast 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 and an injection molding method for injecting molten metal into a die to form a molded product. [Background technology]

[0002] In conventional die casting machines, the molten metal melted in a melting furnace is measured and pumped up with a ladle for each shot, and the pumped molten metal is supplied to the inlet of the injection sleeve. The molten metal is then injected and filled into the cavity of the mold by the forward movement of an injection plunger that is movably mounted within the injection sleeve, thereby forming a green body.

[0003] The injection process, in which molten metal is injected into the cavity of a mold, consists of a low-speed injection process followed by a high-speed injection process. In the high-speed injection process, the molten metal must be injected to fill the mold at an injection speed that is about one order of magnitude faster than the injection speed of the injection molding machine that molds plastic products.

[0004] Furthermore, after the high-speed injection step is completed, a pressure increase step is carried out 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 that performs a low-speed injection process and a high-speed injection process, and then performs a final pressure increase process using a piston pressed by a ball screw driven by an electric servo motor.

[0006] If the change in the moving speed of the injection plunger during a series of injection steps and the change in the hydraulic pressure (injection cylinder internal pressure) pressing the injection plunger are graphed, then it will look like, for example, the one shown in FIG.

[0007] At the beginning of the injection process, a low-speed injection process is performed for about 1 to 2 seconds by hydraulic drive, and the molten metal begins to fill the cavity. Then, just before the molten metal fills the cavity (a few hundredths of a second), a high-speed injection process is performed by hydraulic drive as well.

[0008] After the high-speed injection process is completed, the electric servo motor operates rapidly to increase the hydraulic pressure in one go, and when the required pressure is reached, the electric servo motor is suddenly decelerated to keep the hydraulic pressure constant.

[0009] After the hydraulic pressure becomes constant, it is maintained for a predetermined period of time to complete the injection process. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2011-224626 A Summary of the Invention [Problem to be solved by the invention]

[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 increase process depends on the acceleration of the electric servo motor, so it was difficult to sufficiently guarantee the speed at which the hydraulic pressure is increased to the predetermined pressure (i.e., the rise time of pressure increase).

[0012] In addition, if a large, high-output electric servo motor was installed to speed up the pressure boosting start-up time, this would in turn increase the cost of the entire die casting machine.

[0013] Furthermore, if one were to try to speed up the rise time of the pressure boost by relying on the acceleration characteristics of the electric servo motor, it would be necessary to continue accelerating until the hydraulic pressure reached a specified pressure, at which point the electric servo motor would need to be suddenly decelerated. This rapid deceleration from acceleration to deceleration could cause the hydraulic pressure to spike and become higher than the specified pressure, creating the problem of an overshoot.

[0014] The present invention has been made in consideration of the above problems, and its purpose is to provide a die casting machine that can ensure a sufficient speed at which the hydraulic pressure is increased to a specified pressure after the pressure increasing process begins, and that can avoid overshooting, without being equipped with an electric servo motor that is larger and has a higher output than necessary. [Means for solving the problem]

[0015] According to one aspect of the present invention, A die casting machine having an injection mechanism, a hydraulic operation mechanism, and an electric pressure mechanism, The injection mechanism has an injection plunger that injects molten metal into the cavity, the hydraulic operation mechanism includes an injection cylinder that houses the injection plunger, a hydraulic pump, an accumulator, a low-speed flow rate control valve, a high-speed flow rate control valve, and a control means; the electric pressure mechanism includes an electric servo motor, a ball screw driven by the electric servo motor, and a pressure piston pushed out by the ball screw, The control means performs a low-speed injection process in which the injection plunger is operated using a low-speed flow rate control valve, a subsequent high-speed injection process in which the injection plunger is operated using a high-speed flow rate control valve, and a subsequent pressure increasing process in which the pressure of the hydraulic oil in the injection cylinder is increased by the pressure increasing piston, and operates the electric servo motor before the completion of the high-speed injection process so that the preparation operation time of the electric pressure mechanism is completed at the completion of the high-speed injection process. A die casting machine is 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 operation mechanism, and an electric pressure mechanism, The injection mechanism has an injection plunger that injects molten metal into the cavity, the hydraulic operation mechanism includes an injection cylinder that houses the injection plunger, a hydraulic pump, an accumulator, a low-speed flow rate control valve, a high-speed flow rate control valve, and a control means; the electric pressure mechanism includes an electric servo motor, a ball screw driven by the electric servo motor, and a pressure piston pushed out by the ball screw, a low-speed injection step of operating the injection plunger using a low-speed flow rate control valve; a subsequent high-speed injection step of operating the injection plunger using a high-speed side flow rate control valve; and a pressure increasing step of increasing the pressure of the hydraulic oil in the injection cylinder by the pressure increasing piston. and a step of operating the electric servo motor by the control means before the completion of the high-speed injection step so that a preparatory operation time of the electric pressure mechanism is completed at the time when the high-speed injection step is completed. An injection molding method is provided. Effect 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 preparatory operation time of the electric pressurizing mechanism is completed at the completion of the high speed injection process, so that pressure increase can be started at any speed of the electric servo motor. This makes it possible to sufficiently ensure the speed at which the hydraulic pressure is increased to a predetermined pressure after the pressure increase process starts using a relatively small and low output electric servo motor, and also reduces the possibility of the hydraulic oil pressure overshooting because the electric servo motor can be decelerated from a non-accelerating state. [Brief description of the drawings]

[0018] [Figure 1]FIG. 1 is a diagram showing an example of a die casting machine 10 according to an embodiment. [Diagram 2] 2 is a diagram showing an example of an electric pressure mechanism 34 in the die casting machine 10 according to the embodiment. FIG. [Diagram 3] 5 is a graph showing changes in the moving speed of an injection plunger 38, changes in the internal pressure of an injection cylinder 42, and changes in the speed of an electric servo motor 60 during an injection process of a die casting machine 10 according to an embodiment. [Figure 4] 1 is a graph showing a change in the moving speed of an injection plunger, a change in the internal pressure of an injection cylinder, and a change in the speed of an electric servo motor in an injection process of the conventional technology. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] (Configuration of die casting machine 10) As shown in FIG. 1, the die casting machine 10 according to this embodiment generally includes a die unit 12 and an injection unit 14.

[0020] The mold device 12 generally comprises a fixed mold 22 mounted on a fixed die plate 20 and a movable mold 26 mounted on a movable die plate 24, and a cavity 28 is formed by closing the fixed mold 22 and the movable mold 26.

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

[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 provided integrally with the fixed die plate 20, and is a cylindrical member having a supply port 43 formed at its upper portion through which the molten metal is supplied.

[0024] The injection plunger 38 is a generally rod-shaped member that is provided within the injection sleeve 36 so as to be capable of advancing and retreating.

[0025] The injection piston 40 is formed on the rear end side of the injection plunger 38 (the end opposite to the end in contact with the molten metal).

[0026] The injection cylinder 42 is a cylindrical member through which the injection piston 40 advances and retreats, and is filled with hydraulic oil O. When viewed from 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 space on the opposite side is called the in-side B.

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

[0028] The oil piping 44 sends the hydraulic oil O pressurized by the hydraulic pump 46 to the injection cylinder 42 via the accumulator 54, the low-speed side flow rate control valve 50, and the high-speed side flow rate control valve 52, and also forms a flow path for returning the hydraulic oil O coming out of the injection cylinder 42 to its original position via the control valve 48.

[0029] The hydraulic pump 46 is for pressurizing the hydraulic oil O to a pressure required for the low-speed injection stroke and the high-speed injection stroke of the injection plunger 38.

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

[0031] The low-speed flow rate adjustment valve 50 is a valve for adjusting the flow rate of the hydraulic oil O supplied from the accumulator 54 or the like to the inside B of the injection cylinder 42 in the low-speed injection process.

[0032] The high-speed side flow rate adjustment valve 52 is a valve for adjusting the flow rate of the hydraulic oil O supplied from the accumulator 54 or the like to the IN side B of the injection cylinder 42 in the high-speed injection process.

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

[0034] The pressure sensor 56 is an instrument for measuring the pressure of the hydraulic oil O in the inside B of the injection cylinder 42.

[0035] The control means 58 has a role of operating the hydraulic pump 46, the control valve 48, the low-speed side flow rate adjustment valve 50, and the high-speed side flow rate adjustment valve 52 while detecting position information of the injection piston 40 and a pressure signal from the pressure sensor 56 when performing the low-speed injection process, the high-speed injection process, the pressure boosting process, and the return process of the injection plunger 38. The 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 Fig. 2. The electric pressurizing mechanism 34 is a mechanism for further pressurizing the hydraulic oil O sent into the inside B of the injection cylinder 42, and generally includes 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 Fig. 2). The ball screw 62 is composed of a screw shaft 68 and a nut 70.

[0037] The electric servo motor 60 has a role of rotating a screw shaft 68 of the ball screw 62 via a belt or the like (or a gear) and sliding a nut 70 along the screw shaft 68 .

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

[0039] The nut 70 of the ball screw 62 is fixed to an intermediate holding member 80, which has a guide bar insertion hole 82 through which the guide bar 66 is inserted. By inserting the guide bar 66 into the guide bar insertion hole 82, the intermediate holding member 80 is guided by the guide bar 66, and the nut 70 can advance and retreat in a predetermined direction (downward in the figure) without wobbling. In addition, because the intermediate holding member 80 is guided by the guide bar 66, the pressurizing piston 64 can advance and retreat in a predetermined direction (downward in the figure) without wobbling.

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

[0041] The pressure applying piston 64 has a tip end inserted into the inside B of the injection cylinder 42 in the hydraulic operating mechanism 32 so as to be able to protrude and retract. When the nut 70 of the ball screw 62 moves downward in the figure, the pressure applying piston 64 enters the inside B and pressurizes the hydraulic oil O filled in the inside B.

[0042] Thus, 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 the intermediate holding member 80, 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 oil O. This eliminates the need to slide the injection piston 40 itself, making it possible to provide a die casting machine 10 that can simplify the entire device and reduce costs.

[0043] Furthermore, by connecting the end of the pressurizing piston 64 in series to the nut 70 of the ball screw 62, the weight that needs to be driven by the ball screw (driving weight) can be made lighter than in a structure in which, for example, a movable plate that presses the pressurizing piston is installed between two ball screws and the pressing force of the ball screw is applied to the pressurizing piston via the movable plate, and the inertial force is reduced, thereby making it possible to avoid overshooting of the pressure of the working oil O caused by the pressurizing piston.

[0044] In this embodiment, the ball screw 62 and the pressure piston 64 are arranged to move in the vertical direction. This allows the dimensions of the electric pressure mechanism 34 and the entire die casting machine 10 in the lateral direction to be reduced, making it possible to provide a die casting machine 10 that can be placed in a relatively narrow space.

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

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

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

[0048] Thereafter, the hydraulic pump 46 is operated to fill the accumulator 54 with hydraulic oil O at a predetermined pressure. At the same time, the injection sleeve 36 is filled with molten metal that has been separately prepared.

[0049] The low-speed injection process is started. The low-speed flow rate control valve 50 in the hydraulic operation mechanism 32 is opened, and hydraulic oil O from the accumulator 54 (and hydraulic pump 46) is supplied to the inside B of the injection cylinder 42, and the injection plunger 38 is moved at a predetermined speed to fill the molten metal into the cavity 28. This low-speed injection process continues for several seconds (1 to 2 seconds).

[0050] Thereafter, the high-speed injection process begins. In addition to the low-speed flow rate control valve 50 in the hydraulic operation mechanism 32, the high-speed flow rate control valve 52 is opened, hydraulic oil O is supplied to the inside B of the injection cylinder 42, and the injection plunger 38 is moved at a predetermined speed to fill the cavity 28 with molten metal. The high-speed injection process lasts for about a few hundredths of a second. When the high-speed injection process is completed, the low-speed flow rate control valve 50 and the high-speed flow rate 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. That is, the operation of the electric servo motor 60 is started prior to the start of the pressure increasing process, and the operation of the nut 70 and the pressurizing piston 64 is started so that the pressurizing piston 64 of the electric pressurizing mechanism 34 is ready to pressurize the hydraulic oil O at the timing when the above-mentioned high-speed injection process is completed.

[0052] This is because immediately after the electric servo motor 60 of the electric pressure mechanism 34 starts operating, the rotational force of the electric servo motor 60 is not sufficiently transmitted to the nut 70 via the screw shaft 68 due to factors such as a slight stretch in the belt between the electric servo motor 60 and the screw shaft 68 of the ball screw 62, backlash between the screw shaft 68 and the nut 70, and inertia due to the driving weight, and it is not until a short time has passed since the electric servo motor 60 started operating that the rotational force is sufficiently transmitted to the nut 70. This time is called the "preparatory operation time."

[0053] If the pressure increase rise time in the pressure increase step is slow, the molten metal filled in the cavity 28 will solidify more rapidly, which may result in a deterioration in the quality of the finished molded product.

[0054] For this reason, if the electric servo motor 60 is started to operate at the timing when the high-speed injection process is completed, it is difficult to sufficiently guarantee the speed at which the hydraulic pressure is increased to a predetermined pressure after the pressure increase process starts (i.e., the rise time of pressure increase), because the speed at which the hydraulic pressure is increased to a predetermined pressure after the pressure increase process starts depends on the acceleration property of the electric servo motor.

[0055] Furthermore, if a large, high-output electric servo motor is installed to speed up the pressure boosting start-up time, this in turn leads to an increase in the cost of the entire die casting machine.

[0056] Furthermore, if one tries to speed up the rise time of the pressure boost by relying on the acceleration characteristics of the electric servo motor, it is necessary to continue accelerating until the hydraulic pressure reaches a specified pressure, at which point the electric servo motor must be suddenly decelerated. This flow from acceleration to sudden deceleration can easily cause the hydraulic pressure to spike and become higher than the specified pressure, resulting in an overshoot.

[0057] In this regard, in the electric pressurizing mechanism 34 according to this embodiment, as described above, the operation of the electric servo motor 60 is started prior to the start of the pressure increase process, and the operation of the nut 70 and the pressure increase piston 64 is started. As a result, the preparatory operation time has elapsed at the time of completion of the high-speed injection process which requires pressure increase, and pressure increase can be started at any speed of the electric servo motor 60.

[0058] This makes it possible to use a relatively small, low-output electric servo motor 60 to sufficiently ensure the speed at which the hydraulic pressure is increased to a specified pressure after entering the pressure increase process, and also reduces the possibility of the pressure of the hydraulic oil O overshooting, since the electric servo motor 60 can be decelerated from a non-accelerating state.

[0059] In addition, since the timing at which the electric servo motor 60 starts operating prior to the start of the pressure boosting step depends on the preparatory operation time, the start timing may be during the low-speed injection step or during the high-speed injection step. Of course, when the electric servo motor 60 starts operating, the amount of hydraulic oil O flowing into the injection cylinder 42 through the low-speed side flow rate control valve 50 and the high-speed side flow rate control valve 52 is reduced by the amount of movement of the pressurizing piston 64.

[0060] (Variation 1) In the die casting machine 10 according to the embodiment described above, an example of so-called "in-throttling" for adjusting the flow rate of the hydraulic oil O flowing into the IN side B of the injection cylinder 42 in the low-speed injection process and the high-speed injection process has been shown, but instead of this, so-called "out-throttling" for adjusting the flow rate of the hydraulic oil O flowing out from the OUT side A of the injection cylinder 42 may be used. In the case of this "out-throttling", the low-speed side flow rate control valve 50 and the high-speed side flow rate control valve 52 are attached to the oil piping 44 connected to the OUT side A of the injection cylinder 42.

[0061] (Variation 2) Furthermore, in the die casting machine 10 according to the embodiment described above, the pressure applying piston 64 is connected in series to the nut 70 constituting the ball screw 62 in the electric pressure applying mechanism 34, and the nut 70 and the pressure applying piston 64 are moved up and down by rotating the screw shaft 68 with the electric servo motor 60. Alternatively, the pressure applying piston 64 may be connected in series to the screw shaft 68, and the screw shaft 68 and the pressure applying piston 64 may be moved up and down by rotating the nut 70 with the electric servo motor 60.

[0062] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the scope and meaning equivalent to the claims. [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 operation mechanism, 34...Electric pressure mechanism, 36...Injection sleeve, 38...Injection plunger, 40...Injection piston, 42...Injection cylinder, 43...Water supply port, 44...Oil piping, 46...Hydraulic pump, 48...Control valve, 48a...First control valve, 48b...Second control valve, 50...Low speed side flow rate control valve, 52...High-speed side 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...Threaded shaft, 70...Nut, 72...Servomotor mount, 74...Threaded shaft bearing, 76...Guide bar first holding portion, 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 oil; A: outer side of the injection piston 40; B: inner side of the injection piston 40

Claims

1. A die casting machine having an injection mechanism, a hydraulic operation mechanism, and an electric pressure mechanism, The injection mechanism has an injection plunger that injects molten metal into the cavity, the hydraulic operation mechanism includes an injection cylinder that houses the injection plunger, a hydraulic pump, an accumulator, a low-speed flow rate control valve, a high-speed flow rate control valve, and a control means; the electric pressure mechanism includes an electric servo motor, a ball screw driven by the electric servo motor, and a pressure piston pushed out by the ball screw, The control means performs a low-speed injection process in which the injection plunger is operated using a low-speed flow rate control valve, a subsequent high-speed injection process in which the injection plunger is operated using a high-speed flow rate control valve, and a subsequent pressure increasing process in which the pressure of the hydraulic oil in the injection cylinder is increased by the pressure increasing piston, and operates the electric servo motor before the completion of the high-speed injection process so that the preparation operation time of the electric pressure mechanism is completed at the completion of the high-speed injection process. Die casting machine.

2. An injection molding method using a die casting machine having an injection mechanism, a hydraulic operation mechanism, and an electric pressure mechanism, The injection mechanism has an injection plunger that injects molten metal into the cavity, the hydraulic operation mechanism includes an injection cylinder that houses the injection plunger, a hydraulic pump, an accumulator, a low-speed flow rate control valve, a high-speed flow rate control valve, and a control means; the electric pressure mechanism includes an electric servo motor, a ball screw driven by the electric servo motor, and a pressure piston pushed out by the ball screw, a low-speed injection step of operating the injection plunger using a low-speed flow rate control valve; a subsequent high-speed injection step of operating the injection plunger using a high-speed side flow rate control valve; and a pressure increasing step of increasing the pressure of the hydraulic oil in the injection cylinder by the pressure increasing piston. and a step of operating the electric servo motor by the control means before the completion of the high-speed injection step so that a preparatory operation time of the electric pressure mechanism is completed at the time when the high-speed injection step is completed. Injection molding method.

Images