JP7546465B2 - Die Casting Machine - Google Patents

Description

The present invention relates to a die casting machine that injects molten metal into a die to form a molded product.

Conventionally, there has been known a die casting machine that includes a plunger disposed in a sleeve that communicates with the cavity of the die, and a hydraulic cylinder that moves the plunger back and forth within the sleeve (see, for example, Patent Document 1).

There are also die casting machines that use a servo valve, such as that described in Patent Document 2, placed in the return oil path from the rod chamber of the hydraulic cylinder to the hydraulic oil tank to control the forward speed of the plunger.

JP 2019-155378 A Japanese Unexamined Patent Publication No. 53-6775

A servo valve with the above configuration is susceptible to the influence of foreign matter (so-called contamination) such as metal powder contained in the hydraulic oil. If the spool of the servo valve is damaged by contamination, there is a problem in that the forward speed of the plunger cannot be properly controlled.

In addition, to increase the size of die casting machines (to increase the amount of molten metal that can be injected at one time), the flow rate of hydraulic oil flowing through the return flow path must be increased, which inevitably leads to a larger servo valve. However, large servo valves are very expensive, which is one of the factors that prevents die casting machines from being made larger.

The present invention was made in consideration of the above circumstances, and its purpose is to provide a technology that reduces downtime caused by servo valve malfunctions and enables large-scale production at low cost in die casting machines that use servo valves to control the forward speed of the plunger.

In order to achieve the above object, the present invention provides a die casting machine comprising: a sleeve communicating with a cavity formed in a die; a plunger that advances within the sleeve toward the cavity to supply molten metal within the sleeve to the cavity; a hydraulic cylinder that advances the plunger by supplying hydraulic oil to a head chamber and retracts the plunger by supplying hydraulic oil to a rod chamber; a hydraulic circuit that supplies and discharges hydraulic oil to the head chamber and the rod chamber ; an input unit that receives an input of a forward movement speed of the plunger; and a control device that controls the hydraulic circuit, wherein the hydraulic circuit comprises a hydraulic oil tank that stores hydraulic oil, an accumulator that supplies pre-pressurized hydraulic oil to the head chamber through a head-side supply flow path, and a hydraulic cylinder that supplies hydraulic oil from the rod chamber to the head chamber through a head-side supply flow path. The control device is characterized in that it comprises a first servo valve arranged in a return flow path from the hydraulic oil tank to the hydraulic oil tank and capable of adjusting its opening between an allowable position where the return flow path is opened to allow the plunger to advance and a braking position where the return flow path is blocked to brake the advancement of the plunger, and a second servo valve arranged in parallel to the first servo valve in the return flow path and capable of adjusting its opening between the allowable position and the braking position, and when the forward speed input to the input unit is faster than a threshold speed, the control device uses both the first servo valve and the second servo valve to control the forward speed of the plunger, and when the forward speed input to the input unit is equal to or lower than the threshold speed, the control device uses one of the first servo valve and the second servo valve to control the forward speed of the plunger .

This invention reduces downtime caused by servo valve malfunctions and enables larger die casting machines at low cost.

FIG. 2 is a side view of the die casting machine according to the embodiment. FIG. 2 is a circuit diagram of a hydraulic circuit. FIG. 2 is a hardware configuration diagram of a die casting machine. 13 is a flowchart of a forward speed setting process. 4 is a flowchart of an injection control process. 4 is a flowchart of a forward speed control process.

Figure 1 is a side view of a die-casting machine 10 according to this embodiment. The die-casting machine 10 injects molten metal into a die to produce a molded product. As shown in Figure 1, the die-casting machine 10 mainly comprises a clamping device 20 and an injection device 30.

The clamping device 20 opens, closes, and clamps the mold 21. Specifically, the clamping device 20 mainly comprises a fixed die plate 23 that supports the fixed side mold 22, and a movable die plate 25 that supports the movable side mold 24. The fixed side mold 22 and the movable side mold 24 are supported so as to face each other in the left-right direction (horizontal direction) of the die casting machine 10.

The movable die plate 25 moves left and right along the tie bars 28 as the driving force of the die opening/closing cylinder 26 is transmitted through the toggle link mechanism 27. When the movable die plate 25 moves leftward, the fixed die 22 and the movable die 24 move apart (mold opening). On the other hand, when the movable die plate 25 moves rightward, the fixed die 22 and the movable die 24 come into contact (mold closing). When further pressure is applied in a direction that moves the movable die plate 25 rightward, the fixed die 22 and the movable die 24 are clamped.

The injection device 30 injects molten metal into the clamped mold 21. The injection device 30 mainly comprises an injection sleeve 31, a plunger 32, a hydraulic cylinder 33, and a hydraulic circuit 40. The injection device 30 according to this embodiment is disposed horizontally apart from the clamping device 20 (to the right of the clamping device 20).

The injection sleeve 31 is a cylindrical member attached to the fixed die plate 23. The tip of the injection sleeve 31 is connected to the internal space (hereinafter referred to as the "cavity") of the clamped die 21. The injection sleeve 31 also stores molten metal supplied by a ladle (not shown).

The plunger 32 is housed in the injection sleeve 31 so that it can move forward and backward. When the plunger 32 moves forward, the molten metal stored in the injection sleeve 31 is supplied to the cavity. On the other hand, when the plunger 32 moves backward, a space is formed in the injection sleeve 31 to store the molten metal supplied from the ladle.

The hydraulic cylinder 33 advances and retreats the plunger 32 by expanding and contracting as hydraulic oil is supplied and discharged (hereinafter referred to as "supply and discharge"). The hydraulic oil is supplied and discharged to and from the hydraulic cylinder 33 by a hydraulic circuit 40. As shown in FIG. 2, the hydraulic cylinder 33 is composed of a cylinder tube 34, a piston 35, and a rod 36.

The piston 35 is configured to be movable within the cylinder tube 34. The piston 35 also divides the interior of the cylinder tube 34 into a head chamber 37 and a rod chamber 38. The rod 36 has a base end connected to the piston 35, protrudes outside the cylinder tube 34, and has a tip connected to the plunger 32.

When hydraulic oil is supplied to the head chamber 37 and hydraulic oil is discharged from the rod chamber 38, the piston 35 moves toward the rod chamber 38 and the rod 36 extends. This causes the plunger 32 to move forward within the injection sleeve 31. On the other hand, when hydraulic oil is supplied to the rod chamber 38 and hydraulic oil is discharged from the head chamber 37, the piston 35 moves toward the head chamber 37 and the rod 36 contracts. This causes the plunger 32 to move backward within the injection sleeve 31.

As shown in FIG. 2, the position of the rod 36 is detected by a position sensor 39. The position sensor 39 detects the position of the rod 36 and outputs a position signal indicating the detection result to a control device 60, which will be described later. The position sensor 39 is, for example, a linear encoder.

Figure 2 is a circuit diagram of the hydraulic circuit 40. As shown in Figure 2, the hydraulic circuit 40 mainly includes a hydraulic oil tank 41, a motor 42, a hydraulic pump 43, an accumulator 44, a charge valve 45, a forward control valve 46, a check valve 47, a filter 48, a reverse control valve 49, a first servo valve 50, and a second servo valve 51. Hereinafter, the first servo valve 50 and the second servo valve 51 may be collectively referred to as "servo valves 50, 51."

The hydraulic pump 43 and the accumulator 44 are connected by a charge flow path _L1 . The accumulator 44 and the head chamber 37 of the hydraulic cylinder 33 are connected by a head side supply flow path _L2 branching off from the charge flow path _L1 . The hydraulic pump 43 and the rod chamber 38 of the hydraulic cylinder 33 are connected by a rod side supply flow path _L3 branching off from the charge flow path _L1 . The rod chamber 38 of the hydraulic cylinder 33 and the servo valves 50, 51 are connected by a return flow path _L4 branching off from the rod side supply flow path _L3 .

The hydraulic oil tank 41 stores hydraulic oil. The motor 42 generates a driving force for driving the hydraulic pump 43. The driving force of the motor 42 is transmitted to the hydraulic pump 43, which pumps the hydraulic oil stored in the hydraulic oil tank 41 to the charge flow path _L1 .

The accumulator 44 stores (accumulates pressure) the hydraulic oil in a compressed state and supplies the compressed hydraulic oil to the head chamber 37 of the hydraulic cylinder 33. More specifically, the accumulator 44 accumulates pressure in the hydraulic oil supplied from the hydraulic pump 43 through a charge flow path _L1 . In addition, the hydraulic oil discharged from the accumulator 44 is supplied to the head chamber 37 through a head-side supply flow path _L2 .

The charge valve 45 is disposed in the charge flow passage _L1 . More specifically, the charge valve 45 is disposed on the hydraulic pump 43 side of the branching position of the charge flow passage _L1 with the head side supply flow passage _L2 and on the accumulator 44 side of the branching position of the charge flow passage L1 with the rod side supply flow passage _L3 . The charge valve 45 is configured to be switchable between a non-charge position A and a charge position B.

The non-charge position A is a position that blocks the charge flow path _L1 and makes it impossible for the hydraulic oil supplied from the hydraulic pump 43 to be charged to the accumulator 44. The charge position B is a position that opens the charge flow path _L1 and makes it possible for the hydraulic oil supplied from the hydraulic pump 43 to be charged (accumulated) in the accumulator 44.

The initial position of the charge valve 45 is the non-charge position A. The charge valve 45 is switched from the non-charge position A to the charge position B by the application of a control voltage from the control device 60. The charge valve 45 is again switched from the charge position B to the non-charge position A by the application of the control voltage from the control device 60 ceasing.

The forward control valve 46 is disposed in the head-side supply flow passage _L2 . The forward control valve 46 is configured to be switchable between a return position C and a supply position D. The return position C is a position that blocks communication between the accumulator 44 and the head chamber 37 and causes the hydraulic oil in the head chamber 37 to flow back to the hydraulic oil tank 41. The supply position D is a position that supplies the hydraulic oil stored in the accumulator 44 to the head chamber 37 and blocks communication between the head chamber 37 and the hydraulic oil tank 41.

The initial position of the forward control valve 46 is the return position C. In addition, the forward control valve 46 is switched from the return position C to the supply position D by the application of a control voltage from the control device 60. In addition, the forward control valve 46 is switched again from the supply position D to the return position C by stopping the application of the control voltage from the control device 60.

The check valve 47 is disposed in the rod side supply flow path _L3 . More specifically, the check valve 47 is disposed on the hydraulic pump 43 side of the branch position of the rod side supply flow path _L3 with the return flow path _L4 . The check valve 47 allows the flow of hydraulic oil from the hydraulic pump 43 to the rod chamber 38 and blocks the flow of hydraulic oil from the rod chamber 38 to the hydraulic pump 43.

The filter 48 is disposed in the rod-side supply flow passage _L3 . More specifically, the filter 48 is disposed closer to the hydraulic pump 43 than the check valve 47 and closer to the rod chamber 38 than the retreat control valve 49. The filter 48 removes foreign matter (e.g., metal powder) contained in the hydraulic oil as the hydraulic oil supplied from the hydraulic pump 43 passes through it. The filter 48 is also configured to be removable (replaceable).

The reverse control valve 49 is disposed in the rod side supply flow passage _L3 . More specifically, the reverse control valve 49 is disposed on the hydraulic pump 43 side of the check valve 47 (more specifically, the filter 48) in the rod side supply flow passage _L3 . The reverse control valve 49 is configured to be switchable between a closed position E and an open position F.

The closed position E is a position where the rod side supply passage _L3 is closed to stop the supply of hydraulic oil from the hydraulic pump 43 to the rod chamber 38. The open position F is a position where the rod side supply passage _L3 is opened to supply hydraulic oil from the hydraulic pump 43 to the rod chamber 38.

The initial position of the reverse control valve 49 is the closed position E. The reverse control valve 49 is switched from the closed position E to the open position F by the application of a control voltage from the control device 60. The reverse control valve 49 is again switched from the open position F to the closed position E by stopping the application of the control voltage from the control device 60.

The servo valves 50 and 51 are arranged in parallel in the return flow path _L4 . The return flow path _L4 from the rod chamber 38 to the hydraulic oil tank 41 has a route that passes through the first servo valve 50 and a route that passes through the second servo valve 51. The servo valves 50 and 51 are proportional valves that can adjust the spool opening (opening) between a braking position G, a loop position H, and an allowable position I, which will be described later, according to the control of the control device 60. It is desirable that the servo valves 50 and 51 have the same flow characteristics. Since the servo valves 50 and 51 have a common configuration, the first servo valve 50 will be described in detail below.

The first servo valve 50 has a pair of pilot ports 50a, 50b. In the first servo valve 50, pilot pressure oil is supplied from an accumulator (not shown) to one of the pair of pilot ports 50a, 50b, so that the spool moves between the braking position G, the loop position H, and the allowable position I. In addition, a filter 53 is disposed in the flow path from the accumulator to the pilot ports 50a, 50b.

The braking position G is a position where the return flow path _L4 is blocked to prevent the hydraulic oil in the rod chamber 38 from returning to the hydraulic oil tank 41 (in other words, the forward movement of the plunger 32 is braked). The loop position H is a position where the rod chamber 38 side of the return flow path _L4 and the hydraulic oil tank 41 side of the return flow path _L4 form independent loop flow paths. The allowing position I is a position where the return flow path _L4 is opened to allow the hydraulic oil in the rod chamber 38 to return to the hydraulic oil tank 41 (in other words, the forward movement of the plunger 32 is allowed).

The initial position of the first servo valve 50 is the braking position G. In addition, the servo amplifier (not shown) adjusts the spool opening from the braking position G toward the loop position H or the allowable position I by controlling the amount of pilot pressure oil supplied to the pilot ports 50a, 50b according to the command value of the forward speed of the plunger 32 output from the control device 60. Furthermore, the servo amplifier detects the actual forward speed of the plunger 32 (hereinafter referred to as the "actual value") and adjusts the spool opening so that the actual value approaches the command value.

The first servo valve 50 is also provided with a failure detection sensor 50c. The failure detection sensor 50c detects a failure in the first servo valve 50 and outputs a failure signal indicating the detection result to the control device 60. The specific configuration of the failure detection sensor 50c is not particularly limited, but the following configuration is possible, for example.

As an example, the failure detection sensor 50c may be a pressure sensor that detects the hydraulic pressure (primary pressure) upstream of the first servo valve 50 and the hydraulic pressure (secondary pressure) downstream of the first servo valve 50, and outputs a pressure signal (failure signal) indicating the detected pressure to the control device 60. The control device 60 then determines whether the first servo valve 50 has failed based on the relationship between the command value output to the servo amplifier and the pressure difference between the primary pressure and the secondary pressure.

As another example, the failure detection sensor 50c may be a position sensor that detects the position of the spool of the first servo valve 50 and outputs a position signal (failure signal) indicating the detected position to the control device 60. The control device 60 then determines whether the first servo valve 50 has failed based on the relationship between the command value output to the servo amplifier and the position of the spool.

Figure 3 is a hardware configuration diagram of the die casting machine 10. The die casting machine 10 includes a control device 60. The control device 60 includes, for example, a CPU (Central Processing Unit) 61, which is a calculation means, a ROM (Read Only Memory) 62 that stores various programs, and a RAM (Random Access Memory) 63, which is a working area for the calculation means. The CPU 61 may then read and execute the programs stored in the ROM 62 to realize the various processes described below.

However, the specific configuration of the control device 60 is not limited to this, and may be realized by hardware such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array).

The control device 60 controls the operation of the entire die casting machine 10. More specifically, the control device 60 acquires a position signal output from the position sensor 39 and a fault signal output from the fault detection sensors 50c, 51c. The control device 60 also displays information on the display input device 64 functioning as a display unit, and accepts information input through the display input device 64 functioning as an input unit. The control device 60 also applies and stops applying control voltages to the charge valve 45, the forward control valve 46, and the reverse control valve 49. Furthermore, the control device 60 controls the forward speed of the plunger 32 by outputting command values to the servo amplifiers of the servo valves 50, 51 (so-called ALL-OUT control).

More specifically, the control device 60 switches the forward control valve 46 from the return position C to the supply position D, thereby supplying hydraulic oil at a predetermined pressure (flow rate) from the accumulator 44 to the head chamber 37 through the head side supply flow path _L2 . In addition, the control device 60 adjusts the flow rate of hydraulic oil returning from the rod chamber 38 to the hydraulic oil tank 41 through the return flow path _L4 by adjusting the spool openings of the servo valves 50 and 51.

That is, the control device 60 accelerates the plunger 32 by increasing the spool opening of the servo valves 50 and 51. On the other hand, the control device 60 decelerates (brakes) the plunger 32 by decreasing the spool opening of the servo valves 50 and 51. Also, the smaller the spool opening of the servo valves 51 and 51, the greater the deceleration (braking force) of the plunger 32.

The display input device 64 is a user interface that includes a display that displays various information to be notified to the operator, and buttons, switches, dials, etc. that accept operations by the operator. The display input device 64 may also include a touch panel superimposed on the display. The display input device 64 accepts input operations by the operator and outputs an input signal corresponding to the accepted input operation to the control device 60.

Next, the forward speed setting process will be described with reference to FIG. 4. FIG. 4 is a flowchart of the forward speed setting process. The forward speed setting process is a process in which the operator sets the forward speed V of the plunger 32. The control device 60 starts the forward speed setting process, for example, in response to an instruction from the operator via the display input device 64.

First, the control device 60 judges whether the servo valves 50, 51 are faulty or not based on the fault signals output from the fault detection sensors 50c, 51c (S11). Then, when the control device 60 judges that at least one of the servo valves 50, 51 is not faulty, it prompts the operator to input the forward speed V of the plunger 32 through the display input device 64. On the other hand, although not shown, when the control device 60 judges that both the servo valves 50, 51 are faulty, it prompts the operator to perform maintenance of the die casting machine 10 through the display input device 64 and ends the forward speed setting process without executing the processes from step S12 onwards.

More specifically, when the control device 60 determines that neither of the servo valves 50, 51 is faulty (S11: No), it inputs a forward speed V within the range of a lower limit speed (MIN) and an upper limit speed (MAX) (S12). On the other hand, when the control device 60 determines that one of the servo valves 50, 51 is faulty and the other is not faulty (S11: Yes), it inputs a forward speed V within a predetermined range of a lower limit speed (MIN) and a threshold speed ( _Vth ) (S13).

The lower limit speed is a predetermined lower limit value of the forward speed of the plunger 32, and is a speed slower than the upper limit speed and the threshold speed. The lower limit speed is a value that can be achieved using only one of the servo valves 50, 51.

The upper speed limit is a predetermined upper limit value of the forward speed of the plunger 32, and is a speed higher than the lower speed limit and the threshold speed. The upper speed limit cannot be achieved by using only one of the servo valves 50 and 51, but is a value that can be achieved by using both servo valves 50 and 51. The upper speed limit is achieved, for example, by setting the spool opening of both servo valves 50 and 51 to maximum (position I).

The threshold speed is a predetermined speed between the lower limit speed and the upper limit speed. The threshold speed is a value that can be achieved by using only one of the servo valves 50, 51. The threshold speed is achieved, for example, by setting the spool opening of one of the servo valves 50, 51 to the maximum (position I) and the spool opening of the other of the servo valves 50, 51 to the minimum (position G). The threshold speed in this case is half the upper limit speed.

The control device 60 waits to execute the processing from step S15 onwards until the operator inputs the forward speed V through the display input device 64 (S14: No). Then, when the operator inputs the forward speed V through the display input device 64 (S14: Yes), the control device 60 stores the input forward speed V in the RAM 63 (S15) and ends the forward speed setting process.

Next, the injection control process will be described with reference to Fig. 5. Fig. 5 is a flowchart of the injection control process. The injection control process is a process for continuously molding a plurality of molded products. At the start of the injection control process, it is assumed that the mold 21 is clamped, molten metal is stored in the injection sleeve 31, and hydraulic oil at a predetermined pressure is stored in the accumulator 44. The number of molded products molded in the injection control process is represented by the molding number _Mth , and the variable for holding the current molding number of molded products is represented by M.

First, the control device 60 initializes the variable M (=1). Next, the control device 60 sets the charge valve 45 to the non-charge position A, the forward control valve 46 to the supply position D, the reverse control valve 49 to the closed position E, and adjusts the spool opening of the servo valve 50 according to FIG. 6 (S21, injection forward). FIG. 6 is a flowchart of the forward speed control process.

The control device 60 compares the forward speed V set in the forward speed setting process with the threshold speed _Vth (S31). If the forward speed V is faster than the threshold speed _Vth (S31: Yes), the control device 60 adjusts the spool openings of both servo valves 50, 51 in accordance with the forward speed V (S32). That is, the higher the forward speed V, the larger the spool openings of both servo valves 50, 51.

Furthermore, when the forward speed V is equal to or lower than the threshold speed _Vth (S31: No), the control device 60 determines whether or not one of the servo valves 50, 51 is malfunctioning (S33). When the control device 60 determines that one of the servo valves 50, 51 is malfunctioning (S33: Yes), it adjusts the spool opening of the other of the servo valves 50, 51 in accordance with the forward speed V, and maintains one of the servo valves 50, 51 (i.e., the malfunctioning servo valve) in the braking position G (S34).

Furthermore, when the control device 60 determines that neither of the servo valves 50, 51 is faulty (S33: No), it determines whether the variable M is an odd number (S35). When the variable M is an odd number (S35: Yes), the control device 60 adjusts the spool opening of the first servo valve 50 according to the forward speed V and maintains the second servo valve 51 in the braking position G (S36). On the other hand, when the variable M is an even number (S35: No), the control device 60 adjusts the spool opening of the second servo valve 51 according to the forward speed V and maintains the first servo valve 50 in the braking position G (S37).

As a result, hydraulic oil is supplied from the accumulator 44 to the head chamber 37 through the head side supply flow passage _L2 , and the hydraulic oil is discharged from the rod chamber 38 to the hydraulic oil tank 41 through the return flow passage _L4 . As a result, the plunger 32 advances at the forward movement speed V set in the forward movement speed setting process, and the molten metal in the injection sleeve 31 is injected into the cavity.

Next, the control device 60 maintains the state of step S21 until the plunger 32 reaches a predetermined forward position (S22: No) based on the position signal output from the position sensor 39. Then, after the plunger 32 reaches the forward position (S22: Yes), the control device 60 causes the clamping device 20 to open the mold 21 and causes the robot arm (not shown) to remove the molded product held by the movable mold 24.

In addition, in conjunction with the mold opening operation by the mold clamping device 20, the control device 60 sets one of the servo valves 50, 51 to the braking position G and adjusts the other of the servo valves 50, 51 to a spool opening corresponding to a predetermined ejection speed (S23, ejection). The states of the other valves 45, 46, 49 are the same as in step S21. As a result, the plunger 32 decelerates (brakes) from the forward speed to the ejection speed, and is pressed against the biscuit at a low speed, ejecting the biscuit from the fixed mold 22 in conjunction with the mold opening operation.

Note that the biscuit refers to the solidified metal remaining in the space (sprue) between the injection sleeve 31 and the cavity in the opened fixed mold 21. The ejection speed is sufficiently slower than the forward speed. In step S23, which of the servo valves 50 and 51 is set to the braking position G may be the same as in steps S35 to S37 in FIG. 6, for example. Furthermore, during the processing of step S23, hydraulic oil may be supplied from the hydraulic pump 43 through a flow path (not shown) instead of being supplied from the accumulator 44.

Next, the control device 60 maintains the state of step S23 from the execution of step S23 until the biscuit is pushed out (S24: No). Then, at the timing when the biscuit is pushed out (S24: Yes), the control device 60 sets the charge valve 45 to the non-charge position A, the forward control valve 46 to the return position C, the reverse control valve 49 to the open position F, and the servo valves 50, 51 to the brake position G (S25, injection reverse). As a result, hydraulic oil is supplied from the hydraulic pump 43 to the rod chamber 38 through the rod side supply flow path _L3 , and hydraulic oil is discharged from the head chamber 37 to the hydraulic oil tank 41 through the forward control valve 46.

Next, the control device 60 maintains the state of step S25 based on the position signal output from the position sensor 39 until the plunger 32 reaches a predetermined retracted position (S26: No). Then, when the plunger 32 reaches the retracted position (S26: Yes), the control device 60 sets the charge valve 45 to the non-charged position A, the forward control valve 46 to the reflux position C, the retract control valve 49 to the blocked position E, and the servo valves 50 and 51 to the braked position G (S27, injection operation completed). This stops the plunger 32 in the retracted position.

Although not shown, the control device 60 stores molten metal in the injection sleeve 31 in parallel with the processing of steps S25 to S27. Although not shown, the control device 60 switches the charge valve 45 to the charge position B when the pressure of the hydraulic oil in the accumulator 44 falls below a lower limit. This causes hydraulic oil to be supplied from the hydraulic pump 43 to the accumulator 44 through the charge flow path _L1 . The control device 60 then switches the charge valve 45 to the non-charge position A when the pressure of the hydraulic oil in the accumulator 44 reaches an upper limit. The process of charging the hydraulic oil to the accumulator 44 is performed in parallel with, for example, opening the mold, removing the molded product, and replenishing the molten metal.

Next, the control device 60 compares the variable M with the molding number _Mth (S28). If the control device 60 determines that the variable M has not reached the molding number _Mth (S28: No), it adds 1 to the variable M (S29) and executes the injection process of steps S21 to S27 again. On the other hand, if the control device 60 determines that the variable M has reached the molding number _Mth (S28: Yes), it ends the injection control process.

That is, the control device 60 repeats the injection process of steps S21 to S29 until the molding number _Mth of molded products is molded. When the forward speed V is equal to or lower than the threshold speed _Vth and neither of the servo valves 50, 51 is broken, the control device 60 controls the forward speed V of the plunger 32 by alternately using the servo valves 50, 51 in step S21 (S35 to S37 in FIG. 6), which is repeatedly executed.

The above embodiment provides the following advantages:

According to the above embodiment, since the servo valves 50, 51 are arranged in parallel in the return flow path _L4 , even if one of the servo valves 50, 51 fails, the ALL-OUT control can be continued by the other servo valve 50, 51. In addition, by performing the ALL-OUT control using both of the servo valves 50, 51, the amount of molten metal that can be injected at one time by the small servo valves 50, 51 can be increased. In other words, downtime due to malfunctions of the servo valves 50, 51 can be reduced, and the die casting machine 10 can be enlarged at low cost.

Furthermore, according to the above embodiment, when the forward speed V is equal to or lower than the threshold speed _Vth , the servo valves 50, 51 are alternately used to control the forward speed V of the plunger 32, thereby preventing the spool from sticking due to not using the servo valves 50, 51 for a long period of time. Note that, in the above embodiment, an example in which the servo valves 50, 51 are alternately used once each has been described, but they may be alternately used N times each (N is an integer equal to or greater than 1).

Furthermore, according to the above embodiment, if one of the servo valves 50, 51 fails, the forward speed V that can be set in the forward speed setting process is limited to a range between the lower limit speed (MIN) and the threshold speed (Vth), and ALL-OUT control is performed using the other of the servo valves 50, 51. This allows injection molding to continue within the limited performance range.

The above-described embodiments are illustrative examples of the present invention, and are not intended to limit the scope of the present invention to these embodiments. Those skilled in the art can implement the present invention in various other forms without departing from the spirit of the present invention.

10...die casting machine, 20...mold clamping device, 21...mold, 22...fixed side mold, 23...fixed die plate, 24...movable side mold, 25...movable die plate, 26...mold opening and closing cylinder, 27...toggle link mechanism, 28...tie bar, 30...injection device, 31...injection sleeve, 32...plunger, 33...hydraulic cylinder, 34...cylinder tube, 35...piston, 36...rod, 37...head chamber, 38...rod chamber, 39...position Sensor, 40...hydraulic circuit, 41...hydraulic oil tank, 42...motor, 43...hydraulic pump, 44...accumulator, 45...charge valve, 46...forward control valve, 47...check valve, 48...filter, 49...reverse control valve, 50, 51...servo valve, 50a, 50b, 51a, 51b...pilot port, 50c, 51c...failure detection sensor, 60...control device, 61...CPU, 62...ROM, 64...alarm device

Claims (3)

a sleeve communicating with a cavity formed in a mold;
a plunger that advances within the sleeve toward the cavity to supply molten metal within the sleeve to the cavity;
a hydraulic cylinder that advances the plunger by supplying hydraulic oil to a head chamber and retracts the plunger by supplying hydraulic oil to a rod chamber;
a hydraulic circuit that supplies and discharges hydraulic oil to the head chamber and the rod chamber ;
An input unit that receives an input of an advance speed of the plunger;
A control device for controlling the hydraulic circuit ,
The hydraulic circuit includes:
A hydraulic oil tank for storing hydraulic oil;
an accumulator that supplies hydraulic oil that has been previously stored under pressure to the head chamber through a head-side supply passage;
a first servo valve arranged in a return flow passage leading from the rod chamber to the hydraulic oil tank, the first servo valve being capable of adjusting an opening between an allowance position where the return flow passage is opened to allow the plunger to advance and a braking position where the return flow passage is blocked to brake the advancement of the plunger;
a second servo valve arranged in parallel with the first servo valve in the return flow path and capable of adjusting an opening degree between the permitting position and the braking position ;
The control device includes:
when the advancement speed input to the input section is greater than a threshold speed, using both the first servo valve and the second servo valve to control the advancement speed of the plunger;
A die casting machine characterized in that, when the forward speed input to the input section is equal to or lower than the threshold speed, one of the first servo valve and the second servo valve is used to control the forward speed of the plunger . The die casting machine of claim 1, characterized in that when the plunger is repeatedly advanced at an advancement speed equal to or lower than the threshold speed, the control device controls the advancement speed of the plunger by alternately using the first servo valve and the second servo valve N times (N is an integer greater than or equal to 1 ). a sensor for detecting a failure of the first servo valve and the second servo valve;
The die casting machine of claim 1 or 2, characterized in that when a failure of one of the first servo valve and the second servo valve is detected by the sensor, the control device limits the forward speed that can be input to the input section to less than the threshold speed, and uses the other of the first servo valve and the second servo valve to control the forward speed of the plunger.

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