Die casting machine, control device and program for die casting machine, and casting method

Abstract

To realize the dissolution of a delay till pressure increase is started from the completion of filling and the waveforms of velocities and pressures corresponding to casting conditions.SOLUTION: A die cast machine control device 30 can set a precedent switching position Pp going back a delay displacement as the displacement of a plunger 12 corresponding to a delay time Td from a pressure increase switching position Pvp, based on the pressure increase switching position Pvp equivalent to a position of switching from an injection pattern and injection filling to pressure increase for increasing the pressure of molten metal and the delay time Td required for switching from the completion of the filling to the start of the pressure increase. When a length from the pressure increase switching position Pvp to a velocity switching position Pn immediately before the pressure increase switching position Pvp is shorter than delay displacement, the control device 30 sets the precedent switching position Pp going back above one or more velocity switching positions Pn from the pressure increase position Pvp, and outputs a command of starting the pressure increase at the precedent switching position Pp in an injection stroke.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a die casting machine, a control device and a program used for setting and controlling an injection device of the die casting machine, and a casting method. [Background technology]

[0002] Casting using a die-casting machine involves an injection filling process in which the plunger of the injection device is advanced to push out the molten metal in the sleeve and fill the cavity, and a pressure boosting process in which the plunger presses against the molten metal that has filled the entire cavity, increasing the molten metal pressure (casting pressure) and applying a specified pressure to the molten metal. The plunger is driven by an injection cylinder (hydraulic cylinder) connected to a plunger rod.

[0003] Patent Document 1 describes a hydraulic circuit including a hydraulic cylinder, an accumulator, and multiple valves. By flowing hydraulic oil from the accumulator into the head side of the injection cylinder, the plunger advances using the hydraulic pressure as a driving force, and the molten metal is injected. After that, when a valve included in the hydraulic circuit is operated to switch from the injection filling system to the boosting system, a specified pressure is applied to the molten metal via the plunger due to the flow of hydraulic oil from the boosting system into the injection cylinder, so that the space caused by the entrapment of gas in the molten metal is collapsed, and the molten metal is replenished in the cavity to compensate for the shrinkage caused by the solidification of the molten metal.

[0004] The control device for the injection device described in Patent Document 2 has a filling pressure increase completion time T T , which corresponds to the time from when gate resistance occurs in the injection cylinder to when the casting pressure reaches a set pressure, in order to manage the time lag from the completion of filling to the start of pressure increase (pressure increase start). C Based on the measurement result, the filling pressure increase completion time T C The operation of the injection cylinder is controlled so that the target value is reached. Specifically, the filling time from when gate resistance occurs in the injection cylinder to when filling is completed and surge pressure occurs in the injection cylinder, the time lag from when surge pressure occurs in the injection cylinder to when the casting pressure starts to rise, and the pressure rise time from when the casting pressure starts to rise to when the casting pressure reaches the set pressure are measured. Based on the results of these measurements, the filling pressure rise completion time T C The control device corrects the control parameters related to the plunger speed and the valve opening of the hydraulic circuit so that Vv becomes the target value, and the filling time and pressure rise time are corrected accordingly.

[0005] In other words, Patent Document 2 specifies the time T C Through this management, we aim to centralize management while also including time lags that may result in values ​​greater than expected. According to Patent Document 2, when a surge pressure is detected in the injection cylinder or the plunger reaches a predetermined position, and thus a condition for starting boost is met, measurement of the filling time is terminated and measurement of the time lag is started, and the boost operation is started by issuing a command to start boosting to the valve in the hydraulic circuit. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6582834 [Patent Document 2] JP 2007-245231 A Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 2, a time lag is permitted between the time when the control device issues a command to start increasing the pressure to the valve of the hydraulic circuit as a result of surge pressure occurring in the injection cylinder due to completion of filling of the cavity, and the time when the plunger is pushed by the hydraulic pressure and the casting pressure starts to increase, i.e., a delay in starting the pressure increase. Such a time lag inevitably occurs due to the time required for signal transmission, control processing, valve operation, and hydraulic oil movement. However, in order to start increasing the pressure immediately after filling is completed and to propagate the pressure sufficiently throughout the entire cavity before the molten metal solidifies, and thereby to obtain a quality product, it is desirable to eliminate any delay in starting the pressure increase as much as possible.

[0008] In order to eliminate the delay in starting the boost process, the position of the plunger is detected and the boost process is started when the plunger reaches a position that is a time lag prior to the completion of filling. However, since the advance switch position is set based on the plunger speed corresponding to the plunger position, the advance switch position is not necessarily set to an appropriate position depending on the casting conditions. If the advance switch position is set to an unintended position, it is not possible to realize the waveforms of speed and pressure that correspond to the casting conditions. In view of the above, an object of the present invention is to eliminate the delay between the completion of filling and the start of pressure boosting by setting an appropriate advance switch position, and to realize speed and pressure waveforms corresponding to the casting conditions. [Means for solving the problem]

[0009] In order to eliminate the delay in starting the boosting process, the inventors of the present invention have tried to set a precedence switching position for switching to the boosting process prior to the completion of filling for various casting conditions. The control device of the die casting machine detects the position of the plunger using a linear encoder, etc., and controls the injection device based on predetermined casting conditions including the plunger speed and casting pressure. Specifically, the control device controls the speed at which the plunger moves to a predetermined injection speed, and transitions from speed control to pressure control when the valve switches from the injection filling system to the boosting system. While the plunger is being moved moment by moment, when it is detected that the plunger has reached a preceding switching position, which is a displacement amount calculated from the plunger speed and time lag, which is located back from the position at the time of completion of filling, a switching command is output from the control device to the valve of the hydraulic circuit. However, since the advance switching position changes with changes in the plunger speed, the inventors of the present invention have found that there is a drawback to the advance switching position set for some casting conditions, as described below.

[0010] The injection operation by the plunger is typically performed by keeping the plunger moving speed low until halfway through the injection filling process, and then increasing the plunger moving speed towards the end of the injection filling process, in order to avoid entraining air in the molten metal. In recent years, the high-speed section has tended to become shorter against the background of the increase in the speed of the injection stroke. Therefore, the high-speed section may be so short that the advance switching position, which is back by a specified time lag based on the plunger speed, is set in the low-speed section of the injection stroke prior to the completion of filling in the high-speed section. In other words, the high-speed section is short relative to the displacement of the plunger corresponding to the delay in the start of boosting. Under such casting conditions, the advance switching position, which is back by a specified time lag based on the plunger speed in the low-speed section, is set in the high-speed section, and when the low-speed section is switched to the high-speed section, the advance switching position is set in the low-speed section. In that case, even if a command to start boosting is issued at the advance switching position prior to the completion of filling, the advance switching position is in the low-speed section that has already been passed, so there is no way to eliminate the delay in starting boosting. In this case, there is no other way than to issue a command to start boosting immediately after switching from the low-speed section to the high-speed section. Even if the high-speed section is not short, if the time lag is long, the advance switch position that is back by a specified time lag based on the plunger speed may be set in the low-speed section of the injection stroke prior to the completion of filling in the high-speed section, as described above. In this case, too, the advance switch position that has passed may be set unintentionally at the time of switching from the low-speed section to the high-speed section.

[0011] Furthermore, in the casting conditions in which the plunger is decelerated after the low-speed section and the high-speed section of the injection stroke, the advance switch position, which is set based on the plunger speed before the completion of filling, may be set to a position that is further back than the displacement amount required to eliminate the delay in starting boosting. In that case, after reaching the advance switch position, there is a time lag and the hydraulic circuit switches to the boosting system before the completion of filling. In that case, the plunger speed increases rapidly because the filling is not yet complete, and the hydraulic pressure for boosting is consumed for the speed increase, resulting in a decrease in the casting pressure.

[0012] In all of the above-mentioned casting conditions, the advance switching position is set to an unintended position, so that the speed-pressure waveform corresponding to the casting conditions cannot be realized, and it is difficult to obtain a quality product. Alternatively, it may be possible to output a command to start increasing the pressure when a pressure sensor or the like detects that the molten metal has reached the cavity. However, this would lead to a delay in detecting the arrival of the molten metal, and so it would be difficult to fully eliminate the delay in starting to increase the pressure after filling is complete.

[0013] The present invention has been made based on the above-mentioned new findings. The present invention is a control device used to set up and control an injection device of a die casting machine. The speed of a plunger provided in the injection device changes at a plurality of speed switching positions during an injection stroke for injecting molten metal into a cavity. The control device is capable of setting a preceding switching position that is obtained by going back from the boost switching position by a delayed displacement amount as the displacement amount of the plunger corresponding to the delay time, based on an injection pattern that can identify a plurality of speed switching positions and speeds that respectively correspond to the plurality of speed switching positions, a boost switching position that corresponds to a position at which switching is made from injection filling, which involves injecting and filling the molten metal into the cavity, to boosting, which increases the pressure of the molten metal in the cavity, and a delay time required for switching from completion of filling to start of boosting. When the distance from the pressure increase switching position to the speed switching position immediately preceding the pressure increase switching position is shorter than the delay displacement amount, the control device sets a preceding switching position that is one or more speed switching positions back from the pressure increase switching position, and outputs a command to start pressure increase at the preceding switching position in the injection stroke.

[0014] In the control device for a die casting machine of the present invention, the injection stroke includes a plurality of sections separated by a plurality of speed switching positions, and the injection stroke includes as sections an acceleration section in which the moving plunger is accelerated from a first speed, and a high-speed section in which the plunger is moved at a second speed after passing through the acceleration section, and it is preferable that the pressure boost switching position is located in the high-speed section, and that the length from the pressure boost switching position to the speed switching position corresponding to the start of the high-speed section is shorter than the delay displacement amount.

[0015] In the control device for a die casting machine of the present invention, the injection stroke includes a plurality of sections separated by a plurality of speed switching positions, and the injection stroke includes as sections an acceleration section in which the moving plunger is accelerated from a first speed, a high-speed section in which the plunger is moved at a second speed through the acceleration section, a deceleration section following the high-speed section, and a low-speed section before completion of filling in which the plunger is moved at a third speed through the deceleration section, and it is preferable that the pressure increase switching position is located in the low-speed section before completion of filling, and that the length from the pressure increase switching position to the speed switching position corresponding to the start of the low-speed section before completion of filling is shorter than the delay displacement amount.

[0016] The control device for a die casting machine of the present invention preferably includes a memory unit for storing data, and when the control device acquires a preceding switching position for each of a plurality of injection patterns used in the injection device, it links the preceding switching position to the injection pattern and stores it as data in the memory unit.

[0017] The control device for a die casting machine of the present invention preferably includes a leading switch position calculation unit that calculates a leading switch position, and the leading switch position calculation unit preferably includes a retroactive time calculation unit that calculates a retroactive time from the pressure boost switch position to each of a plurality of speed switch positions for each speed switch position, a previous position identification unit that identifies a previous position, which is the speed switch position immediately before the leading switch position, from the retroactive time and the delay time, and a leading switch position calculation unit that converts the time from the previous position to the leading switch position into the leading switch position.

[0018] The die casting machine of the present invention includes the above-mentioned die casting control device, an injection device, and a hydraulic circuit used to drive the injection device.

[0019] The present invention also relates to a program for use in setting and controlling an injection device of a die casting machine. The injection device includes a plunger whose speed changes at a plurality of speed switching positions during an injection stroke for injecting molten metal into a cavity. The program of the present invention can set a preceding switch position that is obtained by going back from the boost switch position by a delayed displacement amount as the displacement amount of the plunger corresponding to the delay time, based on a plurality of speed switch positions and an injection pattern that can identify speeds corresponding to each of the plurality of speed switch positions, a boost switch position that corresponds to a position at which to switch from injection filling, which involves injecting and filling the molten metal into the cavity, to boost pressure, which increases the pressure of the molten metal in the cavity, and a delay time required for switching from completion of filling to start of boost pressure. Furthermore, when the distance from the pressure boost switch position to the speed switch position immediately preceding the pressure boost switch position is shorter than the delay displacement amount, the program sets a preceding switch position that is one or more speed switch positions back from the pressure boost switch position, and outputs a command to start pressure boost at the preceding switch position in the injection stroke.

[0020] The present invention is a casting method in which molten metal is injected and filled into a cavity while changing the speed of a plunger provided in an injection device of a die casting machine at a plurality of speed switching positions in the injection stroke of the plunger, and includes the steps of: setting a leading switching position that goes back beyond one or more speed switching positions from the pressure boost switching position and a delayed displacement amount as the displacement amount of the plunger corresponding to the delay time, based on an injection pattern that can identify a plurality of speed switching positions and speeds corresponding to the plurality of speed switching positions; a pressure boost switching position that corresponds to a position at which the injection filling, which injects and fills the cavity with molten metal, is switched to pressure boosting, which increases the pressure of the molten metal in the cavity, and a delay time required for switching from completion of filling to start of pressure boosting; and outputting a command to start pressure boosting at the leading switching position in the injection stroke. Effect of the Invention

[0021] According to the present invention, a leading switch position that goes back from the boost pressure switch position beyond one or more speed switch positions by a plunger delay displacement amount corresponding to the delay time can be calculated based on the boost pressure switch position, delay time, and injection pattern, and set in the control device. A boost pressure switch command is output at the set leading switch position, thereby eliminating delay or advance in the boost pressure start relative to the completion of filling, and realizing a speed-pressure waveform corresponding to the casting conditions to manufacture a quality product. [Brief description of the drawings]

[0022] [Figure 1] FIG. 2 is a diagram showing a schematic diagram of an injection device of a die casting machine according to an embodiment of the present invention, a control device used for setting and controlling the injection device, and a mold. [Diagram 2] 1 is a graph showing an example of plunger speed and casting pressure during casting. [Diagram 3] 3 is a graph showing injection patterns corresponding to casting conditions similar to those in FIG. 2. [Figure 4] FIG. 2 is a schematic diagram of an example of a hydraulic circuit for driving the injection device shown in FIG. 1. [Diagram 5]FIG. 2A is a block diagram showing the general configuration of the control device shown in FIG. 1; FIG. 2B is a schematic diagram showing the internal configuration of a program setting module; and FIG. 2C is a diagram showing an example of an injection pattern stored in a storage unit. [Figure 6] 4 is a diagram for explaining a procedure for calculating a preceding switching position that matches the emission pattern shown in FIG. 3. [Figure 7] 13 is a graph showing an example of another ejection pattern. [Figure 8] 8 is a graph showing plunger speed and casting pressure corresponding to the injection pattern shown in FIG. 7. [Figure 9] 8 is a diagram showing an example of calculation of a preceding switching position that matches the injection pattern shown in FIG. 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. The die casting machine 1 shown in Figure 1 includes an injection device 10 that injects molten metal such as an aluminum alloy into a cavity 4 formed by a fixed mold 2 and a movable mold 3, a clamping device 5 that applies a clamping force to the fixed mold 2 and the movable mold 3, a hydraulic circuit 20 (Figure 4) that drives the injection device 10, and a control device 30 used to set and control the injection device 10. The mold clamping device 5 includes a fixed platen 51, and a movable platen and tie bars (not shown).

[0024] (injection device) The injection device 10 is provided on a fixed platen 51 and includes a sleeve 11 into the inside of which molten metal is supplied, and a plunger 12 that is driven so as to be able to advance and retreat relative to the sleeve 11. The plunger 12 includes a tip 121 that pushes out the molten metal 13 toward the cavity 4, and a rod 122 that supports the tip 121. The rod 122 is coupled via a coupling 123 to a piston rod 210R provided in the injection cylinder 21 that constitutes the hydraulic circuit 20.

[0025] The plunger 12, driven by a pressure determined by the pressure on the piston head 210H side and the pressure on the piston rod 210R side of the injection cylinder 21, advances toward the cavity 4 while being driven and controlled according to predetermined casting conditions, thereby injecting the molten metal 13. The plunger 12 advances from the origin position until it stops as the molten metal is completely filled into the entire cavity 4. The range of advance of the plunger 12 is called the injection stroke.

[0026] The molten metal injected by the plunger 12 is filled into the cavity 4 from the gate 7 through the runner 6. Upon completion of filling the entire cavity 4 with the molten metal, the hydraulic source connected to the injection cylinder 21 is switched, and the process moves from the injection filling process, in which injection and filling are performed, to a pressure increase process, in which the plunger 12 increases the pressure of the molten metal in the cavity 4. At this time, the drive control of the plunger 12 is switched from the control based on the speed of the plunger 12 to the control based on a value correlated with the pressure (casting pressure) of the molten metal in the cavity 4, typically the pressure on the piston head 210H side and the pressure on the piston rod 210R side of the injection cylinder 21. For example, a value calculated by subtracting the product of the pressure on the piston rod 210R side and the piston rod side area 210RS from the product of the pressure on the piston head 210H side and the piston head side area 210HS by the tip area 121S can be used for the drive control of the plunger 12.

[0027] (Casting Process) The die casting machine 1 is capable of repeatedly performing a casting cycle consisting of processes such as mold clamping, pouring, injection filling, pressure increase, cooling, mold opening, product removal, and supply of mold release agent to the mold according to the casting conditions. 2 shows an example of the speed of the plunger 12 and the casting pressure in the casting process using the die casting machine 1. The position on the injection stroke corresponding to the time of switching from the injection filling process A1 to the pressure boosting process A2 is called the pressure boosting switching position P vp It is called. In Fig. 2, the speed of the plunger 12 is indicated by a dashed line, and the casting pressure is indicated by a solid line. The casting pressure corresponds to the pressure calculated using the head side pressure (thick dashed line) and the rod side pressure (dash-dotted line) of the injection cylinder 21. In the pressure range of Fig. 2, the casting pressure is higher than the head side pressure. The same is true in Fig. 8.

[0028] The casting pressure indicated by the dotted line in FIG. 2 and the head side pressure indicated by the thin dashed line indicate Comparative Example 1 for this embodiment. s ) is the time when the molten metal is completely filled into the cavity 4. f For delay time T d In contrast to Comparative Example 1, this embodiment is delayed by t f From the time when pressure increase starts t s This will eliminate delays up to Delay time T d corresponds to the time required for, for example, signal transmission, control processing, operation of the valves of the hydraulic circuit 20, and movement of hydraulic oil.

[0029] In the injection filling step A1, control is performed so that the movement of the plunger 12 follows an injection pattern related to the position and speed of the plunger 12. In Figures 2 and 3, the injection pattern is shown by a solid line connecting the plots of black circles. To detect the position and speed of the plunger 12, a sensor 8 (FIG. 1), such as a linear encoder mounted on the piston rod 210R, can be used.

[0030] In the pressure increasing step A2, under control based on the pressure on the head side and the pressure on the rod side of the injection cylinder 21, the molten metal is pressed by the plunger 12, and a specified casting pressure is applied to the molten metal while replenishing the cavity 4 with the amount of molten metal that has contracted due to solidification. In the pressure increasing step A2, the casting pressure is increased to a specified value, and then the molten metal in the cavity 4 is solidified while being kept at the specified value (pressure holding) until the end of the pressure increasing step A2. Thereafter, the molds 2 and 3 are opened to remove the product from the cavity 4, and the plunger 12 is retracted to the origin position, and the process moves to the next casting cycle.

[0031] (Injection pattern) FIG. 3 shows an injection pattern based on one casting condition. The horizontal axis of FIG. 3 indicates the position of the plunger 12 on the injection stroke, and the vertical axis indicates the moving speed of the plunger 12. The speed of the plunger 12 is switched at a plurality of speed-switching positions P1, P2, and P3 on the injection stroke. According to the injection pattern, it is possible to specify the speed-switching positions P1, P2, and P3, and the speeds of the plunger 12 corresponding to the speed-switching positions P1, P2, and P3, respectively. The preceding switching positions P p As described later, the pressure boost switching position P vp , delay time T d , and is set based on the injection pattern. The injection stroke of the plunger 12 includes a plurality of sections S1, S2, S3, and S4 that are divided by speed switching positions P1, P2, and P3.

[0032] From the start to the middle of the injection filling process A1, in order to prevent air from being entrained in the molten metal, it is desirable to move the plunger 12 at a relatively slow speed, but to rapidly accelerate the plunger 12 at the speed switching position P2 to perform injection and complete filling while the molten metal is hot in a short time. The speed switching position P2 corresponds to the position of the plunger 12 when the molten metal reaches the gate 7, for example.

[0033] According to the injection pattern shown in FIG. 3, the plunger 12 starts moving forward at the speed switching position P0, and the plunger 12 is accelerated to a target first speed V1 at a predetermined acceleration (first section S1). From the speed switching position P1 to the speed switching position P2, the speed of the plunger 12 is maintained at the first speed V1 (second section S2). Thereafter, the target speed of the plunger 12 is switched to the second speed V2 at the speed switching position P2, and the plunger 12 is accelerated from the first speed V1 to the second speed V2 at a predetermined acceleration (third section S3). Then, the plunger 12 continues to move at the second speed V2 (fourth section S4). The fourth section S4 corresponds to the section from the speed switching position P3 to the end position P4 of the injection stroke. The actual behavior of the plunger 12 in the fourth section S4 is, as shown in FIG. 2, a continuous movement from the end of the injection stroke (t f ), the plunger 12 slows down and stops. f The position of the plunger 12 is P f Then, P f <P4である。

[0034] (Hydraulic circuit) 4 shows an example of the configuration of the hydraulic circuit 20. The hydraulic circuit 20 includes an injection cylinder 21 that hydraulically drives the plunger 12 of the injection device 10, a charging accumulator 22, a boosting accumulator 23, a hydraulic pump 24, a flow rate regulating valve 25 that can adjust the flow rate of the hydraulic oil supplied to the injection cylinder 21, on-off valves 261 to 264 that are opened and closed at appropriate times, a check valve 27 that prevents backflow of the hydraulic oil to the hydraulic pump 24, and a storage tank 28 that stores the hydraulic oil.

[0035] The injection cylinder 21 includes a cylinder body 211, a piston 210, an inflow oil chamber C1 on the piston head 210H side, and a discharge oil chamber C2 on the piston rod 210R side. The inflow oil chamber C1 is switchably connected to the charging accumulator 22 and the boosting accumulator 23 by opening and closing the on-off valves 261 and 262. The discharge oil chamber C2 is connected to a storage tank 28 via a flow control valve 25 whose spool is driven by a servo motor 25A. The flow control valve 25 adjusts the discharge flow rate of the hydraulic oil from the discharge oil chamber C2, thereby controlling the moving speed of the plunger 12.

[0036] The charging accumulator 22 and the boosting accumulator 23 are configured to be able to supply an inert gas such as nitrogen gas from a gas supply source (not shown) to a section above the pistons 22A and 23A in each cylinder. The charging accumulator 22 supplies hydraulic oil to the inflow oil chamber C1 by the stored pressure. The boosting accumulator 23 is configured similarly.

[0037] When storing pressure in the charging accumulator 22, the on-off valves 261, 263 are opened and the on-off valves 262, 264 are closed, and the hydraulic oil in the storage tank 28 is pumped by the hydraulic pump 24 to the charging accumulator 22 until the pressure of the hydraulic oil in the charging chamber 22B reaches a predetermined value required for sufficiently and rapidly accelerating the plunger 12 to the injection charging step A1 and injecting it at high speed. When the pressure storage in the charging accumulator 22 is completed, the on-off valves 261, 263 are closed.

[0038] When storing pressure in the boost accumulator 23, the on-off valves 262, 263 are opened and the on-off valves 261, 264 are closed. With this, the hydraulic oil in the storage tank 28 is pumped to the boost accumulator 23 by the hydraulic pump 24 until the pressure of the hydraulic oil in the filling chamber 23B reaches a predetermined value required to apply a specified casting pressure to the molten metal in the cavity 4. When the accumulation of pressure in the pressure-boosting accumulator 23 is completed, the on-off valves 262, 263 are closed. The injection charging step A1 is started with pressure stored in the charging accumulator 22 and the boosting accumulator 23. After the injection charging step A1 and the boosting step A2 are completed, the hydraulic oil is pumped to the discharge oil chamber C2 by a system (not shown) of the hydraulic circuit 20, and the hydraulic oil in the inlet oil chamber C1 is drained to the tank, thereby retracting the plunger 12.

[0039] Various known hydraulic circuits for die casting can be used instead of the hydraulic circuit 20. Hydraulic circuits that can be substituted for the hydraulic circuit 20 are described in, for example, Japanese Patent No. 6582834. The hydraulic circuit 20 does not necessarily need to have two accumulators 22, 23, one for injection filling and one for boosting, but it is sufficient if it has an injection filling system and a boosting system that can be switched to provide the required speed during injection filling and the required pressure during boosting from the injection cylinder 21 to the plunger 12.

[0040] (Control device) The control device 30 includes a control device main body 31, and a monitor 32 and an external storage medium 33 connected to the control device main body 31, as shown in an example of a hardware configuration in FIG. The control device main body 31 is composed of a computer device or the like, and is equipped with a calculation unit 311 such as a CPU (Central Processing Unit), a memory 312, a storage unit 313 (storage medium) that stores data such as setting values ​​and programs, and an input / output unit 314.

[0041] The control device 30 controls at least the plunger 12 of the injection device 10 and the hydraulic circuit 20 that drives the plunger 12, among various devices included in the die casting machine 1, in accordance with casting conditions set according to the product. This control device 30 may constitute a part of a control device that controls the operation of the die casting machine 1 throughout the entire casting process in cooperation with not only the injection device 10 and the hydraulic circuit 20, but also the mold clamping device 5, a water heater (not shown), a product removal mechanism, a vacuum suction device, etc.

[0042] The control device 30 determines the boost switch position P vp , leading switch position P p , and the delay time T d and can be stored in the storage unit 313. Pressure boost switch position P vp and delay time T dFor example, a value input by an operator using the input / output unit 314 based on the results of a test or simulation can be set in the control device 30. vp As the pressure, for example, the position of the plunger 12 when the pressure on the piston head 210H side of the injection cylinder 21 reaches a specified pressure can be adopted. Delay time T d is a value specific to the die casting machine 1 used. Even if the die casting machines 1 have the same configuration, the delay time T d The value may vary. Preceding switch position P p As the value, a value calculated by executing a computer program (hereinafter, the program) installed in the control device 30 can be set in the control device 30.

[0043] In addition, the control device 30 issues control commands to the flow control valve 25 and the on-off valves 261-264 of the hydraulic circuit 20 based on the installed program, and operates these valves to apply a driving force to the plunger 12 to perform the injection filling process A1 and the pressure boosting process A2. The program installed in the control device 30 includes at least the preceding switching position P p and a drive control module that drives and controls the plunger 12 through the operation of a valve in the hydraulic circuit 20. As shown in Fig. 5(b), the setting module includes a retroactive time calculation unit 315, a previous position identification unit 316, and a preceding switching position calculation unit 317.

[0044] The memory unit 313 stores the boost switch position P vp , leading switch position P p , and the delay time T d , the injection pattern relating to the position and speed of the plunger 12 (FIG. 5(c)), and the preceding switching position P p The control circuit stores a program used for setting the parameters and controlling the drive of the plunger 12, as well as data necessary for executing the program.

[0045] As shown in Fig. 5(c), the injection pattern is made up of data including at least positions P1, P2, and P3 where the speed of the plunger 12 is switched, a start position P0 and an end position P4 of the injection pattern, and speeds V0, V1, V2, and V3 corresponding to each position. The injection pattern is such that the speed is switched at least at two positions after the start of injection. Hereinafter, the positions P0 to P4, including the start position P0 and end position P4 of the injection pattern, are referred to as speed switching positions. The injection pattern is sufficient as long as it includes information that can identify a plurality of speed switching positions of the plunger 12 and the speeds that correspond to the respective speed switching positions. For example, the injection pattern may be one that includes the speed switching positions and the elapsed time from the start position of the injection stroke.

[0046] The memory unit 313 stores a plurality of injection patterns that can correspond to various casting conditions used in the die casting machine 1 in an appropriate data format such as table data. vp and the preceding switching position P p is set for each injection pattern and is stored in the storage unit 313 in a state linked to a specific injection pattern.

[0047] At the start of the injection filling process A1, the control device 30 opens the on-off valves 261, 264 to supply hydraulic oil from the filling accumulator 22 to the inflow oil chamber C1 of the injection cylinder 21, and also gives the flow rate control valve 25 an opening corresponding to the first speed V1, which is the target value for the speed of the plunger 12. Thereafter, the flow rate control valve 25 is given an opening corresponding to the second speed V2 at the speed switching position P1, thereby rapidly accelerating the plunger 12 and injecting the molten metal into the cavity 4. The control device 30 determines whether the preceding switching position P p When the sensor 8 or the like detects that the plunger 12 has reached the pressure boosting accumulator 23, a pressure boosting start command is generated to start boosting the pressure, thereby closing the on-off valve 261 and opening the on-off valve 262, and switching the hydraulic power source connected to the injection cylinder 21 from the filling accumulator 22 to the pressure boosting accumulator 23.

[0048] When the filling of the molten metal in the cavity 4 is nearing completion, the casting pressure draws an upward curve, as shown in Figure 2. It is desirable to make this upward curve steep enough to prevent burrs from forming, and to minimize the time required for the pressure to rise. By transmitting sufficient pressure throughout the entire cavity 4 before the molten metal solidifies, the air in the molten metal is crushed, resulting in a densified product. Therefore, the time when the filling of the cavity 4 is completed (t f ) and immediately begin increasing pressure. However, when filling is completed, t f The pressure boost switching position P corresponds to the position of the plunger 12. vp Even if a pressure boost start command is issued from the control device 30, the time required to detect that the plunger 12 has reached the position, the response time from when the pressure boost start command is issued until the on-off valve 261 closes and the on-off valve 262 opens, the time required for hydraulic oil to be supplied from the pressure boost accumulator 23 to the inflow oil chamber C1 and for the plunger 12 to be moved by the injection cylinder 21, and other times required for signal transmission of detection signals and control commands and control processing, are included in the filling completion time t f At the start of pressure increase, t s is delayed. Delay time T d corresponds to the cumulative time of these electrical and mechanical delays.

[0049] Due to the above delay, the boost switch command is vp The preceding switching position P p It is necessary to generate the signal at the preceding switching position P p is the boost switch position P vp From the delay time T d Therefore, the control device 30 sets the pressure boost switching position P vp and delay time T d In addition, the advance switching position P p Calculate.

[0050] (Calculation and setting of advance switching position) 6 and 3, the preceding switching position Pp An example of a procedure for calculating and setting the preceding switch position P for each of a plurality of injection patterns used in the injection unit 10 will be described. p Calculate and set. 6 shows in table form the speed switching positions P0 to P4 of the injection pattern, and the first section S1, second section S2, third section S3, and fourth section S4 of the injection stroke divided by the speed switching positions P1 to P3. The subscript n (0, 1, 2,...) is used to refer to the speed switching positions. The injection pattern shown in FIG. 3 is characterized in that the plunger 12 is rapidly accelerated to perform filling at high speed, and therefore the speed is switched to high speed at the speed switching position P2 and then the filling completion time t f The length (the displacement of the plunger 12) is the delay time T d The problem is that it is short compared to the

[0051] In this injection pattern, when filling is completed, t f Pressure boost switching position P vp From the boost switch position P vp The length to the speed change position P3 immediately before the delay time T d In this case, if the delay time T d and the current speed (V1 or V2) of the moving plunger 12, the boost switch position P vp The leading switch position P p Then, the preceding switching position P p The higher the speed of the plunger 12, the more it is displaced toward the rear side of the injection stroke (the side away from the cavity 4). Therefore, when the speed of the plunger 12 is switched from a low speed to a high speed, the previous leading switch position P p Even if a pressure increase switching command is issued in section S3 or section S4 after switching from low speed to high speed, the delay in starting pressure increase relative to the completion of filling is not sufficiently resolved.

[0052] As shown in Figure 3, when the injection pattern is completed, t f Pressure boost switching position P vpFrom the boost switch position P vp Even if the requirement that the length to the speed switching position P3 immediately before the delay time T is shorter than the delay displacement amount of the plunger 12 (hereinafter, requirement A) is met, the delay time T d The leading switch position P p It is possible to get and set it. When the injection pattern selected for casting satisfies requirement A, the control device 30 sets the boost pressure switching position P vp to one or more speed change positions P n The preceding switching position P p Then, the preset preceding switching position P p The pressure boost start command is output. The control device 30 judges whether the selected injection pattern satisfies the above requirement A, and if so, sets the preceding switching position P p is calculated and set, for example, according to steps 1 to 6.

[0053] Step 1: The time T of each of the first to fourth sections S1, S2, S3, and S4 of the injection pattern n Calculate (T1~T4). Due to the speed of the injection pattern, the second section S2 and the fourth section S4 correspond to constant speed sections in which the plunger 12 moves at a constant speed, and the first section S1 and the third section S3 correspond to constant acceleration sections in which the plunger 12 is accelerated at a constant acceleration. The time for the constant velocity section is calculated using formula (1).

[0054]

number

[0055] The time of the constant acceleration section is calculated using formula (2) based on the basic equation of constant acceleration linear motion.

[0056]

number

[0057] The acceleration in the first section S1 and the third section S3 does not necessarily have to be constant. For example, the speed may change gradually around the positions P0 and P2. Even in this case, for example, the speed change position is determined as the inflection point of the speed, and the time of the section between the adjacent speed change positions can be obtained by appropriate calculation.

[0058] Step 2: Adjacent speed change positions P n and P n+1 By comparing with the pressure boost switching position P vp It is then determined between which of the adjacent speed change positions P1 to P4 the speed change position exists. In this embodiment, the pressure increase switching position P is between the speed switching positions P3 and P4. vp There is a pressure boost switch position P vp A circle (○) is marked in the column for the section SA (here, the fourth section S4) in which the

[0059] Step 3: Booster switch position P vp From the start point of each section S1 to S4 (speed switching position P n ) retroactive time T bn Calculate. Here, the boost pressure switching position P vp For the section SA where vp to the previous speed change position P n In the case of a constant acceleration section, the time to vp If the section SA is a constant velocity section, T in equation (4) is vp Let us assume that:

[0060]

number

number

[0061] Equation (3) is a modification of the basic equation (5) for uniformly accelerated motion. Inis the initial velocity.

[0062]

number

[0063] Pressure boost switch position P vp From the boost switch position P vp The retroactive time T b3 is T in Eq. (4). vp It is. Pressure boost switch position P vp From the start point P2 of the third section S3, the retroactive time T b2 is the retrospective time T b3 This is the sum of the time T3 found in step 1, so T b3 +T3. Similarly, the retroactive time T b1 is T b2 +T2, and the retroactive time T b0 is T b1 +T1. The processes of steps 1 to 3 are performed by the retroactive time calculation unit 315 (FIG. 5(b)) of the calculation and setting module.

[0064] Step 4: Pressure boost switch position P vp From the start point of each section (speed switching position P n ) retroactive time T bn and the delay time T d Therefore, the leading switching position P p In other words, the pressure boost switching position P vp to delay time T d The position that is the delay displacement amount corresponding to the preceding switching position P p ) and each retrospective time T bn When comparing with the preceding switching position P p The section where the preceding switching position P exists can be specified. p A double circle (◎) is placed in the column for the section SB (here, the second section S2) in which The process of step 4 is performed by the previous position identification unit 316 of the calculation and setting module. p The speed change position P immediately before n (Previous position) is identified.

[0065] Step 5: From the start point (previous position) of the section SB obtained in step 4 to the preceding switching position P p Time until T p is calculated using equation (6).

number

[0066] Step 6: The time T obtained in step 5 p From the leading switch position P p Calculate. The processes in steps 5 and 6 are performed by the preceding switching position calculation unit 317 in the calculation and setting module. If section SB is a constant velocity section, use formula (7). If section SB is a constant acceleration section, use formula (8).

[0067]

number

number

[0068] According to the above steps 1 to 6, the boost pressure switching position P vp to one or more speed change positions P n (Here, P3, P2) beyond the delay time T d The preceding switching position P p is calculated. The control device 30 calculates the preceding switching position P p are associated with the injection pattern and stored as data in a setting area in the storage unit 313.

[0069] In addition, even if the injection pattern selected for casting does not meet requirement A, the preceding switching position P can be set in the same manner as in steps 1 to 6 above. p In this case, the boost pressure switching position P vp and the preceding switching position P p is the same as the section SB in which

[0070] If the requirement A is not met, the control device 30 does not follow the above steps 1 to 6 and sets the filling completion time t f The speed of the plunger 12 and the delay time T d The leading switch position P as a product of p Alternatively, the speed and delay time T can be set based on the speed that changes moment by moment during the movement of the plunger 12. d The leading switch position P as a product of p By updating the p can be set. The control device 30 sets the advance switching position P p When obtaining the above, it is determined whether or not the requirement A is satisfied, and if so, the preceding switching position P is determined by steps 1 to 6. p If not applicable, the speed of the plunger 12 and the delay time T d The preceding switching position P p and a second setting mode for setting the

[0071] (Preceding switch position P p (Actions and effects of the settings) The control device 30 sets the boost switch position P vp , delay time T d , and the leading switching position P based on the injection pattern p After the step of calculating and setting (precedent switching position setting step) is completed, the preceding switching position P associated with the injection pattern selected according to the casting conditions is selected from the setting area of ​​the storage unit 313. p The injection filling step A1 is carried out while detecting the position of the plunger 12 by the sensor 8 or the like. pWhen it is detected that the plunger 12 has reached the pressure boosting accumulator 23, a pressure boosting switch command is output (pressure boosting switch command output step). By outputting the pressure boosting switch command, the on-off valve 261 closes and the on-off valve 262 opens, so that the hydraulic oil flows from the pressure boosting accumulator 23 into the inflow oil chamber C1, and the specified casting pressure is applied to the plunger 12.

[0072] As shown by the dotted line in FIG. 2, the casting pressure in Comparative Example 1 is f If a pressure boost start command is issued at the time of filling completion t f The delay time T d However, according to this embodiment, when the filling is completed, t f Prior to the preceding switching position P p The boost switch command is output at the preceding switch position P p Delay time T from arrival at d When filling is completed after t f Since the pressure increase starts at the time of filling completion t f As shown by the solid line in Fig. 2, the casting pressure in this embodiment increases continuously from the end of the injection filling step A1 to the pressure increasing step A2.

[0073] Delay time T d The delay time T d The preceding switching position P calculated based on p If the boost switch command is output at , there is no delay in detecting the position of the plunger 12, and the delay from the completion of filling to the start of boosting is eliminated. d Even if there is variation in the delay time T d Since the delay due to the variation in is within the allowable limit, the delay in the start of pressure increase relative to the completion of filling can be sufficiently eliminated.

[0074] By eliminating the delay between the completion of filling and the start of pressure increase, the time required to increase the pressure of the molten metal can be shortened, while achieving a speed and pressure waveform that corresponds to the casting conditions, allowing the production of quality products. In addition, the shortened cycle time can improve productivity.

[0075] (Another injection pattern) 7 to 9, the preceding switching position P corresponding to another injection pattern is p The setting of the above and the control of the injection unit 10 based on the setting will be described below. The injection pattern shown in Fig. 7 is characterized in that after the plunger 12 is rapidly accelerated to the second speed V2, the opening of the flow control valve 25 is reduced to brake and decelerate the plunger 12 prior to the natural deceleration of the plunger 12 accompanying the completion of filling. Except for this point, the injection pattern shown in Fig. 7 is similar to the injection pattern shown in Fig. 3. The plunger 12 starts to decelerate at the speed switching position P4 while moving at the second speed V2, passes through a fifth section S5 (deceleration section) required for deceleration, and is controlled to the third speed V3 in a sixth section S6 (low speed section before filling completion).

[0076] Similar to the injection pattern shown in FIG. 3, the injection pattern shown in FIG. 7 also starts at the end of filling t f Pressure boost switching position P vp From the boost switch position P vp The length to the speed change position P5 immediately before the delay time T d Since this is shorter than the displacement amount (delay displacement amount) of the plunger 12 corresponding to the above, the above requirement A is met. When the injection pattern shown in FIG. 7 is selected, the delay time T d The pressure boost switching position P vp The leading switch position P p If the above is set, the advance switching position P should be set to a position that is longer than necessary in consideration of the speed V3 before the filling is completed. p The preceding switching position P p The boosting start, which is initiated by the boosting switch command issued at t fIf the injection speed is faster than the injection speed, it is difficult to control the movement of the plunger 12 to follow the injection pattern, as shown in Comparative Example 2 of FIG. 8, and this affects the oil pressure of the injection cylinder 21 and the casting pressure.

[0077] In Fig. 8, the casting pressure indicated by the dotted line, the head side pressure indicated by the thin dashed line, the rod side pressure indicated by the thin dashed double-dot line, and the speed of the plunger 12 indicated by the thin broken line indicate Comparative Example 2 for this embodiment. Fig. 8 shows B1 to B4, which will be referred to below. In Comparative Example 2, the time when the filling is completed t f Based on the boost switch command output at a time earlier than the time when the hydraulic oil flows from the boost accumulator 23 to the head side (inflow oil chamber C1) of the injection cylinder 21. At this time, since the filling is not completed, the plunger 12 has room to move forward. Therefore, the speed of the plunger 12 increases suddenly (see B1), and the hydraulic oil on the rod side (discharge oil chamber C2) of the injection cylinder 21 is excessively compressed due to the sudden acceleration of the plunger 12, and then is rapidly depressurized (see B2). After the rod side pressure starts to decrease, the casting pressure increases rapidly, but the pressure oil supplied from the boost accumulator 23 to the injection cylinder 21 is consumed to increase the speed of the plunger 12, so the casting pressure falls short of the specified value (see B3). Also, the rod side pressure typically decreases at the same time as the casting pressure increases, but in Comparative Example 2, the rod side pressure increased to an excessive pressure due to the sudden acceleration of the plunger 12, so it takes extra time for the rod side pressure to decrease (see B4). Unlike Comparative Example 2, this embodiment can realize velocity and pressure waveforms corresponding to the casting conditions.

[0078] According to the control device 30, the preceding switching position P corresponding to the injection pattern of FIG. p Similarly to the calculation and setting of , the preceding switching position P corresponding to the injection pattern in FIG. p An example of the procedure will be briefly described with reference to FIG. Step 1: The time T of each of the first to sixth sections S1 to S6 of the injection pattern n Calculate (T1~T6). Step 2: Pressure boost switch position P vp In this example, it is between the speed switching positions P5 and P6, and between the pressure boosting switching positions P vp A circle (○) is marked in the column for section SA (sixth section S6) in which this exists.

[0079] Step 3: Booster switch position P vp From the start point of each section S1 to S6 (speed switching position P n ) retroactive time T bn Calculate the boost pressure switching position P vp For the section SA where vp to the previous speed change position P n Time until T vp Let us assume that: Step 4: Pressure boost switch position P vp to delay time T d The position that is the delay displacement amount corresponding to the preceding switching position P p ) and each retrospective time T bn By comparing with the preceding switching position P p The preceding switching position P p A double circle (◎) is placed in the column for section SB (fourth section S4) in which this exists.

[0080] Step 5: Start point of section SB (speed switching position P n ) to the preceding switching position P p Time until T p T bn -T d It is calculated as follows. Step 6: The time T obtained in step 5 p From the leading switch position P p Calculate.

[0081] As a result, the boost pressure switching position P vp From the delay time T d The preceding switching position P pcan be calculated and set in the control device 30. The control device 30 determines the advance switching position P associated with the injection pattern selected according to the casting conditions. p is read from the storage unit 313, and the injection filling step A1 is carried out. At this time, the filling completion time t f Prior to the preceding switching position P p The boost switch command is output at the preceding switch position P p Delay time T from arrival at d After that, when filling is completed, t f At the same time, pressure increase for the molten metal begins. At this time, since the filling of the molten metal into the cavity 4 is completed, the speed of the plunger 12 does not increase with the inflow of hydraulic oil into the inlet oil chamber C1 on the head side, and the rod side pressure does not increase excessively. As shown by the solid line in Figure 8, the casting pressure increases continuously from the end of the injection filling process A1 to the pressure increasing process A2.

[0082] As described above, the boost pressure switching position P vp , delay time T d , and the preceding switching position P set based on the injection pattern p When the pressure boost switch command is output, the pressure boost switch command is f This makes it possible to avoid deterioration in casting quality and productivity due to a delay or an early start of pressure increase relative to the casting temperature, thereby providing a quality product.

[0083] In addition to the above, the configurations given in the above embodiments can be selected or appropriately changed to other configurations without departing from the spirit of the present invention. [Explanation of symbols]

[0084] 1. Die casting machine 2 Fixed mold 3 Movable mold 4 Cavity 5 Mold clamping device 6 Runner 7 Gate 8 Sensors 10 Injection device 11 Sleeve 12 Plunger 13 Molten metal 20 Hydraulic circuit 21 Injection cylinder 22 Charging accumulator 22A, 23A Piston 22B,23B Filling chamber 23 Pressure booster accumulator 24 Hydraulic Pump 25 Flow control valve 25A servo motor 27 Check valve 28 Storage Tank 30 Control device 31 Control device main body 32 Monitors 33 External storage medium 51 Fixed Platen 121 Chips 121S Chip area 122 Rod 123 Coupling 210 Piston 210H Piston Head 210HS Piston head side area 210R piston rod 210RS Piston rod side area 211 Cylinder body 261~264 On-off valve 311 Arithmetic unit 312 Memory 313 Storage section 314 Input / output section 315 Retrospective time calculation section 316 Last Position Identification Unit 317 Preceding Switching Position Calculation Unit A Requirements A1 Injection filling process A2 Pressure increase process C1 Inflow oil chamber C2 Drain oil chamber P n ,P n-1 ,P n+1 ,P0~P6 speed switching position Pp Switch position first P vp Increase pressure switching position S1 Section 1 S2 Section 2 S3 Section 3 (Acceleration Section) S4 Section 4 (High-speed section) S5 Section 5 (Deceleration Section) S6 Section 6 (low speed section before filling) SA,SB interval t,T n ,T1~T6 time T bn ,T b0 ~T b5 Back in time T d Delay time T p ,T vp time V In Initial velocity V pn ,V p0 ~V p6 speed t f When filling is completed t s When pressure increase starts α,α n ,α n+1 ,α1~α6 acceleration

Claims

1. A control device used to set and control an injection device of a die casting machine, comprising: The plunger of the injection device changes speed at a plurality of speed switching positions in an injection stroke for injecting molten metal into a cavity, The control device includes: an injection pattern capable of identifying the plurality of speed switching positions and the speeds corresponding to the plurality of speed switching positions; a pressure increase switching position corresponding to a position for switching from injection filling, which injects and fills the molten metal into the cavity, to pressure increase, which increases the pressure of the molten metal in the cavity; Based on the delay time required for switching from the completion of the filling to the start of the pressure increase, A preceding switching position can be set by tracing back a delay displacement amount as a displacement amount of the plunger corresponding to the delay time from the pressure boost switching position, The control device includes: When the length from the pressure increase switching position to the speed switching position immediately before the pressure increase switching position is shorter than the delay displacement amount, the preceding switching position is set to be located back from the pressure increase switching position by more than one speed switching position, and a command to start the pressure increase at the preceding switching position in the injection stroke is output; and The control device includes: a preceding switch position calculation unit that calculates the preceding switch position from the pressure increase switch position, The preceding switching position calculation unit is a retroactive time calculation unit that calculates a retroactive time from the pressure increase switching position to each of the plurality of speed switching positions for each of the speed switching positions; a previous position specifying unit that specifies a previous position, which is the speed switching position immediately before the preceding switching position, based on the retroactive time and the delay time; and a preceding switching position calculation unit that converts a time from the previous position to the preceding switching position into the preceding switching position. Control device for die casting machines.

2. The injection stroke includes a plurality of sections that are divided by the plurality of speed switching positions, The injection stroke includes, as the section, an acceleration section in which the moving plunger is accelerated from a first speed, and a high speed section in which the plunger is moved at a second speed after passing through the acceleration section, The pressure boost switch position is in the high speed section, A length from the pressure boost switching position to the speed switching position corresponding to the start point of the high speed section is shorter than the delay displacement amount. The control device for a die casting machine according to claim 1.

3. The injection stroke includes a plurality of sections that are divided by the plurality of speed switching positions, The injection stroke includes, as the sections, an acceleration section in which the moving plunger is accelerated from a first speed, a high-speed section in which the plunger is moved at a second speed through the acceleration section, a deceleration section following the high-speed section, and a low-speed section before the completion of filling in which the plunger is moved at a third speed through the deceleration section, The pressure increase switching position is in the low speed section before the completion of filling, A length from the pressure increase switching position to the speed switching position corresponding to the start point of the low speed section before the completion of filling is shorter than the delay displacement amount. The control device for a die casting machine according to claim 1.

4. The control device includes a storage unit that stores data, when the control device acquires the preceding switching position for each of the plurality of injection patterns used in the injection device, the control device associates the preceding switching position with the injection pattern and stores the preceding switching position as data in the storage unit. The control device for a die casting machine according to any one of claims 1 to 3.

5. A die casting machine control device according to any one of claims 1 to 4, The injection device; A hydraulic circuit used to drive the injection device. Die casting machine.

6. A casting method for injecting and filling a molten metal into a cavity while changing the speed of a plunger provided in an injection device of a die casting machine at a plurality of speed switching positions in an injection stroke of the plunger, comprising: a first step of setting a preceding switching position that goes back beyond one or more of the speed switching positions from the pressure increase switching position and a delay displacement amount as a displacement amount of the plunger corresponding to the delay time, based on the multiple speed switching positions, an injection pattern that can identify the speeds corresponding to the multiple speed switching positions, a pressure increase switching position that corresponds to a position where a switching is made from an injection filling in which the molten metal is injected and filled into the cavity to a pressure increase in which a pressure of the molten metal in the cavity is increased, and a delay time required for switching from the completion of the filling to the start of the pressure increase; and a second step of outputting a command to start the pressure increase at the advance switch position in the injection stroke, In the first step, calculating a retroactive time from the pressure increase switching position to each of the plurality of speed switching positions for each of the speed switching positions; A previous position, which is the speed switching position immediately before the preceding switching position, is identified from the retroactive time and the delay time; The time from the immediately preceding position to the preceding switching position is converted into the preceding switching position. Casting method.

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