JPH09323150A - Method and device for controlling injection of die casting machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection control method which can produce high quality die casting products without causing any burrs even by using high speed casting and low precise die, and a device therefor. SOLUTION: A pressure boosting control valve 21 is defined as a flow rate variable type, and a main spool 211 is constituted of a two-way valve 212 provided with non-return valve function and a positional director 213 for servo control. By this constitution, a working oil supplying flow rate to a pressure boosting cylinder device 20 is not ON/OFF control but is made variable, and the occurrence of the burrs can be prevented by controlling the pressure boosting operation according to the burr critical curve, thus the high quality die casting products can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection control method and a control apparatus for a die casting machine, and more particularly, to an injection control of a die casting machine for producing a high-quality die casting product without burrs.

[0002]

2. Description of the Related Art It has been known that the quality of a die cast product is greatly affected by an injection speed and an injection pressure when a molten metal is filled in a mold. In particular, it is necessary to perform sufficient pressurization within the time until the molten metal is solidified, and a die casting machine having a two-stage drive cylinder device for injection and pressure is used.

In general, in this type of die casting machine, the injection plunger is first advanced at a low speed, and filling of the mold cavity with the molten metal is started so as to avoid foaming of the molten metal. When the tip of the molten metal reaches the gate of the mold and the pressure of the injection cylinder device for filling rises, the injection plunger is advanced at high speed to avoid the temperature drop of the molten metal, and the molten metal is rapidly injected into the mold cavity. Fill.

Following these injection operations, whether the mold is filled with molten metal and the pressure of the injection cylinder device is further increased,
Alternatively, when the injection plunger advances to a predetermined position corresponding to the completion of filling, a high pressure is applied to the injection cylinder device by the pressure boosting cylinder device to increase the pressure applied to the molten metal in the mold by the injection plunger. .

A conventional two-stage cylinder type die casting machine will be specifically described below. In FIG. 7, a die casting machine 90 supplies a molten metal 92 to be filled into a mold cavity 91 into an injection sleeve 93, and a filling injection cylinder device 95.
The injection plunger 94 is driven to perform injection, and after filling is completed, the working oil on the back side of the injection cylinder device 95 is pressurized to a high pressure by a large-diameter booster cylinder device 96, and is injected into the mold cavity 91 via the injection cylinder device 95. The pressure of the filled molten metal 92 is increased.

FIG. 8 shows an injection speed transition CV and an injection pressure transition CP in the injection operation or the boosting operation in the die casting machine 90. In this figure, the advance of the injection cylinder device 95 is initially advanced at a low speed VL, and at time t1
At a stretch, it is filled with high-speed VH at once,
The cylinder is braked by the charging pressure of
Is activated to raise the pressure, the molten metal 92 in the mold cavity 91 reaches the pressure PH, and the injection cylinder 95 further advances and stops at time t3. This position is the stroke end of the injection cylinder device 95.

The linkage control (switching from the injection operation to the boosting operation) between the injection cylinder device 95 and the boosting cylinder device 96 in such a die casting machine 90 includes a sequence valve system for detecting a change in the injection pressure and performing switching. In addition, a limit switch method is adopted in which the switching is performed by detecting the forward position of the injection plunger. Among them, the following hydraulic circuit is used in the sequence valve system.

In FIG. 9, an injection cylinder device 95 includes:
An injection-side hydraulic circuit 114 is connected to an accumulator 113 via a check valve 111 and an injection speed adjusting valve 112. The boost valve cylinder 96 has a sequence valve 115
A boost pressure side hydraulic circuit 117 is connected to an accumulator 113 via a pilot-operated boost pressure control valve 116 which is opened and closed by the pressure control.

The sequence valve 115 is connected to the injection side hydraulic circuit 1
When the pressure of 14 exceeds a preset pressure start pressure, the pressure control valve 116 is set to be opened. Accordingly, the operation of the injection speed adjustment valve 112 starts the forward movement of the injection cylinder device 95 to perform injection, and the filling pressure increases with the completion of the filling of the molten metal into the mold, and reaches a predetermined pressure start pressure. At this time, the sequence valve 115 is activated and the boost control valve 116
Is opened, the forward movement of the booster cylinder device 96 is started, and the pressure is increased.

FIG. 10 specifically shows the peripheral portions of the injection cylinder device 95 and the boost cylinder device 96.
The injection cylinder device 95 has an injection piston 95A inside, and the injection piston 95A is adapted to move forward on the back side thereof by the hydraulic pressure of hydraulic oil supplied from the injection hydraulic circuit 114. Hydraulic oil from the injection-side hydraulic circuit 114 is adjusted in flow rate by the injection speed adjusting valve 112, whereby the injection piston 95A
Is switched between forward and stop, and the forward speed is adjusted.

The pressurizing cylinder device 96 has a pressurizing piston 96A inside, and the pressurizing piston 96A moves forward by the hydraulic pressure of hydraulic oil supplied from a pressurizing hydraulic circuit 117 on the back side thereof.
The injection piston 95A is adapted to be pressurized from the rear surface via the intermediate member 95B of the injection cylinder device 95. The hydraulic fluid from the boost hydraulic circuit 117 is intermittently controlled by the boost control valve 116, and the forward movement and the stop of the boost piston 96A are thereby switched. The intermittent operation of the boost control valve 116 is performed by the sequence valve 1
Done at 15. As the sequence valve 115, an electromagnetic valve or the like that switches according to the filling pressure by appropriate means is used.

[0012]

By the way, in the conventional two-stage die casting machine as described above, in the step-up operation of boosting the injection cylinder device by the boost cylinder device,
The flow rate of the hydraulic oil supplied to the boosting cylinder device is constant without being variably controlled. This is because the hydraulic oil to the boosting cylinder device is interrupted by a boosting control valve, and a conventional on-off 2-position switching type constant flow valve is conventionally used as the boosting control valve.

Since the supply of hydraulic oil to such a booster cylinder device is at a constant flow rate, the boosting characteristic of the casting pressure is shown in FIG.
, And the rising curve becomes a quadratic curve whose slope gradually becomes gentler as it approaches the maximum pressure PH. This is because the injection plunger receives resistance as the molten metal solidifies in the mold, and the pressure rise becomes slow. Specifically, the casting pressure P is proportional to the square root of the product of the elapsed time t and the coefficient a.

On the other hand, in a boosting operation, a burr critical boosting curve is known. The burr is generated when molten metal leaks out from the divided surface of the mold when excessive pressure is applied to the mold during pressurization. However, no burr is generated if the pressure is below the burr critical pressure rise curve. The burr critical curve is given as a curve CX in which the casting pressure P is proportional to the product of the square of the elapsed time t and the coefficient a (see FIG. 8). Bali Critical Curve CX
However, such a quadratic curve is caused by the fact that the molten metal in the mold is not solidified at the expected stage of pressurization, the fluidity of the molten metal is high, and leakage from the dividing surface is likely to occur, and high pressure On the other hand, when the molten metal solidifies over time, it does not easily leak to the divided surface, and no burr occurs even when high pressure is applied.

Therefore, in a conventional die-casting machine in which the supply of hydraulic oil to the pressurizing cylinder device is at a constant flow rate, the pressurizing characteristic of the casting pressure cannot be brought close to the burr critical curve. In the case where a mold having a low accuracy of the dividing surface is used, burrs occur frequently, and a problem has arisen that a high-quality die-cast product cannot be produced.

It is an object of the present invention to provide an injection control method and apparatus for a die casting machine which can produce high quality die cast products without burrs even in high speed casting and low precision dies.

[0017]

According to the method of the present invention, an injection plunger for injecting molten metal into a casting mold, an injection cylinder device for driving the injection plunger, and a boosting cylinder device for increasing the hydraulic pressure applied to the injection cylinder device. And a flow rate control valve having a check valve function, the flow rate control valve having a main spool for controlling the flow rate of hydraulic oil to the pressure boosting cylinder device. Of the main spool of the flow control valve and a booster control device that quantitatively controls the main spool of the flow control valve based on a predetermined program. , The main spool is controlled to an arbitrary opening from the full opening to the final opening, and the casting die is free from any burr on a predetermined critical curve. And controlling the boosting operation so that the relationship between the casting pressure and the boosting time according to curve changes.

In this way, during the pressure raising operation, the flow rate of the hydraulic oil supplied to the pressure raising cylinder device can be varied instead of on / off, and the generation of burrs can be prevented by controlling the pressure raising operation according to the burr critical curve. Can be prevented, which allows the production of high quality die cast products.

In this method, the injection plunger is advanced by the injection cylinder device to start the injection operation, and a high response electrohydraulic servo two-way valve installed in the hydraulic oil discharge path of the injection cylinder device is used. The back pressure control valve controls the back pressure of the injection cylinder device to perform feedback control of the forward position and speed of the injection plunger, and when the injection cylinder device reaches the deceleration start position a predetermined distance before the stroke end, When the injection cylinder device is decelerated, and when the injection cylinder device reaches the back pressure release position on the stroke end side from the deceleration start position, the back pressure control valve is fully opened to release the back pressure of the injection cylinder device, and the injection is performed. When the cylinder device reaches the boosting start position near the back pressure release position, the booster cylinder device raises the pressure. It starts operation, and it is desirable to perform the boost control by the opening control of the main spool.

With this configuration, even in the injection operation,
Backward pressure can be variably controlled by the back pressure of the injection cylinder device, and when shifting to boosting operation, the back pressure control of the injection cylinder device can be released to effectively boost the pressure, producing high-quality die cast products. Is effective for.

The apparatus of the present invention is of a boosting type having an injection plunger for injecting molten metal into a casting mold, an injection cylinder device for driving the injection plunger, and a boosting cylinder device for boosting the hydraulic pressure applied to the injection cylinder device. An injection control device for a die-casting machine, wherein the injection control device controls the back pressure on the hydraulic oil discharge side of the injection cylinder device to perform position feedback control of the injection plunger,
Casting pressure adjusting means for quantitatively controlling the hydraulic pressure of the hydraulic oil applied to the boosting cylinder device to a pressure corresponding to a preset ultimate pressure of the casting pressure, and the boosting cylinder controlled by the casting pressure adjusting means. A flow control valve having a main spool for controlling the flow rate of hydraulic oil to the device and having a check valve function, a position detector for detecting the opening of the main spool of the flow control valve, and a predetermined program based on a predetermined program. Then, during the boosting operation by the boosting cylinder device, the main spool is controlled to an arbitrary opening degree from the full opening to the final opening degree, so that the casting die is free from burrs and has a predetermined critical curve. And a boost control device that controls the boost operation so that the relationship between the casting pressure and the boost time changes according to a curve.

In this way, a device that realizes cooperation with the variable operation of the hydraulic oil supply during the boosting operation and the back pressure control during the injection operation described above can be obtained, and a high quality die cast product can be manufactured.

In this apparatus, the boost control means is
A control target pressure value is preset for each predetermined elapsed time from the start of pressurization, and the opening degree of the main spool is set so that the casting pressure at each elapsed time becomes the control target pressure value for each predetermined elapsed time written. It is desirable to be characterized by controlling.

With this configuration, the flow rate of the hydraulic fluid on the left side of the pressure booster can be controlled easily, reliably and accurately every predetermined elapsed time, which is effective for realizing the variable pressure type booster control.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. The present embodiment is implemented by modifying the control method of an existing die casting machine, and a die, an injection plunger, and the like, which are main parts of the die casting machine, are of an existing type (for example, the aforementioned die casting machine).
90) may be employed as appropriate, and a description thereof will be omitted. Then, the injection cylinder device, the boost cylinder device, and the hydraulic circuit for supplying hydraulic oil to them, which are different from the existing ones, will be described below.

In FIG. 1, the injection cylinder device 10 includes:
An injection hydraulic circuit 14 is connected to the injection accumulator 13 via a pilot check valve 11 for interrupting the injection operation. Check valve 11 is an electromagnetic switching valve 12 for opening and closing
By operating this switching valve 12, the check valve 11 is opened, hydraulic oil from the injection side accumulator 13 is supplied to the injection cylinder device 10, and the injection piston
15 are going to move forward. Check valve 11
When the flow of hydraulic oil from the injection side accumulator 13 to the injection cylinder device 10 stops and the pressure difference between the inlet side and the outlet side disappears, the internal spring moves the valve element to prevent the reverse flow of hydraulic oil during boosting operation. It is designed to prevent it.

The injection cylinder device 11 includes an injection piston 15
A hydraulic oil discharge path 16 for discharging hydraulic oil on the front side is connected to the hydraulic oil discharge path 16, and a flow rate control valve 17 for controlling an injection speed is connected to the hydraulic oil discharge path 16. Injection speed control flow control valve 17
Is composed of a high-speed response type large flow rate servo valve.The opening is adjusted to narrow the hydraulic oil discharge path 16 when the injection cylinder device 11 moves forward, and apply a back pressure to the injection piston 15 to adjust the advance speed. I can do it.

The boost cylinder device 20 includes a boost control valve 21 for controlling a boost time, the opening of which is controlled by a pilot servo valve 22.
Pressure side hydraulic circuit that reaches the pressure side accumulator 23 via the
24 is connected, and the boost servo control valve 21 is opened by operating the pilot servo valve 22, and the hydraulic oil from the boost accumulator 23 is supplied to the boost cylinder device 20, and the boost piston
25 are going forward.

As shown in FIG. 2, the boost control valve 21 constitutes an electrohydraulic two-stage servo valve in which the high-speed response type pilot servo valve 22 serves as an auxiliary servo valve and the main spool 211 serves as a main servo valve. The main spool 211 has a flow control two-way valve 212 with a check valve function at one end and a position detector 213 at the other end. By controlling the pilot servo valve 22 by feeding back the opening position by the position detector 213, the boost control valve 21 can be adjusted to an arbitrary opening.

As a result, the boost control valve 21 is a check valve,
In addition to the function as a two-way valve, it also has a function as a flow control valve. That is, at the time of the injection operation before the boost operation, if the boost servo control valve 21 is closed by operating the pilot servo valve 22, the hydraulic oil from the boost accumulator 23 is supplied to the boost cylinder device 20. While not being supplied, backflow from the booster cylinder device 20 is prevented. On the other hand, during the boost operation, the pilot servo valve 22
To open the pressure control valve 21 and
By arbitrarily adjusting the opening position of 2, the hydraulic oil from the booster accumulator 23 is supplied to the booster cylinder device 20, and the flow rate of the hydraulic oil to the booster cylinder device 20 can be arbitrarily adjusted.

Returning to FIG. 1, the injection-side accumulator 13 and the pressure-increasing accumulator 23 are connected to a hydraulic oil supply passage 31 from a hydraulic source, and high-pressure hydraulic oil is supplied to each. An electromagnetic accumulator filling switching valve 32 is installed in the middle of the hydraulic oil supply path 31 to intermittently supply hydraulic oil to the accumulators 13 and 23. A branch path 33 from the hydraulic oil supply path 31 is connected to the back side of the booster accumulator 23, and an electromagnetic casting pressure control valve 34 is provided in the middle of the branch path 33.

This casting pressure control valve 34 feeds hydraulic oil from a hydraulic pressure source to increase the back pressure of the pressure increasing side accumulator 23, so that the maximum oil pressure of the pressure increasing side hydraulic circuit 24 becomes high, and in addition to the pressure increasing cylinder device 20, The maximum casting pressure that can be achieved is increased. Conversely, by discharging the hydraulic oil by the casting pressure control valve 34 and lowering the back pressure of the booster side accumulator 23, the maximum hydraulic pressure of the booster side hydraulic circuit 24 becomes lower, and the maximum casting pressure applied to the booster cylinder device 20 is reduced. Will be alleviated.

A pressure sensor 35 for detecting the pressure on the back side is installed in the boosting side accumulator 23 so that the back pressure value of the boosting side accumulator 23 can be referred to when adjusting the casting pressure. The injection cylinder device 10 is provided with a pressure sensor 36 for detecting the casting pressure so that the injection pressure value can be directly referred to when adjusting the casting pressure. In reality, the injection pressure PR is a value obtained by multiplying the detected pressure PS by the square of (D1 / D2), depending on the ratio of the diameter D1 of the injection piston 15 and the diameter D2 of the injection plunger 151.

The injection cylinder device 10 includes an injection plunger.
An encoder 152 that detects the forward movement position of the 151 is installed so that the stroke position during the injection operation can be directly detected.

A control device 40 is provided to receive signals from each of these sensors and control the operation of each valve. The control device 40 is mainly configured by an existing computer system, a programmable controller, and the like.
Each of the valves is operated in a predetermined procedure based on a preset operation program to execute an injection operation or a boosting operation.

The control device 40 has a control circuit for controlling the boost control valve 21 to cause the boost cylinder device 20 to perform a boost operation. In FIG. 4, the control device 40 has a servo amplifier 41, and sends an open / close command to the boost control valve 21 via the servo amplifier 41 when performing the boost operation based on a preset program. When the boost control valve 21 opens, the boost cylinder device 20 operates in accordance with the opening, and the opening of the boost control valve 21 (open position of the main spool 211) in that state is detected by the position detector 213. , And is returned to the control device 40 via the position feedback amplifier 42. As a result, feedback control of the boost control valve 21 is performed, and the boost characteristics of the boost operation can be finely controlled.

FIG. 5 shows another form of the feedback control system of the boost control valve 21. In this figure, the command based on the preset program is the preamplifier 43.
And it is sent to the boost control valve 21 via the main amplifier 44.
The boost control valve 21 opens and the boost cylinder device 20
Is activated, and the opening of the boost control valve 21 in that state is detected by the position detector 213, which is the same as the control system of FIG. 4 described above, but the opening signal from the position detector 213 indicates the position. After passing through the feedback amplifier 42, a part is returned to the main amplifier 44 as a minor feedback signal and a part is returned to the preamplifier 43 as a position feedback signal. By doing so, the stability and accuracy of the servo control system can be improved.

In the above-mentioned configuration, the control device 40
Controls each part based on a predetermined program and executes a desired injection operation or boosting operation. That is, when the molten metal is supplied to the injection sleeve and it is ready to be injected into the mold, the check valve 11 is opened to supply the hydraulic oil from the injection side accumulator 13 to the injection cylinder device 10, and the injection plunger 151. To move forward. At this time, the injection speed control flow rate control valve 17 is throttled so that the injection speed is low.

Next, when the injection plunger 151 moves forward to the position where the molten metal reaches the mold gate, the injection speed controlling flow control valve 17 is opened to switch the injection at high speed to fill the mold with the molten metal at a stretch. When the injection plunger 151 advances to a position where the molten metal fills the mold, the check valve 1
The injection operation is stopped by closing 1, the injection speed control flow control valve 17 is opened in preparation for the pressure increasing operation, and the back pressure braking of the injection plunger 151 is completely released.

Now, operate the pilot servo valve 22,
Open the pressurizing control valve 21 to a predetermined opening, and pressurize the accumulator
Hydraulic oil from 23 is supplied to the pressurizing cylinder device 20 to pressurize the injection plunger 151 from the back of the injection piston 15. At this time, the opening of the boost control valve 21 is throttled, and the opening is changed in the middle to control the pressure in the middle of boosting and the time to reach the maximum pressure. Draw a boost curve that is asymptotic to the critical curve.

In FIG. 6, the pressure increasing curve CP1 is a gradually increasing pressure increasing curve that can be obtained even with an existing die casting machine. On the other hand, when the opening degree of the boost control valve 21 is reduced, the slope of the pressure increase becomes gentle as shown by the boost curve CP2, and the time to reach the maximum pressure PH becomes longer. And furthermore, the pressure increase control valve
When the opening degree of the throttle valve 21 is reduced, the pressure rises rapidly later as in the boost curve CP3, and reaches the maximum pressure PH at time t4. The boost curve CP3 is similar to the burr critical curve CX in FIG.

In the control device 40, the above-described control for narrowing the opening of the boost control valve 21 and changing the opening midway is performed by pre-storing the opening target value every predetermined time from the start of the boosting operation. It is realized by performing feedback control of the boost control valve 21 while sequentially changing the opening to be currently taken as a target according to the lapse of time from the start of the boost operation during operation. Further, by the learning function of the control device 40, the actual injection pressure is checked from the pressure sensor 36 at the time of the previous pressurization operation, the deviation from the assumed injection pressure is taken, and the opening target value of the boost control valve 21 is set. It can be corrected. The processing of these control target data and the correction by the learning function can be appropriately realized by the existing software technology.

According to the present embodiment, the flow rate of the hydraulic oil supplied to the boosting cylinder device 20 can be changed by the boosting control valve 21 and the control device 40 during the boosting operation instead of on / off. By controlling the boosting operation in accordance with the curve CX, it is possible to prevent the occurrence of burrs beforehand, whereby high-quality die-cast products can be produced.

Particularly, the boost control valve 21 is connected to the main spool 211.
Since the two-way valve with check valve function is configured to be servo-controllable by the position controller 213, the above boost control can be reliably performed with a simple configuration.

Further, the injection speed controlling flow control valve 17 can variably control the forward movement state of the injection cylinder device 10 by the back pressure even during the injection operation, and when the pressure increasing operation is started, the back pressure of the injection cylinder device 10 is changed. The pressure control can be released to effectively increase the pressure, which is effective for producing high quality die cast products. Further, the control device 40 can easily, reliably, and accurately control the hydraulic oil flow rate at the same time as the pressure increase at every predetermined elapsed time, which is effective in realizing the above-described variable flow rate type pressure increase control.

Further, since the injection side accumulator 13 and the boosting side accumulator 23 are separated, the pressure setting for the injection operation and the boosting operation can be individually performed. Since the back pressure of the boosting side accumulator is adjusted by the casting pressure control valve 34, arbitrary adjustment of the maximum pressure by the boosting operation can be performed easily and reliably.

It should be noted that the present invention is not limited to the above-described embodiment, and the following modifications and the like are also included in the present invention. That is, the injection side accumulator
The booster 13 and the accumulator 23 may be shared instead of being provided separately. Further, the accumulator filling switching valve 32, the pressure sensors 35 and 36 of each section, the encoder 152, and the like may be appropriately replaced with another configuration, or may be omitted as necessary. Furthermore, the shape, size, material, and the like of each component such as the boost control valve 21 and the flow rate control valve 17 for controlling the injection speed may be appropriately selected in implementation.

[0048]

As described above, according to the present invention,
During boosting operation, the flow rate of hydraulic oil supplied to the boosting cylinder device can be set to a variable flow rate instead of on / off, and burr can be prevented by controlling the boosting operation according to the burr critical curve. Be able to produce quality die casting products.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a sectional view showing the cylinder device of the embodiment.

FIG. 3 is an enlarged sectional view showing a main part of the cylinder device.

FIG. 4 is a block diagram showing a control system of the embodiment.

FIG. 5 is a block diagram showing another form of the control system of the embodiment.

FIG. 6 is a graph showing an injection or boosting operation of the embodiment.

FIG. 7 is a sectional view showing a basic configuration of a conventional die casting machine.

FIG. 8 is a graph showing an injection or boosting operation of a conventional die casting machine.

FIG. 9 is a circuit diagram showing a hydraulic circuit of a conventional die casting machine.

FIG. 10 is a sectional view showing a conventional cylinder device.

[Explanation of symbols]

 10 Injection cylinder device 13 Injection side accumulator 15 Injection piston 151 Injection plunger 16 Hydraulic oil discharge route 17 Injection speed control flow control valve 21 Boost control valve 211 Main spool 212 Two-way valve with check valve function 213 Position detector 23 Boost side Accumulator 34 Casting pressure control valve 40 Controller

Claims (4)

[Claims] 1. An injection of a boosting type die casting machine having an injection plunger for injecting molten metal into a casting mold, an injection cylinder device for driving the injection plunger, and a boosting cylinder device for boosting the hydraulic pressure applied to the injection cylinder device. A control method, comprising: a flow control valve having a main spool for controlling a flow rate of hydraulic oil to the boost cylinder device and having a check valve function; and a position for detecting an opening degree of the main spool of the flow control valve. A detector and a boost control device that quantitatively controls the main spool of the flow control valve based on a predetermined program are used, and during the boost operation by the boost cylinder device, the main spool is fully opened to the final opening degree. Control to an arbitrary opening between and until casting pressure and pressure rise according to an arbitrary curve along a predetermined critical curve that does not cause burrs in the casting mold. Injection control method for a die casting machine and controlling the boosting operation so that the relationship changes with. 2. The injection control method for a die casting machine according to claim 1, wherein the injection cylinder device advances the injection plunger to start an injection operation, and the injection cylinder device is installed in a hydraulic oil discharge path of the injection cylinder device. With a back pressure control valve using a high response electro-hydraulic servo two-way valve, the back pressure of the injection cylinder device is controlled to feedback-control the forward position and speed of the injection plunger, and the injection cylinder device has its stroke end The injection cylinder device is decelerated when the deceleration start position before the predetermined distance is reached, and when the injection cylinder device reaches the back pressure release position on the stroke end side from the deceleration start position, the back pressure control valve is fully opened to cause the injection cylinder. The back pressure of the device is released, and the injection cylinder device is near the back pressure release position The starts the boosting operation by the boost cylinder device, and an injection control method for a die casting machine and performing step-up control by the opening control of the main spool reaches the location. 3. A pressurizing die casting machine having an injection plunger for injecting a molten metal into a casting mold, an injection cylinder device for driving the injection plunger, and a boosting cylinder device for boosting the hydraulic pressure applied to the injection cylinder device. A control device, in which injection control means for controlling back pressure on the hydraulic oil discharge side of the injection cylinder device to perform position feedback control of the injection plunger, and hydraulic pressure of hydraulic oil applied to the boost cylinder device are preset. The casting pressure adjusting means for quantitatively controlling the pressure corresponding to the highest reached casting pressure, and the main spool for controlling the flow rate of the hydraulic oil to the boosting cylinder device which is controlled by the casting pressure adjusting means. Flow control valve having a check valve function and position detection for detecting the opening of the main spool of this flow control valve Based on a predetermined program, the main spool is controlled to an arbitrary opening between the full opening and the final opening during the boosting operation by the boosting cylinder device so that a burr does not occur in the casting mold. An injection control device for a die casting machine, comprising: a boost control device that controls the boost operation so that the relationship between the casting pressure and the boost time changes according to an arbitrary curve along the critical curve. 4. The injection control device for a die casting machine according to claim 3, wherein the boost control means sets a control target pressure value in advance every predetermined elapsed time from the start of boosting, and each elapsed time thereof. In the injection control device for a die casting machine, the opening of the main spool is controlled so that the casting pressure reaches a control target pressure value for each predetermined elapsed time.