JP7628457B2 - Die casting device and die casting manufacturing method - Google Patents

Description

The present invention relates to a die casting device and a die casting manufacturing method.

In a die casting machine, after the fixed and movable dies are mated, molten metal is injected into the cavity formed inside, and a product is formed that matches the shape of the cavity. The molten metal pushed out from the injection device fills the cavity through a gate. Since the cavity is filled with gas (air), a gas vent passage is opened in the cavity in advance, and when the molten metal is filled into the cavity, the internal gas is pushed out into the gas vent passage, which is then released into the atmosphere.

It is generally known that in aluminum alloy castings, internal voids (cavities) occur during solidification shrinkage, centered around the part where the molten metal filled in the mold solidifies most slowly during casting. For example, when an aluminum alloy casting is used to construct a component to which compressive pressure is applied, such as a cylinder block for an internal combustion engine, pressure leakage is likely to occur when the above-mentioned cavities are concentrated and connected to each other. Therefore, in order to improve product yield, it is necessary to suppress the occurrence of cavities large enough to lead to pressure leakage.

Patent document 1 describes an injection device having a position sensor that detects the position of a plunger that can slide inside a sleeve that leads into a mold, an injection pressure sensor that detects the injection pressure that the plunger applies to the molding material in the sleeve, and a control device, in which the control device has a gate arrival time determination unit that determines the gate arrival time when the plunger reaches a predetermined gate arrival position as injection progresses based on the detection value of the position sensor, and a filling start time determination unit that determines the filling start time when the injection pressure exceeds a predetermined filling start pressure as injection progresses within a predetermined monitoring period including the gate arrival time based on the detection value of the injection pressure sensor. The injection device described in patent document 1 is said to be able to appropriately determine the start of filling of the molding material.

Patent Document 2 describes a blowhole tendency management device that has a recess measurement unit that measures the amount of recesses in the appearance characteristic parts of the surface of a casting, and an estimation unit that estimates the amount of blowholes based on the correlation between the amount of recesses measured by the recess measurement unit and the amount of blowholes inside the casting. The blowhole tendency management device described in Patent Document 2 is said to be able to estimate the amount of blowholes in a short time and with high accuracy.

JP 2019-150861 A JP 2016-68100 A

However, in the devices of Patent Documents 1 and 2, although the casting conditions are managed, it cannot be said that the management conditions and traceability of defective products have been established.
The conditions that will definitely result in a defective product are rejected (discarded) by the die-casting machine, but the current situation is that defective products are being produced even though the conditions are cleared. The fact that the occurrence of blowholes that cannot be detected by appearance cannot be detected from the casting conditions is one of the factors that makes it difficult to establish the quality of high-pressure die-cast products.
They are trying to extract factors that cause defects from data on defective products by saving as much data as possible, not only on injection conditions but also on mold cooling conditions, amount of release agent applied, dilution rate, amount of injection lubricant applied, etc., but they are not getting sufficient results.

One of the causes of blowholes is insufficient pressure due to the pressure not being transmitted to the product even when the die casting equipment is applying pressure normally.
In addition, although the method of detecting the pressure inside the mold is possible in experiments, etc., it is not durable enough for mass production and cannot be used under the current circumstances.

The present invention was made in light of this background, and aims to provide a die-casting device and a die-casting manufacturing method that enable real-time verification of internal quality that cannot be detected by appearance.

In order to solve the above problem, the die casting machine described in claim 1 is a die casting machine that has a fixed mold and a movable mold, and molds a casting product by injecting molten metal into a cavity formed by the fixed mold and the movable mold using the pushing force of a plunger that slides inside a sleeve, and is equipped with a position detection means that detects the position of the plunger, an injection pressure detection means that detects the injection pressure inside the sleeve, and a control device that controls the pushing force of the plunger, and the control device detects the peak pressure of the injection pressure generated in the pressure boosting process after the plunger completes injection, detects the injection position when the injection pressure reaches the peak pressure, and predicts the occurrence of defects in the casting product according to the boosted pressure distance moved by the plunger from the injection position after the peak pressure is reached.

The present invention provides a die-casting device and a die-casting manufacturing method that allows for real-time verification of internal quality that cannot be detected by appearance.

1 is a diagram showing an overall configuration of a die casting apparatus according to an embodiment of the present invention; 3A to 3C are diagrams illustrating an injection process and an injection waveform of the die casting device according to the embodiment of the present invention. FIG. 3 is a table showing the notation of each part of the injection process and the injection waveform in FIG. 2 . 3A to 3C are diagrams illustrating a velocity curve, a pressure curve, and an injection position in an injection process of a die casting device according to an embodiment of the present invention. FIG. 5 is an enlarged view showing the velocity curve, pressure curve, injection position, and peak pressure position in the injection process of FIG. 4. 5 is a flowchart showing a die-casting pressure transmission failure determination process of the die-casting device according to the embodiment of the present invention. FIG. 13 is a diagram showing an example of actual measurement of a die-casting pressure transmission failure judgment of the die-casting device according to the embodiment of the present invention. 13 is a flowchart showing a die-casting pressure transmission failure determination process of a die-casting device according to a modified example of an embodiment of the present invention.

Next, a die casting apparatus and a die casting manufacturing method according to an embodiment of the present invention will be described in detail with reference to the drawings as appropriate. This embodiment is an example of application to a high pressure die casting apparatus. In each drawing, common parts are given the same reference numerals and duplicated explanations will be omitted.
(Embodiment)
FIG. 1 is a diagram showing the overall configuration of a die casting apparatus according to an embodiment of the present invention.
As shown in FIG. 1, a die casting apparatus 10 includes a fixed mold 11, a movable mold 12, and a cavity 13 that serves as a mold and is formed between the fixed mold 11 and the movable mold 12.
A molten metal supply unit 14 is disposed in the fixed die 11, and the molten metal supply unit 14 includes a cylindrical sleeve 15, a molten metal supply port 16 that opens at the top of the base end side of the sleeve 15, and a plunger 17 as a pressing member that can move forward and backward and slides along the inner circumferential surface of the sleeve 15. The plunger 17 has a plunger tip 17a that can slide in the forward and backward directions within the sleeve 15, and a plunger rod 17b whose tip is fixed to the plunger tip 17a.

The tip of the sleeve 15 communicates with a runner 18. The runner 18 extends into the movable mold 12 and is connected to the cavity 13 via a gate 19. The gate 19 introduces molten metal (hereinafter referred to as molten metal 20) made of aluminum or an aluminum alloy extruded from the sleeve 15, which is a molten metal injection portion, into the cavity 13.
Molten metal 20 is supplied from a ladle 21 through a melt supply port 16 into the sleeve 15 , and the melt 20 is injected into the cavity 13 through a gate 19 by pushing out a plunger 17 .

(Injection drive unit 30)
The plunger 17 is actuated by an injection drive unit 30 .
The injection drive unit 30 is of a hydraulic type and includes an injection cylinder 32 that drives the plunger 17, and an injection control drive unit 33 that supplies hydraulic fluid (e.g., oil) to the injection cylinder 32. In detail, the injection drive unit 30 includes an injection piston 31, an injection cylinder 32, and an injection control drive unit 33 for performing the injection and filling process, a booster piston 34, a large-diameter booster cylinder 35, and a booster control drive unit 36 for performing the boosting process, a piston rod 37, and a coupling unit 38 that mechanically couples the plunger rod 17b and the piston rod 37.
The injection control drive unit 33 supplies hydraulic fluid to the injection cylinder 32. The boost control drive unit 36 supplies hydraulic fluid to the boost cylinder 35.

The injection control drive unit 33 and the boost control drive unit 36 are specifically hydraulic devices. This hydraulic device has, for example, a tank that stores hydraulic fluid, a pump (hydraulic pressure source) that can pump out the hydraulic fluid from the tank, an accumulator (hydraulic pressure source) that can release the accumulated hydraulic fluid, multiple flow paths that connect these and the injection cylinder 32 to each other, and multiple valves (all not shown) that control the flow of hydraulic fluid in the multiple flow paths.

In this hydraulic device, hydraulic fluid stored in a tank is supplied to the accumulator via the corresponding flow path and the corresponding valve by a pump, whereby pressure is accumulated in the accumulator. For example, hydraulic fluid is supplied from the accumulator to the head side chamber 32h via the corresponding flow path and the corresponding valve, whereby the injection piston 31 advances. The corresponding valve is a pressure compensated flow control valve (flow adjustment valve) and also a servo valve, and the flow rate of hydraulic fluid discharged from the rod side chamber 32r is controlled by this valve, thereby controlling the speed of the injection piston 31 (plunger 17).
In addition, the hydraulic fluid is supplied from the accumulator to the rear chamber 32e via the corresponding flow passage and the corresponding valve, whereby the booster piston 34 boosts the pressure.

An oil chamber is formed between the injection piston 31 and the booster piston 34, and a predetermined amount of pressurized oil is supplied to each injection cylinder 32 and booster cylinder 35 from the injection control drive unit 33 and booster control drive unit 36 via openings 32a and 35a.

The piston rod 37 is disposed within the injection cylinder 32. The interior of the injection cylinder 32 is divided into a rod side chamber 32r from which the piston rod 37 extends, and a head side chamber 32h on the opposite side. By selectively supplying hydraulic fluid to the rod side chamber 32r and the head side chamber 32h, the injection piston 31 slides back and forth within the injection cylinder 32.

The injection cylinder 32 and booster cylinder 35 are cylindrical bodies with a circular internal cross-sectional shape, and the booster cylinder 35 is formed with a larger diameter than the injection cylinder 32.

The booster piston 34 has a small diameter portion 34a that can slide inside the rear end of the injection cylinder 32 (head side chamber 32h in the illustrated example), and a large diameter portion 34b that can slide inside the booster cylinder 35. The inside of the booster cylinder 35 is divided by the large diameter portion 34b into a front side chamber 35f on the injection cylinder 32 side and a rear side chamber 35e on the opposite side.

Therefore, when the front chamber 35f is depressurized, due to the difference between the working area of the small diameter portion 34a in the head side chamber 32h and the working area of the large diameter portion 34b in the rear side chamber 35e, the booster piston 34 can apply a higher pressure to the hydraulic fluid in the head side chamber 32h than the pressure it receives from the hydraulic fluid in the rear side chamber 35e. This allows the booster cylinder 35 to perform a boosting function.

The injection cylinder 32 is arranged coaxially with the plunger 17. The piston rod 37 is connected to the plunger 17 via a coupling 38. The injection cylinder 32 and the booster cylinder 35 are fixedly mounted to a clamping device (not shown). The movement of the injection piston 31 relative to the injection cylinder 32 causes the plunger 17 (plunger tip 17a) to advance or retreat within the sleeve 15.

(Position and speed detection of plunger 17)
A position sensor 40 (position detection means) that detects the position of the plunger 17 is installed on the plunger rod 17b, and outputs a position detection signal S-1 to a controller 50 (control device). The position sensor 40 detects the position of the piston rod 37 relative to the injection cylinder 32, and indirectly detects the position of the plunger 17. For example, the position sensor 40 may be fixedly provided on the piston rod 37 and constitute a magnetic or optical linear encoder together with a scale portion (not shown) that extends in the axial direction of the piston rod 37, or may be constituted by a laser length measuring device that measures the distance to a member fixed to the piston rod 37.
The position sensor 40 and the controller 50 are able to obtain (detect) the velocity of the plunger 17 by differentiating the detected position of the plunger 17 .

(Calculation of pressure applied by plunger 17 to molten metal 20)
The injection cylinder 32 is provided with a head side pressure sensor 41 (injection pressure detection means) that detects the pressure in the head side chamber, and a rod side pressure sensor 42 (injection pressure detection means) that detects the pressure in the rod side chamber, and these sensors output detection signals S-2 and S-3 to the controller 50, respectively.
The head side pressure sensor 41 and rod side pressure sensor 42 of the injection cylinder 32 are used to indirectly detect the pressure that the plunger 17 applies to the molten metal 20, such as the pressure (injection pressure) that the plunger 17 applies to the molten metal 20 when injecting the molten metal 20 into the cavity 13. The controller 50 can calculate the pressure that the plunger 17 applies to the molten metal 20, based on the detection value of the head side pressure sensor 41, the detection value of the rod side pressure sensor 42, the pressure-receiving area in the head side chamber 32h of the injection piston 31, the pressure-receiving area in the rod side chamber 32r of the injection piston 31, and the contact area of the plunger 17 with respect to the molten metal.

(controller)
The controller 50 includes a CPU 51 , a memory 52 , an input circuit 53 , and an output circuit 54 .
The CPU 51 reads out a control program stored in a ROM or an EEPROM (Electrically Erasable Programmable Read-Only Memory), which is an electrically rewritable non-volatile memory, expands it in a RAM, and performs injection control, while executing a die-casting forging condition management program 52a to predict the occurrence of defects (see FIG. 6). The CPU 51 outputs control signals (control commands) for controlling each part via an output circuit 54 based on an input signal input via an input circuit 53.
The memory 52 is composed of a ROM, a RAM, an EEPROM, etc., which store various processing programs. The memory 52 also includes an external storage device such as a hard disk drive (HDD). The memory 52 stores control programs including a die cast forging condition management program 52a.

The controller 50 detects the peak pressure of the injection pressure generated in the pressure boosting process after the plunger 17 completes injection, detects the injection position when this injection pressure reaches the peak pressure, and predicts the occurrence of defects in the casting product according to the boosted pressure distance that the plunger 17 moves again from the injection position after the peak pressure stops. The distance that the plunger 17 moves again from the injection position after the peak pressure is the boosted pressure distance that the plunger 17 moves forward following the solidification and shrinkage of the molten metal 20 as it cools.

The controller 50 predicts the occurrence of a defect when the pressure increase distance that the plunger 17 moves again from the injection position after the peak pressure is equal to or greater than a solidification shrinkage distance that is preset based on the solidification shrinkage rate of the molten metal.
When the pressure increase distance is less than a solidification shrinkage distance that is set in advance based on the solidification shrinkage rate of the molten metal, the controller 50 determines that a defect including the occurrence of a casting cavity has occurred.
The controller 50 determines that an abnormality has occurred when the pressure increase distance is less than a solidification shrinkage distance that is preset based on the solidification shrinkage rate of the molten metal, or when the pressure increase distance is equal to or greater than a predetermined abnormality determination value.
The controller 50 predicts the occurrence of defects in the casting product based on the pressure increase distance that the plunger 17 moves again from the injection position within a predetermined time after the peak pressure.

The input circuit 53 receives input signals from an input device 55 such as a keyboard or a mouse, a position signal S-1 from the position sensor 40, a signal S-2 from the head side pressure sensor 41, and a signal S-3 from the rod side pressure sensor 42.
The output circuit 54 outputs a signal for outputting the prediction result, etc. (for example, a display signal for displaying on the display unit 56). The output circuit 54 also has a driver for driving a pump motor provided in a hydraulic device (not shown) constituting the injection control drive unit 33 and the pressure boost control drive unit 36, and outputs a control signal to the motor and an opening/closing drive signal to each valve via the driver.

(Outline of die casting operation of die casting device 10)
Fig. 2 is a diagram for explaining the injection process and injection waveform of the die casting device 10. The horizontal axis of Fig. 2 indicates time t, with the further to the right, the later the time. The vertical axis on the left side of Fig. 2 indicates the injection speed (speed of the plunger 17), with the value increasing upward. The vertical axis on the right side of Fig. 2 indicates the injection pressure (position of the plunger), with the value increasing upward, with the value decreasing toward the fixed die 11 and the movable die 12.
The velocity curve shows the change in injection velocity over time. The pressure curve shows the change in injection pressure over time.

Fig. 3 is a diagram showing a table of terms for notating each part of the injection process and injection waveform in Fig. 2. The symbols a to p in Fig. 2 correspond to the symbols a to p in Fig. 3, respectively.
The low-speed injection time a is the time during which the injection piston 31 moves at a low speed.
The high-speed injection time b is the time during which the injection piston 31 moves at high speed.
The low-speed injection acceleration time c is the time from when the injection piston 31 starts to move until it reaches the set low-speed injection speed.
The high-speed injection acceleration d is the time required to reach the set high-speed injection speed from the low-speed injection speed.

The filling pressure rise time e is the time from when the injection piston 31 has completed filling the cavity 13 with the molten metal 20 until the pressure applied to the injection piston 31 reaches the accumulator set pressure.
The boosting time lag f is the time from when the injection piston 31 has completed filling the molten metal 20 into the cavity 13 until when the injection piston 31 starts to move.
The boosting time g is the time from when the boosting piston 34 starts to move until when the boosting output is reached from the filling output.
The pressure increase time h is the time from when the injection piston 31 completes filling the cavity 13 with the molten metal 20 to when the booster piston 34 completes its operation.

The low speed injection pressure i is the pressure within the injection piston 31 when the injection piston 31 is moving forward at a low speed.
High speed injection pressure j is the pressure exerted on the injection piston 31 during high speed injection.
The filling completion pressure k is the pressure inside the injection cylinder 32 when the injection piston 31 has completed filling the molten metal 20 into the cavity 13 and before the injection piston 31 starts moving.
The boost pressure l is the pressure within the injection piston 31 when it completes its motion.
The booster surge pressure m is the surge pressure generated in the injection piston 31 when the booster piston 34 starts to move.

The low injection speed n is the injection speed in the first stage of the injection process.
The high injection speed o is the highest injection speed during the injection process.
The fast average injection velocity p is the average value of the speed at which the injection piston moves at fast velocity.

The die casting machine 10 performs low-speed injection (time t0-t1), high-speed injection (time t1-t2), pressure increase (time t3-t4), and pressure hold (time t4 and after). Note that the series of operations from low-speed injection to pressure hold is sometimes called one shot.

<Low speed injection: t0 to t1>
In the initial stage of injection, low-speed injection (see t0 to t1 in FIG. 3) is performed in which the plunger 17 is advanced at a relatively low speed, thereby suppressing entrainment of air by the molten metal 20.
Immediately before the start of low-speed injection, the die casting apparatus 10 is in the state shown in Fig. 1. That is, the injection piston 31 and the booster piston 34 of the injection cylinder 32 are in their initial positions, such as their retraction limits. The position D of the plunger 17 at this time is shown as position D0 in Fig. 4, which will be described later.

The controller 50 determines whether or not a specific injection start condition is met, and when it determines that the condition is met, it starts low-speed injection. Specifically, the controller 50 opens the corresponding valve to supply hydraulic fluid from the accumulator to the head side chamber 32h, and opens the corresponding valve to allow the hydraulic fluid to be discharged from the rod side chamber 32r. The injection start conditions include completion of clamping of the fixed mold 11 and the movable mold 12, and completion of the supply of molten metal 20 to the sleeve 15 by the ladle 21, etc.

The speed of the plunger 17 during low-speed injection is controlled by feedback controlling the opening of the valve based on the speed of the plunger 17 detected by the position sensor 40, for example.
The speed of the plunger 17 is, for example, a constant low-speed injection speed. The value of the low-speed injection speed is appropriately set by the operator via the input device 55. Note that the injection pressure during low-speed injection is maintained at a relatively low pressure because the injection speed is relatively low.

<High speed injection: t1-t2>
Next, high-speed injection (see t1 to t2 in Figure 3) is performed by advancing the plunger 17 at a relatively high speed, so that the molten metal 20 is quickly filled into the fixed mold 11 and the movable mold 12 without being delayed by the solidification of the molten metal 20.
When a predetermined high-speed switching condition is satisfied, the controller 50 switches the speed of the plunger 17 to a high-speed injection speed higher than the low-speed injection speed, and performs high-speed injection. Specifically, the controller 50 increases the opening of the corresponding valve while supplying hydraulic fluid from the accumulator to the head side chamber 32h following the low-speed injection. The injection pressure during high-speed injection is higher than the injection pressure during low-speed injection.

The high-speed switching condition is, for example, that the plunger 17 reaches a predetermined high-speed switching position D1 (see FIG. 4). The controller 50 may determine whether the high-speed switching condition is met based on the detection value of the position sensor 40 or the elapsed time from the start of injection.

During high-speed injection (times t1 to t2), when control is switched from low-speed injection to high-speed injection, the injection pressure rises once, then falls, rises again, and falls again. Thereafter, the injection pressure rises rapidly due to factors such as the filling of the fixed die 11 and the movable die 12 with molten metal 20. The injection speed also drops once between the time when the injection is switched to high-speed injection and the time when the high-speed injection ends.

<Deceleration injection: t2 to t3>
When the cavity 13 is filled to a certain extent with the molten metal 20, the plunger 17 is decelerated by a reaction force from the filled molten metal 20, while the injection pressure rises rapidly as shown in Fig. 2. Appropriate deceleration control may be performed, such as reducing the opening of the valve when a predetermined deceleration start condition is satisfied, such as when the plunger 17 reaches a predetermined deceleration position. The deceleration control reduces the impact at the completion of filling.

When injection including low-speed injection and high-speed injection is performed, the high-speed switch position is generally set to the position when the molten metal 20 reaches the gate 19. Also, when the molten metal 20 is filled into the fixed mold 11 and the movable mold 12, as shown in Figure 2, the injection speed drops sharply and the injection pressure rises sharply.

<Pressure boost: t3 to t4>
By performing the step of filling the molten metal 20 with the liquid (see t1 to t2), the molten metal 20 is promptly filled into the fixed die 11 and the movable die 12 without delaying the solidification of the molten metal 20, and then a step of increasing the pressure of the molten metal 20 (see t3 to t4 in FIG. 3) is performed.

The controller 50 judges whether a predetermined pressure boosting start condition is satisfied, and starts pressure boosting when it is judged that the condition is satisfied. Specifically, for example, the controller 50 first opens the corresponding first valve when the first condition is satisfied. As a result, the hydraulic fluid is supplied from the accumulator to the rear side chamber 32e, and the pressure boosting piston 34 starts moving forward. Next, when the second condition is satisfied, the controller 50 changes the opening of the corresponding second valve to that for pressure boosting. That is, the controller 50 ends the speed control and starts the pressure control. Note that the discharge of the hydraulic fluid from the head side chamber 32h is prohibited by the valve being a pilot type check valve that closes automatically. By such an operation, the injection pressure increases and reaches a predetermined casting pressure (final pressure).
As shown in FIG. 2, the injection pressure is held constant during boosting.

<Pressure holding: t4~>
The increased pressure is maintained until dwell time (see t4 in Figure 3). This reduces sink marks on the molded product.
After the pressure is increased, the controller 50 maintains the state in which the injection pressure is at the final pressure. During this time, the molten metal is cooled and solidified. When the molten metal has solidified, the controller 50 stops the supply of hydraulic pressure from the accumulator to the rear chamber 32e and ends the pressure dwell. The mold is then opened and the casting product is ejected.
The outline of the die casting operation of the die casting apparatus 10 has been described above.

(Explanation of the principle)
Although casting conditions have been managed for some time, it cannot be said that the management conditions and traceability of defective products have been established.
One of the reasons why quality of die cast products cannot be established is that the occurrence of blowholes that cannot be detected by appearance cannot be detected from the casting conditions.
We are trying to extract factors that cause defects from data on defective products by saving as much data as possible, not only on injection conditions but also on mold cooling conditions, amount of release agent applied, dilution rate, amount of injection lubricant applied, etc., but we have not had any satisfactory results so far.
One of the causes of blowholes is insufficient pressure due to the pressure not being transmitted to the product even when the die casting equipment is applying pressure normally.

Although it is possible to detect the pressure inside the mold in experiments, it is not durable enough for mass production and cannot be used at present.

The 16 items of injection shown in Figures 2 and 3 (items marked a to p in Figure 3) are unable to detect the transmission of pressure to the die-cast product. The amount of pressure transmitted to the molten aluminum 20 was not managed at all during the mass production stage. The present invention determines the amount of pressure transmitted to the molten aluminum 20 without adding any new detection components. Incidentally, it is possible to determine the amount of pressure applied to the molten aluminum 20 by providing an expensive sensor that detects pressure in the mold. However, sensors that detect high-temperature, high-pressure molten metal 20 are very expensive and have low durability, and in reality they become unusable after a few dozen shots.

The inventors have devised a method to detect pressure transmission to die-cast products by calculating new control values from injection data.

As shown in Figures 2 and 3, die casting injection involves a pressure boosting process after high-speed injection. This high-speed injection is used to boost the pressure after filling the molten aluminum 20, crushing any cavities. If the pressure transmission of the boosted pressure is sufficient, the injection position will advance slowly after high-speed injection, and the pressure will be transmitted to the product. The slow advance occurs when the molten metal 20 solidifies and shrinks as it cools, and at that time the injection position (position of the plunger 17) advances to follow it. It was known that the injection position advances slowly, but no attention had been paid to the amount of chasing (following amount).

The inventors noticed that when the molten aluminum 20 solidifies, it shrinks and its volume is reduced to 0.92 (6/1000 reduction).

That is, the molten aluminum 20 solidifies and shrinks, reducing its volume to 0.92, and the amount of the shrinkage is ejected forward as a riser. Therefore, the amount of shrinkage or more becomes the boost pressure transmission effect.

The 0.92 reduction in the amount of solidification shrinkage is balanced by slowly advancing the booster. However, if the slow advance of the booster is the same as the amount of solidification shrinkage, it can be determined that the pressure is not transmitted to the molten metal 20 even if pressure is applied mechanically, that is, if the advance distance is only the amount of solidification shrinkage, the pressure is not transmitted. This allows a pass/fail judgment to be made.
Although the slow forward movement distance varies depending on the model, if the boost forward movement distance is less than the minimum amount of solidification shrinkage (6/1000), it can be determined to be a defective product. According to actual measurements by the inventors, it has been found that a 0.92 reduction in the amount of solidification shrinkage requires an advance of about 2%.

Next, the effects of the die casting apparatus 10 configured as described above will be described.
FIG. 4 is a diagram for explaining the velocity curve, pressure curve, and injection position in the injection process of the die casting device 10 based on the above basic principle. FIG. 5 is an enlarged view showing the velocity curve, pressure curve, injection position, and peak pressure position in the injection process of FIG. 4. In FIG. 4, the physical quantities indicated by the horizontal and vertical axes are the same as those in FIG. 3. The horizontal axis of FIG. 4 indicates time t, and the time is later toward the right. The vertical axis on the left side of FIG. 4 indicates the injection speed (the speed of the plunger 17), and the value is larger toward the top. The vertical axis on the right side of FIG. 4 indicates the injection pressure and the position D of the plunger 17, and the value is closer to the fixed mold 11 and the movable mold 12 toward the top. The velocity curve indicates the change in the injection speed over time. The pressure curve indicates the change in the injection pressure over time. The thick dashed line in FIG. 4 indicates the change in the injection position, i.e., the change in the position D of the plunger 17, over time, and when the plunger 17 is at the most retreated position, the injection position is D=0.

As shown in Figures 4 and 5, the position of the plunger 17 (the stop position of the plunger 17) when the injection pressure in the sleeve 15 reaches its peak P is D2, and the time at this point is t11. Here, the trigger for this die casting pressure transmission failure judgment is the peak P of the injection pressure, but the injection position is detected by taking data from the position of the plunger 17.

As explained in the above principle, during injection, movement is observed within a predetermined time (e.g., 5 seconds) after the peak pressure of the plunger 17. The position after the movement within the predetermined time is D3, and the time at which this occurs is t12.

When the plunger 17 completes injection and enters the pressure increase process, a peak pressure occurs. That is, as shown in Figures 4 and 5, the volume (see symbol q in Figure 4) enclosed by the time t11 when the injection pressure in the sleeve 15 reaches its peak P and the distance D3 traveled in 5 seconds, as shown by the thick line in Figures 4 and 5, is calculated.

6 is a flow chart showing a process for determining a poor die-casting pressure transmission in a die-casting machine. This flow is a casting management program executed by the CPU 51 of the controller 50 in FIG. 1. This flow is executed for each shot.
This program starts when the die casting apparatus 10 is turned on.
In step S<b>1 , the controller 50 detects the position of the plunger 17 .
In step S2, the controller 50 detects (calculates) the speed of the plunger 17.
In step S3, the controller 50 detects the peak P of the injection pressure by the head side pressure sensor 41 in the injection cylinder 32 (see FIG. 1).
In step S4, the controller 50 determines whether or not injection has been performed. If injection has not been performed, the process returns to START.
If injection has been performed, the controller 50 detects the injection position in step S5. The injection position (see the thick dashed lines in Figs. 4 and 5) is detected by the position sensor 40 (see Fig. 1).

In step S6, the controller 50 determines whether or not the injection pressure has reached the peak pressure of injection. If the injection pressure has not reached the peak pressure (die preheat casting), the process returns to step S5.
When the injection pressure reaches the peak pressure, the controller 50 detects the injection position in step S7. The injection pressure until it reaches the peak pressure P has various pressure curves depending on the casting conditions (the pressure curve in FIG. 4 is an example). However, no matter what pressure curve is taken, the injection pressure peak P exists (injection generates a peak due to inertia because a heavy object is stopped suddenly), so this injection pressure peak P can be used as the starting point.

Incidentally, in conventional die casting machines, the velocity curve and pressure curve up to time t11 in Figure 4 (up to the stop of plunger 17) have been considered, but there have been no examples of using data from time t11 to time t12 in Figure 4 (up to the injection position) as in this embodiment, and this is the first time that the inventors have disclosed this.

In step S8, the position of the plunger 17 (pressure boost distance) after a predetermined time (e.g., 5 seconds) is detected.

In step S9, the occurrence of blowholes is predicted based on the distance the plunger 17 has moved after the peak pressure. Specifically, the controller 50 converts the distance (mm) it has moved again after stopping into volume, and if the volume change is 0.92 (6/1000) or less, it is determined to be defective. However, since the characteristics of the slow forward movement distance differ depending on the model, it is better to obtain the slow forward movement distance for each model in advance by actual measurement, etc., store it in memory 52, and use the correction value to make corrections for each model.

The method for determining whether a pressure boost advance distance is less than the amount of solidification shrinkage is defective will be described in more detail.
The following formulas (1) to (3) are used as parameters.
Pressure increase distance = Distance traveled by the injection for 5 seconds from the peak pressure P of the injection ... (1)
Solidification shrinkage=cast weight×(1−solidification shrinkage rate) (2)
Shrinkage tracking = solidification shrinkage / injection cross section … (3)
The pressure increase distance is detected from the injection position (the position of the plunger 17). The solidification shrinkage and shrinkage tracking are obtained in advance by actual measurement.

Moreover, from the above formulas (1) to (3), formula (4) can be obtained. An actual measurement example using the pressurization distance of formula (4) will be described later with reference to FIG.
Pressure increase distance - solidification shrinkage = pressure increase distance ... (4)

As the molten aluminum 20 solidifies and shrinks, the plunger 17 advances by 0.92 shrinkage. Any movement beyond this amount results in a boost pressure transmission effect. In other words, if the plunger 17 does not move a distance that exceeds the set distance, it can be determined that a defect, including the occurrence of a casting cavity, has occurred.

Returning to the flow of FIG. 6, in step S10, the controller 50 determines whether the pressure increase distance is abnormally long (whether the pressure increase distance is equal to or greater than a predetermined abnormality determination value).
If the boost distance is not abnormally long (S10: No), it is either a <non-defective zone> or a <cavity zone> (see FIG. 7 ). In order to determine whether it is a <non-defective zone> or a <cavity zone>, in step S11 the controller 50 determines whether the boost distance is equal to or less than the solidification shrinkage distance.

If the pressure increase distance is greater than the solidification shrinkage distance (S11: No), it is in the "non-defective zone" (see FIG. 7), and the controller 50 outputs a normality determination result in step S12, and ends the processing of this flow.
If the boost distance is equal to or less than the solidification shrinkage distance (S11: Yes), it is a <blowhole zone> (see FIG. 7), and in step S13 the controller 50 outputs the blowhole prediction result and ends the processing of this flow.
The normality judgment result and the blowhole prediction result are output, for example, as a display output on the display unit 56, as an output to a printer or the like not shown, as an external output via a communication unit not shown, or as storage of the prediction results in an external storage device.

If the pressure increase distance is abnormally long in step S10 (S10: Yes), it is in the <variable zone> (see FIG. 7), and in step S14 the controller 50 outputs the variability prediction abnormality result and ends the processing of this flow.

Fig. 7 is a diagram showing an example of actual measurement of the die casting pressure transmission failure judgment of a die casting machine. The vertical axis shows the pressurization distance for each shot shown in formula (4), and the horizontal axis shows the number of shots expressed in units of 20 shots. The example in Fig. 7 shows a casting example of 533 shots.
Based on the pressure increase distance shown in Figure 7, the judgment zone is divided into a "non-defective zone" corresponding to a case where the pressure increase distance is greater than the solidification shrinkage distance, a "cavity zone" corresponding to a case where the pressure increase distance is equal to or less than the solidification shrinkage distance, and a "burr zone" corresponding to a case where the pressure increase distance is abnormally long.
In Fig. 7, the pressurizing distance of 3.0 indicated by the symbol r in Fig. 7 is the pass line in the <pass zone>. In each shot, the pressurizing distance generally satisfies the control conditions (not a defective product) (see step S12 "normal judgment result" in the flow in Fig. 6).

The pressurizing distance of 0.0 indicated by the symbol s in Fig. 7 is the defective product judgment region (<blowhole zone>). This pressurizing distance of 0.0 is an example when solidification shrinkage is set to 0 in formula (3). For example, in Fig. 7, the boost pressure near the number of shots of 20, 58, and 96 (see symbol t in Fig. 7) falls within the defective product judgment region, and it is judged that there is a boost pressure transmission failure (see step S13 "blowhole prediction result" in the flow in Fig. 6). In this case, the product is dismissed (removed) as defective.
Here, if the boost pressure transmission failure occurs frequently in each shot, deterioration of the injection parts is suspected, and measures such as replacing the injection parts are taken. The pass/fail judgment result shown in Figure 7 is reflected in the output in steps S12, S13, and S14 of the flow in Figure 6.

In the actual measurement example of die casting shown in Figure 7, if the pressurization distance is large (for example, near shot 153) (see symbol u in Figure 7), there is a possibility of burrs occurring, where molten aluminum leaks out of the mold (see step S14 "burr prediction abnormality result" in the flow in Figure 6). Burrs occur when pressure is released from the mold, and there is a possibility that pressure is not being transmitted to the product. Generally, the molten metal flow is good, but the internal quality cannot be guaranteed. In other words, the molten metal flow is good, but there is a possibility that pressure is not being transmitted to the product properly. In addition, problems that may occur after burrs occur include the burrs being caught in the mold and inducing mold collapse, being caught in the product and causing defects, and the burrs preventing air from being exhausted from the mold, which can also be a reason to immediately inspect and maintain the mold.

[Modification]
8 is a flow chart showing a die-casting pressure transmission failure determination process of a die-casting device according to a modified example of this embodiment, in which the same steps as those in FIG.
In FIG. 8, if the pressure increase distance is greater than the solidification shrinkage distance in step S11 (S11: No), the occurrence of blowholes is predicted in step S21 based on the distance the plunger 17 has moved after the peak pressure has been applied.
In step S22, the controller 50 outputs the prediction result and ends the process of this flow.
If the pressure increase distance is abnormally long in step S10 (S10: Yes), or if the pressure increase distance is equal to or less than the solidification shrinkage distance in step S11 (S14: Yes), the controller 50 outputs an abnormality result in step S23 and ends the processing of this flow.
In this way, as long as it includes a step of predicting the occurrence of blowholes based on the distance traveled by the plunger 17 after the peak pressure is reached, the step may be executed at any timing.

[effect]
As described above, the die casting apparatus 10 of this embodiment is a die casting apparatus that includes a fixed mold 11 and a movable mold 12, and that molds a casting product by injecting molten metal 20 into a cavity 13 formed by the fixed mold 11 and the movable mold 12 using the extrusion force of the plunger 17 sliding inside the sleeve 15. The die casting apparatus is equipped with a position sensor 40 that detects the position of the plunger 17, a head side pressure sensor 41 and a rod side pressure sensor 42 that detect the injection pressure inside the sleeve 15, and a controller 50 that controls the extrusion force of the plunger 17. The controller 50 detects the peak pressure of the injection pressure generated in the pressure increase process after the plunger 17 reaches its peak pressure, and detects the injection position when this injection pressure reaches the peak pressure, and predicts the occurrence of defects in the casting product based on the pressure increase distance moved from the injection position after the plunger 17 stops.

Conventionally, defective products were identified through visual inspection or pressure leak inspection after processing. The present invention makes it possible to verify internal quality that cannot be detected by appearance. In other words, it is possible to predict the occurrence of blowholes without checking the cast product after processing. In addition, the occurrence of burrs can be detected and used as a criterion for inspection and maintenance of dies.

The ability to detect internal defects during the casting process has the following unique advantages:
1. Defective products can be found during production, making it possible to take corrective measures on the spot, such as by modifying equipment, and reducing the occurrence of defective products in later processes.

2. By discarding products with defective numerical values, it is possible to reduce processing defects and prevent defective products from being sent to subsequent processes.

3. It will improve the internal quality, and if the casting product is a vehicle part, it will help prevent oil leaks and other problems after the delivery of the completed vehicle.

4. The present invention can predict the occurrence of blowholes without adding new parts by calculating new control values from injection data. This allows for general-purpose application at low cost.

5. It is possible to determine how much pressure is being transmitted to the molten aluminum without installing expensive sensors, making it low-cost and versatile.

In addition, in the die casting device 10, the controller 50 predicts the occurrence of defects when the pressure increase distance is less than or equal to a solidification shrinkage distance that is preset based on the solidification shrinkage rate of the molten metal.

In this way, if the boost distance is less than the solidification shrinkage distance, there is a possibility of defects occurring. By prioritizing defect prediction when there is a possibility of defects occurring, it is possible to speed up processing and make effective use of processing resources. In other words, real-time processing at low cost becomes possible, and defects can be predicted in real time for each shot.

In addition, in the die casting device 10, the controller 50 determines that a defect, including the occurrence of a casting cavity, has occurred if the pressure increase distance is less than or equal to a solidification shrinkage distance that is preset based on the solidification shrinkage rate of the molten metal.

In this way, if the boost distance is less than the solidification shrinkage distance, it is assumed that there is an abnormality. It is possible to determine in real time whether there are any defects such as the occurrence of blowholes.

In addition, in the die casting device 10, the controller 50 determines that an abnormality exists if the pressure increase distance is equal to or less than a solidification shrinkage distance that is preset based on the solidification shrinkage rate of the molten metal, or if it is equal to or greater than a predetermined abnormality determination value.

By doing this, in addition to determining whether a product is defective due to the occurrence of blowholes, etc., it is possible to predict product defects due to burrs at an early stage.

In addition, in the die casting device 10, the controller 50 predicts the occurrence of defects in the casting product based on the pressure increase distance that the plunger 17 moves from the injection position within a specified time after the peak pressure.

In this way, by using the distance traveled within a specified time, the time required to complete a prediction determination can be shortened. In addition, since the processing is completed in real time, it can be executed as background processing. This makes it possible to improve workability by shortening the time in manufacturing processes such as production lines.

The above-described embodiments are merely examples of the realization of the present invention. Therefore, the technical scope of the present invention should not be interpreted as being limited by these. This is because the present invention can be embodied in various forms without departing from the spirit or main characteristics thereof.
For example, the present invention can be applied to casting methods having an injection function, such as squeeze casting, hot chamber die casting, and hybrid full casting.

REFERENCE SIGNS LIST 10 Die casting device 11 Fixed die 12 Movable die 13 Cavity 14 Molten metal supply section 15 Sleeve 17 Plunger 17a Plunger tip 17b Plunger rod 18 Runner 19 Gate 20 Molten metal (molten metal)
30 Injection drive unit 33 Injection control drive unit 36 Pressure boost control drive unit 40 Position sensor (position detection means)
41 Head side pressure sensor (injection pressure detection means)
42 Rod side pressure sensor (injection pressure detection means)
50 Controller (control device)
P: Peak pressure position D3: Pressure increase distance S6: Step for detecting the peak pressure of the injection pressure generated in the pressure increase process after the plunger completes injection S7: Step for detecting the injection position when the injection pressure reaches the peak pressure S9, S21: Step for predicting the occurrence of defects in the casting product according to the pressure increase distance moved from the injection position after the plunger reaches the peak pressure

Claims (6)

A die casting apparatus comprising a fixed die and a movable die, the die casting apparatus forming a casting product by injecting molten metal into a cavity formed by the fixed die and the movable die using an extrusion force of a plunger that slides inside a sleeve,
a position detection means for detecting the position of the plunger;
an injection pressure detection means for detecting the injection pressure in the sleeve;
A control device that controls the pushing force of the plunger,
The control device includes:
Detecting a peak pressure of the injection pressure generated in a pressure increasing process after the plunger completes injection, and detecting an injection position when the injection pressure reaches the peak pressure;
a pressure increase distance traveled by the plunger from the injection position after the peak pressure is reached, to predict the occurrence of defects in the casting product. The control device includes:
2. The die casting apparatus according to claim 1, further comprising a step of: predicting the occurrence of a defect when the pressure increase distance is equal to or smaller than a solidification shrinkage distance that is preset based on a solidification shrinkage rate of the molten metal. The control device includes:
The die casting apparatus according to claim 1, characterized in that, when the pressure increase distance is equal to or less than a solidification shrinkage distance that is preset based on a solidification shrinkage rate of the molten metal, it is determined that a defect including the occurrence of a casting cavity has occurred. The control device includes:
The die casting apparatus according to claim 1, characterized in that it is determined that an abnormality has occurred when the pressure increase distance is equal to or less than a solidification shrinkage distance that is preset based on a solidification shrinkage rate of the molten metal, or when the pressure increase distance is equal to or more than a predetermined abnormality determination value. The control device includes:
Detecting a peak pressure of the injection pressure generated in a pressure increasing process after the plunger completes injection, and detecting an injection position when the injection pressure reaches the peak pressure;
2. The die casting apparatus according to claim 1, wherein a prediction of occurrence of a defect in the casting product is made based on a pressure increase distance traveled by the plunger from the injection position within a predetermined time after the peak pressure is reached. A die casting manufacturing method for a die casting apparatus including a fixed die and a movable die, the die casting apparatus forming a cavity between the fixed die and the movable die by using an extrusion force of a plunger that slides in a sleeve to inject molten metal into the cavity to form a casting product, the method comprising the steps of:
The die casting apparatus comprises:
detecting a peak pressure of the injection pressure generated in a pressure increasing process after the plunger completes injection;
detecting a position of injection when the injection pressure reaches a peak pressure;
and predicting the occurrence of defects in the casting product based on a pressure increase distance traveled by the plunger from the injection position after the peak pressure is reached.

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