Die casting method for aluminum alloy die casting test

Abstract

The invention discloses a die-casting method for an aluminum alloy die-casting test. The die-casting method comprises the following steps that (1) air exhaust (internal air) is conducted at an air exhaust connecting through hole; (2) exhausting until the gas pressure in the die-casting cavity is 0, stopping exhausting, inflating at the inflating connector until the pressure in the die-casting cavity is more than 0.5 MPA, and stopping inflating; (3) air inflation at the air inflation connecting port is stopped, air exhaust is conducted at the air exhaust connecting through hole till the air pressure in the die-casting cavity is zero, and air inflation is conducted at the air inflation connecting port till the pressure in the die-casting cavity is 0.5 MPA or above; (4) the injection head retracts to the left side of the pouring gate, and the air exhaust connecting through hole is also inflated; the gas backpressure at the mold filling tail end can be reduced, and the die-casting effect is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of materials testing technology, and more specifically to a die-casting method for testing aluminum alloy die casting. Background Technology

[0002] Currently, the back pressure of gas at the end of the filling process in integrated die-casting parts (gas back pressure refers to the pressure opposite to the flow direction of gas when it flows in a closed container or pipeline due to obstacles or bends) is difficult to control, seriously affecting the quality and mechanical properties of the castings, and is one of the key challenges limiting its large-scale production. In traditional high-pressure casting, the back pressure problem is mainly solved by vacuuming the mold cavity and designing venting channels. However, the mold cavity of ultra-large integrated parts has a large volume, wide spatial span, and fast melt filling speed. After vacuuming using traditional methods, there is a lot of residual gas in the mold cavity, which cannot solve the back pressure problem.

[0003] The multi-vacuum valve multi-stage vacuuming method currently used in the industry has alleviated the above problems to some extent, but at the same time, it has the problems of complex vacuum system control and difficulty in coordination with the injection process (for example, an integrated die-casting mold has 8-10 vacuum valves), and cannot ideally solve the back pressure problem at the end of the filling process (the finished product at the end contains a large number of pores and a large amount of nitrogen inside). Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a die-casting method for aluminum alloy die-casting experiments, which can reduce the gas back pressure at the end of the filling process and ensure the die-casting effect.

[0005] The solution of the present invention to the aforementioned technical problem is: A die-casting method for testing aluminum alloy die casting includes the following steps: (1) A die-casting cavity is formed between the moving mold and the fixed mold. An air inlet is formed in the die-casting cavity. A casting feed pipe is connected to the lower part of the die-casting cavity. An injection head extends into the left end of the casting feed pipe. The injection head is located on the right side of the gate formed at the top left of the casting feed pipe. An air extraction connection hole is formed on the top plate of the casting feed pipe at the right side of the injection head. Air is extracted (internal air) through the air extraction connection hole. (2) When the gas pressure in the die-casting cavity is less than 80 mbar, stop pumping and fill the cavity with gas at the filling port (11) until the pressure in the die-casting cavity is the same as the surrounding atmospheric pressure, then stop filling. (3) Stop inflating at the inflation port, and then evacuate at the evacuation port until the gas pressure in the die-casting cavity is 0. Then, inflate at the inflation port until the pressure in the die-casting cavity is above 0.5 MPa. (4) The injection head retracts to the left side of the gate, and air is also introduced at the air extraction connection hole; (5) The injection head continues to move to the left until it no longer covers the gate; (6) Pour the molten aluminum alloy at the gate to the required amount; (7) Stop filling the air and start evacuating the air from the air extraction connection hole and the air filling connection port. At the same time, push the injection head to the right to bring the aluminum alloy melt into the die casting cavity. (8) After the injection head passes through the air extraction connection through hole to the right, the air extraction connection through hole stops sucking air. The injection head continues to push to the right until the aluminum alloy melt reaches the die casting cavity when it is one-tenth to one-fifth away from the highest point. Then the air filling connection port stops sucking air. (9) The injection head is pushed to the rightmost end of the casting feed pipe to complete the die casting; (10) Push the moving mold to the right to open the die-casting cavity and remove the die-cast product.

[0006] The outstanding effects of this invention are: Before die casting, a vacuum is first drawn, then a mixture of oxygen and carbon dioxide is introduced into the die casting cavity, followed by another vacuum. This replaces the residual gas in the mold cavity with a "low back pressure" gas composed of oxygen and carbon dioxide. This "low back pressure" gas can react quickly with the molten aluminum alloy, reducing the back pressure of the gas at the end of the filling process, allowing it to react with the molten aluminum alloy and form part of the molded part. On the other hand, vacuuming reduces the total amount of "low back pressure" gas, avoiding excessive oxide inclusions as seen in oxygen-filled die casting. Attached Figure Description

[0007] Figure 1 This is a simplified structural principle diagram of the present invention; Figure 2 This is a simplified schematic diagram of the entire processing technology of the present invention (excluding the air intake and exhaust system); Figure 3 This is a partial structural diagram of the air intake and exhaust system; Figure 4 This is a comparative analysis of porosity defects in a conventional vacuum die-casting casting and the casting of this invention, obtained by ordinary industrial CT scanning with a resolution of 0.3 mm. Figure 5 This is a comparative analysis of the characterization results of micron-scale CT and SEM at a resolution of 10 μm on the end samples of pore defects in ordinary vacuum die-casting castings and castings of the present invention. Detailed Implementation

[0008] For example, see below. Figures 1 to 3 As shown, a die-casting method for aluminum alloy die-casting experiments includes the following steps: In this embodiment, the die-casting structure forms a die-casting cavity between the moving mold 10 and the fixed mold 20. The lower part of the fixed mold 20 has a mounting hole. The right end of the casting feed pipe 30 is located in the mounting hole, and its outer side wall is fixed to the inner side wall of the mounting hole. The casting feed pipe 30 communicates with the die-casting cavity. The left side wall of the moving mold 10 presses against the right side wall of the fixed mold 20. An inflation port 11 is formed on the top surface of the die-casting cavity, located on the top plate of the moving mold 10. An injection head 40 extends into the left inlet of the casting feed pipe 30. The injection head 40 is located to the right of the gate 31 formed at the top left of the casting feed pipe 30. The casting head 40 is located at the right side of the right side of the injection head 40. The top plate of the feed pipe 30 is formed with an air extraction connection through hole 32. A moving cylinder is fixed on the frame connecting plate on the right side of the right side wall of the moving mold 10. The end of the push rod of the moving cylinder extends out of the frame connecting plate and is fixed on the right side wall of the moving mold 10. At the same time, a guide rod is fixed on the right side wall of the moving mold 10. The guide rod is inserted into the guide through hole on the frame connecting plate. Meanwhile, the left end of the injection head 40 is fixed with a push rod of the pushing cylinder. The pushing cylinder is fixed on the mounting bracket on the left side of the casting feed pipe 30. The moving cylinder, frame connecting plate, guide rod, mounting bracket, pushing cylinder and other components are all conventional structures and will not be described in detail here. They are also omitted in the attached drawings.

[0009] The outer wall of the injection head 40 is in close contact with and cooperates with the inner wall of the casting feed pipe 30. A gas pressure sensor 1 is fixed on the top surface of the die-casting cavity, and the gas pressure sensor 1 is located on the moving mold 10.

[0010] Furthermore, both the air extraction connection hole 32 and the air inflation connection port 11 are connected to a main connecting pipe 2, and the end of the main connecting pipe 2 is connected to the air inlet / outlet system 50.

[0011] Furthermore, the air intake and exhaust system 50 includes a hybrid system 51 and a vacuum pump 52. The outlet of the hybrid system 51 is connected to the inlet of the first solenoid valve 53 through a connecting pipe. The outlet of the first solenoid valve 53 is connected to one end of a three-way connector. The inlet of the vacuum pump 52 is connected to the outlet of the second solenoid valve 54 through a connecting pipe. The inlet of the second solenoid valve 54 is connected to the other end of the three-way connector 55. The other end of the three-way connector 55 is connected to one end of the third solenoid valve 56 through a connecting pipe. The other end of the third solenoid valve 56 is connected to the corresponding end of the main connecting pipe 2.

[0012] Furthermore, the air mixing system 51 includes a main housing 511 (the top and bottom plates of the main housing 511 are detachable structures, which are fixedly connected to the top and bottom surfaces of the main housing 511 by bolts, and sealing rings are clamped between the main housing 511 and the top and bottom surfaces of the main housing 511), a middle partition 512 is fixed in the middle of the main housing 511, the middle partition 512 divides the main housing 511 into an upper cavity 513 and a lower cavity 514, and a first pusher is fixed to the upper and lower parts of the left side wall of the main housing 511 respectively. The cylinder 515 and the second push cylinder 516, the ends of the push rods of the first push cylinder 515 and the second push cylinder 516 extend into the corresponding upper cavity 513 or lower cavity 514 and are fixed with an upper push block 517. A sealing ring 518 is nested in the annular groove formed on the outer side of the upper push block 517. The outer side wall of the sealing ring 518 is close to the inner side wall of the upper cavity 513 or the lower cavity 514 and covers the air inlet hole formed on the top plate of the upper cavity 513 or the air inlet hole formed on the bottom plate of the lower cavity 514. A mixing shell 60 is fixed on the right side wall of the right side plate of the main housing 511. Exhaust holes 3 are formed on the right side plates of the upper cavity 513 and the lower cavity 514. The left end of the air guide pipe 61 is inserted into the corresponding exhaust hole 3, and its outer side wall is welded and fixed to the inner side wall of the corresponding exhaust hole 3. The air guide pipe 61 is inserted into the mixing shell 60. The right end of the air guide pipe 61 is inserted into the guide sleeve 62 fixed on the inner side wall of the right side plate of the mixing shell 60. An annular groove is formed on the inner side wall of the guide sleeve 62. The second sealing ring 63 is nested in the annular groove. The outer side wall of the right end of the air guide pipe 61 is pressed against the inner side wall of the corresponding second sealing ring 63. A side air outlet 64 is formed on the middle side wall of the air duct 61, which communicates with the mixing shell 60. A transverse push rod 5 is fixed to the middle of the right end face of the upper push block 517. The right part of the transverse push rod 5 is inserted into the corresponding air duct 61. A right guide block 6 is fixed to the right part of the transverse push rod 5. The right guide block 6 is inserted into the air duct 61. An outer annular groove is formed on the outer side wall of the right guide block 6, and a third sealing ring 7 is nested on it. The outer side wall of the third sealing ring 7 is close to the inner side wall of the air duct 61 and covers the corresponding side air outlet 64.

[0013] Furthermore, the upper push block 517 is formed with a left-right through-hole 519.

[0014] Furthermore, the air inlet at the upper cavity 513 is connected to an upper connecting pipe, the upper part of which is connected to a first air inlet solenoid valve 8. The inlet of the first air inlet solenoid valve 8 is connected to one end of a differential pressure flow meter 500 through a connecting pipe, and the other end of the differential pressure flow meter 500 is connected to the outlet of the oxygen storage tank 200 through a connecting pipe. The air inlet at the lower cavity 514 is connected to a lower connecting pipe, the lower part of which is connected to a second air inlet solenoid valve 9. The inlet of the second air inlet solenoid valve 9 is connected to one end of a second differential pressure flow meter 501 through a connecting pipe, and the other end of the second differential pressure flow meter 501 is connected to the outlet of the oxygen storage tank 200 through a connecting pipe.

[0015] The air extraction connection through hole 32 is an oblique through hole extending obliquely to the left and upward.

[0016] (1) Air is pumped out through the air connection hole 32 (the corresponding third solenoid valve 56 is opened, the second solenoid valve 54 is opened, and the vacuum pump 52 is run to achieve air pumping). When the gas pressure in the die-casting cavity is less than 80 mbar, stop the evacuation and fill the cavity with gas at the filling port (11) until the pressure in the die-casting cavity is the same as the surrounding atmospheric pressure. Then stop filling the cavity. (2) When the pressure sensed by the gas pressure sensor 1 is less than 80 mbar, the sensor will send the sensing signal to the control host (all electrical components and hydraulic and pneumatic components in this embodiment are controlled by the control host, which is a conventional structure and will not be described in detail here). The control host will then control the corresponding vacuum pump 52 to stop running, close the second solenoid valve 54, stop pumping, and charge the gas at the gas filling port 11 (by opening the corresponding third solenoid valve 56 and the first solenoid valve 53, and at the same time, the gas mixing system 51 runs to achieve gas filling. In this embodiment, the gas being transported is oxygen, carbon dioxide, or a mixture of oxygen and carbon dioxide) until the pressure in the die-casting cavity is above 0.5 MPa (sensed by the gas pressure sensor 1). Then, the control host will stop the gas filling. (3) Stop inflation at inflation port 11 and pump air through hole 32 (the principle is the same as above, and will not be described in detail here) until the gas pressure in the die casting cavity is 0. Then, start inflation at inflation port 11 until the pressure in the die casting cavity is above 0.5MPA. In the above process, the air in the die-casting cavity is replaced with oxygen or carbon dioxide or a mixture of both to ensure that the gas can react with the aluminum alloy melt 100 and reduce back pressure problems. (4) The injection head 40 retracts to the left side of the gate 31, and air is also injected at the air extraction connection through hole 32; (5) The injection head 40 continues to move to the left until it no longer covers the gate 31; (6) Cast the aluminum alloy melt 100 at gate 31 to the required casting amount. During casting, the aluminum alloy melt 100 will react with the gas it comes into contact with. (7) The air extraction connection hole 32 and the air filling connection port 11 stop filling and start air extraction (this process is to reduce the reaction between the aluminum alloy melt 100 and the gas). At the same time, the injection head 40 pushes to the right to put the aluminum alloy melt 100 into the die casting cavity. During the pushing, the top surface of the aluminum alloy melt 100 will not reach the top of the inner wall of the casting feed pipe 30, that is, it will not enter the air extraction connection hole 32. (8) After the injection head 40 passes through the air extraction connection through hole 32 to the right, the air extraction connection through hole 32 stops sucking air, and the injection head 40 continues to push to the right until the aluminum alloy melt 100 reaches the die casting cavity when it is one-tenth to one-fifth away from the highest point, the air filling connection port 11 stops sucking air. (9) The injection head 40 continues to push to the rightmost end of the casting feed pipe 30 to complete the die casting. In this embodiment, the whole process is completed in about 5 seconds. Therefore, when the gas connection port 11 stops absorbing gas in step (8), when the aluminum alloy melt 100 reaches the die casting cavity at one-tenth to one-fifth of the distance from the highest point, the aluminum alloy melt 100 continuously fills the die casting cavity with the push of the injection head 40. In this embodiment, the gas in the die casting cavity will react with the aluminum alloy melt 100 throughout the process, so that there will be no excess gas in the die casting cavity, so that there will be basically no pores in the die casting product, thus ensuring the casting effect.

[0017] (10) Push the moving mold 10 to the right to open the die-casting cavity, remove the die-cast product, and analyze the product.

[0018] The operating principle of the gas mixing system 51 in this embodiment is as follows: the oxygen and carbon dioxide stored in the oxygen storage tank 200 and the carbon dioxide storage tank 300 have the same pressure. When only oxygen is needed, the first intake solenoid valve 8 opens, which can be pushed by the push rod of the first push cylinder 515, causing the corresponding upper push block 517 to move to the right, so that the air inlet hole formed on the top plate of the upper cavity 513 is not covered. At the same time, the right guide block 6 does not cover the corresponding side outlet hole 64. At this time, the oxygen in the oxygen storage tank 200 will enter the upper cavity 513, and then enter the air guide pipe 61 through the air guide hole 519, and then enter the mixing shell 60. Then, it enters the first solenoid valve 53 through the outlet of the air outlet pipe connected to the mixing shell 60. The first solenoid valve 53 opens, the third solenoid valve 56 opens, and the oxygen will enter the casting feed pipe 30 through the gate 31. The corresponding differential pressure flow meter 500 can sense its delivery volume and achieve precise control.

[0019] Similarly, when only carbon dioxide is needed, the second intake solenoid valve 9 only needs to be opened, and the push rod of the second push cylinder 516 is pushed. The principle is the same as above, and will not be described in detail here. At this time, the second differential pressure flow meter 501 can sense its delivery volume.

[0020] When a mixture of carbon dioxide and oxygen is required, the first intake solenoid valve 8 and the second intake solenoid valve 9 can be opened. The push rods of the first push cylinder 515 and the second push cylinder 516 are pushed to achieve air intake. The differential pressure flow meter 500 and the second differential pressure flow meter 501 constantly sense the amount of oxygen and carbon dioxide delivered. When the amount delivered reaches the required amount, the corresponding first intake solenoid valve 8 or the second intake solenoid valve 9 is controlled to close. At the same time, the push rods of the first push cylinder 515 or the second push cylinder 516 return to their original positions.

[0021] In this embodiment, before injection, a "low back pressure" gas (oxygen, carbon dioxide, or a mixture of both) is introduced into the die-casting cavity, followed by vacuuming. This replaces the residual gas in the die-casting cavity with the "low back pressure" gas. On one hand, the "low back pressure" gas reacts rapidly with the molten aluminum alloy 100, reducing the back pressure at the end of the filling process, achieving an effect similar to oxygen-filled die casting. On the other hand, vacuuming reduces the total amount of "low back pressure" gas, avoiding excessive oxide inclusions as seen in oxygen-filled die casting. Simultaneously, the design of the "low back pressure" gas ensures a certain reaction rate between the cavity gas and the melt, while avoiding the violent combustion and large amounts of uncontrollable oxide inclusions that occur during the pouring of the melt into the injection chamber, as seen in oxygen-filled die casting. This reduces the content of gas entrapment defects in the casting, significantly reducing the formation of porosity within the casting and improving the mechanical performance stability of the integrated die-casting machine.

[0022] This embodiment compares and analyzes experimental die-cast parts (pre-filled "low back pressure" gas die-casting) with ordinary vacuum die-cast parts, such as... Figure 4 and Figure 5 As shown, Figure 4 In the image, the left side shows ordinary vacuum die casting, and the right side shows die casting according to this embodiment. Figure 5 The upper part is a conventional vacuum die-casting casting, and the lower part is the die-casting casting of this embodiment. The overall defects of both types of castings were analyzed using conventional industrial CT scanning, with further micron-level CT scanning and SEM microstructure characterization performed at the filling end. For example... Figure 5 As shown, under ordinary industrial CT scanning conditions with a spatial resolution of 0.3 mm, neither method of preparing castings exhibited porosity defects. However, the results of micron-level CT scanning with a resolution of 10 μm differed from the SEM characterization results. Figure 5 The results show that the pre-filling "low back pressure" gas method can significantly reduce the size and number of porosity defects at the end of the casting filling process. Therefore, the effect of this embodiment is significant and effective.

[0023] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A die-casting method for aluminum alloy die-casting experiments, characterized in that: It includes the following steps: (1) A die casting cavity is formed between the moving mold (10) and the fixed mold (20). An air inlet (11) is formed in the die casting cavity. A casting feed pipe (30) is connected to the lower part of the die casting cavity. An injection head (40) is inserted into the left end of the casting feed pipe (30). The injection head (40) is located on the right side of the gate (31) formed at the left side of the top of the casting feed pipe (30). An air extraction connection hole (32) is formed on the top plate of the casting feed pipe (30) on the right side of the injection head (40). Air is extracted at the air extraction connection hole (32). (2) When the gas pressure in the die-casting cavity is less than 80 mbar, stop pumping and fill the cavity with gas at the filling port (11) until the pressure in the die-casting cavity is the same as the surrounding atmospheric pressure, then stop filling. (3) Stop filling the gas at the gas filling port (11), and then evacuate the gas at the gas extraction port (32) until the gas pressure in the die casting cavity is 0. Then fill the gas at the gas filling port (11) until the pressure in the die casting cavity is above 0.5MPA. (4) The injection head (40) retracts to the left side of the gate (31), and air is also injected at the air extraction connection through hole (32); (5) The injection head (40) continues to move to the left until it no longer covers the gate (31). (6) Cast the molten aluminum alloy (100) at the gate (31) to the required casting volume; (7) The air extraction connection hole (32) and the air filling connection port (11) stop filling and start evacuation. At the same time, the injection head (40) is pushed to the right to bring the aluminum alloy melt (100) into the die casting cavity. (8) After the injection head (40) passes through the air extraction connection through hole (32) to the right, the air extraction connection through hole (32) stops sucking air, and the injection head (40) continues to push to the right until the aluminum alloy melt (100) reaches the die casting cavity when it is one-tenth to one-fifth away from the highest point, and the air filling connection (11) stops sucking air. (9) The injection head (40) is pushed to the rightmost end of the casting feed pipe (30) to complete the die casting; (10) Push the moving mold (10) to the right to open the die-casting cavity and remove the die-cast product.

2. The die-casting method for aluminum alloy die-casting experiments according to claim 1, characterized in that: The lower part of the fixed mold (20) is formed with an installation hole. The right end of the casting feed pipe (30) is in the installation hole and fixed on the inner side wall of the installation hole. The left side wall of the moving mold (10) is pressed against the right side wall of the fixed mold (20). The top surface of the die casting cavity is formed with an air inlet (11) on the top plate of the moving mold (10).

3. The die-casting method for aluminum alloy die-casting experiments according to claim 1, characterized in that: The outer wall of the injection head (40) is in close contact with and cooperates with the inner wall of the casting feed pipe (30).

4. The die-casting method for aluminum alloy die-casting experiments according to claim 1, characterized in that: The air extraction connection through hole (32) is an oblique through hole that extends obliquely to the left and upward.

5. The die-casting method for aluminum alloy die-casting experiments according to claim 2, characterized in that: A gas pressure sensor (1) is fixed on the top surface of the die-casting cavity, and the gas pressure sensor (1) is located on the moving mold (10).

6. The die-casting method for aluminum alloy die-casting experiments according to claim 1, characterized in that: The main connecting pipe (2) is connected to both the air extraction connection hole (32) and the air filling connection port (11), and the end of the main connecting pipe (2) is connected to the air inlet / outlet system (50).

7. The die-casting method for aluminum alloy die-casting experiments according to claim 6, characterized in that: The air intake and exhaust system (50) includes a hybrid system (51) and a vacuum pump (52). The outlet of the hybrid system (51) is connected to the inlet of the first solenoid valve (53) through a connecting pipe. The outlet of the first solenoid valve (53) is connected to one end of a three-way connector. The inlet of the vacuum pump (52) is connected to the outlet of the second solenoid valve (54) through a connecting pipe. The inlet of the second solenoid valve (54) is connected to the other end of the three-way connector (55). The other end of the three-way connector (55) is connected to one end of the third solenoid valve (56) through a connecting pipe. The other end of the third solenoid valve (56) is connected to the corresponding end of the main connecting pipe (2).

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