An aluminum alloy vacuum casting process with optimized evacuation timing

Abstract

An aluminum alloy vacuum casting process for optimizing the timing of the evacuation, comprising the following steps: Step A, start clamping; Step B, after 0.5S of starting clamping, the clamping is completed, and the vacuum pump starts high-speed evacuation of the mold cavity; Step C, after 1S of starting clamping, the punch starts to move forward at a low speed from the starting point at the rear end of the plenum; the vacuum pump maintains high-speed evacuation; Step D, after 1.3S of starting clamping, the vacuum pump reduces the evacuation rate to a low speed; Step E, after 1.4S of starting clamping, the punch moves forward at a low speed to just beyond the liquid injection port of the plenum, and then starts to accelerate; Step F, after 1.45S of starting clamping, the punch just accelerates to a high speed and no longer accelerates; Step G, after 1.5S of starting clamping, the vacuum pump restores the evacuation rate to a high speed, Step H, after 1.7S of starting clamping, the punch just reaches the front end of the plenum to complete the injection, and the vacuum pump starts medium-speed evacuation, and the mold starts to maintain pressure; Step I, after 6.5S of starting clamping, the mold pressure maintaining is completed, and the vacuum pump stops evacuation.

Description

Technical Field

[0001] This invention relates to an optimized vacuum casting process for aluminum alloys. Background Technology

[0002] Patent document CN 113523223 A discloses a vacuum die-casting method and apparatus for aluminum / magnesium alloys. Sections

[0058] to

[0060] disclose steps A: mold closing; step B: vacuuming; after mold closing, the vacuum valve 13 of the vacuum system is opened, connecting the vacuum system to the mold cavity 3, and a vacuum is drawn into the sealed space composed of the mold cavity 3, the die-casting machine pressure chamber 4, and the ejector pin sealing plate cavity 19 until the vacuum degree of the sealed space is ≤50 mbar, then the vacuum valve 13 is closed; step C: quantitative pouring; step D: injection molding. In other words, after the vacuum valve is evacuated, it is in a closed state. The punch is located behind the injection port of the pressure chamber, and high-speed injection propels the molten aluminum alloy along the pressure chamber, thus sending it into the mold cavity. The patent literature states that closing the vacuum valve after vacuuming only maintains a constant vacuum level in the mold cavity under ideal conditions. However, in real-world environments, unexpected gas may inevitably enter the mold cavity. For example, the sealing performance of the sealing structure may decrease at high temperatures, allowing outside air to enter the mold cavity. Alternatively, the release agent inside the mold cavity may evaporate at high temperatures, releasing water vapor and other gases into the cavity. Since the vacuum valve is closed, these gases will not be removed but will remain inside the mold cavity and be accidentally drawn into the molten aluminum alloy entering the cavity. This can cause unintended porosity to form inside the molded aluminum alloy during cooling and molding, resulting in poor quality of the finished casting. Summary of the Invention

[0003] The inventor has been researching a vacuum casting process without disclosing its details. In this process, a vacuum valve maintains high-speed evacuation after drawing sufficient vacuum into the mold cavity. Any gas accidentally entering the mold cavity is then removed by the vacuum valve, preventing it from remaining and being accidentally entrained by the molten aluminum alloy injected into the cavity. However, the molten aluminum alloy accelerates from a stationary state to high speed in a very short time during the initial high-speed injection. This acceleration is highly unstable, and the high-speed evacuation by the vacuum valve further exacerbates this instability. Consequently, the molten aluminum alloy does not flow smoothly into the mold cavity but is prone to accidental splashing, leading to uneven casting.

[0004] Therefore, the present invention aims to provide a vacuum casting process with optimized evacuation timing, so that when the molten aluminum alloy is injected into the mold cavity at high speed, it is less likely to be accidentally entrained by gas, and it is less likely to be accidentally splashed when entering the mold cavity.

[0005] An optimized vacuum casting process for aluminum alloy includes the following steps: Step A: Start mold closing; Step B: 0.5 seconds after mold closing, the mold closing is complete, and the vacuum pump starts high-speed evacuation of the mold cavity; Step C: 1 second after mold closing, molten aluminum alloy flows into the pressure chamber through the injection port, and the punch begins to move forward at low speed from the rear end of the pressure chamber; the vacuum pump maintains high-speed evacuation to remove any unexpected gas in the mold cavity; Step D: 1.3 seconds after mold closing, the punch moves forward at low speed to the injection port that is close to the pressure chamber, and the vacuum pump reduces the evacuation rate to a low speed; Step E: Start mold closing. 1.4 seconds later, the punch moves forward at low speed until it just passes the injection port of the pressure chamber, then it begins to accelerate forward to inject the molten aluminum alloy in the pressure chamber into the mold cavity at high speed; Step F, 1.45 seconds after the mold begins to close, the punch accelerates to high speed and stops accelerating; Step G, 1.5 seconds after the mold begins to close, the vacuum pump restores the evacuation rate to high speed; Step H, 1.7 seconds after the mold begins to close, the punch just reaches the end point of the front end of the pressure chamber to complete the injection, the vacuum pump starts to evacuate at medium speed, and the mold begins to hold pressure; Step I, 6.5 seconds after the mold begins to close, the mold pressure holding ends, and the vacuum pump stops evacuating.

[0006] Furthermore, the low-speed pumping rate is 10% to 20% of the high-speed pumping rate.

[0007] Furthermore, the medium-speed pumping rate is 40% to 50% of the high-speed pumping rate.

[0008] Furthermore, the low-speed forward movement speed of the punch is 0.2 m / s ~ 0.25 m / s, and the high-speed forward movement speed is 4 m / s ~ 6 m / s.

[0009] 1.4 seconds after mold closing begins, the punch moves forward at low speed until it just passes the injection port of the pressure chamber. It then accelerates forward, injecting the molten aluminum alloy from the pressure chamber into the mold cavity at high speed. During this acceleration, the molten aluminum alloy becomes unstable. At this time, the vacuum pump continues to pump air instead of stopping, continuously removing any unexpected gas from the mold cavity to prevent gas from being accidentally entrained when the molten aluminum alloy is injected into the mold cavity at high speed. The pumping speed is reduced to a low speed 0.1 seconds beforehand (1.3 seconds after mold closing begins), thus preventing a significant increase in the instability of the molten aluminum alloy. This makes it less likely for the molten aluminum alloy to exceed the critical point of instability and splash accidentally when entering the mold cavity. The vacuum pump maintains this low-speed pumping speed until the punch completes its acceleration (1.45 seconds after mold closing begins), and then resumes high-speed pumping 0.05 seconds later (1.5 seconds after mold closing begins), ensuring that the pumping speed remains low throughout the punch acceleration period and avoiding a significant increase in the instability of the molten aluminum alloy. After 1.5 seconds of mold closing, the molten aluminum alloy stops accelerating, resulting in lower instability. Even with the influence of vacuum pump evacuation, its instability is unlikely to exceed the critical point. Therefore, the vacuum pump resumes high-speed evacuation to quickly remove any unexpected gas from the mold cavity. Only 0.2 seconds (from 1.3 to 1.5 seconds after mold closing) are for low-speed evacuation, while 0.8 seconds (from 0.5 to 1.3 seconds after mold closing) are for high-speed evacuation. The low-speed evacuation time accounts for a small proportion of the total evacuation time, thus maintaining the vacuum level of the mold cavity better, resulting in better quality of the finished casting. Attached Figure Description

[0010] Figure 1 This is a flowchart of the vacuum casting process; Figure 2 This is a schematic diagram of the structure of a vacuum casting equipment; In the diagram: 1. Punch; 2. Pressure chamber; 3. Injection port; 4. End point; 5. Mold cavity. Detailed Implementation

[0011] The present invention will be further described in detail below with reference to specific embodiments.

[0012] This invention provides an optimized vacuum casting process for aluminum alloys, such as... Figure 1 As shown, the steps include steps A through I.

[0013] Step A: Begin mold closing.

[0014] Step B: 0.5 seconds after the mold closing begins, the mold closing is complete, and the vacuum pump starts to pump air into the mold cavity 5 at high speed with maximum power, thereby quickly creating a vacuum in the mold cavity 5.

[0015] Step C: After the mold closes for 1 second, the molten aluminum alloy flows into the pressure chamber 2 through the injection port 3. The punch 1 moves forward at a low speed of 0.2 m / s to 0.25 m / s from the rear end of the pressure chamber 2. At this time, the vacuum pump has already drawn the mold cavity 5 into a vacuum, but it still maintains high-speed pumping to quickly remove any gas that may have accidentally appeared in the mold cavity 5.

[0016] Step D: 1.3 seconds after the mold starts closing, the punch 1 moves forward at low speed to the injection port 3 of the pressure chamber 2. It will start to accelerate after passing the injection port 3 and enter the high-speed injection state. The vacuum pump reduces the pumping speed to 10% to 20% of the high-speed pumping speed in advance before the punch 1 enters the high-speed injection state, and performs low-speed pumping.

[0017] In step E, 1.4 seconds after the mold closes, punch 1 moves forward at low speed until it just passes the injection port 3 of pressure chamber 2, then accelerates to inject molten aluminum alloy into mold cavity 5. During the acceleration of punch 1, the molten aluminum alloy in pressure chamber 2 is accelerated. The molten aluminum alloy is in an unstable state during acceleration and is relatively easy to be disturbed. If it is disturbed significantly, it is easy to exceed the critical point, causing it to splash when entering mold cavity 5, affecting the quality of the casting. To prevent this from happening, the vacuum pump has been reduced to a low speed for evacuation 0.1 seconds in advance (i.e., 1.3 seconds after the mold closes in step D), which has very little disturbance to the molten aluminum alloy and will not cause the instability of the molten aluminum alloy during acceleration to exceed the critical point, thus making it less likely for the molten aluminum alloy to splash.

[0018] Step F: 1.45 seconds after the mold is closed, the punch 1 accelerates to a high speed of 4 m / s ~ 6 m / s, then stops accelerating and maintains this speed for high-speed injection. Step G: 1.5 seconds after the mold closing begins, 0.05 seconds have passed since the punch 1 stopped accelerating. This ensures that both the punch 1 and the molten aluminum alloy are at a constant speed, and the instability of the molten aluminum alloy is lower than during acceleration, making it less likely to exceed the critical point. Therefore, the vacuum pump resumes its high-speed pumping rate, which quickly removes any unexpected gas from the mold cavity 5 without causing the molten aluminum alloy to exceed the critical point and splash.

[0019] Step H: 1.7 seconds after mold closing begins, punch 1 reaches the front end 4 of pressure chamber 2 to complete injection. The vacuum pump then begins to pump air at a medium speed of 40%~50% of its high-speed pumping rate. The mold then begins to hold pressure.

[0020] Step I: After 6.5 seconds of mold closing, the mold pressure holding ends and the vacuum pump stops pumping air.

[0021] The above description is merely an embodiment of the present invention and does not limit the scope of patent protection. Any non-substantial changes or substitutions made by those skilled in the art based on the present invention still fall within the scope of patent protection.

Claims

1. An optimized vacuum casting process for aluminum alloys, characterized in that, Includes the following steps: Step A: Begin mold closing; Step B: 0.5 seconds after the mold closing begins, the mold closing is complete, and the vacuum pump starts to pump air into the mold cavity at high speed. Step C: 1 second after the mold closes, the molten aluminum alloy flows into the pressure chamber through the injection port, and the punch moves forward at a low speed from the rear end of the pressure chamber; the vacuum pump maintains high-speed air extraction to remove any gas that may have appeared unexpectedly in the mold cavity. Step D: 1.3 seconds after the mold starts closing, the punch moves forward at a low speed to the injection port that is close to the pressure chamber, and the vacuum pump reduces the pumping speed to a low speed. Step E: 1.4 seconds after the mold starts closing, the punch moves forward at low speed until it just passes the injection port of the pressure chamber, and then it starts to accelerate forward to inject the molten aluminum alloy in the pressure chamber into the mold cavity at high speed. Step F: 1.45 seconds after the mold closing begins, the punch accelerates to high speed and then stops accelerating. Step G: 1.5 seconds after the mold closes, the vacuum pump restores the pumping speed to high speed. Step H: 1.7 seconds after the mold starts closing, the punch just reaches the end of the front end of the pressure chamber to complete the injection. The vacuum pump starts to pump air at medium speed, and the mold starts to hold pressure. Step I: After 6.5 seconds of mold closing, the mold pressure holding ends and the vacuum pump stops pumping air.

2. The aluminum alloy vacuum casting process with optimized evacuation timing as described in claim 1, characterized in that: The low-speed pumping rate is 10% to 20% of the high-speed pumping rate.

3. The aluminum alloy vacuum casting process with optimized evacuation timing as described in claim 1, characterized in that: The medium-speed pumping rate is 40% to 50% of the high-speed pumping rate.

4. The aluminum alloy vacuum casting process with optimized evacuation timing as described in claim 1, characterized in that: The punch moves forward at a low speed of 0.2 m / s to 0.25 m / s and at a high speed of 4 m / s to 6 m / s.

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