Die casting is a casting process in which liquid metal is injected at high speed under high pressure to fill the mold cavity, and then solidified and formed under pressure. Due to the high-speed injection filling characteristics of die-casting, the entrapment of gas in the mold cavity leads to defects in the die-casting parts, resulting in high scrap rates, poor microstructure, and poor mechanical properties. In order to reduce or eliminate the adverse effects of cavity gas on die-casting forming, improve the process quality and mechanical properties of die-casting parts, many new die-casting methods have been developed at home and abroad, such as laminar filling method or ultra-low speed die-casting method, oxygen filled die-casting method, vacuum die-casting method, etc. Among them, vacuum die-casting method has been widely promoted and applied due to its good application effect and high reliability.
The three-dimensional chilled exhaust valve is developed based on the ordinary chilled exhaust valve, which designs the "one" straight exhaust channel into a "W" - shaped curve structure. Its main purpose is to increase the width of the exhaust channel and increase the exhaust area. When this type of vacuum valve is applied in the vacuum die-casting process, under the same vacuum die-casting parameters, its pumping efficiency is equivalent to that of a mechanical cut-off vacuum valve, and its reliability is equivalent to that of a regular chilled exhaust valve. Based on the characteristics of the three-dimensional cryogenic exhaust valve, a vacuum control system was developed, and computer filling simulation, mold scheme optimization, and experiments were carried out for the actual production of oil pan parts, verifying that the three-dimensional cryogenic exhaust valve has the advantages of high pumping efficiency, high reliability, and low maintenance cost.

Graphic and textual results

The three-dimensional cryogenic exhaust valve is developed on the basis of ordinary cryogenic exhaust valves, focusing on solving the problem of significantly increasing the exhaust cross-sectional area of the exhaust channel without increasing the projection area of the vacuum valve exhaust channel (i.e. without increasing the locking force), thereby improving the pumping speed. When the thickness of the exhaust passage is constant, the exhaust passage width of the three-dimensional chilled exhaust valve will be 2-4 times that of the ordinary exhaust valve, which means that the exhaust area can be increased by 1-3 times. Therefore, the pumping efficiency of the three-dimensional chilled exhaust valve is 2-4 times that of the ordinary exhaust vacuum valve.

To explore the application effect of the three-dimensional cooling exhaust valve, a die-casting oil pan part was selected for testing. The product structure is shown in Figure 4. Its external dimensions are 477.8mm × 336mm × 115.2mm, and the casting mass is 4.1kg. The oil pan originally used a common chilled exhaust valve, and its die-casting process is shown in Figure 5. If the ordinary cryogenic exhaust valve is changed to a three-dimensional cryogenic exhaust valve, it is necessary to understand the filling process of the original plan, optimize the original plan, and finally form a suitable pouring system and exhaust system for the three-dimensional cryogenic exhaust valve. Analyze the flow state of aluminum liquid during the filling process of the original plan, as shown in Figure 6.

he three-dimensional cooling exhaust valve can efficiently extract gas from the mold cavity, achieving the goal of eliminating or reducing gas induced process defects, improving the internal quality of castings, and improving the appearance quality of products. The three-dimensional cryogenic exhaust valve die-casting inherits the advantages of ordinary exhaust block vacuum die-casting process while greatly improving the quality of castings, increasing the process yield and qualification rate, and is suitable for the production of complex die-casting parts.

Author of this article:
Xu Feiyue, Chen Jianhong, Continuation of Three Excellencies, An Zhaoyong, Yu Liang
Guangdong Hongtu Technology Co., Ltd
Wang came to China
Australian Federal Institute for Science and Industry Research
Source of this article: Journal of Special Casting and Nonferrous Alloys