Die casting is a casting process that allows liquid metal to rapidly spray and fill the mold cavity under high pressure, and then solidify and form 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 rate, unsatisfactory 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 both domestically and internationally, such as laminar flow 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 on the basis of the ordinary chilled exhaust valve. The straight exhaust channel is designed as a "W" - shaped curve structure, with the main purpose of increasing the width of the exhaust channel and increasing the exhaust area. When this type of vacuum valve is applied to 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 quenching exhaust valve, a vacuum control system was developed, and computer filling simulation, mold scheme optimization, and experiments were carried out for actual production of oil pan parts. It was verified that the three-dimensional quenching exhaust valve has the advantages of high pumping efficiency, high reliability, and low maintenance cost.

   Graphic and textual results

   The three-dimensional quenching exhaust valve is developed on the basis of the ordinary quenching exhaust valve, 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. not increasing the locking force), thereby improving the pumping speed. When the thickness of the exhaust duct is constant, the exhaust channel width of the three-dimensional chilled exhaust valve will be 2-4 times that of a regular exhaust valve, which means that the exhaust area can be increased by 1-3 times. Therefore, the extraction efficiency of the three-dimensional chilled exhaust valve is 2-4 times that of a regular exhaust vacuum valve.

Figure 1 Schematic diagram of exhaust channels for ordinary and three-dimensional chilled exhaust valves.

Figure 2 Comparison of Two Vacuum Valves

Figure 3 Schematic diagram of vacuum control system

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

Figure 4 Oil Pan Structure Diagram

Figure 5 Original Die Casting Process Plan

Figure 6 Flow Analysis of the Original Die Casting Process Plan

Figure 7 Optimized Die Casting Process Plan

Figure 8 Flow analysis of optimized die casting process plan

Table 1 Parameter Changes Before and After Optimization

Figure 9 Mold diagram for installing a three-dimensional chilled exhaust valve

Figure 10 Comparison of Two Casting Schemes

Figure 11 Comparison of Internal Quality Inspection Results of Oil Pan

Table 2 Product Scrap Rate Statistics (%)

   The three-dimensional quenching exhaust valve can efficiently extract gas from the mold cavity, eliminate or reduce gas induced process defects, improve the internal quality of castings, and improve the appearance quality of products. The three-dimensional quenching exhaust valve die-casting inherits the advantages of the ordinary exhaust block vacuum die-casting process, greatly improves the quality of the castings, increases 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, Continues Three Guis, An Zhaoyong, Yu Liang

Guangdong Hongtu Technology Co., Ltd

Wang Laihua

Commonwealth Institute of Science and Industry in Australia

Source of this article: Journal of Special Casting and Nonferrous Alloy