The essence of pressure casting (die casting for short) is to make liquid or semi liquid metal fill the die casting mold cavity at a high speed under the action of high pressure, and form and solidify under pressure to obtain castings.

1. Die casting features

High pressure and high-speed filling die-casting mold are two characteristics of die-casting. Its commonly used injection specific pressure ranges from thousands to tens of thousands of kPa, or even as high as 2 ×。 The filling speed is about 10~ / s, sometimes even more than / s. The filling time is very short, generally within the range of 0.01~0.2s. Compared with other casting methods, die casting has the following three advantages:

1. good product quality

High dimensional accuracy of castings, generally equivalent to grade 6~7, or even grade 4; Good surface finish, generally equivalent to grade 5~8; The strength and hardness are higher, the strength is generally 25~30% higher than that of sand casting, but the elongation is reduced by about 70%; Stable size and good interchangeability; It can die cast thin-walled and complex castings. For example, at present, the minimum wall thickness of zinc alloy die castings can reach 0.3mm; Aluminum alloy castings can reach 0.5mm; The minimum casting hole diameter is 0.7mm; The minimum pitch is 0.

2. high production efficiency

The productivity of the machine is high. For example, the domestic J Ⅲ 3 horizontal cold air die casting machine can die cast ~ times every eight hours, and the small hot chamber die casting machine can die cast ~ times every eight hours; The service life of die-casting mold is long. A pair of die-casting mold and die-casting bell alloy can have a service life of hundreds of thousands or even millions of times; Easy to realize mechanization and automation.
3. excellent economic effect

Because the die-casting parts have the advantages of accurate size and smooth surface. Generally, it is not directly used for machining, or the processing volume is very small, so it not only improves the metal utilization, but also reduces a large number of processing equipment and man hours; Easy casting price; Combined die casting can be used for other metallic or non-metallic materials. Save both assembly time and metal.

Although die casting has many advantages, it also has some disadvantages that need to be solved. For example:

1). During die casting, due to the high speed of filling the mold cavity with liquid metal and the unstable flow state, the general die casting method is adopted, so the castings are prone to produce air holes and cannot be heat treated;

2). It is difficult to die cast the castings with complex concave;

3). High melting point alloys (such as copper and ferrous metals), low die casting die life;

4). It is not suitable for small batch production. The main reason is that the manufacturing cost of die-casting mold is high, the production efficiency of die-casting machine is high, and small batch production is uneconomical.

2. Application scope and development trend of die casting

Die casting is one of the most advanced metal forming methods. It is an effective way to achieve less chip and no chip. It is widely used and develops rapidly. At present, die-casting alloys are no longer limited to non-ferrous metals such as zinc, aluminum, magnesium and copper, but also gradually expanded to die-casting cast iron and steel castings.

The size and weight of die castings depend on the power of the die casting machine. Due to the increasing power of die casting machine, the shape and size of castings can range from a few millimeters to 1 ~ 2m; The weight can range from a few grams to tens of kilograms. Aluminum castings with diameter of 2M and weight of can be die cast abroad. Die casting is no longer limited to the automobile industry and instrument industry, but gradually expanded to other industrial sectors, such as agricultural machinery, machine tool industry, electronic industry, national defense industry, computer, medical devices, clocks, cameras and daily hardware. In the aspect of die-casting technology, new technologies such as vacuum die-casting, oxygen die-casting, precision and dense die-casting and the application of soluble cores have emerged.