The essence of pressure casting (referred to as die casting) is a method of filling the die-casting mold cavity with liquid or semi-liquid metal at a high speed under high pressure, and forming and solidifying under pressure to obtain castings. .
Die-casting characteristics
High-pressure and high-speed filling of die-casting molds are the two major characteristics of die-casting. Its commonly used injection specific pressure ranges from several thousand to tens of thousands of kPa, or even as high as 2×105kPa. The filling speed is about 10~50m/s, and sometimes it can even reach more than 100m/s. The filling time is very short, generally in the range of 0.01~0.2s. Compared with other casting methods, die casting has the following three advantages:
1. Good product quality
The dimensional accuracy of castings is high, generally equivalent to level 6~7, or even up to 4 Grade; surface finish is good, generally equivalent to grade 5-8; strength and hardness are high, the strength is generally 25-30% higher than sand casting, but the elongation is reduced by about 70%; dimensional stability, good interchangeability; can be die-cast thin Wall complex casting. For example, the current 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; and the minimum pitch is 0.75mm.
2. High production efficiency
The machine has high productivity. For example, the domestic JIII3 horizontal cold air die casting machine can perform an average of 600 to 700 die castings in eight hours, and the small hot chamber die casting machine can perform an average of 600 to 700 die castings per hour. It can die-cast 3,000 to 7,000 times in eight hours; the die-casting mold has a long life. A pair of die-casting molds and die-casting bell alloys can have a life of hundreds of thousands or even millions of times; it is easy to realize mechanization and automation.
3. Excellent economic effect
Due to the advantages of precise size and smooth surface of die-casting parts. Generally, it is no longer mechanically processed but used directly, or the processing amount is very small, so it not only improves the metal utilization rate, but also reduces a lot of processing equipment and man-hours; the price of castings is easy; combined die-casting can be used to make other metal or non-metallic materials . Saves both assembly time and metal.
Although die casting has many advantages, it also has some disadvantages that have yet to be solved. For example:
1. During die-casting, due to the high speed of liquid metal filling the cavity and unstable flow state, the general die-casting method is used. The casting is prone to pores and cannot be heat treated
;
2. For castings with complex concavities, die-casting is more difficult;
3) For high-melting-point alloys (such as copper, ferrous metals), the life of the die-casting mold is low;
4) It is not suitable for small batch production. The main reason is that the manufacturing cost of die-casting molds is high, the production efficiency of the die-casting machine is high, and small batch production is uneconomical.
Die-casting application scope and development trend
Die-casting is one of the most advanced metal forming methods. It is an effective way to achieve less and no chips. It is widely used and is developing rapidly. At present, die-casting alloys are no longer limited to non-ferrous metals such as zinc, aluminum, magnesium and copper, and are gradually being used to die-cast cast iron and steel castings.
The size and weight of die-casting parts depend on the power of the die-casting machine. As the power of die-casting machines continues to increase, the size of castings can range from a few millimeters to 1 to 2 meters; the weight can range from a few grams to tens of kilograms. Overseas, aluminum castings with a diameter of 2m and a weight of 50kg can be die-cast. Die castings are no longer limited to the automobile industry and instrument industry, and have gradually expanded to other industrial sectors, such as agricultural machinery, machine tool industry, electronics industry, defense industry, computers, medical equipment, clocks, cameras, and daily hardware, etc. industry. In terms of die-casting technology, new processes such as vacuum die-casting, oxygenated die-casting, precision die-casting, and the application of soluble cores have emerged.