Pressure casting has two characteristics of high pressure and high speed filling and die casting. Its commonly used injection specific pressure is from several thousand to several tens of thousands of kPa, and even up to 2 × 105 kPa. The filling speed is about 10~50m/s, and sometimes it can 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:
Good product quality
Casting dimensional accuracy is high, generally equivalent to 6~7, even up to 4; good surface finish, generally equivalent to 5~8; high strength and hardness, generally higher than sand casting by 25~30%, but extended The rate is reduced by about 70%; the size is stable and the interchangeability is good; the thin-walled complex casting can be die-cast. For example, the current zinc alloy die castings have a minimum wall thickness of 0.3 mm; aluminum alloy castings up to 0.5 mm; the minimum cast diameter is 0.7 mm; and the minimum pitch is 0.75 mm.
high productivity
The machine has high productivity. For example, the domestic JIII3 horizontal cold chamber die casting machine can die-cast 600-700 times on average, and the small hot chamber die-casting machine can die-cast 3000~7000 times every eight hours. The die-casting type has a long service life and a die-casting type. Die-casting alloys with a life span of several hundred thousand times or even millions of times; easy to mechanize and automate.
Excellent economic effect
Due to the precise size of the die casting, the surface is smooth and so on. Generally, it is no longer mechanically processed and used directly, or the processing amount is small, so that the utilization rate of the metal is improved, and a large amount of processing equipment and man-hours are reduced; the price of the casting is easy; the combined die-casting can be used for other metal or non-metal materials. Saves assembly time and saves metal.
Die casting disadvantage
Although die casting has many advantages, it also has some shortcomings that have yet to be resolved. Such as:
1). During the die casting, because the liquid metal filling cavity has a high velocity and the flow state is unstable, the general die casting method is adopted, and the casting is prone to generate pores and cannot be heat treated;
2). Die casting is difficult for complex concave castings;
3). High melting point alloys (such as copper, ferrous metals), die casting type has a lower life;
4). It is not suitable for small batch production. The main reason is that the die casting type has high manufacturing cost, the die casting machine has high production efficiency, and the small batch production is uneconomical.
2. Application range 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 chipping and no chipping. 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 are also being used to die cast cast iron and cast steel.
The size and weight of the die casting depends on the power of the die casting machine. Due to the increasing power of the die casting machine, the shape of the casting can range from a few millimeters to 1-2 m; the weight can range from a few grams to several tens of kilograms. Foreignly, aluminum castings with a diameter of 2m and a weight of 50kg can be die-cast. Die-casting parts are no longer limited to the automotive industry and instrument industry, and gradually expand to dozens of other industrial sectors, such as agricultural machinery, machine tool industry, electronics industry, defense industry, computers, medical equipment, watches, cameras and daily-use hardware. industry. In the die-casting technology, new processes such as vacuum die-casting, oxygen-added die-casting, precision-speed die-casting, and application of soluble cores have emerged.