Die casting: high and low points
1 high pressure casting (referred to as casting) is the essence of under high pressure, the liquid or semi liquid metal with high speed filling pressure casting (die casting) cavity, and forming under pressure and solidification and casting method. The pressure casting, there are two characteristics of high pressure and high pressure mold filling. It is commonly used in the injection pressure is from several thousand to tens of thousands of kPa, even up to 2 * 105kPa. The filling speed of about 10~50m/s, sometimes even 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 and high dimension accuracy of castings; good surface smoothness, generally equivalent to 5~8; the hardness and strength of high strength than sand casting to improve 25~30%, but the elongation decreased about 70%; dimensional stability, good interchangeability; can die casting complex thin-wall castings. High efficiency machine with high productivity, such as domestic J III 3 type horizontal cold air machine an average of eight hours can be 600 ~ 700 times of small die casting, hot chamber die casting machine every eight hours can be 3000~7000 times of die casting; long life, a pair of pressing mould, die casting bell alloy, life of up to tens of million times, or even millions of times; easy to realize mechanization and automation. The economic effect is good because of casting dimension precision, surface finish and other advantages of pan.General no longer machining and use directly or processing capacity is very small, so it improves the utilization rate of the metal, and reduce the processing equipment and a large number of working hours; the price of the casting is easy; can be used in combination with other casting metal or non-metal materials. Save time and save metal assembly.
Die casting defects
Die casting have many advantages, but there are also some shortcomings, remains to be solved. Such as:
1). Casting the liquid metal mould filling high speed, flow instability, so the general casting method, the casting is easy to produce internal pores, the elongation is not good, can not be heat treated;
2). The concave complex casting, die casting is difficult;
3). High melting point alloys (such as copper, ferrous metal), die life is low;
4). For small batch production, the main reason is the die manufacturing cost is high, the production efficiency of the die casting machine, small batch production is not economic;
5). The cost of equipment and molds.
2 low pressure casting
(1) when pouring pressure and speed can be adjusted, so it can be applied to a variety of different moulds (such as metal and sand etc.), all kinds of alloy casting and various sizes of castings.
(2) the end of injection mold filling, filling smoothly, no splash phenomenon can be avoided in gas and scour on the wall and the core, improve the qualified rate of castings.
(3) casting under pressure casting crystallization, compact structure, clear, smooth surface, high mechanical properties, it is beneficial for large thin-walled casting.
(4) save riser, metal utilization rate increased to 90 ~ 98%.
5) low labor intensity, good working conditions, simple equipment, easy to realize mechanization and automation. The advantages and disadvantages of  (relative gravity type casting gold) advantages and disadvantages:
1) the casting rate is very high. (85~95%)
Because there is no riser and the sprue gate is small, therefore, greatly reduce the material cost and the processing time can be.
2) to get the perfect casting.
Easy to form the directional solidification, small internal defects.
3) in gas, less debris.
You can change the compression speed, melt by laminar filling.
4) can use sand core.
5) automation is easy to realize, can be more than one job, working procedure.
6) is not affected by the proficiency of the operator.
7) the use of wide range of materials.
8) can enhance the performance of heat treatment.
1) gate scheme of freedom, thus limiting the product.
(gate location, limit the number of products, internal wall thickness etc.)
2) casting production cycle is long, the poor.
In order to maintain directional solidification and melt fluidity, higher mold temperature, slow solidification rate.
3) near the gate of the tissue is thick, the mechanical performance is not high under the.
4) requires a comprehensive and rigorous management (temperature and pressure).