Published in： 2021-01-19 14:02:15, published via： cyanbat | clicks: 0 | Information Sources：
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It is a process in which molten metal is filled into a mold under high pressure and high speed, and crystallized and solidified under high pressure to form a casting. High pressure and high speed are the main characteristics of die casting. The commonly used pressure is tens of megapascals, the filling speed (inner gate speed) is about 16 to 80 m/s, and the time for molten metal to fill the mold cavity is extremely short, about 0.01 to 0.2 seconds.
Definitionedit
Because the products produced by this method have the advantages of high production efficiency, simple procedures, higher tolerance levels of castings, good surface roughness, and high mechanical strength, it can save a lot of machining procedures and equipment, and save raw materials. So it has become An important part of my country's foundry industry.
The die-casting process is a process in which the three elements of die-casting machine, die-casting mold and alloy are organically combined and used comprehensively. The process of filling the cavity with metal during die casting is a process that unifies the process factors such as pressure, speed, temperature and time. At the same time, these process factors influence each other, restrict each other, and complement each other. Only by selecting and adjusting these factors correctly and making them consistent can the expected results be obtained. Therefore, in the die-casting process, not only the manufacturability of the casting structure, the advanced nature of the die-casting mold, the performance and structure of the die-casting machine, the adaptability of the die-casting alloy selection and the standardization of the smelting process should be paid more attention to; pressure, temperature and time should be paid more attention. And other process parameters play an important role in the quality of castings. In the die-casting process, attention should be paid to effective control of these parameters.
Stressedit
Injection force
Injection force is the force that pushes the movement of the injection piston in the injection mechanism of the die casting machine. It reflects the function of the die casting machine
A main parameter.
The size of the injection force is determined by the cross-sectional area of the injection cylinder and the pressure of the working fluid. The calculation formula of the injection force is as follows:
P injection force = P injection cylinder×π×D2/4
Where: P injection force-injection force (N-N)
P injection cylinder-the pressure of the working fluid in the injection cylinder (Pa-Pa)
D-Injection cylinder diameter (m-meter)
π=3.1416
Specific pressure
The pressure per unit area of the molten metal in the pressure chamber is called the specific pressure. The specific pressure is also the injection force and the pressure chamber
The conversion result of the ratio relationship of the cross-sectional area. The calculation formula is as follows:
P specific pressure = P injection force / F pressure chamber cross-sectional area
Where: P specific pressure-specific pressure (Pa-Pa)
P injection force-injection force (N-N)
F pressure chamber cross-sectional area-pressure chamber cross-sectional area (m2-m2)
That is, the cross-sectional area of F pressure chamber = πD2/4 where D (m-meter) is the diameter of the pressure chamber
π=3.1416
The role of stress
(1) The influence of specific pressure on the mechanical properties of castings
The specific pressure increases, the crystals are finer, and the fine-grained layer is thickened. Due to the improved filling characteristics, the surface quality is improved, and the pores
The impact is reduced, and the tensile strength is increased, but the elongation is reduced.
(2) Impact on filling conditions
The alloy melt fills the cavity under the action of high specific pressure, the alloy temperature rises, and the fluidity improves, which is beneficial to casting
Improve the quality of parts.
Selection of specific pressure
(1) Consider the strength requirements of castings
Divide castings into two types with strength requirements and general requirements. For those with strength requirements, they should have
Good density. This is a high boost pressure.
(2) Consider the wall thickness of the casting
In general, when die-casting thin-walled castings, the flow resistance in the cavity is relatively large, and the inner gate also adopts a thinner thickness, so it has a large resistance, so a large filling pressure is required to ensure that the needs are met. Inner gate speed. For thick-walled castings, on the one hand, the selected inner gate speed is lower, and the solidification time of the metal is longer, so a smaller filling pressure can be used; on the other hand, in order to make the casting have a certain Density, also need to have
Sufficient boost pressure can meet the requirements. For castings with complex shapes, the filling pressure should be higher. In addition, such as the type of alloy, the size of the gate speed, the power of the die-casting machine's mold clamping ability and the strength of the mold, etc. , Should be properly considered. The filling specific pressure is mainly calculated based on the selected gate speed. As for the boosting specific pressure, according to the alloy type, you can refer to the following table for selection. When the cavity is exhausted If the conditions are good, and the ratio of the thickness of the inner gate to the wall thickness of the casting is appropriate, a low boost pressure can be selected. The worse the exhaust condition, the smaller the ratio of the thickness of the inner gate to the wall thickness of the casting, the higher the boost ratio The pressure should be higher.
It is recommended to use the booster specific pressure range table
Part Type Aluminum Alloy Zinc Alloy Brass
Parts bearing light load 30～40MPa 13～20MPa 30～40MPa
Parts with heavy load 40～80MPa 20～30MPa 40～60MPa
Air-tight surface large-wall thin parts 80～120MPa 25～40MPa 80～100MPa