Die casting technology is the use of machine, mold and alloy and other three elements, the pressure, speed and time of the unified process. For metal hot working, the existence of pressure is the main feature of die casting process to distinguish other casting methods. Pressure casting is a kind of special casting method with less cutting and no cutting which develops rapidly in modern metal working technology. It is the process of filling the casting mold with molten metal under high pressure and high speed, and forming the casting by crystallization and solidification under high pressure. High pressure and high speed are the main characteristics of pressure casting. The commonly used pressure is tens of mpa, the filling speed (inner gate speed) is about 16 ~ 80 m/s, and the time of filling the mold cavity with liquid metal is very short, about 0.01 ~ 0.2 s.
define
Because of the high production efficiency, simple working procedure, high tolerance level of castings, good surface roughness, high mechanical strength, which can leave out the machining procedure and equipment, and saving raw materials, the production of products by this method has become an important part of our foundry industry.
Die casting process is a process of organic combination of three elements of die casting machine die casting and alloy. The process of metal filling cavity in die casting is the process of unifying technological factors such as pressure, speed, temperature and time.
At the same time, these technological factors influence each other, restrict each other, and complement each other. Only the correct selection and adjustment of these factors, so that they are consistent, can obtain the expected results. Therefore, in the process of die casting, we should not only pay attention to the technology of casting structure, the advancement of die casting die, the performance of die casting machine and the benign structure, the adaptability of die casting alloy selection and the standardization of melting process; More attention should be paid to the important effect of process parameters such as pressure, temperature and time on casting quality. In the process of die casting, we should pay attention to the effective control of these parameters.
pressure
The force that press a shot
The ejection force is the force that pushes the ejection piston to move in the ejection mechanism of die casting machine. It reflects the function of die casting machine
A primary parameter.
The injection force is determined by the cross-sectional area of the injection cylinder and the pressure of the working fluid. The ejection force is calculated by the following formula:
P injection force =P injection cylinder ×π× D1/4
Where 😛 ejection force - ejection force (N- N)
P injection cylinder - Pressure of working fluid in injection cylinder (PA-pa)
Diameter of D- injection cylinder (m- m)
PI = 3.1416
Specific pressure
The pressure per unit area of the molten metal in the press chamber is called the specific pressure. Specific pressure is also the injection force and pressure chamber
The result of the ratio relation conversion of cross-sectional area. The calculation formula is as follows:
P specific pressure =P injection force /F chamber cross-sectional area
Where 😛 specific pressure - specific pressure (PA-pa)
P Ejection force - Ejection force (N- N)
F Pressure chamber cross-sectional area - Pressure chamber cross-sectional area (M2-m 2)
That is, the cross-sectional area of F chamber =πD2/4 where D(m-m) is the diameter of the chamber
PI = 3.1416
The role of stress
(1) Effect of specific pressure on mechanical properties of castings
The specific pressure increases, the crystallization is fine, the fine crystal layer thickens, due to the improvement of filling characteristics, the surface quality is improved, and the porosity is improved
As a result, the tensile strength is increased, but the elongation is decreased.
(2) Influence on filling conditions
When the molten alloy fills the cavity under the action of high specific pressure, the temperature of the alloy increases and the fluidity improves, which is beneficial to casting
Part quality improvement.
The choice of specific pressure
(1) According to the strength requirements of the castingThe castings are divided into two categories of strength requirements and general requirements. For those with strength requirements, there should be
Good density. This should be used with high boost specific pressure.
(2) According to the casting wall thickness
In general, when die-casting thin-wall castings, the flow resistance in the cavity is large, and the inner gate is also thinner, so there is a large resistance, so there must be a large filling specific pressure to ensure that the required speed of the inner gate. For thick-walled castings, on the one hand, the selected inner gate speed is low, and the solidification time of the metal is longer, so the filling pressure can be smaller; On the other hand, in order to make the casting have a certain density, it is also necessary to have
Sufficient boost specific pressure to 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 inner gate speed, the power of the die casting machine closing capacity and the strength of the die, should be taken into account. The filling pressure is mainly calculated according to the selected inner gate velocity. As for the size of the supercharging specific pressure, according to the alloy type, can refer to the following table value selection. When the cavity exhaust conditions are good and the ratio of the inner gate thickness to the casting wall thickness is appropriate, a low boost pressure specific pressure can be selected. The worse the exhaust condition is, the smaller the ratio of inner gate thickness to casting wall thickness is, the higher the specific pressure is.
It is recommended to use the booster specific pressure range meter
Part Type Aluminum alloy zinc alloy brass
Bearing light load parts 30 ~ 40MPa 13 ~ 20MPa 30 ~ 40MPa
The parts under large load 40 ~ 80MPa 20 ~ 30MPa 40 ~ 60MPa
Air tight surface large wall thin parts 80 ~ 120MPa25 ~ 40MPa 80 ~ 100MPa
