The existence of pressure is the main feature of the die casting process that distinguishes other casting methods. The injection force is the force that pushes 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 magnitude 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 pressure-injection force (N-cow)
P injection cylinder – pressure of working fluid in the injection cylinder (Pa-Pa)
D-injection cylinder diameter (m-meter)
π=3.1416 The pressure of the molten metal in the pressure chamber per unit area is called the specific pressure. The specific pressure is also the injection force and the pressure chamber.
The result of the conversion of the ratio of the cross-sectional area. The calculation formula is as follows:
P specific pressure = P pressure / F pressure chamber cross-sectional area
Where: P specific pressure – specific pressure (Pa-Pa)
P pressure-injection force (N-cow)
F pressure chamber cross-sectional area – pressure chamber cross-sectional area (m2-meter 2)
That is, the cross-sectional area of the F pressure chamber = πD2/4 where D (m-meter) is the diameter of the pressure chamber
π=3.1416 (1) Effect of specific pressure on mechanical properties of castings
The specific pressure is increased, the crystal is fine, the fine crystal layer is thickened, and the surface quality is improved due to the improvement of the filling property.
The effect is reduced, so that the tensile strength is increased, but the elongation is reduced.
Influence on filling conditions
The alloy melt 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.
The quality of the parts is improved. (1) According to the strength requirements of the castings
The castings are divided into two categories: strength requirements and general requirements. For strength requirements, they should have
Good density. This is to use a high pressure ratio.
According to the wall thickness of the casting
Under normal circumstances, when die-casting thin-walled castings, the flow resistance in the cavity is large, and the ingate is also thinner, so it has a large resistance, so it is necessary to have a larger filling specific pressure to ensure that it is needed. Insulation speed. For thick-walled castings, on the one hand, the selected ingate speed is lower, and the solidification time of the metal is longer, and a smaller filling specific pressure can be used; on the other hand, in order to make the casting have a certain Density, you need to have Sufficient pressurization specific pressure can meet the requirements.
For complex shapes, the filling specific pressure should be higher. In addition, such as the type of alloy, the size of the gate, the power of the mold clamping machine and the strength of the mold, etc. All should be properly considered. The size of the filling specific pressure is mainly calculated according to the selected ingate speed. As for the pressure ratio of the supercharging pressure, according to the alloy category, it can be selected with reference to the following table. When the cavity is exhausted Good condition, if the ratio of the thickness of the gate to the wall thickness of the casting is appropriate, the low pressure ratio can be selected. The worse the exhaust condition, the smaller the ratio of the thickness of the gate to the wall thickness of the casting, the pressure ratio The higher the pressure should be.
Recommended pressure ratio range of die casting process
Part Type Aluminum Alloy Zinc Alloy Brass
Parts subject to light load 30～40MPa 13～20MPa 30～40MPa
Parts subject to heavy load 40～80MPa 20～30MPa 40～60MPa
Airtight surface large wall thin parts 80～120MPa25～40MPa 80～100MPa