There are several die-casting processes for aluminum alloy. Gravity die casting and pressure die casting, pressure casting is divided into high pressure casting and low pressure casting.
Gravity die casting
Gravity casting refers to a process in which molten aluminum is poured into the mold by gravity under the action of the earth's gravity. In a broad sense, gravity casting is divided into: sand mold casting, metal mold (steel mold) casting, lost foam casting, etc. Gravity casting in a narrow sense refers specifically to metal mold casting. Metal mold casting is divided into upright manual casting and tilt casting. The most commonly used metal mold (steel mold) casting is tilt casting. The mold is made of heat-resistant alloy steel, and the strength, size, and appearance of the cast aluminum castings are higher than those of other casting processes. The molten aluminum for gravity casting is generally poured into the gate manually, relying on the weight of the molten metal to fill the cavity, exhaust, cool, and open the mold to obtain the sample. The process flow is generally: molten aluminum melting, pouring mold filling, exhaust , cooling, mold opening, cleaning, heat treatment, and processing.
High pressure die casting
High-pressure casting is what we usually call die casting. The aluminum liquid is poured into the pressure chamber, the mold cavity is filled at high speed by its pressure, and the liquid aluminum is solidified under pressure to form an aluminum casting. A method in which liquid or semi-solid metal or alloy, or liquid metal or alloy containing a reinforcement phase, is filled into the cavity of a die-casting mold at a high speed under high pressure, and the metal or alloy is solidified under pressure to form a casting. The commonly used pressure during die casting is 4-500MPa, and the metal filling speed is 0.5-120m/s. Therefore, the filling time of molten metal is very short, and the mold cavity can be filled in about 0.01-0.2 seconds (depending on the size of the casting). Therefore, high pressure and high speed are the fundamental differences between die casting and other casting methods, and they are also important features.
Low pressure die casting
In the sealed crucible (or sealed tank), dry compressed air is introduced. Under the action of gas pressure, the metal liquid rises along the riser tube into the sprue, enters the mold cavity smoothly through the inner runner, and keeps the crucible gas pressure on the inner liquid surface. until the casting is completely solidified. Then the gas pressure on the liquid surface is released, allowing the unsolidified metal liquid in the liquid riser to flow back to the crucible. Reopen the mold and remove the casting. This casting method has good feeding and dense casting structure. It is easy to cast large, thin-walled and complex castings without the need for risers, and the metal yield reaches 95%. No pollution, easy to realize automation. However, the equipment cost is higher and the production efficiency is lower. Generally used for casting non-ferrous alloys.