Differences between gravity die casting and die casting
Gravity casting refers to the process in which molten metal is injected into the mold under the action of the earth's gravity, also known as casting. The generalized gravity casting includes sand mold casting, metal mold casting, investment casting, lost foam casting, mud mold casting, etc; The narrow sense of gravity casting specifically refers to metal mold casting. The metal liquid is generally poured into the gate manually, and the product is obtained by filling the cavity, venting, cooling and mold opening with the metal liquid. Its technological process includes: smelting, casting filling, exhaust, cooling, mold opening, heat treatment and metal processing. Die casting is divided into high pressure casting and low pressure casting. High pressure casting is a casting method in which molten alloy liquid is poured into the pressure chamber to fill the cavity of steel mould at high speed, and the alloy liquid is solidified under pressure to form castings. High pressure die casting is distinguished from other casting methods by its high pressure and high speed. ① The molten metal fills the mold cavity under pressure, and crystallizes and solidifies under higher pressure. The common pressure is 15-100MPa. ② The metal liquid fills the mold cavity at a high speed, usually within 10-50 m/s, and some can exceed 80 m/s (the linear velocity leading into the mold cavity through the ingate - the ingate velocity). Therefore, the filling time of the metal liquid is extremely short, about 0.01-0.2 seconds (depending on the size of the casting). The technological process of low pressure casting is as follows: in a sealed crucible (or sealed tank), dry compressed air is introduced. Under the effect of gas pressure, the metal liquid rises along the riser into the sprue, enters the mold cavity steadily through the ingate, and maintains the gas pressure on the liquid surface in the crucible. Until the casting is completely solidified. Then release the gas pressure on the liquid surface, so that the unconsolidated metal liquid in the riser flows back to the crucible. Re open the mold and take out the casting. It can also be said that low pressure casting is a compromise between high pressure casting and gravity casting.
1. Sand mold casting is a traditional casting technology which takes sand as the main molding material. Sand mold generally adopts gravity casting, and low pressure casting, centrifugal casting and other processes can also be adopted when there are special requirements. Sand casting has a wide range of adaptability. Small pieces, large pieces, simple pieces, complex pieces, single pieces and large quantities are used. The mold used for sand mold casting was usually made of wood, commonly known as wood mold. In order to change the defects of wood mold, such as easy deformation and damage, Xudong Precision Casting Factory has changed into aluminum mold or resin mold with high dimensional accuracy and long service life, except for sand mold castings produced by single piece.
2. Metal casting is a modern technology of casting hollow casting die with heat-resistant alloy steel. The metal mold can be gravity cast or die cast. The metal mold can be reused for many times. Each time the molten metal is poured, a casting can be obtained. The service life is long and the production efficiency is high. Metal castings not only have good dimensional accuracy and clean surface, but also have higher strength than sand mold when pouring the same metal liquid, so they are not easy to be damaged. Therefore, when large quantities of medium and small nonferrous metal castings are produced, the melting point of casting materials is too high, and metal mold castings are generally preferred.
3. Die casting is the metal mold pressure of the die casting machine, and is the casting technology with the highest production efficiency at present. Die casting machine is divided into hot chamber die casting machine and cold chamber die casting machine. The hot chamber die-casting machine has a high degree of automation, less material loss and higher production efficiency than the cold chamber die-casting machine. However, due to the restriction of the heat resistance of the machine parts, it can only be used for the casting production of low melting point materials such as zinc alloy and magnesium alloy. The aluminum alloy die castings widely used today can only be produced on cold chamber die casting machines due to their high melting point.