In recent years, in order to pursue the reasonable structure and lightweight of parts and components, the parts originally composed of several simple castings, forgings and machined parts have been replaced by a whole casting. These castings generally have the following characteristics:
(1) Complex: the contour structure of the casting is complex, the internal cavity and boss are many, the transition of thin and thick section is sudden;
(2) Thin wall: the minimum wall thickness of the casting is generally less than 4 mm, and even less than 2 mm locally. These thin wall parts are often the inner cavity of the casting, which are composed of complex curved surfaces and cannot be machined;
(3) Precision: the inner cavity and shape of the casting often require one-time forming to make it close to the final shape of the part or component, with little or no machining, which is called near net shape casting;
(4) High requirements for body performance: the requirements for anatomical mechanical properties of the designated parts of the casting body are higher than those of the national and aviation standards, and some special-purpose Aerospace castings even meet or exceed the requirements of ams-a-21180 class I castings of the US military standard;
(5) High internal quality requirements: the internal quality requirements meet the requirements of class I castings, 100% of which are subject to X-ray inspection and 100% of which are subject to fluorescent inspection.
The mechanical properties, internal quality and dimensional accuracy of the castings produced by the traditional gravity casting method often fail to meet the technical requirements, and defects such as insufficient casting and cold shut will occur, and the intact castings will not be obtained. Therefore, it is very important to select the suitable casting forming process according to the specific characteristics and technical requirements of the casting. At present, theof complex, thin-walled and precision castings mainly includes , gypsum casting, investment casting, etc.
The disadvantages of the traditional sand gravity casting complex thin-walled aluminum alloy castings: relying on the gravity filling, the filling speed is slow, and it is difficult to complete the filling for 2-3 mm thin-walled castings; the size accuracy of sand mold and sand core is low, and the process of forming mold and core is easy to lead to size out of tolerance; the surface finish is low.
However, sand casting also has the advantages that other casting methods do not have: good air permeability of sand mold, less porosity and pinhole of casting; good yielding, low tendency of hot cracking; high mechanical properties and internal quality of casting; unlimited by casting size, it can produce super large castings; very low cost.