Various casting processes have been developed over the time by foundries and researchers, each with its own characteristics and applications of the metal castings to meet specific engineering and service requirements. Generally speaking, according to if the casting molds could be reused or not, the casting processes could be divided into Expendable Mold Casting, Permanent Mold Casting and Composite Mold Casting. The expendable mold casting could also divided into sand casting, shell mold casting, investment casting and lost foam casting, while the permanent mold casting mainly covers gravity die casting, low pressure die casting and high pressure die casting.
1. Expendable Mold Casting
The expendable molds are typically made of sand, plaster, ceramics, and similar materials. Generally mixed with various binders, or bonding agents. A typical sand mold consists of 90% sand, 7% clay, and 3% water. These materials are refractory (withstand high temperature of molten metal). After the casting has solidified, the expendable mold in these processes is broken up to remove the final metal castings.
2. Permanent Mold Casting
The permanent molds are mainly made of metals that maintain strength at high temperatures. They are used repeatedly. Designed so that the metal castings can be removed easily and mold can be used again. The permanent mold casting uses better heat conductor than expandable nonmetallic molds; hence, solidifying casting is subjected to a higher rate of cooling, which affects the microstructure and the grain size.
3. Composite Mold Casting
The composite molds are made of two or more different materials (such as sand, graphite, and metal) combining the advantages of each material. The composite molds have a permanent and an expendable portion and are used in various casting processes to improve mold strength, control the cooling rates, and optimize the overall economics of the casting process.
Post time: Feb-18-2021