Define the casting process, describe the processes of sand casting, pressure die casting and lost wax casting. list out the Advantages and disadvantages of the casting process involved.
The processes of sand casting
Step by step
A solid replica of the required object is made: the ‘pattern’. Sand is then rammed around the pattern in a ‘moulding box’. When the pattern is removed it leaves a shaped cavity behind. The runners (where the fluid is poured in) and risers (where excess fluid can escape) also act as reservoirs of liquid to top up the casting as the metal contracts on cooling. The process can be used, perhaps surprisingly, to make hollow castings. To do this, ‘cores’ are inserted into moulds to produce shapes that would be difficult or impossible to make by just using a pattern. The mould is destroyed when the solid casting is removed.
The processes of pressure die casting
Step by step
Pressure-die casting is a development of gravity-die casting in which the molten metal is injected into a steel mould under pressure, it is the metal equivalent of injection moulding. The basic die casting process consists of injecting molten metal under high pressure into a steel mold called a die. Die casting machines are typically rated in clamping tons equal to the amount of pressure they can exert on the die. Machine sizes range from 400 tons to 4000 tons. Regardless of their size, the only fundamental difference in die casting machines is the method used to inject molten metal into a die. The two methods are hot chamber or cold chamber. A complete die casting cycle can vary from less than one second for small components weighing less than an ounce, to two-to-three minutes for a casting of several pounds, making die casting the fastest technique available for producing precise non-ferrous metal parts.
The processes of lost wax casting.