- Jun 19, 2018 -
A casting may be defined as a " metal object obtained by allowing molten metal to solidify in a mold ", the shape of the object being determined by the shape of the mold cavity.Certain advantages are inherent in the metal casting process. These often form the basis for choosing casting over other shaping processes such as machining, forging, welding, stamping, rolling, extruding, etc.
Some of the reasons for the success of the casting process are: The most intricate of shapes, both external and internal, may be cast. As a result, many other operations, such as machining, forging, and welding, can be minimized or eliminated. Because of their physical properties, some metals can only be cast to shape since they cannot be hot-worked into bars, rods, plates, or other shapes from ingot form as a preliminary to other processing. Construction may be simplified. Objects may be cast in a single piece which would otherwise require assembly of several pieces if made by other methods.
Metal casting is a process highly adaptable to the requirements of mass production. Large numbers of a given casting may be produced very rapidly. For example, in the automotive industry hundreds of thousands of cast engine blocks and transmission cases are produced each year. Extremely large, heavy metal objects may be cast when they would be difficult or economically impossible to produce otherwise. Large pump housing, valves, and hydroelectric plant parts weighing up to 200 tons illustrate this advantage of the casting process.
Some engineering properties are obtained more favorably in cast metals. Examples are :More uniform properties from a directional standpoint; i.e., cast metals exhibit the same properties regardless of which direction is selected for the test piece relative to the original casting. This is not generally true for wrought metals.. Strength and lightness in certain light metal alloys, which can be produced only as castings. Good bearing qualities are obtained in casting metals.
There are many more advantages to the metal-casting process; of course it is also true that conditions may exist where the casting process must give way to other methods of manufacture, when other processes may be more efficient. For example, machining procedures smooth surfaces and dimensional accuracy not obtainable in any other way; forging aids in developing the ultimate of fiber strength and toughness in steel; welding provides a convenient method of joining or fabricating wrought or cast products into more complex structures; and stamping produces lightweight sheet metal parts. Thus the engineer may select from a number of metal processing methods that one or combination, which is most suited to the needs of his work.