Casting Processes of Metals
China precision machining 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. Casting is basically melting a solid material, heating to a special temperature, and pouring the molten material into a cavity or mold, which is in proper shape. Casting has been known by human being since the 4th century B.C.
In all casting processes six basic factors are involved. These are as follows:
1. China precision machining A mold cavity, having the desired shape and size and with due allowance for shrinkage of the solidifying metal, must be produced. Any complexity of shape desired in the finished casting must exist in the cavity. Consequently, the mold material mustsuch as to reproduce the desired detail and also have a refractory character so that it will not be significantly affected by the molten metal that it contains. Either a new mold must be prepared for each casting, or it must be made from a material that can withstand being used for repeated castings, the latter being called permanent molds.
2. A suitable means must be available for melting the metal that is to be cast, providing not only adequate temperature, but also satisfactory quality and quantity at low cost.
3. The molten metal must be introduced into the mold in such a manner that all air or gases in the mold, prior to pouring or generated by the action of the hot metal upon the mold, will escape, and the mold will be completely filled. A quality casting must be dense and free from defects such as air holes.
4. Provision must be made so that the mold will not cause too much restraint to the shrinkage that accompanies cooling after the metal has solidified. Otherwise, the casting will crack while its strength is low. In addition, the design of the casting must be such that solidification and solidification shrinkage can occur without producing cracks and internal porosity or voids.
5．It must be possible to remove the casting from the mold so a permanent mold must be made in two or more sections.
6．After removal from the mold, finishing operations may need to be performed to remove extraneous material that is attached to China precision machining the casting as the result of the method of introducing the metal into the cavity, or is picked up from the mold through contact with the metal.