外文翻译--铸造和铸造过程.doc

Casting and its processes Introduction Manufacturing process can be classified into two general groups known as primary and secondary processes. The primary processes, namely, casting, forging, cold heading, cold extruding, brake forming, and so on, are those that convert raw material into shapes. These forming methods include both hot and cold working processes and, in general, will still require further finishing operations in order to obtain an end product. The secondary processes are those that bring the part to the dimensions and surface finish specified. One may also include in the secondary processes such operations as heat treating and surface treatments for corrosion resistance, hardness, and appearance. Secondary processes are planning , turning ,milling, drilling , boring , reaming , broaching , grinding , honing ,lapping , polishing , and special methods of metal removal such as electrochemical machining. Operations like screw cutting, tapping, thread milling, gear cutting, and so on ,are secondary processes that are merely adaptations of one of the aforementioned processes that are merely adaption of one of the aforementioned processes. A complete discussion of these procedures is beyond the scope of this text. Therefore, we will confine ourselves to succinct descriptions of the most prominent techniques. 1.2 Castings Castings are identified by the type of mold or the force required toy fill the mold. Molds are either permanent or expendable. The pattern of sand, shell, and plaster molds, however, can be used repeatedly for making new molds. As the metal cools, it takes the shape of the cavity. The basic casting methods are described below. Sand castings. 1. The green sand process is one in which most, bonded sands packed around a wood or metal pattern. The pattern is then removed and molten metal is poured into the cavity .When the metal solidifies, the mold is broken and the casting is removed . Almost any metal can be used, with virtually no l