Fundamental of Materials Forming,-Casting basic concept,Main contents,1、铸造的概念及特点、铸造技术的发展；Fundamentals of Metal-Casting 2、金属铸造工艺Metal-Casting Processes砂型铸造及其工艺设计；特种铸造及其工艺； 3、铸件的结构设计、材料及经济性Metal Casting: Design, Materials, and Economics 5、先进铸造技术。Advanced Casting,Sand Casting,Sand Casting process,The concept for Casting,Schematic illustration of a typical riser-gated casting. Risers serve as reservoirs, supplying molten metal to the casting as it shrinks during solidification. See also Fig. 11.4 Source: American Foundrymens Society.,Why Sand Casting?,In metal casting work, as with almost every kind of manufacture, high precision means high cost. In a case we are making a small number of objects so we cant really afford to make a sophisticated metal mold (i.e. we cant do die casting). The usual approach in this case is to make disposable molds out of sand or plaster. The kind of disposable mold, and the techniques used to make the mold, are again determined by questions of cost and quality. For a very intricate, precise result, lost wax or lost polystyrene foam casting is used. For less intricate workpieces, or lower precision requirements, direct sand casting can be adequate.,What is Sand Casting?,All casting, not just sand casting, is about pouring or squirting a molten substance into a cavity. All casting methods require two basic things: A cavity which is the shape of the desired final object, and A way to put molten substance into the cavity. In the sand casting process, the cavity is made of sand which is held together by a binder (a substance that holds the sand grains together).,Sand casting is used to produce a wide variety of metal components with complex geometries. These parts can vary greatly in size and weight, ranging from a couple ounces to several tons. Some smaller sand cast parts include components as gears, pulleys, crankshafts, connecting rods, and propellers. Larger applications include housings for large equipment and heavy machine bases. Sand casting is also common in producing automobile components, such as engine blocks, engine manifolds, cylinder heads, and transmission cases.,Die-Casting Examples,Figure 11.1 (a) The Polaroid PDC-2000 digital camera with a AZ91D die-cast, high purity magnesium case. (b) Two-piece Polaroid camera case made by the hot-chamber die casting process. Source: Courtesy of Polaroid Corporation and Chicago White Metal Casting, Inc.,Casting Examples,Figure 11.2 Typical gray-iron castings used in automobiles, including transmission valve body (left) and hub rotor with disk-brake cylinder (front). Source: Courtesy of Central Foundry Division of General Motors Corporation.,Figure 11.3 A cast transmission housing.,Solidification Processes,Starting work material is either a liquid or is in a highly plastic condition, and a part is created through solidification of the material Solidification processes can be classified according to engineering material processed: Metals Ceramics, specifically glasses Polymers and polymer matrix composites (PMCs),Classification of solidification processes,Casting,Process in which molten metal flows by gravity or other force into a mold where it solidifies in the shape of the mold cavity The term casting also applies to the part made in the process Steps in casting seem simple: Melt the metal Pour it into a mold Let it freeze,Capabilities and Advantages of Casting,Can create complex part geometries Can create both external and internal shapes Some casting processes are net shape; others are near net shape Can produce very large parts Some casting methods are suited to mass production,Disadvantages of Casting,Different disadvantages for different casting processes: Limitations on mechanical properties Poor dimensional accuracy and surface finish for some processes; e.g., sand casting Safety hazards to workers due to hot molten metals Environmental problems,Parts Made by Casting,Big parts: engine blocks and heads for automotive vehicles, wood burning stoves, machine frames, railway wheels, pipes, church bells, big statues, and pump housings Small parts: dental crowns, jewelry, small statues, and frying pans All varieties of metals can be cast, ferrous and nonferrous,Overview of Casting Technology,Casting is usually performed in a foundry Foundry = factory equipped for making molds, melting and handling molten metal, performing the casting process, and cleaning the finished casting Workers who perform casting are called foundrymen,The Mold in Casting,Contains cavity whose geometry determines part shape Actual size and shape of cavity must be slightly oversized to allow for shrinkage of metal during solidification and cooling Molds are made of a variety of materials, including sand, plaster, ceramic, and metal,Two forms of mold: (a) open mold, simply a container in the shape of the desired part; and (b) closed mold, in which the mold geometry is more complex and requires a gating system (passageway) leading into the cavity,