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Metal casting is one of the most important metal part production process avaliable in manufacturing industry. There are various kinds of metal casting processes avaliable in industry, and selection of proper metal casting process for your material and shape of product is very important thing. This article about metal casting processes;
Metal casting is a process that molten metal is poured inside a mold cavity in which the cavity is obtained via pattern of the produced metal part from it. Until solidification, molten metal reside inside mold cavity. After the solidification, metal part is taken from mold cavity. Additional machining operations can be applied to cast metal part to obtain net shape from it.
All the metal casting processes are classified into two groups; Expandable mold metal casting processes and permanent mold metal casting processes.
In expandable mold metal casting processes, the obtained mold for casting operation is destroyed to extract the solidified metal part from it.
Sand metal casting method is one of the most used method to produce metal parts. Wide variety of metal parts and wide variety of material can be cast in sand casting processes. In sand casting, mold cavity and mold is made from sand which is mixed with special resins to obtain a solid mold cavity. Sprues, gates, cores are placed in a specific orientation. Risers are also very important structures in sand casting processes.
In this kind of metal casting process, the mold cavity is obtained with sand again. The shape is given to sand with a special application of vacuum on sand with the use of films, and these two parts of sand molds are combined. Then, molten metal is poured inside the mold cavity.
Shell molding method is an another expandable mold casting method that the mold is made from sand. In this process, metal pattern is heated, then sand that is mixed with special resins is spilled on these heated metal patterns. With the application of heat, resin inside the sand is cured, a solid half of mold is obtained. Two halves of sand shells are combined and metal is poured inside it. After the solidification, metal part is extracted by destroying the sand shell mold.
In plaster and ceramic mold metal casting methods, there is no use of sand to obtain mold cavities. In here, as you understand from the name, plaster and ceramic materials are used to obtain mold cavities. In slurry form of ceramic and plaster, required mold cavity shape is given, after the solidification plaster or ceramic, molten metal is poured inside the mold. Obtained metal parts are very good in terms of surface characteristics.
In investment casting method, pattern tree in which lots of patterns are combined to each other with sprues and gates, is produced by using a special wax. Then this wax is dipped into slurry of refractory material, and coated with it. When the refractory slurry coating is solidified, heat is applied to melt the wax. So, mold is obtained to pour molten metal inside it.
Patterns are made from polystyrene foams in expanded polystyrene process, and sand is used to obtain mold cavity by using these foam patterns. Molten metal is poured directly on these foam pattern, and this foam pattern is turned into gas state with the extreme heat of molten metal. Molten metal immediately takes the place of polystyrene foam pattern and metal part is obtained.
Permanent-mold metal casting methods are the metal casting methods in which the created mold is not destroyed, and can be used in lots of casting processes. The permanent means that, there is no need for making a new mold for each cycle of metal casting. In general, molds are made from metals.
As you understand from its name that in squeeze casting, molten metal is poured inside a half of metal mold, then other half of metal mold is presses on the first half. With this pressure application, molten metal fills all the cavities inside metal mold.
In general, gravitational force is used for filling the mold cavities with molten metal. But in centrifugal casting methods, centrifugal force is obtained by rotating the mold. This centrifugal force, presses the molten metal inside cavities. There are three types of centrifugal metal casting processes avaliable in industry; First one is true centrifugal metal casting prosses in which the molten metal is poured inside a hollow tube mold to obtain hollow tube shapes such as bushings, rings etc. The second one is the semicentrifugal metal casting process in which the shapes like pulleys and rims that has radial symmetries are cast. The last one is centrifuge casting which has similar characteristics with semicentrifugal metal casting. Just a bunch of parts that have not radial symmetry are produced.
As you see above, fully liquid metal is used to fill the mold cavities generally. But in semi-solid metal casting process, metal alloys that in temperature between solidus and liquidus curves are cast. Different kinds of methods are used generally for different materials. In these temperatures, metal alloy acts as slurry. And this slurry-like metal alloy is forced into molds with screw mechanisms.
Die casting process is one of the most used permanent-mold metal casting method. The word of ‘die’ refers the use of metal mold halves in die casting process. Molten metal is forced inside metal molds with the force of plunger mechanisms. These plunger mechanisms are generally hydraulic mechanisms. There are two types of die casting processes; The first one is the cold-chamber die casting process in which the molten metal is supplied to cold chamber, that plunger pushes this molten metal inside the mold. The second die casting process is the hot-chamber die casting process in which the solid metal is supplied inside hot chamber, and the chamber of die casting machine is constantly hot. Plunger pushes the part of the molten metal inside this hot chamber. When the chamber is running out of molten metal, solid metal is added.
As you understand that, this article is a source of vast of information about metal casting processes. These are the general processes that are used in metal casting industry.
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