Introduction to Metal Casting | Casting terms | Advantages and Disadvantages Of Casting
Casting is a manufacturing process by which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process.
|Examples Of Casting Parts|
Metal Casting is one of the oldest materials shaping methods known. Casting means pouring molten metal into a mold with a cavity of the shape to be made, and allowing it to solidify. When solidified, the desired metal object is taken out from the mold either by breaking the mold or taking the mold apart. The solidified object is called the casting. By this process, intricate parts can be given strength and rigidity frequently not obtainable by any other manufacturing process. The mold, into which the metal is poured, is made of some heat resisting material. Sand is most often used as it resists the high temperature of the molten metal. Permanent molds of metal can also be used to cast products.
- Flask: A metal or wood frame, without fixed top or bottom, in which the mold is formed. Depending upon the position of the flask in the molding structure, it is referred to by various names such as drag – lower molding flask, cope – upper molding flask, cheek – intermediate molding flask used in three piece molding
- Pattern: It is the replica of the final object to be made. The mold cavity is made with the help of pattern.
- Parting line: This is the dividing line between the two molding flasks that makes up the mold.
- Molding sand: Sand, which binds strongly without losing its permeability to air or gases. It is a mixture of silica sand, clay, and moisture in appropriate proportions.
- Facing sand: The small amount of carbonaceous material sprinkled on the inner surface of the mold cavity to give a better surface finish to the castings.
- Core: A separate part of the mold, made of sand and generally baked, which is used to create openings and various shaped cavities in the castings.
- Pouring basin: A small funnel shaped cavity at the top of the mold into which the molten metal is poured.
- Sprue: The passage through which the molten metal, from the pouring basin, reaches the mold cavity. In many cases it controls the flow of metal into the mold.
- Runner: The channel through which the molten metal is carried from the sprue to the gate.
- Gate: A channel through which the molten metal enters the mold cavity.
- Chaplets: Chaplets are used to support the cores inside the mold cavity to take care of its own weight and overcome the metallostatic force.
- Riser: A column of molten metal placed in the mold to feed the castings as it shrinks and solidifies. Also known as “feed head”.
- Vent: Small opening in the mold to facilitate escape of air and gases.
Advantages Of casting
The metal casting process is extensively used in manufacturing because of its many advantages.
- Molten material can flow into very small sections so that intricate shapes can be made by this process. As a result, many other operations, such as machining, forging, and welding, can be minimized or eliminated.
- It is possible to cast practically any material that is ferrous or non-ferrous.
- As the metal can be placed exactly where it is required, large saving in weight can be achieved.
- The necessary tools required for casting molds are very simple and inexpensive. As a result, for production of a small lot, it is the ideal process.
- There are certain parts made from metals and alloys that can only be processed this way.
- Size and weight of the product is not a limitation for the casting process.
Limitations of casting
- Dimensional accuracy and surface finish of the castings made by sand casting processes are a limitation to this technique. Many new casting processes have been developed which can take into consideration the aspects of dimensional accuracy and surface finish. Some of these processes are die casting process, investment casting process, vacuum-sealed molding process, and shell molding process.
- The metal casting process is a labor intensive process