How It's Made Jesus by Metal Casting
In Casting (metalworking) and jewellery making, casting is a process in which a liquid metal is somehow delivered into a mold (it is usually delivered by a crucible) that contains a hollow shape (i.e., a 3-dimensional negative image) of the intended shape. The metal is poured into the mold through a hollow channel called a sprue. The metal and mold are then cooled, and the metal part (the casting) is extracted.
Casting is most often used for making complex shapes that would be difficult or uneconomical to make by other methods:
Casting processes have been known for thousands of years, and have been widely used for sculpture (especially in bronze) and tools. Traditional techniques include lost-wax casting (which may be further divided into centrifugal casting and vacuum assist direct pour casting), plaster mold casting and sand casting.
The modern casting process is subdivided into two main categories: expendable and non-expendable casting. It is further broken down by the mold material, such as sand or metal, and pouring method, such as gravity, vacuum, or low pressure.
Permanent mold casting is a metal casting process that employs reusable molds("permanent molds"), usually made from metal. The most common process uses gravity to fill the mold.
However, gas pressure or a vacuum are also used. A variation on the typical gravity casting process, called slush casting, produces hollow castings. Common casting metals are aluminum, magnesium, and copper alloys.
Cooling curves are important in controlling the quality of a casting. The most important part of the cooling curve is the cooling rate which affects the micro structure and properties. Generally speaking, an area of the casting which is cooled quickly will have a fine grain structure and an area which cools slowly will have a coarse grain structure. Below is an example cooling curve of a pure metal or eutectic alloy, with defining terminology.
There are a few common methods for filling the mold cavity: gravity, low-pressure, high-pressure, and vacuum.Vacuum filling, also known as counter-gravity filling, is more metal efficient than gravity pouring because less material solidifies in the gating system. Gravity pouring only has a 15 to 50% metal yield as compared to 60 to 95% for vacuum pouring.
