Editing Metal casting (section)

==Expendable mold casting==
Expendable mold casting is a generic classification that includes sand, plastic, shell, plaster, and investment (lost-wax technique) moldings. This method of mold casting involves the use of temporary, non-reusable molds.

[[File:Casting processes.svg|class=skin-invert-image|700px]]

===Sand casting===
{{Main article|Sand casting}}

Sand casting is one of the most popular and simplest types of casting, and has been used for centuries. Sand casting allows for smaller batches than permanent mold casting and at a very reasonable cost. Not only does this method allow manufacturers to create products at a low cost, but there are other benefits to sand casting, such as very small-size operations. The process allows for castings small enough fit in the palm of one's hand to those large enough for a train car bed (one casting can create the entire bed for one rail car). Sand casting also allows most metals to be cast depending on the type of sand used for the molds.<ref>{{harvnb|Schleg|Kohloff|Sylvia|American Foundry Society|2003}}, chapters 2–4.</ref>
[[File:Iron bell cooling after iron pour.jpg|left|thumb|Iron bell cooling after iron pour]]
[[File:Personal protective equipment to shield from radiant heat and molten splashes - zoomed in.jpg|left|thumb|Personal protective equipment to shield from radiant heat and molten splashes]]

Sand casting requires a lead time of days, or even weeks sometimes, for production at high output rates (1–20 pieces/hr-mold) and is unsurpassed for large-part production. Green (moist) sand, which is black in color, has almost no part weight limit, whereas dry sand has a practical part mass limit of {{convert|2300|-|2700|kg|lb|abbr=on}}. Minimum part weight ranges from {{convert|0.075|-|0.1|kg|lb|abbr=on}}. The sand is bonded using clays, chemical binders, or polymerized oils (such as motor oil). Sand can be recycled many times in most operations and requires little maintenance.

===Loam molding===
{{Main article|Loam molding}}
Loam molding has been used to produce large symmetrical objects such as cannon and church bells. Loam is a mixture of clay and sand with straw or dung. A model of the produced is formed in a friable material (the chemise). The mold is formed around this chemise by covering it with loam.  This is then baked (fired) and the chemise removed. The mold is then stood upright in a pit in front of the furnace for the molten metal to be poured. Afterwards the mold is broken off. Molds can thus only be used once, so that other methods are preferred for most purposes.

===Plaster mold casting===
{{Main article|Plaster mold casting}}

Plaster casting is similar to sand casting except that [[plaster of paris]] is used instead of sand as a mold material. Generally, the form takes less than a week to prepare, after which a production rate of 1–10&nbsp;units/hr-mold is achieved, with items as massive as {{convert|45|kg|lb|abbr=on}} and as small as {{convert|30|g|oz|abbr=on|0}} with very good [[surface finish]] and close [[Engineering tolerance|tolerances]].<ref name="met">{{harvnb|Kalpakjian|Schmid|2006}}.</ref> Plaster casting is an inexpensive alternative to other molding processes for complex parts due to the low cost of the plaster and its ability to produce [[near net shape]] castings. The biggest disadvantage is that it can only be used with low melting point non-ferrous materials, such as [[aluminium]], [[copper]], [[magnesium]], and [[zinc]].<ref>{{Harvnb|Degarmo|Black|Kohser|2003|p=315}}</ref>

===Shell molding===
{{Main article|Shell molding}}

Shell molding is similar to sand casting, but the molding cavity is formed by a hardened "shell" of sand instead of a flask filled with sand. The sand used is finer than sand casting sand and is mixed with a [[resin]] so that it can be heated by the pattern and hardened into a shell around the pattern. Because of the resin and finer sand, it gives a much finer surface finish. The process is easily automated and more precise than sand casting. Common metals that are cast include [[cast iron]], aluminium, magnesium, and copper alloys. This process is ideal for complex items that are small to medium-sized.

===Investment casting===
[[Image:Nuclear valve 01.jpg|frame|An investment-cast valve cover]]
{{Main article|Investment casting}}
{{See also|Lost-wax casting}}

Investment casting (known as [[lost-wax casting]] in art) is a process that has been practiced for thousands of years, with the lost-wax process being one of the oldest known metal forming techniques. From 5000 years ago, when [[beeswax]] formed the pattern, to today's high technology waxes, refractory materials, and specialist alloys, the castings ensure high-quality components are produced with the key benefits of accuracy, repeatability, versatility,  and integrity.

Investment casting derives its name from the fact that the pattern is invested, or surrounded, with a refractory material. The wax patterns require extreme care for they are not strong enough to withstand forces encountered during the mold making. One advantage of investment casting is that the wax can be reused.<ref name=met/>

The process is suitable for repeatable production of net shape components from a variety of different metals and high performance alloys. Although generally used for small castings, this process has been used to produce complete aircraft door frames, with [[steel]] castings of up to 300&nbsp;kg and [[aluminium]] castings of up to 30&nbsp;kg. Compared to other casting processes such as [[die casting]] or [[sand casting]], it can be an expensive process. However, the components that can be produced using investment casting can incorporate intricate contours, and in most cases the components are cast near net shape, so require little or no rework once cast.

===Waste molding of plaster===
{{Unreferenced section|date=February 2009}}

A durable plaster intermediate is often used as a stage toward the production of a bronze sculpture or as a pointing guide for the creation of a carved stone. With the completion of a plaster, the work is more durable (if stored indoors) than a clay original which must be kept moist to avoid cracking. With the low cost plaster at hand, the expensive work of [[bronze]] casting or stone carving may be deferred until a patron is found, and as such work is considered to be a technical, rather than artistic process, it may even be deferred beyond the lifetime of the artist.

In waste molding a simple and thin plaster mold, reinforced by sisal or burlap, is cast over the original clay mixture. When cured, it is then removed from the damp clay, incidentally destroying the fine details in undercuts present in the clay, but which are now captured in the mold. The mold may then at any later time (but only once) be used to cast a plaster positive image, identical to the original clay. The surface of this plaster may be further refined and may be painted and waxed to resemble a finished bronze casting.

===Evaporative-pattern casting===
{{Main article|Evaporative-pattern casting}}

This is a class of casting processes that use pattern materials that evaporate during the pour, which means there is no need to remove the pattern material from the mold before casting. The two main processes are lost-foam casting and full-mold casting.

====Lost-foam casting====
{{Main article|Lost-foam casting}}

Lost-foam casting is a type of evaporative-pattern casting process that is similar to investment casting except foam is used for the pattern instead of wax. This process takes advantage of the low [[boiling point]] of foam to simplify the investment casting process by removing the need to melt the wax out of the mold.

====Full-mold casting====
{{Main article|Full-mold casting}}

Full-mold casting is an evaporative-pattern casting process which is a combination of sand casting and [[lost-foam casting]]. It uses an [[expanded polystyrene]] foam pattern which is then surrounded by sand, much like sand casting. The metal is then poured directly into the mold, which vaporizes the foam upon contact.