Casting terms and definitions
Manufacturing process used to produce solid metal pieces called castings. Molten metal is poured into a mold. Once in the mold, the metal cools and solidifies in the shape of the mold cavity.
Casting offers exceptional freedom in forming intricate components. It is also conducive to high-volume production runs, where material quantities can be efficiently controlled to minimize waste and reduce cost. The casting process is also called founding.
Facility that produces metal castings and offers related services such as mold-making, melting, pouring, degassing, heat treating, surface cleaning, and other finishing operations. Please refer to What is a Foundry? for more information on the work of foundries. Explore current innovations in Foundry: a Rich History and Promising Future.
Casting method in which a reusable mold is rotated at high speed to force molten metal against the inside walls. Centrifugal casting allows castings to be formed at almost any length or wall thickness without the use of a core. Finished products are free from parting lines, gates and risers. Centrifugal casting is often used to make stock pipes and tubes for further machining.
Casting method in which molten metal is injected into the mold (or die) under pressure. Two hardened dies are pressed together to form the mold cavity. Once the injected metal has cooled, dies are separated and the casting ejected. Die casting can achieve high dimensional accuracy, intricate detail and smooth cast surfaces that require minimal additional machining. Dies are expensive to produce, making them more suitable for high-volume runs. Ferrous metals are rarely used as an injection material.
Casting method typically used for intricate pieces that require a high degree of accuracy with minimal machining. It can be used to create products with smooth surfaces and no parting lines. Due to high setup costs, investment casting is most suitable for high-volume production.
The steps of investment casting are as follows:
- Use an injection mold to form wax patterns in the shape of the final product;
- Coat the wax patterns in ceramic to form disposable ceramic molds;
- Heat ceramic molds to melt and drain wax;
- Pour molten metal into the ceramic molds;
- Remove ceramic molds to reveal the solidified metal casting;
- Removing any gates, risers or other excess metal from the finished product. Investment casting is also referred to as lost-wax casting.
Explore in-depth the process of investment casting.
Casting method characterized by the use of sand as the mold material. Molding sand is typically mixed with a bonding agent such as clay and moistened with water or other liquid to create suitable mold strength and plasticity (See green sand). The mold cavity is formed by compacting sand into a mold box (or flask) around the pattern. The pattern is then removed from the newly formed mold cavity. Once molten metal has been poured and allowed to cool, sand is removed to reveal the final casting. Finished surfaces are not as smooth as with other methods, and additional machining, including the removal of gates and risers, is typically required. Sand casting is one of the most common methods used by foundries; it can be used for both short- and long-run productions.
Combination of metals which may contain other non-metal elements. Alloys are typically produced to achieve desirable material properties related to strength, hardness, corrosion resistance, conductivity, melting point and cost.
Non-ferrous metal that is notably lightweight and corrosion-resistant. Its low melting point makes aluminum highly castable. Aluminum is commonly alloyed with copper, zinc, magnesium, manganese and silicon.
Steel that contains 0.12-2.0 percent carbon and up to 10.5 percent alloy content. Carbon steels are often categorized as either high carbon or low carbon. High carbon content increases hardness at the expense of ductility, and vice versa. Carbon steels do not include stainless steels.
Group of iron alloys that contain approximately 2-4 percent carbon along with 1-3 percent silicon and other trace elements. Most cast irons, with the notable exception of malleable cast iron, are brittle. White cast iron and gray cast iron are widely used for their castability, machinability and resistance to wear. Learn more about cast (and wrought) iron.
A modern iteration of cast iron; ductile iron has superior ductility and impact resistance. Ductile iron is made using small amounts of magnesium or cerium to manipulate carbon into spherical formations that won’t crack under stress. Also referred to as ductile cast iron, nodular cast iron, spheroidal graphite iron and spheroidal graphite cast iron.
Metal alloy that has iron as its main constituent.
Metal alloy that is not ferrous (does not contain iron in significant amounts).
Steel that contains 10.5-30 percent chromium. The high chromium content provides stainless steel with natural corrosion resistance. Chromium oxidizes to form a non-reactive barrier that protects the internal structure. Numerous grades of stainless steel incorporate alloy ingredients such as nickel, molybdenum, titanium, aluminum, copper, nitrogen, sulfur, phosphorous and selenium. Explore more about stainless steel.
Steel that has been alloyed with elements in addition to carbon to achieve desirable properties related to strength, hardness, and resistance to wear and corrosion. Common ingredients include manganese, nickel, chromium, molybdenum, vanadium, silicon and boron.
Specialized form of casting that involves carbon and alloy steels.
Other foundry process terms
Form of heat treatment where metal is heated to and held at a high temperature, then cooled at a controlled rate. Annealing is used to alter chemical or physical properties, especially hardness.
Process for hardening ferrous alloys so that surface layers are made substantially harder than interior or core materials.
Engineering drawing that shows the final shape of a part to be cast. It includes all information related to dimensions, tolerances, machining and any other data necessary to determine foundry procedures.
Top half of a pattern, flask, mold or core.
Insert used to create mold cavities and openings that cannot be formed using a pattern on its own. Cores are often formed from molding sand to ensure adequate strength, hardenability and removability during shakeout. Cores will increase the cost of a casting and should be used only when necessary.
Enclosed mold in which sand can be packed to form a core.
Process for removing unwanted gasses from casting materials, typically by pumping a neutral gas through molten metal. Unwanted gases form in metal castings through mechanical entrapment or by chemical reactions within liquid metal. If not removed, unwanted gases can create porosity in metals, which can compromise strength and integrity.
Taper applied to a pattern’s vertical surfaces. The taper facilitates clean and easy removal of a pattern from a mold. Minimum section thicknesses should be maintained when including drafts in pattern designs.
Bottom half of a pattern, flask, mold or core.
Excess material formed on an object during the casting process, typically resulting from gaps formed within a parting line.
Container, comprised of two halves, a cope and drag, used to form sand molds. A pattern is placed inside the flask, typically fastened to a match plate, and packed with sand. The cope and drag are separated, the pattern is removed and the two parts are reassembled to form the mold cavity.
Channel that carries molten metal between mold cavities that would be otherwise separated. Gates are formed into a mold extraneous of the desired final product and must be removed by machining once a casting has cooled.
Network of connected channels that carries molten metal into the mold cavity. Excess material solidified in the gating system, called gates, must be removed by machining once casting has cooled.
Green sand casting:
Type of sand casting characterized by the use of a wet sand mixture to create a mold. Dry sand molds are limited in the amount of weight they can support; green sand molds can support a much higher mass. In addition to water, bentonite, clay, and anthracite are normal components of green sand mixtures.
Controlled temperature applications, including heating and/or cooling, used to produce desired properties in solid-state metals.
Pattern free from any mounting plate, which results in castings with minimal gates and risers. Unmounted or loose patterns are rarely used by foundries, except for prototypes and very large castings.
Process of mechanically removing excess material by cutting, drilling, grinding or sanding. Many sand-casted products require machining to achieve smooth surfaces free from any gates and risers.
Amount of additional material intentionally cast to provide excess stock for machining.
Minimum section thickness:
Minimum thickness a section can be cast, based on material fluidity, desired quality and the area and complexity of a casting’s surface.
Structure into which molten metal is poured to form a casting. Molds can be reusable (as in die casting) or disposable (as in sand and investment casting).
Pattern fastened to a board or match plate, which can then be fixed into a flask. Mounted patterns allow for quicker and better-quality mold making, while also allowing groups, or sets, of parts to be formed in a single mold.
Seam formed between cope and drag portions of a mold, where additional material may accumulate and show as a raised line, called flashing, on a casting. Machining can be used to minimize or remove the appearance of a parting line.
Object made in the shape of the object to be cast. Patterns are used to form the mold cavities into which molten metal will be poured. They can be made into a single piece or split patterns comprising upper and lower sections.
Form of heat treatment involving precipitation from a solid solution, used to improve certain mechanical properties.
Hardening method achieved through rapid cooling, typically by immersing in water, oil or other solution.
Reservoir cavity included in the design of a mold to counteract the effects of material shrinkage during cooling. As casting materials shrink they draw additional material from risers to prevent cavity formation. Risers should cool and solidify with the slowest components of a casting—usually the thickest and largest part—and should contain enough material to compensate shrinkage.
Amount of contraction that occurs when casting materials harden and cool to room temperature. Pattern and mold design should account for shrinkage according to properties of the casting material.
Measure of impurities and/or discontinuities such as sand inclusions, slag inclusions, macro porosity (pores greater than 50 nm in diameter) and shrinkage.
Passage through which molten metal is poured to fill the mold cavity. A sprue also refers to the excess material solidified in the passageway that must be removed once cooled.
Form of heat treatment, where hardened steel is reheated to a temperature below the critical range to soften it and improve impact strength.
Permissible range of variation, given in nominal dimensions, for a finished product. Accepted tolerances are typically agreed upon by both supplier and customer, and should be indicated in casting drawings.