Casting: Manufacturing process where molten metal is poured into a mold and allowed to cool and solidify. Casting is a versatile process that 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. Casting can refer to the solid product of the casting process.
Foundry: Facility that produces metal castings and offers related services such as mold-making, melting, pouring, degating, heat treating, surface cleaning and other finishing operations.
Centrifugal casting: Casting method that involves rotating a permanent mold at high speed to force molten metal against inside walls. It allows castings to be formed at almost any length at different thicknesses—without the use of a core. Finished products are free from parting lines and gates and risers. Centrifugal casting is often used to make stock pipes and tubes for further machining.
Die casting: Casting method that involves injecting molten metal under pressure into a mold, or die. Two dies are cast and machined, then pressed together to form the mold cavity. Once injected metal has cooled, dies are separated and the casting ejected. Die casting can achieve high dimensional accuracy, great 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.
Investment casting: Casting method used typically for intricate products requiring a high degree of accuracy with minimal machining. It can be used to create products with smooth surfaces and no parting lines. Due to higher setup costs, it is often more suitable for high-volume production. Investment casting typically involves (1) using an injection mold to form wax patterns in the shape of the final product; (2) coating wax patterns in ceramic to form disposable molds; (3) heating ceramic molds to melt and drain wax; (4) pouring molten metal into ceramic molds; (5) removing ceramic molds to reveal the final casting; (6) removing any gates, risers or other excess metal from the finished product. Investment casting is also referred to as lost-wax casting.
Sand casting: Casting method characterized by the use of sand as a mold material. 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. (Sand prepared in this way is also known as green sand.) Sand is compacted into a mold box, or flask, around a model, or pattern, in the shape of the final desired product. Once molten metal has been poured and cooled, 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 and can be used for both short- and long-run productions.
Alloy: Combination of metals which may contain other non-metal components. Alloys are typically produced by mixing melted ingredients to achieve desirable material properties related to strength, hardness, corrosion resistance, conductivity, melting point and cost.
Aluminum: Non-ferrous metal used widely for its lightweight and corrosion-resistant characteristics. Its low melting point makes it highly castable. Aluminum is commonly alloyed with copper, zinc, magnesium, manganese and silicon.
Carbon steel: Steel that contains carbon as its only required alloy ingredient (between 0.12–2.0 percent). Higher carbon content typically increases hardness at the expense of ductility. Carbon steel is often used to refer to steels (including alloy steels) that are not stainless steels.
Sand molds ready for pour
Cast iron: 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 exception of malleable cast iron, are highly brittle. However, common cast iron materials such as white cast iron and gray cast iron are used widely for their castability, machinability and resistance to wear.
Ductile iron: Cast iron with more ductility and better resistance to impact and fatigue than other cast irons. Ductile iron is made using small amounts of magnesium or cerium to manipulate carbon into spherical formations that won't compromise structural integrity under stress. Also referred to as ductile cast iron, nodular cast iron, spheroidal graphite iron and spheroidal graphite cast iron.
Ferrous alloy: Metal alloy that has iron as its main constituent.
Non-ferrous alloy: Metal alloy that is not ferrous (does not contain iron in significant amounts).
Stainless steel: Steel that typically contains between 10–30 percent chromium content to achieve high resistance to corrosion through passivation. Chromium oxidizes to form a natural, non-reactive barrier to corrosion, protecting internal stainless steel structures. Numerous grades of stainless steel incorporate alloy ingredients such as nickel, molybdenum, titanium, aluminum, copper, nitrogen, sulfur, phosphorous and selenium.
Steel alloy: Steel that has been alloyed with materials, 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.
Steel casting: Specialized form of casting that involves various types of carbon and alloy steels.
Other foundry process terms
Annealing: Form of heat treatment where metal is heated to and held at a high temperature and then cooled at a controlled rate to lower hardness or alter other mechanical or physical properties.
Foundry workers pouring molten metal
Case hardening: Process for hardening ferrous alloys so that surface layers are made substantially harder than interior or core materials.
Casting drawing: Engineering drawing that shows the final shape of a part to be casted. It includes all information related to dimensions, tolerances, machining and any other data necessary to determine foundry procedures.
Cope: Top half of a pattern, flask, mold or core.
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.
Core box: Enclosed mold in which sand can be packed to form a core.
Degassing: 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.
Draft: Taper applied to a pattern's vertical surfaces, allowing a pattern to be removed from a mold cleanly and with little effort. Minimum section thicknesses should be maintained when including drafts in pattern designs.
Drag: Bottom half of a pattern, flask, mold or core.
Flashing: Excess material formed on an object during the casting process, typically resulting from gaps formed within a parting line.
Flask: 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.
Gate: 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.
Gating system: Network of connected channels that carries molten metal into mold cavities. 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. Where dry sand molds are limited is in the amount of weight they can support, green sand molds can support a much higher mass. Aside from water, additives such as bentonite, or clay, and anthracite are often added to green sand mixtures.
Heat treatment: Controlled temperature applications, including heating and/or cooling, used to produce desired properties in solid-state metals.
Loose pattern: Pattern free from any mounting plate, which results in castings with minimal gates and risers. Loose, or unmounted, patterns are rarely used by foundries, except for prototypes and very large castings.
Machining allowance: Amount of additional material intentionally cast to provide excess stock for machining.
Machining: 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.
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.
Mold: Structure into which molten metal is poured and cooled to form a final casted product. Molds can be reusable (as in die casting) or disposable (as in sand and investment casting).
Mounted pattern: 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.
Parting line: 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.
Pattern: Object made in the shape of the object to be cast. Patterns are used to form mold cavities into which molten metal will be poured. They can be made into one single piece or split patterns comprising upper and lower sections.
Precipitation hardening: Form of heat treatment involving precipitation from a solid solution, used to improve certain mechanical properties.
Quenching: Hardening method achieved through rapid cooling, typically by immersing in water, oil or other solution.
Riser: 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.
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 casting material.
Soundness: Measure of impurities and/or discontinuities such as sand inclusions, slag inclusions, macro porosity (pores greater than 50 nm in diameter) and shrinkage.
Sprue: Passage 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.
Tempering: Form of heat treatment, where hardened steel is reheated to a temperature below the critical range to soften it and improve impact strength.
Tolerance: 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.