Frequently Asked Questions: Custom Metal Casting & Foundry Services
Answers to common questions for custom metal casting & foundry services
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What is the definition of casting?
Casting is a 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 also refer to the solid product of the casting process.
What is a metal casting?
A metal casting is the product created by the metal-casting process. It is formed from molten metal and formed according to the shape of its mold cavity.
What kind of metal is used in castings?
Any metal that can be melted can be cast. Cast steel foundries use different metals depending on the desired structural and performance qualities. Ferrous metals in particular are used for their strong mechanical properties, while nonferrous metals are used for other qualities related to weight, conductivity, magnetic characteristics and corrosion resistance.
Ferrous Metals: Metals which contain iron.
Examples of Ferrous Metals
- Cast iron, gray Iron, ductile iron, malleable iron, cast steel (ASTM A27 cast steel is commonly used), compacted graphite iron, stainless steel and manganese steel.
Nonferrous Metals: Metals which do not contain iron.
Example of Nonferrous Metals
- Aluminum, copper alloy, brass, bronze, zinc, magnesium, carbon and low-alloy titanium, corrosion-resistant nickel, heat-resistant cobalt, manganese and tin.
What are common uses for castings?
Casting allows for exceptional freedom of form in manufacturing goods for all aspects of society. Due to the range of materials and processes available, a vast amount of products can be made for high-volume production to suit many different applications. Many cast metal products offer exceptional strength and durability, making them useful for heavy machine applications in industries related to farming, automobiles, railroads, home appliances, building architecture, ship building, oil and gas extraction, water processing, forestry and mining—to name a few.
How much do metal castings cost?
A range of factors will contribute to the overall cost of a casting project.
- What will the casting be used for?
- What are its dimensions?
- What metallurgical properties are required?
- Will the casting need to account for mechanical stress or thermal factors?
- How many castings are required?
- What type of finishing work will be required?
For more information on costs for a particular project, request a quote at our Custom Metal & Foundry Services page.
What casting methods are available?
A range of casting methods are available, but three of the most common forms include sand casting (expendable mold, permanent pattern), die casting (permanent mold) and investment casting (expendable mold, expendable pattern).
- Sand casting is a 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.") Prepared 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 casting. Sand-casted 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.
- Die casting is a 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 the 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 is a 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, but has a higher cost for high-volume runs. Investment casting typically involves (1) forming a gelatin mold around a solid object or form; (2) carefully removing the gelatin mold and filling or coating it with a layer of hard wax to desired thickness of the final casting; (3) removing the gelatin mold and applying heat resistant clay to wax shell; (4) baking to harden clay and remove wax; (5) pouring molten material into the hardened mold; and (6) breaking away the clay mold to reveal the final casting. Investment casting is also referred to as lost-wax casting.
What are "green sand" castings?
Green sand casting is a 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. Green sand castings are castings that have been produced with green sand molds.
How are wrought iron and cast iron different?
The primary material difference between wrought and cast iron is in their respective carbon content and the inclusion of slag, a byproduct of smelted ore. Cast iron has a much higher carbon content (between 2.1 and 4 percent) than wrought iron (less than 0.08 percent). Wrought iron also contains up to 2 percent of slag, which gives it its fibrous appearance. A more important distinction between the two metals is in how they are used. Cast iron is a harder material and has a lower melting point due to its higher carbon content, making it much more suitable for melting and casting. Wrought iron is more malleable and is more easily worked with tools. Wrought iron is rarely used for casting, as melting removes its workable properties. While wrought iron was used extensively in the past, it has been replaced almost entirely with the development of higher-quality and more economical steel.
What is the difference between a foundry and casting?
A foundry is a place where metal castings are produced. Casting is the process of pouring liquid metal into the hollow cavity of a mold to form a desired shape upon solidification.