Castings and Cast Metal Components
Cast components are used in every aspect of modern life. The casting process involves pouring molten metal into a mould with a hollow cavity of the desired shape; the metal is allowed to solidify before being removed from the mould. The process requires close control of all the aspects from design, to pattern or toolmaking, mould materials, metal melting and treatment, through to pouring and then finishing and quality assurance processes.
Most metals and alloys can be cast and there is a wide range of casting processes that can be used to produce engineered components in a wide range of sizes and quantities, from one-offs through to high volumes. Castings are produced by foundries who use a range of processes depending on the metal alloy, quantity, surface finish, mechanical and physical properties, shape, complexity and size of the component required.
Castings are vital for all parts of the modern world and UK foundries supply all sectors including automotive, aerospace, rail, power generation, chemical, medical and marine, not to mention art castings.
The industry is, and always will be, a vital way to re-cycle scrap metal into valuable new components and so is part of the circular economy. The metal used in casting has usually been re-processed from scrap into a raw material and recycling is what the industry does as standard.
Casting can enable a complex part to be made in one piece, often eliminating machining, assembly and fabrication steps and can be a very cost effective route to manufacture.
Sand casting involves the use of a mould made from sand, generally silica sand. The sand is bound together around a pattern, which is designed in the shape of the component to be made – the pattern is removed and molten metal is poured into the cavity. The pattern may be re-used and the sand can generally be recycled. There are two main types of sand casting – chemically bonded or greensand casting.
Chemically Bonded sand is mixed with a binder and hardener in a high-speed mixer before it is used to make the mould. The sand can generally be reused and the process can be used to make low, medium or high volumes of parts to high tolerances.
In greensand casting the sand grains are bound together with clay. A highly flexible process, greensand casting can be used for high volume, fully automated casting or for very low numbers of parts. The sand can be re-used over and over again making greensand casting one of the most cost effective and environmentally friendly of all the casting processes.
Diecasting involves the use of steel dies to form the cavity. In high pressure diecasting the molten metal is forced into the die under high pressure to rapidly fill the cavity making it ideal for high volume production, such as for the automotive industry. Low pressure diecasting and gravity diecasting are also commonly used to make near net-shape cast components with a high quality surface finish.
Used to produce large numbers of high quality castings for aerospace and medical applications, investment casting uses a wax copy of the component, dipped (invested) in a ceramic slurry to produce a ceramic mould. The wax is then removed to leave the ceramic shell, into which molten metal is poured. Also known as the lost wax process, it is used extensively for special purpose, high integrity parts and with specialised alloys.
The casting industry has embraced additive manufacturing for rapid-protyping, one-offs and low series runs, making use of printed sand moulds or printed patterns for investment casting. In addition, printed metal parts are used for tool and die reclamation and repair as well as jigs and fixings.