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Lost Wax & Lost Foam Casting Processes
By Colin Croucher
Investment or lost wax casting is a versatile but ancient process, it is used to manufacture a huge variety of parts ranging from turbocharger wheels to golf club heads, from electronic boxes to hip replacement implants.
The industry, though heavily dependent on aerospace and defence outlets, has expanded to meet a widening range of applications. Modern investment casting has its roots in the heavy demands of the Second World War, but it was the adoption of jet propulsion for military and then for civilian aircraft that stimulated the transformation of the ancient craft of lost wax casting into one of the foremost techniques of modern industry.
Investment casting expanded greatly worldwide during the 1980s, in particular to meet growing demands for aircraft engine and airframe parts. Today, investment casting is a leading part of the foundry industry, with investment castings now accounting for 15% by value of all cast metal production in the UK.
It really is the modernisation of an ancient art.
Lost wax casting has been used for at least six millennia for sculpture and jewellery. About one hundred years ago, dental inlays and, later, surgical implants were made using the technique. World War two accelerated the demand for new technology and then with the introduction of gas turbines for military aircraft propulsion transformed the ancient craft into a modern metal-forming process.
Turbine blades and vanes had to withstand higher temperatures as designers increased engine efficiency by raising inlet gas temperatures. Modern technology has certainly benefited from a very old and ancient metal casting process. The lost wax casting technique eventually led to the development of the process known as Lost Foam Casting. What is Lost Foam Casting?
Lost foam casting or (LFC) is a type of metal casting process that uses expendable foam patterns to produce castings. Lost foam casting utilises a foam pattern which remains in the mould during metal pouring. The foam pattern is replaced by molten metal, producing the casting.
The use of foam patterns for metal casting was patented by H.F. Shroyer during then year of 1958. In Shroyer's patent, a pattern was machined from a block of expanded polystyrene (EPS) and supported by bonded sand during pouring. This process is known as the full mould process.
With the full mould process, the pattern is usually machined from an EPS block and is used to make large, one-of-a kind castings. The full mould process was originally known as the lost foam process. However, current patents have required that the generic term for the process is known as full mould.
It wasn't until 1964 when, M.C. Fleming's used unbonded dry silica sand with the process. This is known today as lost foam casting (LFC). With LFC, the foam pattern is moulded from polystyrene beads. LFC is differentiated from the full mould method by the use of unbonded sand (LFC) as opposed to bonded sand (full mould process).
Foam casting techniques have been referred to by a variety of generic and proprietary names. Among these are lost foam, evaporative pattern casting, evaporative foam casting, full mould, Styrocast, Foamcast, Styrocast, and foam vaporization casting.
All these terms have led to much confusion about the process for the design engineer, casting user and casting producer. The lost foam process has even been adopted by people who practice the art of home hobby foundry work, it provides a relatively simple & inexpensive method of producing metal castings in the backyard foundry.
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