The methods of aluminium precision casting were developed in the USA, from where it was imported to Sweden in the 1950s. Aluminium cast in plaster moulds formed on solid patterns, Solid Plaster Mould-SPM, and aluminium cast in ceramic moulds on lost wax patterns (Investment) are called Precision Castings. Precision Castings essentially have the same properties as high pressure die cast aluminium in terms of surface finish and precision but can be produced in smaller volumes, 5 – 1000 pcs/year, at a lower total cost.
The method of plaster mould casting is similar to sand mould casting but gives better surfaces and makes it possible to cast thinner crossections. Investment casting is based on pre-cast wax patterns that are embedded into ceramic forms and subsequently burned out before the form is being filled with molten aluminium, this method is suitable for castings with intricate geometries.
The two methods give greater freedom of design than what is possible with the high pressure die casting method. The components can, for example, be undercut and have zero draft. Precision Castings are suitable for lightweight designs, since cross sections as thin as 0.8 mm can be cast and heat treated. Plaster mould casting, according to the SPM-method, is best suitable for somewhat larger castings, 1 to 50 kg, in series from 5 to 500 pcs/year. Investment casting is ideal for smaller and more intricate castings with weights between 100 g and 3 kg and series up to 1000 pcs/year.