Sand casting involves gravity casting of molten metal into a sand mould, which is then broken to extract the component and reused in the next mould an unlimited number of times. The advantages include the possibility of economical production from a single prototype up to a medium series, the possibility of making even very complex shapes with many cores, the large dimensions achievable and a good quality of the finished casting. This technology has limitations in terms of the minimum thickness of the walls, about 3-5 mm, a low dimensional tolerance and a medium-high roughness surface compared to other casting technologies. Furthermore, it is not suitable for the large-scale production of serial components due to the low speed of the production process.
Shell casting consists of pouring molten metal into permanent steel moulds. This process is used for metals with a low melting point such as aluminium and bronze. Advantages include the possibility of producing more components at lower costs, improved mechanical properties due to rapid cooling of the metal and the possibility of obtaining thinner thicknesses with better surface roughness. However, tooling costs are higher than for sand production and the technology is not suitable for large or heavy components, and it is difficult to apply it to complex, core-rich components.
Low pressure casting consists of pushing molten metal from the bottom of a permanent mould by means of gas pressure. This technology is used for medium to high production of components, it allows a very good quality of the melt in terms of defects and mechanical characteristics and is moderately automatable, allowing a good production rate. The surface finish is better than that of shell production, which also reduces casting anals and vents, making deburring easier. The investments for this technology are on average high, in addition to the steel mould a dedicated machine is required to handle the metal, this limits the flexibility in terms of the size of the components that can be made and moves the use of this technology only to high repetitive components.
Pressure casting takes place by pushing the molten metal into a steel mould with high pressure using a piston. This is also used for low melting temperature alloys such as aluminium and zamak, and is the technology with the highest productivity rate, as it has a very short cycle time and allows large series of products to be produced at low cost. It also allows the production of the thinnest thicknesses, 1.5-2 mm, with very low surface roughness. However, this process requires moulds and machinery with high costs, which can only be amortised thanks to large series production. Moreover, due to the great turbulence of the metal, the castings are characterised by microporosity that does not allow particularly high mechanical characteristics to be achieved. Unlike with shell casting and low pressure, die-cast components cannot have disposable cores, which makes it difficult to reproduce moulds with particularly complex undercuts.
This technology consists of making a wax model in the shape of the parts to be made, including the casting cavities. It is then immersed in a mixture of refractory powders that polymerise to become extremely solid, and is then fired, allowing the wax to evaporate to make room for the metal to be cast. In this case, a variety of alloys can be cast, including steel, aluminium, gold and silver. The advantage of this solution is the great flexibility of use as it does not require expensive models and has an excellent finish and the ability to produce very complex shapes. Due to the long production times, it is not suitable for large production runs.
