The Airset sand casting method, developed in the mid-20th century, was first deployed in our foundry more than 20 years ago. The company quickly recognised how this modern form of aluminium sand casting would complement the more traditional method of sand casting.
The Airset moulding method of sand casting to make aluminium castings differs quite markedly from the greensand casting method. When making airset sand castings, the sand is mixed with a chemical resin binder, giving additional strength to the mould created. When this strength is combined with the accuracy provided by the computerised mixing systems that Precision Casting has invested in, the result is the ability to cast thinner wall sections and larger parts.
The sand casting process uses a pattern to create a hollow cavity in the sand, which matches the shape of the finished part required. The pattern equipment is generally made from resin. The pattern itself is slightly larger than the finished part, to allow for the contraction of the metal during cooling.
Patterns can be made using traditional manual pattern-making skills or, more often now, using 3D models through CAD/CAM to a CNC machine, which cuts a resin material to shape. Additional tooling is usually needed to make cores, which are used to create undercuts, hollows, or cavities within the final part itself.
In order to get the metal into the mould, a runner system is added to the pattern. It is designed to ensure that once the metal has flowed through the down sprue, it will be filtered and its flow controlled to avoid turbulence while the mould is filled. Any thick sections can be chilled to promote accelerated solidification of material, by the addition of pieces of iron or steel, which preferentially cool where required. Risers are added to create reservoirs of molten metal to feed the casting as it shrinks during the cooling/solidification stage.
The dimensional accuracy of airset sand casting in general is superior to that of the levels achievable in the greensand moulding process and often approaches those obtainable using the gravity die casting technique.
