Aluminium Sand Casting

The aluminium sand casting process is a type of metal casting process used to produce small to large size casting using aluminium metal.

The process involves pouring molten metal into a sand mould (a sand mould is made from a mixture of sand, clay, and moisture) and allowing aluminium to solidify in the sand mould cavity to produce the required aluminium casting.

Step-by-Step Process For Aluminium Sand Casting

Pattern Making

The aluminium casting process starts by making a pattern first. This pattern is used to make a mould cavity in the sand mould.

The pattern used in the aluminium sand casting process is close to the size and shape of the final casting. The pattern can be a bit undersized and oversized depending on the material to be cast to compensate for the shrinkage and expansion of the metal during the solidification process.

In case of aluminium casting, the pattern should be oversized to compensate for the tolerance allowance and losses during the casting process.

The pattern made from metal, plastic or wood, depending upon the shape and size of the final casting, is used to produce a mould cavity between the cope and the drag. Pattern material is chosen based on the size, complexity and shape of the casting.

Sand Mould Making

Sand mould is made by mixing sand, clay, moisture, and additives together to form a solid structure. Sand mould is divided into three parts: mainly cope, drag and cheek.

The pouring basin, sprue, runner, gates, mould cavity and riser are carved into the mould for the aluminium metal to flow smoothly during the casting process.

Sand mould can be green sand mould, dry sand mould or skin dried depending upon the size, shape and design of the final casting to be produced.

Melting Aluminium Metal, Pouring Operation & Solidification

Once the final sand mould is prepared, aluminium ingots are melted in the furnace, and this molten aluminium is poured into the pouring basin through a ladle. Aluminium metal is allowed to flow from the pouring basin, sprue, runner, in-gate, mould cavity, and riser.

Aluminium metal in the mould is then allowed to solidify uniformly to form the final casting.

Secondary Manufacturing Operation For Aluminium Casting

Once the liquid aluminium metal becomes solid in the sand mould, sand casting is taken out to perform secondary manufacturing operations such as cutting risers, gates, runners, sand blasting, heat treatment, surface finishing and drilling operations.

Types of Aluminium Casting

Green sand aluminium casting.
Dry sand aluminium casting.
No-bake aluminium sand casting.
Shell aluminium casting.
CO2 sand aluminium casting.

Alloys Used In Aluminium Casting

Alloys used in aluminium casting are used to improve the flow of the molten metal in the mould, reduce shrinkage during solidification, reduce corrosion, improve strength, hardness and wear resistance of the final casting.

Common aluminium alloys used in the sand casting process are as follows:

A319.0 (AlSi5Cu3Mn), C355.0 (AlSi5Cu1Mg), A356.0 (AlSi7Mg), 319.0 (AlSi5Cu3Mn) and A206.0 (AlCu4.5Mg).

Advantages & Disadvantages of Aluminium Casting

Advantages of Aluminium Casting

Aluminium casting has a high-strength-to-weight ratio.
Casting produced from this process is a corrosion-resistant casting that is better than that of brass, bronze, and copper.
The machinability of this casting process is higher than copper alloy, stainless steel, cast iron, and magnesium cast iron.
The cost of this casting is lower than that of other metal castings, such as stainless steel.
The density of aluminium is lower than that of stainless steel and cast iron, making this casting lightweight, ideal for producing castings for the automotive, aerospace, military, and marine industries.
As the pouring temperature, melting point of aluminium, and solidifying temperature of aluminium are lower, the resources required by the process are less.

Disadvantages of Aluminium Casting

These castings are less corrosion-resistant than stainless steel castings.
Aluminium casting is less heat and wear resistant than copper, brass and bronze.
Aluminium has a higher volumetric shrinkage rate than stainless steel and cast iron castings.
Mould design requires chills and risers to compensate for uneven solidification.
The weldability of casting is lower, making repair and maintenance difficult.
Volumetric shrinkage of this casting is higher than cast iron casting, increasing the need for risers, chills and padding.
Gas porosity, surface roughness, misrun, oxides, shrinkage cavity, and hot tearing are common casing defects and are higher than those of cast iron and bronze metal.

Application of Aluminium Casting

Gears, agricultural equipment, pulleys and brackets.
Engineblocks, covers and housing.
Motors, pumps, propellers and compressor housing.
Aluminium doors and windows.
Panels, anchors and blocks.
Gearbox, brakes, valves, pulley and differentials.
Beds of lathe machine, milling machine, shaper machine and grinding machine.

Aluminium Sand Casting | Mechgrace