Aluminum casting refers to the casting process using aluminum alloys. Compared to steel casting & iron casting, the most typical feature is its light weight. The typical alloying elements of aluminum material are copper, magnesium, manganese, silicon, tin and zinc. Aluminum is lightweight, has excellent strength, high thermal and electrical conductivity, high reflectivity, good corrosion resistance, excellent workability, and attractive appearance. It can be given almost any finish. It is nonmagnetic, nontoxic, and non-sparking.
The high thermal conductivity of aluminum is a marked advantage in any application where it is desirable to conduct or dissipate heat quickly and uniformly. On a weight basis, aluminum is the most efficient heat conductor of the common metals.
Casting is the original and most widely used method of forming aluminum into products. Technical advances have been made, but the principle remains the same: Molten aluminum is poured into a mold to duplicate a desired pattern.
Aluminum Casting Methods
High pressure aluminum die casting is a manufacturing process in which molten metal (aluminum) is injected with a die casting machine under force using high pressure into a steel mold or die to form products. Precisely formed aluminum parts requiring a minimum of machining and finishing can be produced through this casting method. High pressure aluminum die casting is mainly used for thin wall thickness aluminum products with high volume production.
Low Pressure Aluminum Die Casting
In the low pressure die casting process the metal is transferred from an air tight furnace through a rising tube into a metallic tool. The casting temperature is about 750°C.
Low pressure aluminum die casting is competitive casting method when the production quantity is relatively small and/or when heat treatment is needed to improve the mechanical properties. The tolerances and the surface finish are the same as achieved by gravity die casting. The tooling costs are somewhat higher than by sand casting. For its low pressure, this manufacturing process is more suitable for thick aluminum products, even small volume is feasible.
Aluminum Gravity Casting (Permanent Mold Casting)
Aluminum gravity casting involves molds and cores of steel or other metal. Molten aluminum is usually poured into the mold, although a vacuum is sometimes applied. Aluminum gravity castings can be made stronger than either die or sand castings. Aluminum gravity casting is also named as permanent mold casting. Semi-permanent mold casting techniques are used when permanent cores would be impossible to remove from the finished part.
Aluminum Sand Casting
Sand casting is the most versatile method for producing aluminum products. The process starts with a pattern that is a copy of the finished casting. Virtually any pattern can be pressed into a fine sand mixture to form the mold into which the aluminum is poured. The pattern is slightly larger than the part to be made, to allow for aluminum shrinkage during solidification and cooling. As compared to die and permanent mold casting, sand casting is slow process but usually more economical for small quantities, intricate designs or when a very large casting is required.
Comparison of Aluminum Casting Methods
|Sand casting||Gravity die casting||Low pressure die casting||High pressure die casting|
|Weight of the casting, kg||0.1 … 500||0.01 … 50||1 … 70||0.01 … 30|
|Annual volume||1 … 5000||100 … 50 000||100 … 10 000||5000 … 1 000 000|
|Pattern / tooling cost||Relatively low||Moderate||Moderate||High|
|Cost of changes||Low||Moderate||Moderate||High|
|Flexibility of design||High||High||Relatively high||Relatively high|
|Minimum wall thickness, mm||4 … 6||3 … 4||3 … 4||0.8 … 1.5|
|Dimension accuracy||Fairly good||Good||Good||Very good|
|Possible surface roughness, Ra||> 6.3-12.3||≥ 3.2 (2.5)||≥ 3.2||≥ 1.6 (0.8)|
|Delivery time for samples, weeks||3 … 5||4 … 5||5 … 6||4 … 5|
|Special features||Also with sand cores and heat-treated||Also with sand cores and heat-treated||Also with sand cores and heat-treated||Also heat treated (in special conditions)|