Unlike aluminum forging, 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.
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 die 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 die castings can be made stronger than either die or sand castings. Aluminum gravity die casting is also named as aluminum gravity casting in China . 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)|
Common Aluminum Casting Alloys in China
There’re lots aluminum alloys in market, but not all of them are suitable for casting process. For example, parts made from 6061 aluminum alloys could only be forged or machined to the specification. Common aluminum casting alloys in China are as follows:
ASTM A356 is the aluminum casting alloy for gravity die casting process. Such aluminium casting alloy is with good liquidity, no hot tearing susceptibility, small shrinkage rate. Gravity die casting of A356 alloy can achieve better size accuracy and surface finish than sand casting process, that will save machining cost. T6 heat treatment could be done to improve the properties, especially the strength of the parts. Mainly used for marine parts, truck parts, impeller, housings, exhaust manifold, etc.
ASTM A380 is by far the most widely used alloy for pressure die casting process. This type aluminum casting alloy is with good thermal conductivity, pressure bearing, high temperature resistance and easy to be machined. Unlike A356 alloy, it could not be heat treated after casting. It may be specialized for most product applications. Some of the uses of this alloy include electronic and communications equipment, automotive components, engine brackets, transmission and gear cases, appliances, lawn mower housings, furniture components, hand and power tools.
Advantages of Aluminum Casting
Now that we know aluminum casting methods, the next question you are probably asking is, “What are the advantages?”
Aluminum casting is especially important in the manufacturing industry for commercial and industrial products. Therefore, let’s share with you the advantages of aluminum casting.
First, aluminum castings can allow the attainment of complex designs and forms for die cast parts. This means that manufacturers can easily order customized castings that will be suitable for their production needs.
Second, aluminum castings allow producers to manufacture parts at an extremely higher and faster rate than other alloy materials. Aluminum die casting can also achieve near net shape so the process of machining can be eliminated to produce finished parts.
Third, aluminum castings have the strength of steel but very lightweight. The appearance and aesthetic value of aluminum parts are also superior to other metal alloys. However, aluminum die cast parts are cheaper so end consumers can get high quality metal products at very affordable prices.
Lastly, castings made from aluminum are versatile, corrosion resistant, and can be used for different purposes. These qualities allow manufacturers to produce multiple products using aluminum parts. The finished products also have longer lifetimes thus giving consumers more value for their money.
Applications of Aluminum Casting
Due to its light weight and good corrosion resistance, cast aluminum components are widely used in the aerospace industry, which accounts for approximately 80% of the structure of an aircraft. Aluminum casting is applied in aerospace after Second World War, it show great advantages that is demands by this industry.
To decrease the weight of vehicles, automotive manufacturers are replacing steel material with aluminum material. Besides light weight, aluminum casting can meet the demand of high strength for automotive industry as well. Aluminum foundries are continously optimizing their casting methods possible to simplifly the manufacturing process to offer a reasonable price for each cast aluminum automotive part.
Common aluminum castings for automotive industry include: oil pumps, water pump housings, connectors, transmission parts, and a wide variety of brackets. The use of cast aluminum parts greatly promotes the innovation of automotive industry.
In addition to cast stainless steel, cast aluminum is popular in creating marine hardwares as well. Common cast aluminum marine parts are: cleats, handles, brackets, covers, and so on. Marine hardwares cast from aluminum is always corrosion resistant and last long.
Similar to automotive industry, aluminum casting can also creat some significant components for agriculture machines. Typical cast aluminum parts for agriculture are: crankcase housings, gearbox housings, and motor housings, etc. Of course, considering the cost saving, most agricultural components are produced in cast steel.
The durability and reliability of aluminum casting makes it ideal for lighting use. Cast aluminum light is non-toxic, lightweight, and corrosion resistant. The popular aluminum casting methods for lighting production is gravity die casting and pressure die casting, which is relatively economical and time saving.
Choosing a proper aluminum casting method can meet the stability and characteristics of the design required. The ease of production, weight of the final product, and exceptional resilience all make aluminum casting popular for lighting industry.
Heatsinks are commonly used for electronic products which can effectively remove heat. Considering heatsinks are relatively thin and complex, they are general produce by aluminum die casting process, which can minimize machining, save production cost and improve the production speed. CFS Foundry can cast aluminum heatsinks to each drawing’s specification and design.
Bracket is a common component for industrial use and home use, which is generally made in aluminum casting. Aluminum casting can provide near net shape bracket, and there is no need to do further welding or assembly. Cast in one piece, the cast aluminum bracket is stronger and more durable. And holes can be cast out directly without secondary operation.